JP2002256382A - Wear resistant steel sheet and production method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wear resistant steel sheet whose strength and wear resistance are stably secured and which has excellent low temperature toughness and low temperature welding crack resistance as well, and a production method therefor. SOLUTION: The steel sheet consists of steel containing, as chemical components, by mass, 0.10 to 0.30% C, 0.1 to 1.0% Si, 0.1 to 2.0% Mn, <=0.02% P and <=0.005% S and the balance substantially iron. The steel has a hardenability index H of >=1.0, a carbon equivalent Ceq of <=0.05%, Brinell hardness HB of >=360, and Charpy absorbed energy at -40 deg.C vE-40 of >=27 J; wherein, H=C×(1+0.5Si)×(1+3Mn)×(1+0.3Cu)×(1+0.5Ni)×(1+2Cr)×(1+3 Mo)×(1+1.5V)×(1+5Nb)×(1+300B), and Ceq=C+Mn/6+(Cu+Ni)/15+(Cr+Mo+V)/5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wear-resistant steel plate used for industrial machines and transport equipment, and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, steel plates for construction equipment have been required to have higher strength and higher wear resistance than ever before, especially due to the lightening of transportation equipment such as trucks, civil engineering equipment and mining equipment. ing. In particular, industrial machinery, parts, transportation equipment, etc. used in the fields of construction, civil engineering, mining (for example,
For excavators, bulldozers, hoppers, buckets, and the like, steel having excellent wear resistance is used to secure their life. In order to improve the wear resistance, it is necessary to increase the hardness of the steel plate surface,
It is preferable to have the degree or more. A member used in a particularly severe wear environment may require a surface hardness of about 400 or more Brinell hardness.

However, when the hardness is increased, there is a problem that the low-temperature toughness is deteriorated and the low-temperature weld cracking property is deteriorated due to the brittleness of the material or the increase in the amount of carbon. Considering the operation in a low temperature range of about −40 ° C., if the wear resistance is good but the low temperature toughness is low, brittle fracture occurs and seriously hinders the operation. Therefore, a wear-resistant steel sheet having a Brinell hardness of about 360 or more and excellent in low-temperature toughness has been desired.

[0004] To meet such demands, several methods have been studied. For example, Japanese Patent Application Laid-Open No. 60-243250 proposes a wear-resistant steel plate having excellent weldability. In this technique, the amount of P is specified to be 0.010% or less to improve weldability. Japanese Patent Application Laid-Open No. 63-307249 proposes a wear-resistant steel plate for welding. In this technique, the carbon equivalent is specified as 0.35 to 0.65% to improve weldability. Further, Japanese Patent Application Laid-Open No. 63-169359 proposes a wear-resistant steel plate excellent in weldability that can withstand use in cold regions. In this technique, the C content is set to 0.1 to 0.2% in order to secure weldability.

[0005]

In the technique described in JP-A-60-243250, the C content is as high as 0.3 to 0.5%, and no consideration is given to toughness. Also, since the carbon equivalent is considerably high (> 0.5%), it can be said that this steel cannot be expected very much in terms of weldability.

In the technique described in Japanese Patent Application Laid-Open No. 63-307249,
Although the carbon equivalent is specified as 0.35 to 0.65%, the C amount is 0.
It is set to a rather high value of 2 to 0.4%, and the toughness at -40 ° C is insufficient.

In the technique described in Japanese Patent Application Laid-Open No. 63-169359,
Although the C content is set to 0.1 to 0.2% in order to secure weldability, the nitrogen content needs to be limited to 0.0025% or less, which may increase the cost. In addition, since hardenability is not taken into consideration, there is a problem that, as described below, a thick steel plate having a thickness of about 20 mm or more cannot stably secure a Brinell hardness of about 360 or more.

That is, when the plate thickness is increased, the hardness may decrease from the surface layer portion to the central portion of the plate thickness, and the life as a wear-resistant member cannot be secured. In order to improve the life of the wear-resistant member, it is effective to make the hardness in the plate thickness direction uniform. However, in the field of wear-resistant steel, there is no example from such a viewpoint.

As described above, considering use in a low temperature range of about -40 ° C., not only high strength and wear resistance, but also
It is desirable that low temperature toughness be maintained. In the prior art,
It is difficult to improve low-temperature toughness and low-temperature weld cracking while ensuring high strength and wear resistance stably.

An object of the present invention is to solve these problems,
An object of the present invention is to provide a wear-resistant steel plate having excellent low-temperature toughness and low-temperature weld cracking property while stably ensuring strength and wear resistance, and a method for producing the same.

Another object of the present invention is to provide a wear-resistant steel plate having a small difference in hardness in the thickness direction and a method of manufacturing the same.

[0012]

The above object is achieved by the following invention.

(A) As a chemical component, mass%, C: 0.10 to
0.30%, Si: 0.1-1.0%, Mn: 0.1-2.0%, P: 0.02% or less, S:
0.005% or less, the balance is a steel substantially consisting of iron, the hardenability index H represented by the formula (1) is 1.0 or more, the carbon equivalent Ceq represented by the formula (2) is 0.50% or less, And Brinell hardness
HB is more than 360, Charpy absorbed energy at -40 ℃
A wear-resistant steel plate wherein vE-40 is 27 J or more.

H = C × (1 + 0.5Si) × (1 + 3Mn) × (1 + 0.3Cu) × (1 + 0.5Ni) × (1 + 2Cr) × (1 + 3Mo) × (1 + 1.5 (V) × (1 + 5Nb) × (1 + 300B) (1) Ceq = C + Mn / 6 + (Cu + Ni) / 15 + (Cr + Mo + V) / 5 (2) It represents the content (mass%) of each element.

(B) The chemical composition of the steel is mass%, and Cu:
0.1-1.0%, Ni: 0.1-2.0%, Cr: 0.1-1.0%, Mo: 0.1-2.0
%, Nb: 0.005 to 0.1%, V: 0.01 to 0.5%, Ti: 0.005 to 0.05%,
B: The wear-resistant steel sheet according to (a), comprising one or more selected from 0.0005 to 0.0025%.

(C) C: 0.15% by mass as a chemical component
~ 0.30%, Si: 0.1 ~ 1.0%, Mn: 0.1 ~ 2.0%, P: 0.02% or less,
S: contains 0.005% or less, the balance is steel substantially consisting of iron, the hardenability index H shown by the formula (1) is 1.2 or more, the formula (2)
A wear-resistant steel sheet characterized by having a carbon equivalent Ceq of 0.50% or less, a Brinell hardness HB of 400 or more, and a Charpy absorbed energy vE-40 at -40 ° C of 27 J or more.

H = C × (1 + 0.5Si) × (1 + 3Mn) × (1 + 0.3Cu) × (1 + 0.5Ni) × (1 + 2Cr) × (1 + 3Mo) × (1 + 1.5 (V) × (1 + 5Nb) × (1 + 300B) (1) Ceq = C + Mn / 6 + (Cu + Ni) / 15 + (Cr + Mo + V) / 5 (2) Indicates the content (mass%) of each element.

[0018] In the wear-resistant steel sheet described in (d) and (c), the chemical component is mass% in addition to the described chemical component.
In, Cu: 0.1-1.0%, Ni: 0.1-2.0%, Cr: 0.1-1.0%, Mo:
0.1-2.0%, Nb: 0.005-0.1%, V: 0.01-0.5%, Ti: 0.005
A wear-resistant steel sheet characterized by containing at least one of 0.05% to 0.05% and B: 0.0005% to 0.0025%.

A method for producing a wear-resistant steel sheet, comprising hot rolling a steel having the chemical composition described in (e), (c) or (d), and then quenching the steel at a temperature of at least the Ar3 point.

(F) The steel having the chemical composition described in any of (a) to (d) is heated to 950 to 1250 ° C.
A method for producing a wear-resistant steel plate, comprising hot rolling and quenching at a rolling reduction of 30% or more at 00 ° C or less.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention has been made based on the knowledge obtained through intensive studies to provide a wear-resistant steel plate having both weldability and toughness. It is a carbon equivalent
Adjusting the hardenability index H to a predetermined value instead of suppressing Ceq to a low value is effective in ensuring both weldability and toughness while securing hardness and wear resistance.

Hereinafter, the reasons for limiting the chemical components of the present invention will be described. In the following description, all units shown in% are mass
%.

C: 0.10 to 0.30% C is an important element for increasing the hardness of steel.
0.10% or more is required to ensure hardenability. However, when C is added in a large amount exceeding 0.30%, weldability, toughness, and workability are deteriorated. Therefore, the amount of C is 0.10 ~
It was specified as 0.30%. When the Brinell hardness HB is 400 or more, C is preferably 0.15% or more.

Si: 0.1-1.0% Si is an effective element as a deoxidizing element, and it is necessary to add 0.1% or more. In addition, although it is an element effective for solid solution strengthening, if the addition amount exceeds 1.0%, problems such as a decrease in ductility and toughness and an increase in inclusions arise. Therefore, the amount of Si is defined as 0.1 to 1.0%.

Mn: 0.1 to 2.0% Mn is an effective element from the viewpoint of ensuring hardenability,
The above addition is necessary. On the other hand, if added in excess of 2.0%, the weldability will deteriorate. For this reason, the amount of Mn was specified to be 0.1 to 2.0%.

P: not more than 0.02% P is preferably an impurity element in a small amount. If P is contained in a large amount exceeding 0.02%, toughness is deteriorated. Therefore, the P content was specified to be 0.02% or less.

S: 0.005% or less S is preferably an impurity element and a small amount is preferable. If the content of S exceeds 0.005%, the toughness is deteriorated. Therefore, the amount of S is 0.00
It is specified as 5% or less.

Hereinafter, in the present invention, one or more of the following elements may be contained as necessary. Hereinafter, the reasons for limiting these additional elements will be described.

Cu: 0.1-1.5% Cu is an element that enhances hardenability, but if it is less than 0.1%, this effect cannot be exerted. On the other hand, if the addition exceeds 2.0%, the hot workability decreases and the alloy cost also increases. Therefore, when adding Cu, it is made into the range of 0.1 to 2.0%.

Ni: 0.1-2.0% Ni is an element that enhances hardenability and improves low-temperature toughness. However, if it is less than 0.1%, this effect cannot be exerted. On the other hand, if the addition exceeds 2.0%, the alloy cost increases. Therefore, when Ni is added, the content is in the range of 0.1 to 2.0%.

Cr: 0.1-1.5% Cr is an element that enhances the hardenability, but if it is less than 0.1%, this effect cannot be exerted. On the other hand, if the addition exceeds 1.5%, the weldability deteriorates and the alloy cost increases. Therefore, when Cr is added, the content is in the range of 0.1 to 1.5%.

Mo: 0.1-2.0% Mo is an element that enhances the hardenability, but if it is less than 0.1%, this effect cannot be exerted. On the other hand, when the addition exceeds 2.0%, the weldability is deteriorated and the alloy cost is increased. Therefore, when Mo is added, the content is in the range of 0.1 to 2.0%. Particularly preferably, the content is 0.1 to 1.0%.

V: 0.01 to 0.5% V is an element effective for precipitation hardening and has an effect of increasing the hardness of steel. This effect is not exhibited when the content is less than 0.01%, and the weldability is deteriorated when the content exceeds 0.5%. Therefore, when V is added, the content is in the range of 0.01 to 0.5%.

Nb: 0.005 to 0.1% Nb is an element effective for precipitation strengthening, has the effect of increasing the hardness of steel, and also has the effect of improving the toughness by making the structure finer. These effects are not exhibited at less than 0.005%, and when added over 0.1%, the weldability deteriorates.
Therefore, when Nb is added, the content is in the range of 0.005 to 0.1%.

Ti: 0.005 to 0.05% Ti is effective in improving the toughness and fixing hardenability by fixing solid solution N harmful to the toughness as TiN. This effect is not exhibited at less than 0.005%, and toughness is rather deteriorated at an addition of more than 0.05%. Therefore, Ti
Is added in the range of 0.005 to 0.05%.

B: 0.0005 to 0.0025% B is an element that enhances the hardenability by adding a small amount, but 0.000 to 0.0025%.
If it is less than 5%, this effect cannot be exerted. on the other hand,
If the addition exceeds 0.0025%, the toughness decreases. Therefore, B
Is added in the range of 0.0005 to 0.0025%.

After setting the chemical components in the above range, the hardenability index is defined in the following range.

Hardenability index H: 1.0 or more The hardenability index H is represented by the following formula (1) and is related to the structure after quenching, and as a result, has a great influence on the hardness of steel. If the quenchability index H is less than 1.0, the structure does not become a completely quenched structure, or even if the surface structure is a completely quenched structure, if it is a completely quenched structure from the surface layer to the center of the sheet thickness. And the hardness is reduced to a Brinell hardness of less than 360. Therefore, the hardenability index H is specified to be 1.0 or more. When Brinell hardness is 400 or more, hardenability index H
Is preferably set to 1.2 or more.

H = C × (1 + 0.5Si) × (1 + 3Mn) × (1 + 0.3Cu) × (1 + 0.5Ni) × (1 + 2Cr) × (1 + 3Mo) × (1 + 1.5 V) × (1 + 5Nb) × (1 + 300B) …… (1) Carbon equivalent Ceq: 0.50% or less Carbon equivalent Ceq is expressed by the following equation (2), and has a significant effect on toughness and weldability. give. If the carbon equivalent Ceq exceeds 0.50%, the predetermined low-temperature toughness cannot be obtained, and the weldability also deteriorates. Therefore, the carbon equivalent Ceq is set to 0.50% or less.

Ceq = C + Mn / 6 + (Cu + Ni) / 15 + (Cr + Mo + V) / 5 (2) In practicing the invention, the chemical components may be adjusted as described above. However, the characteristics of some of the chemical components can be improved by the following.

As for the amount of C, when the amount of addition is too large, it approaches the upper limit of Ceq, and other alloying elements such as Mn cannot be sufficiently added. Therefore, C is preferably set to 0.25% or less.

With respect to Nb, if the amount of Nb is too large, the effect of refining the structure is reduced, and improvement in toughness may not be expected. Therefore, it is preferable that the addition amount of Nb be 0.05% or less.

When Cu, Ni, Cr, Mo, and V are added, they are 0.5%, 1.0%, 1.0%, and 0.5%, respectively, in order to secure hardenability and avoid an increase in alloy cost. , 0.1%
It is preferable to set the following.

FIG. 1 shows the effect of carbon equivalent Ceq on toughness. As shown in FIG. 1, the carbon equivalent Ceq is 0.45%
When the temperature exceeds 40 ° C., the absorption energy vE-40 at −40 ° C. is remarkably reduced, and when Ceq exceeds 0.50%, vE−40 ≧ 27J cannot be stably secured. From this, it is necessary to make the carbon equivalent Ceq at least 0.50% or less, but to obtain vE-40 ≧ 27J stably and obtain higher toughness, the carbon equivalent Ceq is required.
Is preferably set to 0.45% or less.

Further, the weldability was determined by a y-type welding crack test in covered arc welding in accordance with JIS standard Z 3153. As a result, it was also found that when the carbon equivalent Ceq exceeds 0.50%, welding cracks are likely to occur.

FIG. 2 shows the effect of the hardenability index H on the hardness after quenching. As shown in FIG. 2, when the hardenability index H is 1.0 or more, the surface hardness (Brinell hardness) is 36.
0 or more, when the hardenability index H is 1.2 or more, the surface hardness (Brinell hardness) is 400 or more, but when H is less than 1.0, the structure does not become a complete hardened structure, the hardness is large descend. On the other hand, when the sheet thickness is 30 mm or more, if the quenchability index H is less than 1.5, even if the surface hardness of the steel sheet is HB360 or more, the structure at the center of the sheet thickness does not become a complete quenched structure, May be greatly reduced. Therefore,
When it is 30 mm or more, it is preferable to set the hardenability index H to 1.5 or more. The thickness of the steel plate is 30mm or more, and the hardness of the steel plate surface
In the case where HB is 400 or more, it is preferable that H is 2.0 or more in order to completely harden the structure up to the structure at the center of the sheet thickness. The case where the plate thickness is 30 mm or more will be described later because the rolling reduction during the production of the steel plate is also involved.

Summarizing such findings, in order to provide a wear-resistant steel sheet excellent in both weldability and toughness as-quenched, at least the carbon equivalent Ceq should be 0.50% or less, and the hardenability index
H must be 1.0 or more, and Brinell hardness
In order to stably secure more than 400 properties, carbon equivalent Ceq
Is set to 0.45% or less, and the hardenability index H is set to 2.0 or more.

A steel plate having the above chemical composition is used to manufacture a wear-resistant steel plate.

In the present invention, the steel having the above-mentioned chemical components is hot-rolled, whereby the coarse structure as cast is refined to improve the toughness. The hot rolling may be performed under normal manufacturing conditions, and the slab may be heated to a temperature at which rolling can be performed, and then rolled to a target thickness.

The hardened steel sheet after rolling can be adjusted in hardness and low-temperature toughness to the target ranges by quenching if it is a chemical component of the present invention.

In the hot rolling, if the heating temperature is too high, the structure grains become coarse and the toughness is deteriorated, and a flaw may occur on the surface of the steel sheet. Therefore, the heating temperature is desirably 1250 ° C. or less. On the other hand, if the heating temperature is too low, in the case of direct quenching, the quenching start temperature decreases, and the desired performance may not be obtained.Therefore, the temperature is set so that quenching can be started from at least the Ar3 point or higher. There is a need to. If the heating temperature is low, the structure grains may be mixed and the toughness may be deteriorated.

In the hot rolling, an effective reduction is applied in the vicinity of the recrystallization temperature of austenite, whereby
Hardness and toughness can be increased from the surface layer of the steel sheet to the central part of the sheet thickness. In order to obtain the effect, it is desirable to perform hot rolling at a temperature of 900 ° C. or less so that the rolling reduction is 15% or more.

Regarding the quenching, after completion of hot rolling, the steel sheet may be quenched from a temperature of Ar3 point or higher without leaving it to cool, or a steel sheet cooled to a temperature of Ar1 point or lower may be cooled to Ar3 point.
It may be quenched by reheating to a temperature above the point. In the case of quenching after reheating, if the reheating temperature is too high, the structure of the steel sheet becomes coarse and the toughness may be deteriorated. Therefore, the reheating temperature is desirably 1150 ° C or lower. Further, if necessary, the cooling can be stopped at a temperature equal to or lower than the Ar3 point during quenching. The structure after cooling is preferably mainly composed of martensite.

For example, a steel having the above chemical components, having a hardenability index H represented by the formula (1) of 1.2 or more and a carbon equivalent Ceq represented by the formula (2) of 0.50% or less is hot-rolled. Rolled, then quenched, Brinell hardness HB more than 400, -40 ℃
Abrasion-resistant steel sheets having a Charpy absorbed energy vE-40 of 27 J or more can be manufactured.

Next, a description will be given of a case of manufacturing a thick steel plate in which hardenability is a problem. FIG. 3 shows that the wear-resistant steel of the present invention was heated to 1200 ° C.
Brinell hardness H with respect to reduction ratio and quenching index H when hot-rolled at 5% to produce a steel plate with a thickness of 30 mm or more
4 shows the relationship between B and ΔHV (difference in Vickers hardness between the surface layer part of the steel sheet and the center part of the sheet thickness). The wear-resistant steel plate of the present invention has a thickness of 20 mm.
To the extent it can be produced using the above method without any problem, but if the thickness is 30 mm or more, it is difficult to burn to the center of the thickness if the rolling reduction at 900 ° C or less is low, and the steel sheet surface and steel sheet The difference in hardness at the center of the plate thickness increases. 900 ℃
In the case where the reduction ratio is high in the following, the martensitic transformation in the central part of the sheet thickness is promoted by the strain caused by the reduction, and the difference in hardness between the steel sheet surface and the central part of the sheet thickness becomes small.

According to FIG. 3, the rolling reduction during hot rolling is 30%.
If it is above, quenching index is H1.0 or more and Brinell hardness 36
A wear-resistant steel plate having a quenching index H of 1.2 or more and a Brinell hardness of 400 or more can be obtained. Further, ΔHV, which is the difference between Vickers hardness between the surface layer portion of the steel sheet and the central portion of the thickness, is 50 or less, and the hardness is stably secured up to the central portion of the thickness.
Therefore, steel having the chemical composition of the present invention can be used at 950 to 1250.
It can be seen that the wear-resistant steel sheet of the present invention can be manufactured regardless of the sheet thickness by heating to 900 ° C., hot rolling at 900 ° C. or lower with a draft of 30% or more, and quenching.

According to FIG. 3, the rolling reduction during hot rolling is
If it is less than 30%, even if the quenchability index H is 1.0 or more, ΔHV exceeds 50, and the hardness at the center of the sheet thickness may be reduced. However, even when the rolling reduction during hot rolling is less than 30%, if the quenching index H is 1.5 or more, the Brinell hardness HB is 360 or more and ΔHV is 50 or less, and the quenching index H is 2.0
It can be seen that a wear-resistant steel plate having a Brinell hardness of 400 or more and ΔHV of 50 or less can be obtained if the above is satisfied. Therefore, it has the chemical component of the present invention, and the hardenability index H is
Heating steel of 1.5 or more to 950 to 1250 ° C, hot rolling to a thickness of 30mm or more with a rolling reduction of less than 30% at 900 ° C or less, and quenching to achieve a Brinell hardness of 360 or more in the thickness direction Wear-resistant steel plate with uniform hardness and hardenability index H of 2.0
The above steel is heated to 950 to 1250 ° C, hot rolled to a thickness of 30mm or more with a rolling reduction of less than 30% at 900 ° C or less, and hardened in the thickness direction with a Brinell hardness of 400 or more by quenching. It is possible to manufacture a wear-resistant steel plate having a uniform thickness.

Therefore, when the quenchability index H ≧ 1.5, HB ≧ 360 regardless of the rolling reduction, and the hardness in the thickness direction can be made uniform. In addition, the hardenability index H ≧
In the case of 2.0, HB ≧ 400 irrespective of the rolling reduction, and the hardness in the thickness direction can be made uniform. However, a higher rolling reduction is preferable in that the difference in hardness between the central part of the sheet thickness and the surface layer part is small, and even when the sheet thickness is less than 30 mm, 900 is preferable.
When the rolling reduction at 30 ° C. or less is 30% or more, the difference in hardness between the central portion of the plate thickness and the surface layer portion is reduced, which is more preferable.

[0059]

EXAMPLES (Example 1) Steel having the composition shown in Table 1
A to Q steel slabs were heated to 1150 ° C, hot-rolled to a thickness of 9 to 50mm at a rolling reduction of 20% at 900 ° C or lower, and then directly quenched, or allowed to cool and then reheated and quenched. . Steel A to K,
M and O are steels of the present invention, and steels L, N, P and Q are comparative steels.

[0060]

[Table 1]

With respect to the obtained steel sheet, hardness, low-temperature toughness and weldability were examined as characteristic values. Surface hardness is JIS standard Z
In accordance with 2243, using an average value of five points randomly selected and measured on the surface of the steel plate from which black scale was removed, HB 360 or more was regarded as acceptable, and HB 400 or more was regarded as a particularly preferable range. The hardness in the thickness direction was evaluated by Vickers hardness HV in accordance with JIS standard Z2244. Using the average value of Vickers hardness HV at each of the five points measured at 2 mm below the steel sheet surface and at the center of the sheet thickness, the difference in hardness between the surface layer and the center of the sheet thickness ΔHV ≤ 50 was calculated as the hardness in the sheet thickness direction. The steel sheet was evaluated as having a small difference.

The low temperature toughness is -40 in accordance with JIS standard Z2242.
Measure the Charpy-Shock absorption energy at ℃, vE-40
≧ 27J was accepted. The weldability was evaluated based on the presence or absence of cracks in a y-type weld crack test at a preheating temperature of 125 ° C. in accordance with JIS standard Z3157. The obtained characteristic values are shown in Table 2 together with the production method.

[0063]

[Table 2]

As shown in Table 2, the steel of the present invention has a sufficient low-temperature toughness and a good weld cracking property, as well as a high surface hardness and a center thickness in a plate thickness effective as a wear-resistant steel plate. .

On the other hand, the comparative steel L had a C content outside the range of the present invention, and did not have good weld cracking properties. The comparative steel N has a carbon equivalent Ceq outside the range of the present invention, and does not have sufficient low-temperature toughness and good weld cracking properties. Comparative steel
As for P and Q, the P amount and the S amount respectively exceed the range of the present invention, and sufficient low-temperature toughness has not been obtained.

The steel O of the present invention has a chemical composition within the range of the present invention, and has a Brinell hardness HB of 400 or more, but a plate thickness of 30 mm.
On the other hand, the quenchability index H was less than 1.5, the hardness decreased at the center of the sheet thickness, and ΔHV> 50. Therefore, when the plate thickness is large, it is preferable to adjust the hardenability index H to 1.5 or more in order to obtain sufficient hardness at the plate thickness central portion.

(Example 2) Steel slabs of the steels A to Q having the component compositions shown in Table 3 were prepared by using the production methods shown in Table 4 to obtain sheet thicknesses of 9 to 5 mm.
After hot rolling to 0 mm, it was directly quenched to produce No. 1 to No. 17 steel plates. Steels A to K are steels of the present invention, and steels L to Q are comparative steels.

[0068]

[Table 3]

With respect to the obtained steel sheet, hardness, low-temperature toughness, and weldability were examined as characteristic values. Surface hardness is JIS standard Z
According to 2243, the average value of five points randomly selected and measured on the surface of the steel sheet from which the black scale was removed was used, and an HB of 360 or more was judged as acceptable. The hardness in the thickness direction was evaluated by Vickers hardness HV in accordance with JIS standard Z2244. Using the average value of Vickers hardness HV at each of the five points measured at 2 mm below the steel sheet surface and at the center of the sheet thickness, the difference in hardness between the surface layer and the center of the sheet thickness ΔHV ≤ 50 was calculated as the hardness in the sheet thickness direction. The steel sheet was evaluated as having a small difference.

The low temperature toughness is -40 in accordance with JIS standard Z2242.
Measure the Charpy-Shock absorption energy at ℃, vE-40
≧ 27J was accepted. Weldability is evaluated based on low-temperature cracking resistance of welding, conforming to JIS standard Z3157, with a preheating temperature of 125 ° C.
Evaluation was made based on the presence or absence of cracks in a mold welding crack test. Table 4 also shows the obtained characteristic values.

[0071]

[Table 4]

As shown in Table 4, the steel sheets of the present invention Nos. 1 to 5 and 7 to 11 have a high surface hardness effective as a wear-resistant steel sheet, have a uniform hardness in the thickness direction, and have a sufficient hardness. Low temperature toughness,
And has good weld cracking properties.

On the other hand, the No. 6 steel sheet has a heating temperature of 12
The temperature is higher than 50 ° C, and the low-temperature toughness is deteriorated due to coarsening of the grains. Comparative steel L had a C content outside the range of the present invention, and No. 12 steel sheet did not have good low-temperature toughness and weld cracking properties.
Comparative steel M has a low C content, and No. 13 steel sheet does not have a hardness higher than HB360. The comparative steel N has a carbon equivalent Ceq outside the range of the present invention, and the No. 14 steel sheet does not have sufficient low-temperature toughness. In Comparative Steels P and Q, the P content and the S content respectively exceeded the range of the present invention, and the steel sheets of Nos. 16 and 17 did not have sufficient low-temperature toughness.

Comparative steel O has an H of less than 1.0 and the chemical composition is outside the scope of the present invention. No.15 steel sheet has Brinell hardness H
B is 360 or more, but since the hardenability is low, the hardness is reduced at the central portion of the sheet thickness, and ΔHV> 50.

[0075]

The present invention suppresses the carbon equivalent Ceq of wear-resistant steel sheets to a low level, and has a hardenability index H related to the structure after quenching.
Is adjusted to a predetermined value, it is possible to secure the surface hardness and the hardness at the center of the plate thickness, and to improve the low-temperature toughness and low-temperature weld cracking. Further, a wear-resistant steel plate having a small difference in hardness in the thickness direction can be obtained. As a result, it is possible to obtain a steel material such as a thick steel plate which has excellent wear resistance, low-temperature toughness, and weld cracking resistance, and can withstand use in a low-temperature region, and has an effect of enabling use in a low-temperature region such as a machine part. is there.

[Brief description of the drawings]

FIG. 1 is a graph showing the effect of carbon equivalent Ceq on toughness.

FIG. 2 is a view showing the influence of a hardenability index H on hardness after quenching.

FIG. 3 is a graph showing a relationship between HB and ΔHV with respect to a reduction ratio and a hardenability index H.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Takashi Abe Inventor 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. F-term (reference) 4K032 AA02 AA05 AA11 AA14 AA16 AA19 AA20 AA22 AA23 AA24 AA27 AA29 AA31 AA35 AA36 BA01 CA01 CA02 CA03 CB01 CB02

Claims (6)

[Claims] Claims: 1. Mass% as a chemical component, C: 0.10 to 0.30
%, Si: 0.1 to 1.0%, Mn: 0.1 to 2.0%, P: 0.02% or less, S: 0.00
5% or less, the balance is steel substantially consisting of iron,
The hardenability index H represented by the formula (1) is 1.0 or more, the carbon equivalent Ceq represented by the formula (2) is 0.50% or less, and the Brinell hardness HB is
Above 360, Charpy absorbed energy at -40 ℃ vE-4
A wear-resistant steel sheet wherein 0 is 27 J or more. H = C × (1 + 0.5Si) × (1 + 3Mn) × (1 + 0.3Cu) × (1 + 0.5Ni) × (1 + 2Cr) × (1 + 3Mo) × (1 + 1.5V) × (1 + 5Nb) × (1 + 300B) (1) Ceq = C + Mn / 6 + (Cu + Ni) / 15 + (Cr + Mo + V) / 5 (2) Indicates the content (mass%). 2. The chemical composition of steel is mass%, and further, Cu: 0.1
~ 1.0%, Ni: 0.1 ~ 2.0%, Cr: 0.1 ~ 1.0%, Mo: 0.1 ~ 2.0%,
Nb: 0.005 to 0.1%, V: 0.01 to 0.5%, Ti: 0.005 to 0.05%, B:
The wear-resistant steel sheet according to claim 1, comprising one or more selected from 0.0005 to 0.0025%. 3. The chemical component as mass%, C: 0.15 to 0.30
%, Si: 0.1 to 1.0%, Mn: 0.1 to 2.0%, P: 0.02% or less, S: 0.00
5% or less, the balance is steel substantially consisting of iron,
The hardenability index H represented by the formula (1) is 1.2 or more, the carbon equivalent Ceq represented by the formula (2) is 0.50% or less, and the Brinell hardness HB is
Charpy absorbed energy vE-4 at -40 ° C over 400
A wear-resistant steel sheet wherein 0 is 27 J or more. H = C × (1 + 0.5Si) × (1 + 3Mn) × (1 + 0.3Cu) × (1 + 0.5Ni) × (1 + 2Cr) × (1 + 3Mo) × (1 + 1.5V) × (1 + 5Nb) × (1 + 300B) (1) Ceq = C + Mn / 6 + (Cu + Ni) / 15 + (Cr + Mo + V) / 5 (2) Indicates the content (mass%). 4. The wear-resistant steel sheet according to claim 3, wherein the chemical component is mass% in addition to the described chemical component, and Cu:
1-1.0%, Ni: 0.1-2.0%, Cr: 0.1-1.0%, Mo: 0.1-2.0
%, Nb: 0.005 to 0.1%, V: 0.01 to 0.5%, Ti: 0.005 to 0.05%,
B: A wear-resistant steel sheet containing one or more of 0.0005 to 0.0025%. 5. A method for producing a wear-resistant steel sheet, comprising hot rolling a steel having the chemical composition according to claim 3 or 4, and then quenching the steel at a temperature of at least the Ar3 point. 6. The steel having the chemical composition according to claim 1 is heated to 950 to 1250 ° C.
A method for producing a wear-resistant steel sheet, comprising hot rolling and quenching with a rolling reduction at 30 ° C. or less at 30% or more.