JP2007092155A - Wear resistant steel sheet having excellent low temperature toughness and its production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wear resistant steel sheet combining wear resistance and low temperature toughness, and to provide its production method. <P>SOLUTION: The wear resistant steel sheet has a composition comprising, by mass, 0.10 to 0.30% C, 0.05 to 1.0% Si, 0.1 to 2.0% Mn, ≤0.020% P, ≤0.005% S, 0.10 to 1.40% W and 0.0003 to 0.0020% B, and, further comprising 0.005 to 0.1% Ti and/or 0.035 to 0.1% Al, and the balance Fe with inevitable impurities. Thus, the steel sheet has high hardness in the surface layer part, and has excellent wear resistance and excellent low temperature toughness as well. Instead of single incorporation of W, Mo and W may be compositely comprised so as to satisfy 2Mo+W: 0.10 to 1.40%. The steel sheet may further comprise Nb and/or one or two groups selected from a group (a): one or more selected from Cu, Ni, Cr and V, and a group (b): one or more selected from Ca and rare earth metals. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a wear-resistant steel plate suitable for members of industrial machines, transportation equipment and the like, and a method for producing the same, and more particularly to improvement of low-temperature toughness.

Industrial machinery and transport equipment used in the fields of construction, civil engineering, mining, etc. (for example, power shovels, bulldozers, hoppers, buckets, etc.) generally have excellent wear resistance because the life is determined by the amount of wear of the members. Steel material is used.
In order to improve the wear resistance, it is necessary to make the steel surface hardened and harden the surface layer portion. In general, the hardness of a steel material after quenching can be increased by increasing the amount of C in the steel. However, when the amount of C is increased to increase the hardness, the material becomes brittle and the low-temperature toughness decreases. When the working environment is, for example, a low temperature range of 0 ° C. or less, even if the wear resistance is excellent, if the low temperature toughness is low, brittle fracture occurs and seriously hinders the work. For this reason, there is a demand for wear-resistant steel sheets that have wear resistance and are excellent in low-temperature toughness.

In response to such a requirement, for example, Patent Document 1 includes C: 0.30 to 0.50%, contains an appropriate amount of Si, Mn, Al, N, and further an appropriate amount of Ti, Nb, B, and further Cr. : Hot rolled steel slab containing 0.10 to 0.50%, Mo: 0.05 to 1.00%, then quenched from temperature above Ar ₃ transformation point, followed by tempering to obtain high strength wear resistant steel, low temperature A method for producing a high hardness wear resistant steel having excellent toughness has been proposed. In the technique described in Patent Document 1, hardenability is improved by adding a large amount of Cr and Mo, grain boundaries are strengthened and low temperature toughness is improved, and low temperature toughness is further improved by tempering. It is said.

  Patent Document 2 includes C: 0.18 to 0.25%, Si: 0.10 to 0.30%, Mn: 0.03 to 0.10%, contains appropriate amounts of Nb, Al, N, and B, and Cr: 1.00 to A high tough wear-resistant steel sheet excellent in toughness and delayed fracture resistance after water quenching and tempering treatment containing 2.00%, Mo: more than 0.50 to 0.80% has been proposed. In the technology described in Patent Document 2, by suppressing the Mn content and containing a large amount of Cr and Mo, the hardenability is improved, the predetermined hardness can be secured, and the toughness and delayed fracture resistance are improved. However, low temperature toughness is improved by tempering.

  Patent Document 3 includes C: 0.30 to 0.45%, Si: 0.10 to 0.50%, Mn: 0.30 to 1.20%, contains appropriate amounts of Nb and / or Ti, Al, and B, and Cr: High tough wear-resistant steels containing 0.50 to 1.40% and Mo: 0.15 to 0.55% have been proposed. According to the technique described in Patent Document 3, it is said that by containing a large amount of Cr and Mo, the hardenability is improved and the grain boundaries are strengthened to improve the low temperature toughness.

Patent Document 4 includes C: 0.05 to 0.40%, Cr: 0.1 to 2.0%, and further includes appropriate amounts of Si, Mn, Ti, B, Al, and N, or Cu, Ni, Mo, and V. the composition of the steel containing, after hot rolling at 900 ° C. or less in austenite non-recrystallization region of cumulative rolling reduction of 50% or more, and quenching from _three or more Ar, a method of manufacturing wear-resistant steel that returns thereafter sintered Has been proposed. Thereby, the structure in which the austenite grains are expanded is directly quenched and tempered to obtain a tempered martensite structure in which the prior austenite grains are expanded, whereby the low temperature toughness is remarkably improved.
Japanese Patent Laid-Open No. 08-041535 Japanese Patent Laid-Open No. 02-179842 JP-A 61-166554 JP 2002-20837 A

However, the techniques described in Patent Document 1, Patent Document 2, and Patent Document 3 that require a large amount of alloy elements have a problem of causing a rise in manufacturing costs. Further, the techniques described in Patent Documents 1 and 2 However, since tempering is an indispensable requirement, the hardness, which is the most important characteristic of wear-resistant steel, is reduced, so that there is a problem that wear resistance is reduced.
Moreover, in the technique described in Patent Document 4, it is necessary to lower the finishing temperature of the hot rolling, so that the deformation resistance of the steel increases and the load on the motor that drives the roll of the rolling mill increases. In addition to the problem of difficulty in manufacturing, strict temperature control is required for stable manufacturing. Therefore, the technique described in Patent Document 4 has a problem that it is not always an easy process in actual operation.

  The present invention has been made in view of the problems of the prior art, and is inexpensive and easy to provide a wear-resistant steel sheet that is inexpensive and has excellent low-temperature toughness, and that is not accompanied by process difficulties. Furthermore, it aims at providing the manufacturing method of an abrasion-resistant steel plate which can manufacture the abrasion-resistant steel plate which has the outstanding low temperature toughness. The “steel having excellent low-temperature toughness” in the present invention has a fracture surface transition temperature vTrs in a Charpy impact test in accordance with the provisions of JIS Z 2242-2005 of 0 ° C. or less, preferably −20 ° C. or less. It shall mean a steel plate. In addition, the “abrasion resistant steel plate” in the present invention refers to a steel plate having a surface layer portion hardness of 300 HB or more. The wear-resistant steel plate referred to in the present invention can be preferably applied to a steel plate having a thickness of 5 to 100 mm, but is not particularly limited thereto.

  In order to achieve the above-mentioned object, the present inventors have conducted extensive research on various factors affecting the low temperature toughness of wear-resistant steel sheets. As a result, by containing trace B as an essential component, and further containing Ti and / or Al, the hardenability is improved and the steel sheet structure can be easily martensitic, and has a high surface hardness. It was found that a wear-resistant steel sheet having both excellent wear resistance and excellent low-temperature toughness can be produced.

However, depending on the quenching conditions, the present inventors may precipitate B as M ₂₃ (CB) ₆ immediately before quenching, which not only loses the effect of improving hardenability, but also significantly lowers the low temperature toughness. I found out that there was. Therefore, as a result of further studies, the present inventors have been able to effectively suppress the precipitation of B by containing an appropriate amount of W or further Mo together with B, and the low temperature toughness of the wear-resistant steel sheet has been dramatically improved. I found it to improve.

First, the experimental results on which the present invention is based will be described.
In mass%, 0.14% C-0.34% Si-1.45% Mn-0.012% P-0.002% S-0.012% Ti-0.0028% Al-0.0012% B as a basic component, W in the range of 0 to 1.05% The steel material (slab) having the composition contained was heated to 1100 ° C. and hot-rolled to obtain a hot-rolled sheet having a sheet thickness of 14 mm and a sheet thickness of 25 mm. The finish rolling temperature was 920 ° C. as the surface temperature. Immediately after hot rolling, the hot-rolled sheet was subjected to a direct quenching treatment in which it was cooled to room temperature. In addition, the cooling start temperature of the direct quenching treatment is, when the plate thickness is 14 mm, the surface temperature is 880 ° C at the tip of the hot-rolled sheet and the surface temperature is 780 ° C at the tail end of the hot-rolled sheet. In the case of 25 mm, the surface temperature was 880 ° C. at the front end of the hot-rolled sheet and the surface temperature was 820 ° C. at the tail end of the hot-rolled sheet. The length of the hot-rolled sheet was 28 m when the plate thickness was 14 mm, and 21 m when the plate thickness was 25 mm.

From the obtained hot-rolled sheet, a V-notch test piece was collected in accordance with JIS Z 2242-2005, a Charpy impact test was conducted at a test temperature of −40 ° C., and absorbed energy vE _-40 (J) Asked. Three tests were performed each, and the arithmetic average value thereof was defined as the absorbed energy vE- _{40 of the} steel sheet.
The obtained results are shown in FIG. 1 and FIG. 2 in relation to vE _-40 (J) and W content. FIG. 1 shows a case where the plate thickness is 14 mm, and FIG. 2 shows a case where the plate thickness is 25 mm. In either case, the content of W is 0.10% by mass or more, and high toughness with a vE- ₄₀ of 27 J or more is obtained at both the front end portion and the tail end portion of the hot-rolled sheet. When it is necessary to further reduce the low-temperature toughness difference between the tip end portion and the tail end portion of the hot-rolled sheet, it is preferable to set W: 0.30% by mass or more from FIGS. In addition, according to examination of the present inventors, it was guessed that the improvement of the low temperature toughness by such W content was based on the precipitation inhibitory effect of B by W content.

The present invention has been completed based on the above-described findings and further studies. That is, the gist of the present invention is as follows.
(1) By mass%, C: 0.10 to 0.30%, Si: 0.05 to 1.0%, Mn: 0.1 to 2.0%, P: 0.020% or less, S: 0.005% or less, W: 0.10 to 1.40%, B: 0.0003 A wear-resistant steel sheet having excellent low-temperature toughness, characterized by containing ~ 0.0020%, further containing Ti: 0.005-0.1% and / or Al: 0.035-0.1%, and having the balance Fe and inevitable impurities .

(2) In (1), instead of W in the above composition, Mo and W are expressed in mass%, and the following formula (1)
0.10 ≦ 2Mo + W ≦ 1.40 ……… (1)
(Where Mo, W: content of each element (mass%))
A wear-resistant steel sheet characterized by having a composition that satisfies the requirements.

(3) In (1) or (2), in addition to the said composition, it is set as the composition which contains Nb: 0.005-0.05% by the mass% further, It is characterized by the above-mentioned.
(4) In any one of (1) to (3), in addition to the above-described composition, the following groups a to b: a group: Cu: 0.1 to 1%, Ni: 0.1 to 2%, Cr : 0.1 to 1%, V: 0.01 to 1% or two or more of
Group b: A wear-resistant steel plate characterized by having a composition containing one or two groups selected from one or two of Ca: 0.0002 to 0.0050% and REM: 0.0002 to 0.0050%.

(5) In any one of (1) to (4), it has a martensite phase of 90% by volume or more in the as-quenched state, or further has a structure in which the average grain size of the prior austenite grains is 30 μm or less. Features a wear-resistant steel plate.
(6) The wear-resistant steel sheet according to any one of (1) to (5), wherein the hardness of the surface layer portion is 300 HBW or more.

  (7) By mass%, C: 0.10 to 0.30%, Si: 0.05 to 1.0%, Mn: 0.1 to 2.0%, P: 0.020% or less, S: 0.005% or less, W: 0.10 to 1.40%, B: 0.0003 A steel material containing ~ 0.0020%, further containing Ti: 0.005-0.1% and / or Al: 0.035-0.1%, and having a composition comprising the balance Fe and unavoidable impurities, is subjected to hot rolling to obtain a steel plate And a method for producing a wear-resistant steel sheet having excellent low temperature toughness, characterized by quenching immediately after completion of the hot rolling.

(8) In (7), in place of W in the composition, Mo and W are expressed in mass%, and the following formula (1)
0.10 ≦ 2Mo + W ≦ 1.40 ……… (1)
(Where Mo, W: content of each element (mass%))
A method for producing a wear-resistant steel sheet, characterized in that the composition is contained so as to satisfy the requirements.

(9) A method for producing a wear-resistant steel sheet according to (7) or (8), wherein the composition further comprises Nb: 0.005 to 0.05% by mass% in addition to the above composition.
(10) In any one of (7) to (9), in addition to the above-mentioned composition, the following groups a to b: a group: Cu: 0.1 to 1%, Ni: 0.1 to 2%, Cr : 0.1 to 1%, V: 0.01 to 1% or two or more of
Group b: Ca: 0.0002 to 0.0050%, REM: 0.0002 to 0.0050% of a wear resistant steel sheet characterized by having a composition containing one or two groups selected from one or two of them Production method.

(11) The method for producing a wear-resistant steel sheet according to any one of (7) to (10), wherein a quenching start temperature of the quenching is not less than an Ar ₃ transformation point.
(12) In any one of (7) to (10), instead of quenching immediately after completion of the hot rolling, it is allowed to cool after completion of the hot rolling, and then reheated and quenched. A method for manufacturing a wear-resistant steel sheet.

  (13) The method for producing a wear-resistant steel sheet according to (12), wherein the reheating temperature is 850 to 950 ° C.

  According to the present invention, a wear-resistant steel sheet having high surface hardness, excellent wear resistance, and excellent low-temperature toughness can be produced inexpensively and easily without accompanying process difficulties, There are remarkable effects in the industry.

First, the reasons for limiting the composition of the steel sheet of the present invention will be described. Hereinafter, the mass% in the composition is simply expressed as%.
C: 0.10 to 0.30%
C is an important element that increases the hardness of the steel sheet by solid solution, ensuring the necessary hardness for wear-resistant steel, 300HBW or more at the surface layer of the steel sheet, and imparting the desired wear resistance to the steel sheet Therefore, the content of 0.10% or more is required in the present invention. On the other hand, when it contains more than 0.30%, weldability, toughness and workability are lowered. For this reason, in this invention, C was limited to the range of 0.10 to 0.30%. In order to secure 360HBW or more in the surface layer part of the steel plate required for parts used in harsh environments such as mines that mine hard ore, C should be 0.13% or more. Moreover, in order to ensure 450HBW or more in the surface layer portion of the steel sheet, it is preferably 0.23% or more.

Si: 0.05-1.0%
Si effectively acts as a deoxidizer in molten steel, and is an effective element for strengthening steel by solid solution strengthening. Such an effect is recognized with a content of 0.05% or more. On the other hand, if the content exceeds 1.0%, problems such as a decrease in toughness and an increase in inclusions occur. For this reason, Si was limited to the range of 0.05 to 1.0%. In addition, from the viewpoint of suppressing generation of surface flaws on the hot-rolled sheet, the content is preferably 0.15 to 0.45%.

Mn: 0.1-2.0%
Mn is an effective element for improving hardenability, and in the present invention, it is necessary to contain 0.1% or more from the viewpoint of ensuring hardenability. On the other hand, if the content exceeds 2.0%, the weldability decreases. For this reason, Mn was limited to the range of 0.1 to 2.0%. From the viewpoint of securing hardenability at low cost, it is preferably 0.50% or more.

P: 0.020% or less When P is contained in a large amount, the low temperature toughness is lowered. Therefore, in the present invention, it is desirable to reduce it as much as possible, but it is acceptable up to 0.020%. For this reason, the upper limit of P was limited to 0.020%.
S: 0.005% or less S mainly forms MnS in steel and exists as inclusions (sulfides), acts as a starting point for fracture occurrence, and lowers low-temperature toughness. For this reason, in the present invention, it is desirable to reduce S as much as possible, but up to 0.005% is acceptable, so the upper limit of S is limited to 0.005%.

One or two selected from Ti: 0.005-0.1% and Al: 0.035-0.1%
Ti and Al both combine with N to form TiN and AlN, and contribute to improving toughness by reducing solid N, which is harmful to toughness, and ensuring solid solution B that is effective in improving hardenability. Have. In the present invention, one or two of Ti and Al are selected and contained. Such an effect becomes remarkable by containing Ti: 0.005% or more and Al: 0.035% or more, respectively. On the other hand, when Ti and Al are contained in excess of 0.1%, low temperature toughness is lowered. For this reason, Ti was limited to 0.005 to 0.1% and Al was limited to 0.035 to 0.1%. Preferably, Ti is 0.005 to 0.03% and Al is 0.035 to 0.06%.

B: 0.0003-0.0020%
B is an effective element that remarkably improves hardenability when contained in a trace amount, and in the present invention, it is necessary to contain 0.0003% or more for improving hardenability. On the other hand, when it contains exceeding 0.0020%, low temperature toughness will fall. For this reason, in this invention, B was limited to 0.0003 to 0.0020% of range. The relationship between the fracture surface transition temperature vTrs and the B content is shown in FIG. From FIG. 3, it can be seen that when the B content exceeds 0.0020%, vTrs increases rapidly and low temperature toughness decreases. This is because when B exceeds 0.0020%, B precipitates as M ₂₃ (CB) ₆ .

W: 0.10 to 1.40%
W is an important element in the present invention in order to improve the low temperature toughness of the steel sheet. In the present invention in which a small amount of B is essential, W is an effective element that suppresses the precipitation of B, and the inclusion of W suppresses the precipitation of B and improves the hardenability, thereby reducing the low temperature toughness. It becomes possible to improve. In order to obtain such an effect, the content of 0.10% or more is required. On the other hand, if W is contained in excess of 1.40%, the weldability is lowered and the manufacturing cost is increased. For this reason, W was limited to 0.10 to 1.40%. In addition, as shown in FIGS. 1 and 2, from the viewpoint of reducing the toughness variation in the longitudinal direction of the steel sheet, it is preferable to contain 0.30% or more.

  Although the above-described components are used as basic components, in the present invention, instead of the above-described inclusion of W alone, a combination of W and Mo may be used. Even if W and Mo are contained in combination, the effect of suppressing the precipitation of B can be expected as in the case of containing W alone. When W and Mo are contained in combination, the contents of Mo and W are preferably adjusted so that 2Mo + W satisfies the range of 0.10 to 1.40% (the expression (1) is satisfied).

0.10 ≦ 2Mo + W ≦ 1.40 ……… (1)
(Where Mo, W: content of each element (mass%))
If 2Mo + W is less than 0.10%, the desired effect described above cannot be expected. On the other hand, if 2Mo + W is contained in a large amount exceeding 1.40%, the weldability is lowered and the manufacturing cost is increased. For this reason, when it contains Mo and W in combination, it is preferable to limit the amount of (2Mn + W) to a range of 0.10 to 1.40% that satisfies the expression (1).

Moreover, in this invention, in addition to the above-mentioned component, you may contain Nb further.
Nb: 0.005-0.05%
Nb is an element that combines with N or further C and precipitates as nitrides or carbonitrides and contributes effectively to grain refinement, and has the effect of further improving low-temperature toughness through grain refinement. Have. In this invention, it can contain as needed. Such an effect becomes noticeable when the content is 0.005% or more. However, when the content exceeds 0.05%, the weldability is lowered. For this reason, Nb is preferably limited to a range of 0.005 to 0.05%. In addition, More preferably, it is 0.005-0.03%.

Moreover, in this invention, in addition to the above-mentioned component, it can contain 1 group or 2 groups further selected from the following a group-b group.
Group a: Cu: 0.1 to 1%, Ni: 0.1 to 2%, Cr: 0.1 to 1%, V: 0.01 to 1% or more of Cu, Ni, Cr, and V in Group a are These are elements that improve the hardenability, and can be selected as necessary and contain one or more.

Cu is an element that enhances hardenability, but if it is less than 0.1%, this effect cannot be exhibited. On the other hand, if the content exceeds 1%, the hot workability is lowered and the manufacturing cost is increased. For this reason, it is preferable to limit Cu to the range of 0.1 to 1%. In addition, More preferably, it is 0.1 to 0.5%.
Ni, like Cu, is an element that improves hardenability and further improves low-temperature toughness. Such an effect is recognized when the content is 0.1% or more. On the other hand, if the content exceeds 2%, the production cost increases. For this reason, it is preferable to limit Ni to 0.1 to 2% of range. In addition, More preferably, it is 0.1 to 0.5%.

Cr is an element that enhances hardenability like Cu and Ni. Such an effect is recognized when the content is 0.1% or more. On the other hand, if the content exceeds 1%, the weldability is lowered and the manufacturing cost is increased. For this reason, Cr is preferably limited to a range of 0.1 to 1%. More preferably, it is 0.1% or more and less than 0.5%.
V is an element which improves hardenability like Cu and the like. Such an effect is recognized when the content is 0.01% or more. However, if the content exceeds 1%, the weldability decreases. For this reason, V is preferably limited to a range of 0.01 to 1%. In addition, More preferably, it is 0.01 to 0.5%.

Group b: Ca: 0.0002 to 0.0050%, REM: One or two of 0.0002 to 0.0050% Group B, Ca and REM fix S and suppress the generation of MnS causing a decrease in toughness. Such an effect is recognized when Ca and REM are contained in amounts of 0.0002% or more. However, when Ca and REM are contained in excess of 0.0050%, low temperature toughness is lowered. For this reason, it is preferable to limit Ca and REM to the range of 0.0002 to 0.0050%, respectively.

The balance other than the components described above is Fe and inevitable impurities. As unavoidable impurities, Al: less than 0.035%, N: 0.01% or less, O: 0.01% or less, Zr: 0.01% or less, Co: 0.01% or less, Sn: 0.01% or less, Sb: 0.01% or less, Pb: 0.01% or less is acceptable.
Moreover, in this invention, it is preferable to restrict | limit the carbon equivalent Ceq defined by following (2) Formula to 0.60% or less from a viewpoint of weldability improvement including the component in an above-described range.
Ceq = C + Mn / 6 + (Cu + Ni) / 15 + (Cr + Mo + V) / 5 (2)
(Here, C, Mn, Cu, Ni, Cr, Mo, V: content of each element (mass%))
When the carbon equivalent Ceq increases, it is necessary to perform pre-heat treatment and post-heat treatment at the time of welding. In particular, when Ceq exceeds 0.60%, cold cracking occurs in the weld even if preheating at 200 ° C. is performed. For this reason, it is preferable that Ceq is 0.60% or less from the viewpoint of welding workability. Further, when preheating is omitted, it is more preferable that Ceq is 0.43% or less.

The wear-resistant steel sheet of the present invention preferably has the above-described composition and further has a structure in which the martensite phase fraction in the as-quenched state is 90% or more by volume. When the martensite phase fraction is less than 90%, it is difficult to ensure desired wear resistance and low temperature toughness. In order to further improve low temperature toughness, the absorbed energy vE- ₄₀ at −40 ° C. in the Charpy impact test is 27 J or more, the prior austenite (γ) grain size should be 30 μm or less in average grain size. desirable.

Next, the preferable manufacturing method of the abrasion-resistant steel plate of this invention is demonstrated.
It is preferable that the molten steel having the above composition is melted by a known melting method such as a converter and used as a steel material (slab) by a continuous casting method or an ingot-bundling method. These steel materials are hot-rolled with or without heating to obtain a steel plate (hot-rolled steel plate) having a desired thickness. In the present invention, it is preferable to perform a direct quenching process in which quenching is performed immediately after the end of hot rolling. The quenching start temperature is more preferably set to a temperature equal to or higher than the Ar ₃ transformation point. The quenching cooling is not particularly limited as long as it is a cooling rate at which a martensite phase is formed, but it is preferably water-cooled to a temperature below the Ms point, preferably to 300 ° C. or below.

  Further, instead of quenching immediately after the end of hot rolling, a reheating quenching process may be performed in which the sample is allowed to cool after the end of hot rolling, and then reheated to a predetermined heating temperature and further quenched. The predetermined reheating temperature is desirably 850 to 950 ° C. The quenching cooling is not particularly limited as long as it is a cooling rate at which a martensite phase is formed, but it is preferably water-cooled to a temperature below the Ms point, preferably to 300 ° C. or below.

  Note that, even after tempering at a low temperature of 300 ° C. or lower after the above-described quenching treatment, the characteristics of the steel sheet of the present invention are not impaired.

  Molten steel having the composition shown in Table 1 was melted to obtain a steel material (slab). These steel materials (slabs) were hot-rolled at the heating temperature and finish rolling temperature under the conditions shown in Table 2 to obtain hot-rolled sheets having the thicknesses shown in Table 2. Some hot-rolled sheets were directly quenched after the hot rolling. In addition, some hot-rolled sheets were subjected to a reheating quenching process in which the sheets were allowed to cool after hot rolling, reheated, and then quenched. Table 2 shows the quenching conditions.

The obtained steel sheet was subjected to structure observation, surface layer hardness test, low temperature toughness test, and weldability test. The test method is as follows.
(1) Microstructure observation A test piece is collected from the obtained steel sheet, and the structure is observed with an optical microscope and a transmission electron microscope at a position of 1/4 t in the thickness direction of the cross section parallel to the rolling direction. (Martensite fraction) and average particle size of prior austenite grains (old γ grains) were determined.

(2) Hardness test of the surface layer A specimen was taken from the obtained steel sheet, and the surface layer was measured with a Brinell hardness meter (ball indenter diameter: 10 mm, test force: 29.42 kN) in accordance with the provisions of JIS Z 2243. The hardness HBW10 / 3000 was measured. The measurement points were 5 points randomly selected on the surface, and the average value was the hardness HBW10 / 3000 of the surface layer portion of each steel plate.

(3) Low temperature toughness test V-notch specimens were collected from the obtained steel sheet in accordance with the provisions of JIS Z 2242-2005 so that the length direction was parallel to the rolling direction at 1 / 4t of the plate thickness. Then, a Charpy impact test was conducted to determine the fracture surface transition temperature vTrs, and the low temperature toughness was evaluated.
(4) Weldability test From the obtained steel plate, y-type weld crack specimens were collected, and in accordance with the provisions of JIS Z 3158, a y-type weld crack test was performed with preheating temperatures of 25 ° C and 200 ° C. The test piece was examined for the presence of cracks and the weldability was evaluated.

  The obtained results are shown in Table 3.

  The examples of the present invention have high surface layer hardness and excellent low temperature toughness. On the other hand, in the comparative example outside the scope of the present invention, the low temperature toughness is lowered.

It is a graph which shows the influence of W content which has on vE- _{40 of a} 14 mm thick steel plate. It is a graph which shows the influence of W content which has on vE- _{40 of a} 25 mm thick steel plate. It is a graph which shows the relationship between a fracture surface transition temperature and B content.

Claims (13)

% By mass
C: 0.10 to 0.30%, Si: 0.05 to 1.0%,
Mn: 0.1 to 2.0%, P: 0.020% or less,
S: 0.005% or less, W: 0.10 to 1.40%,
B: 0.0003-0.0020%
And further comprising Ti: 0.005 to 0.1% and / or Al: 0.035 to 0.1%, and having a composition comprising the balance Fe and inevitable impurities, a wear-resistant steel sheet having excellent low-temperature toughness. The wear-resistant steel sheet according to claim 1, wherein Mo and W are contained in mass% so as to satisfy the following formula (1) instead of W in the composition.
Record
0.10 ≦ 2Mo + W ≦ 1.40 (1)
Here, Mo, W: Content of each element (mass%)   The wear-resistant steel sheet according to claim 1 or 2, further comprising Nb: 0.005 to 0.05% by mass% in addition to the composition. The composition according to any one of claims 1 to 3, wherein the composition further contains 1 group or 2 groups selected from the following groups a to b in addition to the initial composition: Wear-resistant steel plate.
A group: Cu: 0.1 to 1%, Ni: 0.1 to 2%, Cr: 0.1 to 1%, V: 0.01 to 1%, or one or more of them,
Group b: Ca: 0.0002 to 0.0050%, REM: One or two of 0.0002 to 0.0050%   5. The resistance to resistance according to claim 1, which has a martensite phase of 90% by volume or more in the as-quenched state, or further has a structure in which the average grain size of the prior austenite grains is 30 μm or less. Wear steel plate.   The wear-resistant steel sheet according to any one of claims 1 to 5, wherein the hardness of the surface layer part is 300 HBW or more. % By mass
C: 0.10 to 0.30%, Si: 0.05 to 1.0%,
Mn: 0.1 to 2.0%, P: 0.020% or less,
S: 0.005% or less, W: 0.10 to 1.40%,
B: 0.0003-0.0020%
In addition, in addition to Ti: 0.005-0.1% and / or Al: 0.035-0.1%, a steel material having a composition consisting of the balance Fe and unavoidable impurities is hot-rolled to form a steel sheet. A method for producing a wear-resistant steel sheet excellent in low-temperature toughness, characterized by quenching immediately after completion of the hot rolling. The method for producing a wear-resistant steel sheet according to claim 7, wherein Mo and W are contained in mass% so as to satisfy the following expression (1) instead of W in the composition.
Record
0.10 ≦ 2Mo + W ≦ 1.40 (1)
Here, Mo, W: Content of each element (mass%)   The method for producing a wear-resistant steel sheet according to claim 7 or 8, further comprising Nb: 0.005 to 0.05% by mass% in addition to the composition. The composition according to any one of claims 7 to 9, wherein in addition to the composition, the composition further contains, in mass%, one group or two groups selected from the following groups a to b. A method for producing a wear-resistant steel sheet.
A group: Cu: 0.1 to 1%, Ni: 0.1 to 2%, Cr: 0.1 to 1%, V: 0.01 to 1%, or one or more of them,
Group b: Ca: 0.0002 to 0.0050%, REM: One or two of 0.0002 to 0.0050% Method for producing a wear-resistant steel sheet according to any one of claims 7 to 10 hardening start temperature of the hardening is equal to or is Ar ₃ transformation point or more.   The manufacture of the wear-resistant steel sheet according to any one of claims 7 to 10, wherein the steel sheet is cooled after the hot rolling is finished and then re-heated and hardened instead of quenching immediately after the hot rolling is finished. Method.   The method for producing a wear-resistant steel sheet according to claim 12, wherein the reheating temperature is 850 to 950 ° C.

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