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    • 专利摘要:
    abstract patent of invention: "hot-rolled steel sheet with high resistance that has excellent cooking hardness and low temperature toughness with maximum tensile strength of 980 mpa or more". the present invention relates to a hot-rolled steel sheet with high strength that consists, in mass%, of 0.01% to 0.2% carbon, 0% to 2.5% silicon, 0% to 4.0% manganese, 0% to 2.0% aluminum, 0% to 0.01% nitrogen, 0% to 2.0% copper, 0% to 2.0 % nickel, 0% to 1.0% molybdenum, 0% to 0.3% vanadium, 0% to 2.0% chromium, 0% to 0.01% magnesium, 0 % to 0.01% calcium, 0% to 0.1% rare earth metals, 0% to 0.01% boron, no more than 0.10% phosphorus, no more than 0 , 03% sulfur, no more than 0.01% oxygen and a total of 0.01 to 0.30% of either or both of titanium and niobium, with the remainder comprising iron and unavoidable impurities. the steel sheet has a displacement density that is greater than or equal to 5 × 1013 (1 / m2) and less than or equal to 1 × 1016 (1 / m2) and comprises, in the fraction of total volume, at least 90 % tempered martensite or lower bainite containing at least 1 × 106 iron carbide / mm2.
    公开号:BR112015011302B1
    申请号:R112015011302-8
    申请日:2014-02-25
    公开日:2020-02-27
    发明作者:Masafumi Azuma；Hiroshi Shuto；Tatsuo Yokoi；Yuuki Kanzawa；Akihiro Uenishi
    申请人:Nippon Steel Corporation；
    IPC主号:
    专利说明:

    Descriptive Report of the Invention Patent for HOT LAMINATED STEEL SHEET AND ITS PROCESS FOR PRODUCTION.
    FIELD OF TECHNIQUE [001] The present invention relates to a hot-rolled steel sheet with high strength that has excellent cooking hardness and low temperature toughness with a maximum tensile strength of 980 MPa or more, and a method for produce such hot rolled steel sheet with high strength. The present invention relates to a steel sheet that has excellent hardenability, after molding and coating coating treatment and excellent low temperature toughness to have the ability to be used in extremely cold areas.
    BACKGROUND OF THE TECHNIQUE [002] To reduce the amount of carbon dioxide gas escaping from automobiles, automobile chassis are being reduced in weight with the use of high-strength steel plates. In addition, to ensure the safety of drivers and passengers, in addition to soft steel plates, more and more high-strength steel plates with a maximum tensile strength of 980 MPa or more are becoming used for automobile chassis. In order to further reduce the weight of the automobile chassis, the strength of the steel plates with high strength during use has to be greater than before. However, the increase in strength of steel sheets typically leads to the degradation of material characteristics such as plasticity (ability to be processed). Thus, it is essential for the development of steel sheets with high strength how much the strength is increased without the degradation of material characteristics.
    [003] The steel sheets that are used are required to have a
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    2/49 performance such that it is unlikely that the limbs will be damaged even when impacted by a collision or the like after steel sheets are molded and attached to automobiles as components. In particular, in order to guarantee impact resistance in cold areas, there is also a demand for increased low temperature toughness. Low temperature toughness is defined by vTrs (Charpy fraction discordance temperature), for example. For this reason, the impact resistance of the steel materials above needs to be considered. In addition, high strength steel sheets are unlikely to be plastically deformed and will occur more easily; thus, toughness is required as significant characteristics.
    [004] As one of the methods to increase the resistance of steel sheets without degradation in plasticity, there is a method of baking hardening with the use of coating baking. This method increases the resistance of automobile members as follows: through heat treatment at the time of coating cooking treatment, the dissolved C present in a steel plate concentrates on discrepancies formed during molding or is precipitated as carbides. Since the hardening is carried out after the baking hardening effect in this method, there is no degradation in the formability of the press due to the increase in resistance. Thus, it is expected that this method will be used for the structural members of automobiles. As an index for the evaluation of the baking hardening effect, a test method is known in which 2% of pre-deformation is checked at room temperature and, then, the heat treatment is carried out at 170 ° C for 20 minutes to perform the assessment at the time of the double traction test.
    [005] Both the disagreements formed at the time of production and the disagreements formed at the time of processing to
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    3/49 presses contribute to baking hardening; therefore, their sum, which is the density of disagreement and the amount of C dissolved in the steel plate, are important for the baking hardening effect. An example of a steel plate that has an excellent baking hardening effect while having a large amount of dissolved C is the steel plate shown in Patent Document 1 or 2. As a steel plate that guarantees more excellent baking hardening effect, it is known a steel plate that includes N plus dissolved C and that has an excellent baking hardening effect (Patent Documents 3 and 4).
    [006] Although the steel sheets shown in Patent Documents 1 to 4 can guarantee excellent baking hardening effect, these steel sheets are not suitable for the production of high strength steel sheets with a maximum tensile strength of 980 or more which can contribute to the high strength of structural members and to the reduction in weight due to the fact of the basic phase structure and a single ferrite phase.
    [007] In contrast, being extremely tough, a martensite structure is typically used as a main phase or the second phase in steel sheets that have a strength as high as 980 MPa or more to increase strength.
    [008] However, since martensite includes an enormous amount of disagreement, it is difficult to obtain an excellent baking hardening effect. This is due to the fact that the density of disagreement is high compared to the amount of C dissolved in the steel. In general, when the amount of dissolved C is small compared to the discrepancy density in a steel plate, the baking hardening effect is reduced. In this way, when sweet steel that does not include many discrepancies and single-stage martensite steel are compared to each other, if the amount of dissolved C is the
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    4/49 same, the baking hardening effect of the single phase of martensite is more reduced.
    [009] Therefore, as the steel sheets with which it was tried to guarantee more excellent baking hardening effect, steel sheets are known to have greater resistance by adding an element (s) such as Cu, Mo, W and / or similar steel and precipitating the carbides of these elements at the time of cooking coating (Patent Documents 5 and 6). However, these steel sheets are not highly economical due to the fact that the addition of expensive elements is necessary. In addition, although carbides from these elements are used, it has still been difficult to guarantee strength of 980 MPa or more.
    [0010] Meanwhile, as for a method for increasing the toughness of a high strength steel plate, for example, Patent Document 7 discloses a method for producing such steel plate. A method is known in which the aspect ratio of a martensitic phase is adjusted, the martensitic phase is used as a main phase (Patent Document 7).
    [0011] In general, it is known that the aspect ratio of martensite depends on the aspect ratio of the austenite grains before processing. That is, martensite that has a high aspect ratio means martensite transformed from non-recrystallized austenite (austenite that is extended through lamination) and martensite that has a low aspect ratio means martensite transformed from austenite recrystallized.
    [0012] From the above description, in order to reduce the aspect ratio of the steel sheet of Patent Document 7, it is necessary to recrystallize austenite; in addition, in order to recrystallize austenite, it is necessary to increase the temperature of the final lamination. In this way, the grain size of austenite and also the grain size of
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    5/49 martensites tend to be large. In general, grain refining is known to be effective in increasing toughness. A reduction in the aspect ratio can reduce the factors that worsen the toughness due to the shape, but it accompanies the toughness degradation due to the thick crystal grains; therefore, there is a limit to the increase in toughness. Furthermore, Patent Document 7 does not mention anything about the baking hardening effect that a study of the present application has focused on and Patent Document 7 hardly guarantees sufficient baking hardening effect.
    [0013] Furthermore, Patent Document 8 reveals that it is possible to increase low temperature toughness and toughness by finely precipitating ferrite carbides that have an average grain size of 5 to 10 pm. By precipitating C dissolved in steel as carbides that include Ti and the like, the strength of the steel plate is increased, so that the amount of C dissolved in steel is considered to be small and the excellent baking hardening effect is unlikely to be obtained.
    [0014] Thus, it is difficult for a steel sheet with high strength with 980 MPa or more to have both excellent baking hardening effect and excellent low temperature toughness. PREVIOUS TECHNICAL DOCUMENTS
    PATENT DOCUMENTS [0015] Patent Document 1 JP H5-55586B [0016] Patent Document 2 JP 3404798B [0017] Patent Document 3 JP 4362948B [0018] Patent Document 4 JP 4524859B [0019] Patent Document 5 JP 3822711B [0020] Patent Document 6 JP 3860787B [0021] Patent Document 7 JP 2011-52321A [0022] Patent Document 8 JP 2011-17044A
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    6/49
    SUMMARY OF THE INVENTION
    PROBLEMS TO BE SOLVED BY THE INVENTION [0023] The present invention was realized in view of the above problems and an object of the present invention is to provide a hot rolled steel sheet that has excellent baking hardening effect and low temperature toughness with a tensile strength maximum of 980 MPa or more and a method for producing such steel sheet in a stable manner.
    MEANS TO SOLVE THE PROBLEM (S) [0024] The present inventors have successfully produced a hot-rolled steel plate with high strength that has excellent baking hardening effect and low temperature toughness with a maximum tensile strength of 980 MPa or more, optimizing the composition of the steel plate and the conditions for producing the steel plate and controlling the structure of the steel plate. A summary of the steel sheet is as follows.
    (1) [0025] A high-strength hot-rolled steel sheet with a maximum tensile strength of 980 MPa or more, the steel sheet having a composition consisting of, in% by mass, [0026] C: from 0.01% to 0.2%, [0027] Si: from 0% to 2.5%, [0028] Mn: from 0% to 4.0%, [0029] Al: from 0% to 2, 0%, [0030] N: from 0% to 0.01%, [0031] Cu: from 0% to 2.0%, [0032] Ni: from 0% to 2.0%, [0033] Mo: from 0% to 1.0%, [0034] V: from 0% to 0.3%, [0035] Cr: from 0% to 2.0%,
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    7/49 [0036] Mg: from 0% to 0.01%, [0037] Ca from 0% to 0.01%, [0038] REM: from 0% to 0.1%, [0039] B: from 0% to 0.01%, [0040] P: less than or equal to 0.10%, [0041] S: less than or equal to 0.03%, [0042] O: less than or equal to 0.01%, [0043] one or more among Ti and Nb: 0.01% to 0.30% in total and [0044] the balance being Fe and unavoidable impurities, [0045] in which the steel plate has a structure in which a fraction of total volume between one or both of tempered martensite and lower bainite is 90% or more and a density of discrepancy in martensite and lower bainite is greater than or equal to 5x10 13 (1 / m 2 ) and less than or equal to 1x10 16 (1 / m 2 ).
    (2) [0046] The hot-rolled steel plate with high resistance according to (1), where the one or both of tempered martensite and lower bainite includes 1x10 6 (numbers / mm 2 ) or more carbides based on iron.
    (3) [0047] The hot-rolled steel plate with high resistance according to (1), in which one or both of tempered martensite and lower bainite has an effective crystal size less than or equal to 10 pm.
    (4) [0048] The hot-rolled steel plate with high resistance according to (1), which includes one or more among, in mass%, [0049] Cu: from 0.01% to 2.0% , [0050] Ni: from 0.01% to 2.0%, [0051] Mo: from 0.01% to 1.0%,
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    8/49 [0052] V: from 0.01% to 0.3% and [0053] Cr: from 0.01% to 2.0%.
    (5) [0054] The hot-rolled steel plate with high resistance according to (1), which includes one or more among,% by mass, [0055] Mg: from 0.0005% to 0.01%, [0056] Ca: from 0.0005% to 0.01% and [0057] REM: from 0.0005% to 0.1%.
    (6) [0058] The hot-rolled steel plate with high resistance according to (1), which includes,% by mass, [0059] B: from 0.0002% to 0.01%.
    (7) [0060] A method for producing a high-strength hot-rolled steel sheet with a maximum tensile strength of 980 MPa or more, the method including:
    [0061] to heat, optionally after cooling, a hot-rolled die-casting plate to a temperature of 1,200 ° C or more, the hot-rolled plate having a composition consisting of,% by mass, [0062] C : from 0.01% to 0.2%, [0063] Si: from 0% to 2.5%, [0064] Mn: from 0% to 4.0%, [0065] Al: from 0% to 2 , 0%, [0066] N: from 0% to 0.01%, [0067] Cu: from 0% to 2.0%, [0068] Ni: from 0% to 2.0%, [0069] Mo : from 0% to 1.0%, [0070] V: from 0% to 0.3%, [0071] Cr: from 0% to 2.0%,
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    9/49 [0072] Mg: from 0% to 0.01%, [0073] Ca: from 0% to 0.01%, [0074] REM: from 0% to 0.1%, [0075] B: 0% to 0.01%, [0076] P: less than or equal to 0.10%, [0077] S: less than or equal to 0.03%, [0078] O: less than or equal to 0.01% , [0079] one or more among Ti and Nb: 0.01% to 0.30% in total and [0080] the balance being Fe and unavoidable impurities;
    [0081] complete the hot lamination at a temperature of 900 ° C or more;
    [0082] cool the steel sheet at a cooling speed of 50 ° C / s or more, on average, from a final rolling temperature to 400 ° C;
    [0083] set a cooling speed of no more than 50 ° C / s at a temperature of less than 400 ° C and [0084] wind the steel sheet.
    (8) [0085] The method for producing a hot-rolled steel sheet with high strength according to (7), which additionally includes:
    [0086] perform the galvanizing treatment or galvanizing and annealing treatment.
    EFFECTS OF THE INVENTION [0087] In accordance with the present invention, it is possible to provide a steel sheet with high strength that has excellent baking hardening effect and low temperature toughness with a maximum tensile strength of 980 MPa or more. With the use of this steel plate, it is easy to process the steel plate with high strength and it is also possible to use the steel plate with high strength
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    10/49 system processed with high durability in extremely cold areas; thus, the industrial contribution of the high strength steel sheet is very remarkable.
    MODE (S) FOR CARRYING OUT THE INVENTION [0088] The content of the present invention will be described in detail below.
    [0089] According to the intensive study of the present inventors, a steel sheet structure has a discrepancy density greater than or equal to 5χ10 13 (1 / m 2 ) and less than or equal to 1x10 16 (1 / m 2 ) and includes one or both of tempered martensite and lower bainite, each of which includes 1x10 6 (numbers / mm 2 ) or more iron-based carbides, in a total volume fraction of 90% or more. The present inventors have concluded that the effective crystal size of tempered martensite and lower bainite is preferably 10 pm or less so that a high strength of 980 MPa or more and excellent baking hardening effect and low temperature toughness can be guaranteed. In this document, the effective crystal size means a region surrounded by grain boundaries that have an orientation difference of 15 ° or more, which can be measured using EBSD, for example. The details of it will be described below.
    STEEL PLATE MICRO-STRUCTURE [0090] First, a microstructure of a hot-rolled steel sheet according to the present invention will be described.
    [0091] In this steel plate, the main phase is one or both of tempered martensite and lower bainite in a fraction of total volume of 90% or more, so that a maximum tensile strength of 980 MPa or more is guaranteed. Thus, the main phase must be one or both of tempered martensite and lower bainite.
    [0092] In the present invention, the tempered martensite is the microes
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    11/49 most important structure for having a high resistance, excellent baking hardening effect and excellent low temperature toughness. Tempered martensite is an aggregation of lath-shaped crystal grains that includes iron-based carbides within the lath that have a main geometric axis of 5 nm or more. Furthermore, these carbides belong to a plurality of variants, in other words, a plurality of iron-based carbides that extend in different directions.
    [0093] The tempered martensite structure can be obtained by decreasing the cooling speed at the time of cooling performed at a temperature less than or equal to the point Ms (the temperature at which the martensitic transformation begins) or by producing a martensite structure and then tempering it from 100 ° C to 600 ° C. In the present invention, precipitation is controlled by cooling the control to a temperature below 400 ° C.
    [0094] The lower bainite is also an aggregation of lath-shaped crystal grains that includes iron-based carbides within the lath that have a main geometric axis of 5 nm or more. In addition, these carbides belong to a single variant, in other words, a group of iron-based carbides that extend in the same direction. Observing the carbide extension direction makes it easier to discriminate between tempered martensite and lower bainite. In this document, the group of carbides based on iron that extends in the same direction as a difference in the direction of extension in the group of carbides based on iron is within 5 °.
    [0095] When the total volume fraction of one or both of tempered martensite and lower bainite is less than 90%, a high tensile strength of 980 MPa or more cannot be guaranteed and a maximum tensile strength of 980 MPa or more, which is
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    12/49 one of the requirements of the present invention, cannot be guaranteed. Thus, the lower limit of the total volume fraction of one or both of tempered martensite and lower bainite is 90%. On the other hand, even when the total volume fraction is 100%, the high strength, excellent baking hardening effect and excellent low temperature toughness, which are effects of the present invention, are shown.
    [0096] In the steel plate structure, like another structure, one or more of ferrite, fresh martensite, upper bainite, perlite and retained austenite can be contained in a total volume fraction of 10% or less as unavoidable impurities.
    [0097] In this document, fresh martensite is defined as martensite that does not include carbides. Although fresh martensite has high strength, low temperature toughness is poor; therefore, its volume fraction needs to be limited to 10% or less. In addition, the density of disagreement is extremely high and the baking hardening effect is poor. Thus, the volume fraction of the same needs to be limited to 10% or less.
    [0098] Retained austenite is transformed into fresh martensite when a steel material is plastically deformed at the time of baking hardening effect or when a car member is plastically deformed at the time of the collision and then the retained austenite has similar adverse effects to those of the fresh martensite described above. In this way, the volume fraction needs to be limited to 10% or less.
    [0099] The upper bainite is an aggregation of lath-shaped crystal grains and is an aggregation of slats that include carbides between the slats. The carbides included between the slats serve as a starting point for the fracture and decrease the low temperature toughness. Furthermore, since the upper bainite is formed in tempera
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    13/49 higher than lower bainite, the resistance is low and its excessive formation is difficult to guarantee a maximum tensile strength of 980 MPa or more. This effect will be obvious if the volume fraction of the upper bainite exceeds 10% and, therefore, the volume fraction of the upper bainite needs to be limited to 10% or less.
    [00100] Ferrite means a volume of crystal grains and the structure that does not include, within the structure, an inferior structure like a clapboard. Since ferrite is the softest structure and leads to a reduction in strength in order to guarantee a maximum tensile strength of 980 MPa or more, it is necessary to have a limit that is 10% or less. In addition, since ferrite is much softer than tempered martensite or lower bainite, which is included in the main phase, deformation is concentrated at the interface between these structures to easily serve as a starting point for a fracture, resulting in bad low temperature toughness. These effects will be obvious if the volume fraction exceeds 10% and, therefore, the volume fraction of the volume needs to be limited to 10% or less.
    [00101] Perlite leads to decreased strength and degradation of low temperature toughness, in the same way as ferrite; therefore, its volume fraction needs to be limited to 10% or less.
    [00102] Regarding the steel plate according to the present invention, which has the structure described above, the identification of tempered martensite, fresh martensite, bainite, ferrite, perlite, austenite and the balance included in them, the determination of existing positions and measurement of area fractions can be performed by corroding a cross-section in the rolling direction of the steel sheet or a cross-section in a direction perpendicular to the rolling direction with the use of a nital reagent and a reagent disclosed in the JP document S59-219473A and then looking at the steel plate through a
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    14/49 transmission and scanning electron microscope at a magnification of 1,000 to 100,000.
    [00103] Structure discrimination is also possible through analysis of crystal orientations using a FESEMEBSP method or measuring the hardness of a micro-region as a measurement of micro-Vickers hardness. For example, as described above, tempered martensite, upper bainite and lower bainite are different from each other in the carbide formation sites and in the relationship of crystal orientations (extension directions). Thus, observing the iron-based carbides inside the lath-shaped crystal grains through an FE-SEM to examine its extension directions, it is possible to easily discriminate between bainite and tempered martensite.
    [00104] In the present invention, the volume fractions of ferrite, perlite, bainite, tempered martensite and fresh martensite are obtained as follows: the samples are extracted as observation surfaces with the use of transversal cuts in the thickness direction of the plate, which is parallel to the rolling direction of the steel sheet; the observation surfaces are polished and etched by nital and a range of 1/8 to 3/8 thickness that centralizes 1/4 of the plate thickness is observed through a scanning electron microscope with field emission (FE-SEM ) to measure area fractions such as volume fractions. The measurement is performed in ten fields at an enlargement of 5,000 for each sample and an average is used as the area fractions.
    [00105] Since the fresh martensite and retained austenite are not corroded sufficiently by nital etching, in observation by FE-SEM, it is possible to clearly distinguish between the structures described above (ferrite, bainite ferrite, bainite and tempered martensite). In this way, it is possible to obtain the fraction of sea volume
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    15/49 fresh tensite as a difference between the fraction of area of an uncorroded region observed by FE-SEM and the fraction of retained austenite area measured using X-rays.
    [00106] The density of disagreement in the structure of one or both of tempered martensite and lower bainite needs to be limited to 1χ10 16 (1 / m 2 ) or less. This is to obtain the excellent baking hardening effect. In general, the density of discrepancies in the tempered martensite is high, so that the excellent baking hardening effect cannot be guaranteed. In this way, by controlling the cooling conditions in the hot rolling, in particular, by setting the cooling speed at temperatures below 400 ° C to below 50 ° C / s, the excellent baking ha rdening effect can be obtained.
    [00107] On the other hand, if the density of disagreement is less than 5χ10 13 (1 / m 2 ), it will be difficult to guarantee a resistance of 980 MPa or more and, thus, the lower limit of the density of disagreement is defined in 5χ10 13 (1 / m 2 ), desirably a value in the range of 8χ10 13 to 8χ10 15 (1 / m 2 ), most desirably a value in the range of 1χ10 14 to 5χ10 15 (1 / m 2 ).
    [00108] The discrepancy density can be obtained by observing the use of X-rays or a transmission type electron microscope, as long as the discrepancy density can be measured. In the present invention, by observing thin film using an electron microscope, the density of discordance is measured. In measurement, the film thickness of a measurement region and then the number of discrepancies in the volume is measured, so that the density is measured. The measurement is performed in ten fields at an enlargement of 10,000 for each sample to calculate the density of discrepancy.
    [00109] One or both of tempered martensite and bainite inf
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    16/49 above according to the present invention desirably include 1x10 6 (numbers / mm 2 ) or more iron-based carbides. This is to increase the low temperature toughness of the base phase and to achieve a balance between high strength and excellent low temperature toughness. That is, even though the cooled martensite without any additional treatment has a high resistance, its toughness is poor and an improvement is necessary. In this way, by precipitating 1x10 6 (numbers / mm 2 ) or more iron-based carbides, the toughness of the main phase is improved.
    [00110] According to the study of the present inventors in the relationship between the low temperature toughness and the numerical density of iron-based carbides, it was revealed that the excellent low temperature toughness can be guaranteed by defining the numerical density of carbides in one or both of tempered martensite and lower bainite to 1x10 6 (numbers / mm 2 ) or more. Thus, the numerical density of carbides in one or both of tempered martensite and lower bainite is set to 1x10 6 (numbers / mm 2 ) or more, desirably 5x10 6 (numbers / mm 2 ) or more, more desirably 1x10 7 (numbers / mm 2 ) or more.
    [00111] In addition, the size of carbides precipitated through the above treatment in the present invention is small, which is 300 nm or less and most of the carbides are precipitated in the martensite or bainite slats; thus, it is assumed that the low temperature toughness is not worsened.
    [00112] The numerical density of carbides is measured as follows: the samples are extracted as observation surfaces with the use of cross-sections in the direction of the plate thickness, which is parallel to the rolling direction of the steel plate; the observation surfaces are polished and etched by nital and a strip of 1/8 to 3/8 thickness that centralizes 1/4 of the plate thickness is observed
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    17/49 using a field-emitting scanning electron microscope (FE-SEM). The numerical density measurement of iron-based carbides is performed in ten fields at an enlargement of 5,000 for each sample.
    [00113] In order to further increase the low temperature toughness, one or both of tempered martensite and lower bainite are included as the main phase and, in addition, their effective crystal size is set at 10 pm or less. The effects of increasing low temperature toughness become obvious by setting the effective crystal size to 10 pm or less; in this way, the effective crystal size is set to 10 pm or less, desirably 8 pm or less. The effective crystal size mentioned in this document means a region surrounded by grain boundaries that have a crystal orientation difference of 15 ° or more, which will be described later, and corresponds to a block grain size of martensite or bainite.
    [00114] Next, the methods for identifying an average crystal grain size and structure will be described. In the present invention, the average crystal grain size, ferrite and retained austenite are defined using a standard electron backscattering diffraction image microscopy (EBSP-OIM TM ). The EBSP-OIM TM method is configured by a device and software by means of which a highly tilted sample is irradiated with electron beams in a scanning electron microscope (SEM), the Kikuchi patterns formed by backscattering are imaged by a camera with high sensitivity and computer image processing is performed to measure the crystal orientation of the irradiation point in a short period of time. In the EBSP method, it is possible to quantitatively analyze the microstructure and the crystal orientations on the surface of the volume sample, the area of analysis is a region that
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    18/49 can be observed by an SEM and, depending on the resolution of the SEM, a resolution of a minimum of 20 nm can be analyzed. In the present invention, from an image mapped by setting the difference in orientation in crystal grains to 15 °, which is the limit of high angle grain boundaries commonly recognized as the crystal grain boundaries, the grains are visualized and the average crystal grain size is obtained.
    [00115] The aspect ratio of effective crystal grains (in this document, this means a region surrounded by grain boundaries of 15 ° or more) of tempered and baitite martensite is desirably 2 or less. Grains flattened in a specific direction have high anisotropy and often have low toughness due to the fact that cracks propagate along the grain boundaries at the time of the Charpy test. In this way, it is necessary to produce the effective crystal grains as isomeric as possible. In the present invention, a cross-section of the steel sheet in the rolling direction is observed and a ratio (= L / T) of the length in the rolling direction (L) to the length in the thickness direction of the sheet (T) has been defined as the aspect ratio.
    CHEMICAL COMPOSITION OF STEEL SHEET [00116] Next, the reasons for the limits in the chemical composition of the hot-rolled steel sheet with high strength according to the present invention will be described. It should be noted that this% as mass% of the content medium.
    [00117] C: from 0.01% to 0.2%.
    [00118] C contributes to an increase in the resistance of the base material and the improvement in the baking hardening effect and also generates iron-based carbides such as cementite (Fe3C), which serves as a starting point for breaking at the time of bore expansion . If the C content is less than 0.01%, the effect of increasing the resistance
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    19/49 as a result of the reinforcement of the structure by a low temperature transformation generation phase cannot be obtained. If the content exceeds 0.2%, the ductility will be decreased and the iron-based carbides like cementite (Fe3C), which serve as a starting point for breaking in a two-dimensional shear plane at the time of the drilling process, will be increased , resulting in degradation of formability such as hole expandability. Therefore, the C content is limited to the range of 0.01% to 0.2%.
    [00119] Si: from 0% to 2.5%.
    [00120] Si contributes to an increase in the strength of the base material and can be used as a molten steel deoxidizer. Thus, preferably 0.001% or more of Si is contained as needed. However, if the content exceeds 2.5%, the effect of contributing to the increase in strength will be saturated; thus, the Si content is limited to 2.5% or less. In addition, when 0.1% or more of Si is contained, as the content is increased, the precipitation of iron-based carbides such as cementite is suppressed more in the material structure, contributing to the increase in strength and expandability the hole. If the Si content exceeds 2.5%, the effect of suppressing the precipitation of iron-based carbides will be saturated. Therefore, the desirable range of Si content is 0.1% to 2.5%.
    [00121] Mn: from 0% to 4%.
    [00122] Mn can be obtained so that the steel plate structure can have a main phase of one or more among tempered martensite and lower bainite through hardening by sudden cooling, in addition to solution reinforcement. If the addition is carried out in such a way that the Mn content exceeds 4%, that effect will be saturated. On the other hand, if the Mn content is less than 1%, the effects of suppressing ferritic and bainitic transformation will not be shown easily during cooling. Thus, the Mn content is
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    20/49 is 1% or more, more desirably from 1.4% to 3.0%. [00123] One or both of Ti and Nb: 0.01% to 0.30% in total [00124] Each of Ti and Nb is the most important constituent element in order to achieve both excellent low temperature toughness and high strength of 980 MPa or more. The carbonitrides of the same or dissolved Ti and Nb delay the growth of grains at the time of hot rolling, thus contributing to the refining of the grain size of a hot rolled plate and to the increase in low temperature toughness. Dissolved N is important because dissolved N promotes grain growth. At the same time, Ti is particularly important because Ti can exist as TiN to contribute to the increase in low temperature toughness by refining the grain size when heating the hot rolled plate. In order to obtain a grain size of the hot rolled sheet that is 10 pm or less, 0.01% or more of Ti and Nb, alone or in combination, needs to be contained. If the total content of Ti and Nb exceeds 0.30%, the above effect will be saturated and economic efficiency will be reduced. Therefore, the content of Ti and Nb in total is desirably in the range of 0.02% to 0.25%, more desirably in the range of 0.04% to 0.20%.
    [00125] Al: from 0% to 2.0% [00126] Al may be contained due to the fact that Al suppresses the formation of coarse cementite and increases the low temperature toughness. In addition, Al can be used as a deoxidizer. However, excessive Al will increase the amount of thick Al-based inclusions, resulting in degradation of bore expandability and surface scratches. Therefore, the upper limit for Al content is 2.0%, desirably 1.5%. Since it is difficult to contain 0.001% or less of Al, this is a substantial lower limit.
    [00127] N: from 0% to 0.01%.
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    21/49 [00128] N may be contained due to the fact that N increases the baking hardening effect. However, N can lead to the formation of bubbles at the same time as welding, which can decrease the resistance of welded parts. Thus, the N content must be 0.01% or less. On the other hand, the N content that is 0.0005% or less is not economically effective and therefore the N content is desirably 0.0005% or more.
    [00129] The above elements are the basic chemical composition of the hot-rolled steel sheet according to the present invention and the following composition may additionally be contained.
    [00130] One or more of Cu, Ni, Mo, V and Cr may be contained due to the fact that these elements suppress the ferritic transformation at the time of cooling and change the structure of the steel sheet to one or both within a martensite structure tempered and a lower bainite structure. In addition, one or more of these elements may be contained due to the fact that these elements have an effect of increasing the strength of the hot-rolled steel sheet by reinforcing precipitation or reinforcing solution. However, if the content of each of Cu, Ni, Mo, V and Cu is less than 0.01%, the above effects will not be sufficiently shown. In addition, if the Cu content exceeds 2.0%, the Ni content exceeds 2.0%, the Mo content exceeds 1.0%, the V content exceeds 0.3% and the Cr content exceeds 2 , 0%, the above effects will be saturated and economic efficiency will be diminished. Therefore, it is desirable that, in a case where one or more of Cu, Ni, Mo, V and Cr are contained as needed, the contents of Cu, Ni, Mo, V and Cr vary from 0.01% to 2, 0%, from 0.01% to 2.0%, from 0.01% to 1.0%, from 0.01% to 0.3% and from 0.01% to 2.0%, respectively.
    [00131] One or more of Mg, Ca and REM (rare earth metal) may be contained due to the fact that these elements control the
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    22/49 form of non-metal inclusions that serve as a fracture starting point and a factor of processability degradation in order to increase processability. When the total content of Ca, REM and Mg is 0.0005%, the effects will be obvious. Thus, in a case where one or more of these elements are contained, their total content needs to be 0.0005% or more. In addition, if the Mg content exceeds 0.01%, the Ca content exceeds 0.01% and the REM content exceeds 0.1%, the above effects will be saturated and the economic effectiveness will be diminished. Therefore, it is desirable that the Mg content, the Ca content and the REM content vary from 0.0005% to 0.01%, from 0.0005% to 0.01% and from 0.0005% to 0, 1%, respectively.
    [00132] B contributes to change the structure of the steel sheet to one or both of a tempered martensite structure and a lower bainite structure through the delay of the ferritic transformation. In addition, like C, by segregating B at the grain boundaries to increase the grain boundary resistance, the low temperature toughness is increased. Then, B may be contained in the steel plate. However, this effect becomes obvious when the B content in the steel sheet is 0.0002% or more; thus, its lower limit is desirably 0.0002%. On the other hand, if the B content exceeds 0.01%, the effect is saturated and the economic efficiency is reduced; thus, the upper limit is 0.01%. The B content is desirably in the range of 0.0005% to 0.005%, more desirably from 0.0007% to 0.0030%.
    [00133] As for the other elements, even when one or more of Zr, Sn, Co, Zn and W are contained in a total content of 1% or less, the effects of the present invention are confirmed not to be damaged. Among these elements, Sn can generate scratches when hot rolling; thus, its content is desirably 0.05% or less.
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    23/49 [00134] In the present invention, the composition in addition to that above is Fe, but the unavoidable impurities that are mixed from raw materials for melting, such as scrap or refractories, are acceptable. Typical impurities are as follows.
    [00135] P: 0.10% or less [00136] P, which is an impurity contained in pig iron, is segregated at the grain boundaries and as the grain content is increased, the low temperature toughness is decreased further. Thus, the P content is desirably as low as possible and is 0.10% or less due to the fact that the content that is more than 0.10% will adversely affect processability and weldability. In particular, considering the weldability, the P content is desirably 0.03% or less. The lower the P content, the more preferable it is; however, more than necessary reduction will overload a steelmaking process with a heavy load. In this way, the lower limit of the P content can be 0.001%.
    [00137] S: 0.03% or less [00138] S is also an impurity contained in pig iron. If the S content is too high, the break will be generated at the time of the hot rolling and also the inclusions like MnS, which worsen the bore expandability, will be generated. Therefore, the S content should be as low as possible and 0.03% or less is within an acceptable range. Therefore, the S content is 0.03% or less. It is observed that, in a case where a certain hole expandability is required, the S content is preferably 0.01% or less, more preferably 0.005% or less. The lower the S content, the more preferable it is; however, more than necessary reduction will overload a steelmaking process with a heavy load. In this way, the lower limit of the
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    24/49
    S can be 0.0001%.
    [00139] O: 0.01% or less [00140] Excess O generates thick oxides that serve as a fracture starting point in steel and causes brittle fracture or hydrogen-induced cracking, so that the O content is 0 , 01 or less. For spot weldability, the O content is desirably 0.03% or less. The O content can be 0.0005% or more due to the fact that O disperses a large amount of fine oxides at the time of melting steel deoxidation.
    [00141] The hot-rolled steel sheet with high resistance according to the present invention, which has the structure and chemical composition described above, can have high resistance to corrosion including, on its surface, a galvanized layer by immersion at hot through hot dip galvanizing treatment and a galvanized and annealing layer through galvanizing and annealing treatment (galvanizing and annealing treatment means the treatment using a hot dip plating process and an alloy forming process) . It is observed that the plated layer is not limited to pure zinc and any elements such as Si, Mg, Zn, Al, Fe, Mn, Ca and Zr can be added in order to further increase the corrosion resistance. The inclusion of such a plated layer does not damage the excellent baking hardening effect and low temperature toughness of the present invention.
    [00142] Alternatively, the effects of the present invention can be shown by including a surface treatment layer formed by any one of the following: formation of an organic film, film lamination, treatment of organic salts / inorganic salts, treatment of not chrome and the like.
    METHOD FOR PRODUCING STEEL SHEET [00143] The following describes a method for producing steel sheet
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    25/49 steel according to the present invention.
    [00144] In order to achieve the excellent baking hardening effect and low temperature toughness, it is important that the disagreement density is 1x10 16 (1 / m 2 ) or less, the amount of iron-based carbides is 1x10 6 (numbers / mm 2 ) or more, and the total content of one or both of tempered martensite and lower bainite, each of which has a grain size of 10 pm or less, either 90% or more. Details of the production conditions to satisfy all of the above conditions will be described below.
    [00145] There is no particular limitation in the production method before hot rolling. That is, subsequent to melting in a high furnace, electric furnace, or similar, secondary refining is carried out in various ways so that the composition is adjusted to be the above composition, followed by normal continuous casting, an ingot method, casting of thin hot-rolled plate, or the like.
    [00146] In the case of continuous casting, cooling can be carried out to make the temperature low and then reheating can be carried out before hot rolling, an ingot can be hot rolled without cooling to room temperature, or a hot rolled die-cast plate can be hot rolled continuously. As long as the composition can be controlled within the range according to the present invention, scrap can be used as a raw material.
    [00147] The steel sheet with high resistance according to the present invention is obtained when the following requirements are satisfied.
    [00148] To produce the steel sheet with high resistance, melting is carried out to obtain a predetermined steel sheet composition, and then, optionally, after cooling, a plate
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    26/49 hot rolled hot-rolled casting is heated to a temperature of 1,200 ° C or more, hot rolling is completed to a temperature of 900 ° C or more, the steel plate is cooled at a speed cooling temperature of 50 ° C / s or more on average, from a final rolling temperature to 400 ° C and the steel sheet is coiled at a temperature of less than 400 ° C and a cooling speed of no more than 50 ° C / s. In this way, it is possible to produce a hot-rolled steel sheet with high strength that has excellent baking hardening effect and low temperature toughness with a maximum tensile strength of 980 MPa or more.
    [00149] The temperature for heating the hot rolled plate in hot rolling needs to be 1,200 ° C or more. In the steel plate according to the present invention, austenite grains are prevented from becoming thick by the use of dissolved Ti and Nb, and therefore it is necessary to dissolve the NbC and TiC that were precipitated at the time of casting. If the temperature for heating the hot-rolled plate is less than 1,200 ° C, the carbides of Nb and Ti will take a long time to melt, and thus the crystal grain size will not be refined after that and the effect of increased low temperature toughness caused by refinement will not be shown. Therefore, the temperature for heating the hot-rolled plate must be 1,200 ° C or more. The effect of the present invention can be shown even without any particular upper limit on the temperature for heating the hot-rolled plate; however, an excessively high temperature for heating is not economically efficient. Therefore, the upper temperature limit for heating the hot-rolled plate is desirably less than 1300 ° C.
    [00150] The final laminating temperature must be 900 ° C or
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    27/49 more. Large amounts of Ti and Nb are added to the steel sheet according to the present invention in order to refine the austenite grain size. Therefore, if the final lamination is carried out at a temperature in the range of less than 900 ° C, it is unlikely that austenite will be recrystallized and grains that extend in the direction of the lamination will be generated, which easily causes the degradation of toughness. In addition, when non-recrystallized austenite is transformed into martensite or bainite, discharges accumulated in austenite are passed to martensite or bainite, so that the density of discrepancy in the steel plate cannot be within the range regulated in the present invention, which results in the degradation of baking hardening effect. Therefore, the final laminating temperature is 900 ° C or more.
    [00151] It is necessary to cool to an average cooling speed of 50 ° C / s or more from the final lamination temperature to 400 ° C. If the cooling speed is less than 50 ° C / s, ferrite will be formed in the middle of the cooling process, and it will be difficult to make the volume ratio of the main phase, one or both of tempered martensite and lower bainite, 90% or more . Therefore, the average cooling speed must be 50 ° C / s or more. However, if no ferrite is formed during the cooling process, air cooling can be carried out at temperatures from the final rolling temperature up to 400 ° C.
    [00152] It should be noted that it is preferable to set the cooling speed of a point Bs at the temperature at which the lower bainite is generated (hereinafter referred to as the lower bainite generation temperature) at 50 ° C / s or more. This is done to prevent the formation of superior bainite. If the cooling speed of point Bs at the lower bainite generation temperature is less than 50 ° C / s, the upper bainite will be generated; additionally, fresh martensite (martensite
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    28/49 which has a high density of disagreement) will be generated between slats of bainite, or retained austenite (will be transformed into martensite that has a high density of disagreement at the time of processing) will exist, which results in the degradation of the baking hardening effect and low temperature toughness. It should be noted that the point Bs is the temperature at which the upper bainite begins to be generated, the temperature that is defined depends on the composition, and is 550 ° C for convenience. Although also defined depending on the composition, the lower bainite generation temperature is 400 ° C for convenience. From the final laminating temperature up to 400 ° C, the average cooling speed is set to 50 ° C / s or more, and the cooling speed especially from 550 ° C to 400 ° C is set to 50 ° C / s or more.
    [00153] It should be noted that the setting of the average cooling speed to 50 ° C / s or more from the final rolling temperature up to 400 ° C includes the case where the cooling speed is set to 50 ° C / s or more from the final laminating temperature up to 550 ° C and the cooling speed is set to less than 50 ° C / s from 550 ° C to 400 ° C. However, under this condition, the upper bainite is easily generated, and more than 10% of the upper bainite can be partially generated. Therefore, it is preferable to set the cooling speed to 50 ° C / s or more from 550 ° C to 400 ° C.
    [00154] The maximum cooling speed at temperatures below 400 ° C must be less than 50 ° C / s. This is done to make a main phase of one or both of tempered martensite and lower bainite in which the density of discrepancy and the numerical density of iron-based carbides are defined within the above range. If the maximum cooling speed is 50 ° C / s or more, the iron-based carbides and the density of discord
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    29/49 will not be within the above range, and the excellent baking hardening effect and toughness are not achieved. Thus, the maximum cooling speed must be less than 50 ° C / s.
    [00155] In the present context, cooling to temperatures of less than 400 ° C and the cooling speed of not more than 50 ° C / s are achieved by air cooling, for example. Cooling in the present context not only dignifies cooling, but also includes the rewinding of the steel sheet in isothermal retention, that is, rewinding at temperatures below 400 ° C. In addition, the cooling speed is controlled in this temperature range so that the density of discrepancy and the numerical density of iron-based carbides in the structure steel plate are controlled. Thus, after cooling is performed so that the temperature becomes the temperature at which the martensitic transformation begins (point Ms) or less, even when the temperature is increased and reheating is carried out, it is still possible to obtain a tensile strength maximum 980 MPa or more, excellent baking hardening effect, and excellent toughness, which are the effects of the present invention.
    [00156] In general, the transformation of ferrite needs to be suppressed to obtain martensite, and cooling to 50 ° C / s or more is considered necessary. Additionally, at low temperatures, there are disagreements over a temperature range called the film boiling range, in which the heat exchange coefficient is relatively low and cooling is difficult, for a temperature range called the nucleated temperature boiling range in which the heat exchange coefficient is high and cooling is easy. In a case in which cooling is stopped at a temperature range of less than 400 ° C, the rewinding temperature is likely to vary, and therefore the material quality varies. So, typically, the embobin temperature
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    30/49 was often set at temperatures above 400 ° C or at room temperature.
    [00157] As a result, it is admitted that it has not been found in the related technique that rewinding at temperatures below 400 ° C or a decrease in cooling speed can lead to a maximum tensile strength of 980 MPa or more, an effect excellent baking hardening, and an excellent toughness temperature.
    [00158] It should be noted that, in order to increase the ductility by correcting the steel sheet and the formation of mobile discrepancies, after all the steps are finished, the finishing lamination is performed in a desirable manner to a reduction of 0.1 % to 2%. In addition, after all steps are completed, in order to remove the scales attached to the surface of the hot rolled steel sheet thus obtained, the hot rolled steel sheet can be blasted as needed. In addition, after pickling, the resulting hot-rolled steel sheet can be subjected to finish or cold rolling to a reduction of 10% or less in an online or offline manner.
    [00159] The steel sheet of the present invention is produced by continuous casting, rough rolling, final rolling, or pickling, which is a typical hot rolling process; however, even when part of them is omitted in production, the effects of the present invention, which are a maximum tensile strength of 980 MPa or more, excellent baking hardening effect, and excellent low temperature toughness, can be ensured.
    [00160] Additionally, after the hot-rolled steel sheet is produced, even when the heat treatment is carried out in a temperature range of 100 ° C to 600 ° C in an online or offline method in order to precipitate carbides, the effects of the present invention, which are excellent baking hardening effect, low toughness
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    31/49 x excellent temperature, and a maximum tensile strength of 980 MPa or more, can be ensured.
    [00161] The steel sheet that has a maximum tensile strength of 980 MPa or more in the present invention means a steel sheet that has 980 MPa or more maximum tensile strength measured by the stress test in accordance with JIS Z 2241 with use of JIS test piece No. 5, that is, cut in a direction perpendicular to the direction of the hot rolling mill.
    [00162] The steel plate that has an excellent baking hardening effect in the present invention means a steel plate that has 60 MPa or more, desirably 80 MPa or more, difference in the conventional limit of elasticity at the time of shrinkage test after 2% of the traction pre-strain is transmitted, followed by heat treatment at 170 ° C for 20 minutes. The difference above corresponds to the baking hardening (BH) effect measured according to the coating hardening baking test methods described by an appendix to JIS G 3135.
    [00163] The steel sheet which has excellent tenacity at low temperatures in the present invention means a steel sheet which has -40 ° C of fraction discrepancy temperature (vTrs) measured by the Charpy test conducted in accordance with JIS Z 2242 In the present invention, since the target steel sheet is used primarily for automotive applications, the thickness is typically about 3 mm. Thus, the surface of the hot-rolled steel plate is ground and the steel plate is processed in a 2.5 mm sub-size test piece.
    EXAMPLES [00164] The technical content of the present invention will be described considering the Examples of the present invention.
    [00165] As Examples, inventive steels A to S that satisfy
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    32/49 the conditions of the present invention and comparative steels a to k, component compositions of which are shown in Table 1, and results of studies thereof will be described.
    [00166] After these steels were cast, these steels were either directly heated to a temperature of 1,030 ° C to 1,300 ° C, or the steels were cooled to room temperature and then reheated to that temperature range. Then, hot rolling was performed under the conditions shown in Tables 2-1 and 2-2, final rolling was performed at temperatures from 760 ° C to 1.0 30 ° C, and cooling and rewinding were performed under conditions shown in Tables 2-1 and 2-2. Thus, hot-rolled steel sheets having a thickness of 3.2 mm were produced. Then, pickling was carried out and 5% of the finishing lamination was carried out.
    [00167] Several test pieces were cut from the hot-rolled steel sheets thus obtained to perform material quality testing and structure observation.
    [00168] The stress test was conducted by cutting the JIS No. 5 test pieces in a direction perpendicular to the lamination direction, in accordance with JIS Z 2242.
    [00169] The baking hardening effect was measured by cutting the JIS No. 5 test pieces in a direction perpendicular to the lamination direction, in accordance with a coating hardening baking test method described in an appendix to JIS G 3135. A pre-tension was 2% and the heat treatment conditions were 170 ° C χ 20 minutes.
    [00170] The Charpy trial was conducted in accordance with JIS Z 2242, and fracture discordance temperatures were measured. Since each of the steel sheets of the present invention had a thickness of less than 10 mm, both surfaces of the hot-rolled steel sheet were ground to have a 2.5 mm thickness. 870190075401, from 05/08/2019, p. . 41/66
    33/49 weight, and then the Charpy trial was conducted.
    [00171] Some of the steel sheets were obtained as hot-dip galvanized steel sheet (GI) and galvanized steel sheet (GA) by heating the hot-rolled steel sheet to 660 ° C to 720 ° C, and perform the hot dip galvanizing treatment or plating treatment followed by heat treatment of alloy formation at 540 ° C to 580 ° C, for which the material quality test is conducted.
    [00172] The microstructure observation was performed by the above method and each structure was measured by volume fraction, discrepancy density, numerical density of iron-based carbides, effective crystal size, and aspect ratio.
    [00173] Tables 3-1 and 3-2 show the results.
    [00174] It is clear that only the stocks that satisfy the conditions of the present invention had a maximum tensile strength of 980 MPa or more, excellent baking hardening effect, and excellent low temperature toughness.
    [00175] In contrast, steels A-3, B-4, E-4, J-4, M-4, and S-4 were not able to have the fraction of structure and size of crystal effective within the range of present invention, and had lower strength and low low temperature toughness due to the fact that Ti and Nb carbides that were precipitated at the time of casting are unlikely to be dissolved due to the temperature for heating the hot rolled plate to be less than 1,200 ° C, although the other hot rolling conditions were within the range of the present invention.
    [00176] The A-4, B-5, J-5, M-5, and S-5 steels were formed at a final rolling temperature too low for the rolling to be carried out in a non-recrystallized austenite strip. Therefore, the density of discrepancy in the hot-rolled sheet was high
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    34/49 too much and the baking hardening effect was low, and in addition, the grains were extended in the direction of lamination and the aspect ratio was high. Therefore, steels A-4, B-5, J-5, M-5, and S-5 had a high aspect ratio and low toughness.
    [00177] A-5, B-6, J-6, M-6, and S-6 steels were formed at a cooling speed of less than 50 ° C / s from the final rolling temperature to 400 ° C, so that a large amount of ferrite is formed during cooling. Therefore, high resistance was hardly ensured and the interface between ferrite and martensite served as a starting point for fracture. Therefore, steels A-5, B-6, J-6, M-6, and S-6 had low low temperature toughness.
    [00178] A-6, B-7, J-7, M-7, and S-7 steels were formed at a maximum cooling speed of 50 ° C / s or higher temperatures of less than 400 ° C, so that the density of discrepancy in the martensite was high and the baking hardening effect was low. Additionally, the amount of carbide precipitation was insufficient, and therefore, steels A-6, B-7, J-7, M-7, and S-7 had low tenacity at low temperature.
    [00179] It should be noted that, in steel B-3 in the Examples, in a case where the cooling speed was set at 45 ° C / s from 550 ° C to 400 ° C, the average cooling speed was 80 ° C / s from 950 ° C, which is the final lamination temperature, up to 400 ° C. Therefore, an average cooling speed of 50 ° C or more was satisfied; however, a steel plate structure included 10% or more of upper bainite partially and the quality of the material of the same varied.
    [00180] An A-7 steel was formed at a rewinding temperature as high as 480 ° C, so that the steel plate structure became the upper bainite structure. Therefore, the maximum tensile strength of 980 MPa or more was difficult to obtain and carbon
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    35/49 rough iron-based surfaces precipitated between existing slats in the upper bainite structure that served as a starting point for fracture. Therefore, A-7 steel had low low temperature toughness.
    [00181] B-8, J-8, and M-8 steels were formed at coiling temperatures as high as 580 ° C to 620 ° C, so that the steel sheet structure became a mixed structure of ferrite and perlite which includes Ti and Nb carbides. Therefore, most of the C in the steel plate was precipitated as carbides, and a sufficient amount of dissolved C was not ensured. Therefore, steels B-8, J-8, and M-8 had a low baking hardening effect.
    [00182] Additionally, as shown in steels A-8, A-9, B-9, B-10, E-6, E-7, J-9, J-10, M-9, M-10, S -9 and S-10, even when galvanizing and annealing treatment or galvanizing and annealing treatment is carried out, the quality of the material of the present invention can be ensured.
    [00183] In contrast, aak steels whose component steel plate components were not within the range of the present invention were not able to have a maximum tensile strength of 980 MPa or more, with excellent baking hardening effect, and the toughness of excellent low temperature as defined in the present invention.
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    TABLE 1
    Steel Ç Si Mn P s Al N 0 You Nb Others Note THE 0.054 1.32 2.34 0.009 0.0009 0.029 0.0024 0.0022 0.192 - - Inv. Steel B 0.063 1.16 2.91 0.012 0.0024 0.033 0.0021 0.0016 0.103 0.021 - Inv. Steel Ç 0.069 0.76 2.31 0.015 0.0023 0.024 0.0021 0.0016 0.062 0.031 Cu = 0.23 Inv. Steel D 0.070 0.59 2.39 0.007 0.0016 0.018 0.0029 0.0020 0.049 0.039 Ni = 0.42 Inv. Steel AND 0.068 0.72 1.89 0.010 0.0038 0.016 0.0027 0.0023 - 0.087 Mo = 0.38 Inv. Steel F 0.059 1.76 2.42 0.008 0.0043 0.011 0.0026 0.0015 0.024 0.016 V = 0.046 Inv. Steel G 0.068 1.06 1.78 0.006 0.0012 0.032 0.0025 0.0027 0.101 - Cr = 0.62 Inv. Steel H 0.082 0.64 2.28 0.009 0.0005 0.006 0.0027 0.0021 0.089 - Mg = 0.0014 Inv. Steel I 0.060 0.54 2.30 0.014 0.0038 0.010 0.0032 0.0016 0.102 - Ca = 0.0008 Inv. Steel J 0.073 0.08 2.53 0.018 0.0026 1,080 0.0072 0.0009 0.052 0.012 B = 0.0028 Inv. Steel K 0.070 0.84 2.32 0.007 0.0019 0.020 0.0016 0.0018 0.027 0.011 REM = 0.0038 Inv. Steel L. 0.103 0.89 2.27 0.009 0.0030 0.017 0.0030 0.0016 0.086 - - Inv. Steel M 0.109 0.92 2.07 0.012 0.0024 0.034 0.0320 0.0022 0.049 0.025 B = 0.0013 Inv. Steel N 0.107 0.85 1.64 0.011 0.0027 0.016 0.0016 0.0018 0.099 - Cr = 1.26 Inv. Steel 0 0.111 0.69 2.31 0.016 0.0007 0.010 0.0027 0.0021 0.095 - Ca = 0.0022 Inv. Steel
    36/49
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    P 0.114 0.13 1.89 0.012 0.0025 0.642 0.0026 0.0012 0.071 0.016 Mo = 0.19,B = 0.0009 Inv. Steel Q 0.157 1.22 2.34 0.010 0.0018 0.030 0.0030 0.0023 0.048 0.009 B = 0.0009 Inv. Steel R 0.161 1.08 2.31 0.009 0.0021 0.028 0.0024 0.0018 0.062 - - Inv. Steel s 0.200 0.87 2.11 0.013 0.0032 0.020 0.0023 0.0021 0.067 0.002 Cr = 0.29 Inv. Steel The 0.002 0.34 1.32 0.062 0.0056 0.034 0.0033 0.0032 0.019 0.042 - Comp. Steel B 0.620 1.32 2.16 0.013 0.0034 0.024 0.0021 0.0017 0.021 0.029 - Comp. Steel ç 0.084 3.09 2.34 0.021 0.0029 0.029 0.0023 0.0016 0.086 0.012 - Comp. Steel d 0.072 0.86 5.61 0.032 0.0032 0.021 0.0019 0.0021 0.105- Comp. Steel f 0.063 0.84 2.13 0.109 0.0018 0.034 0.0035 0.0018 0.079 0.024 - Comp. Steel g 0.065 0.73 1.89 0.018 0.0510 0.013 0.0031 0.0020 0.099 0.013 - Comp. Steel H 0.073 0.69 1.99 0.008 0.0016 2,462 0.0030 0.0043 0.104 0.011 - Comp. Steel i 0.084 0.75 2.05 0.013 0.0025 0.046 0.0490 0.0026 0.076 0.020 - Comp. Steel j 0.091 0.81 2.13 0.016 0.0036 0.023 0.0025 0.0027 - - - Comp. Steel k 0.076 0.82 1.97 0.009 0.0045 0.034 0.0029 0.0023 0.406 0.023 - Comp. Steel
    37/49
    The bands in addition to those of the present invention are underlined.
    Petition 870190075401, of 08/05/2019, p. 46/66
    TABLE 2-1
    Steel Temperature for heating the hot-rolled plate (° C) Final rolling temperature (° C) Average final cooling speed up to 400 ° C (° C / s) Cooling speed from 550 ° C to 400 ° C (° C / s) Maximum cooling speed at less than 400 ° C (° C / s) Coiling temperature 1 ° C Note TO 1 1,240 960 50 73 40 Room temperature. Inv. Steel A-2 1,230 940 50 73 <0.1 330 Inv. Steel A-3 1,030 910 100 123 30 Room temperature. Comp. Steel A-4 1,240 820 70 93 35 Room temperature. Comp. Steel A-5 1,230 940 20 43 20 Room temperature. Comp. Steel A-6 1,220 960 70 93 120 Room temperature. Comp. Steel A-7 1,250 970 50 73 <0.1 480 Comp. Steel A-8 1,240 950 60 83 40 Room temperature. Inv. Steel A-9 1,240 950 60 83 40 Room temperature. Inv. Steel B-1 1,260 950 50 73 40 Room temperature. Inv. Steel B-2 1,240 940 60 83 <0.1 390 Inv. Steel B-3 1,250 950 120 143 <0.1 220 Inv. Steel B-4 1,060 900 60 83 40 Room temperature. Comp. Steel B-5 1,230 810 50 73 30 Room temperature. Comp. Steel B-6 1,260 960 15 38 35 Room temperature. Comp. Steel
    38/49
    Petition 870190075401, of 08/05/2019, p. 47/66
    B-7 1,240 950 70 93 80 Room temperature. Comp. Steel B-8 1,230 950 70 93 <0.1 580 Comp. Steel B-9 1,260 980 60 83 40 Room temperature. Inv. Steel B-10 1,260 980 60 83 40 Room temperature. Inv. Steel C-1 1,250 970 60 83 20 Room temperature. Inv. Steel D-1 1,270 940 60 83 30 Room temperature. Inv. Steel E-1 1,260 1,030 70 93 20 Room temperature. Inv. Steel E-2 1,250 1,000 120 143 <0.1 340 Inv. Steel E-3 1,250 1,020 100 123 <0.1 240 Inv. Steel E-4 1,060 910 60 83 40 Room temperature. Comp. Steel E-5 1,240 950 120 143 100 Room temperature. Comp. Steel E-6 1,260 1,000 60 83 25 Room temperature. Inv. Steel E-7 1,260 1,000 60 83 25 Room temperature. Inv. Steel F-1 1,240 920 60 83 30 Room temperature. Inv. Steel G-1 1,300 950 50 73 40 Room temperature. Inv. Steel H-1 1,250 930 60 83 30 Room temperature. Inv. Steel I-1 1,260 960 50 73 20 Room temperature. Inv. Steel J-1 1,250 950 80 103 35 Room temperature. Inv. Steel J-2 1,270 970 60 83 <0.1 390 Inv. Steel J-3 1,230 960 120 143 <0.1 220 Inv. Steel J-4 1,090 900 90 113 40 Room temperature. Comp. Steel
    39/49
    Petition 870190075401, of 08/05/2019, p. 48/66
    J-5
    1,240
    830
    J-6
    1,250
    920
    J-7
    1,230
    950
    J-8
    1,260
    930
    103
    J-9
    1,230
    940
    J-10
    1,230
    940 <0.1 <0.1 <0.1
    Room temperature.
    Room temperature.
    Room temperature.
    620
    350
    350
    The bands in addition to those of the present invention are underlined.
    Petition 870190075401, of 08/05/2019, p. 49/66
    Comp. Steel
    Comp. Steel
    Comp. Steel
    Comp. Steel
    Inv. Steel
    Inv. Steel
    40/49
    TABLE 2-2
    Steel Temperature for heating the hot-rolled plate (° C) Final rolling temperature (° C) Average final cooling speed up to 400 ° C (° C / s) Cooling speed from 550 ° C to 400 C / s) (° C / s) Maximum cooling speed at less than 400 ° C (° C / s) Coiling temperature (° C) Note K-1 1,240 970 60 83 20 Room temperature. Inv. Steel L-1 1,230 950 60 83 40 Room temperature. Inv. Steel M-1 1,280 980 70 93 30 Room temperature. Inv. Steel M-2 1,230 940 80 103 <0.1 330 Inv. Steel M-3 1,250 950 60 83 <0.1 160 Inv. Steel M-4 1,100 910 90 113 20 Room temperature. Comp. Steel M-5 1,250 760 100 123 40 Room temperature. Comp. Steel M-6 1,260 940 20 43 30 Room temperature. Comp. Steel M-7 1,240 930 80 103 100 Room temperature. Comp. Steel M-8 1,230 960 70 93 <0.1 600 Comp. Steel M-9 1,240 950 80 103 <0.1 310 Inv. Steel M-10 1,240 950 80 103 <0.1 310 Inv. Steel N-1 1,250 980 80 103 20 Room temperature. Inv. Steel 0-1 1,240 950 60 83 30 Room temperature. Inv. Steel P-1 1,240 960 60 83 25 Room temperature. Inv. Steel Q-1 1,240 940 60 83 40 Room temperature. Inv. Steel
    41/49
    Petition 870190075401, of 08/05/2019, p. 50/66
    R-1 1,260 950 70 93 30 Room temperature. Inv. Steel S-1 1,230 970 80 103 20 Room temperature. Inv. Steel S-2 1,220 980 60 83 <0.1 360 Inv. Steel S-3 1,270 940 80 103 <0.1 200 Inv. Steel S-4 1,060 950 70 93 30 Room temperature. Comp. Steel S-5 1,230 830 150 173 20 Room temperature. Comp. Steel S-6 1,250 960 10 33 20 Room temperature. Comp. Steel S-7 1,230 970 70 93 120 Room temperature. Comp. Steel S-8 1,280 960 80 103 <0.1 290 Inv. Steel S-9 1,270 950 80 103 <0.1 290 Inv. Steel to 1 1,210 920 60 83 20 Room temperature. Comp. Steel b-1 1,260 950 80 103 25 Room temperature. Comp. Steel c-1 1,240 940 60 83 20 Room temperature. Comp. Steel d-1 1,230 930 70 93 20 Room temperature. Comp. Steel f-1 1,250 1,020 100 123 25 Room temperature. Comp. Steel g-1 1,240 940 60 83 20 Room temperature. Comp. Steel h-1 1,200 930 80 103 10 Room temperature. Comp. Steel i-1 1,230 950 70 93 40 Room temperature. Comp. Steel j -1 1,200 920 60 83 30 Room temperature. Comp. Steel k-1 1,240 920 80 103 40 Room temperature. Comp. Steel
    The bands in addition to those of the present invention are underlined.
    42/49
    Petition 870190075401, of 08/05/2019, p. 51/66
    TABLE 3-1
    Steel Steel Dude * Temperate Martensite Bottom Bainite Balance Other structures Discordance density x10 15 (1 / m 2 ) Numerical density of iron-based carbides x10 6 (1 / mm 2 ) Effective crystal grain size (pm) Aspect ratio YP (MPa) TS (MPa) El(%) vTrs (° C) BH (MPa) Note TO 1 HR 100 0 03.2 3.4 7.8 1.2 782 1,023 12 -60 170 Inv. Steel A-2 HR 71 29 0 - 2.3 6.3 8.3 1.3- 934 1,007 13 -70 110 Inv. Steel A-3 HR 69 0 31 Ferrite 1.8 5.2 12.9 1.1 692 892 13 50 80 Comp. Steel A-4 HR 100 0 0 - 10.8 4.8 5.5 23 957 1,093 9 0 20 Comp. Steel A-5 HR 66 0 34 Ferrite 1.6 5.9 7.2 1.4 705 924 14 30 40 Comp. Steel A-6 HR 0 0 100 Fresh Martensite 12.8 04 7.9 1.0 746 1,057 9 -20 20 Comp. Steel A-7 HR 0 0 100 Upper Bainite 0.8 08 9.2 0.8 576 824 15 -10 50 Comp. Steel A-8 GI 100 0 03 4.5 7.7 1.0 852 998 14 -50 140 Inv. Steel A-9 GA 100 0 0 - 2.6 6.8 6.6 1.1 880 983 14 -50 120 Inv. Steel B-1 HR 98 0 2 Ferrite 2.9 3.7 6.5 1.1 769 1,027 12 -50 160 Inv. Steel B-2 HR 25 75 0 - 1.6 3.9 7.2 1.3 882 1,019 13 -60 120 Inv. Steel
    43/49
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    B-3 HR 88 12 02.5 6.9 6.5 1.0 949 1,004 13 -70 100 Inv. Steel B-4 HR 66 0 34 Ferrite 1.8 4.2 12.7 1.2 672 867 14 30 90 Comp. Steel B-5 HR 100 0 0 - 10.3 4.8 4.8 2.5 912 1,055 10 -20 10 Comp. Steel B-6 HR 27 0 73 Ferrite 0.8 4.3 6.4 1.1 558 792 18 -30 40 Comp. Steel B-7 HR 0 0 100 Fresh Martensite 21.3 09 5.1 0.9 752 1,093 9 0 25 Comp. Steel B-8 HR 0 0 100 Ferrite and Perlite 0.02 00 7.4 1.2 736 842 15 -10 20 Comp. Steel B-9 GI 100 0 0 - 2.3 3.5 6.7 1.0 899 1,002 14 -50 120 Inv. Steel B-10 GA 100 0 01.9 3.4 6.7 1.1 948 984 14 -50 100 Inv. Steel C-1 HR 100 0 0 - 3.5 4.9 6.3 1.0 773 1,035 13 -50 150 Inv. Steel D-1 HR 100 0 0 - 3.2 3.7 6.5 1.3 781 1,042 12 -40 160 Inv. Steel E-1 HR 100 0 0 - 3.3 5.3 5.9 0.9 762 1,026 12 -50 140 Inv. Steel E-2 HR 71 29 0 - 1.4 4.5 7.3 0.9 934 989 14 -50 110 Inv. Steel E-3 HR 91 9 0 - 2.5 7.6 6.8 1.0 862 1,007 13 -60 100 Inv. Steel E-4 HR 80 0 20 Ferrite 2.1 4.6 11.6 1.8 816 923 13 0 80 Comp. Steel E-5 HR 0 0 100 Fresh Martensite 12.6 08 6.7 1.2 843 1,092 11 20 50 Comp. Steel E-6 GI 100 0 02.8 5.5 6.1 1.0 879 1,021 13 -50 130 Inv. Steel
    44/49
    Petition 870190075401, of 08/05/2019, p. 53/66
    E-7 GA 100 0 0 - 2.3 5.8 6.0 1.1 924 991 13 -50 110 Inv. Steel F-1 HR 100 0 0 - 4.2 5.1 5.7 1.3 749 1,042 12 -40 150 Inv. Steel G-1 HR 100 0 0 - 3.8 4.0 7.3 1.1 761 1,006 13 -50 160 Inv. Steel H-1 HR 100 0 0 - 3.5 4.5 7.9 1.5 782 1124 13 -50 150 Inv. Steel I-1 HR 100 0 0 - 2.9 5.3 7.1 1.0 781 1,019 14 -40 130 Inv. Steel J-1 HR 100 0 0 - 4.2 4.2 6.0 1.1 746 1,047 12 -60 150 Inv. Steel J-2 HR 53 47 0 - 2.1 3.4 7.5 0.9 873 1,007 14 -50 110 Inv. Steel J-3 HR 91 9 0 - 3.1 5.9 6.4 1.1 972 1,026 13 -70 90 Inv. Steel J-4 HR 67 0 33 Ferrite 2.4 3.9 11.9 0.9 624 842 15 30 60 Comp. Steel J-5 HR 100 0 0 - 11.3 4.3 3.8 21 924 1,072 9 -30 20 Comp. Steel J-6 HR 54 0 46 Ferrite 1.8 5.0 5.3 1.7 643 879 17 -20 50 Comp. Steel J-7 HR 0 0 100 Fresh Martensite 17.4 07 6.5 1.0 806 1,112 8 -10 25 Comp. Steel J-8 HR 0 0 100 Ferrite and Perlite 0.02 0.0 8.1 1.4 887 935 14 -50 30 Comp. Steel J-9 GI 70 30 0 - 1.9 5.1 6.8 0.9 910 1,031 13 -50 120 Inv. Steel J-10 GA 70 30 0 - 1.4 4.6 6.9 0.9 948 1,018 13 -50 100 Inv. Steel
    HR represents the hot-rolled steel sheet, GI represents the hot-dip galvanized steel sheet, GA represents the galvanized steel sheet. The bands in addition to those of the present invention are underlined.
    45/49
    Petition 870190075401, of 08/05/2019, p. 54/66
    TABLE 3-2
    Steel Steel grid Temperate Martensite Bottom Bainite Balance Other structures Disagreement density x 10 15 (1 / m 2 ) Numerical density of iron-based carbides x 10 6 (1 / mm 2 ) Effective crystal grain size (pm) Aspect ratio YP (MPa) TS (MPa) El(%) vTrs(° C) BH (MPa) Note K-1 HR 100 0 0 - 3.4 6.3 6.6 0.8 802 1,046 12 -50 100 Inv. Steel L-1 HR 100 0 0 - 4.2 7.4 7.9 1.1 945 1,208 11 -40 130 Inv. Steel M-1 BR. 100 0 0 - 3.8 8.2 6.3 0.8 947 1,231 10 -40 120 Inv. Steel M-2 HR 67 33 0 - 1.9 10.4 7.2 1.1 1,108 1,193 11 -50 140 Inv. Steel M-3 HR 95 5 0 - 3.9 4.2 6.6 1.0 1,078 1,210 10 -60 100 Inv. Steel M-4 HR 72 0 28 Ferrite 2.7 7.2 12.2 0.9 692 963 12 0 70 Comp. Steel M-5 HR 100 0 0 - 11.9 8.4 3.2 43 997 1,309 6 -20 20 Comp. Steel
    46/49
    Petition 870190075401, of 08/05/2019, p. 55/66
    M-6 HR 64 36 0 - 1.5 9.5 6.2 1.0 849 942 13 20 50 Comp. Steel M-7 HR 0 0 100 Fresh Martensite 19.6 09 6.3 1.4 962 1,324 7 -20 20 Comp. Steel M-8 HR 0 0 100 Ferrite and Perlite 0.02 0.0 8.4 1.2 948 973 15 -30 10 Comp. Steel M-9 GI 72 28 0 - 2.5 8.3 7.0 1.0 1,088 1,172 13 -50 120 Inv. Steel M-10 GA 72 28 0 - 1.3 8.1 7.1 1.0 1,128 1,152 12 -50 100 Inv. Steel N-1 HR 100 0 0 - 4.1 10.4 8.2 1.1 960 1,223 12 -60 120 Inv. Steel 0-1 HR 100 0 0 - 4.0 8.9 8.3 1.2 951 1,242 12 -60 110 Inv. Steel P-1 HR 100 0 0 - 3.8 10.6 6.4 1.1 976 1,199 13 -60 140 Inv. Steel Q-1 HR 100 0 0 - 4.3 16.2 6.7 1.0 1,076 1,372 11 -60 130 Inv. Steel R-1 HR 100 0 0 - 4.5 17.5 8.9 1.2 1,069 1,381 11 -50 110 Inv. Steel S-1 HR 100 0 0 - 3.5 19.5 5.8 0.9 1,168 1,530 9 -40 100 Inv. Steel
    47/49
    Petition 870190075401, of 08/05/2019, p. 56/66
    S-2 HR 33 67 0 - 1.7 22.6 6.9 1.0 1,384 1,473 10 -60 120 Inv. Steel S-3 HR 87 13 0 - 2.8 16.8 5.9 1.2 1,286 1,503 9 -50 110 Inv. Steel S-4 HR 73 0 27 Ferrite 0.01 15.6 10.8 1.1 862 1,372 8 -20 60 Comp. Steel S-5 HR 100 0 0 - 10.3 16.7 3.9 29 1,386 1,603 4 -30 40 Comp. Steel S-6 HR 83 0 17 Ferrite 2.6 18.3 6.2 1.2 903 1,402 8 -10 50 Comp. Steel S-7 HR 0 0 100 Fresh Martensite 18.3 03 6.5 1.1 1,032 1,638 6 -10 50 Comp. Steel S-8 GI 68 32 0 - 3.4 13.9 6.5 1.0 1,385 1,492 10 -50 120 Inv. Steel S-9 GA 68 32 0 - 1.1 12.1 6.5 1.1 1,421 1,470 11 -50 100 Inv. Steel to 1 HR 0 0 100 Ferrite 0.01 00 16.2 1.4 330 462 34 -80 0 Comp. Steel b-1 HR 91 0 9 Retained austenite 32.5 04 3.8 1.2 1,826 2,429 4 60 90 Comp. Steel c-1 HR 84 0 16 Ferrite 3.1 2.1 5.4 1.0 892 1,086 14 0 120 Comp. Steel
    48/49
    Petition 870190075401, of 08/05/2019, p. 57/66
    d-1 Hlt. 100 0 0 - 12.1 0.9 4.9 1.1 926 1,118 11 -20 80 Comp. Steel f-1 HR 100 0 0 - 2.9 3.9 6.4 0.8 826 1,031 8 0 120 Comp. Steel g-1 HR 100 0 0 - 4.2 4.2 5.9 1.2 842 1,007 9 -10 130 Comp. Steel h-1 HR 66 0 34 Ferrite 2.3 3.7 5.0 1.2 501 832 15 -20 80 Comp. Steel i-1 HR 100 0 0 - 3.1 4.0 6.2 1.1 792 1,042 13 -30 210 Comp. Steel j-1 HR 100 0 0 - 3.5 3.9 13.2 1.5 803 1,038 12 -10 100 Comp. Steel k-1 HR 100 0 04.2 4.5 3.2 1.4 783 1,019 13 -10 120 Comp. Steel
    HR represents the hot-rolled steel sheet, GI represents the hot-dip galvanized steel sheet, GA represents the galvanized steel sheet. The ranges in addition to those of the present invention are underlined.
    权利要求:
    Claims (8)
    [1]
    1. High-strength hot-rolled steel sheet with a maximum tensile strength of 980 MPa or more, the steel sheet being characterized by the fact that it has a composition consisting of,% by mass,
    C: from 0.01% to 0.2%,
    Si: from 0% to 2.5%,
    Mn: from 0% to 4.0%,
    Al: from 0% to 2.0%,
    N: from 0% to 0.01%,
    Cu: from 0% to 2.0%,
    Ni: from 0% to 2.0%,
    Mo: from 0% to 1.0%,
    V: from 0% to 0.3%,
    Cr: from 0% to 2.0%,
    Mg: from 0% to 0.01%,
    Ca: from 0% to 0.01%,
    REM: from 0% to 0.1%,
    B: from 0% to 0.01%,
    P: less than or equal to 0.10%,
    S: less than or equal to 0.03%,
    O: less than or equal to 0.01%, one or both of Ti and Nb: from 0.01% to 0.30% in total, and the balance is Fe and unavoidable impurities, in which the steel plate has a structure in which a fraction of the total volume of one or both of tempered martensite and lower bainite is 90% or more and a density of discrepancy in martensite and lower bainite is greater than or equal to 5x10 13 (1 / m 2 ) and less or equal to 1x10 16 (1 / m 2 ).
    [2]
    2. High-strength hot-rolled steel sheet of
    Petition 870190075401, of 08/05/2019, p. 59/66
    2/4 according to claim 1, characterized by the fact that the one or both of the tempered martensite and the lower bainite include 1x10 6 (numbers / mm 2 ) or more iron-based carbides.
    [3]
    3. Hot-rolled steel sheet with high resistance, according to claim 1, characterized by the fact that one or both of the tempered martensite and the lower bainite have an effective crystal size less than or equal to 10 pm.
    [4]
    4. Hot-rolled steel sheet with high resistance, according to claim 1, characterized by the fact that it comprises one or more among,% by mass,
    Cu: from 0.01% to 2.0%,
    Ni: from 0.01% to 2.0%,
    Mo: from 0.01% to 1.0%,
    V: from 0.01% to 0.3%, and
    Cr: from 0.01% to 2.0%.
    [5]
    5. Hot-rolled steel plate with high resistance, according to claim 1, characterized by the fact that it comprises one or more among,% by mass,
    Mg: from 0.0005% to 0.01%,
    Ca: from 0.0005% to 0.01%, and
    REM: from 0.0005% to 0.1%.
    [6]
    6. Hot-rolled steel plate with high resistance, according to claim 1, characterized by the fact that it comprises,% by mass,
    B: from 0.0002% to 0.01%.
    [7]
    7. Method for producing a hot-rolled steel sheet with high strength with a maximum tensile strength of 980 MPa or more, the method being characterized by the fact that it comprises:
    heat, optionally after cooling, a laminated plate
    Petition 870190075401, of 08/05/2019, p. 60/66
    3/4 hot-melt casting up to a temperature of 1,200 ° C or more, with the hot-rolled casting plate having a composition consisting of,% by mass,
    C: from 0.01% to 0.2%,
    Si: from 0% to 2.5%,
    Mn: from 0% to 4.0%,
    Al: from 0% to 2.0%,
    N: from 0% to 0.01%,
    Cu: from 0% to 2.0%,
    Ni: from 0% to 2.0%,
    Mo: from 0% to 1.0%,
    V: from 0% to 0.3%,
    Cr: from 0% to 2.0%,
    Mg: from 0% to 0.01%,
    Ca: from 0% to 0.01%,
    REM: from 0% to 0.1%,
    B: from 0% to 0.01%,
    P: less than or equal to 0.10%,
    S: less than or equal to 0.03%,
    O: less than or equal to 0.01%, one or both of Ti and Nb: from 0.01% to 0.30% in total and the balance being Fe and unavoidable impurities;
    complete hot rolling at a temperature of 900 ° C or more;
    cooling the steel sheet to a cooling speed of 50 ° C / s or more on average from a final rolling temperature to 400 ° C;
    set a cooling speed of no more than
    50 ° C / s at a temperature below 400 ° C and wind the steel sheet.
    Petition 870190075401, of 08/05/2019, p. 61/66
    4/4
    [8]
    8. Method, according to claim 7, characterized by the fact that it additionally comprises:
    perform galvanizing treatment or galvanizing and annealing treatment.
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    同族专利:
    公开号 | 公开日
    KR101748510B1|2017-06-16|
    TW201437388A|2014-10-01|
    EP2907886A1|2015-08-19|
    US20150329950A1|2015-11-19|
    MX2015006209A|2015-08-10|
    CN104968822A|2015-10-07|
    KR20150110700A|2015-10-02|
    JP6008039B2|2016-10-19|
    ES2703779T3|2019-03-12|
    CN104968822B|2017-07-18|
    BR112015011302A2|2017-07-11|
    JPWO2014132968A1|2017-02-02|
    EP2907886A4|2016-06-08|
    TWI550101B|2016-09-21|
    EP2907886B1|2018-10-17|
    US10196726B2|2019-02-05|
    PL2907886T3|2019-04-30|
    WO2014132968A1|2014-09-04|
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    法律状态:
    2018-11-13| B06F| Objections, documents and/or translations needed after an examination request according [chapter 6.6 patent gazette]|
    2019-05-07| B06A| Patent application procedure suspended [chapter 6.1 patent gazette]|
    2019-09-10| B25D| Requested change of name of applicant approved|Owner name: NIPPON STEEL CORPORATION (JP) |
    2019-12-31| B09A| Decision: intention to grant [chapter 9.1 patent gazette]|
    2020-02-27| B16A| Patent or certificate of addition of invention granted [chapter 16.1 patent gazette]|Free format text: PRAZO DE VALIDADE: 20 (VINTE) ANOS CONTADOS A PARTIR DE 25/02/2014, OBSERVADAS AS CONDICOES LEGAIS. |
    2021-12-21| B21F| Lapse acc. art. 78, item iv - on non-payment of the annual fees in time|Free format text: REFERENTE A 8A ANUIDADE. |
    优先权:
    申请号 | 申请日 | 专利标题
    JP2013-035597|2013-02-26|
    JP2013035597|2013-02-26|
    PCT/JP2014/054570|WO2014132968A1|2013-02-26|2014-02-25|HIGH-STRENGTH HOT-ROLLED STEEL SHEET HAVING MAXIMUM TENSILE STRENGTH OF 980 MPa OR ABOVE, AND HAVING EXCELLENT AND BAKING HARDENABILITY AND LOW-TEMPERATURE TOUGHNESS|
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