JP6149778B2 - Steel plate with excellent wear resistance and method for producing the same - Google Patents

Description

  The present invention relates to a thick steel plate suitable for use in members that require wear resistance against rocks, sand, ores, slurry-like substances, etc., such as industrial machines, transportation and transportation equipment, and a method for producing the same.

  Used in construction, civil engineering, mining, etc., for example, industrial machines such as power shovels, bulldozers, hoppers, buckets, dump trucks, transportation of steel pipes for transporting slurries, etc. Wear occurs.

  Conventionally, increasing the hardness of steel has been known to improve its wear resistance. To date, a large amount of alloying elements has been added as a component application that requires some wear resistance. Steel materials with increased hardness have been used.

  However, it is known that if the hardness of the steel material is increased in order to improve the wear resistance, the workability is greatly reduced, and it is difficult to apply a high-hardness material as a member application that requires processing. there were.

  Therefore, a steel material that is excellent in workability while maintaining excellent wear resistance is demanded. For example, Patent Document 1 includes 0.13% to 0.18% C by mass%, Si, It contains Mn, P, S, Al, B, and N in appropriate amounts, and further Cr is 0.5% to 2.0%, Mo is 0.03% to 0.3%, and Nb is 0.03% to 0%. A steel sheet is proposed that has a content of 0.1%, a component composition that satisfies HI of 0.7 or more, Ceq of more than 0.50, and HB of 360 to 440 at 25 ° C. Yes. Here, HI = [C] +0.59 [Si] −0.58 [Mn] +0.29 [Cr] +0.39 [Mo] +2.11 ([Nb] −0.02) −0.72 [ Ti] +0.56 [V], Ceq = [C] + [Si] / 24 + [Mn] / 6 + [Ni] / 40 + [Cr] / 5 + [Mo] / 4 + [V] / 14 Is content (mass%).

  Patent Document 1 describes that according to the above technique, it is possible to improve the wear resistance at high temperatures by forming a martensitic structure of HB400 class by quenching heat treatment and further increasing the amount of dissolved Nb.

Patent Document 2 contains 0.10% to 0.45% C in mass%, contains appropriate amounts of Si, Mn, P, S, and N, and further contains 0.10% to 1.0% Ti. Containing TiC precipitates having a size of 0.5 μm or more, or composite precipitates of TiC and TiN, TiS, including 400 or more per 1 mm ² , and Ti * which can be expressed by a specific formula is 0.05% to 0% A steel sheet characterized by less than 4% has been proposed.

  Patent Document 3 contains 0.05 to 0.35% of C by mass%, contains appropriate amounts of Si, Mn, and Al, further contains 0.1 to 1.2% of Ti, and A wear-resistant steel sheet with excellent workability, characterized in that DI * expressed by a specific formula is less than 60, a ferrite phase-bainite phase is a base phase, and a hard phase is dispersed in the base phase, has been proposed. ing.

  Patent Documents 2 and 3 describe that according to the above technique, it is possible to improve wear resistance at low cost by generating precipitates mainly composed of coarse TiC during solidification.

Japanese Patent No. 4590012 Japanese Patent No. 3089882 JP 2010-222682 A

  However, since the technique described in Patent Document 1 performs a quenching process and has a martensite structure, the hardness is HB360 or higher and the hardness is high, and it is difficult to say that the workability is good. Therefore, the alloy cost increases.

  Since the techniques described in Patent Documents 2 and 3 form coarse TiC at the time of solidification, it is necessary to carry out slab surface maintenance before rolling, which increases the manufacturing cost and the high-temperature wear resistance is unknown. .

  Therefore, an object of the present invention is to provide a thick steel plate that is inexpensive, has excellent workability, and has excellent wear resistance, and a method for producing the same.

  In order to achieve the above-mentioned object, the present inventors conducted extensive studies on the influence of various factors on the wear resistance. As a result, the composition of the steel material is optimized, the value defined by the sum of the contents of the plurality of alloy elements in the component composition is set to a constant value, the area fraction of the bainite phase is 60% or more, and the island martensite in the bainite phase It is good without excessively hardening the steel material by making the steel structure with a site area fraction of 5% or more and less than 20% and the remainder being one or more of ferrite phase, pearlite, martensite phase The present inventors have found that excellent wear resistance can be achieved while maintaining excellent workability.

The present invention has been completed based on the above findings and further studies. That is, the gist of the present invention is as follows.
[1] By mass%
C: 0.200 to 0.350%,
Si: 0.05 to 0.45%,
Mn: 0.50 to 2.00%,
P: 0.020% or less,
S: 0.005% or less,
Al: 0.005 to 0.100%,
Including a CI defined by the following formula (1) satisfying 40 or more,
A composition comprising the balance Fe and inevitable impurities;
The area fraction of the bainite phase is 60% or more, and the island-like martensite in the bainite phase is 5% or more and less than 20% in the area fraction with respect to the entire structure,
A thick steel plate having excellent wear resistance, wherein the remainder has a steel structure composed of one or more of a ferrite phase, a pearlite, and a martensite phase.
CI = 60C + 8Si + 22Mn + 10 (Cu + Ni) + 14Cr + 21Mo + 15V (1)
In the formula, each alloy element has a content (% by mass). However, the content of elements not contained is zero.
[2]
Furthermore, in mass%,
Cu: 0.03-1.00%,
Ni: 0.03-2.00%,
Cr: 0.05 to 2.00%,
Mo: 0.05-1.00%,
V: 0.005-0.100%,
Nb: 0.005 to 0.100%,
Ti: 0.005 to 0.100%,
B: 0.0003 to 0.0030%,
The thick steel plate having excellent wear resistance according to [1], comprising at least one selected from the group consisting of:
[3]
Furthermore, in mass%,
REM: 0.0005 to 0.0080%,
Ca: 0.0005 to 0.0050%,
Mg: 0.0005 to 0.0050%
The thick steel plate having excellent wear resistance according to [1] or [2], comprising at least one selected from the group consisting of:
[4]
After the slab or steel slab comprising the steel composition described in any one of [1] to [3] is heated to 950 to 1250 ° C., hot rolling is performed at a temperature of Ar ₃ or higher, A method for producing a thick steel plate having excellent wear resistance, wherein accelerated cooling is performed from 400 ° C. to 650 ° C. immediately after rolling at a cooling rate of 5 ° C./sec or more.
[5]
After heating the slab or steel slab comprising the steel composition described in any one of [1] to [3] to 950 to 1250 ° C., performing hot rolling and air cooling to less than 400 ° C., A method for producing a thick steel plate having excellent wear resistance, wherein the steel plate is reheated to Ac _{3 to} 950 ° C. and immediately cooled to 400 ° C. to 650 ° C. at a cooling rate of 5 ° C./sec or more.

  ADVANTAGE OF THE INVENTION According to this invention, the abrasion-resistant steel plate which is excellent in workability and has the outstanding abrasion resistance stably can be manufactured easily and stably, and it has a remarkable industrial effect.

The figure explaining an abrasion tester.

In the present invention, the component composition and the steel structure are defined.
[Ingredient composition]
In the description,% is mass%.
C: 0.200 to 0.350%
C is an element that contributes to the formation of island martensite, and is an important element for obtaining excellent wear resistance. If it is less than 0.200%, the above-mentioned effects cannot be obtained sufficiently. On the other hand, a large content exceeding 0.350% decreases weldability and workability. For this reason, it limited to the range of 0.200 to 0.350%. In addition, Preferably it is 0.210-0.300%.

Si: 0.05 to 0.45%
Si is an effective element that acts as a deoxidizer for molten steel, and is an effective element that improves the hardenability and contributes to the formation of island martensite. In order to ensure such an effect, the content of 0.05% or more is required. On the other hand, when it contains more than 0.45%, weldability will fall. For this reason, it limited to 0.05 to 0.45% of range. In addition, Preferably it is 0.15-0.40%.

Mn: 0.50 to 2.00%
Mn is an effective element having an effect of improving the hardenability and contributing to the generation of island martensite. In order to ensure such an effect, it is necessary to contain 0.50% or more. On the other hand, if it is contained in a large amount exceeding 2.00%, the weldability is lowered, and a large amount of MnS that is the starting point of fracture during processing such as bending is generated. For this reason, it limited to 0.50 to 2.00% of range. In addition, Preferably it is 0.60 to 1.70%.

P: 0.020% or less P is desirably reduced as much as possible because it causes a decrease in toughness when contained in a large amount in steel, but it is acceptable up to 0.020%. For this reason, it was limited to 0.020% or less. In addition, since excessive reduction causes the refining cost to rise, it is desirable to set it as 0.005% or more.

S: 0.005% or less S, if contained in a large amount in steel, precipitates as MnS, causes deterioration of toughness, and becomes a starting point of fracture during processing. % Is acceptable. For this reason, it was limited to 0.005% or less. In addition, since excessive reduction leads to an increase in refining cost, it is desirable to make it 0.0005% or more.

Al: 0.005 to 0.100%
Al is an effective element that acts as a deoxidizer for molten steel. In order to acquire such an effect, 0.005% or more of content is required. If it is less than 0.005%, these effects cannot be sufficiently obtained. On the other hand, when it contains exceeding 0.100%, weldability and toughness will fall. For this reason, it limited to 0.005 to 0.100% of range. In addition, Preferably it is 0.015-0.040%.

CI = 60C + 8Si + 22Mn + 10 (Cu + Ni) + 14Cr + 21Mo + 15V ≧ 40
In the formula, each alloy element indicates the content (% by mass), and the element not included is calculated as zero.
When the CI is less than 40, the hardenability is insufficient, the above steel structure is not obtained, and good wear resistance cannot be obtained. Therefore, CI was limited to 40 or more. In addition, Preferably it is 44 or more.

  Although the above components are the basic component composition and the balance is Fe and inevitable impurities, in order to improve the characteristics, Cu, Ni, Cr, Mo, V, Nb, Ti, B, REM, Ca, and Mg are selected as selective elements. Alternatively, two or more kinds can be selected and contained.

Cu: 0.03-1.00%,
Cu is an element having an effect of improving the hardenability and contributing to the generation of island martensite. In order to acquire such an effect, it is necessary to contain 0.03% or more. On the other hand, when it contains exceeding 1.00%, hot workability will fall and manufacturing cost will also rise. For this reason, when it contains, it is preferable to limit to 0.03 to 1.00% of range. In addition, it is more preferable to limit to the range of 0.03-0.50% from a viewpoint of suppression of a fall of hot workability and cost reduction.

Ni: 0.03-2.00%,
Ni is an element that improves the hardenability and contributes to the improvement of low temperature toughness. In order to obtain such an effect, a content of 0.03% or more is required. On the other hand, the content exceeding 2.00% increases the production cost. For this reason, when it contains, it is preferable to limit to 0.03 to 2.00% of range. In addition, it is more preferable to limit to 0.03 to 0.50% of range from a viewpoint of cost reduction.

Cr: 0.05 to 2.00%,
Cr is an element that has the effect of improving hardenability and contributing to the formation of island martensite. In order to acquire such an effect, 0.05% or more of content is required. On the other hand, when it contains exceeding 2.00%, weldability will fall and manufacturing cost will rise. For this reason, when it contains, it limits to 0.05 to 2.00% of range. In addition, Preferably it is 0.07 to 1.50%, More preferably, it is 0.20 to 1.00% of range.

Mo: 0.05-1.00%,
Mo is an element having an effect of improving hardenability and contributing to the generation of island martensite. In order to acquire such an effect, 0.05% or more of content is required. On the other hand, when it contains exceeding 1.00%, weldability will fall and manufacturing cost will also rise. For this reason, when it contains, it limits to 0.05 to 1.00% of range. In addition, Preferably, it is 0.10 to 0.80%, More preferably, it is 0.20 to 0.50%.

V: 0.005-0.100%
V is an element that improves hardenability and precipitates as carbonitride to contribute to improvement of toughness through the effect of refining the structure. In order to acquire such an effect, it is necessary to contain 0.005% or more. On the other hand, if it exceeds 0.100%, the weldability is lowered. For this reason, when it contains, it limits to 0.005 to 0.100% of range.

Nb: 0.005 to 0.100%
Nb is an element that precipitates as carbonitride and contributes effectively to improving toughness through refinement of the structure. In order to acquire such an effect, 0.005% or more of content is required. On the other hand, if the content exceeds 0.100%, weldability decreases. For this reason, when it contains, it limits to 0.005 to 0.100% of range. In addition, from a viewpoint of refinement | miniaturization of a structure, it is preferable to set it as the range of 0.010-0.030%.

Ti: 0.005 to 0.100%
Ti is an element that precipitates as TiN and contributes to improvement of toughness through fixation of solute N. In order to acquire such an effect, it is necessary to contain 0.005% or more. On the other hand, when it contains exceeding 0.100%, coarse carbonitride precipitates and toughness falls. For this reason, when it contains, it limits to 0.005 to 0.100% of range. In addition, it is preferable to limit to 0.005 to 0.030% of range from a viewpoint of cost reduction.

B: 0.0003 to 0.0030%,
B is an element that contributes to improving the hardenability when contained in a small amount. In order to acquire such an effect, it is necessary to contain 0.0003% or more. On the other hand, when it contains exceeding 0.0030%, toughness will fall. For this reason, when it contains, it limits to 0.0003 to 0.0030% of range.

REM: 0.0005 to 0.0080%
REM fixes S and suppresses the production of MnS that causes toughness reduction and fracture during processing. In order to acquire such an effect, it is necessary to contain 0.0005% or more. On the other hand, if the content exceeds 0.0080%, the amount of inclusions in the steel increases, leading to a decrease in toughness. For this reason, when it contains, it limits to 0.0005 to 0.0080% of range. In addition, Preferably it is 0.0005 to 0.0020%.

Ca: 0.0005 to 0.0050%,
Ca fixes S and suppresses generation of MnS that causes toughness reduction and fracture during processing. In order to acquire such an effect, it is necessary to contain 0.0005% or more. On the other hand, if the content exceeds 0.0050%, the amount of inclusions in the steel increases, leading to a decrease in toughness. For this reason, when it contains, it limits to 0.0005 to 0.0050% of range. In addition, Preferably it is 0.0005 to 0.0030%.

Mg: 0.0005 to 0.0050%
Mg fixes S and suppresses the production of MnS that causes toughness reduction and fracture during processing. In order to acquire such an effect, it is necessary to contain 0.0005% or more. On the other hand, if the content exceeds 0.0050%, the amount of inclusions in the steel increases, leading to a decrease in toughness. For this reason, when it contains, it is preferable to limit to 0.0005 to 0.0050% of range. In addition, Preferably it is 0.0005 to 0.0040%.

[Steel structure]
Steel structure containing a bainite phase in an area fraction of 60% or more, further including island-like martensite in the bainite phase in an area fraction of 5 to 20%, with the balance being one or more of ferrite phase, pearlite and martensite phase. And By setting it as such a structure fraction, the plastic deformability of a steel plate improves and favorable workability is obtained. In addition, excellent wear resistance can be obtained without excessively increasing the hardness of the steel sheet.

Bainitic phase: 60% or more in area fraction If the fraction of bainite phase is less than 60% in area fraction, desired wear resistance and workability cannot be secured, so the area fraction is set to 60% or more. Preferably it is 80% or more.

Island-like martensite: 5% or more and less than 20% in the area fraction Island-like martensite is finely dispersed in the bainite phase and has high hardness, which contributes to improvement in wear resistance. If the fraction of island martensite is less than 5% in terms of area fraction, desired wear resistance cannot be ensured. On the other hand, if it is 20% or more, the effect of improving the wear resistance is saturated, and the workability and toughness deteriorate due to excessive increase in the hardness of the steel sheet, so the area fraction is 5% or more and less than 20%. . The island martensite is generated between the laths of the bainite phase or at the grain boundaries of the bainite phase, and is very small. Therefore, it is difficult to separate it from the bainite phase with an optical microscope. For this reason, island-like martensite is considered part of the bainite phase. That is, the area of the bainite phase includes the area of island martensite. However, the area fraction of island martensite is calculated for the entire structure.

  The balance of the steel structure is one or more of ferrite phase, pearlite and martensite phase.

Next, the manufacturing method of the thick steel plate concerning this invention is demonstrated.
When the steel material having the above-described composition is maintained at a predetermined temperature after casting, it is not cooled, or once cooled, heated, hot-rolled, and then rolled into a desired size and shape. And The method for producing the steel material is not particularly limited, but the molten steel is melted by a known melting method such as a converter, and a slab having a predetermined size is obtained by a known casting method such as a continuous casting method. preferable. It is good also as a slab by the ingot-making-bundling rolling method.

  The slab heating temperature is limited to a range of 950 to 1250 ° C. If it is less than 950 ° C., the deformation resistance is high, the rolling load becomes excessive, and the rolling efficiency is impaired. Moreover, in order to stably obtain the wear resistance characteristics, it is necessary to uniformly generate island martensite throughout the steel sheet, but if it is less than 950 ° C., C present in the microsegregation part in the steel material, Diffusion of segregating elements such as Mn is insufficient, and island martensite is preferentially generated in the segregating portion, resulting in uneven distribution. On the other hand, at a high temperature exceeding 1250 ° C., the yield decreases due to excessive scale generation and the energy consumption increases, so the heating temperature is limited to the range of 950 to 1250 ° C.

In hot rolling, the rolling finishing temperature is Ar ₃ or higher. When the rolling finishing temperature is less than Ar ₃ , ferrite is generated and a sufficient amount of bainite is not generated. Therefore, the rolling finishing temperature is Ar ₃ or higher. The Ar ₃ transformation point can be measured from a thermal expansion curve when cooling from austenite.

  After the hot rolling is finished, accelerated cooling is started. The cooling rate is 5 ° C./sec or more, and the cooling stop temperature is 400 ° C. to 650 ° C. When the cooling rate is less than 5 ° C./sec, ferrite is generated and a sufficient amount of bainite is not generated.

  When the cooling stop temperature is less than 400 ° C., the bainite transformation is completed, and thus a sufficient amount of island martensite is not generated. On the other hand, when the cooling stop temperature exceeds 650 ° C., C is consumed in the pearlite generated during the subsequent air cooling, and a sufficient amount of island martensite is not generated, so the temperature is set to 400 to 650 ° C.

After completion of hot rolling, instead of the step of performing accelerated cooling, after completion of hot rolling, the ferrite transformation or bainite transformation is allowed to cool to less than 400 ° C, and then reheated to Ac ₃ or more and 950 ° C or less, Thereafter, the accelerated cooling may be performed.

Is less than the reheat temperature Ac _3, does not occur sufficiently reverse transformation from ferrite to austenite. When the reheating temperature exceeds 950 ° C., the austenite grain size becomes coarse and adversely affects the toughness, leading to an increase in energy consumption. Therefore, the reheating temperature is set to Ac _{3 to} 950 ° C. The Ac ₃ transformation point can be measured from a thermal expansion curve when heating from ferrite to austenite.

Molten steel having the composition shown in Table 1 was melted in a vacuum melting furnace and cast into a mold to obtain a 150 kg steel ingot (slab). The obtained slab was heated and subjected to accelerated cooling after hot rolling. In some steel plates, after the hot rolling was completed, air cooling was performed, and after reheating, accelerated cooling was performed.
A test piece was collected from the obtained steel sheet and subjected to a structure observation and a wear test. The test method was as follows.
(1) Microstructure observation From a 1/4 position of the thickness of the obtained steel sheet, a specimen for microstructural observation was collected so that the observation surface had a cross section parallel to the rolling direction, and then polished to a mirror surface and etched by nital. The organization was revealed. Thereafter, three visual fields were randomly observed and photographed at a magnification of 400 times using an optical microscope, the bainite phase was visually identified, and the area ratio was calculated. Further, the same specimen for woven observation was mirror-polished again to reveal island martensite by a two-step etching method. Thereafter, 10 visual fields were observed and photographed from a portion having a bainite structure at a magnification of 2000 using a scanning electron microscope, and the area ratio of island martensite was calculated using image analysis software. In addition, the area ratio of a bainite phase and an island-like martensite is an area ratio with respect to the whole structure | tissue.
(2) Abrasion test Abrasion test piece (size: 10mm thickness x 25mm width x 75mm length) is taken from the obtained steel sheet so that the position 0.5mm from the steel sheet surface becomes the test surface (wear surface). Then, it was mounted on the wear tester shown in FIG.

  The wear test piece was attached so that the surface of the test machine rotor was perpendicular to the rotation axis of the tester rotor and the surface of 25 mm × 75 mm was in the circumferential tangent direction of the rotation circle, and then the wear material was introduced inside. As the wear material, a meteorite having an average particle diameter of 30 mm was used.

The test conditions were such that the rotor was rotated at 600 times / min and the drum was rotated at 45 times / min. The test was completed after rotating the rotor until the total number of rotations reached 10,000. After completion of the test, the weight of each test piece was measured. The difference between the weight after the test and the initial weight (= weight reduction amount) is calculated, the weight reduction amount of SS400 (JIS G3101 general structural rolled steel) is used as a reference value, and the wear resistance ratio (= (reference value) / ( The weight reduction amount of the test piece)) was calculated. The case where the wear resistance ratio was 1.5 or more was evaluated as “excellent in wear resistance”.
(3) Bending workability Based on JIS Z2248 (2006), using a steel sample (width 100 mm x length 300 mm x original thickness of steel plate; tmm), a bending radius of 2.0 t (t = plate thickness) The 180 degree bending test by the press bending method was performed under the conditions. If the sample after the bending test had no tears or other defects, the bending workability was considered good.

  Table 2 shows the results of the above test items according to the manufacturing conditions. No. In the present invention examples 1 to 15, 17, 18, and 20, the wear resistance ratio was 1.5 or more, and excellent wear resistance was confirmed. On the other hand, no. No. 16 is inferior in bending workability because the bainite fraction and the island-like martensite fraction of the steel structure do not satisfy the provisions of the present invention. Moreover, No. of the comparative example. In No. 19, the bainite fraction and the island-like martensite fraction of the steel structure do not satisfy the provisions of the present invention, and are inferior in wear resistance. No. In Nos. 21 to 23, among the steel structures, the island-like martensite fraction did not satisfy the provisions of the present invention, and the wear resistance was poor.

Claims (5)

% By mass
C: 0.200 to 0.350%,
Si: 0.05 to 0.45%,
Mn: 0.50 to 2.00%,
P: 0.020% or less,
S: 0.005% or less,
Al: 0.005 to 0.100%,
Including a CI defined by the following formula (1) satisfying 40 or more,
A composition comprising the balance Fe and inevitable impurities;
The area fraction of the bainite phase is 60% or more, and the island-like martensite in the bainite phase is 5% or more and less than 20% in the area fraction with respect to the entire structure,
A thick steel plate having excellent wear resistance, wherein the remainder has a steel structure composed of one or more of a ferrite phase, a pearlite, and a martensite phase.
CI = 60C + 8Si + 22Mn + 10 (Cu + Ni) + 14Cr + 21Mo + 15V (1)
In the formula, each alloy element has a content (% by mass). However, the content of elements not contained is zero. % By mass
C: 0.210 to 0.350%,
Si: 0.05 to 0.45%,
Mn: 0.50 to 2.00%,
P: 0.020% or less,
S: 0.005% or less,
Al: 0.005 to 0.036%,
Furthermore , Cu: 0.03-1.00%,
Ni: 0.03-2.00%,
Cr: 0.05~ 1.00%,
Mo: 0.05-1.00%,
V: 0.005-0.100%,
Nb: 0.005 to 0.100%,
Ti: 0.005 % or more and less than 0.100%,
B: 0.0003 to 0.0030%,
One or more selected from the group consisting of,
Including CI defined by the following formula (1) to satisfy 40 or more,
A composition comprising the balance Fe and inevitable impurities;
The area fraction of the bainite phase is 60% or more, and the island-like martensite in the bainite phase is 5% or more and less than 20% in the area fraction with respect to the entire structure,
A thick steel plate having excellent wear resistance, wherein the remainder has a steel structure composed of one or more of a ferrite phase, a pearlite, and a martensite phase.
CI = 60C + 8Si + 22Mn + 10 (Cu + Ni) + 14Cr + 21Mo + 15V (1)
In the formula, each alloy element has a content (% by mass). However, the content of elements not contained is zero. Furthermore, in mass%,
REM: 0.0005 to 0.0080%,
Ca: 0.0005 to 0.0050%,
Mg: 0.0005 to 0.0050%
The thick steel plate having excellent wear resistance according to claim 1, comprising at least one selected from the group consisting of: It is a manufacturing method of the thick steel plate excellent in abrasion resistance as described in any one of Claims 1 thru | or ₃ , Comprising: After heating a slab or a steel slab to 950-1250 degreeC, it complete | finishes at the temperature more than Ar3 A method for producing a thick steel plate having excellent wear resistance, characterized by performing hot rolling and performing accelerated cooling to 400 ° C. to 650 ° C. immediately after the hot rolling at a cooling rate of 5 ° C./sec or more. It is a manufacturing method of the thick steel plate excellent in abrasion resistance as described in any one of Claims 1 thru | or 3, Comprising : A slab or a steel slab is hot-rolled after heating at 950-1250 degreeC, 400 After air cooling to less than 0 ° C., reheat to Ac _{3 to} 950 ° C., and immediately after reheating, cool to 400 ° C. to 650 ° C. at a cooling rate of 5 ° C./sec or more. An excellent method for manufacturing thick steel plates.

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