KR20120071614A - Thick plate having excellent wear resistant and low-temperature toughness, and method for manufacturing the same - Google Patents

Abstract

PURPOSE: A wear-resistant thick plate with excellent low-temperature toughness for very thick articles and a manufacturing method thereof are provided to secure a martensite structure of 80vol.% or more in the center of a steel plate through reheating and quenching processes, thereby obtaining high hardness. CONSTITUTION: A wear-resistant thick plate with excellent low-temperature toughness for very thick articles comprises C of 0.19-0.30wt.%, Si of 0.15-0.3wt.%, Mn of 0.5-2.0wt.%, Cr of 0.1-1.5wt.%, Mo of 0.1-0.5wt.%, Ni of 0.1-0.5wt.%, V of 0.01-0.2wt.%, B of 0.0005-0.0050wt.%, Sol. Al of 0.005-0.1wt.%, P of 0.015wt.% or less, S of 0.010wt.% or less, one or more selected from the group consisting of Cu of 0.1-1.0wt.%, Ti of 0.01-0.03wt.%, and Nb of 0.01-0.05wt.%, and Fe and inevitable impurities of the remaining amount. The AGS(Austenite Grain Size) of the thick plate is average 30micron meters or less and 7 or greater in the standard of ASTM(American Society for Testing and Materials) E112. The matrix microstructure of the thick plate has 80vol.% of martensite including micro carbide/nitride.

Description

Thick Plate Having Excellent Wear Resistant And Low-Temperature Toughness, And Method For Manufacturing The Same}

The present invention relates to a thick steel plate for wear resistance and a method of manufacturing the same, which are used in fork cranes, bulldozers, excavators and grinders, and more particularly, to ultra-thick materials having excellent low-temperature toughness through alloy design, application of controlled rolling and accelerated cooling It relates to a thick steel sheet for wear resistance and a method of manufacturing the same.

In the case of heavy equipment used in many industries such as construction, civil engineering, mining, and cement industry, abrasion wear is seriously required, and thus, materials that exhibit wear resistance are required.

In addition, the recent increase in the amount of wear during use as the size of the heavy equipment is increased, the demand for the application of the ultra-thick wear-resistant steel for the extension of the service life of the equipment is increasing, along with the severe use of the environment for the purpose of use In addition to strength, hardness, and wear resistance, excellent low temperature impact toughness properties are required.

In general, the wear resistance is improved as the hardness is increased, so the material applied to the forklift, bulldozer, excavator, and rock drill is required to have a hardness value of 360HB or more based on Brinell hardness.

In order to obtain such high hardness, a method of quenching after reheating to a temperature of Ac ₃ or more after rolling is generally widely used.

In this regard, Japanese Patent Laid-Open No. 2-179842, Japanese Patent Laid-Open No. 8-41535, and Japanese Patent Laid-Open No. 61-166954 disclose that surface hardness is increased by adding a high C content and a large amount of hardening enhancement elements such as Cr and Mo. A method is disclosed.

However, in order to manufacture the ultra-thick steel sheet, it is required to add more hardenable elements in the center of the steel sheet to secure the hardenability, and as the amount of C and the hardenable alloy is added in large amounts, the manufacturing cost increases and the weldability and low temperature toughness are increased. There is a problem of this deterioration.

In addition, in recent years, as the use environment of heavy equipment becomes severe, the requirements of low temperature impact toughness become strict.

As a method for satisfying such low temperature impact toughness requirements, Japanese Patent Application Laid-Open No. 10-102185 et al. Provides a method for imparting toughness of a steel sheet by removing residual stress of the steel sheet through low temperature consideration (about 200 ° C. to 550 ° C.) after reheating quenching. Is disclosed.

However, this method has a problem in that the productivity is drastically decreased due to the time required for raising and lowering the temperature of the heat treatment furnace in the field application, and also in the case of the sour processing at an excessively high temperature because the optimum consideration conditions are not applied. The hardness and abrasion resistance are reduced, and when the soaking temperature is too low or the soaking time is not sufficient, it is difficult to derive optimum solubility conditions, such as failure to remove the residual stress and the toughness.

In addition, Japanese Patent Application Laid-Open No. 2002-20837 discloses an example of a method of securing low temperature toughness by adjusting a manufacturing method other than alloy composition control. In this method, the re-rolling is performed by reheating to austenite temperature after rolling and performing re-rolling. Although a method of improving toughness by miniaturizing austenite grains has been disclosed by applying the present invention, there is a problem in that it is difficult to apply a method of reheat rolling in the field application.

It is an object of the present invention to provide a thick steel plate for extremely thick wear resistance and a method of manufacturing the same having excellent wear resistance with respect to the entire thickness and low temperature toughness.

According to an aspect of the present invention, in weight%, C: 0.19 to 0.30%, Si: 0.15 to 0.3%, Mn: 0.5 to 2.0%, Cr: 0.1 to 1.5%, Mo: 0.1 to 0.5%, Ni: 0.1 0.5 wt%, V: 0.01-0.2 wt%, B: 0.0005-0.0050%, Sol.Al:0.005-0.1%, P: 0.015% or less, and S: 0.010% or less, and further Cu: 0.1 It includes one or two or more selected from the group consisting of ~ 1.0wt%, Ti: 0.01 ~ 0.03% and Nb: 0.01 ~ 0.05%, the remainder is composed of inevitable impurities and Fe, H value [H value = 2 (0.024C) ^1/2 ⅹ (Si + 1) ⅹ (3.5Mn + 1) ⅹ (2Cr + 1) ⅹ (0.5Ni + 1) ⅹ (3.0Mo + 1) ⅹ (1.8V + 1) ⅹ1.3 ] Is at least 120; In addition, the primary austenite grain size (AGS) is 7 or more according to ASTM E112, and the average is 30 μm or less, and the matrix microstructure includes more than 80% by volume of martensite containing fine carbon / nitride therein and has a total thickness hardness. A thick steel plate for wear resistance of extreme thick products having a low temperature toughness of 360 HB or more as Brinell hardness value is provided.

The matrix microstructure may be composed of martensite tissue of 80% by volume or more and bainite tissue of 20% by volume or less.

The carbon / nitride is 100 nm or less fine M ₃ X, M ₂ X and MX [M = Fe, Cr, Mo, Ti, Nb; X = C, N] It may be one kind or two or more kinds of carbon / nitride.

According to another aspect of the present invention, in weight%, C: 0.19 to 0.30%, Si: 0.15 to 0.3%, Mn: 0.5 to 2.0%, Cr: 0.1 to 1.5%, Mo: 0.1 to 0.5%, Ni: 0.1 0.5 wt%, V: 0.01 to 0.2 wt%, B: 0.0005 to 0.0050%, Sol.Al: 0.005 to 0.1%, P: 0.015% or less, S: 0.010% or less, and further Cu: 0.1 to 1.0 wt%, Ti: 0.01 to 0.03% and Nb: 0.01 to 0.05%, including one or two or more selected from the group consisting of the remainder being composed of inevitable impurities and Fe; H value [H value = 2 (0.024C) ^1/2 ⅹ (Si + 1) ⅹ (3.5Mn + 1) ⅹ (2Cr + 1) ⅹ (0.5Ni + 1) ⅹ (3.0Mo + 1) ⅹ ( 1.8V + 1) ⅹ1.3] is 120 or more heated slab to a temperature of 1100 ℃ ~ 1250 ℃, 40% or more cumulative rolling at a temperature between Tnr ~ Ar ₃ After the hot rolling over Ar ₃ , Accelerated cooling is performed at a cooling rate of 5 ℃ / s or more at the temperature of 400 ℃ or lower, and then reheated to 880 ℃ ~ 930 ℃ and maintained for 1.6t + 10 ~ 30 minutes (t is the thickness of steel). Next, there is provided a method for producing a thick steel plate for wear resistance of ultra-thick material excellent in low temperature toughness of cooling to a temperature of less than 300 ℃ at a cooling rate of 10 ℃ / s or more in the center.

Tnr and Ar ₃ are defined as follows.

Tnr = 887 + 464C + 890Ti + 363Al-357Si + (6445Nb-644 (Nb) ^1/2 ) + (732V-230 (V) ^1/2 )

Ar ₃ = 910-310C-80Mn-20Cu-15Cr-55Ni-80Mo + 0.35 (t-8) [t = plate thickness (mm)]

According to the present invention, it is possible to use heavy equipment and the like in the harsh environment such as the cold place by providing the wear-resistant ultra thick steel sheet having excellent wear resistance with respect to the entire thickness and excellent low temperature toughness.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

(Lecture composition and organization)

C: 0.19 to 0.30% by weight (hereinafter also referred to simply as "%")

The C is effective in increasing strength and hardness in steel having martensitic structure and is beneficial for improving the hardenability, but when the content thereof is high, the weldability and toughness are reduced, and thus the weldability and toughness are not required. In order to ensure the hardness, the content is preferably limited to 0.19 ~ 0.30%.

Si: 0.15 to 0.3%

The Si is an element exhibiting an increase in strength due to deoxidation and solid solution strengthening, but when the content thereof is high, the weldability decreases and the toughness of the weld part decreases as well as the toughness of the base material. Therefore, the content thereof is preferably limited to 0.15 to 0.3%.

Al: 0.005 ~ 0.1%

The Al is a strong deoxidizer to lower the oxygen content in the molten steel is effective in the production of clean steel, but when the addition of 0.1% or more increases the manufacturing cost is preferably limited to 0.005 ~ 0.1%.

Mn: 0.5 ~ 2.0%

Since Mn is an element that suppresses the formation of ferrite and increases the hardenability by effectively lowering the Ar ₃ temperature, thereby increasing the strength of the material, it is preferable to add a large amount to secure the hardness of the core material, but the carbon equivalent increases the weldability of the material. Since lowering the content is preferably limited to 0.5 to 2.0%.

Cr: 0.1 to 1.5%

Cr is an element that increases the hardenability to increase the strength of the material and to form fine carbides and nitrides to refine the structure to improve the strength, hardness, etc., but when excessive addition decreases the weldability and causes a cost increase, The content is preferably limited to 0.1 to 1.5%.

Mo: 0.1 to 0.5%

Mo is a very effective element to increase the hardenability of the material and to increase the strength, hardness by forming fine carbides, such as Cr, but when added to a large amount of expensive elements to increase the manufacturing cost and lower the weldability, the content is 0.1 It is desirable to limit to 0.5%.

Ni: 0.1 ~ 0.5%

Ni is an element or expensive element that greatly improves low-temperature toughness despite an increase in hardenability and an increase in strength and hardness due to a solid-solution strengthening effect. Therefore, Ni is an increase factor of manufacturing cost when excessively added, and thus the content is 0.1 to 0.5%. It is preferable to limit to.

V: 0.01 to 0.2%

The V is one of the important elements in the present invention to suppress the growth of austenite grains and to improve the hardenability of the material by forming VC carbide during hot rolling after hot rolling, but to improve the low temperature toughness, but it is an excessive element Since the addition is a rising factor of the manufacturing cost, the content is preferably limited to 0.01 ~ 0.2%.

B: 0.0005 to 0.0050%

The B is effective to increase the hardenability of the material even with a small amount of addition, and increase the strength, and the effect is very high in the complex addition with Mo, V, Ti, but the toughness and weldability when excessive addition, The content is preferably limited to 0.0005 to 0.0050%.

Cu: 0.1 ~ 1.0%

The Cu improves the hardenability of the material, and due to the solid solution strengthening element or surface strength when excessive addition or excessive addition and inhibits hot workability, the content is preferably limited to 0.1 ~ 1.0%.

Ti: 0.01 to 0.03%

Ti is an element maximizing the effect of B, which is an important element for improving the hardenability, and Ti is inhibited by the formation of TiN, thereby increasing the solid solution B to maximize the hardenability improvement by B, and precipitated TiN is austenite. The pinning of the nitrite grains has the effect of suppressing the coarsening of the grains, but due to the coarsening of Ti precipitates when excessively added, there is a problem of deterioration of toughness and segregation and oxide formation during steelmaking. It is desirable to limit to 0.03%.

Nb: 0.01 to 0.05%

Nb is an important element that is dissolved in austenite to increase the hardenability of austenite, and precipitates carbonitrides such as Nb (C, N) to suppress the increase in strength and austenite grain growth, but when added in large quantities Since the formation of coarse precipitated phase is a starting point of brittle fracture, the toughness is reduced, the content is preferably limited to 0.01 ~ 0.05%.

P: 0.015% or less

The P is an element that lowers the low-temperature toughness, but the content of the P is controlled to be low. However, the process for removing is difficult, and excessive cost is required. Therefore, the content is preferably controlled in the range of 0.015% or less.

S: 0.01% or less

S is an element that reduces low-temperature toughness, such as P, so that MnS inclusions in steel lower the physical properties of the steel, and thus S must be kept low. However, since the removal process is difficult, excessive cost is required. .

H value: 120 or more

H value = 2 (0.024C) ^1/2 ⅹ (Si + 1) ⅹ (3.5Mn + 1) ⅹ (2Cr + 1) ⅹ (0.5Ni + 1) ⅹ (3.0Mo + 1) ⅹ (1.8V + 1 The reason for limiting the H value defined by 1.3 is over 120. If the H value is less than 120, the hardness value of 360HB or more can not be obtained because the martensite structure of more than 80% by volume cannot be secured in the center of steel sheet of 50mmt or more. This is because there is no wear resistance.

Hereinafter, the manufacturing method of this invention is demonstrated.

When the steel formed as described above is subjected to air-cooling after general rolling and then subjected to reheat quenching treatment, low-temperature toughness is lowered by obtaining martensite structure having coarse primary austenite grains (AGS).

Therefore, in the present invention, as described below, the steel formed as described above, by volume control and accelerated cooling, has an average volume of 80 microns having a fine initial austenite grain size of 30 µm or less, which is 7 or more based on ASTM E112, based on ASTM E112. It provides a thick steel sheet having a martensite structure of at least%.

Here, primary austenite means austenite before transformation.

The thick steel plate may be composed of martensite and the remaining bainite structure of 80% by volume or more.

In addition, fine carbon / nitride is formed in the internal structure of the steel sheet, that is, the grains.

The carbon / nitride includes fine M ₃ X, M ₂ X, and MX [M = Fe, Cr, Mo, Ti, Nb; X = C, N] One or two or more of carbon / nitrides may be mentioned.

The reason for the control rolling and accelerated cooling during hot rolling is to form a fine austenite structure through the control rolling and immediately accelerate the cooling to suppress the coarsening of the austenite grains and to suppress the precipitation of VC as much as possible to reheat it. As austenite phase is formed from fine needle-like ferrite grains formed by accelerated cooling or fine carbon / nitride in bainite, fine austenite grains can be obtained. Finally, it is possible to form fine austenite grains, thereby improving low-temperature toughness, and obtaining a synergistic effect of strength and hardness as fine carbon / nitride remains in the heat-treated tissue.

In the present invention, the steel slab formed as described above is heated, but the heating temperature is preferably set to 1100 ° C to 1250 ° C.

The reason why the heating temperature of the steel slab is set to 1100 to 1250 ° C. is that when the heating temperature of the steel slab is less than 1100 ° C., it is difficult to dissolve solute atoms such as Nb, and when the temperature exceeds 1250 ° C., coarsening of austenite grains occurs. This is because it is difficult to suppress.

After that, hot rolling ends the hot rolling after cumulative rolling of 40% or more at a temperature between Tnr and Ar ₃ .

The reason why rolling is performed between Tnr and Ar ₃ is that when the rolling is terminated above the Tnr temperature, coarsening of austenite grains may occur due to austenite recrystallization, and when rolling is terminated at a temperature below Ar ₃ . This is because as the ferrite phase is formed during rolling, it is difficult to secure a uniform material and a decrease in strength may occur.

Tnr = 887 + 464C + 890Ti + 363Al-357Si + (6445Nb-644 (Nb) ^1/2 ) + (732V-230 (V) ^1/2 )

Ar ₃ = 910-310C-80Mn-20Cu-15Cr-55Ni-80Mo + 0.35 (t-8) [t = plate thickness (mm)]

In addition, when the cumulative reduction ratio is 40% or less, a uniform rolled structure may not be obtained until the center of the ultra-thick material is manufactured, and non-uniformity of material may occur in the thickness direction, and micronization of austenite grains may not be obtained.

The hot-rolled steel sheet by the above method is subjected to accelerated cooling at a central cooling rate of 5 ° C./s or more at a temperature of 400 ° C. or less immediately after the end of rolling.

The reason why the accelerated cooling is performed is that when the accelerated cooling is not performed, the austenitic grains refined through the control rolling are coarsened in the air cooling process, and thus finally fine grains cannot be obtained.

The reason why the cooling rate is limited to 5 ° C / s or more during accelerated cooling is that when the cooling rate is less than 5 ° C / s, fine needle-like ferrite or bainite structure cannot be obtained, and thus the grain refining effect cannot be obtained after the reheating quenching treatment. .

After completion of controlled rolling and accelerated cooling, the cooled steel sheet is reheated for 1.6t + (10 ~ 30 minutes) [t is the thickness of steel (mm)] at 880 ~ 930 ℃, but 300 at 10 ℃ / s or more The quenching treatment is carried out to a temperature of not more than ° C.

If the reheating temperature is lower than 880 ℃, it is difficult to re-employment of the employment element is difficult to secure the strength, it is difficult to secure a uniform carbide after cooling, and when it is higher than 930 ℃ grain growth occurs to cause toughness.

In addition, the reason for limiting the reheating time to 1.6t + (10 to 30 minutes) [where t is the thickness of the steel (mm)] is less than the above time, so that the homogenization of the tissue is difficult and the productivity is inhibited at the above holding time. Because.

In addition, the reason why the cooling rate is limited to 10 ° C / s or more is that at a cooling rate of 10 ° C / s or less, it is difficult to secure martensite structure of 80% by volume or more to the center of the ultra-thin material.

The steel sheet of the present invention manufactured through the heat treatment process has a martensite structure of 80% by volume or more in the total thickness of the ultra-thick steel plate of 50mmt or more, and forms fine carbon / nitride inside the grains, and has a hardness value of 360HB or more at the total thickness. It has a fine primary austenite grain size of 30 μm or less on average based on ASTM E112, and the Charpy impact energy value at −40 ° C. satisfies 40 J or more, thereby ensuring excellent wear resistance and low temperature toughness.

The microstructure may be composed of martensite tissue of 80% by volume or more and bainite tissue of 20% by volume or less.

The carbon / nitride is 100 nm or less fine M ₃ X, M ₂ X and MX [M = Fe, Cr, Mo, Ti, Nb; X = C, N] It may be one kind or two or more kinds of carbon / nitride.

Hereinafter, the present invention will be described in more detail with reference to Examples.

(Example)

To prepare a slab having a chemical composition as shown in Table 1, and then heated in a temperature range of 1100 ℃ ~ 1250 ℃ and subjected to rolling and accelerated cooling under the conditions shown in Table 2 and then subjected to the reheat quenching treatment at 910 ℃ It was.

For steel sheets manufactured under the following conditions, primary austenite grain size (AGS), hardness and Charpy impact toughness values of the steel sheets were measured, and the results are shown in Table 2 below.

Hardness measurement was measured with a Brinell hardness tester in accordance with the ISO-6506 standard, and cut after polishing the 1 / 2t point of the steel sheet. The measured value was measured five times at random and used the average value.

The primary austenite grain size (AGS) is obtained by mirror-polishing specimens from 1 / 2t of steel plate, and then etched with AGS corrosion solution and observed 500 times using an optical microscope.The average grain size is measured by image analysis. I got it.

The low temperature toughness of the base material was obtained by taking the specimen from 1 / 2t of steel plate and making V notched specimens, and performing the Charpy impact test five times at -40 ℃.

Steel grade
Chemical composition (% by weight) Ceq
H
C Si Mn P S Al Cr Ni Cu V B Ti Nb Mo

foot
persons
River A 0.19 0.3 1.6 0.01 0.002 0.03 0.5 0.3 0.2 0.05 0.0020 0.015 0.02 0.3 0.66 182 B 0.22 0.3 1.5 0.01 0.002 0.03 0.5 0.2 0.2 0.05 0.0020 0.015 0.02 0.2 0.65 150 C 0.25 0.2 1.3 0.01 0.002 0.03 0.4 0.3 0.2 0.05 0.0020 0.015 0.02 0.3 0.65 146 D 0.2 0.3 1.5 0.01 0.002 0.03 0.5 0.3 0.2 0.1 0.0020 0.015 0.02 0.2 0.64 161 E 0.22 0.3 1.4 0.01 0.002 0.03 0.5 0.3 0.2 0.1 0.0020 0.015 0.02 0.2 0.65 160 F 0.24 0.2 1.3 0.01 0.002 0.03 0.4 0.3 0 0.1 0.0020 0.015 0.02 0.2 0.62 130 G 0.24 0.3 0.85 0.006 0.001 0.05 0.8 0.5 0 0.02 0.0020 0.015 0.015 0.3 0.64 166 H 0.25 0.3 1.4 0.01 0.002 0.03 0.4 0.3 0 0.02 0.0020 0.015 0.02 0.2 0.63 135 I 0.23 0.3 1.6 0.01 0.002 0.03 0.4 0.3 0 0.02 0.0020 0.015 0.02 0.2 0.64 144 J 0.27 0.2 1.2 0.01 0.002 0.03 0.5 0.3 0 0.02 0.0020 0.015 0.02 0.2 0.63 126

ratio
School
River K 0.15 0.3 1.2 0.010 0.001 0.035 0.4 0.3 0 0 0.0014 0.015 0.02 0.2 0.49 89 L 0.14 0.4 1.3 0.010 0.009 0.03 0.1 0 0 0.01 0.0040 0.02 0.02 0.15 0.41 53 M 0.12 0.3 1.1 0.011 0.001 0.05 1.0 0.05 0 0.01 0.0015 0.02 0.015 0.2 0.57 112 N 0.16 0.2 1.1 0.011 0.001 0.10 0.6 0 0 0 0.0020 0 0.02 0.2 0.50 84 O 0.15 0.3 1.3 0.015 0.002 0.04 0.3 0 0 0 0.0010 0.01 0 0 0.43 46 P 0.1 0.3 1.3 0.008 0.002 0.03 0.5 0 0 0 0.0020 0.015 0.02 0.2 0.46 75 Q 0.35 0.2 1.1 0.008 0.002 0.03 0.5 0.3 0.2 0 0.0020 0 0 0.2 0.71 130

Specimen No. Steel grade Plate thickness
(mm) Tnr
(℃) Ar ₃
(℃) Rolling finish
Temperature (℃) Accelerated cooling
speed
(℃ / s) AGS
(Μm) Longitude value
[1 / 2t]
(HB) vE [-40 ℃]
(J) Invention 1 A 80 915 665 800 5 29 405 45 Invention 2 B 50 929 677 750 10 25 396 59 Invention 3 C 50 979 672 750 8 25 387 68 Invention 4 D 70 935 678 800 7 30 395 53 Invention 5 E 60 945 654 800 10 24 401 55 Invention 6 F 60 989 687 800 10 26 375 58 Invention Material7 G 80 923 698 750 5 30 384 49 Invention Material 8 H 50 940 676 750 10 23 378 56 Invention Material 9 I 60 931 666 800 8 26 381 57 Invention 10 J 50 976 690 750 10 22 375 68 Comparative Material 1 K 70 913 723 1050 - 85 240 12 Comparative Material 2 L 50 860 743 1000 - 70 260 18 Comparative Material 3 M 80 874 745 1020 - 90 320 13 Comparative Material 4 N 50 964 741 980 - 68 290 22 Comparative Material 5 O 50 873 749 950 - 65 210 28 Comparative Material 6 P 50 888 745 1000 - 72 270 15 Comparative Material7 Q 80 989 663 1030 - 92 370 10 Comparative Material 8 A 80 915 665 1000 - 75 398 8 Comparative Material 9 E 50 945 654 1020 - 63 394 11 Comparative Material 10 K 70 913 723 800 5 30 234 34 Comparative Material 11 Q 80 989 663 750 5 29 372 28

As shown in Table 2, in the case of the comparative material (1-6), the amount of addition of C, Ni, V, etc. is small and the H value is designed to be 120 or less due to the lack of addition of the hardenability improving element, and thus the center of the steel sheet even after the hardening treatment. Hardness of more than 360HB could not be obtained by obtaining bainite structure in most areas because it could not secure hardening ability of 80% by volume, and rolling end temperature was over Tnr due to the application of general rolling. As a result, growth of austenite grains occurs during cooling, and coarse AGS is obtained after the reheat treatment quenching treatment, so that excellent low-temperature toughness cannot be obtained.

In addition, in the case of the comparative material 7-9, the H value is designed to be 120 or more, but it is not possible to obtain the effect of improving the low temperature toughness due to the refinement of the austenite grains by applying general rolling.

In addition, in the case of the comparative material 10, austenitic grain refining effect can be obtained by applying controlled rolling at Tnr ~ Ar ₃ temperature and performing accelerated cooling, but when manufacturing the ultra-thick material as the H value is designed to be 120 or less. Since the hardenability of the core is not secured, martensite structure of more than 80% by volume is not obtained, and bainite structure is obtained in most areas, and thus hardness and excellent low temperature impact toughness of 360HB cannot be obtained.

In addition, in the case of the comparative steel 11, the H value was designed to be 120 or more, and control rolling was applied at Tnr ~ Ar ₃ temperature and accelerated cooling to obtain the austenite refining effect, but the C content exceeded the scope of the present invention. As it is added, excellent low temperature impact toughness cannot be obtained.

On the contrary, in the case of the invention material (1-10), all of the component systems controlled by the present invention are satisfied, and control rolling is performed in the temperature range of Tnr to Ar _3, cooling at a cooling rate of 3 ° C./s or more, and reheat quenching treatment. By carrying out the martensite structure of 80% by volume or more in the center of the steel sheet can be secured to obtain an excellent hardness value and at the same time it can be seen that the low temperature impact toughness is very excellent due to the austenite micronization effect.

Claims (4)

By weight%, C: 0.19-0.30%, Si: 0.15-0.3%, Mn: 0.5-2.0%, Cr: 0.1-1.5%, Mo: 0.1-0.5%, Ni: 0.1-0.5 wt%, V: 0.01 0.2 wt%, B: 0.0005-0.050%, Sol.Al:0.005-0.1%, P: 0.015% or less, and S: 0.010% or less, further Cu: 0.1-1.0 wt%, Ti: 0.01 At least one selected from the group consisting of ˜0.03% and Nb: 0.01˜0.05%, the remainder being composed of inevitable impurities and Fe, and the H value [H value = 2 (0.024C) ^1/2 ⅹ (Si + 1) ⅹ (3.5Mn + 1) ⅹ (2Cr + 1) ⅹ (0.5Ni + 1) ⅹ (3.0Mo + 1) ⅹ (1.8V + 1) ⅹ1.3] is at least 120; And
The primary austenite grain size (AGS) is 7 or more based on ASTM E112, average 30 μm or less, and the matrix microstructure contains 80% by volume or more martensite containing fine carbon / nitride inside, and the total thickness hardness value. A thick steel plate for extremely thick wear resistance that has excellent low temperature toughness of 360 HB or higher with this Brinell hardness value. The thick steel sheet for wear resistance according to claim 1, wherein the matrix microstructure comprises 80% by volume or more of martensite and 20% by volume of bainite structure. The method of claim 1, wherein the carbon / nitride is 100 nm or less fine M ₃ X, M ₂ X and MX [M = Fe, Cr, Mo, Ti, Nb; X = C, N] A thick steel plate for wear resistance of ultra-thickness having excellent low temperature toughness, characterized in that it is one kind or two or more kinds of carbon / nitride. By weight%, C: 0.19-0.30%, Si: 0.15-0.3%, Mn: 0.5-2.0%, Cr: 0.1-1.5%, Mo: 0.1-0.5%, Ni: 0.1-0.5 wt%, V: 0.01 0.2 wt%, B: 0.0005 to 0.0050%, Sol.Al: 0.005 to 0.1%, P: 0.015% or less, S: 0.010% or less, and further Cu: 0.1 to 1.0 wt%, Ti: 0.01 to One or two or more selected from the group consisting of 0.03% and Nb: 0.01-0.05%, the remainder being composed of inevitable impurities and Fe; H value [H value = 2 (0.024C) ^1/2 ⅹ (Si + 1) ⅹ (3.5Mn + 1) ⅹ (2Cr + 1) ⅹ (0.5Ni + 1) ⅹ (3.0Mo + 1) ⅹ ( 1.8V + 1) ⅹ1.3] above 120 is heated to a temperature of 1100 ℃ ~ 1250 ℃, Tnr [Tnr = 887 + 464C + 890 Ti + 363Al-357Si + (6445Nb-644 (Nb) ^1/2 ) + (732V-230 (V) ^1/2 )] ~ Ar ₃ [Ar ₃ = 910-310C-80Mn-20Cu-15Cr-55Ni-80Mo + 0.35 (t-8) (t = plate thickness (mm))] After 40% or more cumulative rolling at the temperature between the end of the hot rolling at Ar ₃ or more, and then accelerated cooling to the cooling rate of 5 ℃ / s or more at the center of the temperature of less than 400 ℃ immediately 880 ℃ ~ 930 ℃ After reheating to temperature, it is maintained for 1.6t + 10 ~ 30 minutes (t is the thickness of steel), and then it is used for extreme wear resistance with excellent low temperature toughness that cools below 300 ℃ with cooling rate of 10 ℃ / s or more at the center. Method of manufacturing thick steel sheet.