KR102009630B1 - Grater - Google Patents

Abstract

The steel sheet which concerns on one aspect of this invention has predetermined chemical composition, the index Q calculated | required by following formula (1) is 0.00 or more, and the carbon equivalent Ceq (%) calculated by following formula (2) is less than 0.800%. While the ratio of the difference between the surface layer portion hardness and the plate thickness center portion hardness to the surface layer portion hardness at room temperature is 15.0% or less, the surface layer portion hardness at room temperature is 400 or more in Vickers hardness, and the plate thickness is 40 mm or more.
Q = 0.18-1.3 (logT) + 0.75 (2.7 x [C] + [Mn] + 0.45 x [Ni] + 0.8 x [Cr] + 2 x [Mo]). (1) Ceq (%) = [C] + [Mn] / 6 + [Si] / 24 + [Ni] / 40 + [Cr] / 5 + [Mo] / 4 + [V] / 4. (2)

Description

Grater

The present invention relates to a steel sheet (abrasion resistant steel sheet) excellent in wear resistance.

This application claims priority in June 21, 2017 based on Japanese Patent Application No. 2017-121641 for which it applied to Japan, and uses the content for it here.

Abrasion resistant steel sheet that can be used for a long period of time even under severe abrasion environments is required for applications such as construction machinery and industrial machinery, and abrasion resistance improvement is also required from the viewpoint of securing a wear margin by increasing the thickness of the sheet. . In general, in order to improve the wear resistance of the steel sheet, it is necessary to increase the hardness of the steel sheet. In the thick wear-resistant steel sheet whose plate | board thickness is 40 mm or more especially, hardness in the surface vicinity of a steel plate may be called "surface layer hardness" hereafter. A surface layer part is an area of 1 mm-5 mm from the surface of a steel plate in a plate thickness direction. In addition, hardness in the center part of the plate | board thickness direction which is hard to obtain hardness may be called "plate thickness center part hardness" hereafter. The center part is 1 / of the plate | board thickness T from the surface of a steel plate in plate thickness direction. It is a problem to secure ± 5 mm (total 10 mm thickness) from a position 2 (that is, T / 2) apart (that is, the center of the plate thickness).

The wear resistant steel sheet is locally exposed to a temperature higher than room temperature, and may be used in a harsh environment. Therefore, the hardness decreases even in a temperature range higher than room temperature (for example, a temperature range of about 150 to 300 ° C). It may be required to be small (excellent high temperature hardness). In order to ensure hardness in the temperature range higher than room temperature (hereinafter may be referred to as "high temperature hardness"), steel sheets which have increased the content of Si have been proposed (for example, Patent Documents 1 to 3, Reference).

Japanese Patent Laid-Open No. 8-41535 Japanese Patent Laid-Open No. 2001-49387 Japanese Patent Laid-Open No. 2002-235144

For example, in patent document 1, the steel content containing Nb is proposed as content of Si is 0.40-1.50 mass% (Hereinafter, a "mass%" will be described simply as "%."). However, in patent document 1, the plate | board thickness of a steel plate is 40 mm or less, it is not described about plate | board thickness center part hardness, and it was not examined from the viewpoint of securing the wear margin by thickening a steel plate.

In Patent Document 2, in order to assume a severe abrasion environment that is locally exposed to a temperature higher than room temperature, and in order to secure the high temperature hardness of the steel, it contains more than 0.5% to 1.2% of Si and uses precipitation strengthening by V carbide A river is proposed. However, steel containing a large amount of V tends to cause cracks in the cast piece, and there is a fear of deterioration in manufacturability.

In patent document 3, in order to ensure the high temperature hardness of a steel plate, the steel plate containing 1.00-1.50% Si is proposed. In Patent Literature 3, while securing the plate thickness center portion hardness of the steel sheet is also considered, the difference between the surface layer portion hardness and the plate thickness center portion hardness (hereinafter, "the hardness difference between the surface layer portion and the plate thickness center portion" or simply "hardness difference" It has not been described in terms of securing the wear margin by thickening the steel sheet.

In consideration of the use environment and the use form of the wear resistant steel sheet, even in a high temperature environment of about 150 to 300 ° C as well as room temperature, when maintaining high hardness or sufficient hardness in the center portion (plate thickness center portion) in the sheet thickness direction is required There is. Although the hardness of a plate | board thickness center part can be easily ensured by increase of content of an alloy component, since weldability falls, it is necessary to provide the upper limit of a carbon equivalent. In order to ensure the hardness of a steel plate in high temperature environment, it is considered that Si addition of more than 1.00% is effective. However, the present inventors found that in steel sheets containing more than 1.00% of Si, there is an unfavorable tendency in the wear resistance of the steel sheet that the difference between the surface layer portion hardness and the plate thickness center portion hardness becomes significantly large.

Until now, there has been no report regarding the relationship between the steel plate containing Si exceeding 1.00%, and the hardness difference, and the examination for reducing the hardness difference in room temperature was not fully made. In view of such a situation, the present invention can maintain a high hardness not only at room temperature but also at a high temperature environment. In particular, in a steel sheet having a plate thickness of 40 mm or more, the carbon equivalent is made less than 0.800%, An object of the present invention is to provide a steel sheet excellent in wear resistance, wherein the difference between the surface layer portion hardness and the plate thickness center portion hardness is 15.0% or less of the surface layer portion hardness.

Steels containing more than 1.00% to 2.00% of Si are advantageous for wear resistance in that hardness at room temperature and high temperature can be ensured. On the other hand, it was found by the present inventors that in the steel sheet containing more than 1.00% of Si and having a sheet thickness of 40 mm or more, a difference between the surface layer hardness and the plate thickness center portion hardness tends to occur at room temperature. This is caused by a decrease in cooling rate and insufficient formation of martensite structure at the central portion in the plate thickness direction of the steel sheet, but the effect of increasing the content of Si is not necessarily clear.

As a result of further studies, the present inventors derived an index Q for reducing the difference between the surface layer hardness and the plate thickness center hardness at room temperature in a steel sheet having a plate thickness of 40 mm or more and containing Si of more than 1.00%. It was. Index Q is calculated | required by following formula (1) which considered the quenchability of an alloying element, and plate | board thickness. However, in following formula (1), alloying elements other than Si (C, Mn, Ni, Cr, Mo) which are necessary in order to make small the difference of the surface layer part hardness and the plate | board thickness center part hardness of the steel plate containing more than 1.00%. Since attention is focused on, the amount of Si is not considered. In addition, below, the hardness in room temperature may be called "room temperature hardness". In addition, below, when it only calls "hardness", hardness in room temperature is shown, and room temperature shows 22 +/- 5 degreeC (17-27 degreeC).

In the steel sheet according to the present invention, when the sheet thickness is 40 mm or more, and the effect of residual stress caused by welding, etc. is affected, delayed cracking by hydrogen is concerned, and the carbon equivalent Ceq (%) obtained by the following formula (2) Is less than 0.800%. By setting the index Q obtained by the following formula (1) to 0.00 or more, the hardness difference between the surface layer portion and the plate thickness center portion at room temperature becomes 15.0% or less of the surface layer portion hardness, the hardness difference is small, the carbon equivalent is low, and the plate thickness is low. A steel sheet of 40 mm or more and excellent in wear resistance can be obtained. In addition, the unit of the index Q calculated | required by substituting plate thickness T and content [X] of each element X as a dimensionless numerical value to following formula (1) is dimensionless. In addition, the unit of carbon equivalent Ceq calculated | required by following formula (2) is "%".

Q = 0.18-1.3 (logT) + 0.75 (2.7 x [C] + [Mn] + 0.45 x [Ni] + 0.8 x [Cr] + 2 x [Mo]). (One)

Ceq (%) = [C] + [Mn] / 6 + [Si] / 24 + [Ni] / 40 + [Cr] / 5 + [Mo] / 4 + [V] / 4. (2)

Here, the index Q of the said Formula (1) calculates by substituting the numerical value of the plate | board thickness T (mm) and the numerical value of content [X] represented by the mass% of each element X, and when it does not contain element X, it is 0. Replace with The carbon equivalent Ceq (%) of the said Formula (2) substitutes and calculates the numerical value of content [X] shown by the mass% of each element X, and substitutes 0 when it does not contain element X.

This invention is made | formed based on such knowledge, The summary is as follows.

[1] The steel sheet according to one aspect of the present invention is% by mass,

C: 0.20 to 0.35%,

Si: greater than 1.00% to 2.00%,

Mn: 0.60-2.00%,

Cr: 0.10 to 2.00%,

Mo: 0.05-1.00%,

Al: 0.010-0.100%,

N: 0.0020 to 0.0100%,

B: 0.0003 to 0.0020%,

P: 0.0200% or less,

S: less than 0.0100%,

Cu: 0 to 0.500%,

Ni: 0 to 1.00%,

Nb: 0 to 0.050%,

V: 0 to 0.120%,

Ti: 0% to 0.025%

Ca: 0 to 0.050%,

Mg: 0 to 0.050%,

REM: 0 to 0.100% and

Balance: Fe and impurities,

The index Q obtained by the following formula (1) is 0.00 or more,

Carbon equivalent Ceq (%) calculated | required by following formula (2) has a chemical composition of less than 0.800%,

While the ratio of the difference between the surface layer hardness and the plate thickness center portion hardness to the surface layer hardness at room temperature is 15.0% or less, the surface layer portion hardness at room temperature is 400 or more in Vickers hardness,

Plate thickness T is 40 mm or more.

Q = 0.18-1.3 (logT) + 0.75 (2.7 x [C] + [Mn] + 0.45 x [Ni] + 0.8 x [Cr] + 2 x [Mo]). (One)

Ceq (%) = [C] + [Mn] / 6 + [Si] / 24 + [Ni] / 40 + [Cr] / 5 + [Mo] / 4 + [V] / 4. (2)

The index Q of the above formula (1) is calculated by substituting the numerical value of the plate thickness T (mm) and the numerical value of the content [X] expressed in mass% of each element X, and in the case of not containing the element X, 0 is substituted. do. The carbon equivalent Ceq (%) of the said Formula (2) substitutes and calculates the numerical value of content [X] shown by the mass% of each element X, and substitutes 0 when it does not contain element X.

[2] In the steel sheet according to the above [1], the index Q is 0.04 or more,

The said ratio may be 13.0% or less.

[3] In the steel sheet according to the above [1] or [2], in mass%,

Ni: You may have the chemical composition which is 0.05 to 1.00%.

[4] In the steel sheet according to any one of [1] to [3], in mass%,

Mn: You may have a chemical composition which is 0.63-2.00%.

According to the above aspect of the present invention, it is possible to maintain a high hardness not only at room temperature but also at a high temperature environment, and particularly in a steel sheet having a plate thickness of 40 mm or more, the carbon equivalent Ceq (%) is less than 0.800%, and at room temperature. The steel plate excellent in abrasion resistance that the difference between the surface layer part hardness and the plate thickness center part hardness of 15.0% or less of the surface layer part hardness can be provided. The steel sheet which concerns on this invention can be used over a long period of time even in the harsh environment where temperature is about 150-300 degreeC, and industrial contribution is very remarkable.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure explaining the temperature change of the difference of the surface hardness of a steel plate, and a reference hardness.
It is a figure explaining the hardness distribution of the plate thickness direction of a steel plate.
3 is a diagram illustrating a relationship between the hardness difference ratio ΔHv / Hvs of the steel sheet and the index Q. FIG.

The relationship between the Si content of a steel plate and the temperature change of hardness is demonstrated, referring FIG. BRIEF DESCRIPTION OF THE DRAWINGS It is a figure explaining the temperature change of the difference of the surface hardness of a steel plate, and a reference hardness. The result of having measured the Vickers hardness (surface hardness) HV5 in the surface of a steel plate from room temperature to 400 degreeC by carrying out the quenching process to the steel plate of plate thickness 40mm which made C content constant, and changed Si content. 1 is shown. The vertical axis | shaft of FIG. 1 is a difference of Vickers hardness (surface hardness) HV5 at each temperature of each steel, and Vickers hardness (reference hardness) HV5 at room temperature of the steel plate whose Si content is 0.25%. In addition, the Vickers hardness HV5 cut out the sample from the position of the depth of 5 mm from the surface of the steel plate, and made the test force 49.03 N (5 kgf) based on JISZ2225-1919, and measured by the high temperature Vickers hardness test. The measurement of the reference hardness was performed by carrying out conditions other than control of temperature similarly to the said high temperature Vickers hardness test.

1 shows that room temperature hardness and high temperature hardness increase with increasing Si content, and also the hardness fall (difference between surface hardness and reference hardness) under high temperature environment becomes small. As described above, the steel sheet containing more than 1.00% to 2.00% of Si is excellent in wear resistance in that hardness at room temperature and high temperature can be ensured.

Next, the hardness distribution (Vickers hardness) in the plate thickness direction after quenching of the steel plate (plate thickness 40mm) containing more than 1.00% is shown in FIG. Vickers hardness HV5 was measured at room temperature with test force of 49.03 N (5 kgf) in accordance with JIS Z 2244: 2009. As shown in FIG. 2, plate | board thickness center part hardness is falling compared with surface layer part hardness. In addition, from the results of the Vickers hardness test, the surface layer hardness Hvs (average value of Vickers hardness measured in the range of 1 mm to 5 mm from the surface of the steel sheet in the plate thickness direction) and the plate thickness center portion hardness Hvc (± from the central portion of the steel sheet in the plate thickness direction). The average value of Vickers hardness measured in the range of 5 mm (total 10 mm thickness) was obtained, and the difference (hardness difference) ΔHv between the plate thickness center part hardness and the surface layer part hardness at room temperature was calculated. That is, ΔHv is represented by the following formula (a).

ΔHv = Hvs—Hvc. (a)

Table 1 shows the results of the Vickers hardness test. From Table 1, it turns out that (DELTA) Hv increases with increase of Si content. Thus, the present inventors obtained the knowledge that the difference between the surface-layer part hardness and the plate | board thickness center part hardness in room temperature tends to generate | occur | produce in the thick steel plate with many Si content.

Then, the present inventors examined the method of reducing the hardness difference of the surface layer part and plate | board thickness center part in room temperature of the steel plate whose sheet thickness contains more than 1.00% of 40 mm or more. MEANS TO SOLVE THE PROBLEM The present inventors examined in order to reduce the hardness difference of a steel plate in consideration of the quenchability and plate | board thickness of an alloy element.

In order to ensure the hardness of the steel sheet, in hot rolling, after reheating the steel sheet at a temperature of Ac ₃ or more at which the transformation to austenite is terminated at the time of temperature rising, water cooling or the like is usually performed. At this time, the surface layer part of a steel plate has a fast cooling rate, and can ensure sufficient hardness. On the other hand, in the sheet thickness center part of a steel plate, since a cooling rate falls compared with a surface layer part, generation | occurrence | production of martensite becomes inadequate and hardness falls.

As mentioned above, a cooling rate falls in the plate | board thickness center part of a steel plate. Therefore, in order to ensure sufficient hardness in the plate | board thickness center part of a steel plate, it is necessary to increase content of an alloying element and to improve quenchability. However, when the content of the alloying element is set to a certain amount, depending on the plate thickness, there is a problem that the quenchability is insufficient, the cost is increased by containing an unnecessary amount of the alloying element, or the weldability is impaired. Therefore, in order to control content of an alloying element in an appropriate range, it is necessary to consider that the cooling rate of a plate | board thickness center part is influenced by plate | board thickness.

The present inventors summarized the relationship between the content of the alloying element having the quenchability and the plate thickness on the hardness difference ratio ΔHv / Hvs of various steels with a plate thickness of 40 mm or more containing more than 1.00% of Si, and the following formula (1 The index Q shown in ()) was derived. Here, hardness difference ratio (DELTA) Hv / Hvs (%) represents the ratio calculated | required and calculated | required the difference of the surface layer part hardness and plate | board thickness center part hardness at room temperature by dividing by the surface layer part hardness as a percentage. In addition, hardness difference ratio (DELTA) Hv / Hvs (%) is represented by following formula (b). In the following formula (b), Hvs is the surface layer hardness (average value of Vickers hardness measured in the range of 1 mm to 5 mm from the surface of the steel sheet in the plate thickness direction), and Hvc is the plate thickness center portion hardness (center portion in the plate thickness direction of the steel sheet). Average value of Vickers hardness measured in the range of ± 5 mm (total 10 mm thickness).

ΔHv / Hvs (%) = 100 × (Hvs-Hvc) / Hvs... (b)

Conventionally, in steels containing more than 1.00% of Si, it has been considered that the quenchability is lowered when the cooling rate is slowed. However, the inventors of the present invention, if alloying elements other than Si (C, Mn, Ni, Cr, Mo) are contained in a steel containing more than 1.00% of Si to ensure quenchability, even if the cooling rate is lowered, the Si is? It was found to contribute to the improvement of character. The following formula (1) is based on the knowledge of the present inventors that it is necessary to ensure alloying resistance by containing alloy elements (C, Mn, Ni, Cr, Mo) other than Si in order to raise the plate thickness center part hardness. The index Q does not include the term of Si content.

Q = 0.18-1.3 (logT) + 0.75 (2.7 x [C] + [Mn] + 0.45 x [Ni] + 0.8 x [Cr] + 2 x [Mo]). (One)

Here, the index Q of the said Formula (1) calculates by substituting the numerical value of the plate | board thickness T (mm) and the numerical value of content [X] represented by the mass% of each element X, and when it does not contain element X, it is 0. Replace with That is, in said Formula (1), the index Q is computed as sheet value T and content [X] of each element as a dimensionless value. In addition, the logarithm of said formula (1) is a logarithm with a base of 10, ie, a commercial logarithm.

3 shows the relationship between the hardness difference ratio ΔHv / Hvs (%) and the indicator Q. In FIG. From FIG. 3, it was found that when the hardness difference ratio ΔHv / Hvs (%) is set to 15.0% or less of the surface layer hardness Hvs as a criterion for extending the life of the thick steel sheet, it is necessary to set Q≥0.00. . Moreover, it turned out that it is necessary to set it to Q≥0.04 when setting hardness difference ratio (DELTA) Hv / Hvs (%) to 13.0% or less of surface layer hardness Hvs.

In addition, since the steel plate concerning this embodiment has a plate | board thickness of 40 mm or more, since the hydrogen embrittlement cracking under the influence of residual stress by welding is concerned, the carbon equivalent Ceq (%) represented by following formula (2) is taken into consideration. It is less than 0.800%. In addition, since it is necessary to consider the weldability of a steel plate, following formula (2) contains the term of Si content.

Ceq (%) = [C] + [Mn] / 6 + [Si] / 24 + [Ni] / 40 + [Cr] / 5 + [Mo] / 4 + [V] / 4. (2)

The carbon equivalent Ceq (%) of the said Formula (2) substitutes and calculates the numerical value of content [X] shown by the mass% of each element X, and substitutes 0 when it does not contain element X. The unit of carbon equivalent Ceq calculated by said Formula (2) is "%".

By setting the index Q of the formula (1) to 0.00 or more, the hardness difference ΔHv of the surface layer portion and the sheet thickness center portion of the steel sheet at room temperature is 15.0% or less of the surface layer portion hardness Hvs, the hardness difference is small, and the carbon equivalent is less than 0.800%. A steel sheet having a plate thickness of 40 mm or more and excellent in wear resistance can be obtained.

Hereinafter, the steel plate which concerns on this embodiment is demonstrated in detail. First, the chemical composition of the steel plate which concerns on this embodiment is demonstrated. In addition, unless otherwise indicated,% with respect to a chemical composition means the mass%.

<C: 0.20 to 0.35%>

C is an element effective for improving the hardness, and the C content is made 0.20% or more in order to secure the hardness of the steel sheet. Preferably C content is 0.22% or more, More preferably, you may be 0.24% or more. On the other hand, when C content exceeds 0.35%, since the hardness rises, hydrogen embrittlement susceptibility becomes high, and the generation | occurrence | production of the crack by hydrogen embrittlement is feared, and C content is made into 0.35% or less. Preferably, the C content is 0.32% or less, more preferably 0.30% or less.

<Si: more than 1.00% to 2.00%>

Si is a deoxidizer and is also an effective element for improving the hardness of a steel sheet. In this embodiment, Si is a very important element in order to maintain the hardness of a steel plate in high temperature environment. In order to acquire the effect of Si containing, Si content is made into 1.00% or more. Preferably, Si content is 1.10% or more, More preferably, it is 1.20% or more or 1.30% or more. On the other hand, when Si content exceeds 2.00%, since toughness of a steel plate may be impaired, Si content shall be 2.00% or less. Preferably, Si content is 1.90% or less, More preferably, you may be 1.80% or less.

<Mn: 0.60 to 2.00%>

Mn is an element which improves quenchability and improves hardness, and it is necessary to contain 0.60% or more in order to secure the hardness of the steel sheet. Preferably Mn content is 0.70% or more, More preferably, you may be 0.80% or more. On the other hand, when Mn is contained excessively, toughness may fall, and formation of cementite may be accelerated | stimulated and the fall of the high temperature hardness of a steel plate may result as a result. Therefore, Mn content is made into 2.00% or less. Preferably, Mn content is made 1.50% or less or 1.35% or less, more preferably 1.20% or less or 1.00% or less.

<Cr: 0.10 to 2.00%>

Cr is an element which improves quenchability and improves the toughness and hardness of the steel sheet. In order to secure the toughness and hardness of a steel plate, Cr content is made into 0.10% or more. Preferably Cr content is 0.50% or more, More preferably, you may be 0.80% or more. On the other hand, when Cr content exceeds 2.00%, since toughness of a steel plate will fall, Cr content shall be 2.00% or less. Preferably Cr content is 1.70% or less, More preferably, you may be 1.50% or less.

<Mo: 0.05 to 1.00%>

Mo is also an element which raises quenchability and improves the hardness of a steel plate. In addition, Mo is an effective element in order to maintain the hardness of a steel plate even in high temperature environment. Therefore, Mo content is made into 0.05% or more. Preferably Mo content is 0.10% or more, More preferably, you may be 0.20% or more. On the other hand, when Mo content exceeds 1.00%, since toughness of a steel plate will fall, Mo content shall be 1.00% or less. Preferably Mo content is 0.60% or less, More preferably, you may be 0.40% or less.

<Al: 0.010 to 0.100%>

Al is an effective element as a deoxidizer. In addition, Al forms N and AlN, refines the crystal grains, and improves the toughness of the steel sheet. Therefore, Al content is made into 0.010% or more. Preferably, Al content is made into 0.020% or more, More preferably, you may be 0.030% or more. On the other hand, when Al is contained excessively, since the toughness of a steel plate will generate | occur | produce, Al content shall be 0.100% or less. Preferably, Al content is made into 0.080% or less, More preferably, you may be 0.070% or less.

<N: 0.0020 to 0.0100%>

N is an element which forms nitride with Al, Ti, refines a crystal grain, and improves toughness of a steel plate. Therefore, N content is made into 0.0020% or more. Preferably, N content is made into 0.0030% or more, More preferably, you may be 0.0040% or more. On the other hand, when it contains N excessively, coarse nitride will produce | generate and will reduce toughness of a steel plate, Therefore, N content is made into 0.0100% or less. Preferably N content is 0.0080% or less, More preferably, you may be 0.0060% or less.

<B: 0.0003 to 0.0020%>

B is an element which improves the quenchability of steel remarkably, and is especially effective in the improvement of the hardness of the plate | board thickness center part of a steel plate. Therefore, B content is made into 0.0003% or more. Preferably B content is 0.0005% or more, More preferably, it is 0.0007% or more, More preferably, you may be 0.0010% or more. On the other hand, when it contains B excessively, since boride is formed, quenchability falls, and hardness of a steel plate cannot be ensured, B content is made into 0.0020% or less. Preferably B content is 0.0018% or less, More preferably, you may be 0.0016% or less.

<P: 0.0200% or less>

Since P is an impurity and reduces the toughness and workability of the steel sheet, the P content is limited to 0.0200% or less. Preferably P content is 0.0150% or less, More preferably, you may be 0.0100% or less. The lower limit of the P content is preferably 0%, but from the viewpoint of the manufacturing cost, the P content may be 0.0001% or more.

<S: less than 0.0100%>

S is also an impurity similarly to P, and the S content is limited to less than 0.0100% in that the toughness of the steel sheet is lowered. Preferably S content is 0.0070% or less, More preferably, it is 0.0050% or less, More preferably, you may be 0.0030% or less. The lower limit of the S content is preferably 0%, but from the viewpoint of the manufacturing cost, the S content may be 0.0001% or more.

In the steel sheet according to the present embodiment, one or two or more of Cu, Ni, Nb, V, and Ti may be selectively contained for the purpose of improving mechanical properties such as hardness and toughness of the steel sheet. The minimum of content of these components is 0%.

<Cu: 0 to 0.500%>

Cu is an element which forms a fine precipitate and contributes to the improvement of the strength of a steel plate, and may contain 0.001% or more. More preferably, Cu content is 0.050% or more, More preferably, you may be 0.100% or more. On the other hand, when Cu is excessively contained, the wear resistance of the steel sheet is deteriorated, so the upper limit of the Cu content is 0.500% or less. More preferably, Cu content is 0.450% or less, More preferably, you may be 0.400% or less.

<Ni: 0 to 1.00%>

Ni is an element which improves the quenchability of steel and contributes to the improvement of the hardness of a steel plate, and may contain 0.05% or more. More preferably, Ni content is 0.10% or more, More preferably, you may be 0.20% or more. On the other hand, since Ni is an expensive alloying element, the Ni content is made 1.00% or less from the viewpoint of cost. More preferably, Ni content is 0.70% or less, More preferably, you may be 0.50% or less.

<Nb: 0 to 0.050%>

Nb is an element which contributes to atomization of crystal grains by forming nitrides and suppressing recrystallization, and may contain 0.005% or more in order to improve the toughness of the steel sheet. More preferably, Nb content is made into 0.007% or more, More preferably, you may be 0.010% or more. On the other hand, when Nb is contained excessively, the toughness of the steel sheet may be lowered, so the Nb content is made 0.050% or less. More preferably, Nb content is 0.030% or less, More preferably, you may be 0.020% or less.

<V: 0 to 0.120%>

V is an element which contributes to the improvement of the hardness of a steel plate, and may contain 0.010% or more. More preferably, V content is 0.020% or more, More preferably, you may be 0.040% or more. On the other hand, when V is excessively contained, cracks in the cast piece may occur and the manufacturability may be impaired. Therefore, the V content is 0.120% or less. More preferably, V content is 0.100% or less, More preferably, you may be 0.070% or less.

<Ti: 0 to 0.025%>

Ti is an element which forms TiN, refines a crystal grain, and improves toughness of a steel plate, and may contain 0.005% or more. More preferably, Ti content is 0.007% or more, More preferably, you may be 0.010% or more. On the other hand, when Ti is excessively contained, the toughness of the steel sheet may be lowered, so that the Ti content is 0.025% or less. More preferably, Ti content is 0.020% or less, More preferably, you may be 0.015% or less.

In order to control the form of the inclusions in the steel, one or two or more of Ca, Mg, and REM may be selectively contained. The minimum of content of these components is 0%.

<Ca: 0 to 0.050%>

<Mg: 0 to 0.050%>

<REM: 0 to 0.100%>

Ca, Mg, and REM are all elements which combine with S to form sulfides and form inclusions that are difficult to be stretched by hot rolling, and mainly contribute to the improvement of steel sheet toughness. On the other hand, when Ca, Mg, and REM are excessively contained, these elements may form coarse oxide with O, and the toughness of a steel plate may fall. For this reason, Ca content and Mg content are 0.050% or less, respectively, and REM content is 0.100% or less. More preferably, Ca content, Mg content, and REM content are respectively 0.020% or less, More preferably, you may be 0.010% or less or 0.005% or less. On the other hand, in order to acquire the toughness improvement effect of a steel plate, it is preferable to make Ca content and Mg content into 0.0005% or more, respectively, and REM content into 0.001% or more. More preferably, the Ca content and the Mg content are 0.0007% or more, and the REM content is 0.002% or more, respectively.

REM (rare earth metal element) means a total of 17 elements composed of Sc, Y and lanthanoids. Content of REM means the total content of these 17 elements.

Remainder of the chemical composition of the steel plate which concerns on this embodiment is Fe and an impurity. Here, the impurity is a component that is mixed by various factors of the manufacturing process, including raw materials such as ore, scrap, and the like when manufacturing the steel sheet industrially, within a range that does not adversely affect the properties of the steel sheet according to the present embodiment. It means to be allowed. However, in the steel plate which concerns on this embodiment, it is necessary to define an upper limit about P and S among impurities as mentioned above.

As impurities in steel, O, Sb, Sn, and As may be mixed in one kind or two or more kinds. Even if these impurities are mixed, there is no problem as long as it is a normal mixing level (range of content) of the wear resistant steel. Therefore, these content is restrict | limited to the normal mixing level of the following wear resistant steel. The minimum of content of these impurities is 0%.

<O: 0.006% or less>

Although O may be mixed as an impurity in steel, since it is an element which forms coarse oxide, it is preferable that O content is small. In particular, when the O content exceeds 0.006%, coarse oxide is formed in the steel, and the wear resistance of the steel sheet is deteriorated, so the O content is set to 0.006% or less. Preferably O content is 0.005% or less, More preferably, you may be 0.004% or less.

<Sb: 0.01% or less>

Sb is an element mixed from scrap as steel raw materials. In particular, when Sb is excessively contained, the wear resistance of the steel sheet is deteriorated, so the Sb content is made 0.01% or less. Preferably, Sb content is made into 0.007% or less and 0.005% or less.

<Sn: 0.01% or less>

Sn is an element mixed from scrap as steel raw material similarly to Sb. In particular, when Sn is excessively contained, the wear resistance of the steel sheet is deteriorated, so the Sn content is made 0.01% or less. Preferably, Sn content is made into 0.007% or less and 0.005% or less.

<As: 0.01% or less>

As is an element mixed from scrap as steel raw material similarly to Sb and Sn. In particular, when As is excessively contained, the wear resistance of the steel sheet is deteriorated, so the As content is made 0.01% or less. Preferably, the As content is made 0.007% or less and 0.005% or less.

The steel sheet according to the present embodiment uses the index Q determined by the following formula (1) so that the hardness difference between the surface layer portion and the sheet thickness center portion of the steel sheet at room temperature is small, and the ratio of the hardness difference with respect to the surface layer portion hardness is 15.0% or less. 0.00 or more. The index Q is calculated by substituting the numerical value of the plate thickness T (mm) and the content [X] expressed in mass% of each element X as a dimensionless numerical value, and containing no element X. 0. In order to reduce the hardness difference between the surface layer portion and the sheet thickness center portion of the steel sheet, the index Q is preferably 0.01 or more, more preferably 0.04 or more, still more preferably 0.05 or more, and even more preferably 0.10 or more. Although the upper limit of the indicator Q is not particularly defined, when the indicator Q is increased, the carbon equivalent Ceq (%) also becomes large, and thus is limited by itself. In order to ensure weldability by setting the carbon equivalent Ceq (%) to less than 0.800%, the index Q is preferably 1.10 or less. More preferably, index Q is 0.80 or less or 0.50 or less, More preferably, it is 0.30 or less or 0.20 or less.

Q = 0.18-1.3 (logT) + 0.75 (2.7 x [C] + [Mn] + 0.45 x [Ni] + 0.8 x [Cr] + 2 x [Mo]). (One)

In the steel sheet according to the present embodiment, the carbon equivalent Ceq (%) is made less than 0.800% in order to suppress welding cracking and to secure weldability of the steel sheet. Carbon equivalent Ceq (%) also calculates by substituting the numerical value of content [X] shown by the mass% of each element, and when it does not contain element X, [X] makes 0. The lower limit of the carbon equivalent Ceq (%) is not particularly defined. However, when the carbon equivalent Ceq (%) is made small, the index Q is also reduced. In order to make index Q into 0.00 or more and to make small hardness difference, carbon equivalent Ceq (%) is 0.507% or more. In order to improve the wear resistance of the steel sheet, the carbon equivalent Ceq (%) is more preferably 0.600% or more, and even more preferably 0.650% or more. More preferably, the carbon equivalent Ceq (%) is 0.700% or more. In order to improve the weldability of the steel sheet, the carbon equivalent Ceq (%) may be 0.785% or less, 0.770% or less, or 0.760% or less.

Ceq (%) = [C] + [Mn] / 6 + [Si] / 24 + [Ni] / 40 + [Cr] / 5 + [Mo] / 4 + [V] / 4. (2)

In the steel sheet according to the present embodiment, the difference (hardness difference) between the surface layer portion hardness and the plate thickness center portion hardness at room temperature is small, and the ratio of the surface layer portion hardness to the surface layer portion hardness and the sheet thickness center portion hardness is 15.0% or less. It can exert excellent wear resistance over a long period of time. Although the hardness difference ratio (DELTA) Hv / Hvs (%) is so preferable that it is small, it is difficult to set it as less than 0% or less than 1.0%. For this reason, the lower limit may be 0% or 1.0%. In consideration of the increase in the cost accompanying the increase in the content of the alloying element, the hardness difference ratio ΔHv / Hvs (%) may be 3.0% or more. Surface layer hardness and plate | board thickness center part hardness are Vickers hardness HV5 in room temperature, and are measured based on JISZ2244: 2009. The surface layer part hardness is an average value of Vickers hardness HV5 measured in the range of 1 mm-5 mm from the surface in the plate thickness direction of a steel plate making the cross section parallel to the rolling direction and plate thickness direction of a steel plate. In the measurement of the surface layer part hardness of a steel plate, Vickers hardness in 5 points | pieces and a total of 25 points | pieces is measured in at least 1 mm in the said range. Plate thickness center part hardness is an average value of Vickers hardness HV5 measured in the said measurement surface in the range of +/- 5 mm (total 10 mm thickness) from the center part of the plate thickness direction of a steel plate. In the measurement of the central hardness of the steel sheet, Vickers hardness in five points and a total of 55 points is measured at least every 1 mm in the above range.

In the steel sheet according to the present embodiment, the surface layer portion hardness Hvs at room temperature is 400 or more in Vickers hardness (HV5). If the surface layer portion hardness Hvs is less than 400 as the Vickers hardness (HV5), the surface layer portion of the steel sheet is insufficient, and thus it cannot be used for applications such as construction machinery and industrial machinery. In order to improve abrasion resistance, the surface layer portion hardness Hvs at room temperature may be 440 or more, 460 or more, 480 or more or 500 or more as Vickers hardness (Hv5).

Moreover, the steel plate which concerns on this embodiment shows the very high hardness from surface layer part to plate | board thickness center part, and tensile strength is also very high. If necessary, the tensile strength TS at room temperature may be 1000 MPa or more, 1200 MPa or more, 1350 MPa or more, or 1500 MPa or more. Although the upper limit of the said tensile strength does not need to be specifically determined, It is good also as 2300 Mpa or less. In addition, a tensile strength collects a round bar test piece from the position (T / 4) which is 1/4 of plate | board thickness T from the whole thickness test piece (that is, plate-shaped test piece) or the steel plate surface, and measures it based on JISZ2241: 2011. .

The steel sheet according to the present embodiment is a steel sheet produced by hot rolling, and the sheet thickness is 40 mm or more, preferably 42 mm or more or 50 mm or more, more preferably 60 mm or more or 80 mm or more. The upper limit of the plate thickness is not particularly defined and may be 150 mm depending on the use. In consideration of the homogenization of the plate thickness direction characteristic of the steel sheet, the plate thickness may be 100 mm or less.

The manufacturing method of the steel plate which concerns on this embodiment is demonstrated. In this embodiment, the steel piece which has said chemical composition can be manufactured by a well-known method, such as a continuous casting method or an ingot-disintegration method, after melt | dissolving by a normal refining process, such as a converter and an electric furnace, and there is no restriction | limiting in particular.

In this embodiment, the steel piece obtained by casting is hot-rolled, it is cooled by water as it is, or it is air-cooled, it is then reheated and quenched, and a steel plate is manufactured. However, the steel sheet is left quenched and heat treatment such as tempering is not performed.

After the steel is melted and cast, hot rolling may be performed as it is, but the steel strip may be cooled to room temperature once, reheated to a temperature equal to or higher than Ac ₃ , and hot rolling may be performed. Ac ₃ point is the temperature which the structure of the steel became austenite by which temperature rising (the austenite transformation was completed). In order to reduce the deformation resistance, the heating temperature of hot rolling becomes like this. Preferably it is 900 degreeC or more, More preferably, it is 1000 degreeC or more. On the other hand, when the heating temperature of hot rolling is too high, since a structure may coarsen and the low-temperature toughness of a steel plate may fall, 1250 degrees C or less is preferable. More preferably, heating temperature is 1200 degrees C or less, More preferably, you may be 1150 degrees C or less.

Hot rolling is preferably terminated at a temperature of Ar ₃ point or more disclosed ferrite transformation by the temperature reduction. Ac ₃ point and Ar ₃ point can collect | require a test piece from a steel piece, and can obtain | require it from the thermal expansion behavior at the time of heating and cooling. Immediately after the hot rolling, the steel sheet is quenched to a temperature of 250 ° C. or less, or the steel sheet cooled after the hot rolling is reheated to a temperature of ₃ Ac or more, and quenched to a temperature of 250 ° C. or less.

EXAMPLE

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated more concretely by giving the Example of the steel plate which concerns on this invention. However, the present invention is not limited to the following examples from the original, and may be carried out by appropriately changing the range within a range that may be suitable for the purpose of the present invention, and all of them are included in the technical scope of the present invention.

The steel which has a chemical composition shown in Table 2 was melted, it hot-rolled after casting, it was made into the steel plate of the plate thickness shown in Table 3, and air-cooled to room temperature. Then, after heating up to the quenching temperature shown in Table 3, quenching was performed and the steel plate whose plate | board thickness is 40 mm or more was manufactured. A test piece was taken from the obtained steel sheet, and the cross section parallel to the rolling direction and the sheet thickness direction of the steel sheet was used as the test surface, and the test force was measured at room temperature based on the Vickers hardness of the surface layer portion and the sheet thickness center portion in accordance with JIS Z 2244: 2009. It measured by 49.03N (5kgf). The Vickers hardness (surface layer hardness) Hvs of the surface layer portion measures the Vickers hardness at 5 points per 25 mm and 25 points in total in the range (surface layer portion) of 1 mm to 5 mm from the surface in the sheet thickness direction of the steel sheet, and their average value ( Arithmetic mean). Vickers hardness (plate thickness center part hardness) Hvc measures the Vickers hardness in 5 points | pieces and a total of 55 points | pieces every 1 mm in the range of +/- 5 mm (total 10 mm thickness) from the center part of the plate thickness direction of a steel plate, And these average values (arithmetic mean). The hardness difference ratio (DELTA) Hv / Hvs (%) which shows the hardness difference of the surface layer part and center part of the steel plate in room temperature was obtained using the value of surface layer part hardness Hvs and sheet thickness center part hardness Hvc obtained in this way. In addition, hardness difference ratio (DELTA) Hv / Hvs (%) is represented by following formula (b).

ΔHv / Hvs (%) = 100 × (Hvs-Hvc) / Hvs... (b)

Moreover, the sample was cut out from the steel plate, and the high temperature Vickers hardness test was done at 400 degreeC with the test force as 9.807N (1 kgf) based on JISZ2225-1919. This obtained the high temperature hardness (HV1) of the said surface layer part of a steel plate. In addition, the measurement of the high temperature hardness of the surface layer part was performed similarly to the said surface layer part Vickers hardness test (room temperature) except conditions of temperature control and test force. Moreover, the full size V notch Charpy test piece of the direction parallel to a rolling direction is cut out from the position T / 4 of plate | board thickness T from the surface of a steel plate, and it is 0 degreeC based on JISZ2242: 2005. Charpy absorbed energy (vE ₀ ) was measured.

The criteria for judging each evaluation item are as follows. Surface layer hardness Hvs (HV5) and plate | board thickness center part hardness Hvc (HV5) judged that all were 400 or more from a viewpoint of abrasion resistance, and 600 or less from a viewpoint of cutting workability. The high temperature hardness (HV5) of the surface layer portion was judged to be 300 or more from the viewpoint of wear resistance at high temperature. Charpy absorption energy of 0 degreeC judged that 15J or more was favorable.

The results are shown in Table 3. No. In each of 1 to 18, each parameter of the chemical composition including the index Q and the carbon equivalent Ceq (%) and the sheet thickness T is within the scope of the present invention, and the hardness difference ratio ΔHv / Hvs of the surface layer portion and the center portion is also 15.0% or less. All of these steels are steel sheets excellent in surface layer hardness Hvs, sheet thickness center portion hardness Hvc, surface layer portion high temperature hardness, and Charpy absorbed energy of 0 ° C.

On the other hand, No. 101-115 are comparative examples, and the chemical composition containing a Q value is outside the scope of the present invention. No. 101-103 is an example in which Q value became low in relation to plate | board thickness, and hardness difference ratio (DELTA) Hv / Hvs (%) exceeded 15.0%.

No. 106 is an example in which Si content is insufficient and the high temperature hardness of the surface layer part fell. Meanwhile, No. 107 has many Si contents, and is an example with reduced toughness.

No. 104, 108, and 114 are examples in which the C content, the Mn content, and the B content are insufficient, and the surface layer portion hardness Hvs, the sheet thickness center portion hardness Hvc, and the surface layer portion have a high temperature hardness.

No. lacking Cr content 110 is an example in which toughness was also reduced by adding to the surface layer portion hardness Hvs, the plate thickness center portion hardness Hvc, and the surface layer portion high temperature hardness.

No. lacking Mo content 112 is an example in which the plate thickness center portion hardness Hvc and the surface layer portion have high temperature hardness and toughness.

No. 105 is high in C content, and it is an example in which surface layer hardness Hvs became excessively high.

No. high in Mn content 109, No. with high Cr content 111, No. with high Mo content 113 is an example of reduced toughness.

No. with excessive B content 115 is an example in which the surface layer portion hardness Hvs, the plate thickness center portion hardness Hvc, and the surface layer portion have a high temperature hardness.

In addition, in all the Examples, O content was 0.006% or less, and Sb content, Sn content, and As content were all 0.01% or less.

Thus, Comparative Example No. 1, in which at least one of the chemical composition and the Q value is outside the scope of the present invention. In 101-115, at least one of hardness difference ratio (DELTA) Hv / Hvs, surface layer part hardness Hvs, plate | board thickness center part hardness Hvc, surface layer part high temperature hardness, and toughness did not reach the evaluation criteria judged as favorable.

Claims (5)

In mass%,
C: 0.20 to 0.35%,
Si: greater than 1.00% to 2.00%,
Mn: 0.60-2.00%,
Cr: 0.10 to 2.00%,
Mo: 0.05-1.00%,
Al: 0.010-0.100%,
N: 0.0020 to 0.0100%,
B: 0.0003 to 0.0020%,
P: 0.0200% or less,
S: less than 0.0100%,
Cu: 0 to 0.500%,
Ni: 0 to 1.00%,
Nb: 0 to 0.050%,
V: 0 to 0.120%,
Ti: 0% to 0.025%
Ca: 0 to 0.050%,
Mg: 0 to 0.050%,
REM: 0 to 0.100% and
Balance: Fe and impurities,
The index Q obtained by the following formula (1) is 0.00 or more,
Carbon equivalent Ceq (%) calculated | required by following formula (2) has a chemical composition of less than 0.800%,
While the ratio of the difference between the surface layer hardness and the plate thickness center portion hardness to the surface layer hardness at room temperature is 15.0% or less, the surface layer portion hardness at room temperature is 400 or more in Vickers hardness,
Steel sheet with a plate thickness T of 40 mm or more.
Q = 0.18-1.3 (logT) + 0.75 (2.7 x [C] + [Mn] + 0.45 x [Ni] + 0.8 x [Cr] + 2 x [Mo]). (One)
Ceq (%) = [C] + [Mn] / 6 + [Si] / 24 + [Ni] / 40 + [Cr] / 5 + [Mo] / 4 + [V] / 4. (2)
The index Q of the above formula (1) is calculated by substituting the numerical value of the plate thickness T (mm) and the numerical value of the content [X] expressed by the mass% of each element X. do. The carbon equivalent Ceq (%) of the said Formula (2) substitutes and calculates the numerical value of content [X] shown by the mass% of each element X, and substitutes 0 when it does not contain element X. The method of claim 1,
The indicator Q is 0.04 or greater,
The steel plate whose said ratio is 13.0% or less. The method according to claim 1 or 2,
In mass%,
Ni: 0.05 to 1.00%
Steel plate with phosphorus chemical composition. The method according to claim 1 or 2,
In mass%,
Mn: 0.63-2.00%
Steel plate with phosphorus chemical composition. The method of claim 3,
In mass%,
Mn: 0.63-2.00%
Steel plate with phosphorus chemical composition.

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