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    • 专利摘要:
    ABRASION-RESISTANT STEEL PLATE THAT HAS TENACITY AT LOW TEMPERATURE AND RESISTANCE TO FRAGILIZATION BY HYDROGEN AND METHOD FOR MANUFACTURING THE SAME. An abrasion-resistant steel plate, resistant to hydrogen embrittlement and low temperature toughness, and method of manufacture are provided. The plate has a Brinell hardness of 401 or more, at least 50/100 m2 of fine precipitates with a maximum diameter of 50 nm in martensite steel with crystal grains surrounded by grain contours with a high angle of minimum disorientation of 15 ° and medium size 20 m. The steel contains, in mass%, C: 0.20 to 0.30%, Si: 0.05 to 0.5%, Mn: 0.5 to 1.5%, Cr: 0.05 to 1, 20%, Nb: 0.01 to 0.08%, B: 0.0005 to 0.003%, Al: 0.01 to 0.08%, N: 0.0005 to 0.008%, P: 0.05% or less, S: 0.005% or less, O: 0.008% or less, and, as required, one or more rare earth elements among Mo, V, Ti, Nd, Cu, Ni, W, Ca and Mg, and satisfies 0 , 03 (less than equal) Nb + Ti + Al + V (less than equal) 0.14, the rest consists of Fe and impurities. The steel is melted and, after rolling, is reheated to the transformation point of Ac3 or greater, and cooled from the transformation point of Ar3 or greater to 250 ° C or less through (...).
    公开号:BR112015020012B1
    申请号:R112015020012-5
    申请日:2014-03-19
    公开日:2020-11-17
    发明作者:Shinichi Miura；Nobuyuki Ishikawa；Akihide Nagao
    申请人:Jfe Steel Corporation；
    IPC主号:
    专利说明:

    TECHNICAL FIELD
    [0001] The present invention relates to abrasion-resistant steel plates that have excellent low temperature toughness and resistance to hydrogen embrittlement, and methods for making such steel plates. In particular, the invention relates to techniques suitable for abrasion-resistant steel plates with excellent low temperature toughness and resistance to hydrogen embrittlement which has a Brinell hardness of 401 or more. BACKGROUND TECHNIQUE
    [0002] In recent years there has been a tendency to increase the hardness of steel plates that are used in the field of industrial machinery in abrasive environments such as mines, civil engineering, agricultural machinery and construction in order, for example, to extend life useful with regard to ore crushing capacity.
    [0003] However, the increase in steel hardness is generally accompanied by decreases in low temperature toughness and resistance to hydrogen embrittlement and, consequently, causes a risk of the steel cracking during use. Thus, there has been a strong demand for improvements in low temperature toughness and resistance to hydrogen embrittlement of high hardness abrasion resistant steel plates, in particular, abrasion resistant steel plates that have a Brinell hardness of 401 or more .
    [0004] Approaches for producing abrasion-resistant steel plates with excellent low temperature toughness and resistance to hydrogen embrittlement and methods for making such steel plates have been proposed in the art as in Patent Literature 1, 2, 3 and 4 in which resistance to hydrogen embrittlement and low temperature toughness are improved by optimizing the temperature index and the carbon equivalent or by dispersing hardened second phase particles in a pearlite phase. CITATION LIST PATENT LITERATURE
    [0005] PTL 1: Publication of Japanese Unexamined Patent Application No. 2002-256382
    [0006] PTL 2: Japanese Patent No. 3698082
    [0007] PTL 3: Japanese Patent No. 4238832
    [0008] PTL 4: Publication of Japanese Unexamined Patent Application No. 2010-174284 SUMMARY OF THE INVENTION TECHNICAL PROBLEM
    [0009] However, conventional methods such as those described in Patent Literature 1, 2, 3 and 4 have problems in that the energy absorbed Charpy at -40 ° C which is obtained in a stable manner is limited to about 50 to 100 J and, in addition, resistance to hydrogen embrittlement is decreased. Thus, there are demands for abrasion-resistant steel plates that have greater tenacity at low temperature and resistance to hydrogen embrittlement and for methods that have the ability to manufacture such steel plates.
    [0010] The present invention was made in the light of the circumstances in the technique discussed above. It is, therefore, an object of the invention to provide abrasion resistant steel plates that have a Brinell hardness of 401 or more and still exhibit superior hydrogen embrittlement resistance and low temperature toughness for conventional abrasion resistant steel plates, and to provide methods for making such steel plates. SOLUTION TO THE PROBLEM
    [0011] Three basic quality design guidelines to improve low temperature toughness and resistance to hydrogen embrittlement of martensitic steel on clapboard as cooled are to reduce the size of high angle grain contours that often determine the fracture facet sizes, decrease the amount of impurities such as phosphorus and sulfur that reduce the bond strength to grain boundaries and reduce the size and amount of inclusions that induce brittleness at low temperature.
    [0012] The present inventors have carried out extensive studies aimed at improving the toughness at low temperature and the resistance to hydrogen embrittlement of abrasion-resistant steel plates based on the point of view above. As a result, the present inventors have found that the thickening of reheated auscultite grains is suppressed by dispersing a large amount of fine precipitates such as Nb carbonitride which has a diameter of no more than 50 nm and, consequently, the size The number of packages that determine the fracture facet sizes is significantly reduced to make it possible to obtain abrasion-resistant steel plates that have higher temperature toughness and resistance to hydrogen embrittlement than conventional materials.
    [0013] The present invention has been completed through further studies based on the above finding, and provides the following abrasion resistant steel plates which have excellent low temperature toughness and resistance to hydrogen embrittlement and methods for making such steel plates . (1) An abrasion resistant steel plate with excellent low temperature toughness and resistance to hydrogen embrittlement that has a chemical composition including, in mass%, C: 0.20 to 0.30%, Si: 0.05 0.5%, Mn: 0.5 to 1.5%, Cr: 0.05 to 1.20%, Nb: 0.01 to 0.08%, B: 0.0005 to 0.003%, Al: 0.01 to 0.08%, N: 0.0005 to 0.008%, P: no more than 0.05%, S: no more than 0.005% and O: no more than 0.008%, the equilibrium is Fe and unavoidable impurities, and the steel plate includes fine precipitates of 50 nm or less in diameter with a density of 50 or more particles per 100 pm2, with the steel plate having a martensitic slat structure from the steel plate surface to at least a depth of 1/4 of the plate thickness, the martensitic slat structure having an average grain size of no more than 20 pm, where the average grain size is the size medium grain crystal grains surrounded by high angle grain outlines that have an orientation difference of 15 ° or more, the steel plate having a Brinell hardness (HBW10 / 3000) of 401 or more. (2) The abrasion-resistant steel plate with excellent low temperature toughness and resistance to hydrogen embrittlement described according to (1), in which the chemical composition additionally includes, in mass%, one or two or more Mo : not more than 0.8%, V: not more than 0.2% and Ti: not more than 0.05%. (3) The abrasion-resistant steel plate with excellent low temperature toughness and resistance to hydrogen embrittlement described according to (1) or (2), in which the chemical composition additionally includes, in mass%, one or two or more than Nd: not more than 1%, Cu: not more than 1%, Ni: not more than 1%, W: not more than 1%, Ca: not more than 0.005%, Mg: no more than 0.005% and REM: no more than 0.02% (note: REM is an abbreviation for rare earth metal). (4) The abrasion-resistant steel plate with excellent low temperature toughness and resistance to hydrogen embrittlement described according to any one of (1) to (3), in which the contents of Nb, Ti, Al and V satisfy 0.03 <Nb + Ti + Al + V <0.14 where Nb, Ti, Al and V are 0 when these elements are not added. (5) The abrasion-resistant steel plate with excellent low temperature toughness and resistance to hydrogen embrittlement described according to any one of (1) to (4), where the plate thickness is 6 to 125 mm. (6) The abrasion-resistant steel plate described according to any one of (1) to (5), in which the energy absorbed Charpy at -40 ° C is not less than 27 J and the safety index (% ) resistance to delayed fracture is not less than 50%, and the safety index is defined as a ratio (%) of the reduction in area displayed when the steel plate contains 0.5 ppm by mass of diffusible hydrogen for the reduction of area obtained when the steel plate does not contain diffusible hydrogen. (7) A method for making an abrasion-resistant steel plate with excellent low temperature toughness and resistance to hydrogen embrittlement includes melting a steel that has the chemical composition described according to any one of (1) to (4), hot-laminate the plate to a steel plate that has a prescribed plate thickness, reheat the steel plate to the Aça OR transformation point above, and subsequently cool the steel plate by cooling with water from a temperature from not less than the Ara transformation point to a temperature of not more than 250 ° C. (8) The method for making an abrasion-resistant steel plate with excellent low temperature toughness and resistance to hydrogen embrittlement described in accordance with (7), additionally includes reheating the molten plate to 1,100 ° C or above. (9) The method for making an abrasion-resistant steel plate with excellent low temperature toughness and resistance to hydrogen embrittlement described according to (7) or (8), in which the reduction of lamination during hot rolling in a non-recrystallized region is not less than 30%. (10) The method for making an abrasion resistant steel plate with excellent low temperature toughness and resistance to hydrogen embrittlement described according to any of (7) to (9), additionally includes cooling the steel plate hot rolled by cooling with water to a temperature of not more than 250 ° C. (11) The method for making an abrasion-resistant steel plate with excellent low temperature toughness and resistance to hydrogen embrittlement described according to any of (7) to (10), where the reheating of the rolled steel plate hot or cooled with water to the transformation point of Acs or above is carried out at a rate of not less than 1 ° C / s. ADVANTAGE EFFECTS OF THE INVENTION
    [0014] The abrasion-resistant steel plates of the present invention have a Brinell hardness of 401 or more and still exhibit superior low temperature toughness and hydrogen embrittlement, and the methods of the invention can manufacture such steel plates. These advantages are very useful in the industry. DESCRIPTION OF THE MODALITIES
    [0015] The reasons why the microstructure in the invention is limited will be described.
    [0016] An abrasion-resistant steel plate of the present invention includes a clapboard martensitic steel that has a microstructure in which the region from the surface of the steel plate to at least a depth of 1/4 of the plate thickness is one martensitic clapboard structure and the average grain size of crystal grains in clapboard martensitic steel that are surrounded by high angle grain outlines that have an orientation difference of 15 ° or more is no more than 20 pm, preferably, no more than 10 pm and, most preferably, no more than 5 pm.
    [0017] High angle grains serve as locations where landslides are accumulated. In this way, the reduction in the size of high-angle grains is a solution for the concentration of stress due to the accumulation of slips in the grain contours and, therefore, reduces the occurrence of cracks due to the crack caused by fragility, thus improving low temperature toughness and resistance to hydrogen embrittlement. The effects on improving low temperature toughness and resistance to hydrogen embrittlement are increased with decreasing grain sizes. The marking effects can be achieved by controlling the average grain size of crystal grains surrounded by high angle grain outlines that have an orientation difference of 15 ° or more to no more than 20 pm. The average grain size is preferably no more than 10 pm and, most preferably, no more than 5 pm.
    [0018] For example, the crystal orientations can be measured by analyzing the crystal orientations in a 100 pm square region using an EBSP method (backscattered electron pattern). Assuming that the high angle refers to 15 ° or more of difference in grain boundary orientations, the grain diameters surrounded by such grain boundaries are measured and the simple average of the results is determined.
    [0019] In the invention, steel includes fine precipitates that have a diameter of not more than 50 nm, preferably, not more than 20 nm and, more preferably, not more than 10 nm with a density of 50 or more particles per 100 pm2.
    [0020] The main fine precipitates for which the effects have been confirmed are Nb carbonitrides, Ti carbonitrides, Al nitrides and V carbides. However, the precipitates are not limited to them as long as the sizes are satisfied, and may include other forms such as oxides. Fine precipitates that have a smaller diameter and greater density provide greater effects in suppressing the thickening of crystals due to their fixation effect. The size of crystal grains is reduced and resistance to hydrogen embrittlement and low temperature toughness are enhanced by the presence of at least 50 or more fine precipitate particles that have a diameter of no more than 50 nm, preferably not more than 20 nm and, more preferably, not more than 10 nm per 100 pm2.
    [0021] To determine the average particle diameter of fine precipitates, for example, a sample prepared by a carbon extraction reproduction method is observed and photographed by TEM, and the image is analyzed to measure the average particle diameter of 50 or more particles of fine precipitates as the simple average.
    [0022] Brinell hardness is 401 or more in order to obtain high abrasion resistant performance. The plate thickness is 6 to 125 mm which is the general range of the thickness of abrasion resistant steel plates. However, the plate thickness is not limited to that range and the technique of the present invention is applicable to steel plates that have other thicknesses. It is not always necessary for the steel plate to be composed of the martensitic clapboard structure throughout. Depending on the use, for example, the martensitic structure of the slat may extend from the surface of the steel plate to a depth of 1/4 of the plate thickness, and the other region extending from a depth of 1 / 4 at a depth of 3/4 of the plate thickness as measured from the surface can be, for example, lower bainitic structure or upper bainitic structure.
    [0023] A preferred chemical composition and conditions for the manufacture of abrasion-resistant steel plates that have the aforementioned microstructure are limited for the reasons described below.
    [0024] Chemical composition The unit in% in the chemical composition is% by mass.
    [0025] C: 0.20 to 0.30%
    [0026] Carbon is added to guarantee martensite hardness and temperability. These effects are not sufficiently achieved if the amount added is less than 0.20%. On the other hand, adding more than 0.30% carbon results in a decrease in the toughness of base steel and zones affected by welding heat, and also causes a decrease in the weldability marking. Thus, the C content is limited to 0.20 to 0.30%. When, however, the C content exceeds 0.25%, the areas affected by heat subtly decrease toughness and weldability. In this way, the C content is preferably controlled to 0.20 to 0.25%.
    [0027] Si: 0.05 to 0.5%
    [0028] Silicon is added as a deoxidizer in steel production and also as an element to guarantee hardenability. These effects are not sufficiently achieved if the amount added is less than 0.05%. If, on the other hand, more than 0.5% silicon is added, the grain contours are weakened, and the low temperature toughness and resistance to hydrogen embrittlement are decreased. Thus, the Si content is limited to 0.05 to 0.5%.
    [0029] Mn: 0.5 to 1.5%
    [0030] Manganese is added as an element to guarantee hardenability. This effect is not sufficiently achieved if the amount added is less than 0.5%. If, on the other hand, more than 1.5% manganese is added, the resistance in grain boundaries is reduced, and resistance to hydrogen embrittlement and low temperature toughness are decreased. Thus, the Mn content is limited to 0.5 to 1.5%.
    [0031] Cr: 0.05 to 1.20%
    [0032] Chromium is added as an element to guarantee hardenability. This effect is not sufficiently achieved if the amount added is less than 0.05%. On the other hand, adding more than 1.20% chromium results in a decrease in weldability. Thus, the Cr content is limited to 0.05 to 1.20%.
    [0033] Nb: 0.01 to 0.08%
    [0034] Niobium forms Nb carbonitrides in the form of fine precipitates that serve to hold heated austenite grains and thus suppress grain thickening. This effect is not sufficiently achieved if the Nb content is less than 0.01%. On the other hand, adding more than 0.08% niobium causes a decrease in the toughness of areas affected by welding heat. Thus, the Nb content is limited to 0.01 to 0.08%.
    [0035] B: 0.0005 to 0.003%
    [0036] Boron is added as an element to guarantee hardenability. This effect is not sufficiently achieved if the amount added is less than 0.0005%. Adding more than 0.003% of boron causes a decrease in toughness. Thus, the B content is limited to 0.0005 to 0.003%.
    [0037] Al: 0.01 to 0.08%
    [0038] Aluminum is added as a deoxidizer and also forms nitrides of Al in the form of fine precipitates that serve to hold heated austenite grains and thereby suppress grain thickening. In addition, aluminum fixes free nitrogen as nitrides of Al and thereby suppresses the formation of nitrides of B to allow free boron to be used effectively to improve temperability. Thus, in the invention, it is more important to control the Al content. Aluminum needs to be added by 0.01% or more because the above effects are not sufficiently achieved if the Al content is less than 0.01% . Preferably, it is recommended to add 0.02% or more of aluminum and, more preferably, 0.03% or more of aluminum. On the other hand, adding more than 0.08% aluminum increases the likelihood of surface defects on steel plates. Thus, the Al content is limited to 0.01 to 0.08%.
    [0039] N: 0.0005 to 0.008%
    [0040] Nitrogen forms nitrides with elements such as niobium, titanium and aluminum in the form of fine precipitates that serve to hold heated austenite grains and thereby suppress grain thickening. In this way, nitrogen is added to obtain an effect in improving low temperature toughness and resistance to hydrogen embrittlement. The effect on reducing the microstructure size is not sufficiently achieved if the amount added is less than 0.0005%. If, on the other hand, more than 0.008% nitrogen is added, the amount of solute nitrogen is increased so that the toughness of base steel and zones affected by welding heat is decreased. Thus, the N content is limited to 0.0005 to 0.008%.
    [0041] P: no more than 0.05%
    [0042] Phosphorus is an impurity element and is readily segregated into crystal grain outlines. If the P content exceeds 0.05%, the bond strength between adjacent crystal grains is reduced, and resistance to hydrogen embrittlement and low temperature toughness are decreased. Thus, the P content is limited to no more than 0.05%.
    [0043] S: no more than 0.005%
    [0044] Sulfur is an impurity element and is readily segregated into crystal grain outlines. Sulfur also tends to form MnS which is a non-metal inclusion. Adding more than 0.005% sulfur decreases the bond strength between adjacent crystal grains, and also increases the amount of inclusions, resulting in a decrease in low temperature toughness and resistance to hydrogen embrittlement. Thus, the S content is limited to no more than 0.005%.
    [0045] O: no more than 0.008%
    [0046] Oxygen affects the workability of steel by forming oxides with elements such as aluminum. If more than 0.008% oxygen is added, workability is impaired due to the increase in the amount of inclusions. Thus, the O content is limited to no more than 0.008%.
    [0047] The abrasion-resistant steel plate of the invention is composed of the basic components described above and the balance that is Fe and unavoidable impurities.
    [0048] In the invention, the following components can be added according to the desired characteristics.
    [0049] Mo: no more than 0.8%
    [0050] Molybdenum has an effect of improving temperability. However, this effect is not sufficiently achieved if the amount added is less than 0.05%. It is therefore preferable to add 0.05% or more of molybdenum. Economic efficiency is deteriorated if more than 0.8% molybdenum is added. Thus, the molybdenum content, when added, is limited to no more than 0.8%.
    [0051] V: no more than 0.2%
    [0052] Vanadium has an effect of improving temperability and also forms V carbides in the form of fine precipitates that serve to hold heated austenite grains and thereby suppress grain growth. These effects are not sufficiently achieved if the amount added is less than 0.005%. It is therefore preferable to add 0.005% or more of vanadium. However, adding more than 0.2% vanadium results in a decrease in the toughness of areas affected by welding heat. Thus, the vanadium content, when added, is limited to no more than 0.2%.
    [0053] Ti: no more than 0.05%
    [0054] Titanium forms Ti carbonitrides in the form of fine precipitates that serve to hold heated austenite grains and thereby suppress grain growth. In addition, titanium fixes free nitrogen as Ti nitrides and thereby suppresses the formation of B nitrides to allow free boron to be used effectively to improve temperability. However, these effects are not sufficiently achieved if the amount added is less than 0.005%. It is therefore preferable to add 0.005% or more of titanium. However, adding more than 0.05% titanium results in a decrease in the toughness of areas affected by welding heat. Thus, the titanium content, when added, is limited to no more than 0.05%.
    [0055] Nd: not more than 1%
    [0056] Neodymium decreases the amount of sulfur segregated in grain boundaries by incorporating sulfur as inclusions, and thereby improves resistance to hydrogen embrittlement and tenacity at low temperature. However, these effects are not sufficiently achieved if the amount added is less than 0.005%. It is therefore preferable to add 0.005% or more of neodymium. However, adding more than 1% neodymium results in a decrease in the toughness of areas affected by welding heat. Thus, the neodymium content, when added, is limited to no more than 1%.
    [0057] Cu: no more than 1%
    [0058] Copper has an effect of improving temperability. However, this effect is not sufficiently achieved if the amount added is less than 0.05%. It is therefore preferable to add 0.05% or more of copper. If, however, the Cu content exceeds 1%, hot tearing tends to occur during heating and plate welding. Thus, the copper content, when added, is limited to no more than 1%.
    [0059] Ni: no more than 1%
    [0060] Nickel has an effect of improving toughness and temperability. However, this effect is not sufficiently achieved if the amount added is less than 0.05%. It is therefore preferable to add 0.05% or more of nickel. If, however, the Ni content exceeds 1%, the economic efficiency is reduced. Thus, the nickel content, when added, is limited to no more than 1%.
    [0061] W: no more than 1%
    [0062] Tungsten has an effect of improving temperability. This effect is not sufficiently achieved if the amount added is less than 0.05%. It is therefore preferable to add 0.05% or more of tungsten. However, adding more than 1% tungsten causes a decrease in weldability. Thus, the tungsten content, when added, is limited to no more than 1%.
    [0063] Ca: no more than 0.005%
    [0064] Calcium has an effect of controlling the form of inclusion of sulfide in CaS which is a spherical inclusion hardly extended by lamination, instead of MnS which is a form of inclusion readily extended by lamination. However, this effect is not sufficiently achieved if the amount added is less than 0.0005%. It is therefore preferable to add 0.0005% or more of calcium. However, adding more than 0.005% calcium decreases purity and results in a deterioration in quality such as toughness. Thus, the calcium content, when added, is limited to no more than 0.005%.
    [0065] Mg: no more than 0.005%
    [0066] Magnesium is sometimes added as a desulfurizer for hot metal. However, this effect is not sufficiently achieved if the amount added is less than 0.0005%. It is therefore preferable to add 0.0005% or more of magnesium. However, adding more than 0.005% of magnesium causes a decrease in purity. Thus, the amount of magnesium, when added, is limited to no more than 0.005%.
    [0067] REM: no more than 0.02%
    [0068] Rare earth metals form REM (O, S) oxysulfides in steel and thereby decrease the amount of solute sulfur in crystal grain outlines to provide improved SR crack resistance characteristics. However, this effect is not sufficiently achieved if the amount added is less than 0.0005%. It is therefore preferable to add 0.0005% or more rare earth metals. However, adding more than 0.02% of rare earth metals results in excessive formation of REM sulfides in sedimentation zones and causes a decrease in quality. Thus, the amount of rare earth metals, when added, is limited to no more than 0.02%.
    [0069] 0.03 <Nb + Ti + Al + V <0.14
    [0070] Niobium, titanium, aluminum and vanadium form Nb carbonitrides, Ti carbonitrides, Al nitrides and V carbides in the form of fine precipitates that serve to hold the heated austenite grains and thus prevent the thickening of the grains. Detailed studies of the relationship between the contents of these elements and the grain size have shown that a reduction in the marking of the crystal grain size is achieved and improvements in low temperature toughness and resistance to hydrogen embrittlement are obtained when the contents satisfy 0.03 <Nb + Ti + Al + V <0.14. Thus, the levels are preferably controlled to satisfy 0.03 <Nb + Ti + Al + V <0.14. Here, Nb, Ti, Al and V indicate the respective levels (% by mass) and are 0 when these elements are absent. MANUFACTURING CONDITIONS
    [0071] The shapes of the abrasion-resistant steel plates of the invention are not limited to steel plates and can be of any other various shapes such as tubes, shaped steels and rod steels. The temperature and heating rate specified in the manufacturing conditions are parameters that describe the central area of the steel, namely, the center through the plate thickness of a steel plate, the center through the plate thickness of a portion of a shaped steel to which the characteristics of the invention are conferred, or the center of the radial directions of a rod steel. However, the regions close to the central area go through substantially the same temperature history and, therefore, the above parameters do not strictly describe the temperature conditions for the exact center. FOUNDRY CONDITIONS
    [0072] The present invention is effective for steels manufactured under any casting conditions. It is therefore not necessary to stipulate particular limitations on casting conditions. That is, the melting of molten steel and the rolling of molten steel into slabs can be carried out by any methods without limitation. Scorified steels can be used by a process such as a converter steel production process or an electric steel production process, and plates produced by a process such as continuous casting or ingot casting. REHEATING AND Hardening by COOLING
    [0073] The steel plate which has been hot rolled to a prescribed plate thickness is reheated to the point of transformation of Acs or above and is subsequently cooled by cooling with water from a temperature of not less than Ara's transformation point up to a temperature of no more than 250 ° C, thus forming a martensitic clapboard structure.
    [0074] If the reheat temperature is below the transformation point of Acs, part of the ferrite remains untransformed and, consequently, the subsequent water cooling fails to reach the target hardness. If the steel is cooled below the Ara transformation point before water cooling, part of the austenite is transformed into ferrite before water cooling and, consequently, the subsequent water cooling fails to reach the target hardness. If the water cooling is completed at a temperature greater than 250 ° C, the crystal can be partially transformed into different structures from martensite to clapboard, such as bainite. In this way, the reheating temperature is limited to no less than the transformation point of Acs, the initial water cooling temperature is limited to no less than the transformation point of Ars, and the final water cooling temperature is limited to no more than 250 ° C.
    [0075] In the invention, the transformation point of Aca (° C) and the transformation point of Ars (° C) can be obtained using any equations without limitation. For example, Acs = 854 - 180C + 44Si - 14Mn - 17.8Ni - 1.7Cr and Ar3 = 910 - 31OC - 80Mn - 20Cu -15Cr - 55Ni - 80Mo. In the equations, the element symbols indicate the levels (% by mass) in the steel.
    [0076] In the invention, the following limitations on manufacturing conditions can be additionally adopted, according to the desired characteristics. HOT LAMINATION CONDITIONS
    [0077] When appropriate, the plate is reheated to a temperature that is preferably controlled to be not less than 1,100 ° C, more preferably, not less than 1,150 ° C and, even more preferably, not less than 1,200 ° C . The purpose of this control is to allow a larger amount of crystals such as Nb crystals formed in the plate to be dissolved in the plate and to effectively guarantee, in this way, a sufficient amount of fine precipitates that will be formed.
    [0078] When hot rolling is controlled, it is preferable that the rolling reduction in a non-recrystallized region is not less than 30%, more preferably, not less than 40% and, even more preferably, not less than than 50%. The purpose of laminating in a non-recrystallized region with 30% or more reduction is to form fine precipitates through precipitation induced by deformation of precipitates such as Nb carbonitrides. COOLING
    [0079] When water cooling is carried out after the end of hot rolling, it is preferable that the steel plate is forced to cool to a temperature of no more than 250 ° C. The purpose of this cooling is to suppress the growth of fine precipitates that were formed by deformation-induced precipitation during lamination. TEMPERATURE INCREASE RATE DURING REHEATING
    [0080] When the reheat temperature during reheating for cooling hardening is controlled, it is preferable that the steel plate is reheated to the Acs OR above transformation point, at a rate of not less than 1 ° C /s. The purpose of this control is to suppress the growth of fine precipitates formed before reheating and the growth of fine precipitates formed during reheating. The heating method can be any one of, for example, induction heating, electric heating, infrared radiation heating and atmospheric heating, as long as the desired temperature rise rate is achieved.
    [0081] Under the conditions mentioned above, abrasion-resistant steel plates that have fine crystal grains and exhibit excellent low temperature toughness and resistance to hydrogen embrittlement can be obtained. EXAMPLES
    [0082] A to K steels that have a chemical composition described in Table 1 were scorched and cast into plates, which were worked under conditions described in Table 2 to form steel plates. The temperature of the plates was measured with a thermocouple inserted in the central area through the plate thickness.
    [0083] Table 2 describes the structures of the steel plates, the average grain sizes of crystal grains surrounded by high angle grain outlines that have an orientation difference of 15 ° or more, the densities of fine precipitates with a diameter of no more than 50 nm, and Brinell hardnesses, the absorbed energies Charpy at -40 ° C and the safety indexes of delayed fracture resistance of the steel plates obtained.
    [0084] To determine the structures on the steel plate, a sample was collected from a cross-section perpendicular to the rolling direction, the cross-section was polished and speculatively attacked with a methanol solution of nitric acid, and the structures were identified by observation with an optical microscope at x400 magnification in relation to an area that was 0.5 mm below the surface of the steel plate and an area that corresponds to 1/4 of the plate thickness.
    [0085] To measure the crystal orientations, a region of 100 pm square that includes an area that corresponds to 1/4 of the plate thickness was analyzed by an EBSP method (electron backscattering standard). By defining a high angle to be a 15 ° or more difference in grain contour orientations, the grain diameters surrounded by such grain contours were measured and the simple average of the results was obtained.
    [0086] To determine the numerical density of fine precipitates per unit area, a sample prepared from an area corresponding to 1/4 of the plate thickness using a carbon extraction reproduction method was observed and photographed using HAVE. The number of fine precipitates having a diameter of no more than 50 nm was counted, and the numerical density per 100 pm2 was obtained.
    [0087] To determine Brinell hardness, an area that was 0.5 mm below the steel plate surface was tested according to document No. JIS Z2243 (2008) with a testing force of 3,000 kgf using a cemented carbide sphere that has a diameter of 10 mm cylinder (HBW10 / 3000). The energy absorbed Charpy at - 40 ° C was measured according to document No. JIS Z2242 (2005) in relation to the samples with full size V-notch Charpy that had been collected from an area at 1/4 of the plate thickness at along a direction perpendicular to the lamination direction. The data were obtained from three samples that represent the respective conditions, and the results were averaged.
    [0088] To determine the safety index of resistance to delayed fracture, a rod sample was loaded with hydrogen using a cathodic hydrogen loading method.
    [0089] Consequently, the amount of diffusible hydrogen in the sample was increased to approximately 0.5 ppm by mass.
    [0090] Zinc was plated on the sample surface to seal the hydrogen. Subsequently, a tensile test was performed at a deformation rate of 1 x 10 '6 / s, and the reduction in the area of the fractured sample was measured. Separately, a sample without hydrogen loading was subjected to a tensile test at the same strain rate. The safety index was assessed using the following equation.
    [0091] safety index (%) of resistance to delayed fracture = 100x (X1 / X0)
    [0092] Here, X0: reducing the sample area substantially free of diffusible hydrogen, and
    [0093] X1: the reduction of the area of the sample loaded with diffusible hydrogen.
    [0094] The target values (the range of the invention) for Brinell hardness were 401 and above, those for the absorbed energy Charpy at -40 ° C were 27 J and above, and those for the delayed fracture strength index were 50% and above. TABLE 1
    TABLE 2


    [0095] Steel plates Nos. 1a 7, 10, 11e14a16 described in Table 2 satisfied the chemical composition and manufacturing conditions required in the invention. These steel plates also satisfied the average grain size and the density of fine precipitates required in the invention, and reached the target values of Brinell hardness, vE-40 ° C and the index of resistance to fracture delayed in the invention.
    [0096] Steel plates Nos. 10 and 14 met the requirements of the invention and involved a heating temperature higher than that used for Nos steel plates. 1 and 5, respectively. Consequently, the grain size has been reduced, the density of fine precipitates has been increased, and improvements have been obtained in vE-40 ° C and in the safety index of resistance to delayed fracture.
    [0097] Steel plate No. 11 met the requirements of the invention and involved a greater reduction in rolling in a non-recrystallized region than steel plate No. 2. Consequently, the grain size was reduced, the density of fine precipitates was increased and improvements were obtained in vE-40 ° C and in the safety index of resistance to delayed fracture.
    [0098] Steel plate No. 15 met the requirements of the invention and involved water cooling after rolling in contrast to steel plate No. 6. Consequently, the grain size was reduced, the density of fine precipitates was increased and improvements were obtained in vE-40 ° C and in the safety index of resistance to delayed fracture.
    [0099] Steel plate No. 16 met the requirements of the invention and involved a higher rate of temperature increase during reheating when compared to steel plate No. 7. Consequently, the grain size was reduced, the density of fine precipitates was increased and improvements were obtained in vE-40 ° C and in the delay fracture safety index.
    [00100] On the other hand, the Nb content and the (Nb + Ti + Al + V) content on steel plate No. 8, and the Nb content on steel plate No. 9 were below the lower limits of tracks of the invention. Consequently, their average grain sizes, densities of fine precipitates, vE-40 ° C and safety indexes for delayed fracture resistance did not reach the target values.
    [00101] On steel plate No. 12, the region from the surface to a depth of 1/4 of the plate thickness included a two-phase structure, namely ferrite and martensite, due to the reheat temperature being lower than Acs . The failure of sufficient formation of martensitic slat structure resulted in a Brinell hardness below the level required in the invention.
    [00102] On steel plate No. 13, the region from the surface to a depth of 1/4 of the plate thickness included a biphasic structure, namely ferrite and martensite, due to the initial water cooling temperature being less than Ara. The failure of sufficient formation of martensitic slat structure resulted in a Brinell hardness below the level required in the invention.
    [00103] On the other hand, steel plates Nos. 17 and 18 had an Al content below the lower limit of the invention range. Consequently, their average grain sizes, densities of fine precipitates, vE-40 ° C and safety indexes for delayed fracture resistance did not reach the target values.
    权利要求:
    Claims (10)
    [0001]
    1. Abrasion resistant steel plate with excellent low temperature toughness and resistance to hydrogen embrittlement characterized by the fact that it comprises, in mass%, C: 0.20 to 0.30%, Si: 0.05 0.5%, Mn: 0.5 to 1.5%, Cr: 0.05 to 1.20%, Nb: 0.01 to 0.08%, B: 0.0005 to 0.003%, Al: 0.01 to 0.08%, N: 0.0005 to 0.008%, P: no more than 0.05%, S: no more than 0.005% and O: no more than 0.008%, the equilibrium is Fe and unavoidable impurities, and the steel plate includes fine precipitates of 50 nm or less in diameter with a density of 50 or more particles per 100 pm2, with the steel plate having a martensitic slat structure from the steel plate surface to at least a depth of 1/4 of the plate thickness, the martensitic clapboard structure having an average grain size of no more than 20 pm where the average grain size is the size of medium grain crystal grains surrounded by high angle grain outlines that have a difference in orientation of 15 ° or more, the steel plate having a Brinell hardness (HBW10 / 3000) of 401 or more.
    [0002]
    2. Abrasion resistant steel plate with excellent low temperature toughness and resistance to hydrogen embrittlement, according to claim 1, characterized by the fact that the steel plate additionally comprises, in mass%, one or two or more than Mo: not more than 0.8%, V: not more than 0.2% and Ti: not more than 0.05%.
    [0003]
    3. Abrasion-resistant steel plate with excellent low temperature toughness and resistance to hydrogen embrittlement, according to claim 1 or 2, characterized by the fact that the steel plate additionally comprises, in mass%, one or two or more of Nd: not more than 1%, Cu: not more than 1%, Ni: not more than 1%, W: not more than 1%, Ca: not more than 0.005% , Mg: no more than 0.005% and REM: no more than 0.02% (note: REM is an abbreviation for rare earth metal).
    [0004]
    4. Abrasion resistant steel plate with excellent low temperature toughness and resistance to hydrogen embrittlement, according to any one of claims 1 to 3, characterized by the fact that the levels of Nb, Ti, Al and V satisfy 0.03 <Nb + Ti + Al + V <0.14, where Nb, Ti, Al and V indicate the contents (% by mass) of the respective elements and are 0 when Nb, Ti, Al and V are not added -activated.
    [0005]
    5. Abrasion resistant steel plate with excellent low temperature toughness and resistance to hydrogen embrittlement, according to any one of claims 1 to 4, characterized by the fact that the plate thickness is 6 to 125 mm.
    [0006]
    6. Abrasion-resistant steel plate according to any one of claims 1 to 5, characterized by the fact that the energy absorbed Charpy at -40 ° C is not less than 27 J and the safety index (%) of resistance to delayed fracture is not less than 50%, with the safety index being defined as a ratio (%) of the area reduction displayed when the steel plate contains 0.5 ppm by mass of diffusible hydrogen for the reduction of area obtained when the steel plate does not contain diffusible hydrogen.
    [0007]
    7. Method for making an abrasion-resistant steel plate with excellent low temperature toughness and resistance to hydrogen embrittlement, characterized by the fact that it comprises melting a steel that has the chemical composition described as defined in any of claims 1 to 4 , hot-laminate a plate on a steel plate that has a prescribed plate thickness, reheat the steel plate to the transformation point of Acs or above, and subsequently abruptly cool the steel plate by cooling water from a temperature of not less than the Ara transformation point to a temperature of not more than 250 ° C, in which a reduction in lamination during hot rolling in a non-recrystallized region is not less than 30%.
    [0008]
    8. Method for making an abrasion-resistant steel plate with excellent low temperature toughness and resistance to hydrogen embrittlement, according to claim 7, characterized in that it additionally comprises reheating the molten plate to 1,100 ° C or above.
    [0009]
    9. Method for manufacturing an abrasion-resistant steel plate with excellent low temperature toughness and resistance to hydrogen embrittlement, according to claim 7 or 8, characterized by the fact that it additionally comprises cooling the hot-rolled steel plate through cooling with water at a temperature of no more than 250 ° C.
    [0010]
    10. Method for making an abrasion-resistant steel plate with excellent low temperature toughness and resistance to hydrogen embrittlement according to any of claims 7 to 9, characterized by the fact that the re-heating of the hot-rolled steel plate or cooled with water to the Aça OR transformation point above is carried out at a rate of not less than 1 ° C / s.
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    同族专利:
    公开号 | 公开日
    CN105189803B|2018-05-04|
    EP2942415A4|2016-03-02|
    WO2014156078A1|2014-10-02|
    RU2627826C2|2017-08-11|
    JP6235221B2|2017-11-22|
    US10253385B2|2019-04-09|
    US20160060721A1|2016-03-03|
    RU2015146266A|2017-05-03|
    AU2014245634A1|2015-08-20|
    KR20150119116A|2015-10-23|
    CN105189803A|2015-12-23|
    CN107227426B|2019-04-02|
    CL2015002876A1|2016-05-20|
    JP2014194043A|2014-10-09|
    BR112015020012A2|2017-07-18|
    PE20151986A1|2016-01-13|
    EP2942415A1|2015-11-11|
    EP2942415B1|2018-12-19|
    MX2015013577A|2016-02-05|
    AU2014245634B2|2016-06-23|
    CN107227426A|2017-10-03|
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    法律状态:
    2018-11-13| B06F| Objections, documents and/or translations needed after an examination request according art. 34 industrial property law|
    2019-08-06| B06U| Preliminary requirement: requests with searches performed by other patent offices: suspension of the patent application procedure|
    2020-06-30| B09A| Decision: intention to grant|
    2020-11-17| B16A| Patent or certificate of addition of invention granted|Free format text: PRAZO DE VALIDADE: 20 (VINTE) ANOS CONTADOS A PARTIR DE 19/03/2014, OBSERVADAS AS CONDICOES LEGAIS. |
    优先权:
    申请号 | 申请日 | 专利标题
    JP2013069932A|JP6235221B2|2013-03-28|2013-03-28|Wear-resistant thick steel plate having low temperature toughness and hydrogen embrittlement resistance and method for producing the same|
    JP2013-069932|2013-03-28|
    PCT/JP2014/001595|WO2014156078A1|2013-03-28|2014-03-19|Abrasion resistant steel plate having low-temperature toughness and hydrogen embrittlement resistance, and manufacturing method therefor|
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