JP2019123945A - Wear resisting steel sheet and production method therefor - Google Patents

Abstract

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

  The present invention relates to a wear-resistant steel plate, and in particular, a wear-resistant steel plate excellent in bending workability, which is suitable for use as a member of an industrial machine and a transportation device used in the fields of construction, civil engineering and mining etc. On the way.

  Heretofore, it has been known that the wear resistance of steel materials is improved by increasing the hardness. For this reason, for example, a steel material which has been subjected to wear due to soil, sand or the like and which is required to have wear resistance, has been subjected to heat treatment such as quenching to increase its hardness.

  For example, in Patent Document 1, C: 0.10 to 0.20%, Si: 0.03 to 0.75%, Mn: 0.4 to 1.5%, N: 0.0025 by weight%. Steel sheet having a composition containing at most 100% Al, 0.001 to 0.080%, or further containing at least one of Cu, Ni, Cr, Mo, and B, and subjected to hot rolling to form a thick steel plate After that, a method of manufacturing a wear-resistant thick steel plate is described in which the steel is directly quenched or after hot rolling and then allowed to cool, and then reheated to the γ region for quenching. According to the technique described in Patent Document 1, it is supposed that a wear-resistant thick steel plate having a hardness of 340 HB or more as quenched and high toughness and having improved welding low temperature cracking properties can be obtained.

Further, 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 balance Fe and unavoidable A steel made of impurities or further containing one or more of Ti, Mo, and V is subjected to hot rolling at a rolling reduction of 15% or more at a temperature of 900 ° C. to Ar ₃ transformation point, and Ar ₃ transformation A method of producing a wear resistant steel characterized by quenching from temperatures above the point is described. According to the technique described in Patent Document 2, it is considered that a high-hardness wear-resistant steel which is advantageous for wear resistance can be easily obtained.

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

For bending workability, for example, in Patent Document 3, C: 0.05 to 0.20%, Mn: 0.50 to 2.5%, Al: 0.02 to 2.00 in weight%. % By 5% to 50% by area fraction in the ferrite-bainite matrix, for example by heating after quenching to a ferrite-austenite two-phase region between Ac ₃ and Ac ₁ after hot rolling and quenching A wear-resistant steel excellent in workability and weldability in which the martensitic structure of the invention is dispersed is described.

  Further, in Patent Document 4, C: 0.1 to 0.35%, Si: 0.05 to 1.0%, Mn: 0.1 to 2.0%, P: 0.02 by weight%. %, S: 0.05% or less, Nb: 0.005 to 0.03% immediately after hot rolling, cooling is temporarily stopped after cooling to the Ms point ± 25 ° C, and then the cooling is interrupted and the Ms point + 50 A process is described for producing wear resistant steels that recuperate above 0 C and then cool to room temperature. According to Patent Document 4, the minimum hardness in the temperature distribution from the surface of the steel sheet 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 can be obtained. There is.

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

Japanese Patent Application Laid-Open No. 63-169359 Japanese Patent Application Laid-Open No. 64-31928 Patent No. 2864960 Unexamined-Japanese-Patent No. 2006-104489 Patent No. 4899874

  However, in the techniques described in Patent Documents 3 to 5, the hardness of the base phase (matrix) is low, and there is a problem in the wear resistance.

  Then, this invention solves the problem of such a prior art, and an object of this invention is to provide the wear-resistant steel plate which combined bending workability and abrasion resistance, and its manufacturing method.

  MEANS TO SOLVE THE PROBLEM The present inventors repeated earnest examination about various factors which affect the bending workability of a wear-resistant steel plate, in order to achieve the above-mentioned objective. As a result, it was found that the hardness and ductility of the surface layer greatly contribute to the bending workability of the wear resistant steel plate, and the structure of the steel plate surface is made ferrite and the structure inside the steel plate is made martensite. It has been found that bending workability is improved as long as the hardness of the base phase (matrix) which largely affects the hardness of the matrix is not reduced.

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

0.27% C-0.35% Si-0.75% Mn-0.005% P-0.002% S-0.015% Ti-0.03% Al-0.38% by mass After heating at 1150 ° C., a steel material (slab) having a composition containing Cr-0.20 Mo was hot-rolled to a hot-rolled sheet having a thickness of 12 mm. After hot rolling, air cooling was performed, and after reheating at a heating temperature of Ac ₃ point or more shown by the following (1) formula, a quenching treatment was performed to water 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 decarburize C on the surface of the steel sheet using slab heating in order to make the structure of the surface of the steel sheet ferrite and to make the structure inside the steel sheet martensite, and then, in the quenching process, C Ac ₃ point amount is zero, i.e. by performing the hardening process was reheated Ac 3 _{(C = 0)} point below the temperature range, the structure of the steel sheet surface and ferrite, the steel plate inner tissues martensite I thought that I could control it. Then, regarding the reheating temperature, the heat treated material reheated at the Ac _{3 (C = 0)} point or less and the heat treated material reheated above the Ac _{3 (C = 0)} point were respectively studied.

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

  In addition, a bending test piece (width 150 mm × 300 mm length) is taken from the obtained steel plate, and bending angle: bending to 180 ° according to the provisions of JIS Z 2248, bending radius R without occurrence of cracking The limit bending radius R / t was determined by expressing mm) as a ratio to the plate thickness t (mm).

  In addition, the wear resistance of the steel plate 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 in order to remove the influence of surface scale, the portion from 1 mm from the surface of the steel plate was ground away, and the hardness of the steel surface after grinding was measured. . The measurement conformed to JIS Z 2243 (1998). In addition, in the case of a measurement, the tungsten hard ball of diameter 10mm was used, and the load was 3000 kgf.

FIG. 1 (a) is a microphotograph of a cross section perpendicular to the rolling direction of a steel sheet reheated and hardened above the Ac _{3 (C = 0)} point. Moreover, FIG.1 (b) is a microphotograph of the cross section perpendicular | vertical to the rolling direction of the steel plate reheated and hardened below Ac3 _{(C = 0)} point. From the results in 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 equal to or lower than the Ac _{3 (C = 0)} point, it can be seen that ferrite is present on the surface of the steel sheet and martensite is present inside the steel sheet.

  FIG. 2 is a view showing the relationship between the thickness of ferrite on the surface of the steel plate and the limit bending radius, and FIG. 3 is a view showing the relationship between the thickness of ferrite on the surface of the steel plate and the surface hardness. When ferrite having a thickness of 0.03 mm or more and less than 1 mm was provided on the surface of the steel sheet, it was found that the limit bending radius was small, the bending workability was improved, and the hardness was maintained. On the other hand, when ferrite having a thickness of 1 mm or more was provided on the surface of the steel sheet, it was found that although the critical bending radius is small and the bending workability is improved, the hardness is lowered. In addition, it was found that although the hardness was maintained when the steel sheet surface did not have ferrite (0 mm), the critical bending radius was large and the formability was inferior.

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

The present invention has been completed based on such findings, with 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 to 2.00%, N: 0.010% or less, O: 0.010% or less, and the balance from Fe and unavoidable impurities A wear resistant steel plate characterized by having ferrite having a thickness of 0.03 mm or more and less than 1 mm on the surface of the steel plate and having a volume ratio of martensite at a position of 1 mm from the surface of the steel plate .
[2] 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, and the balance from Fe and unavoidable impurities A wear resistant steel plate characterized by having ferrite having a thickness of 0.03 mm or more and less than 1 mm on the surface of the steel plate and having a volume ratio of martensite at a position of 1 mm from the surface of the steel plate .
[3] In addition to the above component compositions, Nb: 0.005 to 0.100%, Ti: 0.005 to 0.100%, B: 0.0001 to 0.0100% by mass% The wear-resistant steel plate as described in [1] or [2], which contains one or more kinds selected from
[4] In addition to the above-mentioned component composition, furthermore, in mass%, Cu: 0.01 to 1.0%, Ni: 0.01 to 5.0%, Mo: 0.1 to 2.0%, V Characterized in that it contains one or more selected from 0.01 to 1.00%, W: 0.01 to 1.00%, and Co: 0.01 to 1.00%. The wear-resistant steel plate according to any one of [1] to [3].
[5] In addition to the above-mentioned component composition, further, by mass%, Ca: 0.0005 to 0.0100%, Mg: 0.0005 to 0.0100%, REM: 0.0005 to 0.0100% The wear resistant steel plate according to any one of [1] to [4], which contains one or more selected from the group consisting of
[6] The inclusions and precipitates having an average particle size of 500 nm or more at a position 1 mm from the surface have a density of 3.0 particles / mm ² or less [1] to [5] Wear-resistant steel sheet as described.
[7] 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 is Fe and inevitable impurities After heating the steel material having the component composition, it is hot-rolled, cooled after the hot-rolling is finished, and then, the hardening treatment is performed to reheat the heating temperature to Ac ₃ point or more and Ac _{3 (C = 0)} point or less A method of manufacturing a wear-resistant steel plate characterized by carrying out. Incidentally, Ac ₃ point and _{Ac 3 (C = 0)} point is represented by the following formulas (1) and (2).
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 x Si-20.4 x Mn-39.8 x Cu-18.1 x Ni-14.8 x Cr + 16.8 x Mo ... ( 2)
However, the element symbol in Formula (1) and Formula (2) is content (mass%) of each element, and when not containing, it is set as 0.
[8] 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, and the balance from Fe and unavoidable impurities after heating a steel material having a chemical composition comprising, hot rolling, the hot rolled completion after cooling, then, the heating temperature is Ac ₃ point or more Ac 3 _{(C = 0)} quenching the reheated below points A method of manufacturing a wear-resistant steel plate characterized in that Incidentally, Ac ₃ point and _{Ac 3 (C = 0)} point is represented by the following formulas (1) and (2).
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 x Si-20.4 x Mn-39.8 x Cu-18.1 x Ni-14.8 x Cr + 16.8 x Mo ... ( 2)
However, the element symbol in Formula (1) and Formula (2) is content (mass%) of each element, and when not containing, it is set as 0.
[9] In addition to the above component compositions, Nb: 0.005 to 0.100%, Ti: 0.005 to 0.100%, B: 0.0001 to 0.0100% by mass% The method for producing a wear-resistant steel sheet according to [7] or [8], comprising one or more selected from the group consisting of
[10] In addition to the component composition, furthermore, by mass%, Cu: 0.01 to 1.0%, Ni: 0.01 to 5.0%, Mo: 0.1 to 2.0%, V Characterized in that it contains one or more selected from 0.01 to 1.00%, W: 0.01 to 1.00%, and Co: 0.01 to 1.00%. The manufacturing method of the wear-resistant steel plate in any one of [7]-[9].
[11] In addition to the above-mentioned component composition, further, by mass%, Ca: 0.0005 to 0.0100%, Mg: 0.0005 to 0.0100%, REM: 0.0005 to 0.0100% The manufacturing method of the wear-resistant steel plate in any one of [7]-[10] characterized by containing 1 type (s) or 2 or more types selected from.

  According to the present invention, a wear-resistant steel plate having both bending workability and wear resistance can be easily manufactured, and the industrially remarkable effect can be obtained.

FIG. 1 is a view showing a microphotograph of a cross section perpendicular to a rolling direction of a wear resistant steel plate according to an embodiment of the present invention, wherein (a) is a microphotograph when there is no ferrite on the steel sheet surface, (b) Is a figure which shows the microphotograph in case a ferrite exists on the steel plate surface. FIG. 2 is a graph showing the relationship between the thickness of ferrite on the surface of the steel plate and the limit bending radius. FIG. 3 is a graph showing the relationship between the thickness and hardness of ferrite on the surface of a steel sheet.

  The wear resistant steel plate of the present invention is, by 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 to 2.00%, N: 0.010% or less, O: 0.010% or less, balance Fe And a component composition consisting of unavoidable impurities.

  More preferably, the wear-resistant steel plate of the present invention is, by mass%, C: 0.10 to 0.45%, Si: 0.05 to 1.00%, Mn: 0.50 to 2.00%, P 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 It has a component composition including the balance Fe and the inevitable impurities.

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

C: 0.10 to 0.45%
C is an effective element that increases matrix phase (matrix) hardness and improves abrasion resistance. In order to acquire such an effect, 0.10% or more needs to be contained. On the other hand, if the content is more than 0.45%, the hardness of the base phase (matrix) excessively increases, and the bending workability decreases. For this reason, C is limited to the range of 0.10 to 0.45%. In addition, Preferably it is 0.13 to 0.42%.

Si: 0.05 to 1.00%
Si is an element that acts as a deoxidizing agent and causes solid solution in steel to increase matrix hardness by solid solution strengthening. In order to acquire such an effect, 0.05% or more needs to be contained. On the other hand, when the content exceeds 1.00%, the ductility and the toughness are lowered, the amount of inclusions is further increased, and the bending workability is lowered. For this reason, Si is limited to a range of 0.05 to 1.00%. In addition, Preferably it is 0.05-0.40%.

Mn: 0.10 to 2.00%
Mn is an effective element that increases matrix phase (matrix) hardness and improves abrasion resistance. In order to acquire such an effect, 0.10% or more needs to be contained. On the other hand, the content exceeding 2.00% reduces the weldability. For this reason, Mn is limited to the range of 0.10 to 2.00%. In addition, preferably it is 0.50 to 2.00%, more preferably 0.60 to 1.80%, still more preferably 0.70 to 1.60%, still more preferably 0.80 to 1.40% is there.

P: 0.020% or less P is an element that adversely affects, for example, segregating at grain boundaries to reduce the toughness of the base material and the weld zone, and as an unavoidable impurity, it is preferable to reduce as much as possible in the present invention It is acceptable if it is 0.020% or less. For this reason, P is limited to 0.020 or less. In addition, it is preferable to make it 0.001% or more, since excessive reduction causes a steep rise in refining costs.

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

Al: 0.050% or less Al is an element that acts as a deoxidizing agent and has the function of refining the crystal grains, and in order to obtain such an effect, it is necessary to contain 0.01% or more. desirable. On the other hand, if the content is more than 0.050%, oxide inclusions increase, the cleanliness decreases, the surface wrinkles frequently occur, the surface property decreases, and the bending workability decreases. Therefore, Al is limited to 0.050% or less. In addition, it is preferably 0.04% or less, more preferably 0.03% or less, and still more preferably 0.02% or less.

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

  The components mentioned above 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%, and B: 0.0001 to 0.0100 as selective elements. 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 If necessary, select one or more selected from 0005 to 0.0100%, Mg: 0.0005 to 0.0100%, and REM: 0.0005 to 0.0100%. , May be contained.

  More preferably, as a selection element, Nb: 0.005 to 0.020%, Ti: 0.005 to 0.017%, B: 0.0001 to 0.0020%, one or two selected from Or more, 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 and contained as necessary.

Nb: 0.005 to 0.100%, Ti: 0.005 to 0.100%, B: 0.0001 to 0.0100% One or more selected from Nb, Ti, and B All are elements effective in increasing matrix phase (matrix) hardness and improving abrasion resistance, and can be selected and contained as necessary, as necessary.

  Nb is an element that increases the base phase (matrix) hardness and contributes to the improvement of the wear resistance, and in order to obtain such an effect, the content needs to be 0.005% or more. On the other hand, if the content is more than 0.100%, a large amount of NbC precipitates and the bending workability is reduced. From such a thing, when it contains, it is preferable to limit Nb to 0.005 to 0.100% of range. In addition, Preferably it is 0.005 to 0.020%, More preferably, it is 0.008 to 0.016%, More preferably, it is 0.009 to 0.014%.

  Ti has a strong tendency to form a nitride and fixes N to reduce solid solution N, thereby improving the toughness of the base material and the weld. When B is added, N is fixed to suppress precipitation of BN, promote the hardenability improvement effect of B, improve hardenability, and contribute 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 reduced. For this reason, when it contains, it is preferable to make Ti into 0.005 to 0.100%. More preferably, it is 0.005 to 0.017%, further preferably 0.007 to 0.015%, and still more preferably 0.009 to 0.013%.

  B is an element which remarkably improves the hardenability even with a very small amount of addition, promotes the formation of martensite, and contributes to the improvement of the wear resistance. In order to obtain such an effect, it is necessary to contain 0.0001% or more. On the other hand, the content exceeding 0.0100% reduces the weldability. For this reason, when it contains, it is preferable to limit B to the range of 0.0001 to 0.0100%. In addition, More preferably, it is 0.0001-0.0020%, More preferably, it is 0.0005-0.0015%. Still more preferably, it is 0.0007 to 0.0013%.

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 One or more selected from 1.00% and Co: 0.01 to 1.00% Cu, Ni, Mo, V, W, and Co all improve the hardenability, and the inside of the steel sheet Add as needed to obtain the hardness of In order to obtain such effects, 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, It is preferable to contain Co: 0.01% or more. On the other hand, Cu: 1.0%, Ni: 5.0%, Mo: 2.0%, V: 1.00%, W: 1.00%, Co: 1.00%, when contained in excess of This leads to deterioration of weldability or increase in alloy cost. From such a thing, when it contains, Cu: 0.01-1.0%, Ni: 0.01-5.0%, Mo: 0.1-2.0%, 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 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: 0.01 to 0.05%.

Ca: 0.0005 to 0.0100%, Mg: 0.0005 to 0.0100%, REM: one or more selected from 0.0005 to 0.0100% Ca, Mg, REM Both are elements that combine with S and suppress the formation of MnS and the like elongated in the rolling direction to control the morphology of sulfide inclusions so as to exhibit a spherical shape and contribute to the improvement of toughness such as welds, As necessary, one or more can be selected and contained. In order to obtain such an effect, it is preferable to contain Ca: 0.0005% or more, Mg: 0.0005% or more, and REM: 0.0005% or more. On the other hand, if the content is more than Ca: 0.0100%, Mg: 0.0100%, REM: 0.0100%, the cleanliness of the steel decreases, the surface wrinkles frequently occur, and the surface properties decrease, and bending occurs. Processability is reduced. From such a thing, when it contains, 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, it is Ca: 0.0005 to 0.0040%, Mg: 0.0005 to 0.0050%, and REM: 0.0005 to 0.0080%.

  The balance other than the above components consists of Fe and unavoidable impurities. As unavoidable impurities, O: 0.010% or less and N: 0.010% or less are acceptable. When O: more than 0.010% or N: more than 0.010%, the generation of a large amount of inclusions makes it easy to generate cracks starting from the inclusions. For this reason, it limits to O: 0.010% or less and N: 0.010% or less. In addition, Preferably it is O: 0.0050% or less, N: 0.0050% or less. More preferably, O: 0.0040% or less and N: 0.0040% or less.

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

Thickness of Ferrite on Surface of Steel Sheet: 0.03 mm or More and Less than 1 mm By making the surface of the steel sheet ferrite, bending workability is improved. 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 reduced, so that the wear resistance is deteriorated. Therefore, the thickness of the ferrite is less than 1 mm. In addition, More preferably, they are 0.05 mm or more and less than 0.5 mm.

The volume fraction of martensite at a position of 1 mm from the steel sheet surface: 90% or more The hardness of the base structure of the steel sheet decreases if the volume fraction of martensite at a position of 1 mm from the steel sheet surface is less than 90%. Is degraded. Therefore, the volume ratio of martensite at a position of 1 mm from the surface of the steel sheet is 90% or more. The structure of the remainder other than martensite is not particularly limited, but ferrite, pearlite, austenite, and bainite may be present. On the other hand, since the higher the volume fraction of martensite, the better, the upper limit of the volume fraction of martensite is not particularly limited, and may be 100%. Further, in the present invention, if the volume ratio of martensite at a position of 1 mm from the steel plate surface is 90% or more, this means that the volume ratio of martensite is 90% or more also for the inside of the steel plate of 1 mm or later on the steel plate surface. Do.

Furthermore, in the steel having the above composition and the above structure, 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.

Suppression of cracks originating from inclusions or precipitates by 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 being 3.0 pieces / mm ² or less The bending processability is improved. The lower limit is not particularly limited because the density of inclusions and precipitates is preferably as low as possible, but excessive reduction causes a rise in the refining cost, and therefore, it is preferable to be 0.1 piece / mm ² or more.

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

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

Method of producing a steel material The method of producing a steel material is not particularly limited, but molten steel having the above-described component composition is melted by a known melting method such as a converter, and known methods such as a continuous casting method It is preferable to use a steel material such as a slab of a predetermined size by a casting method. In addition, there is no problem at all also as steel materials, such as a slab of a predetermined dimension, by the ingot-decomposition rolling method.

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

Heating temperature Ac ₃ point or more _{Ac 3 (C = 0)} point following reheating quenching treatment further After cooling after completion of hot rolling, the following formula (1) and (2) shown are Ac ₃ point or more by the formula A hardening treatment is performed to reheat the heating temperature to a temperature equal to or lower than Ac _{3 (C = 0)} . This is to obtain a martensitic structure by quenching from the austenitic state. If the hardening is less than Ac ₃ point, hardening is not sufficient, the hardness is reduced, and a microstructure with high wear resistance can not be obtained. Further, when the heating temperature exceeds the Ac _{3 (C = 0)} point, the surface of the steel sheet has a martensitic structure, and a desired ferrite structure can not 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 x Si-20.4 x Mn-39.8 x Cu-18.1 x Ni-14.8 x Cr + 16.8 x Mo ... ( 2)
However, the element symbol in Formula (1) and Formula (2) is content (mass%) of each element, and when not containing, it is set as 0.

  The cooling rate of the quenching treatment is not particularly limited as long as it is a cooling rate at which a martensitic structure is formed. Further, the cooling stop temperature is preferably water-cooled to a temperature not higher than the Mf point, preferably not higher than 200 ° C.

The molten steel of the composition shown in Table 1 was melted and used as a steel material (slab). These steel materials (slabs) were subjected to heating and hot rolling under the conditions shown in Table 2 to obtain hot-rolled sheets having the thicknesses shown in Table 2. Thereafter, it was allowed to cool, reheated, and then subjected to quenching and reheat hardening treatment. Mf and Ar ₃ in Table 1 were determined 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 measurement of the thickness of the ferrite on the surface of a steel plate, the volume fraction measurement of martensite, the hardness test of a surface layer part, and the bending test were implemented, respectively. The test method is as follows.
(1) Measurement of Thickness of Ferrite A sample was taken from each steel plate such that a cross section perpendicular to the rolling direction was an observation surface. The sample was mirror-polished and further subjected to nital corrosion, and then three-view photography was performed at × 400 magnification using an optical microscope. The thickness of an arbitrary five ferrites in one field of view was measured to obtain an average value, and the average value of three fields of view was used as the ferrite thickness.
(2) Volume fraction measurement of martensite A sample was taken from each steel plate so that a position of 1 mm from the steel plate surface was an observation position. The surface of the sample was mirror-polished and further subjected to nital corrosion, and then an area of 10 mm × 10 mm was photographed using a scanning electron microscope (SEM). The photographed image was analyzed using an image analysis device to determine the area fraction of martensite. The area fraction of martensite was determined for any three images, and the average value was taken as the volume fraction of martensite in the present invention.
(3) Measurement of Inclusions and Precipitates Samples were taken from each steel plate such that the position 1 mm from the surface of the steel plate was the observation position. The surface of the sample was mirror-polished and an area of 10 mm × 10 mm was photographed using an SEM. The image taken was analyzed using an image analyzer to determine the particle size and number of inclusions and precipitates, and the number of inclusions and precipitates having an average particle size of 500 nm or more was measured to determine the density . The densities of inclusions and precipitates were determined for any three images, 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 plate is mainly determined by the hardness of the surface layer. Therefore, a test piece for hardness measurement was taken from the obtained steel plate, and the hardness at a position of 1 mm in the thickness direction from the surface was measured in accordance with JIS Z 2243 (1998). In order to remove the influence of surface scale and decarburized layer, 1 mm was ground away from the surface, and the surface hardness was measured on the surface of 1 mm from the surface. In addition, in the case of a measurement, the tungsten hard ball of diameter 10mm was used, and the load was 3000 kgf. The hardness passed 360 or more.
(5) Bending test A bending test piece (width 150 mm × 300 mm length) is taken from the obtained steel plate, and bending angle: bending bending to 180 ° according to the provisions of JIS Z 2248, bending radius without cracking. The limit bending radius R / t which represented R (mm) by the ratio with respect to board thickness t (mm) was calculated | required. R / t made 1.5 or less pass.

  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, in the comparative example, the hardness is equal and the bending radius is large, or the hardness is low and the bending radius is small, and the bending workability or the wear resistance is inferior.

The molten steel of the composition shown in Table 3 was melted and used as a steel material (slab). These steel materials (slabs) were subjected to heating and hot rolling under the conditions shown in Table 4 to obtain hot-rolled sheets having the thicknesses shown in Table 4. Thereafter, it was allowed to cool, reheated, and then subjected to quenching and reheat hardening treatment. Ms, Mf and Ar ₃ in Table 3 were determined 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 measurement of the thickness of the ferrite on the surface of a steel plate, the volume fraction measurement of martensite, the hardness test of a surface layer part, and the bending test were implemented, respectively. The test method is as follows.
(1) Measurement of Thickness of Ferrite A sample was taken from each steel plate such that a cross section perpendicular to the rolling direction was an observation surface. The sample was mirror-polished and further subjected to nital corrosion, and then three-view photography was performed at × 400 magnification using an optical microscope. The thickness of an arbitrary five ferrites in one field of view was measured to obtain an average value, and the average value of three fields of view was used as the ferrite thickness.
(2) Volume fraction measurement of martensite A sample was taken from each steel plate so that a position of 1 mm from the steel plate surface was an observation position. The surface of the sample was mirror-polished and further subjected to nital corrosion, and then an area of 10 mm × 10 mm was photographed using a scanning electron microscope (SEM). The photographed image was analyzed using an image analysis device to determine the area fraction of martensite. The area fraction of martensite was determined for any three images, and the average value was taken as the volume fraction of martensite in the present invention.
(3) Measurement of Inclusions and Precipitates Samples were taken from each steel plate such that the position 1 mm from the surface of the steel plate was the observation position. The surface of the sample was mirror-polished and an area of 10 mm × 10 mm was photographed using an SEM. The image taken was analyzed using an image analyzer to determine the particle size and number of inclusions and precipitates, and the number of inclusions and precipitates having an average particle size of 500 nm or more was measured to determine the density . The densities of inclusions and precipitates were determined for any three images, 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 plate is mainly determined by the hardness of the surface layer. Therefore, a test piece for hardness measurement was taken from the obtained steel plate, and the hardness at a position of 1 mm in the thickness direction from the surface was measured in accordance with JIS Z 2243 (1998). In order to remove the influence of surface scale and decarburized layer, 1 mm was ground away from the surface, and the surface hardness was measured on the surface of 1 mm from the surface. In addition, in the case of a measurement, the tungsten hard ball of diameter 10mm was used, and the load was 3000 kgf. The hardness passed 490 or more.
(5) Bending test A bending test piece (width 150 mm × 300 mm length) is taken from the obtained steel plate, and bending angle: bending bending to 180 ° according to the provisions of JIS Z 2248, bending radius without cracking. The limit bending radius R / t which represented R (mm) by the ratio with respect to board thickness t (mm) was calculated | required. R / t passed 2.5 or less.

  The obtained results are shown in Table 4.

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

The molten steel of the composition shown in Table 5 was melted and used as a steel material (slab). These steel materials (slabs) were subjected to heating and hot rolling under the conditions shown in Table 6 to obtain hot-rolled sheets having the thicknesses shown in Table 6. Thereafter, it was allowed to cool, reheated, and then subjected to quenching and reheat hardening treatment. Ms, Mf and Ar ₃ in Table 5 were determined 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 measurement of the thickness of the ferrite on the surface of a steel plate, the volume fraction measurement of martensite, the hardness test of a surface layer part, and the bending test were implemented, respectively. The test method is as follows.
(1) Measurement of Thickness of Ferrite A sample was taken from each steel plate such that a cross section perpendicular to the rolling direction was an observation surface. The sample was mirror-polished and further subjected to nital corrosion, and then three-view photography was performed at × 400 magnification using an optical microscope. The thickness of an arbitrary five ferrites in one field of view was measured to obtain an average value, and the average value of three fields of view was used as the ferrite thickness.
(2) Volume fraction measurement of martensite A sample was taken from each steel plate so that a position of 1 mm from the steel plate surface was an observation position. The surface of the sample was mirror-polished and further subjected to nital corrosion, and then an area of 10 mm × 10 mm was photographed using a scanning electron microscope (SEM). The photographed image was analyzed using an image analysis device to determine the area fraction of martensite. The area fraction of martensite was determined for any three images, and the average value was taken as the volume fraction of martensite in the present invention.
(3) Measurement of Inclusions and Precipitates Samples were taken from each steel plate such that the position 1 mm from the surface of the steel plate was the observation position. The surface of the sample was mirror-polished and an area of 10 mm × 10 mm was photographed using an SEM. The image taken was analyzed using an image analyzer to determine the particle size and number of inclusions and precipitates, and the number of inclusions and precipitates having an average particle size of 500 nm or more was measured to determine the density . The densities of inclusions and precipitates were determined for any three images, 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 plate is mainly determined by the hardness of the surface layer. Therefore, a test piece for hardness measurement was taken from the obtained steel plate, and the hardness at a position of 1 mm in the thickness direction from the surface was measured in accordance with JIS Z 2243 (1998). In order to remove the influence of surface scale and decarburized layer, 1 mm was ground away from the surface, and the surface hardness was measured on the surface of 1 mm from the surface. In addition, in the case of a measurement, the tungsten hard ball of diameter 10mm was used, and the load was 3000 kgf. The hardness passed 560 or more.
(5) Bending test A bending test piece (width 150 mm × 300 mm length) is taken from the obtained steel plate, and bending angle: bending bending to 180 ° according to the provisions of JIS Z 2248, bending radius without cracking. The limit bending radius R / t which represented R (mm) by the ratio with respect to board thickness t (mm) was calculated | required. R / t made 3.5 or less pass.

  The obtained results are shown in Table 6.

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

Claims (9)

  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 by mass% %, Al: 0.050% or less, Cr: 0.37 to 2.00%, N: 0.010% or less, O: 0.010% or less, and further, in mass%, Nb: 0. Containing one or more selected from 005 to 0.019%, Ti: 0.005 to 0.100%, B: 0.0001 to 0.0100%, balance Fe and unavoidable impurities Abrasive resistance characterized in that it has a component composition comprising: ferrite having a thickness of at least 0.03 mm and less than 1 mm on the surface of the steel plate, and a volume fraction of martensite at a position of 1 mm from the surface of the steel plate steel sheet.   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 by mass% %, Al: 0.04% or less, Cr: 0.37 to 2.00%, N: 0.0050% or less, O: 0.0050% or less, and further, by mass%, Nb: 0. Containing one or more selected from 005 to 0.019%, Ti: 0.005 to 0.100%, B: 0.0001 to 0.0100%, balance Fe and unavoidable impurities Abrasive resistance characterized in that it has a component composition comprising: ferrite having a thickness of at least 0.03 mm and less than 1 mm on the surface of the steel plate, and a volume fraction of martensite at a position of 1 mm from the surface of the steel plate steel sheet.   In addition to the above component compositions, furthermore, in mass%, Cu: 0.01 to 1.0%, Ni: 0.01 to 5.0%, Mo: 0.1 to 2.0%, V: 0. One or two or more selected from 01 to 1.00%, W: 0.01 to 1.00%, and Co: 0.01 to 1.00%. The wear-resistant steel plate as described in 1 or 2.   In addition to the above-mentioned component composition, further, in mass%, Ca: 0.0005 to 0.0100%, Mg: 0.0005 to 0.0100%, and REM: 0.0005 to 0.0100% are selected. The wear resistant steel sheet according to any one of claims 1 to 3, which contains one or more kinds. The wear-resistant steel plate according to any one of claims 1 to 4, 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. . 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 by mass% % Or less, Al: 0.050% or less, Cr: 0.37 to 2.00%, N: 0.010% or less, O: 0.010%, further, by mass%, Nb: 0.005 1 0.019%, Ti: 0.005 to 0.100%, B: one or more selected from 0.0001 to 0.0100%, and the balance from Fe and unavoidable impurities The steel material having the following composition is heated and then hot rolled, and cooled after the hot rolling is finished, and then the heating temperature is Ac ₃ or more and Ac _{3 (C = 0)} or less and the holding time is 10 minutes or more Is characterized by performing quenching treatment to reheat by Has the full thickness of the ferrite, the manufacturing method of the wear-resistant steel volume fraction of martensite is 90% or more at a position of 1mm from the surface of the steel sheet. Incidentally, Ac ₃ point and _{Ac 3 (C = 0)} point is represented by the following formulas (1) and (2).
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 x Si-20.4 x Mn-39.8 x Cu-18.1 x Ni-14.8 x Cr + 16.8 x Mo ... ( 2)
However, the element symbol in Formula (1) and Formula (2) is content (mass%) of each element, and when not containing, it is set as 0. 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 by mass% %, Al: 0.04% or less, Cr: 0.37 to 2.00%, N: 0.0050% or less, O: 0.0050% or less, and further, by mass%, Nb: 0. Containing one or more selected from 005 to 0.019%, Ti: 0.005 to 0.100%, B: 0.0001 to 0.0100%, balance Fe and unavoidable impurities after heating a steel material having a chemical composition consisting of, hot rolling, the hot rolled completion after cooling, then, the heating temperature is Ac ₃ point or more Ac 3 _{(C = 0)} point below and holding time 10min It is characterized by performing hardening treatment which reheats by the above, and is 0.03 mm or more on the steel plate surface Has a thickness of ferrite of less than mm, the manufacturing method of the wear-resistant steel volume fraction of martensite is 90% or more at a position of 1mm from the surface of the steel sheet. Incidentally, Ac ₃ point and _{Ac 3 (C = 0)} point is represented by the following formulas (1) and (2).
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 x Si-20.4 x Mn-39.8 x Cu-18.1 x Ni-14.8 x Cr + 16.8 x Mo ... ( 2)
However, the element symbol in Formula (1) and Formula (2) is content (mass%) of each element, and when not containing, it is set as 0.   In addition to the above component compositions, furthermore, in mass%, Cu: 0.01 to 1.0%, Ni: 0.01 to 5.0%, Mo: 0.1 to 2.0%, V: 0. One or two or more selected from 01 to 1.00%, W: 0.01 to 1.00%, and Co: 0.01 to 1.00%. The manufacturing method of the wear-resistant steel plate as described in 6 or 7.   In addition to the above-mentioned component composition, further, in mass%, Ca: 0.0005 to 0.0100%, Mg: 0.0005 to 0.0100%, and REM: 0.0005 to 0.0100% are selected. The method for producing a wear resistant steel sheet according to any one of claims 6 to 8, characterized in that it contains one or more kinds.