Wear resistant steel sheet and method for producing wear resistant steel sheet

Abstract

The present invention provides a wear resistant steel sheet which has both excellent wear resistance and excellent bending workability over a wide width. A wear resistant steel sheet which has a predetermined component composition, wherein: the volume fraction of martensite in a region from the surface to the depth of 1 mm is 90% or more; the number density of TiC precipitates having a circle-equivalent diameter of 0.5 µm or more in the region from the surface to the depth of 1 mm is 400 precipitates / mm2 or more; the Brinell hardness in the region from the surface to the depth of 1 mm is 360 HBW 10 / 3000 or more; and the hardness difference in the width direction in the region from the surface to the depth of 1 mm, said hardness difference being defined as the Vickers hardness difference between two points that are adjacent to each other at a distance of 10 mm in the sheet width direction, is 30 Hv10 or less.

Description

Wear-resistant steel plate and method for manufacturing the same

[0001] The present invention relates to an abrasion-resistant steel plate, particularly to an abrasion-resistant steel plate with excellent wide-width bending workability suitable for use in components of industrial machinery and transport equipment used in fields such as construction, civil engineering, and mining. The present invention also relates to a method for manufacturing the abrasion-resistant steel plate. Here, wide-width bending workability refers to bending workability at steel plate widths of 200 mm or more, which is a problem in actual use.

[0002] It is known that the wear resistance of steel improves with increasing hardness, so for components that are subject to wear from soil, sand, rocks, etc., steel that has been hardened by heat treatment such as quenching has been used.

[0003] For example, Patent Document 1 describes a method for producing a wear-resistant thick steel plate by hot rolling a steel material having a predetermined chemical composition to form a thick steel plate, and then quenching the plate. According to the method described in Patent Document 1, by controlling the contents of C, alloying elements, and N, it is possible to obtain a wear-resistant thick steel plate that has a hardness of 340 HB or more as quenched, high toughness, and improved low-temperature cracking resistance of the weld.

[0004] Furthermore, Patent Document 2 describes a method for producing a wear-resistant steel plate by hot rolling steel having a predetermined chemical composition at a temperature between 900°C and the Ar3 transformation point with a rolling reduction of 15% or more, and then directly quenching the steel from a temperature equal to or higher than the Ar3 transformation point. According to the method described in Patent Document 2, it is said that a wear-resistant steel plate having high hardness can be easily obtained by controlling the chemical composition and quenching conditions.

[0005] In the techniques described in Patent Documents 1 and 2, wear resistance is improved by increasing hardness. On the other hand, there is a growing demand for wear-resistant steel that is excellent not only in wear resistance but also in bending workability in order to apply it to members of various shapes and reduce the number of welding points.

[0006] In response to such demands, for example, Patent Document 3 proposes a wear-resistant steel containing, by weight, 0.05 to 0.20% C, 0.50 to 2.5% Mn, and 0.02 to 2.00% Al, and having an area fraction of martensite of 5% to 50%. According to Patent Document 3, the area fraction of martensite is controlled by heating hot-rolled steel to a temperature in the ferrite-austenite two-phase region between the Ac1 point and the Ac3 point, and then quenching it, thereby obtaining a wear-resistant steel with excellent workability and weldability.

[0007] Furthermore, Patent Document 4 proposes a method for manufacturing a wear-resistant steel plate in which, after hot rolling, steel having a predetermined chemical composition is immediately cooled to Ms point ±25°C, the cooling is interrupted, the steel is reheated to Ms point +50°C or higher, and then cooled to room temperature. According to Patent Document 4, the minimum hardness in a region from the surface to a depth of 5 mm of the steel plate obtained by this manufacturing method is 40 HV or more lower than the maximum hardness in a region further inside the steel plate, and as a result, bending workability is improved.

[0008] Furthermore, Patent Document 5 proposes a method for manufacturing a wear-resistant steel plate, in which steel having a predetermined chemical composition with a DI* (hardenability index) of 60 or more is hot-rolled and then cooled to a temperature range of 400°C or less at an average cooling rate of 0.5 to 2°C / s. According to Patent Document 5, the wear-resistant steel plate obtained by the above manufacturing method contains 400 particles / mm of Ti-based carbides with an average particle size of 0.5 to 50 μm or more. ２ As a result, it is said that a wear-resistant steel having both excellent wear resistance and bending workability can be obtained without heat treatment.

[0009] Japanese Patent Laid-Open No. 63-169359 Japanese Patent Laid-Open No. 64-031928 Japanese Patent Laid-Open No. 07-090477 Japanese Patent Laid-Open No. 2006-104489 Japanese Patent Laid-Open No. 2008-169443

[0010] As described in Patent Documents 3 to 5, conventional methods for improving the bending workability of wear-resistant steel plates are based on the idea of ​​improving wear resistance by controlling the microstructure or by precipitation of carbides while ensuring bending workability by suppressing the hardness of the base phase (matrix) of the steel plate. Therefore, with these methods, it is difficult to sufficiently improve the hardness of the base phase, and it has not been possible to achieve both wear resistance and bending workability.

[0011] On the other hand, the level of wear resistance required is increasing year by year, so there is a demand for technology that can achieve high levels of both wear resistance and bending workability, which are contradictory properties.

[0012] Furthermore, when a wear-resistant steel plate is processed to manufacture final products such as components for civil engineering and construction equipment, bending is generally performed under conditions where the width of the wear-resistant steel plate is 200 mm or more. Generally, bending cracks tend to occur more easily as the plate width increases. Therefore, in order to evaluate the bending workability of a steel plate during actual use, the evaluation should be performed using a steel plate with a width of 200 mm or more. However, the above-mentioned conventional techniques do not take into consideration bending workability at widths of 200 mm or more.

[0013] The present invention aims to solve the above-mentioned problems and to provide a wear-resistant steel plate that combines the contradictory properties of excellent wear resistance and bending workability. In particular, the present invention aims to provide a wear-resistant steel plate that is excellent in bending workability under the severe condition of a steel plate width of 200 mm or more (hereinafter referred to as "wide-width bending workability").

[0014] In order to achieve the above object, the present inventors have investigated various factors that affect the wide-width bending workability of wear-resistant steel plates, and as a result have obtained the following findings (1) to (4).

[0015] (1) The bending workability of a wear-resistant steel plate is greatly affected by the hardness and ductility of the surface layer of the wear-resistant steel plate.

[0016] (2) In particular, if a wear-resistant steel plate has locally hardened or softened portions, strain is concentrated around the softened or hardened portions, reducing ductility and resulting in poor wide-bending workability.

[0017] (3) By reducing the hardness difference in the wear-resistant steel plate, it is possible to improve wide-width bending workability without reducing the hardness of the matrix phase, which has a significant effect on wear resistance.

[0018] (4) When manufacturing a wear-resistant steel plate, quenching is performed from the austenite temperature range, and the difference in cooling rate in the width direction of the steel plate during quenching is reduced, thereby reducing the hardness difference of the wear-resistant steel plate.

[0019] The present invention was completed based on the above findings and further investigations. The gist of the present invention is as follows.

[0020] 1. A steel sheet having a chemical composition containing, by mass%, C: 0.20 to 0.45%, Si: 0.10 to 1.00%, Mn: 0.50 to 2.0%, P: 0.020% or less, S: 0.010% or less, Cr: 0.01 to 2.0%, Ti: 0.10 to 1.00%, B: 0.0003 to 0.0100%, Al: 0.01 to 0.06%, and N: 0.0100% or less, with the balance being Fe and unavoidable impurities, wherein the volume fraction of martensite at a depth of 1 mm from the surface is 90% or more, and the number density of TiC precipitates having an equivalent circular diameter of 0.5 μm or more at a depth of 1 mm from the surface is 400 precipitates / mm ２ or more, the hardness at a depth of 1 mm from the surface is 360HBW 10 / 3000 or more in Brinell hardness, and the widthwise hardness difference, which is defined as the difference in hardness at a depth of 1 mm from the surface between two adjacent points spaced 10 mm apart in the width direction of the plate, is 30Hv10 or less in Vickers hardness.

[0021] 2. The wear-resistant steel plate according to item 1 above, wherein the composition further contains, in mass%, one or more elements selected from the group consisting of Cu: 0.01 to 0.5%, Ni: 0.01 to 3.0%, Mo: 0.1 to 1.0%, V: 0.01 to 0.10%, Nb: 0.005 to 0.020%, W: 0.01 to 0.5%, and Co: 0.01 to 0.5%.

[0022] 3. The wear-resistant steel plate according to item 1 or 2 above, wherein the component composition further contains, in mass%, one or more selected from the group consisting of Ca: 0.0005 to 0.0050%, Mg: 0.0005 to 0.0100%, and REM: 0.0005 to 0.0200%.

[0023] 4. A method for producing a wear-resistant steel plate, comprising the steps of heating a steel material having a chemical composition containing, by mass%, C: 0.20 to 0.45%, Si: 0.10 to 1.00%, Mn: 0.50 to 2.0%, P: 0.020% or less, S: 0.010% or less, Cr: 0.01 to 2.0%, Ti: 0.10 to 1.00%, B: 0.0003 to 0.0100%, Al: 0.01 to 0.06%, and N: 0.0100% or less, the balance being Fe and unavoidable impurities, to a heating temperature of not less than the Ac3 transformation point and not more than 1300°C, hot-rolling the heated steel material to form a hot-rolled steel plate, and quenching the hot-rolled steel plate, wherein the quenching is (a) direct quenching, in which the hot-rolled steel plate is cooled from a cooling start temperature of not less than the Ar3 transformation point to a cooling stop temperature of not more than the Mf point; or (b) reheating quenching, in which the hot-rolled steel plate is cooled, the cooled hot-rolled steel plate is reheated to a reheating temperature of not less than the Ac3 transformation point and not more than 950°C, and the reheated hot-rolled steel plate is cooled from the reheating temperature to a cooling stop temperature of not more than the Mf point, wherein during the cooling process of the quenching, the difference between the average cooling rate at the center position in the width direction of the hot-rolled steel plate and the average cooling rate at a 1 / 4 position in the width direction, and the difference between the average cooling rate at the center position in the width direction and the average cooling rate at a 3 / 4 position in the width direction are each 5°C / s or less.

[0024] 5. The method for producing a wear-resistant steel plate according to claim 4, wherein the cooling stop temperature in the quenching is less than (Mf point - 100°C), and after the quenching, the quenched hot-rolled steel plate is tempered at a tempering temperature of (Mf point - 80°C) or more and (Mf point + 50°C) or less.

[0025] 6. The method for producing a wear-resistant steel plate according to 5 above, wherein the tempering temperature is maintained for 60 seconds or more.

[0026] 7. The method for producing a wear-resistant steel plate according to the above item 5 or 6, wherein the average temperature increase rate in the tempering is 2°C / s or more.

[0027] 8. The method for producing a wear-resistant steel plate according to 4 above, wherein the cooling stop temperature in the quenching is equal to or lower than the Mf point and equal to or higher than (Mf point - 100°C), and the quenched hot-rolled steel plate is air-cooled after the quenching.

[0028] 9. The method for producing a wear-resistant steel plate according to any one of claims 4 to 8, wherein the chemical composition further contains, in mass%, one or more elements selected from the group consisting of Cu: 0.01 to 0.5%, Ni: 0.01 to 3.0%, Mo: 0.1 to 1.0%, V: 0.01 to 0.10%, Nb: 0.005 to 0.020%, W: 0.01 to 0.5%, and Co: 0.01 to 0.5%.

[0029] 10. The method for producing a wear-resistant steel plate according to any one of the above items 4 to 9, wherein the component composition further contains, in mass%, one or more selected from the group consisting of Ca: 0.0005 to 0.0050%, Mg: 0.0005 to 0.0100%, and REM: 0.0005 to 0.0200%.

[0030] According to the present invention, it is possible to produce a wear-resistant steel plate that combines excellent wear resistance and wide-width bending workability. According to the present invention, excellent wide-width bending workability can be achieved without reducing hardness, which affects wear resistance, and therefore it is possible to meet the high level of wear resistance required in recent years. Therefore, the wear-resistant steel plate of the present invention can be extremely suitably used as a material for components of industrial machinery and transport equipment used in fields such as construction, civil engineering, and mining.

[0031] A method for carrying out the present invention will be specifically described below. Note that the following description shows an example of a preferred embodiment of the present invention, and the present invention is not limited thereto.

[0032] [Composition] In the present invention, it is important that the wear-resistant steel plate and the steel material used for producing it have the above-mentioned composition. Therefore, the reason for limiting the composition of the steel in the present invention as described above will first be explained. Note that "%" regarding the composition means "mass %" unless otherwise specified.

[0033] C: 0.20 to 0.45% C is an element that increases the hardness of the matrix phase and improves wear resistance. To achieve this effect, the C content is set to 0.20% or more. The C content is preferably set to 0.25% or more. On the other hand, if the C content exceeds 0.45%, the hardness of the matrix phase increases excessively, resulting in a decrease in wide-width bending workability. Furthermore, if the C content exceeds 0.45%, weldability also decreases. Therefore, the C content is set to 0.45% or less. The C content is preferably set to 0.40% or less.

[0034] Si: 0.10 to 1.00% Si is an element that acts as a deoxidizer. Furthermore, Si has the effect of increasing the hardness of the matrix phase through solid solution strengthening in steel. If the Si content is less than 0.10%, a sufficient deoxidizing effect cannot be obtained, the amount of inclusions increases, ductility decreases, and wide-width bending workability deteriorates. Therefore, the Si content is set to 0.10% or more. The Si content is more preferably set to 0.20% or more. On the other hand, if the Si content exceeds 1.00%, the amount of inclusions increases and ductility decreases, resulting in a decrease in wide-width bending workability. Therefore, the Si content is set to 1.00% or less. The Si content is preferably set to 0.80% or less, and more preferably 0.60% or less.

[0035] Mn: 0.50 to 2.00% Mn is an element that increases the hardness of the matrix phase and improves wear resistance. If the Mn content is less than 0.50%, the hardenability is insufficient and uniform hardness cannot be obtained. Therefore, the Mn content is set to 0.50% or more. The Mn content is preferably set to 0.60% or more, and more preferably set to 0.70% or more. On the other hand, if the Mn content exceeds 2.00%, the hardness difference increases, resulting in a decrease in wide-width bending workability. Therefore, the Mn content is set to 2.00% or less. The Mn content is preferably set to 1.80% or less, and more preferably set to 1.60% or less.

[0036] P: 0.020% or less P is an element contained as an unavoidable impurity, and has adverse effects such as becoming the origin of fracture by segregating at grain boundaries. Therefore, it is desirable to keep the P content as low as possible, but 0.020% or less is acceptable. There is no particular lower limit for the P content, but since it is difficult to reduce it to less than 0.001% in industrial-scale production, from the viewpoint of productivity, it is preferable to set the P content to 0.001% or more.

[0037] S: 0.010% or less S is an element contained as an unavoidable impurity, and exists in steel as sulfide-based inclusions such as MnS, which have adverse effects such as becoming the origin of fracture. Therefore, it is desirable to keep the S content as low as possible, but 0.010% or less is acceptable. Note that there is no particular restriction on the lower limit of the S content, but since it is difficult to reduce it to less than 0.0001% in industrial-scale production, from the viewpoint of productivity, it is preferable to set the S content to 0.0001% or more.

[0038] Cr: 0.01 to 2.0% Cr is an element that functions to improve the hardenability of steel. Adding Cr increases the hardness of the steel after quenching, thereby improving wear resistance. To achieve this effect, the Cr content must be 0.01% or more. Therefore, the Cr content is set to 0.01% or more, preferably 0.05% or more. On the other hand, if the Cr content exceeds 2.0%, the effect of adding Cr saturates and weldability decreases. Therefore, the Cr content is set to 2.0% or less, preferably 1.8% or less.

[0039] Ti: 0.10 to 1.00% Ti is an element that has the property of forming carbides with C and precipitating them. TiC, a carbide of Ti, has high hardness, so the wear resistance of the steel sheet can be improved by precipitating TiC. However, if the Ti content is less than 0.10%, TiC cannot be effectively formed. Therefore, the Ti content is set to 0.10% or more. The Ti content is preferably set to 0.15% or more. On the other hand, if the Ti content exceeds 1.00%, the TiC becomes excessive, which reduces the wide-width bending workability of the steel sheet and increases costs. Therefore, the Ti content is set to 1.00% or less. The Ti content is preferably set to 0.9% or less.

[0040] B: 0.0003 to 0.0100% B is an element that significantly improves hardenability even with trace amounts, thereby improving the hardness of the steel sheet. To achieve this effect, the B content is set to 0.0003% or more. On the other hand, if the B content exceeds 0.0100%, the precipitation of borides and the like will actually reduce hardenability, resulting in a decrease in the hardness of the steel sheet. Therefore, the B content is set to 0.0100% or less. It is preferable that the B content be 0.0050% or less.

[0041] Al: 0.01 to 0.06% Al acts as a deoxidizer and also refines crystal grains by forming nitrides, improving ductility. If the Al content is less than 0.01%, ductility decreases, resulting in poor wide-width bending workability. Therefore, the Al content is set to 0.01% or more. On the other hand, if the Al content exceeds 0.06%, excessive nitrides are formed, increasing the occurrence of surface defects. Furthermore, if the Al content exceeds 0.06%, oxide-based inclusions increase, reducing ductility and, as a result, reducing wide-width bending workability. Therefore, the Al content is set to 0.06% or less. The Al content is preferably set to 0.05% or less, and more preferably 0.04% or less.

[0042] N: 0.0100% or less N is an element contained as an unavoidable impurity and contributes to the refinement of crystal grains by forming nitrides, etc. However, excessive formation of precipitates reduces ductility and wide-width bending workability. Therefore, the N content is set to 0.0100% or less. The N content is preferably set to 0.0060% or less, and more preferably set to 0.0040% or less. Note that there is no particular restriction on the lower limit of the N content, but since it is difficult to reduce it to less than 0.0010% in industrial-scale production, from the viewpoint of productivity, the N content is preferably set to 0.0010% or more.

[0043] The wear-resistant steel plate and steel material in one embodiment of the present invention have a composition comprising the above components with the balance being Fe and unavoidable impurities.

[0044] In another embodiment of the present invention, the above-mentioned composition may further contain one or more selected from the group consisting of Cu: 0.01 to 0.5%, Ni: 0.01 to 3.0%, Mo: 0.1 to 1.0%, V: 0.01 to 0.10%, Nb: 0.005 to 0.020%, W: 0.01 to 0.5%, and Co: 0.01 to 0.5%.

[0045] Cu: 0.01 to 0.5% Cu is an element that improves hardenability and can be added optionally to further improve hardness. When Cu is added, the Cu content is set to 0.01% or more to achieve the above effect. On the other hand, if the Cu content exceeds 0.5%, surface defects are more likely to occur, reducing manufacturability and increasing alloy costs. Therefore, when Cu is added, the Cu content is set to 0.5% or less.

[0046] Ni: 0.01 to 3.0% Ni is an element that improves hardenability and can be added as needed to further improve hardness. When Ni is added, the Ni content is set to 0.01% or more to achieve the above effect. On the other hand, if the Ni content exceeds 3.0%, the alloy cost increases. Therefore, when Ni is added, the Ni content is set to 3.0% or less.

[0047] Mo: 0.1 to 1.0% Mo is an element that improves hardenability and can be added as needed to further improve hardness. When Mo is added, the Mo content is set to 0.1% or more to obtain this effect. On the other hand, if the Mo content exceeds 1.0%, it will deteriorate weldability and increase alloy costs. Therefore, when Mo is added, the Mo content is set to 1.0% or less.

[0048] V: 0.01 to 0.10% V is an element that improves hardenability and can be added optionally to further improve hardness. Furthermore, V is an element that is effective in reducing solute N by precipitating as VN. When V is added, the V content is set to 0.01% or more to obtain this effect. On the other hand, adding more than 0.10% V reduces ductility due to the precipitation of hard VC. Therefore, when V is added, the V content is set to 0.10% or less, preferably 0.08% or less, and more preferably 0.05% or less.

[0049] Nb: 0.005 to 0.020% Nb is an element that increases the hardness of the matrix phase and contributes to further improving wear resistance. Nb also forms carbonitrides and refines prior austenite grains. When Nb is added, the Nb content is set to 0.005% or more, preferably 0.007% or more, in order to obtain the above effect. On the other hand, if the Nb content exceeds 0.020%, a large amount of NbC precipitates, reducing ductility and, as a result, reducing wide-width bending workability. Therefore, when Nb is added, the Nb content is set to 0.020% or less. The Nb content is preferably set to 0.018% or less.

[0050] W: 0.01 to 0.5% W, like Mo, is an element that improves hardenability and can be added as desired. When W is added, the W content is set to 0.01% or more to obtain the above effect. On the other hand, if the W content exceeds 0.5%, the alloy cost increases. Therefore, when W is added, the W content is set to 0.5% or less.

[0051] Co: 0.01 to 0.5% Co is an element that improves hardenability and can be added as desired. When Co is added, the Co content is set to 0.01% or more to obtain the above effect. On the other hand, if the Co content exceeds 0.5%, the alloy cost increases, so when Co is added, the Co content is set to 0.5% or less.

[0052] In another embodiment of the present invention, the above-mentioned composition may further contain, optionally, one or more elements selected from the group consisting of Ca: 0.0005 to 0.0050%, Mg: 0.0005 to 0.0100%, and REM: 0.0005 to 0.0200%.

[0053] Ca: 0.0005 to 0.0050% Ca is an element useful for controlling the morphology of sulfide-based inclusions and can be added as desired. To achieve this effect, 0.0005% or more must be added. Therefore, when Ca is added, the Ca content is set to 0.0005% or more. On the other hand, adding more than 0.0050% increases the amount of inclusions in the steel, leading to a decrease in ductility and a decrease in wide-width bending workability. Therefore, when Ca is added, the Ca content is set to 0.0050% or less, preferably 0.0025% or less.

[0054] Mg: 0.0005 to 0.0100% Mg is an element that forms stable oxides at high temperatures, effectively suppresses coarsening of prior austenite grains, and improves ductility. To achieve this effect, the addition of 0.0005% or more is necessary. Therefore, when Mg is added, the Mg content is set to 0.0005% or more. On the other hand, adding more than 0.0100% increases the amount of inclusions in the steel, leading to a decrease in ductility and a decrease in wide-width bending workability. Therefore, when Mg is added, the Mg content is set to 0.0100% or less, preferably 0.0050% or less.

[0055] REM: 0.0005 to 0.0200% Like Ca, REM (rare earth metals) also have the effect of improving the material quality by forming oxides and sulfides in steel, and to obtain this effect, 0.0005% or more must be added. Therefore, when REM is added, the REM content is set to 0.0005% or more. On the other hand, even if added in excess of 0.0200%, the effect saturates. Therefore, when REM is included, the REM content is set to 0.0200% or less, preferably 0.0100% or less.

[0056] [Microstructure] Martensite volume fraction: 90% or more In the present invention, the volume fraction of martensite at a depth of 1 mm from the surface of the wear-resistant steel plate is set to 90% or more. If the volume fraction of martensite is less than 90%, the hardness of the matrix structure of the wear-resistant steel plate decreases, resulting in poor wear resistance. Therefore, the volume fraction of martensite is set to 90% or more. On the other hand, the higher the volume fraction of martensite, the better, so the upper limit of the volume fraction is not particularly limited and may be 100%. The volume fraction of martensite can be measured by the method described in the examples.

[0057] As long as the volume fraction of martensite is 90% or more, the desired wear resistance can be obtained regardless of the structure of the remainder, and therefore the structure of the remainder other than martensite is not particularly limited and can be any structure. The structure of the remainder may be, for example, one or more structures selected from the group consisting of ferrite, pearlite, austenite, and bainite.

[0058] Number density of TiC precipitates having a size of 0.5 μm or more: 400 pieces / mm ２ In the wear-resistant steel plate of the present invention, wear resistance is improved by controlling the steel composition and structure, as well as by precipitating coarse TiC. TiC is hard and has the effect of improving wear resistance, but TiC with a size of less than 0.5 μm cannot achieve a sufficient effect of improving wear resistance. Furthermore, even when TiC with a size of 0.5 μm or more is precipitated, the number density of the TiC (1 mm ２ Number of pieces per square meter is 400 pieces / mm ２If the density is less than 400 / mm, the effect of improving the wear resistance is hardly obtained. ２ On the other hand, the upper limit of the number density is not particularly limited, but is usually 5000 pieces / mm ２ The TiC precipitates include composite inclusions of TiC with TiN or TiS. The number density is a value measured at a depth of 1 mm from the surface of the wear-resistant steel plate. The "size" of the TiC precipitates is the circle-equivalent diameter of the TiC precipitates. The number density can be measured by the method described in the examples.

[0059] [Hardness] Brinell hardness: 360HBW 10 / 3000 or more The wear-resistant steel plate of the present invention has the above-mentioned composition and, in addition, a Brinell hardness at a depth of 1 mm from the surface of 360HBW 10 / 3000 or more. The reason for limiting the surface hardness is explained below.

[0060] The wear resistance of a steel plate can be improved by increasing the hardness of the surface layer of the steel plate. If the hardness at a depth of 1 mm from the surface of the steel plate is less than 360 HBW in Brinell hardness, sufficient wear resistance cannot be obtained, and the service life during use will be shortened. Therefore, the hardness at a depth of 1 mm from the surface of the steel plate is set to 360 HBW or more in Brinell hardness. Here, the Brinell hardness is the value measured at a position 1 / 4 of the plate width using a tungsten hard ball with a diameter of 10 mm under a load of 3000 kgf (HBW 10 / 3000).

[0061] [Width-direction hardness difference] Width-direction hardness difference: 30 Hv10 or less If a wear-resistant steel plate has locally hardened or softened portions, strain is concentrated around the softened or hardened portions, reducing ductility and making it impossible to obtain excellent wide-width bending workability. Therefore, in the present invention, the width-direction hardness difference, defined as the difference in hardness at a depth of 1 mm from the surface of the wear-resistant steel plate between two adjacent points spaced 10 mm apart in the width direction, is set to 30 Hv10 or less in Vickers hardness. By keeping the hardness difference within this range, good bending properties can be obtained even during wide-width bending work. Furthermore, since steel plates are usually produced while being moved in the longitudinal direction (rolling direction), maintaining uniformity in the width direction (direction perpendicular to the rolling direction) also results in uniformity in the longitudinal direction.

[0062] The widthwise hardness difference can be evaluated by measuring Vickers hardness at 10 mm intervals in the width direction at a position 1 mm deep from the surface of the wear-resistant steel plate and determining the difference in hardness between adjacent measurement points. A widthwise hardness difference of 30 Hv10 or less means that the hardness difference between all two adjacent points is 30 Hv10 or less, in other words, the maximum hardness difference between two adjacent points is 30 Hv10 or less.

[0063] Thermal cutting, such as gas cutting, plasma cutting, and laser cutting, is generally used to cut wear-resistant steel plates. In thermally cut wear-resistant steel plates, the hardness of the edges varies due to the influence of heat during cutting. Therefore, when measuring the hardness difference in the width direction, the heat-affected zones at the edges of the wear-resistant steel plate are excluded from the measurement. More specifically, Vickers hardness measurements are performed at 10 mm intervals in the width direction in an area excluding a 50 mm area on each side of the wear-resistant steel plate in the width direction, and the hardness difference in the width direction can be determined.

[0064] If measurements are taken at intervals greater than 10 mm, changes in hardness that cause deterioration of bending workability cannot be detected. On the other hand, if the measurement interval is made smaller, the detection accuracy of hardness changes increases, but the number of measurement points becomes enormous. Furthermore, as shown in the examples described below, it has been confirmed that excellent performance can actually be obtained by controlling the hardness difference measured at 10 mm intervals. For these reasons, the measurement interval is set to 10 mm.

[0065] [Thickness] The thickness of the wear-resistant steel plate of the present invention is not particularly limited and can be any thickness. However, since wear-resistant steel plates with a thickness of 4 to 60 mm are particularly required to have wide-width bending workability, it is preferable that the thickness of the wear-resistant steel plate be 4 to 60 mm.

[0066] [Manufacturing Method] Next, a manufacturing method of the wear-resistant steel plate according to one embodiment of the present invention will be described. The wear-resistant steel plate according to the present invention can be manufactured by heating a steel material having the above-described composition, hot-rolling it, and then subjecting it to a heat treatment including quenching under the conditions described below.

[0067] [Steel Material] The steel material may be in any form, for example, a steel slab.

[0068] The method for producing the steel material is not particularly limited, but for example, the steel material can be produced by melting molten steel having the above-mentioned composition by a conventional method and casting it. The melting can be carried out by any method, such as a converter, an electric furnace, or an induction furnace. Furthermore, from the viewpoint of productivity, the casting is preferably carried out by a continuous casting method, but may also be carried out by an ingot casting method.

[0069] [Heating] The steel material is heated to a heating temperature prior to hot rolling. The heating may be performed after the steel material obtained by a method such as casting has been cooled once, or the obtained steel material may be heated directly without being cooled.

[0070] Heating temperature: Ac3 transformation point or higher, 1300°C or lower If the heating temperature is lower than the Ac3 transformation point, the microstructure of the heated steel sheet will contain a ferrite phase, which will not only prevent sufficient hardness from being obtained after quenching, but will also prevent the microstructure from being uniform. Therefore, the heating temperature is set to be equal to or higher than the Ac3 transformation point. On the other hand, if the heating temperature is higher than 1300°C, excessive energy will be required during heating, resulting in reduced manufacturability. Therefore, the heating temperature is set to be 1300°C or lower, preferably 1250°C or lower, more preferably 1200°C or lower, and even more preferably 1150°C or lower.

[0071] The Ac3 transformation point can be calculated using the following formula: Ac3 (°C) = 912.0 - 230.5 x C + 31.6 x Si - 20.4 x Mn - 39.8 x Cu - 18.1 x Ni - 14.8 x Cr + 16.8 x Mo (where the element symbols in the formula above represent the content of each element expressed in mass%, and the content of elements that are not contained is set to 0.)

[0072] [Hot Rolling] Next, the heated steel material is hot-rolled to obtain a hot-rolled steel sheet. The conditions for the hot rolling are not particularly limited, and the hot rolling can be performed according to a conventional method. In the present invention, the conditions for the hot rolling are not particularly limited, since the hardness of the steel sheet is controlled in the heat treatment process after the hot rolling. However, from the viewpoint of reducing the deformation resistance of the steel material and reducing the load on the rolling mill, the rolling end temperature is preferably 750°C or higher, more preferably 800°C or higher, and even more preferably 850°C or higher. On the other hand, from the viewpoint of preventing significant coarsening of austenite grains and the resulting decrease in ductility after heat treatment, the rolling end temperature is preferably 1000°C or lower, more preferably 950°C or lower.

[0073] In the present invention, the hot-rolled steel sheet is subjected to a heat treatment including quenching. The heat treatment can be performed by one of the two embodiments described below. In the following description, the "cooling start temperature" refers to the surface temperature of the steel sheet at the start of cooling in the cooling process of quenching. Furthermore, the "cooling stop temperature" refers to the surface temperature of the steel sheet at the end of cooling in the cooling process of quenching.

[0074] In one embodiment of the present invention, after the hot rolling, the obtained hot-rolled steel sheet is quenched. The quenching is performed by either (a) direct quenching (DQ) or (b) reheat quenching (RQ). The cooling method for the quenching is not particularly limited, but water cooling is preferred.

[0075] (a) Direct Quenching (DQ) When the quenching is performed by direct quenching, the hot-rolled steel sheet after the hot rolling is cooled from a cooling start temperature equal to or higher than the Ar3 transformation point to a cooling stop temperature equal to or lower than the Mf point.

[0076] Cooling start temperature: Ar3 transformation point or higher If the cooling start temperature is Ar3 transformation point or higher, quenching starts in the austenite region, making it possible to obtain the desired martensite structure. If the cooling start temperature is below the Ar3 point, ferrite is generated, resulting in a martensite volume fraction of less than 90% in the final microstructure. If the martensite volume fraction is less than 90%, the hardness of the steel sheet cannot be sufficiently improved, resulting in a decrease in the wear resistance of the steel sheet. Furthermore, if the cooling start temperature is below the Ar3 point, a hardness difference occurs in the width direction, resulting in a decrease in wide-width bending workability. On the other hand, the upper limit of the cooling start temperature is not particularly limited, but it is preferably 950°C or lower.

[0077] The Ar3 transformation point can be calculated using the following formula: Ar3 (°C) = 910 - 273 x C - 74 x Mn - 57 x Ni - 16 x Cr - 9 x Mo - 5 x Cu (where the element symbols in the formula above represent the content of each element expressed in mass%, and the content of elements that are not contained is set to 0.)

[0078] Cooling stop temperature: Mf point or lower If the cooling stop temperature is higher than the Mf point, the volume fraction of martensite cannot be sufficiently increased, and the desired hardness cannot be obtained. Furthermore, if the cooling stop temperature is higher than the Mf point, a hardness difference occurs in the width direction, resulting in a decrease in wide-width bending workability. Therefore, the cooling stop temperature is set to the Mf point or lower. From the viewpoint of increasing the volume fraction of martensite, the cooling stop temperature is preferably set to (Mf point - 100°C) or lower, more preferably (Mf point - 120°C) or lower, and even more preferably (Mf point - 150°C) or lower. On the other hand, although there is no particular restriction on the lower limit of the cooling stop temperature, excessive cooling leads to a decrease in manufacturing efficiency, so the cooling stop temperature is preferably set to room temperature or higher.

[0079] (b) Reheat Quenching (RQ) When the quenching is performed by reheat quenching, first, the hot-rolled steel sheet after hot rolling is cooled, and then the cooled hot-rolled steel sheet is reheated to a reheating temperature of not less than the Ac3 transformation point and not more than 950° C. Thereafter, the reheated hot-rolled steel sheet is cooled from the reheating temperature to a cooling stop temperature not more than the Mf point.

[0080] Reheating temperature: Ac3 transformation point or higher, 950°C or lower Reheating a hot-rolled steel sheet to the Ac3 transformation point or higher converts the microstructure to austenite, allowing subsequent quenching (cooling) to obtain a martensite structure. If the reheating temperature is lower than the Ac3 transformation point, ferrite is generated and the steel sheet is not sufficiently quenched, making it impossible to sufficiently improve the hardness of the steel sheet. As a result, the wear resistance of the final steel sheet is reduced. Therefore, the reheating temperature is set to the Ac3 transformation point or higher. On the other hand, if the reheating start temperature is higher than 950°C, the crystal grains become coarse and the workability is reduced. Therefore, the reheating temperature is set to 950°C or lower. Note that cooling can be started from the reheating temperature, for example, immediately after the hot-rolled steel sheet leaves the furnace used for reheating.

[0081] Cooling stop temperature: Mf point or lower If the cooling stop temperature is higher than the Mf point, the volume fraction of martensite cannot be sufficiently increased, and the desired hardness cannot be obtained. Furthermore, if the cooling stop temperature is higher than the Mf point, a hardness difference occurs in the width direction, resulting in a decrease in wide-width bending workability. Therefore, the cooling stop temperature is set to the Mf point or lower. From the viewpoint of increasing the volume fraction of martensite, the cooling stop temperature is preferably set to (Mf point - 100°C) or lower, more preferably (Mf point - 120°C) or lower, and even more preferably (Mf point - 150°C) or lower. On the other hand, although there is no particular restriction on the lower limit of the cooling stop temperature, excessive cooling leads to a decrease in manufacturing efficiency, so the cooling stop temperature is preferably set to room temperature or higher.

[0082] The Mf point can be calculated using the following formula: Mf (°C) = 410.5 - 407.3 x C - 7.3 x Si - 37.8 x Mn - 20.5 x Cu - 19.5 x Ni - 19.8 x Cr - 4.5 x Mo (where the element symbols in the formula above represent the content of each element expressed in mass%, and the content of elements that are not contained is set to 0.)

[0083] (Average Cooling Rate During Quenching) The cooling rate during the quenching cooling process is not particularly limited and can be any value as long as it is a cooling rate that allows the formation of a martensite phase. For example, the average cooling rate from the start of cooling to the end of cooling is preferably 10°C / s or more, more preferably 15°C / s or more, and even more preferably 20°C / s or more. Meanwhile, the higher the average cooling rate, the better, in principle, and therefore the upper limit is not particularly limited. However, since a cooling facility that can accommodate a higher cooling rate is required, the average cooling rate is preferably 150°C / s or less, more preferably 100°C / s or less, and even more preferably 80°C / s or less. Here, the average cooling rate refers to the average cooling rate at the surface temperature at the center position in the width direction of the steel sheet. The surface temperature can be measured using a radiation thermometer or the like.

[0084] (Cooling Rate Difference) In the present invention, during the cooling process of the quenching, the difference between the average cooling rate at the center position in the width direction of the hot-rolled steel sheet and the average cooling rate at the 1 / 4 position in the width direction, and the difference between the average cooling rate at the center position in the width direction and the average cooling rate at the 3 / 4 position in the width direction, are each set to 5°C / s or less. If the difference in the average cooling rates (hereinafter sometimes referred to as the "cooling rate difference") is greater than 5°C / s, the difference in Vickers hardness between two adjacent points will exceed 30Hv10, and wide-width bending workability will deteriorate. Note that the average cooling rate here refers to the average cooling rate at the surface temperature of the steel sheet. The surface temperature can be measured using a radiation thermometer or the like.

[0085] (Tempering) In one embodiment of the present invention, the quenched hot-rolled steel sheet can be further tempered as desired. Tempering can further improve the uniformity of the hardness of the steel sheet. When tempering is performed, the cooling stop temperature in the quenching is preferably set to less than (Mf point - 100°C). After cooling is stopped at the cooling stop temperature, the steel sheet can be heated to the tempering temperature described below.

[0086] Tempering temperature: (Mf point -80°C) or higher, (Mf point +50°C) or lower If the tempering temperature is lower than (Mf point -80°C), the effect of tempering cannot be obtained. Therefore, when tempering is performed, the tempering temperature is set to (Mf point -80°C) or higher, preferably (Mf point -60°C) or higher, and more preferably (Mf point -50°C) or higher. On the other hand, if the tempering temperature is higher than (Mf point +50°C), the decrease in surface hardness becomes significant. Therefore, when tempering is performed, the tempering temperature is set to (Mf point +50°C) or lower, preferably (Mf point +30°C) or lower, and more preferably (Mf point +10°C) or lower.

[0087] Temperature Holding: Once the tempering temperature is reached, the heating can be stopped. However, in one embodiment of the present invention, after heating to the tempering temperature, the tempering temperature can be further held for any holding time. The holding time is not particularly limited, but from the viewpoint of enhancing the tempering effect, it is preferably 60 seconds or more, and more preferably 5 minutes or more. On the other hand, if the holding time is excessively long, the hardness of the steel sheet may decrease. Therefore, when temperature holding is performed, the holding time is preferably 60 minutes or less, more preferably 30 minutes or less, and even more preferably 20 minutes or less.

[0088] Heating Rate: The rate at which the temperature is increased to the tempering temperature during tempering is not particularly limited. However, from the viewpoint of productivity, the average heating rate to the tempering temperature is preferably 0.1°C / s or more, more preferably 0.5°C / s or more. Furthermore, by setting the average heating rate to 2°C / s or more, carbides are finely precipitated, thereby further improving the wide-width bending workability. Therefore, from the viewpoint of further improving the wide-width bending workability, the average heating rate is preferably 2°C / s or more, more preferably 10°C / s or more. On the other hand, although there is no particular upper limit to the average heating rate, excessively increasing the heating rate not only increases the size of the equipment required for reheating, but also increases energy consumption. Therefore, the average heating rate is preferably 30°C / s or less, more preferably 25°C / s or less.

[0089] The heating (temperature increase) in the tempering process is not particularly limited and can be performed by any method. For example, at least one method selected from the group consisting of heating using a heat treatment furnace, high-frequency induction heating, and electrical heating can be used. When the temperature is maintained, it is preferable that the reheating and temperature maintenance be performed using a heat treatment furnace. Furthermore, when the average temperature increase rate is set to 2°C / s or more, it is preferable to heat the material to the tempering temperature by high-frequency induction heating or electrical heating. On the other hand, when a heat treatment furnace is used, it is preferable that the average temperature increase rate is set to 10°C / s or less. Furthermore, the tempering can be performed either offline or online.

[0090] After heating to the tempering temperature and optionally holding the temperature, the heating or temperature holding can be stopped. The cooling method thereafter is not particularly limited, and one or both of air cooling and water cooling can be used. In one embodiment of the present invention, after heating or temperature holding is stopped, the steel sheet can be allowed to cool to room temperature.

[0091] In another embodiment of the present invention, the cooling during the quenching is interrupted at a specific temperature range, and then the steel sheet is air-cooled. This tempers the steel sheet, which can further improve the uniformity of the hardness of the steel sheet, as in the case where tempering is performed in the above embodiment. This embodiment will be described below.

[0092] Cooling stop temperature: Mf point or lower, (Mf point - 100°C) or higher As described above, if the cooling stop temperature in the quenching is higher than the Mf point, the martensite volume fraction cannot be sufficiently increased, and the desired hardness cannot be obtained. Furthermore, if the cooling stop temperature is higher than the Mf point, a hardness difference occurs in the width direction, resulting in a decrease in wide-width bending workability. Therefore, the cooling stop temperature is set to the Mf point or lower. On the other hand, if the cooling stop temperature is lower than (Mf point - 100°C), the tempering effect cannot be obtained even if air cooling is performed after cooling is stopped. Therefore, in this embodiment, the cooling stop temperature is set to (Mf point - 100°C) or higher. From the viewpoint of enhancing the tempering effect by air cooling, the cooling stop temperature is preferably set to (Mf point - 80°C) or higher, and more preferably (Mf point - 50°C) or higher.

[0093] In this embodiment, the tempering effect can be obtained by stopping the cooling at the cooling stop temperature and then performing air cooling. The air cooling can be performed under any conditions without any particular restrictions, but it is preferable to set the cooling rate to 1°C / s or less.

[0094] In order to confirm the effect of the present invention, a wear-resistant steel plate was manufactured according to the procedure described below, and its properties were evaluated.

[0095] First, molten steel having the chemical composition shown in Table 1 was melted to obtain a steel slab as a steel material. The obtained steel slab was heated to the heating temperature shown in Table 2 and then hot-rolled under the conditions shown in Table 2 to obtain a hot-rolled steel plate. The obtained hot-rolled steel plate was subjected to direct quenching or reheating and quenching under the conditions shown in Table 2 to produce a wear-resistant steel plate. In some examples, after quenching, tempering was performed under the conditions shown in Table 2. In examples in which tempering was not performed, after quenching was stopped, the plate was air-cooled at a cooling rate of 1°C / s or less.

[0096] In addition, the "cooling rate difference" column in Table 2 shows the larger of the difference between the average cooling rate at the center position in the width direction of the hot-rolled steel sheet and the average cooling rate at the 1 / 4 position in the width direction, and the difference between the average cooling rate at the center position in the width direction and the average cooling rate at the 3 / 4 position in the width direction during the cooling process of quenching.

[0097] Next, the volume fraction of martensite (M), hardness, maximum difference in hardness in the width direction, and wide-width bending radius of each of the obtained wear-resistant steel plates were evaluated. The evaluation methods were as follows.

[0098] (Volume Fraction of Martensite) A sample was taken from each steel plate so that the observation position was a position 1 mm deep from the surface of the steel plate. The surface of the sample was mirror-polished and further subjected to nital etching, and then an image of a 10 mm x 10 mm area was taken using a scanning electron microscope (SEM). The photographed image was analyzed using an image analyzer to determine the area fraction of martensite. Ten fields of view were randomly observed, and the average value of the obtained area fractions was taken as the volume fraction of martensite.

[0099] (Number Density of TiC Precipitates) A ​​sample was taken from the center of the width direction of each steel sheet so that the observation position was a position 1 mm deep from the surface. The surface of the sample was mirror-polished and further subjected to nital etching, and then an area of ​​10 mm x 10 mm was photographed using an SEM with an analyzer. The photographed image was analyzed using an image analyzer to determine the number density of TiC precipitates having a size of 0.5 μm or more. The size of the TiC precipitates was calculated as a circle-equivalent diameter.

[0100] (Surface Hardness) Hardness measurement specimens were taken from the obtained wear-resistant steel plates, and the Brinell hardness was measured in accordance with the provisions of JIS Z 2243 (1998). The measurement was carried out after grinding off the areas up to a depth of 1 mm from the front and back surfaces of the steel plate to remove the effects of scale and decarburized layers present on the surface of the wear-resistant steel plate. Therefore, the measured hardness is the surface hardness at a depth of 1 mm from the surface of the steel plate. The measurement position in the width direction was 1 / 4 of the plate width. In addition, a tungsten hard ball with a diameter of 10 mm was used for the measurement, and a load of 3000 kgf was used.

[0101] (Width-direction hardness difference) The Vickers hardness at a depth of 1 mm from the surface of the wear-resistant steel plate was measured at 10 mm intervals in the width direction of the plate. In the measurement, both ends of the wear-resistant steel plate, a region of 50 mm per side, were excluded from the measurement range. From the obtained values, the absolute value of the difference in Vickers hardness between two adjacent points was calculated, and the maximum value is shown in Table 3. The test load in the Vickers hardness measurement was 10 kg.

[0102] (Critical bending radius) Bending test specimens measuring 200 mm wide x 300 mm long were taken from the obtained steel plates, and a bending test was performed at a bending angle of 180° in accordance with JIS Z 2248. The critical bending radius R / t was calculated from the minimum bending radius R (mm) at which cracks did not occur and the plate thickness t (mm) in the bending test. The evaluation results obtained by the above method are shown in Table 3. As can be seen from the results shown in Table 3, wear-resistant steel plates satisfying the conditions of the present invention have a surface hardness of 360 HBW 10 / 3000 or more in Brinell hardness, demonstrating excellent wear resistance. In addition, wear-resistant steel plates satisfying the conditions of the present invention had a critical bending radius R / t of 6.0 or less in the bending test, demonstrating good wide-width bending workability. Thus, the wear-resistant steel plates of the present invention combined excellent wear resistance and wide-width bending workability. These results demonstrate that the present invention can improve wide-width bending workability without reducing the surface hardness of the wear-resistant steel plate.

[0103]

[0104]

[0105]

Claims

1. By mass percentage: C: 0.20 - 0.45%, Si: 0.10 - 1.00%, Mn: 0.50 - 2.0%, P: 0.020% or less, S: 0.010% or less, Cr: 0.01 - 2.0%, Ti: 0.10 - 1.00%, B: 0.0003 - 0.0100%, Al: 0.01 - 0.06%, and N: 0.0100% or less, having a component composition consisting of the balance Fe and inevitable impurities, the volume fraction of martensite at a depth of 1 mm from the surface is 90% or more, the number density of TiC precipitates having an equivalent circle diameter of 0.5 μm or more at a depth of 1 mm from the surface is 400 pieces / mm ２ or more, the hardness at a depth of 1 mm from the surface is 360 HBW 10 / 3000 or more in Brinell hardness, the width direction hardness difference defined as the difference between two adjacent points at 10 mm intervals in the plate width direction of the hardness at a depth of 1 mm from the surface is 30 Hv10 or less in Vickers hardness, a wear-resistant steel plate.

2. The wear-resistant steel plate according to claim 1, wherein the component composition further contains one or more selected from the group consisting of, in mass %, Cu: 0.01 to 0.5%, Ni: 0.01 to 3.0%, Mo: 0.1 to 1.0%, V: 0.01 to 0.10%, Nb: 0.005 to 0.020%, W: 0.01 to 0.5%, and Co: 0.01 to 0.5%.

3. The wear-resistant steel plate according to claim 1 or 2, wherein the component composition further contains one or more selected from the group consisting of, in mass %, Ca: 0.0005 to 0.0050%, Mg: 0.0005 to 0.0100%, and REM: 0.0005 to 0.0200%.

4. A method for manufacturing a wear-resistant steel plate, comprising: heating a steel material having a component composition containing, in mass %, C: 0.20 to 0.45%, Si: 0.10 to 1.00%, Mn: 0.50 to 2.0%, P: 0.020% or less, S: 0.010% or less, Cr: 0.01 to 2.0%, Ti: 0.10 to 1.00%, B: 0.0003 to 0.0100%, Al: 0.01 to 0.06%, and N: 0.0100% or less, with the balance being Fe and inevitable impurities, to a heating temperature of not lower than the Ac3 transformation point and not higher than 1300°C; hot rolling the heated steel material to obtain a hot-rolled steel plate; and quenching the hot-rolled steel plate, wherein the quenching is: (a) direct quenching in which the hot-rolled steel plate is cooled from a cooling start temperature of not lower than the Ar3 transformation point to a cooling stop temperature of not higher than the Mf point, or (b) reheat quenching in which the hot-rolled steel plate is cooled, the cooled hot-rolled steel plate is reheated to a reheating temperature of not lower than the Ac3 transformation point and not higher than 950°C, and the reheated hot-rolled steel plate is cooled from the reheating temperature to a cooling stop temperature of not higher than the Mf point, and the difference between the average cooling rate at the center position in the width direction of the hot-rolled steel plate and the average cooling rate at the 1 / 4 position in the width direction, and the difference between the average cooling rate at the center position in the width direction and the average cooling rate at the 3 / 4 position in the width direction during the cooling process of the quenching are each 5°C / s or less.

5. The cooling stop temperature in the quenching is less than (Mf point - 100°C), and after the quenching, the quenched hot-rolled steel sheet is tempered at a tempering temperature of (Mf point - 80°C) or higher and (Mf point + 50°C) or lower. The method for manufacturing a wear-resistant steel sheet according to claim 4.

6. In the tempering, the tempering temperature is held for 60 s or longer. The method for manufacturing a wear-resistant steel sheet according to claim 5.

7. The average heating rate in the tempering is 2°C / s or higher. The method for manufacturing a wear-resistant steel sheet according to claim 5 or 6.

8. The cooling stop temperature in the quenching is equal to or lower than the Mf point and equal to or higher than (Mf point - 100°C), and after the quenching, the quenched hot-rolled steel sheet is air-cooled. The method for manufacturing a wear-resistant steel sheet according to claim 4.

9. The component composition is in mass%, Cu: 0.01 to 0.5%, Ni: 0.01 to 3.0%, Mo: 0.1 to 1.0%, V: 0.01 to 0.10%, Nb: 0.005 to 0.020%, W: 0.01 to 0.5%, and Co: 0.01 to 0.5% The method for manufacturing a wear-resistant steel sheet according to any one of claims 4 to 8, further containing one or more selected from the group consisting of.

10. The component composition is in mass%, Ca: 0.0005 to 0.0050%, Mg: 0.0005 to 0.0100%, and REM: 0.0005 to 0.0200% The method for manufacturing a wear-resistant steel sheet according to any one of claims 4 to 9, further containing one or more selected from the group consisting of.