JP2018048399A - Wear resisting steel sheet and production method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wear resisting steel sheet combining bending workability with wear resistance and a production method therefor.SOLUTION: The wear resisting steel sheet is provided that has a component composition containing, by mass%, C:0.10 to 0.45%, Si:0.05 to 1.00%, Mn:0.10 to 2.00%, P:0.020% or less, S:0.020% or less, Al:0.050% or less, Cr:0.05 to 2.00%, N:0.010% or less, O:0.010% or less, and the balance Fe with inevitable impurities, and that has ferrite with thickness of 0.03 mm or more and less than 1 mm on a steel sheet surface and a volume percentage of martensite at a position 1 mm from the steel sheet surface of 90% or more.SELECTED DRAWING: Figure 1

Description

  TECHNICAL FIELD The present invention relates to a wear-resistant steel sheet, and in particular, an abrasion-resistant steel sheet excellent in bending workability and manufacturing thereof, suitable for use in industrial machinery and materials used in construction, civil engineering, mining, and other fields. Regarding the method.

  Conventionally, it is known that the wear resistance of a steel material is improved by increasing the hardness. For this reason, for example, steel members that have been subjected to wear due to earth, sand, etc. and are required to have wear resistance have been subjected to heat treatment such as quenching to increase the hardness.

  For example, in Patent Document 1, by weight, C: 0.10 to 0.20%, Si: 0.03 to 0.75%, Mn: 0.4 to 1.5%, N: 0.0025 %, Al: 0.001 to 0.080%, or a steel plate having a composition containing at least one of Cu, Ni, Cr, Mo, and B is hot-rolled to a thick steel plate After that, a method for producing a wear-resistant thick steel sheet is described in which it is directly quenched or cooled after hot rolling and then reheated to the γ region and quenched. According to the technique described in Patent Document 1, it is said that a wear-resistant thick steel plate having a hardness of 340 HB or more as it is quenched and high toughness and improved weld cold cracking property is obtained.

In Patent Document 2, C: 0.20 to 0.45%, Si: 0.10 to 1.50%, Mn: 0.60 to 2.50%, Cr: 0.60 to 2.00 %, Al: 0.010 to 0.080%, Nb: 0.010 to 0.100%, B: 0.0010 to 0.0060%, Ca: 0.01% or less, the remainder Fe and inevitable A steel containing impurities or further containing one or more of Ti, Mo and V is hot-rolled at a reduction rate of 15% or more at a temperature of 900 ° C. to Ar ₃ transformation point, and Ar ₃ transformation is performed. A method for producing a wear-resistant steel characterized by quenching from a temperature above the point is described. According to the technique described in Patent Document 2, it is said that wear-resistant steel having high hardness that is advantageous for wear resistance can be easily obtained.

  The techniques described in Patent Documents 1 and 2 improve wear resistance characteristics by increasing the hardness. On the other hand, bending workability is often regarded as important for wear-resistant steel sheets for application to members of various shapes and reduction of welding locations.

Regarding bending workability, for example, in Patent Document 3, in weight percent, C: 0.05 to 0.20%, Mn: 0.50 to 2.5%, Al: 0.02 to 2.00 % Steel is heated to a ferrite-austenite two-phase region between Ac ₃ and Ac ₁ after hot rolling, for example, and then rapidly cooled, so that the area fraction in the ferrite-bainite matrix is 5 to 50%. A wear-resistant steel having excellent workability and weldability in which the martensite structure is dispersed is described.

  In Patent Document 4, the weight percentage is C: 0.1 to 0.35%, Si: 0.05 to 1.0%, Mn: 0.1 to 2.0%, P: 0.02 %, S: 0.05% or less, and Nb: 0.005 to 0.03% of steel is cooled to the Ms point ± 25 ° C. immediately after hot rolling, and then the cooling is interrupted, and the Ms point +50 A method for producing wear-resistant steel is described in which reheating is performed at a temperature higher than or equal to ° C. and then cooled to room temperature. According to Patent Document 4, the minimum hardness in the temperature distribution from the steel sheet surface to a depth of 5 mm is 40 HV or more lower than the maximum hardness in the internal hardness distribution, and a wear-resistant steel excellent in bending workability is obtained. Yes.

Further, in Patent Document 5, in mass%, C: 0.05 to 0.35%, Si: 0.05 to 1.0%, Mn: 0.1 to 2.0%, B: 0.0003 -0.0030%, Ti: 0.10-1.2%, Al: 0.1% or less, further Cu: 0.1-1.0%, Ni: 0.1-0.2%, 1 type or 2 or more types chosen from Cr: 0.1-1.0%, Mo: 0.05-1.0%, W: 0.05-1.0%, or also Nb, A steel containing one or more selected from V and having a DI limited to 60 or more is 400 ° C. or less at a cooling rate of 0.5 to 2 ° C./s at an average cooling rate after hot rolling. The manufacturing method of the abrasion-resistant steel plate which cools to the temperature range is described. As a result, it is possible to obtain a wear resistant steel having improved wear resistance without excessively increasing the hardness by precipitating 400 carbides / mm ² or more of Ti-based carbide having an average particle size of 0.5 to 50 μm or more. Yes.

JP-A 63-169359 JP-A-64-31928 Japanese Patent No. 2864960 Japanese Patent Laid-Open No. 2006-104489 Japanese Patent No. 4899874

  However, in the techniques described in Patent Documents 3 to 5, the hardness of the matrix phase (matrix) is lowered, leaving a problem in wear resistance.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve such problems of the prior art and provide a wear-resistant steel plate having both bending workability and wear resistance and a method for producing the same.

  In order to achieve the above-described object, the present inventors have conducted extensive studies on various factors that affect the bending workability of the wear-resistant steel sheet. As a result, it has been found that the hardness and ductility of the surface layer part greatly contribute to the bending workability of the wear-resistant steel sheet, and the structure of the steel sheet surface is made of ferrite and the structure inside the steel sheet is made of martensite. It has been found that the bending workability is improved within a range in which the hardness of the matrix phase (matrix) that greatly affects the hardness is not lowered.

  First, the experimental results on which the present invention is based will be described.

In mass%, 0.27% C-0.35% Si-0.75% Mn-0.005% P-0.002% S-0.015% Ti-0.03% Al-0.38% A steel material (slab) having a composition containing Cr-0.20Mo was heated to 1150 ° C. and then hot-rolled to obtain a hot-rolled sheet having a thickness of 12 mm. After hot rolling, it was air-cooled, reheated at a heating temperature of ₃ or more points of Ac shown in the following formula (1), and then subjected to a quenching treatment to cool to room temperature.
Ac3 (° C.) = 912.0-230.5 × C + 31.6 × Si-20.4 × Mn-39.8 × Cu-18. 1 × Ni-14.8 × Cr + 16.8 × Mo. 1)
Here, the present inventors decarburized C on the surface of the steel sheet using slab heating in order to change the structure of the steel sheet surface to ferrite and the structure inside the steel sheet to martensite. By reheating at the Ac ₃ point where the amount is 0, that is, below the Ac _{3 (C = 0)} temperature range, and quenching, the structure of the steel sheet surface becomes ferrite and the structure inside the steel sheet becomes martensite. I thought it could be controlled. Then, the reheating temperature, were examined respectively heat-treated material was reheated below Ac 3 _{(C = 0)} point, Ac 3 _{(C = 0)} point than at the reheated heat treatment material.

  About the obtained steel plate, the sample was extract | collected so that a cross section perpendicular | vertical to a rolling direction might become an observation surface. After the observation surface was mirror-polished and further subjected to nital corrosion, a microphotograph of the observation surface was taken using an optical microscope, and the thickness of the ferrite was measured from the taken image.

  In addition, a bending test piece (width 150 mm × 300 mm length) was taken from the obtained steel sheet, and bent according to JIS Z 2248, bending angle: 180 °, bending radius R (where no cracking occurred) mm) was determined as a ratio to the plate thickness t (mm).

  Further, the wear resistance of the steel sheet is mainly determined by the hardness of the surface layer portion. Therefore, a test piece for hardness measurement was taken from the obtained steel plate, and 1 mm from the steel plate surface was ground and removed to remove the influence of the surface scale, and the hardness of the steel plate surface after grinding was measured. . The measurement complied with the provisions of JIS Z 2243 (1998). In the measurement, a tungsten hard sphere having a diameter of 10 mm was used, and the load was 3000 kgf.

FIG. 1A is a microphotograph of a cross section perpendicular to the rolling direction of a steel sheet reheated and quenched beyond the Ac _{3 (C = 0)} point. FIG. 1 (b) is a microphotograph of a cross section perpendicular to the rolling direction of a steel sheet reheated and quenched at an Ac _{3 (C = 0)} point or less. From the results of FIG. 1, it can be seen that when the reheating temperature exceeds the Ac _{3 (C = 0)} point, only martensite is present and there is no ferrite on the steel sheet surface. On the other hand, when the reheating temperature is below the Ac _{3 (C = 0)} point, it can be seen that ferrite is present on the steel sheet surface and martensite is present inside the steel sheet.

  FIG. 2 is a diagram showing the relationship between the ferrite thickness on the steel plate surface and the critical bending radius, and FIG. 3 is a diagram showing the relationship between the ferrite thickness on the steel plate surface and the surface hardness. It was found that when ferrite having a thickness of 0.03 mm or more and less than 1 mm was present on the surface of the steel sheet, the limit bending radius was small, the bending workability was improved, and the hardness was maintained. On the other hand, it was found that when the steel plate surface had ferrite having a thickness of 1 mm or more, the limit bending radius was small and the bending workability was improved, but the hardness was lowered. Further, it was found that when the steel plate surface does not have ferrite (0 mm), the hardness is maintained, but the limit bending radius is large and the workability is inferior.

  From the above, it has been found that a wear-resistant steel sheet having excellent bending workability and wear resistance can be obtained by having a certain thickness of ferrite on the steel sheet surface and martensite inside the steel sheet.

The present invention has been completed based on such findings and further studies. That is, the gist of the present invention is as follows.
[1] By mass%, C: 0.10 to 0.45%, Si: 0.05 to 1.00%, Mn: 0.10 to 2.00%, P: 0.020% or less, S: 0.020% or less, Al: 0.050% or less, Cr: 0.05-2.00%, N: 0.010% or less, O: 0.010% or less, from the balance Fe and unavoidable impurities A wear-resistant steel sheet, characterized by having a ferrite composition with a thickness of 0.03 mm or more and less than 1 mm on the steel sheet surface, and a martensite volume ratio at a position of 1 mm from the steel sheet surface being 90% or more. .
[2] By mass%, C: 0.10 to 0.45%, Si: 0.05 to 1.00%, Mn: 0.50 to 2.00%, P: 0.020% or less, S: 0.020% or less, Al: 0.04% or less, Cr: 0.15 to 0.90%, N: 0.0050% or less, O: 0.0050% or less, from the remainder Fe and inevitable impurities A wear-resistant steel sheet, characterized by having a ferrite composition with a thickness of 0.03 mm or more and less than 1 mm on the steel sheet surface, and a martensite volume ratio at a position of 1 mm from the steel sheet surface being 90% or more. .
[3] In addition to the above component composition, Nb: 0.005 to 0.100%, Ti: 0.005 to 0.100%, and B: 0.0001 to 0.0100% in mass% The wear-resistant steel plate according to [1] or [2], comprising one or more selected from
[4] In addition to the above-described component composition, Cu: 0.01 to 1.0%, Ni: 0.01 to 5.0%, Mo: 0.1 to 2.0%, V : 0.01 to 1.00%, W: 0.01 to 1.00%, Co: containing one or more selected from 0.01 to 1.00% The wear-resistant steel sheet according to any one of [1] to [3].
[5] In addition to the above-described component composition, Ca: 0.0005-0.0100%, Mg: 0.0005-0.0100%, REM: 0.0005-0.0100% The wear-resistant steel plate according to any one of [1] to [4], which contains one or more selected from
[6] The density of inclusions and precipitates having an average particle size of 500 nm or more at a position 1 mm from the surface is 3.0 particles / mm ² or less, according to any one of [1] to [5] The wear-resistant steel sheet described.
[7] By mass%, C: 0.10 to 0.45%, Si: 0.05 to 1.00%, Mn: 0.10 to 2.00%, P: 0.020% or less, S: 0.020% or less, Al: 0.050% or less, Cr: 0.05 to 2.00%, N: 0.010% or less, O: 0.010%, and the balance consisting of Fe and inevitable impurities A steel material having a component composition is heated, then hot rolled, cooled after completion of the hot rolling, and then re-heated at a heating temperature of Ac ₃ points to Ac _{3 (C = 0)} point. A method for producing a wear-resistant steel sheet, comprising: The Ac ₃ point and Ac _{3 (C = 0)} point are represented by the following formulas (1) and (2), respectively.
Ac ₃ (° C.) = 912.0-230.5 × C + 31.6 × Si-20.4 × Mn-39.8 × Cu-18.1 × Ni-14.8 × Cr + 16.8 × Mo. (1)
Ac _{3 (C = 0)} (° C.) = 912.0 + 31.6 × Si−20.4 × Mn−39.8 × Cu−18.1 × Ni−14.8 × Cr + 16.8 × Mo. 2)
However, the element symbol in Formula (1) and Formula (2) is content (mass%) of each element, and is set to 0 when not containing.
[8] By mass%, C: 0.10 to 0.45%, Si: 0.05 to 1.00%, Mn: 0.50 to 2.00%, P: 0.020% or less, S: 0.020% or less, Al: 0.04% or less, Cr: 0.15 to 0.90%, N: 0.0050% or less, O: 0.0050% or less, from the remainder Fe and inevitable impurities A steel material having a component composition is heated, then hot-rolled, cooled after completion of the hot rolling, and then re-heated at a heating temperature of Ac ₃ points or more and Ac _{3 (C = 0)} points or less. A method for producing a wear-resistant steel sheet, comprising: The Ac ₃ point and Ac _{3 (C = 0)} point are represented by the following formulas (1) and (2), respectively.
Ac ₃ (° C.) = 912.0-230.5 × C + 31.6 × Si-20.4 × Mn-39.8 × Cu-18.1 × Ni-14.8 × Cr + 16.8 × Mo. (1)
Ac _{3 (C = 0)} (° C.) = 912.0 + 31.6 × Si−20.4 × Mn−39.8 × Cu−18.1 × Ni−14.8 × Cr + 16.8 × Mo. 2)
However, the element symbol in Formula (1) and Formula (2) is content (mass%) of each element, and is set to 0 when not containing.
[9] In addition to the above component composition, Nb: 0.005 to 0.100%, Ti: 0.005 to 0.100%, and B: 0.0001 to 0.0100% in mass% The method for producing a wear-resistant steel plate according to [7] or [8], comprising one or more selected from the above.
[10] In addition to the above component composition, in addition, by mass, Cu: 0.01 to 1.0%, Ni: 0.01 to 5.0%, Mo: 0.1 to 2.0%, V : 0.01 to 1.00%, W: 0.01 to 1.00%, Co: containing one or more selected from 0.01 to 1.00% The method for producing a wear-resistant steel plate according to any one of [7] to [9].
[11] In addition to the above component composition, Ca: 0.0005-0.0100%, Mg: 0.0005-0.0100%, REM: 0.0005-0.0100% The method for producing a wear-resistant steel plate according to any one of [7] to [10], comprising one or more selected from the above.

  ADVANTAGE OF THE INVENTION According to this invention, the abrasion-resistant steel plate which has bending workability and abrasion resistance can be manufactured easily, and there exists a remarkable effect on industry.

FIG. 1 is a view showing a microphotograph of a cross section perpendicular to the rolling direction for a wear-resistant steel plate according to one embodiment of the present invention, (a) is a microphotograph when there is no ferrite on the steel plate surface, (b). These are figures which show a micro photograph in case a ferrite exists in the steel plate surface. FIG. 2 is a graph showing the relationship between the ferrite thickness on the steel sheet surface and the critical bending radius. FIG. 3 is a graph showing the relationship between the ferrite thickness and hardness on the steel sheet surface.

  The wear-resistant steel sheet of the present invention is in mass%, C: 0.10 to 0.45%, Si: 0.05 to 1.00%, Mn: 0.10 to 2.00%, P: 0.020. %: S: 0.020% or less, Al: 0.050% or less, Cr: 0.05-2.00%, N: 0.010% or less, O: 0.010% or less, and the balance Fe And a component composition consisting of inevitable impurities.

  More preferably, the wear-resistant steel sheet of the present invention is, in mass%, C: 0.10 to 0.45%, Si: 0.05 to 1.00%, Mn: 0.50 to 2.00%, P : 0.020% or less, S: 0.020% or less, Al: 0.04% or less, Cr: 0.15 to 0.90%, N: 0.0050% or less, O: 0.0050% or less In addition, it has a component composition consisting of the remainder Fe and inevitable impurities.

  First, the reason for limiting the composition of the wear-resistant steel sheet of the present invention will be described. Hereinafter, the mass% in the composition is simply expressed as%.

C: 0.10 to 0.45%
C is an effective element that increases the hardness of the matrix phase (matrix) and improves the wear resistance. In order to obtain such an effect, the content of 0.10% or more is required. On the other hand, if the content exceeds 0.45%, the hardness of the matrix phase (matrix) increases excessively and the bending workability decreases. For this reason, C is limited to a range of 0.10 to 0.45%. In addition, Preferably it is 0.13-0.42%.

Si: 0.05-1.00%
Si is an element that acts as a deoxidizer and increases the matrix phase (matrix) hardness by solid solution in steel and by solid solution strengthening. In order to acquire such an effect, 0.05% or more of content is required. On the other hand, if the content exceeds 1.00%, ductility and toughness are lowered, the amount of inclusions is further increased, and bending workability is lowered. For this reason, Si is limited to the range of 0.05 to 1.00%. In addition, Preferably it is 0.05 to 0.40%.

Mn: 0.10 to 2.00%
Mn is an effective element that increases the hardness of the matrix phase (matrix) and improves the wear resistance. In order to obtain such an effect, the content of 0.10% or more is required. On the other hand, containing over 2.00% reduces weldability. For this reason, Mn is limited to 0.10 to 2.00% of range. In addition, Preferably it is 0.50-2.00%, More preferably, it is 0.60-1.80%, More preferably, it is 0.70-1.60%, More preferably, it is 0.80-1.40% is there.

P: 0.020% or less P is an element that has an adverse effect such as segregating at the grain boundary and lowering the toughness of the base metal and the welded portion, and as an inevitable impurity, it is preferable to reduce as much as possible in the present invention. If it is 0.020% or less, it is acceptable. For this reason, P is limited to 0.020 or less. In addition, since excessive reduction causes the refining cost to rise, it is preferable to make it 0.001% or more.

S: 0.020% or less S is an element that exists in steel as sulfide inclusions such as MnS and has an adverse effect such as becoming a starting point of fracture. In the present invention, it is preferable to reduce as much as possible as inevitable impurities, but if it is 0.020% or less, it is acceptable. For this reason, S is limited to 0.020% or less. In addition, Preferably, it is 0.010% or less. In addition, since excessive reduction causes the refining cost to rise, it is preferable to make it 0.0005% or more.

Al: 0.050% or less Al is an element that acts as a deoxidizer and has a function of refining crystal grains. To obtain such an effect, Al should be contained in an amount of 0.01% or more. desirable. On the other hand, when it contains more than 0.050%, oxide inclusions increase, cleanliness decreases, surface defects occur frequently, surface properties decrease, and bending workability decreases. For this reason, Al is limited to 0.050% or less. In addition, Preferably it is 0.04% or less, More preferably, it is 0.03% or less, More preferably, it is 0.02% or less.

Cr: 0.05-2.00%
Cr is an effective element that increases the hardness of the matrix phase (matrix) and improves the wear resistance. In order to acquire such an effect, 0.05% or more of content is required. On the other hand, containing over 2.00% reduces weldability. For this reason, Cr is limited to 0.05 to 2.00% of range. In addition, Preferably it is 0.15-0.90%, More preferably, it is 0.20-0.80%, More preferably, it is 0.30-0.70%.

  The above components are basic components. In the present invention, in addition to the basic composition, Nb: 0.005 to 0.100%, Ti: 0.005 to 0.100%, B: 0.0001 to 0.0100 as a selective element One or more selected from: and / or Cu: 0.01 to 1.0%, Ni: 0.01 to 5.0%, Mo: 0.1 to 2.0%, V: One or more selected from 0.01 to 1.00%, W: 0.01 to 1.00%, Co: 0.01 to 1.00%, and / or Ca: 0 .0005-0.0100%, Mg: 0.0005-0.0100%, REM: 0.0005-0.0100%, or one or more selected from the range , May be included.

  More preferably, as the selective element, one or two selected from Nb: 0.005 to 0.020%, Ti: 0.005 to 0.017%, and B: 0.0001 to 0.0020% More than seeds and / or Cu: 0.01 to 0.2%, Ni: 0.01 to 2.0%, Mo: 0.1 to 0.5%, V: 0.01 to 0.05% W: 0.01 to 0.05%, Co: one or more selected from 0.01 to 0.05%, and / or Ca: 0.0005 to 0.0040%, One or more selected from Mg: 0.0005 to 0.0050% and REM: 0.0005 to 0.0080% may be selected as necessary and contained.

Nb: 0.005 to 0.100%, Ti: 0.005 to 0.100%, B: One or more selected from 0.0001 to 0.0100% Nb, Ti, and B are Any of them is an effective element for increasing the hardness of the matrix phase (matrix) and improving the wear resistance, and can be selected as necessary and contained in one or more kinds.

  Nb is an element that increases the hardness of the matrix phase (matrix) and contributes to the improvement of wear resistance. In order to obtain such an effect, the Nb content needs to be 0.005% or more. On the other hand, when the content exceeds 0.100%, a large amount of NbC is precipitated, and the bending workability is lowered. For these reasons, Nb is preferably limited to a range of 0.005 to 0.100%. In addition, Preferably it is 0.005-0.020%, More preferably, it is 0.008-0.016%, More preferably, it is 0.009-0.014%.

  Ti has a strong tendency to form nitrides, and fixes N to reduce solute N, thereby improving the toughness of the base material and the weld. In addition, when adding B, it is an element that fixes N, suppresses the precipitation of BN, promotes the effect of improving the hardenability of B, improves the hardenability, and contributes to the improvement of wear resistance. is there. In order to acquire such an effect, 0.005% or more needs to be contained. On the other hand, if the content exceeds 0.100%, a large amount of TiC precipitates and the bending workability is lowered. For this reason, when it contains, it is preferable to make Ti into 0.005 to 0.100%. In addition, More preferably, it is 0.005-0.017%, More preferably, it is 0.007-0.015%, More preferably, it is 0.009-0.013%.

  B is an element that significantly improves the hardenability even when added in a trace amount, promotes the formation of martensite, and contributes to the improvement of wear resistance. In order to acquire such an effect, 0.0001% or more needs to be contained. On the other hand, the content exceeding 0.0100% reduces weldability. For this reason, when it contains, it is preferable to limit B to 0.0001 to 0.0100% of range. In addition, More preferably, it is 0.0001 to 0.0020%, More preferably, it is 0.0005 to 0.0015%. Even more preferably, it is 0.0007 to 0.0013%.

Cu: 0.01-1.0%, Ni: 0.01-5.0%, Mo: 0.1-2.0%, V: 0.01-1.00%, W: 0.01- One or more selected from 1.00%, Co: 0.01 to 1.00% Cu, Ni, Mo, V, W, Co all improve the hardenability and increase the inside of the steel sheet. Is added as necessary to obtain a hardness of. In order to obtain such an effect, Cu: 0.01% or more, Ni: 0.01% or more, Mo: 0.1% or more, V: 0.01% or more, W: 0.01% or more, Co: It is preferable to contain 0.01% or more. On the other hand, when it contains exceeding Cu: 1.0%, Ni: 5.0%, Mo: 2.0%, V: 1.00%, W: 1.00%, Co: 1.00%, Degradation of weldability or increase in alloy costs. Therefore, when contained, Cu: 0.01 to 1.0%, Ni: 0.01 to 5.0%, Mo: 0.1 to 2.0%, V: 0.01 ~. It is preferable to limit to 00%, W: 0.01 to 1.00%, and Co: 0.01 to 1.00%. More preferably, Cu: 0.01-0.2%, Ni: 0.01-2.0%, Mo: 0.1-0.5%, V: 0.01-0.05%, W: 0.01 to 0.05%, Co: 0.01 to 0.05%.

One or more selected from Ca: 0.0005-0.0100%, Mg: 0.0005-0.0100%, REM: 0.0005-0.0100% Ca, Mg, REM are Any of them is an element that combines with S and suppresses the formation of MnS or the like that extends long in the rolling direction, controls the form so that the sulfide inclusions have a spherical shape, and contributes to improved toughness of the welded portion, One or more kinds can be selected and contained as required. In order to acquire such an effect, it is preferable to contain Ca: 0.0005% or more, Mg: 0.0005% or more, REM: 0.0005% or more. On the other hand, if it contains more than Ca: 0.0100%, Mg: 0.0100%, REM: 0.0100%, the cleanliness of the steel is lowered, surface flaws occur frequently and the surface properties are lowered, and bending Workability is reduced. Therefore, when it is contained, it may be limited to Ca: 0.0005 to 0.0100%, Mg: 0.0005 to 0.0100%, REM: 0.0005 to 0.0100%. preferable. More preferably, they are Ca: 0.0005-0.0040%, Mg: 0.0005-0.0050%, REM: 0.0005-0.0080%.

  The balance other than the components described above consists of Fe and inevitable impurities. Inevitable impurities include O: 0.010% or less and N: 0.010% or less. If O: exceeds 0.010% or N: exceeds 0.010%, the amount of inclusions to be generated increases, and cracks are likely to occur starting from the inclusions. For this reason, it is limited to O: 0.010% or less and N: 0.010% or less. Preferably, O is 0.0050% or less, and N is 0.0050% or less. More preferably, O: 0.0040% or less and N: 0.0040% or less.

  The wear-resistant steel sheet of the present invention has the above-described composition, has a ferrite having a thickness of 0.03 mm or more and less than 1 mm on the steel sheet surface, and has a martensite volume ratio of 90% or more at a position 1 mm from the steel sheet surface. Organization. The reason for limiting the steel structure as described above will be described below.

Thickness of ferrite on steel plate surface: 0.03 mm or more and less than 1 mm Bending workability is improved by making the steel plate surface ferrite. In order to obtain such an effect, a thickness of 0.03 mm or more is required. On the other hand, if the ferrite is 1 mm or more, the hardness after 1 mm from the surface of the steel sheet is lowered, so that the wear resistance is deteriorated. Therefore, the thickness of the ferrite is less than 1 mm. In addition, More preferably, it is 0.05 mm or more and less than 0.5 mm.

Martensite volume ratio at a position 1 mm from the steel sheet surface: 90% or more When the volume ratio of martensite at a position 1 mm from the steel sheet surface is less than 90%, the hardness of the base structure of the steel sheet decreases, so that the wear resistance Deteriorates. Therefore, the volume ratio of martensite at a position 1 mm from the steel sheet surface is set to 90% or more. The remaining structure other than martensite is not particularly limited, but a ferrite, pearlite, austenite, and bainite structure may exist. On the other hand, since the higher the volume ratio of martensite, the better, the upper limit of the volume ratio of martensite is not particularly limited, and may be 100%. In the present invention, if the volume ratio of martensite at a position 1 mm from the steel sheet surface is 90% or more, it means that the volume ratio of martensite is 90% or more also in the steel sheet interior after 1 mm of the steel sheet surface. To do.

Further, in the steel having the above composition and the above structure, the bending workability is achieved by setting the density of inclusions and precipitates having an average particle diameter of 500 nm or more at a position 1 mm from the steel sheet surface to 3.0 pieces / mm ² or less. Can be further improved.

The density of inclusions and precipitates having an average particle size of 500 nm or more at a position 1 mm from the steel sheet surface is 3.0 pieces / mm ² or less, thereby suppressing cracks originating from the inclusions and precipitates. And bending workability is improved. The lower the density of inclusions and precipitates, the better. Therefore, the lower limit is not particularly limited, but excessive reduction leads to an increase in the refining cost, so 0.1 / mm ² or more is preferable.

  Below, the manufacturing method of the abrasion-resistant steel plate of this invention is demonstrated.

  A steel material having the above component composition is heated and hot-rolled to obtain a wear-resistant steel plate.

Manufacturing method of steel material The manufacturing method of the steel material is not particularly limited, but the molten steel having the above-described component composition is melted by a known melting method such as a converter, and a known method such as a continuous casting method is used. It is preferable to use a steel material such as a slab having a predetermined size by a casting method. In addition, there is no problem even if it is steel materials, such as a slab of a predetermined dimension, by an ingot-making and decomposition rolling method.

Heating the steel material The obtained steel material (slab) is cooled directly or without cooling, and then heated in a heating furnace, preferably at a heating temperature of 900 to 1200 ° C., and further hot-rolled to obtain a desired plate thickness. (Thickness) steel plate. In the present invention, the obtained steel material (slab) is decarburized from the surface by heating, and a ferrite structure having a predetermined thickness can be obtained on the steel sheet surface by performing a quenching treatment at a quenching temperature described later. . The heating temperature is preferably 900 to 1250 ° C. If the heating temperature is less than 900 ° C., the heating temperature is too low and the deformation resistance becomes high, the load on the hot rolling mill increases, and hot rolling becomes difficult. On the other hand, when the temperature is higher than 1250 ° C., the oxidation becomes remarkable, the oxidation loss increases, and the yield decreases. Therefore, the heating temperature is preferably 900 to 1250 ° C. In addition, More preferably, it is 950-1150 degreeC.

Hot rolling Hot rolling is not particularly limited, and hot rolling may be performed by a conventional method.

Quenching treatment in which heating temperature is reheated at Ac ₃ points or more and Ac _{3 (C = 0)} points or less. Further, after cooling after completion of hot rolling, Ac ₃ points or more shown by the following formulas (1) and (2) A quenching process is performed in which reheating is performed at a heating temperature of Ac _{3 (C = 0)} or lower. This is to obtain a martensite structure by quenching from the austenite state. Ac quenching from less than ₃ points does not sufficiently quench, the hardness decreases, and a microstructure with high wear resistance cannot be obtained. On the other hand, if the heating temperature exceeds the Ac _{3 (C = 0)} point, the steel sheet surface has a martensite structure, and a desired ferrite structure cannot be obtained.
Ac ₃ (° C.) = 912.0-230.5 × C + 31.6 × Si-20.4 × Mn-39.8 × Cu-18.1 × Ni-14.8 × Cr + 16.8 × Mo. (1)
Ac _{3 (C = 0)} (° C.) = 912.0 + 31.6 × Si−20.4 × Mn−39.8 × Cu−18.1 × Ni−14.8 × Cr + 16.8 × Mo. 2)
However, the element symbol in Formula (1) and Formula (2) is content (mass%) of each element, and is set to 0 when not containing.

  The cooling rate of the quenching process is not particularly limited as long as it is a cooling rate at which a martensite structure is formed. The cooling stop temperature is preferably water-cooled to a temperature below the Mf point, preferably 200 ° C. or below.

Molten steel having the composition shown in Table 1 was melted to obtain a steel material (slab). These steel materials (slabs) were heated and hot-rolled under the conditions shown in Table 2 to obtain hot-rolled sheets having the thicknesses shown in Table 2. Thereafter, the mixture was allowed to cool, reheated, and then reheated and quenched. In addition, Mf and Ar ₃ in Table 1 were obtained by the following formula.
Mf (° C.) = 410.5−407.3 × C−7.3 × Si-37.8 × Mn−20.5 × Cu−19.5 × Ni−19.8 × Cr−4.5 × Mo
Ar ₃ (° C.) = 910-273 × C-74 × Mn-57 × Ni-16 × Cr-9 × Mo-5 × Cu

About the obtained steel plate, the thickness measurement of the ferrite of the steel plate surface, the volume ratio measurement of a martensite, the hardness test of the surface layer part, and the bending test were each implemented. The test method is as follows.
(1) Measurement of ferrite thickness Samples were taken from each steel sheet so that the cross section perpendicular to the rolling direction was the observation surface. The sample was mirror-polished and further subjected to nital corrosion, and then three field-of-view photographs were taken at × 400 magnification using an optical microscope. The average thickness was determined by measuring the ferrite thickness at any five locations per field of view, and the average value for the three fields of view was defined as the ferrite thickness.
(2) Measurement of martensite volume ratio Samples were taken from each steel sheet so that the position 1 mm from the steel sheet surface was the observation position. The surface of the sample was mirror-polished and further subjected to nital corrosion, and then a range of 10 mm × 10 mm was photographed using a scanning electron microscope (SEM). The photographed image was analyzed using an image analyzer, and the area fraction of martensite was obtained. The area fraction of martensite was determined for any three images, and the average value was taken as the volume ratio of martensite in the present invention.
(3) Inclusion and Precipitate Measurement Samples were taken from each steel sheet so that the position of 1 mm from the steel sheet surface was the observation position. The surface of the sample was mirror-polished and an area of 10 mm × 10 mm was photographed using SEM. By analyzing the photographed image using an image analyzer, the particle size and number of inclusions and precipitates were determined, the number of inclusions and precipitates having an average particle size of 500 nm or more was measured, and the density was determined. . For any three images, the density of inclusions and precipitates was determined, and the average value was taken as the density of inclusions and precipitates in the present invention.
(4) Surface hardness test The wear resistance of the steel sheet is mainly determined by the hardness of the surface layer portion. Therefore, a test piece for hardness measurement was collected from the obtained steel plate, and the hardness at the 1 mm position in the thickness direction from the surface was measured in accordance with the provisions of JIS Z 2243 (1998). In order to remove the influence of the surface scale and the decarburized layer, 1 mm from the surface was ground and removed, and the surface hardness was measured on a surface 1 mm from the surface. In the measurement, a tungsten hard sphere having a diameter of 10 mm was used, and the load was 3000 kgf. Hardness of 360 or more was accepted.
(5) Bending test A bending test piece (width 150 mm x 300 mm length) was taken from the obtained steel sheet, and bent according to JIS Z 2248, bending angle: 180 °, bending radius without cracking. The critical bending radius R / t, which represents R (mm) as a ratio to the plate thickness t (mm), was determined. R / t was determined to be 1.5 or less.

  The obtained results are shown in Table 2.

  The invention example is a wear-resistant steel plate having bending workability and wear resistance. On the other hand, the comparative example has the same hardness and a large bending radius, or has a low hardness and a small bending radius, and is inferior in bending workability or wear resistance.

Molten steel having the composition shown in Table 3 was melted to obtain a steel material (slab). These steel materials (slabs) were heated and hot-rolled under the conditions shown in Table 4 to obtain hot-rolled sheets having a thickness shown in Table 4. Thereafter, the mixture was allowed to cool, reheated, and then reheated and quenched. In addition, Ms, Mf, and Ar ₃ in Table 3 were obtained by the following formula.
Mf (° C.) = 410.5−407.3 × C−7.3 × Si-37.8 × Mn−20.5 × Cu−19.5 × Ni−19.8 × Cr−4.5 × Mo
Ar ₃ (° C.) = 910-273 × C-74 × Mn-57 × Ni-16 × Cr-9 × Mo-5 × Cu

About the obtained steel plate, the thickness measurement of the ferrite of the steel plate surface, the volume ratio measurement of a martensite, the hardness test of the surface layer part, and the bending test were each implemented. The test method is as follows.
(1) Measurement of ferrite thickness Samples were taken from each steel sheet so that the cross section perpendicular to the rolling direction was the observation surface. The sample was mirror-polished and further subjected to nital corrosion, and then three field-of-view photographs were taken at × 400 magnification using an optical microscope. The average thickness was determined by measuring the ferrite thickness at any five locations per field of view, and the average value for the three fields of view was defined as the ferrite thickness.
(2) Measurement of martensite volume ratio Samples were taken from each steel sheet so that the position 1 mm from the steel sheet surface was the observation position. The surface of the sample was mirror-polished and further subjected to nital corrosion, and then a range of 10 mm × 10 mm was photographed using a scanning electron microscope (SEM). The photographed image was analyzed using an image analyzer, and the area fraction of martensite was obtained. The area fraction of martensite was determined for any three images, and the average value was taken as the volume ratio of martensite in the present invention.
(3) Inclusion and Precipitate Measurement Samples were taken from each steel sheet so that the position of 1 mm from the steel sheet surface was the observation position. The surface of the sample was mirror-polished and an area of 10 mm × 10 mm was photographed using SEM. By analyzing the photographed image using an image analyzer, the particle size and number of inclusions and precipitates were determined, the number of inclusions and precipitates having an average particle size of 500 nm or more was measured, and the density was determined. . For any three images, the density of inclusions and precipitates was determined, and the average value was taken as the density of inclusions and precipitates in the present invention.
(4) Surface hardness test The wear resistance of the steel sheet is mainly determined by the hardness of the surface layer portion. Therefore, a test piece for hardness measurement was collected from the obtained steel plate, and the hardness at the 1 mm position in the thickness direction from the surface was measured in accordance with the provisions of JIS Z 2243 (1998). In order to remove the influence of the surface scale and the decarburized layer, 1 mm from the surface was ground and removed, and the surface hardness was measured on a surface 1 mm from the surface. In the measurement, a tungsten hard sphere having a diameter of 10 mm was used, and the load was 3000 kgf. The hardness was 490 or more.
(5) Bending test A bending test piece (width 150 mm x 300 mm length) was taken from the obtained steel sheet, and bent according to JIS Z 2248, bending angle: 180 °, bending radius without cracking. The critical bending radius R / t, which represents R (mm) as a ratio to the plate thickness t (mm), was determined. An R / t of 2.5 or less was accepted.

  Table 4 shows the obtained results.

  The invention example is a wear-resistant steel plate having bending workability and wear resistance. On the other hand, the comparative example has the same hardness and a large bending radius, or has a low hardness and a small bending radius, and is inferior in bending workability or wear resistance.

Molten steel having the composition shown in Table 5 was melted to obtain a steel material (slab). These steel materials (slabs) were heated and hot-rolled under the conditions shown in Table 6 to obtain hot-rolled sheets having the thicknesses shown in Table 6. Thereafter, the mixture was allowed to cool, reheated, and then reheated and quenched. In addition, Ms, Mf, and Ar ₃ in Table 5 were obtained by the following equations.
Mf (° C.) = 410.5−407.3 × C−7.3 × Si-37.8 × Mn−20.5 × Cu−19.5 × Ni−19.8 × Cr−4.5 × Mo
Ar ₃ (° C.) = 910-273 × C-74 × Mn-57 × Ni-16 × Cr-9 × Mo-5 × Cu

About the obtained steel plate, the thickness measurement of the ferrite of the steel plate surface, the volume ratio measurement of a martensite, the hardness test of the surface layer part, and the bending test were each implemented. The test method is as follows.
(1) Measurement of ferrite thickness Samples were taken from each steel sheet so that the cross section perpendicular to the rolling direction was the observation surface. The sample was mirror-polished and further subjected to nital corrosion, and then three field-of-view photographs were taken at × 400 magnification using an optical microscope. The average thickness was determined by measuring the ferrite thickness at any five locations per field of view, and the average value for the three fields of view was defined as the ferrite thickness.
(2) Measurement of martensite volume ratio Samples were taken from each steel sheet so that the position 1 mm from the steel sheet surface was the observation position. The surface of the sample was mirror-polished and further subjected to nital corrosion, and then a range of 10 mm × 10 mm was photographed using a scanning electron microscope (SEM). The photographed image was analyzed using an image analyzer, and the area fraction of martensite was obtained. The area fraction of martensite was determined for any three images, and the average value was taken as the volume ratio of martensite in the present invention.
(3) Inclusion and Precipitate Measurement Samples were taken from each steel sheet so that the position of 1 mm from the steel sheet surface was the observation position. The surface of the sample was mirror-polished and an area of 10 mm × 10 mm was photographed using SEM. By analyzing the photographed image using an image analyzer, the particle size and number of inclusions and precipitates were determined, the number of inclusions and precipitates having an average particle size of 500 nm or more was measured, and the density was determined. . For any three images, the density of inclusions and precipitates was determined, and the average value was taken as the density of inclusions and precipitates in the present invention.
(4) Surface hardness test The wear resistance of the steel sheet is mainly determined by the hardness of the surface layer portion. Therefore, a test piece for hardness measurement was collected from the obtained steel plate, and the hardness at the 1 mm position in the thickness direction from the surface was measured in accordance with the provisions of JIS Z 2243 (1998). In order to remove the influence of the surface scale and the decarburized layer, 1 mm from the surface was ground and removed, and the surface hardness was measured on a surface 1 mm from the surface. In the measurement, a tungsten hard sphere having a diameter of 10 mm was used, and the load was 3000 kgf. The hardness was 560 or more.
(5) Bending test A bending test piece (width 150 mm x 300 mm length) was taken from the obtained steel sheet, and bent according to JIS Z 2248, bending angle: 180 °, bending radius without cracking. The critical bending radius R / t, which represents R (mm) as a ratio to the plate thickness t (mm), was determined. R / t was determined to be 3.5 or less.

  The results obtained are shown in Table 6.

  The invention example is a wear-resistant steel plate having bending workability and wear resistance. On the other hand, the comparative example has the same hardness and a large bending radius, or has a low hardness and a small bending radius, and is inferior in bending workability or wear resistance.

Claims (11)

  In mass%, C: 0.10 to 0.45%, Si: 0.05 to 1.00%, Mn: 0.10 to 2.00%, P: 0.020% or less, S: 0.020 %, Al: 0.050% or less, Cr: 0.05 to 2.00%, N: 0.010% or less, O: 0.010% or less, and the remaining composition of Fe and inevitable impurities A wear-resistant steel sheet having ferrite having a thickness of 0.03 mm or more and less than 1 mm on the steel sheet surface, and having a martensite volume ratio of 90% or more at a position of 1 mm from the steel sheet surface.   In mass%, C: 0.10 to 0.45%, Si: 0.05 to 1.00%, Mn: 0.50 to 2.00%, P: 0.020% or less, S: 0.020 %, Al: 0.04% or less, Cr: 0.15 to 0.90%, N: 0.0050% or less, O: 0.0050% or less, and the component composition consisting of the balance Fe and inevitable impurities A wear-resistant steel sheet having ferrite having a thickness of 0.03 mm or more and less than 1 mm on the steel sheet surface, and having a martensite volume ratio of 90% or more at a position of 1 mm from the steel sheet surface.   In addition to the above component composition, it is further selected by mass% from Nb: 0.005 to 0.100%, Ti: 0.005 to 0.100%, and B: 0.0001 to 0.0100%. The wear-resistant steel sheet according to claim 1 or 2, further comprising one or more kinds.   In addition to the above-mentioned component composition, Cu: 0.01 to 1.0%, Ni: 0.01 to 5.0%, Mo: 0.1 to 2.0%, V: 0.0. One or more kinds selected from 01 to 1.00%, W: 0.01 to 1.00%, and Co: 0.01 to 1.00% are contained. The wear-resistant steel sheet according to any one of 1 to 3.   In addition to the above component composition, it is further selected by mass% from Ca: 0.0005 to 0.0100%, Mg: 0.0005 to 0.0100%, REM: 0.0005 to 0.0100%. The wear-resistant steel sheet according to any one of claims 1 to 4, further comprising one or more kinds. The wear-resistant steel sheet according to any one of claims 1 to 5, wherein the density of inclusions and precipitates having an average particle diameter of 500 nm or more at a position of 1 mm from the surface is 3.0 pieces / mm ² or less. . In mass%, C: 0.10 to 0.45%, Si: 0.05 to 1.00%, Mn: 0.10 to 2.00%, P: 0.020% or less, S: 0.020 %, Al: 0.050% or less, Cr: 0.05-2.00%, N: 0.010% or less, O: 0.010%, and the component composition consisting of the remainder Fe and inevitable impurities After heating the steel material, it is hot-rolled, cooled after the hot rolling is completed, and then subjected to a quenching process in which the heating temperature is reheated at Ac ₃ points or more and Ac _{3 (C = 0)} points or less. A method for producing a wear-resistant steel sheet. The Ac ₃ point and Ac _{3 (C = 0)} point are represented by the following formulas (1) and (2), respectively.
Ac ₃ (° C.) = 912.0-230.5 × C + 31.6 × Si-20.4 × Mn-39.8 × Cu-18.1 × Ni-14.8 × Cr + 16.8 × Mo. (1)
Ac _{3 (C = 0)} (° C.) = 912.0 + 31.6 × Si−20.4 × Mn−39.8 × Cu−18.1 × Ni−14.8 × Cr + 16.8 × Mo. 2)
However, the element symbol in Formula (1) and Formula (2) is content (mass%) of each element, and is set to 0 when not containing. In mass%, C: 0.10 to 0.45%, Si: 0.05 to 1.00%, Mn: 0.50 to 2.00%, P: 0.020% or less, S: 0.020 %, Al: 0.04% or less, Cr: 0.15 to 0.90%, N: 0.0050% or less, O: 0.0050% or less, and the component composition consisting of the balance Fe and inevitable impurities After heating the steel material having heat, it is hot-rolled, cooled after completion of the hot-rolling, and then subjected to a quenching treatment in which the heating temperature is reheated at Ac ₃ points or more and Ac _{3 (C = 0)} points or less. A method for producing a wear-resistant steel sheet. The Ac ₃ point and Ac _{3 (C = 0)} point are represented by the following formulas (1) and (2), respectively.
Ac ₃ (° C.) = 912.0-230.5 × C + 31.6 × Si-20.4 × Mn-39.8 × Cu-18.1 × Ni-14.8 × Cr + 16.8 × Mo. (1)
Ac _{3 (C = 0)} (° C.) = 912.0 + 31.6 × Si−20.4 × Mn−39.8 × Cu−18.1 × Ni−14.8 × Cr + 16.8 × Mo. 2)
However, the element symbol in Formula (1) and Formula (2) is content (mass%) of each element, and is set to 0 when not containing.   In addition to the above component composition, it is further selected by mass% from Nb: 0.005 to 0.100%, Ti: 0.005 to 0.100%, and B: 0.0001 to 0.0100%. 1 or 2 types or more are contained, The manufacturing method of the wear-resistant steel plate of Claim 7 or 8 characterized by the above-mentioned.   In addition to the above-mentioned component composition, Cu: 0.01 to 1.0%, Ni: 0.01 to 5.0%, Mo: 0.1 to 2.0%, V: 0.0. One or more kinds selected from 01 to 1.00%, W: 0.01 to 1.00%, and Co: 0.01 to 1.00% are contained. The manufacturing method of the abrasion-resistant steel plate in any one of 7-9.   In addition to the above component composition, it is further selected by mass% from Ca: 0.0005 to 0.0100%, Mg: 0.0005 to 0.0100%, REM: 0.0005 to 0.0100%. The method for producing a wear-resistant steel sheet according to any one of claims 7 to 10, further comprising one kind or two or more kinds.