Wear-resistant steel plate and method for manufacturing the same

Abstract

The present invention provides a wear-resistant steel plate having both excellent wear resistance and wide bending workability. A wear-resistant steel plate having a predetermined component composition, a volume fraction of martensite at a depth of 1 mm from the surface of 90% or more, a hardness at a depth of 1 mm from the surface of 500 to 650 HBW 10 / 3000 in terms of Brinell hardness, a hardness difference in the width direction of the hardness at a depth of 1 mm from the surface of 30 Hv10 or less in terms of Vickers hardness, and the hardness difference in the width direction is defined as the hardness difference between two points adjacent to each other at an interval of 10 mm in the plate width direction.

Description

Technical Field

[0001] The present invention relates to an abrasion-resistant steel plate, and more particularly to an abrasion-resistant steel plate having excellent wide bending workability and being preferably used as a member of industrial machinery and transportation machinery used in the fields of construction, civil engineering, mining, etc. In addition, the present invention relates to a method for manufacturing the above-mentioned abrasion-resistant steel plate. Here, wide bending workability refers to bending workability in a steel plate with a width of 200 mm or more, which is a problem in actual use. Background Art

[0002] It is known that the wear resistance of steel materials is improved by increasing hardness. Therefore, for members subjected to wear by sand, rock, etc., steel materials that have been hardened by heat treatment such as quenching have been conventionally used.

[0003] For example, Patent Document 1 describes a method for manufacturing a wear-resistant thick steel plate by quenching after hot rolling a steel material having a predetermined composition. According to the method described in Reference Document 1, by controlling the contents of C, alloy elements and N, a wear-resistant thick steel plate having a hardness of 340 HB or more and high toughness in a quenched state and improved low-temperature fracture properties of a welded portion can be produced.

[0004] In addition, Patent Document 2 describes a method for manufacturing a wear-resistant steel plate by hot rolling at a temperature of 900°C to the Ar3 transformation point at a rolling reduction ratio of 15% or more for steel having a predetermined composition, and then directly quenching from a temperature above the Ar3 transformation point. According to the method described in Reference Document 2, a wear-resistant steel plate having high hardness can be easily obtained by controlling the composition and quenching conditions.

[0005] In the above-mentioned technologies described in Patent Documents 1 and 2, wear resistance is improved by increasing hardness. On the other hand, due to the application to components of various shapes and the reduction of welds, the demand for wear-resistant steel having excellent wear resistance and bending workability is increasing.

[0006] In response to such a demand, 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, after hot-rolled steel is heated to a ferrite-austenite two-phase region temperature between the Ac1 point and the Ac3 point, the area fraction of martensite is controlled by rapid cooling, thereby obtaining a wear-resistant steel having excellent workability and weldability.

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

[0008] Furthermore, Patent Document 5 proposes a method for manufacturing a wear-resistant steel plate, wherein a steel having a predetermined composition and 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, for the wear-resistant steel plate obtained by the above-mentioned manufacturing method, 400 Ti-based carbides with an average grain size of 0.5 to 50 μm or more are precipitated / mm 2 As a result of the above, it is possible to obtain wear-resistant steel having both excellent wear resistance and bending workability without performing heat treatment.

[0009] Prior art literature

[0010] Patent Literature

[0011] Patent Document 1: Japanese Patent Application Laid-Open No. 63-169359

[0012] Patent Document 2: Japanese Patent Application Laid-Open No. 64-031928

[0013] Patent Document 3: Japanese Patent Application Laid-Open No. 07-090477

[0014] Patent Document 4: Japanese Patent Application Publication No. 2006-104489

[0015] Patent Document 5: Japanese Patent Application Publication No. 2008-169443 Summary of the invention

[0016] As described in Patent Documents 3 to 5, the methods for improving the bending workability of conventional wear-resistant steel plates are based on the following viewpoints: suppressing the hardness of the matrix phase of the steel plate to ensure bending workability, and improving wear resistance by controlling the microstructure or precipitating carbides. Therefore, in these methods, it is difficult to sufficiently improve the hardness of the matrix phase, and it is impossible to achieve both wear resistance and bending workability.

[0017] On the other hand, the requirements for wear resistance are becoming higher year by year, and therefore, a technology is required that can achieve both wear resistance and bending workability, which are a pair of contradictory properties, at a high standard.

[0018] In addition, when processing wear-resistant steel plates to manufacture civil engineering machinery components as final products, the wear-resistant steel plates are usually bent under the condition that the plate width is 200 mm or more. Generally, bending fracture is more likely to occur as the plate width is wider. Therefore, in order to evaluate the bending workability of steel plates in actual use, steel plates with a plate width of 200 mm or more should be used for evaluation. However, the above-mentioned prior art does not take into account the bending workability of plates with a width of 200 mm or more.

[0019] The present invention aims to solve the above-mentioned problems and provide a wear-resistant steel plate having both excellent wear resistance and bendability, which are contradictory properties. In particular, regarding the above-mentioned bendability, the present invention aims to provide a wear-resistant steel plate having excellent bendability under the severe condition of a steel plate width of 200 mm or more (hereinafter referred to as "wide width bendability").

[0020] To achieve the above object, the present inventors have studied various factors that affect the wide bending workability of wear-resistant steel plates, and as a result, have obtained the following findings (1) to (4).

[0021] (1) The hardness and ductility of the surface layer of the wear-resistant steel plate have a great influence on the bending workability of the wear-resistant steel plate.

[0022] (2) In particular, if a local hardened portion or softened portion exists in the wear-resistant steel plate, strain concentrates around the softened portion or hardened portion, and ductility decreases, thereby reducing wide bending workability.

[0023] (3) By reducing the hardness difference in the wear-resistant steel sheet, the wide bending workability can be improved without reducing the hardness of the matrix phase which has a significant influence on the wear resistance.

[0024] (4) When manufacturing the wear-resistant steel plate, quenching is performed from the austenite temperature region to reduce the difference in cooling rate in the width direction of the steel plate during the quenching, thereby reducing the hardness difference of the wear-resistant steel plate.

[0025] The present invention was completed after further research based on the above findings. The gist of the present invention is as follows.

[0026] 1. A wear-resistant steel plate, comprising the following components in mass %:

[0027] C: more than 0.30% and less than 0.45%,

[0028] Si: 0.05~1.00%,

[0029] Mn: 0.50~2.00%

[0030] P: 0.020% or less,

[0031] S: 0.010% or less,

[0032] Al: 0.01~0.06%,

[0033] Cr: 0.10-1.00%, and

[0034] N: 0.0100% or less,

[0035] The remainder consists of Fe and unavoidable impurities;

[0036] The volume fraction of martensite at a depth of 1 mm from the surface is 90% or more.

[0037] The hardness at a depth of 1 mm from the surface is 500 to 650 HBW 10 / 3000 in terms of Brinell hardness.

[0038] The width direction hardness difference defined as the hardness at a depth of 1 mm from the surface and between two points adjacent to each other at an interval of 10 mm in the plate width direction is 30 Hv10 or less in terms of Vickers hardness.

[0039] 2. The wear-resistant steel plate according to item 1 above, wherein the above component composition, in terms of mass %, further contains

[0040] Nb: 0.005-0.020%,

[0041] Ti: 0.005-0.020%, and

[0042] B: 0.0003~0.0030%

[0043] 1 or more of the following.

[0044] 3. The wear-resistant steel plate according to 1 or 2 above, wherein the above component composition, in terms of mass %, further contains

[0045] Cu: 0.01-0.5%,

[0046] Ni: 0.01~3.0%,

[0047] Mo: 0.1-1.0%,

[0048] V: 0.01~0.10%,

[0049] W: 0.01~0.5%, and

[0050] Co: 0.01~0.5%

[0051] 1 or more of the following.

[0052] 4. The wear-resistant steel plate according to any one of 1 to 3 above, wherein the above component composition further contains, in terms of mass %, selected from

[0053] Ca: 0.0005~0.0050%,

[0054] Mg: 0.0005-0.0100%, and

[0055] REM: 0.0005~0.0200%

[0056] 1 or 2 or more of the above.

[0057] 5. A method for manufacturing a wear-resistant steel plate, wherein a steel billet is heated to a heating temperature of not less than the Ac3 transformation point and not more than 1300° C., wherein the steel billet contains the following composition in terms of mass %:

[0058] C: more than 0.30% and less than 0.45%,

[0059] Si: 0.05~1.00%,

[0060] Mn: 0.50~2.00%

[0061] P: 0.020% or less,

[0062] S: 0.010% or less,

[0063] Al: 0.01~0.06%,

[0064] Cr: 0.10-1.00%, and

[0065] N: 0.0100% or less,

[0066] The remainder consists of Fe and unavoidable impurities;

[0067] The heated steel billet is hot rolled to form a hot rolled steel plate.

[0068] quenching the hot-rolled steel plate;

[0069] The above quenching is:

[0070] (a) direct quenching of the hot rolled steel sheet from a cooling start temperature above the Ar3 transformation point to a cooling stop temperature below the Mf point, or,

[0071] (b) cooling the hot-rolled steel sheet, reheating the cooled hot-rolled steel sheet to a reheating temperature of at least the Ac3 transformation point and not more than 950° C., and cooling the reheated hot-rolled steel sheet from the reheating temperature to a cooling stop temperature of not more than the Mf point, and performing reheating quenching,

[0072] 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 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 both less than 5°C / s.

[0073] 6. The method for producing a wear-resistant steel plate according to 5 above, wherein the cooling stop temperature in the quenching is less than (Mf point - 100°C),

[0074] After the above quenching, the quenched hot-rolled steel sheet is tempered at a tempering temperature of (Mf point - 80°C) to (Mf point + 50°C).

[0075] 7. The method for producing a wear-resistant steel plate according to item 6 above, wherein in the tempering, the tempering temperature is maintained for 60 seconds or more.

[0076] 8. The method for producing a wear-resistant steel plate according to 6 or 7 above, wherein an average temperature increase rate during the tempering is 2° C. / s or more.

[0077] 9. The method for producing a wear-resistant steel plate according to 5 above, wherein the cooling stop temperature in the quenching is not more than the Mf point and not less than (Mf point - 100°C),

[0078] After the above quenching, the quenched hot-rolled steel sheet is air-cooled.

[0079] 10. The method for producing a wear-resistant steel plate according to any one of 5 to 9 above, wherein the above component composition further contains, in mass %, a selected

[0080] Nb: 0.005-0.020%,

[0081] Ti: 0.005-0.020%, and

[0082] B: 0.0003~0.0030%

[0083] 1 or more of the following.

[0084] 11. The method for producing a wear-resistant steel plate according to any one of 5 to 10 above, wherein the above component composition further contains, in terms of mass %, a selected

[0085] Cu: 0.01-0.5%,

[0086] Ni: 0.01~3.0%,

[0087] Mo: 0.1-1.0%,

[0088] V: 0.01~0.10%,

[0089] W: 0.01~0.5%, and

[0090] Co: 0.01~0.5%

[0091] 1 or 2 or more of the above.

[0092] 12. The method for producing a wear-resistant steel plate according to any one of 5 to 11 above, wherein the above component composition further contains, in terms of mass %, a selected

[0093] Ca: 0.0005~0.0050%,

[0094] Mg: 0.0005-0.0100%, and

[0095] REM: 0.0005~0.0200%

[0096] 1 or 2 or more of the above.

[0097] According to the present invention, a wear-resistant steel plate having both excellent wear resistance and wide bending workability can be manufactured. According to the present invention, excellent wide bending workability can be achieved without reducing the hardness that affects wear resistance, and therefore, it is also possible to cope with the high demand standards for wear resistance in recent years. Therefore, the wear-resistant steel plate of the present invention can be used extremely preferably as a material for components of industrial machinery and transportation machinery used in the fields of construction, civil engineering, mining, etc. DETAILED DESCRIPTION

[0098] Hereinafter, a method for carrying out the present invention will be described in detail. It should be noted that the following description shows an example of a preferred embodiment of the present invention, and the present invention is not limited thereto.

[0099] [Ingredients]

[0100] In the present invention, it is important that the wear-resistant steel plate and the steel billet used in its manufacture have the above-mentioned composition. Therefore, the reason why the composition of the steel in the present invention is limited to the above-mentioned composition is first explained. It should be noted that "%" related to the composition means "mass %" unless otherwise specified.

[0101] C: more than 0.30% and less than 0.45%

[0102] C is an element that increases the hardness of the matrix phase and improves wear resistance. In order to obtain this effect, the C content is set to be greater than 0.30%. It is preferred that the C content is set to be greater than 0.35%. On the other hand, if the C content is greater than 0.45%, the hardness of the matrix phase will increase excessively, and the wide bending workability will be significantly reduced. Therefore, the C content is set to be less than 0.45%. It is preferred that the C content is set to be less than 0.43%.

[0103] Si: 0.05~1.00%

[0104] Si is an element that acts as a deoxidizer. In addition, Si has the effect of increasing the hardness of the matrix phase by solid solution strengthening in steel. When the Si content is less than 0.05%, a sufficient deoxidation effect cannot be obtained, the amount of inclusions increases, and as a result, the ductility decreases. Therefore, the Si content is set to 0.05% or more. The Si content is preferably set to 0.10% or more, and more preferably set to 0.20% or more. On the other hand, if the Si content is greater than 1.00%, the amount of inclusions increases, the ductility decreases, and as a result, the wide bending workability decreases. 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 set to 0.60% or less.

[0105] Mn: 0.50~2.00%

[0106] Mn is an element that increases the hardness of the matrix phase and improves wear resistance. When 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 is greater than 2.00%, the hardness is too high, so the wide bending workability will decrease. 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.

[0107] P: 0.020% or less

[0108] P is an element contained as an inevitable impurity, and has adverse effects by segregating at grain boundaries and becoming the starting point of destruction. Therefore, it is desirable to reduce the P content as much as possible, but if it is 0.020% or less, it is acceptable. It should be noted that the lower limit of the P content is not particularly limited, but it is difficult to reduce it to less than 0.001% in industrial-scale production. Therefore, from the perspective of productivity, it is preferred to set the P content to 0.001% or more.

[0109] S: 0.010% or less

[0110] S is an element contained as an inevitable impurity, and is an element that exists in steel as sulfide inclusions such as MnS, and becomes the starting point of destruction, etc., which has adverse effects. Therefore, it is desirable to reduce the S content as much as possible, but it is acceptable if it is 0.010% or less. It should be noted that the lower limit of the S content is not particularly limited, but it is difficult to reduce it to less than 0.0001% in industrial-scale production. Therefore, from the perspective of productivity, it is preferred that the S content be 0.0001% or more.

[0111] Al: 0.01~0.06%

[0112] Al is an element that acts as a deoxidizer and has the function of refining grains and improving ductility by forming nitrides. In order to obtain these effects, the Al content is set to 0.01% or more. On the other hand, if the Al content is greater than 0.06%, nitrides will be excessively formed, and the generation of surface defects will increase. In addition, if the Al content is greater than 0.06%, oxide inclusions will increase and ductility will decrease, resulting in reduced wide bending workability. Therefore, the Al content is set to 0.06% or less. It should be noted that the Al content is preferably set to 0.05% or less, and more preferably set to 0.04% or less.

[0113] Cr: 0.10~1.00%

[0114] Cr is an element that increases the hardness of the matrix phase and improves wear resistance. When the Cr content is less than 0.10%, the effect of improving hardenability due to Cr addition cannot be obtained, and uniform hardness cannot be obtained. Therefore, the Cr content is set to 0.10% or more. The Cr content is preferably set to 0.20% or more, and more preferably set to 0.25% or more. On the other hand, if the Cr content is greater than 1.00%, a decrease in ductility due to the formation of precipitates will occur, and wide bending workability will decrease. Therefore, the Cr content is set to 1.00% or less. The Cr content is preferably set to 0.85% or less, and more preferably set to 0.80% or less.

[0115] N: 0.0100% or less

[0116] N is an element contained as an inevitable impurity, and contributes to the refinement of grains by forming nitrides, etc. However, if precipitates are formed excessively, ductility decreases and wide bending workability decreases. 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. It should be noted that the lower limit of the N content is not particularly limited, but it is difficult to reduce it to less than 0.0010% in industrial-scale manufacturing. Therefore, from the perspective of productivity, it is preferred that the N content be set to 0.0010% or more.

[0117] The wear-resistant steel plate and steel material in one embodiment of the present invention have the above composition and a composition consisting of the remainder consisting of Fe and inevitable impurities.

[0118] In another embodiment of the present invention, the above-mentioned component composition may further contain one or more of Nb: 0.005 to 0.020%, Ti: 0.005 to 0.020%, and B: 0.0003 to 0.0030%.

[0119] Nb: 0.005~0.020%

[0120] Nb is an element that increases the hardness of the matrix phase and contributes to further improving wear resistance. In addition, Nb forms carbonitrides and refines the old austenite grains. When Nb is added, in order to obtain the above-mentioned effect, the Nb content is set to 0.005% or more, preferably 0.007% or more. On the other hand, if the Nb content is greater than 0.020%, NbC will precipitate in large quantities, ductility will decrease, and as a result, wide bending workability will decrease. Therefore, when Nb is added, the Nb content is set to 0.020% or less. It is preferred that the Nb content is set to 0.018% or less.

[0121] Ti: 0.005~0.020%

[0122] Ti is an element that improves ductility by forming nitrides in steel and refining old austenite grains. In addition, when both Ti and B coexist, Ti suppresses the precipitation of BN by fixing N, as a result, the hardenability improvement effect of B increases. In order to obtain these effects, when Ti is added, the Ti content is set to 0.005% or more. It is preferred that the Ti content is set to 0.007% or more. On the other hand, if the Ti content is greater than 0.020%, hard TiC will precipitate in large quantities, and wide bending workability will be reduced. Therefore, when containing Ti, the Ti content is set to 0.020% or less. It is preferred that the Ti content is set to 0.015% or less.

[0123] B: 0.0003~0.0030%

[0124] B is an element that significantly improves hardenability even when added in trace amounts. Therefore, by adding B, the formation of martensite can be promoted, and the wear resistance can be further effectively improved. In order to obtain this effect, when B is added, the B content is set to 0.0003% or more. The B content is preferably set to 0.0005% or more, and more preferably set to 0.0008% or more. On the other hand, if the B content is greater than 0.0030%, an adverse effect will occur, that is, precipitates such as borides that become the starting point of destruction will be formed in large quantities. Therefore, when B is added, the B content is set to 0.0030% or less. It is preferred that the B content is set to 0.0015% or less.

[0125] In addition, in other embodiments of the present invention, the above-mentioned component composition may arbitrarily further contain one or more selected from Cu: 0.01-0.5%, Ni: 0.01-3.0%, Mo: 0.1-1.0%, V: 0.01-0.10%, W: 0.01-0.5%, and Co: 0.01-0.5%.

[0126] Cu: 0.01~0.5%

[0127] Cu is an element that improves hardenability and can be added arbitrarily to further improve hardness. When Cu is added, the Cu content is set to 0.01% or more in order to obtain the above-mentioned effect. On the other hand, if the Cu content is greater than 0.5%, surface defects are likely to occur, manufacturability is reduced, and in addition, the alloy cost increases. Therefore, when Cu is added, the Cu content is set to 0.5% or less.

[0128] Ni: 0.01~3.0%

[0129] Ni is an element that improves hardenability and can be added arbitrarily to further improve hardness. When Ni is added, the Ni content is set to 0.01% or more to obtain the above-mentioned effect. On the other hand, if the Ni content is greater than 3.0%, the alloy cost will increase. Therefore, the Ni content is set to 3.0% or less.

[0130] Mo: 0.1~1.0%

[0131] Mo is an element that improves hardenability and can be added arbitrarily to further improve hardness. When Mo is added, the Mo content is set to 0.1% or more to obtain the above-mentioned effect. On the other hand, if the Mo content exceeds 1.0%, it will lead to deterioration of weldability and increase in alloy cost. Therefore, when Mo is added, the Mo content is set to 1.0% or less.

[0132] V: 0.01~0.10%

[0133] V is an element that improves hardenability and can be added arbitrarily to further improve hardness. In addition, V is an element that contributes to the reduction of solid solution N by precipitating as VN. When V is added, the V content is set to 0.01% or more in order to obtain the above-mentioned effect. On the other hand, if the addition is greater than 0.10%, ductility will be reduced by 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.

[0134] W: 0.01~0.5%

[0135] W, like Mo, is an element that improves hardenability and can be added arbitrarily. When W is added, in order to obtain the above-mentioned effect, the W content is set to 0.01% or more. On the other hand, if the W content is greater than 0.5%, it will lead to an increase in alloy cost. Therefore, when W is added, the W content is set to 0.5% or less.

[0136] Co: 0.01~0.5%

[0137] Co is an element that improves hardenability and can be added arbitrarily. When Co is added, the Co content is set to 0.01% or more in order to obtain the above-mentioned effect. On the other hand, if the Co content is greater than 0.5%, it will lead to an increase in alloy cost. Therefore, when Co is added, the Co content is set to 0.5% or less.

[0138] In another embodiment of the present invention, the above-mentioned component composition may further contain 0.0005% to 0.0050% of Ca, 0.0005% to 0.0100% of Mg, and 0.0005% to 0.0200% of REM.

[0139] 1 or 2 or more of the above.

[0140] Ca: 0.0005~0.0050%

[0141] Ca is an element useful for controlling the morphology of sulfide inclusions, and can be added arbitrarily. In order to exert this effect, addition of 0.0005% or more is necessary. Therefore, when Ca is added, the Ca content is set to 0.0005% or less. On the other hand, if more than 0.0050% is added, the ductility will decrease due to the increase in the amount of inclusions in the steel, and the wide bending workability will decrease. Therefore, when Ca is contained, the Ca content is set to 0.0050% or less, preferably 0.0025% or less.

[0142] Mg: 0.0005~0.0100%

[0143] Mg is an element that forms high temperature stable oxides, effectively suppresses the coarsening of old austenite grains, and improves ductility. In order to exert this effect, an addition of 0.0005% or more is necessary. Therefore, when adding Mg, the Mg content is set to 0.0005% or less. On the other hand, if more than 0.0100% is added, the ductility will be reduced due to the increase in the amount of inclusions in the steel, and the wide bending workability will be reduced. Therefore, when containing Mg, the Mg content is set to 0.0100% or less, preferably 0.0050% or less.

[0144] REM: 0.0005~0.0200%

[0145] REM (rare earth metals) has the effect of improving the quality of steel by forming oxides and sulfides, just like Ca. In order to obtain this effect, it is necessary to add 0.0005% or more. Therefore, when adding REM, the REM content is set to 0.0005% or less. On the other hand, if more than 0.0200% is added, the effect is saturated. Therefore, when REM is contained, the REM content is set to 0.0200% or less, preferably 0.0100% or less.

[0146] [Microstructure]

[0147] Volume ratio of martensite: more than 90%

[0148] 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 basic structure of the wear-resistant steel plate will decrease, and thus the wear resistance will deteriorate. 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, therefore, 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.

[0149] If the volume fraction of martensite is 90% or more, the desired wear resistance can be obtained regardless of the structure of the remaining part, so the structure of the remaining part other than martensite is not particularly limited and can be any structure. The structure of the remaining part can be, for example, one or more of ferrite, pearlite, austenite, and bainite.

[0150] [hardness]

[0151] Brinell hardness: 500~650HBW 10 / 3000

[0152] The wear-resistant steel plate of the present invention has the above-mentioned component composition and has a Brinell hardness of 500 to 650 HBW 10 / 3000 at a depth of 1 mm from the surface. The reasons for limiting the surface hardness are described below.

[0153] The wear resistance of the steel plate can be improved by increasing the hardness of the surface layer of the steel plate. If the hardness of the steel plate at a depth of 1 mm from the surface is less than 500 HBW with a Brinell hardness meter, sufficient wear resistance cannot be obtained and the service life during use will be shortened. Therefore, the hardness of the steel plate at a depth of 1 mm from the surface is set to more than 500 HBW with a Brinell hardness meter. On the other hand, if the hardness of the steel plate at a depth of 1 mm from the surface is greater than 650 HBW with a Brinell hardness meter, the wide bending workability will deteriorate. Therefore, the hardness of the steel plate at a depth of 1 mm from the surface is set to less than 650 HBW with a Brinell hardness meter. It should be noted that here, the above-mentioned Brinell hardness is set to a value (HBW 10 / 3000) at a position of 1 / 4 of the plate width measured using a tungsten hard ball with a diameter of 10 mm and a load of 3000 kgf.

[0154] [Hardness difference in width direction]

[0155] Hardness difference in width direction: 30Hv10 or less

[0156] In the case where there is a local hardened portion or softened portion in the wear-resistant steel plate, the deformation will be concentrated around the softened portion or hardened portion, and the ductility will be reduced, so it is impossible to obtain excellent wide-width bending workability. Therefore, in the present invention, the width direction hardness difference defined as the difference between two points adjacent to each other at an interval of 10 mm in the plate width direction, which is the hardness at a depth of 1 mm from the surface of the wear-resistant steel plate, is set to less than 30Hv10 in terms of Vickers hardness. By making the hardness difference within the above range, good bending characteristics can be obtained even during wide-width bending. In addition, usually, the steel plate is manufactured while moving in the long side direction (rolling direction), so if uniformity is maintained in the width direction (rolling orthogonal direction), the long side direction will also be uniform.

[0157] The above-mentioned width direction hardness difference can be evaluated by measuring the Vickers hardness at a depth of 1 mm from the surface of the wear-resistant steel plate at intervals of 10 mm in the width direction, and finding the difference in hardness between adjacent measurement points. The width direction hardness difference of 30 Hv10 or less means that the hardness difference between all adjacent two points is 30 Hv10 or less, in other words, the maximum value of the hardness difference between two adjacent points is 30 Hv10 or less.

[0158] It should be noted that thermal cutting such as gas cutting, plasma cutting, and laser cutting is generally used for cutting of wear-resistant steel plates. In the thermally cut wear-resistant steel plate, the hardness of the end portion changes due to the influence of heat during cutting. Therefore, in the measurement of the hardness difference in the width direction, the heat-affected portion of the end portion of the wear-resistant steel plate is excluded from the measurement object. More specifically, the Vickers hardness measurement can be performed at intervals of 10 mm in the width direction in a range excluding a range of 50 mm near one side in the width direction of the wear-resistant steel plate to obtain the hardness difference in the width direction.

[0159] If the measurement is performed at intervals greater than 10 mm, the hardness change that causes the deterioration of the bending workability cannot be detected. On the other hand, if the measurement interval is reduced, the detection accuracy of the hardness change is increased, but the number of measurement points becomes huge. In addition, as shown in the examples described later, it can be confirmed that by controlling the hardness difference measured at intervals of 10 mm, an excellent performance can be obtained. Based on the above reasons, the measurement interval is set to 10 mm.

[0160] [Plate thickness]

[0161] The thickness of the wear-resistant steel plate of the present invention is not particularly limited and may be any thickness. However, since wide bending workability is particularly required for wear-resistant steel plates having a thickness of 4 to 60 mm, the thickness of the wear-resistant steel plate is preferably 4 to 60 mm.

[0162] [Manufacturing method]

[0163] Next, a method for producing a wear-resistant steel plate according to an embodiment of the present invention is described. The wear-resistant steel plate of the present invention can be produced by heating a steel billet having the above-mentioned component composition, hot-rolling it, and then subjecting it to heat treatment including quenching under the following conditions.

[0164] [Steel Billet]

[0165] As the steel billet material, any type of billet material may be used. The steel billet material may be, for example, a steel billet.

[0166] The manufacturing method of the steel billet is not particularly limited, and for example, the steel having the above-mentioned composition can be manufactured by melting the molten steel by a conventional method and casting. The melting can be carried out by any method such as a converter, an electric furnace, an induction furnace, etc. In addition, from the viewpoint of productivity, the casting is preferably carried out by a continuous casting method, and can also be carried out by an ingot casting method.

[0167] [heating]

[0168] Prior to hot rolling, the steel slab is heated to a heating temperature. The heating may be performed after the steel slab obtained by casting or the like is cooled once, or the steel slab may be heated directly without cooling the obtained steel slab.

[0169] Heating temperature: above Ac3 phase transition point and below 1300℃

[0170] If the heating temperature is lower than the Ac3 transformation point, the microstructure of the heated steel plate contains a ferrite phase. Therefore, not only can sufficient hardness not be obtained after quenching, but the microstructure is also uneven. Therefore, the heating temperature is set to be above the Ac3 transformation point. On the other hand, if the heating temperature is higher than 1300°C, excessive energy is required during heating, and therefore, manufacturability is reduced. Therefore, the heating temperature is set to be below 1300°C, preferably below 1250°C, more preferably below 1200°C, and further preferably below 1150°C.

[0171] It should be noted that the Ac3 phase transition point can be obtained by the following formula.

[0172] Ac3(℃)=912.0-230.5×C+31.6×Si-20.4×Mn-39.8×Cu-18.1×Ni-14.8×Cr+16.8×Mo

[0173] (The element symbols in the above formulas are the contents of the respective elements expressed in mass %, and the contents of the elements not contained are set to 0.)

[0174] [Hot rolling]

[0175] Next, the heated steel billet is hot rolled to form a hot-rolled steel plate. The conditions for the hot rolling are not particularly limited and can be carried out according to conventional methods. In the present invention, the hardness of the steel plate during the heat treatment after hot rolling is controlled, and therefore, the conditions for hot rolling are not particularly limited. However, from the viewpoint of reducing the deformation resistance of the steel billet and reducing the load on the rolling mill, it is preferred to set the rolling end temperature to above 750°C, more preferably above 800°C, and further preferably above 850°C. On the other hand, from the viewpoint of preventing significant coarsening of austenite grains and the resulting reduction in ductility after heat treatment, the rolling end temperature is preferably set to below 1000°C, and more preferably below 950°C.

[0176] In the present invention, the hot rolled steel sheet is subjected to a heat treatment including quenching. The heat treatment can be performed by any of the following two embodiments. It should be noted that 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. In addition, the "cooling stop temperature" refers to the surface temperature of the steel sheet at the end of cooling in the cooling process of quenching.

[0177] In one embodiment of the present invention, after the hot rolling, the obtained hot rolled steel sheet is quenched. The quenching can be performed by any of (a) direct quenching (DQ) and (b) reheating quenching (RQ). It should be noted that the cooling method in the quenching is not particularly limited, but water cooling is preferred.

[0178] (a) Direct quenching (DQ)

[0179] When the quenching is performed by direct quenching, the hot-rolled steel sheet after the hot rolling is cooled from a cooling start temperature higher than the Ar3 transformation point to a cooling stop temperature lower than the Mf point.

[0180] Cooling start temperature: above Ar3 phase transformation point

[0181] If the cooling start temperature is above the Ar3 transformation point, quenching starts from the austenite region, so the desired martensitic structure can be obtained. If the cooling start temperature is lower than the Ar3 point, ferrite will be generated, so the volume fraction of martensite in the final microstructure is less than 90%. If the volume fraction of martensite is less than 90%, the hardness of the steel plate cannot be fully improved, and as a result, the wear resistance of the steel plate will be reduced. Furthermore, if the cooling start temperature is lower than the Ar3 point, a hardness difference will occur in the width direction, so the wide bending workability will be reduced. On the other hand, the upper limit of the cooling start temperature is not particularly limited, but is preferably below 950°C.

[0182] It should be noted that the Ar3 transformation point can be obtained by the following formula.

[0183] Ar3(℃)=910-273×C-74×Mn-57×Ni-16×Cr-9×Mo-5×Cu

[0184] (The element symbols in the above formulas are the contents of the respective elements expressed in mass %, and the contents of the elements not contained are set to 0.)

[0185] Cooling stop temperature: below Mf point

[0186] If the above-mentioned 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, and therefore, wide-width bending workability is reduced. Therefore, the cooling stop temperature is set below the Mf point. From the viewpoint of increasing the volume fraction of martensite, it is preferred that the above-mentioned cooling stop temperature be set below (Mf point - 100°C), more preferably below (Mf point - 120°C), and further preferably below (Mf point - 150°C). On the other hand, the lower limit of the cooling stop temperature is not particularly limited, but excessive cooling will lead to a decrease in manufacturing efficiency, and therefore, it is preferred that the cooling stop temperature be set above room temperature.

[0187] In addition, the Mf point can be obtained by the following formula.

[0188] Mf(℃)=410.5-407.3×C-7.3×Si-37.8×Mn-20.5×Cu-19.5×Ni-19.8×Cr-4.5×Mo

[0189] (The element symbols in the above formulas are the contents of the respective elements expressed in mass %, and the contents of the elements not contained are set to 0.)

[0190] (b) Reheating quenching (RQ)

[0191] When the quenching is performed by reheating quenching, first, the hot rolled steel sheet after hot rolling is cooled, and 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.

[0192] Reheating temperature: above Ac3 phase transition point and below 950℃

[0193] By reheating the hot-rolled steel sheet to above the Ac3 transformation point, the microstructure can be made austenite, so that a martensitic structure can be obtained by subsequent quenching (cooling). If the reheating temperature is lower than the Ac3 transformation point, ferrite will be generated and cannot be fully quenched, so the hardness of the steel sheet cannot be fully improved, and as a result, the wear resistance of the steel sheet finally obtained will be reduced. Therefore, the above-mentioned reheating temperature is set to above the Ac3 transformation point. On the other hand, if the reheating start temperature is higher than 950°C, the grains will coarsen and the workability will be reduced. Therefore, the above-mentioned reheating temperature is set to below 950°C. It should be noted that in order to start cooling from the above-mentioned reheating temperature, for example, cooling can be started immediately after the hot-rolled steel sheet is taken out of the furnace used for reheating.

[0194] Cooling stop temperature: below Mf point

[0195] If the above-mentioned 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, and therefore, wide-width bending workability is reduced. Therefore, the cooling stop temperature is set below the Mf point. From the viewpoint of increasing the volume fraction of martensite, it is preferred that the above-mentioned cooling stop temperature be set below (Mf point - 100°C), more preferably below (Mf point - 120°C), and further preferably below (Mf point - 150°C). On the other hand, the lower limit of the cooling stop temperature is not particularly limited, but excessive cooling will lead to a decrease in manufacturing efficiency, and therefore, it is preferred that the cooling stop temperature be set above room temperature.

[0196] (Average cooling rate during quenching)

[0197] The cooling rate in the cooling process of the above-mentioned quenching is not particularly limited, and can be any value as long as it is a cooling rate that can form a martensite phase. For example, the average cooling rate from the start of cooling to the stop of cooling is preferably above 10°C / s, more preferably above 15°C / s, and further preferably above 20°C / s. On the other hand, the above-mentioned average cooling rate is, in principle, the higher the better, so the upper limit is not particularly limited. However, in order to increase the cooling rate, corresponding cooling equipment is required, so the above-mentioned average cooling rate is preferably below 150°C / s, more preferably below 100°C / s, and further preferably below 80°C / s. It should be noted that, here, the above-mentioned average cooling rate refers to the average cooling rate of the surface temperature at the center position of the steel plate in the plate width direction. The above-mentioned surface temperature can be measured using a radiation thermometer or the like.

[0198] (Cooling speed difference)

[0199] In the present invention, 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 set to be less than 5°C / s. If the difference in the above average cooling rates (hereinafter sometimes referred to as "cooling rate difference") is greater than 5°C / s, the difference in Vickers hardness between two adjacent points is greater than 30Hv10, and wide bending workability will deteriorate. It should be noted that, here, the average cooling rate refers to the average cooling rate of the surface temperature of the steel plate. The above surface temperature can be measured using a radiation thermometer or the like.

[0200] (Tempering)

[0201] In one embodiment of the present invention, the hot rolled steel sheet after quenching can be further subjected to tempering at will. By performing tempering, the uniformity of the hardness of the steel sheet can be further improved. In the case of performing tempering, the cooling stop temperature in the quenching is preferably 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.

[0202] Tempering temperature: (Mf point -80℃) ~ (Mf point +50℃)

[0203] 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.

[0204] Temperature maintenance

[0205] After reaching the above-mentioned tempering temperature, the heating may be stopped. However, in one embodiment of the present invention, after heating to the tempering temperature, the above-mentioned tempering temperature may be further maintained for an arbitrary holding time interval. The above-mentioned holding time is not particularly limited, but from the viewpoint of improving 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 plate may be reduced. Therefore, when the temperature is maintained, the holding time is preferably 60 minutes or less, more preferably 30 minutes or less, and even more preferably 20 minutes or less.

[0206] Heating rate

[0207] The heating rate to the tempering temperature in the 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, and more preferably 0.5°C / s or more. In addition, by setting the average heating rate to 2°C / s or more, carbides are finely precipitated, and as a result, wide bending workability can be further improved. Therefore, from the viewpoint of further improving wide bending workability, the average heating rate is preferably 2°C / s or more, and more preferably 10°C / s or more. On the other hand, the upper limit of the average heating rate is not particularly limited, but if the heating rate is excessively increased, in addition to the enlargement of the equipment for reheating, the increase in energy consumption also becomes a problem. Therefore, the average heating rate is preferably 30°C / s or less, and more preferably 25°C / s or less.

[0208] The heating (temperature increase) in the above-mentioned tempering can be performed by any method without particular limitation. For example, at least one method of heating using a heat treatment furnace, high-frequency induction heating, and electric heating can be used. When the above-mentioned temperature maintenance is performed, it is preferred to use a heat treatment furnace to implement the above-mentioned reheating and temperature maintenance. In addition, when the above-mentioned average temperature increase rate is set to 2°C / s or more, it is preferred to heat to the tempering temperature by high-frequency induction heating or electric heating. On the other hand, when a heat treatment furnace is used, it is preferred to set the above-mentioned average temperature increase rate to 10°C / s or less. In addition, the above-mentioned tempering can be performed either offline or online.

[0209] After heating to the above-mentioned tempering temperature and optionally maintaining the temperature, the heating or temperature maintenance may be stopped. The cooling method thereafter is not particularly limited, and one or both of air cooling and water cooling may be used. In one embodiment of the present invention, after stopping heating or maintaining the temperature, the steel plate may be cooled to room temperature.

[0210] In another embodiment of the present invention, the cooling during the quenching is interrupted in a specific temperature range, and then air cooling is performed. In this way, the steel plate is tempered, and thus, similar to the case of tempering in the above embodiment, the uniformity of the hardness of the steel plate can be further improved. This embodiment is described below.

[0211] Cooling stop temperature: below Mf point and above (Mf point - 100°C)

[0212] As described above, if the cooling stop temperature in the above-mentioned quenching 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, and therefore, wide-width bending workability is reduced. Therefore, the cooling stop temperature is set below the Mf point. On the other hand, if the cooling stop temperature is less than (Mf point - 100°C), even if air cooling is performed after cooling is stopped, the tempering effect cannot be obtained. Therefore, in the present embodiment, the cooling stop temperature is set to above (Mf point - 100°C). From the viewpoint of improving the tempering effect brought about by air cooling, it is preferred that the above-mentioned cooling stop temperature be set to above (Mf point - 80°C), and more preferably above (Mf point - 50°C).

[0213] In this embodiment, after stopping cooling at the cooling stop temperature, air cooling is performed, so that a tempering effect can be obtained. The air cooling is not particularly limited and can be performed under any conditions, but the cooling rate is preferably set to 1°C / s or less.

[0214] Example

[0215] In order to confirm the effects of the present invention, wear-resistant steel plates were produced according to the following procedure, and their properties were evaluated.

[0216] First, molten steel having the component composition shown in Table 1 is melted to obtain a steel billet as a steel billet material. The obtained steel billet is heated to the heating temperature shown in Table 2, and then hot rolled under the conditions shown in Table 2 to produce a hot-rolled steel plate. The obtained hot-rolled steel plate is subjected to direct quenching or reheating quenching under the conditions shown in Table 2 to produce a wear-resistant steel plate. In some embodiments, after quenching, tempering is performed under the conditions shown in Table 2. It should be noted that in the embodiments where tempering is not performed, air cooling is performed at a cooling rate of less than 1°C / s after quenching is stopped.

[0217] In addition, in the "Cooling rate difference" column of Table 2, the larger value of 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 quenching is shown.

[0218] Next, the obtained wear-resistant steel plates were evaluated for the volume ratio of martensite (M), hardness, maximum value of hardness difference in the width direction, and wide bending radius. The evaluation method is as follows.

[0219] (Volume fraction of martensite)

[0220] Samples were taken from each steel plate at a depth of 1 mm from the surface of the steel plate as the observation position. The surface of the sample was mirror-polished and further corroded with a nitric acid alcohol solution (nital). A scanning electron microscope (SEM) was used to photograph a 10 mm × 10 mm range. The photographed image was analyzed using an image analysis device to determine the area fraction of martensite. Ten fields of view were randomly observed, and the average value of the obtained area fraction was taken as the volume fraction of martensite.

[0221] (Surface hardness)

[0222] A test piece for hardness measurement was taken from the obtained wear-resistant steel plate, and the Brinell hardness was measured according to the provisions of JIS Z 2243 (1998). In order to remove the influence of the oxide scale and decarburized layer on the surface of the wear-resistant steel plate, the area at a depth of 1 mm from the surface of the steel plate was ground and removed, and then the above measurement was carried out. Therefore, the hardness measured is the hardness of the surface at a depth of 1 mm from the surface of the steel plate. It should be noted that the measurement position in the plate width direction is set to 1 / 4 of the plate width. In addition, a tungsten hard ball with a diameter of 10 mm was used during the measurement, and the load was set to 3000 kgf.

[0223] (Hardness difference in width direction)

[0224] The Vickers hardness of the wear-resistant steel plate at a depth of 1 mm from the surface was measured at intervals of 10 mm in the plate width direction. In the above measurement, the two ends of the wear-resistant steel plate and the area of ​​50 mm near one side were excluded from the measurement range. Based on the obtained values, the absolute value of the difference in Vickers hardness between two adjacent points was obtained, and the maximum value is shown in Table 3. The test load in the above Vickers hardness measurement was set to 10 kg.

[0225] (Limiting bending radius)

[0226] A bending test piece of 200 mm wide and 300 mm long was taken from the obtained steel plate, and a bending test with a bending angle of 180° was carried out according to the provisions of JIS Z2248. The limiting bending radius R / t was calculated based on the minimum bending radius R (mm) without fracture in the above bending test and the plate thickness t (mm).

[0227] The evaluation results obtained by the above method are shown in Table 3. According to the results shown in Table 3, the surface hardness of the wear-resistant steel plate that meets the conditions of the present invention is 500-650 HBW 10 / 3000 in Brinell hardness, and the wear resistance is excellent. In addition, if the limit bending radius R / t in the above bending test of the wear-resistant steel plate that meets the conditions of the present invention is 7.0 or less, the wide bending processability is good. In this way, the wear-resistant steel plate of the present invention has both excellent wear resistance and wide bending processability. From this result, it can be seen that according to the present invention, the wide bending processability can be improved without reducing the surface hardness of the wear-resistant steel plate.

[0228]

[0229]

[0230] [Table 3]

[0231] Table 3

[0232]

Claims

1. A method for manufacturing a wear-resistant steel plate, comprising heating a steel billet to a heating temperature of at least Ac3 phase transformation point and not more than 1300° C., The heated steel billet is hot-rolled to form a hot-rolled steel plate. quenching the hot-rolled steel plate; in, The steel billet has the following composition: in mass %, C: more than 0.30% and less than 0.45%, Si: 0.05-1.00%, Mn: 0.50~2.00% P: 0.020% or less, S: 0.010% or less, Al：0.01～0.06％、 Cr: 0.10-1.00%, and N: 0.0100% or less, The remainder consists of Fe and unavoidable impurities; Furthermore, the wear-resistant steel plate has a plate width of 200 mm or more; The volume fraction of martensite at a depth of 1 mm from the surface of the wear-resistant steel plate is 90% or more; The wear-resistant steel plate has a width direction hardness difference defined as the difference between two points adjacent to each other at an interval of 10 mm in the plate width direction at a depth of 1 mm from the surface, which is 30 Hv10 or less in Vickers hardness. The quenching is: (a) direct quenching of the hot-rolled steel sheet from a cooling start temperature above the Ar3 transformation point to a cooling stop temperature below the Mf point, or, (b) cooling the hot-rolled steel sheet, reheating the cooled hot-rolled steel sheet to a reheating temperature of not less than the Ac3 transformation point and not more than 950° C., and cooling the reheated hot-rolled steel sheet from the reheating temperature to a cooling stop temperature not more than the Mf point, and performing reheating quenching; 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 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 both less than 5°C / s.

2. The method for manufacturing a wear-resistant steel plate according to claim 1, wherein: The cooling stop temperature in the quenching is less than (Mf point - 100°C), After the quenching, the quenched hot-rolled steel sheet is tempered at a tempering temperature of (Mf point - 80°C) to (Mf point + 50°C).

3. The method for manufacturing a wear-resistant steel plate according to claim 2, wherein: During the tempering, the tempering temperature is maintained for more than 60 seconds.

4. The method for manufacturing a wear-resistant steel plate according to claim 2 or 3, wherein: The average temperature increase rate during the tempering is 2° C. / s or more.

5. The method for manufacturing a wear-resistant steel plate according to claim 1, wherein: The cooling stop temperature in the quenching is below the Mf point and above (Mf point - 100°C), After the quenching, the quenched hot-rolled steel sheet is air-cooled.

6. The method for manufacturing a wear-resistant steel plate according to claim 1, wherein: The composition is calculated by mass %, further comprising Nb: 0.005-0.020%, Ti: 0.005-0.020%, and B：0.0003～0.0030％ 1 or 2 or more of the above.

7. The method for manufacturing a wear-resistant steel plate according to claim 1, wherein: The composition is calculated by mass %, further comprising Cu: 0.01-0.5%, Ni: 0.01~3.0%, Mo: 0.1-1.0%, V：0.01～0.10％、 W: 0.01~0.5%, and Co: 0.01~0.5% 1 or 2 or more of the above.

8. The method for manufacturing a wear-resistant steel plate according to claim 6, wherein: The composition is calculated by mass %, further comprising Cu: 0.01-0.5%, Ni: 0.01~3.0%, Mo: 0.1-1.0%, V：0.01～0.10％、 W: 0.01~0.5%, and Co: 0.01~0.5% 1 or 2 or more of the above.

9. The method for producing a wear-resistant steel plate according to any one of claims 1 and 6 to 8, wherein: The composition is calculated by mass %, further comprising Ca: 0.0005~0.0050%, Mg: 0.0005-0.0100%, and REM: 0.0005~0.0200% 1 or 2 or more of the above.

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