KR20130096213A - Wear resistant steel plate having excellent low-temperature toughness and weldability, and method for manufacturing the same - Google Patents

Abstract

PURPOSE: A steel sheet for an anti-abrasive with excellent low-temperature toughness and weldability and a manufacturing method thereof are provided to improve weldability and low-temperature toughness by optimizing a steel composition and a manufacture condition. CONSTITUTION: A steel sheet for an anti-abrasive with excellent low-temperature toughness and weldability comprises 0.05-0.18% of C, 0.15-0.3% of Si, 0.5-1.5% of Mn, 0.1-1.0% of Cr, 0.1-0.5% of Mo, 0.1-0.5wt% of Ni, 0.0005-0.0050% of B, 0.01-0.03% of Ti, 0.01-0.05% of Nb, 0.005-0.1% of Sol.Al, less than 0.015% of P, and less than 0.010% of S as a weight%, and a rest comprises Fe and an unavoidable impurity. A Ceq. value (Ceq.= C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15) is less than 0.50. A primary austenite grain particle size (AGS) is more than 8 based on an ASTM E112 and less than an average 20μm. A base micro-structure has a martensite structure more than 90 volume% including a minute coal/nitride in an inside. [Reference numerals] (AA,FF,JJ) Temperature; (BB,GG,KK) Re-heating; (CC,LL) Air cooling; (DD) Quenching; (EE,II,MM) Time; (HH) Direct quenching (1st Q)

Description

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

The present invention relates to a production method of wear-resistant steel used in fork cranes, bulldozers, excavators and rock drills, and more particularly, to a wear-resistant steel sheet having excellent weldability and low-temperature toughness to apply a two-stage hardening treatment, and a method for manufacturing the same. .

Heavy equipment used in many industrial fields such as construction, civil engineering, mining, and cement industry causes severe wear due to friction during work, and therefore, it is necessary to apply materials that exhibit wear resistance characteristics.

Particularly, since the heavy equipment is manufactured through welding, good weldability is required for the material to be applied.

In addition, as the use environment of heavy equipment in the industrial field is severe, such as extreme paper, it requires excellent low temperature impact toughness characteristics along with strength, hardness, and wear resistance.

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 hardening after reheating to a temperature of Ac ₃ or higher after rolling is generally used.

Examples of such methods include Japanese Patent Laid-Open No. 2-179842, Japanese Patent Laid-Open No. 8-41535, and Japanese Patent Laid-Open No. 61-166954. These publications add high C content and a large amount of hardening elements such as Cr and Mo. Thereby increasing the surface hardness.

However, in the case of the conventional methods described above, there is a problem in that manufacturing cost increases and weldability and toughness decrease as C and a hardenable alloy are added in order to secure hardness.

On the other hand, JP 2002-20837, JP 2004-10996 and JP 2006-328512, JP 2000-0038156, JP 2001-0060644 and the like after direct quenching and hardening after rolling without using the reheat quenching method A method of increasing the hardness by securing a martensitic structure using a method that is considered is disclosed.

These methods can reduce alloying elements and improve weldability by using the excellent hardening ability of direct quenching method, but coarsening of austenite grains occurs compared with reheating quenching method, resulting in the reduction of low temperature impact toughness. There is a problem.

In addition, the above methods are difficult to produce due to the manufacturing process is difficult because the rolling processing structure is left to obtain a non-consistent structure, it is difficult to control the shape of the steel sheet due to rapid cooling from high temperature There is a problem.

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

As one method for satisfying such low-temperature toughness demands, JP-A-10-102185 et al. Provide toughness of steel sheet by removing residual stress of steel sheet through low temperature consideration (about 200 ℃ ~ 550 ℃) after reheating and hardening. A method is disclosed.

However, this method has a problem in that the productivity is drastically reduced as the time required for raising and lowering the temperature of the heat treatment furnace in the field application, and also when the treatment at an excessively high temperature due to the failure to apply optimal consideration conditions, hardness and The wear resistance is reduced, and if the temperature is too low or the time is not enough, it is difficult to derive the optimum consideration conditions, such as failure to remove residual stress and toughness.

The present invention is to provide a wear-resistant steel sheet excellent in the weldability and low-temperature toughness to improve the weldability and low-temperature toughness by optimizing the composition and manufacturing conditions of the steel and its manufacturing method.

According to one aspect of the present invention, in weight% C: 0.05 to 0.18%, Si: 0.15 to 0.3%, Mn: 0.5 to 1.5%, Cr: 0.1 to 1.0%, Mo: 0.1 to 0.5%, Ni: 0.1 to 0.5wt%, B: 0.0005 ~ 0.0050%, Ti: 0.01 ~ 0.03%, Nb: 0.01 ~ 0.05%, Sol.Al:0.005~0.1%, P: 0.015% or less, S: 0.010% or less, the rest are unavoidable impurities And Fe, and Ceq. Value [Ceq. = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) / 15] is 0.50 or less; And

The primary austenite grain size (AGS) is 8 or more, based on ASTM E112, and average 20 µm or less, and the known microstructure has a weldability and low temperature toughness having a martensite structure of 90% by volume or more containing fine carbon / nitride therein. An excellent wear resistant steel sheet is provided.

 The matrix microstructure may be composed of 90% by volume or more martensite tissue and 10% by volume or less bainite tissue.

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.

 Preferably, the total thickness hardness value of the said steel sheet is 360HB or more in Brinell hardness value.

According to another aspect of the present invention, by weight% C: 0.05 to 0.18%, Si: 0.15 to 0.3%, Mn: 0.5 to 1.5%, Cr: 0.1 to 1.0%, Mo: 0.1 to 0.5%, Ni: 0.1 to 0.5wt%, B: 0.0005 ~ 0.0050%, Ti: 0.01 ~ 0.03%, Nb: 0.01 ~ 0.05%, Sol.Al:0.005~0.1%, P: 0.015% or less, S: 0.010% or less, the rest are unavoidable impurities And a steel slab composed of Fe and having a Ceq. Value [Ceq. = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) / 15] satisfying 0.50 or less. Reheating to ° C; And

Subjected to a cumulative reduction ratio of 70% or more step-down and rolled from above the recrystallization temperature region with a reduction ratio reduction ratio of 10% or more per pass, and ends the finish rolling at least Ar ₃ temperature, and 5 ~ 15 ℃ / s cooling rate of a temperature not higher than 400 ℃ After quenching, or after finishing rolling, cool to room temperature, and then reheat to 930 ℃ ~ 980 ℃ for 1.6t + 10 ~ 30 minutes (t is the thickness of steel) and then at 5 ~ 15 ℃ / s cooling rate. The first quenching treatment is performed at a temperature of 400 ° C. or lower, and then reheated at 880 ° C. to 930 ° C. for 1.6t + 10 to 30 minutes (t is the thickness of the steel), and then 300 ° C. or lower at a cooling rate of 15 ° C./s or more. Provided is a method for producing a wear resistant steel sheet having excellent weldability and low temperature toughness, including the step of secondary quenching at a temperature of.

According to the present invention, by providing a wear-resistant steel sheet excellent in weldability and low temperature toughness, it is possible to use heavy equipment and the like even in the harsh environment such as extreme paper.

1 is a time-temperature graph showing a conventional heat treatment method and a heat treatment method of the present invention, Figure 1 (a) shows a conventional heat treatment method, Figure 1 (b) and (c) is a heat treatment of the present invention The method is shown.
FIG. 2 shows optical micrographs and austenite grain size (AGS) images of a comparative material 6 outside the scope of the present invention and an inventive material 7 satisfying the scope of the present invention. Represents the thing of the comparative material 6, and FIG.2 (b) shows the thing of the invention material 7.

Hereinafter, the present invention will be described in detail.

In the present invention, it is designed to have a low carbon equivalent (Ceq.) By minimizing the alloying elements added to the steel to improve the weldability and to improve the low temperature toughness by applying a two-stage anneal heat treatment through the control of the cooling rate after rolling Provided is a wear resistant steel sheet excellent in toughness and a method of manufacturing the same.

First, the composition and structure of the steel will be described.

C: 0.05 to 0.18% by weight (hereinafter, also simply referred to as "%")

The C is an element effective to increase the strength and hardness in the steel having martensitic structure, but if the content is high, the weldability and toughness are reduced, so as to secure the hardness required by the present invention without reducing the weldability and toughness, The content is preferably limited to 0.05 to 0.18%.

Si: 0.15 ~ 0.3%

The Si is an element exhibiting strength increase 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 production cost increases when added to 0.1% or more, the content is preferably limited to 0.005 ~ 0.1%.

Mn: 0.5 ~ 1.5%

The Mn is an element that increases the hardenability by effectively suppressing the formation of ferrite and lowering the Ar ₃ temperature, but increases the strength of the material, or decreases the weldability of the material by increasing the carbon equivalent, the content of which is limited to 0.5 ~ 1.5% It is preferable.

Cr: 0.1-1.5%

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%

The Mo is a very effective element to increase the hardenability of the material and to increase the strength, hardness by forming a fine carbide, 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, so the content is 0.1 to 0.5%. It is preferable to limit to.

B: 0.0005 ~ 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%.

Ti: 0.01 ~ 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 coarsening of the grains, but due to the coarsening of Ti precipitates when excessively added, there are problems of deterioration of toughness and segregation and oxide formation during steelmaking. Limiting to ~ 0.03% is effective.

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 the starting point of brittle fracture, the toughness is reduced, the content is preferably limited to 0.01 ~ 0.05%.

P: not more than 0.015%

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: not more than 0.01%

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. .

Ceq. Value: 0.50 or less

In the present invention, the Ceq. Value [Ceq. = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) / 15] is limited to 0.50 or less, because the weldability is lowered when 0.50 or more. This is because additional processes such as preheating and post-heating are required, which leads to difficult working conditions during welding, thereby lowering productivity.

The steel sheet of the present invention has a primary austenite grain size (AGS) of 8 or more on the basis of ASTM E112, which is an average of 20 μm or less, and the matrix microstructure has a martensite structure of 90% by volume or more containing fine carbon / nitride therein. , Excellent weldability and low temperature toughness.

Here, primary austenite represents austenite before transformation.

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.

Preferably, the total thickness hardness value of the steel sheet of the present invention is 360HB or more in Brinell hardness value.

Hereinafter, the manufacturing method of this invention is demonstrated.

When the steel formed as described above is subjected to the reheat quenching treatment as shown in FIG. 1A, martensite structures having coarse primary austenite grains (AGS) are generally formed, thereby lowering low-temperature toughness.

Therefore, in the present invention, by the appropriate rolling and two-stage quenching treatment as described later in the present invention, 90% by volume or more of martensite having a fine initial austenite grain size of 20 µm or less on an average of 8 or more based on ASTM E112. Provide a steel plate with site structure.

The steel sheet may be made of martensite and the remaining bainite structure of 90% 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 kind or two or more kinds of carbon / nitride may be mentioned.

In the present invention, as shown in (b) and (c) of FIG. 1, the quenching treatment is performed in two stages. The reason for performing the quenching treatment in two stages is that the quenching treatment is performed through the proper cooling rate control during the first stage quenching treatment. If more than 90% by volume of bainite structure having carbon / nitride is secured, fine carbides act as nucleation sites of austenite during reheating during the second quenching process, thereby enabling formation of fine austenite grains and improving low temperature toughness. As well as obtaining a synergistic effect of strength and hardness as the fine carbon / nitride remaining in the heat-treated finished tissue.

In addition, the reason for controlling the microstructure as described above is to produce a steel sheet excellent in low temperature toughness of 360HB or more of the hardness value of the target thickness in the present invention.

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.

When the slab heating temperature is less than 1100 ℃, it is difficult to solute the solute atoms such as Nb, and when the slab heating temperature exceeds 1250 ℃, it is difficult to suppress the coarsening of austenite grains, the slab heating temperature is set to 1100 ℃ ~ 1250 ℃ It is preferable.

The steel slabs heated as above are hot rolled.

The hot rolling is preferably carried out under the conditions of rolling down the cumulative rolling rate of 70% or more at a rolling reduction rate of 10% or more per pass in the recrystallization temperature or higher region and ending the finish rolling at an Ar ₃ temperature or higher.

If the cumulative reduction ratio is less than 70% at a temperature above the recrystallization temperature, a uniform rolling structure may not be obtained up to the center of the thick steel plate, and a material deviation may be generated in the thickness direction, and when the finish rolling temperature is less than or equal to Ar ₃ , the austenite As the two-phase and ferrite phases are formed, elements such as Nb and B form carbides and nitrides to precipitate at grain boundaries, so that uniform dispersion of alloying elements cannot be obtained. The bainite structure cannot be obtained and the effect of the two-stage hardening treatment cannot be obtained.

As shown in (b) of FIG. 1, the hot rolled steel sheet as described above is immediately subjected to the first quenching treatment at a cooling rate of 5 to 15 ° C./s from the Ar ₃ temperature to the temperature of 400 ° C. or less immediately after the end of rolling. Alternatively, as shown in (c) of FIG. 1, after the end of rolling, the cooled steel sheet is reheated at 1.6 to + (10 to 30 minutes) (where t is the thickness of the steel) at a temperature of 930 to 980 ° C., 5 to 15 The primary quenching treatment is carried out to a temperature of 400 ° C. or lower at a cooling rate of ° C./s.

When the reheating temperature of the cooled steel sheet after the end of the rolling is lower than 930 ℃, 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 980 ℃ grain growth occurs to reduce the toughness Since it is caused, the reheating temperature of the cooled steel sheet after the end of the rolling is preferably set to 930 ~ 980 ℃.

In addition, the reason for limiting the reheating time of the cooled steel sheet after the end of the rolling to 1.6t + (10 ~ 30 minutes) (where t is the thickness of the steel) is that if the reheating time is shorter than the time it is difficult to homogenize the tissue and the time It is because productivity falls when exceeding.

The reason for controlling the cooling rate to 5 ~ 15 ℃ / s during the first quenching treatment is that when the cooling rate is lower than 5 ℃ / s can not secure more than 90% by volume of bainite, if it is larger than 15 ℃ / s This is because martensite is formed to make it difficult to form fine carbon / nitride.

In addition, the reason why the cooling end temperature is controlled to 400 ° C. or lower during the first quenching treatment is because bainite structure having a fraction of 90% by volume or more may not be secured when the cooling end temperature is higher than 400 ° C.

Next, the steel plate subjected to the primary quenching treatment as described above is reheated at a temperature of 880 ° C to 930 ° C for 1.6t + (10 to 30 minutes) (where t is the thickness of the steel), and then at a cooling rate of 15 ° C / s or more. The secondary quenching treatment is carried out to a temperature of 200 ° C or lower.

As such, the reason for performing the quenching treatment in two stages is that the fine carbon / nitride formed in the bainite during reheating for the second quenching of 90% by volume or more of the bainite structure having the fine carbon / nitride obtained by the first quenching treatment This is because fine austenite grains can be formed by acting as an austenite nucleation site to obtain low temperature toughness, and to obtain martensite structure having a hardness value of 360 HB or more by secondary quenching treatment.

In the second quenching treatment, it is preferable to control the reheating temperature to 880 to 930 ° C. When the reheating temperature is less than 880 ° C, it is difficult to re-employ the employment elements, and some coarse carbides formed in bainite are redissolved. This is because the toughness and non-uniformity of the material may be generated, and when it exceeds 930 ° C, growth of finely formed austenite crystals may occur.

In addition, the reason why the cooling rate is limited to 15 ° C./s or more during the second quenching treatment is that it is difficult to secure martensite structure of 90% by volume or more at a cooling rate of less than 15 ° C./s.

The steel sheet manufactured according to the present invention has a low Ceq design, has excellent weldability and includes more than 90% by volume of martensite structure and residual bainite structure, and has fine carbon / nitride of 100 nm or less, for example, M ₃ X , M ₂ X, MX [M = Fe, Cr, Mo, Ti, Nb], [X = C, N] Forms carbon / nitride and has hardness value over 360HB in total thickness, and over 8 in accordance with ASTM E112 It has a fine primary austenite grain size of 20 mu m or less on average, and the Charpy impact energy value at -40 ° C satisfies 50J or more, and thus has excellent weldability, wear resistance and low temperature toughness.

Hereinafter, the present invention will be described more specifically by way of examples.

(Example)

After manufacturing a steel slab having a chemical composition as shown in Table 1 and then heated in a temperature range of 1100 ℃ ~ 1250 ℃ and rolling down the cumulative reduction rate of more than 70% cumulative reduction rate more than 10% reduction rate per pass in the region above the recrystallization temperature After carrying out the heat treatment and cooling under the thickness of the conditions shown in Table 2, quenching heat treatment conditions to prepare a steel sheet.

For the steel sheet manufactured as described above, primary austenite grain size (AGS), hardness, low temperature toughness and Charpy impact toughness values of the welded HAZ portion were measured, and the results are shown in Table 2 below.

Here, the hardness measurement is made of a Brinell hardness meter in accordance with the ISO-6506 standard, and was measured after grinding by cutting 1 / 4t point of the steel sheet. The measurement was carried out at random five times, the hardness value was used as the average value.

In addition, the primary austenite grain size (AGS) is obtained by mirror-polishing the specimen from 1 / 4t of the steel plate, and then etched it with an AGS corrosion solution, observed 500 times using an optical microscope, and measured the grain size by image analysis. Is the average value.

In addition, the low temperature toughness of the base material is a value obtained by taking a specimen from a 1 / 4t portion of the steel sheet and making a V notched test specimen, and performing the Charpy impact test five times at -40 ° C to obtain an average value.

In addition, the low-temperature toughness of the HAZ part was tested using a HAZ simulation tester under conditions equivalent to a heat input of 5 kJ / mm, and then subjected to a Charpy impact test twice at -20 ° C each to obtain an average value. will be.

In addition, optical micrographs and AGS images of the inventive material 7 and the comparative material 6 of Table 2 were observed, and the results are shown in FIG. 2. In FIG. 2, (a) shows the thing of the comparative material 6, and FIG. 2 (b) shows the thing of the invention material 7. In FIG.

Steel grade
Steel composition (% by weight) Ceq
C Mn Si Cr P S Al Ti Nb Mo Ni B Invention steel

A 0.08 1.0 0.30 0.30 0.012 0.010 0.035 0.015 0.020 0.4 0 0.0015 0.39 B 0.10 1.2 0.30 0.30 0.010 0.010 0.030 0.015 0.015 0.2 0.3 0.0010 0.42 C 0.14 1.2 0.25 0.40 0.010 0.005 0.030 0.015 0.015 0.2 0.3 0.0010 0.48 Comparative steel D 0.2 1.0 0.3 1.0 0.010 0.005 0.030 0 0 0.5 0.3 0.0020 0.69

Psalm No.
River
Bell thickness
1st hardening Secondary hardening AGS
(탆)
Hardness
(HB),
1 / 4t
CVN
-40 ℃
(J)
CVN
-20 ° C
(J)
HAZ Hardening
Way Cooling
Start
Temperature Cooling
End
Temperature Cooling rate Cooling
Start
Temperature Cooling
End
Temperature Cooling
speed
foot
persons
ashes

One A 13 DQ 950 200 10 880 200 18 18 371 105 67 2 A 13 RQ 930 300 8 880 200 20 16 381 112 63 3 B 25 DQ 950 300 12 910 200 18 21 385 94 65 4 B 25 RQ 950 200 10 910 200 18 15 391 103 58 5 B 13 RQ 950 200 10 910 200 18 15 403 96 65 6 C 30 DQ 950 200 8 890 100 16 22 401 98 59 7 C 30 RQ 930 200 8 890 100 16 16 403 100 65

ratio
School
ashes



One A 13 DQ 950 200 20 - - - 75 341 28 13 2 A 13 RQ 930 200 15 - - - 62 346 27 16 3 B 25 RQ 930 300 20 - - - 65 352 26 20 4 C 30 DQ 950 400 20 - - - 70 349 23 15 5 C 30 RQ 930 100 20 - - - 55 365 34 25 6 C 30 DQ 950 500 3 910 200 18 65 360 38 28 7 C 30 RQ 930 200 8 890 100 10 40 352 38 25 8 C 30 RQ 930 200 20 890 100 20 43 420 33 21 9 D 30 DQ 930 200 10 930 200 18 31 432 27 15 10 D 30 RQ 930 200 10 910 200 20 35 438 34 23

As shown in Table 2, in the case of the comparative material (1-5), a direct quenching treatment or a reheat quenching treatment was performed immediately after rolling, and thus the austenite was not sufficiently refined, and thus the excellent toughness of the base material and the HAZ part was not obtained. Do not.

In addition, in the case of the comparative material 6, after the direct treatment immediately after rolling, the reheating secondary quenching treatment was carried out as in the present invention, but the bainite was treated because the cooling rate was too low during the primary quenching treatment. The structure cannot be obtained, and as shown in Fig. 2A, the austenite refining effect cannot be obtained during the second quenching treatment.

In the case of the comparative material 7, the reheating two-stage quenching treatment was carried out as in the present invention, but the two-stage quenching treatment was performed as in the present invention, but the cooling rate was low during the second sintering treatment so that the martensite structure of 90 vol% or more was finally obtained. Can not get high hardness.

In the case of the comparative material 8, the reheating two-stage quenching treatment was performed. As in the present invention, the two-stage quenching treatment was carried out as in the present invention. Because the martensite structure is formed without forming the bainite structure in which nitride is present, it is not possible to obtain the micronized effect of austenite by the fine carbon / nitride in the bainite acting as the austenite nucleus site. Impact toughness cannot be obtained.

In addition, in the case of the comparative materials (9, 10) Ceq is 0.5 or more, which does not correspond to the range to be controlled in the present invention, due to the addition of a large amount of hardenable elements, it is not possible to secure the impact toughness of the base material, weldability Deterioration occurs and excellent impact toughness of the HAZ portion cannot be obtained.

On the contrary, in the case of the invention material (1-7), it satisfies the steel composition and manufacturing conditions of the present invention, and bainite having fine carbon / nitride in the first quenching treatment through optimization of the cooling rate during the two-stage quenching treatment. As the tissue is formed and the fine carbon / nitride acts as the austenite nucleation site during the second quenching treatment, as shown in (b) of FIG. 2, fine austenite is formed and finally, martensite tissue of 90% by volume or more is finally formed. By forming, the hardness value was excellent and the impact toughness of the base material and the HAZ part was very excellent.

Claims (5)

In weight%, C: 0.05 to 0.18%, Si: 0.15 to 0.3%, Mn: 0.5 to 1.5%, Cr: 0.1 to 1.0%, Mo: 0.1 to 0.5%, Ni: 0.1 to 0.5 wt%, B: 0.0005 ~ 0.0050%, Ti: 0.01 ~ 0.03%, Nb: 0.01 ~ 0.05%, Sol.Al:0.005~0.1%, P: 0.015% or less, S: 0.010% or less, the rest is composed of inevitable impurities and Fe, Ceq The value [Ceq. = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) / 15] is 0.50 or less; And the primary austenite grain size (AGS) is 8 or more on the basis of ASTM E112, average 20㎛ or less, and the known microstructure has a weldability and low temperature toughness having a martensite structure of 90% by volume or more containing fine carbon / nitride therein This excellent wear resistant steel sheet.
The wear-resistant steel sheet having excellent weldability and low temperature toughness according to claim 1, wherein the matrix microstructure comprises 90% by volume or more of martensite and 10% 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] Abrasion resistant steel sheet excellent in weldability and low temperature toughness, characterized in that it is one kind or two or more kinds of carbon / nitride.
The steel sheet for wear resistance and low temperature toughness according to any one of claims 1 to 3, wherein the total thickness hardness value of the steel sheet is 360 HB or more as Brinell hardness value.
In weight%, C: 0.05 to 0.18%, Si: 0.15 to 0.3%, Mn: 0.5 to 1.5%, Cr: 0.1 to 1.0%, Mo: 0.1 to 0.5%, Ni: 0.1 to 0.5 wt%, B: 0.0005 ~ 0.0050%, Ti: 0.01 ~ 0.03%, Nb: 0.01 ~ 0.05%, Sol.Al:0.005~0.1%, P: 0.015% or less, S: 0.010% or less, the rest is composed of inevitable impurities and Fe, Ceq Reheating the steel slab with a value [Ceq. = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) / 15] equal to or less than 0.50 to 1100 ° C.-1250 ° C .; And
Subjected to a cumulative reduction ratio of 70% or more step-down and rolled from above the recrystallization temperature region with a reduction ratio reduction ratio of 10% or more per pass, and ends the finish rolling at least Ar ₃ temperature, and 5 ~ 15 ℃ / s cooling rate of a temperature not higher than 400 ℃ After quenching, or after finishing rolling, cool to room temperature, and then reheat to 930 ℃ ~ 980 ℃ for 1.6t + 10 ~ 30 minutes (t is the thickness of steel) and then at 5 ~ 15 ℃ / s cooling rate. The first quenching treatment is performed at a temperature of 400 ° C. or lower, and then reheated at 880 ° C. to 930 ° C. for 1.6t + 10 to 30 minutes (t is the thickness of the steel), and then 300 ° C. or lower at a cooling rate of 15 ° C./s or more. A method for producing a wear-resistant steel sheet excellent in weldability and low temperature toughness, comprising the step of secondary quenching at a temperature of.

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