KR102290780B1 - High manganese austenitic steel having high yield strength and manufacturing method for the same - Google Patents

Abstract

Austenitic high manganese steel having excellent yield strength according to an aspect of the present invention, by weight, C: 0.2 to 0.5%, Mn: 20 to 28%, Si: 0.05 to 0.5%, P: 0.03% or less, S: 0.005% or less, Al: 0.005 to 0.05%, the balance Fe and other unavoidable impurities, and 95 area% or more of austenite as a microstructure, but the grain boundary fraction in the microstructure may be 7 area% or more have.

Description

Austenitic high manganese steel having excellent yield strength and manufacturing method thereof {High manganese austenitic steel having high yield strength and manufacturing method for the same}

The present invention relates to an austenitic high manganese steel material and a method for manufacturing the same, and more particularly, to an austenitic high manganese steel material having excellent ductility and excellent yield strength and a method for manufacturing the same.

Austenitic high-manganese steel has the characteristic of having high toughness because the austenite is stable even in an environment of room temperature or cryogenic temperature by adjusting the contents of manganese (Mn) and carbon (C), which are elements that increase the stability of austenite.

However, in the case of high manganese steel having austenite as the main structure, it has the advantage of excellent low-temperature toughness due to the characteristic of ductile fracture even at low temperatures, but the strength, especially the yield strength, is low due to the face-centered cubic structure, which is a unique crystal structure. There is a technical limit to reducing the cost by lowering the design thickness of the material when designing.

Therefore, in order to increase the strength of austenitic high manganese steel, technologies such as solid solution strengthening through the addition of alloying elements, precipitation hardening through the addition of precipitate forming elements, and pancaking rolling through finish rolling temperature control have been developed. has been proposed However, there are problems such as an increase in economic cost due to the addition of alloying elements, a limitation in the formation of precipitates due to a high solid solution limit of precipitates in austenite, and a decrease in impact toughness due to an increase in strength during pancake rolling through finish rolling temperature control. Due to the presence of this, a significant technical disadvantage is followed by an increase in the strength of high manganese steel. Therefore, there is a need to develop an austenitic high manganese steel material having high strength while maintaining an elongation of a certain level or more through an economical and effective method.

Republic of Korea Patent Publication No. 10-2015-0075324 (published on July 3, 2015)

According to one aspect of the present invention, an austenitic high manganese steel having excellent yield strength and a method for manufacturing the same may be provided.

The subject of the present invention is not limited to the above. A person of ordinary skill in the art will have no difficulty in understanding the further problems of the present invention from the overall content of the present specification.

Austenitic high manganese steel having excellent yield strength according to an aspect of the present invention, by weight, C: 0.2 to 0.5%, Mn: 20 to 28%, Si: 0.05 to 0.5%, P: 0.03% or less, S: 0.005% or less, Al: 0.005 to 0.05%, the balance Fe and other unavoidable impurities, and 95 area% or more of austenite as a microstructure, but the grain boundary fraction in the microstructure may be 7 area% or more have.

The steel may further include 0.0005 to 0.01% of B by weight%.

The steel may further include at least one selected from 1.0% or less of Cu and 5.0% or less of Cr by weight%.

The steel material may satisfy the range of ^{10 to 19 mJ/m 2} of stacking fault energy (SFE) expressed by the following relational formula (1).

[Relational Expression 1]

Stacking Fault Energy (SFE) = -24.9 + 0.814*Mn + 44.3*C - 0.62*Si + 1.06*Cu + 7.9*Al - 0.555*Cr

(In relation 1, Mn, C, Si, Cu, Al, and Cr mean the weight % of each alloy composition)

The grain size of the austenite may be 5 ~ 150㎛.

The intra-grain boundary fraction of the microstructure may be 80 area% or less.

The yield strength of the steel is 400 MPa or more, the tensile strength is 800 MPa or more, the elongation is 30% or more, and the Charpy impact toughness at -196° C. may be 30 J or more (based on a thickness of 5 mm).

The manufacturing method of an austenitic high manganese steel ㅇ having excellent yield strength according to an aspect of the present invention is, in weight%, C: 0.2 to 0.5%, Mn: 20 to 28%, Si: 0.05 to 0.5%, P: Reheating step of reheating the slab containing 0.03% or less, S: 0.005% or less, Al: 0.005 to 0.05%, the remainder Fe and other unavoidable impurities in a temperature range of 1050 to 1300 °C; a hot rolling step of hot rolling the reheated slab to a finish rolling temperature of 800 to 1050° C. to provide a hot rolled material; a cooling step of accelerating cooling the hot-rolled material to a temperature range of 600° C. or less at a cooling rate of 10 to 100° C./s; And it may include a low pressure step of slightly reducing the accelerated-cooled hot-rolled material at a reduction ratio of 0.1 to 10% in a temperature range of 25 ~ 400 ℃.

The slab, by weight, may further include 0.0005 to 0.01% of B.

The slab may further include one or more selected from 1.0% or less of Cu and 5.0% or less of Cr by weight%.

The slab may have a stacking fault energy (SFE) of 10 to 19 mJ/m ² expressed by Relation 1 below.

[Relational Expression 1]

Stacking Fault Energy (SFE) = -24.9 + 0.814*Mn + 44.3*C - 0.62*Si + 1.06*Cu + 7.9*Al - 0.555*Cr

(In Relation 1, Mn, C, Si, Cu, Al, and Cr mean wt% of each component content)

The reduction ratio in the step of reducing the weak pressure may be 1 to 5%.

The means for solving the above problems do not enumerate all the features of the present invention, and various features of the present invention and its advantages and effects may be understood in more detail with reference to the following specific examples.

According to a preferred aspect of the present invention, it is possible to provide an austenitic high manganese steel material having excellent ductility and excellent yield strength and a method for manufacturing the same.

1 is a result of observing the microstructure of specimen 1.
2 is a result of observing the microstructure of the specimen 10.

The present invention relates to an austenitic high manganese steel having excellent yield strength and a method for manufacturing the same, and preferred embodiments of the present invention will be described below. Embodiments of the present invention may be modified in various forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The present embodiments are provided in order to further detail the present invention to those of ordinary skill in the art to which the present invention pertains.

Hereinafter, the steel composition of the present invention will be described in more detail. Hereinafter, unless otherwise indicated, % indicating the content of each element is based on weight.

Austenitic high manganese steel having excellent yield strength according to an aspect of the present invention, by weight, C: 0.2 to 0.5%, Mn: 20 to 28%, Si: 0.05 to 0.5%, P: 0.03% or less, S: 0.005% or less, Al: 0.005 to 0.05%, the balance may include Fe and other unavoidable impurities.

Carbon (C): 0.2-0.5%

Carbon (C) is an effective element for stabilizing austenite of steel and securing strength by solid solution strengthening. Therefore, the present invention may limit the lower limit of the carbon (C) content to 0.2% in order to secure low-temperature toughness and strength. That is, when the carbon (C) content is less than 0.2%, the stability of austenite is insufficient, so stable austenite cannot be obtained at cryogenic temperatures, and processing-induced transformation into ε-martensite and α'-martensite can be easily performed by external stress. This is because it can reduce the toughness and strength of the steel material. A more preferable lower limit of the carbon (C) content may be 0.3%. On the other hand, when the carbon (C) content exceeds a certain range, the toughness of the steel may be rapidly deteriorated due to carbide precipitation, and the strength of the steel may be excessively high and the workability of the steel may be significantly reduced. (C) The upper limit of the content may be limited to 0.5%. More preferably, the upper limit of the carbon (C) content may be 0.45%.

Manganese (Mn): 20-28%

Since manganese (Mn) is an important element serving to stabilize austenite, the present invention may limit the lower limit of the manganese (Mn) content to 20% in order to achieve this effect. That is, since the present invention contains 20% or more of manganese (Mn), it is possible to effectively increase the austenite stability, thereby suppressing the formation of ferrite, ε-martensite and α'-martensite to effectively improve the low-temperature toughness of steel. can be obtained A preferred lower limit of the manganese (Mn) content may be 22%, and a more preferred lower limit of the manganese (Mn) content may be 23%. On the other hand, if the manganese (Mn) content exceeds a certain level range, the effect of increasing the stability of austenite is saturated, while the manufacturing cost is greatly increased, and internal oxidation during hot rolling may occur excessively, resulting in poor surface quality. , the present invention may limit the upper limit of the manganese (Mn) content to 28%. The upper limit of the preferable manganese (Mn) content may be 26%, and the upper limit of the more preferable manganese (Mn) content may be 25%.

Silicon (Si): 0.05 to 0.50%

Silicon (Si), like aluminum (Al), is an element that is indispensable as a deoxidizer and is added in a trace amount. However, when silicon (Si) is excessively added, an oxide is formed at the grain boundary to reduce high-temperature ductility, and there is a risk of lowering the surface quality by inducing cracks, etc., so the present invention sets the upper limit of the silicon (Si) content. It can be limited to 0.50%. On the other hand, excessive cost is required to reduce the silicon (Si) content in steel, and the present invention may limit the lower limit of the silicon (Si) content to 0.05%. Accordingly, the silicon (Si) content of the present invention may be 0.05 to 0.50%.

Phosphorus (P): 0.03% or less

Phosphorus (P) is an element that segregates easily and causes cracks during casting or reduces weldability. Accordingly, the present invention may limit the upper limit of the phosphorus (P) content to 0.03% in order to prevent deterioration of castability and deterioration of weldability. In addition, although the present invention does not specifically limit the lower limit of the phosphorus (P) content, the lower limit may be limited to 0.001% in consideration of the steelmaking burden.

Sulfur (S): 0.005% or less

Sulfur (S) is an element that causes hot brittle defects by formation of inclusions. Therefore, the present invention can limit the upper limit of the sulfur (S) content to 0.005% in order to suppress the occurrence of hot brittleness. In addition, although the present invention does not specifically limit the lower limit of the sulfur (S) content, the lower limit may be limited to 0.0005% in consideration of the steelmaking burden.

Aluminum (Al): 0.05% or less

Aluminum (Al) is a representative element added as a deoxidizer. Accordingly, in the present invention, the lower limit of the aluminum (Al) content may be limited to 0.001% to achieve such an effect, and more preferably, the lower limit of the aluminum (Al) content may be limited to 0.005%. However, aluminum (Al) may react with carbon (C) and nitrogen (N) to form precipitates, and hot workability may be lowered by these precipitates, so the present invention sets the upper limit of the aluminum (Al) content. It can be limited to 0.05%. More preferably, the upper limit of the content of aluminum (Al) may be 0.045%.

The austenitic high manganese steel having excellent yield strength according to an aspect of the present invention may further include 0.0005 to 0.01% of B by weight, and, in addition, from 1.0% or less of Cu and 5.0% or less of Cr. It may further include one or more selected types.

Copper (Cu): 1% or less

Copper (Cu) is an element that stabilizes austenite along with manganese (Mn) and carbon (C), and is an element that contributes to the improvement of low-temperature toughness of steel. In addition, since copper (Cu) has a very low solubility in carbide and a slow diffusion in austenite, it is concentrated at the interface between austenite and carbide and surrounds the nucleus of fine carbide, thereby further diffusion of carbon (C) It is an element that effectively inhibits the formation and growth of carbides. Accordingly, copper (Cu) may be added to secure low-temperature toughness, and copper (Cr) may be added in excess of 0%. A preferable lower limit of the copper (Cu) content may be 0.3%, and a more preferable lower limit of the copper (Cu) content may be 0.4%. On the other hand, when the content of copper (Cu) exceeds 1%, the hot workability of the steel may be reduced, and the present invention may limit the upper limit of the content of copper (Cu) to 1%. The upper limit of the preferable copper (Cu) content may be 0.9%, and the upper limit of the more preferable copper (Cu) content may be 0.7%.

Chromium (Cr): 5.0% or less

Chromium (Cr) is a winsaw that stabilizes austenite up to an appropriate amount and contributes to improvement of impact toughness at low temperatures, and is dissolved in austenite to increase the strength of steel. Moreover, chromium is also an element which improves the corrosion resistance of steel materials. Therefore, chromium (Cr) may be added to achieve this effect, and chromium (Cr) may be added in excess of 0%. A preferable lower limit of the chromium (Cr) content may be 1.2%, and a more preferable lower limit of the chromium (Cr) content may be 2.5%. However, since chromium (Cr) is a carbide-forming element and is also an element that reduces low-temperature impact by forming carbides at the austenite grain boundary, the present invention considers the content relationship with carbon (C) and other elements added together. The upper limit of the chromium (Cr) content may be limited to 5.0%. A preferable upper limit of the chromium (Cr) content may be 4.5%, and a more preferable upper limit of the chromium (Cr) content may be 4.0%.

Boron (B): 0.0005~0.01%

Boron (B) is a grain boundary strengthening element that strengthens the austenite grain boundary, and is an element capable of effectively lowering the high temperature cracking sensitivity of the steel by strengthening the austenite grain boundary even by adding a small amount. Therefore, in order to achieve such an effect, in the present invention, 0.0005% or more of boron (B) may be added. A preferred lower limit of the boron (B) content may be 0.001%, and a more preferred lower limit of the boron (B) content may be 0.002%. On the other hand, if the content of boron (B) exceeds a certain range, segregation at the austenite grain boundary increases the high temperature cracking sensitivity of the steel, so the surface quality of the steel may be reduced. ) may limit the upper limit of the content to 0.01%. A preferable upper limit of the boron (B) content may be 0.008%, and a more preferable upper limit of the boron (B) content may be 0.006%.

The austenitic high manganese steel having excellent yield strength according to an aspect of the present invention may include the remainder Fe and other unavoidable impurities in addition to the above-described components. However, since unintended impurities from raw materials or the surrounding environment may inevitably be mixed in the normal manufacturing process, it cannot be completely excluded. Since these impurities are known to those of ordinary skill in the art, all contents thereof are not specifically mentioned in the present specification. In addition, addition of effective ingredients other than the above composition is not excluded.

The austenitic high manganese steel having excellent yield strength according to an aspect of the present invention may contain 95 area% or more of austenite as a microstructure, thereby effectively securing cryogenic toughness of the steel. The average grain size of austenite may be 5 ~ 150㎛. The average grain size of austenite that can be realized in the manufacturing process is 5 µm or more, and when the average grain size is greatly increased, there is a concern about a decrease in strength of the steel, so the grain size of austenite may be limited to 150 µm or less.

In the austenitic high manganese steel having excellent yield strength according to an aspect of the present invention, the intra-grain boundary fraction may be 7 area% or more, and the preferred intra-grain boundary fraction may be 10% or more. The intra-grain boundary of the present invention may be interpreted as meaning including a newly formed grain boundary in a low-pressure process to be described later. That is, a microstructure having certain grains may be formed in the steel material by a series of processes of slab heating, hot rolling, and cooling, and in some cases, a deformed structure may be formed in a very small amount in one grain. In the case of the present invention, since a slight pressure reduction is performed after cooling, a large amount of new deformed structures can be formed in the crystal grains, and the intra-grain boundaries of the present invention include grain boundaries newly introduced into the grains through the low-pressure reduction process as described above. can be interpreted as Also, the intra-grain boundary of the present invention may be interpreted as a concept including both high- and small-angle grain boundaries. Since the austenitic high manganese steel of the present invention is manufactured by introducing a low-pressure process, intra-grain boundaries of 7 area% or more, preferably 10% or more intra-grain boundaries are formed, thereby effectively securing the yield strength of the steel. can

On the other hand, when grain boundaries are excessively formed in grains, the yield strength of the steel increases while the elongation of the steel rapidly deteriorates. Therefore, the present invention can limit the upper limit of the intra-grain boundary fraction to 80 area% for coexistence of the yield strength and elongation of the steel. More preferably, the upper limit of the intra-grain boundary fraction may be 60 area%.

The austenitic high manganese steel having excellent yield strength according to an aspect of the present invention may include carbide and/or ε-martensite as possible structures other than austenite. When the fraction of carbide and/or ε-martensite exceeds a certain level, the toughness and ductility of the steel may be rapidly reduced, and the present invention reduces the fraction of carbide and/or ε-martensite to 5 area% or less. can be limited

The austenitic high manganese steel having excellent yield strength according to an aspect of the present invention limits the content range of alloy components so ^{that the stacking fault energy (SFE) expressed by the following relation 1 satisfies the range of 10 to 19 mJ/m 2 .} can

[Relational Expression 1]

Stacking Fault Energy (SFE) = -24.9 + 0.814*Mn + 44.3*C - 0.62*Si + 1.06*Cu + 7.9*Al - 0.555*Cr

(In Relation 1, Mn, C, Si, Cu, Al, and Cr mean wt% of each component content)

When the stacking fault energy (SFE) expressed by Relation 1 is ^{less than 10 mJ/m 2} , ε-martensite and α'-martensite may be formed, and in particular, when α'-martensite occurs, the low-temperature toughness decreases rapidly. problems may arise. A more preferable stacking fault energy (SFE) may be 11 mJ/m ^{2 or} more. In addition, the higher the stacking fault energy (SFE) represented by the equation 1 increases the stability of the austenite is undesirable in the light of the efficiency of the alloy element is added if the increase in one, and the value exceeding 19mJ / m ^2. More preferably, the upper limit of the stacking fault energy (SFE) may be ^{16 mJ/m 2 .}

The austenitic high manganese steel having excellent yield strength according to an aspect of the present invention has a yield strength of 400 MPa or more, a tensile strength of 800 MPa or more, an elongation of 30% or more, and a Charpy impact toughness of 30 J or more (based on a thickness of 5 mm) at -196 ° C. Therefore, it is possible to provide a structural steel material particularly suitable for a cryogenic environment.

Hereinafter, the manufacturing method of the present invention will be described in more detail.

The method for manufacturing austenitic high manganese steel having excellent yield strength of the present invention includes a reheating step of reheating the slab in a temperature range of 1050 to 1300 °C; a hot rolling step of hot rolling the reheated slab to a finish rolling temperature of 800 to 1050° C. to provide a hot rolled material; a cooling step of cooling the hot-rolled material to a temperature range of 600° C. or less at a cooling rate of 1 to 100° C.; And it may include a low pressure step of slightly reducing the pressure of the cooled hot-rolled material at a reduction ratio of 0.1 to 10% in a temperature range of 25 ~ 400 ℃.

slab reheat

Since the slab provided in the manufacturing method of the present invention corresponds to the steel composition of the austenitic high manganese steel described above, the description of the steel composition and the stacking fault energy (SFE) of the slab is the above-described austenitic high manganese steel. It is replaced with a description of the steel composition and stacking fault energy (SFE).

The slab provided with the above-described steel composition may be reheated in a temperature range of 1050 to 1300 °C. If the reheating temperature is less than a certain range, there may be a problem that an excessive rolling load is applied during hot rolling, or a problem in which the alloy component is not sufficiently dissolved may occur. The present invention limits the lower limit of the slab reheating temperature range to 1050℃ can On the other hand, when the reheating temperature exceeds a certain range, there is a risk that the strength is reduced due to excessive growth of crystal grains, or the hot-rollability of the steel is deteriorated by reheating exceeding the solidus temperature of the steel. The upper limit of the reheating temperature range may be limited to 1300°C.

hot rolled

The hot rolling process includes a rough rolling process and a finish rolling process, and the reheated slab may be hot rolled and provided as a hot rolled material. At this time, the hot finish rolling is preferably performed in a temperature range of 800 to 1050 ℃. If the hot finish rolling temperature is less than a certain range, excessive rolling load due to an increase in the rolling load may be a problem, and if the hot finish rolling temperature exceeds a certain range, the grains grow coarsely and the target strength cannot be obtained. The rolling reduction during hot rolling may be adjusted in a predetermined range according to the thickness of the desired steel material.

accelerated cooling

The hot-rolled hot-rolled material can be cooled to a cooling stop temperature of 600° C. or less at a cooling rate of 1 to 100° C./s. When the cooling rate is less than a certain range, the ductility of the steel material may be reduced due to carbides precipitated at grain boundaries during cooling and deterioration of wear resistance due to this may be a problem. have. A preferred lower limit of the cooling rate may be 10° C./s, and the cooling method may be accelerated cooling. However, the faster the cooling rate is, the more advantageous the effect of suppressing carbide precipitation is, but in consideration of the fact that a cooling rate exceeding 100°C/s in normal cooling is difficult to implement due to the characteristics of the equipment, the present invention sets the upper limit of the cooling rate to 100°C You can limit it to /s.

In addition, even if the hot-rolled material is cooled by applying a cooling rate of 10°C/s or more, carbides are highly likely to be generated and grown when cooling is stopped at a high temperature, so the present invention limits the cooling stop temperature to 600°C or less. can

under pressure

For the hot-rolled material being cooled or the hot-rolled material for which cooling has been completed, a process of weak rolling at a reduction ratio of 0.1 to 10% in a temperature range of 25 to 400° C. may be involved. When the temperature under low pressure is excessively low, there is a possibility of a phase transformation into ε-martensite or α'-martensite under low pressure, so the present invention can limit the lower limit of the temperature range of the under low pressure process to 25 ° C. The lower limit of the temperature range of the process under low pressure, which is more preferable in terms of load reduction, may be 100°C. If the temperature under low pressure is excessively high, the desired strength improvement effect cannot be achieved, so the present invention may limit the upper limit of the temperature range of the step under low pressure to 400°C.

In the present invention, in order to achieve the desired strength improvement effect, the reduction ratio under low pressure may be limited to 0.1% or more. A preferable lower limit of the reduction ratio under low pressure may be 0.5%, and a more preferable lower limit of the reduction ratio under low pressure may be 1.0%. In addition, the present invention may limit the reduction ratio under weak pressure to 10% or less in order to prevent a decrease in the elongation of the steel material. A preferable upper limit of the reduction ratio under low pressure may be 8%, and a more preferable upper limit of the reduction ratio under low pressure may be 5%.

The austenitic high manganese steel prepared as described above contains 95 area% or more of austenite as a microstructure, the grain boundary fraction in the grains may be 7 area% or more, and the yield strength of 400MPa or more, the tensile strength of 800MPa or more, and the tensile strength of 30% or more. It may have a Charpy impact toughness of 30J or more (based on 5mm thickness) based on elongation and -196°C.

Hereinafter, the present invention will be described in more detail through examples. However, it is necessary to note that the examples described below are for illustrative purposes only and not for limiting the scope of the present invention.

(Example)

Slabs provided with the alloy composition of Table 1 were prepared, and each specimen was prepared by applying the manufacturing process of Table 2. SFE in Table 1 means the stacking fault energy (mJ/m ² ) calculated through Equation 1, and Specimens 1, 6, and 11 in Table 2 refer to the specimens in the case where a weak pressure is not applied.

division Alloy composition (wt%) SFE
(mJ/m ² ) Mn C Si Cu Al Cr P S steel grade 1 23.57 0.41 0.300 0.418 0.0184 3.08 0.012 0.0015 11.1 steel grade 2 24.36 0.44 0.265 0.505 0.0315 3.39 0.011 0.0016 13.16 steel grade 3 22.1 0.385 0.22 0.2 0.026 1.95 0.012 0.0015 9.34

division slab heating hot rolled Cooling under pressure Psalter
No. steel grade furnace temperature
(℃) extraction
Temperature
(℃) finish
rolled
Temperature (℃) final
thickness
(mm) Cooling
speed
(℃/s) Cooling
stop
Temperature
(℃) plate temperature
(℃) reduction rate
(%) One steel grade 1 1186 1178 902 6 10 300 - - 2 steel grade 1 1186 1178 902 6 10 300 25 One 3 steel grade 1 1186 1178 902 6 10 300 25 3 4 steel grade 1 1186 1178 902 6 10 300 25 5 5 steel grade 1 1186 1178 902 6 10 300 25 10 6 steel grade 2 1190 1182 895 8 12 310 - - 7 steel grade 2 1190 1182 895 8 12 310 400 One 8 steel grade 2 1190 1182 895 8 12 310 400 3 9 steel grade 2 1190 1182 895 8 12 310 400 5 10 steel grade 2 1190 1182 895 8 12 310 400 10 11 steel grade 3 1216 1191 929 9 15 290 - -

The microstructure, tensile properties and impact toughness of each specimen were evaluated, and the results are shown in Table 3. The microstructure of each specimen was observed using SEM and EBSD, and the intragranular grain size fraction was measured using the EBSD Image Quality Map.

The tensile properties were tested at room temperature according to ASTM A370, and the impact toughness was measured at -196°C by processing a 5mm thick impact specimen according to the conditions of the same standard.

division microstructure Tensile properties C direction
impact toughness
(J, @-196℃) Psalm No. steel grade within the grain
grain boundary fraction
(area%) yield strength
(MPa) tensile strength
(MPa) elongation
(%) One steel grade 1 6.6 529 877 54 44 2 steel grade 1 30.8 572 922 54 40 3 steel grade 1 54.0 623 952 48 35 4 steel grade 1 59.1 686 988 43 32 5 steel grade 1 68.3 757 1063 34 25 6 steel grade 2 3.5 468 871 61 46 7 steel grade 2 15.9 503 891 60 45 8 steel grade 2 39.2 550 901 58 43 9 steel grade 2 50.5 612 913 54 40 10 steel grade 2 56.7 722 981 48 33 11 steel grade 3 3.1 417 917 53 18

As shown in Tables 1 to 3, in the case of Specimens 2 to 5 and Specimens 7 to 10 satisfying the alloy composition and process conditions of the present invention, the level of about 10% or more compared to Specimen 1 and Specimens 6 not subjected to a weak pressure It can be seen that the yield strength is increased.

1 is a result of observing the microstructure of specimen 1 using EBSD. 1(a) is an IPF map. Representing the same brightness (or saturation) within the boundary means one grain, and representing different brightness (or saturation) means different crystal orientations, that is, different grains. do. FIG. 1(b) is an IQ map for the same tissue as that of FIG.

2 is a result of observing the microstructure of specimen 10 using EBSD. Fig. 2(a) is also an IPF map. Representing the same brightness (or saturation) within the boundary means one grain, and indicating different brightness (or saturation) means different crystal orientations, that is, different grains. do. FIG. 2(b) is also an IQ map for the same tissue as that of FIG. FIG. 2(c) shows the grain boundary angle along the length of the arrow in FIG. 2(b), and it can be confirmed that new grain boundaries having incineration and high angle characteristics are generated inside the crystal grains from the lines A, B, and C. That is, from (a) to (c) of FIG. 2 , it can be confirmed that, unlike in specimen 1, in specimen 10, a large amount of new grain boundaries are formed at the grain boundaries through a low pressure process.

Although the present invention has been described in detail through examples above, other types of embodiments are also possible. Therefore, the spirit and scope of the claims set forth below are not limited to the embodiments.

Claims (12)

delete delete delete delete delete delete delete By weight%, C: 0.2 to 0.5%, Mn: 20 to 28%, Si: 0.05 to 0.5%, P: 0.03% or less, S: 0.005% or less, Al: 0.005 to 0.05%, balance Fe and other unavoidable impurities A reheating step of reheating a slab comprising a 1050 ~ 1300 ℃ temperature range;
a hot rolling step of hot rolling the reheated slab to a finish rolling temperature of 800 to 1050° C. to provide a hot rolled material;
a cooling step of accelerating cooling the hot-rolled material to a temperature range of 600° C. or less at a cooling rate of 10 to 100° C./s; and
It includes a weak pressure reducing step of lightly reducing the accelerated-cooled hot-rolled material at a reduction ratio of 1 to 5% in a temperature range of 25 to 400 °C,
The austenitic steel having a yield strength of 400 MPa or more, a tensile strength of 800 MPa or more, an elongation of 30% or more, and a Charpy impact toughness of 30 J or more (based on a thickness of 5 mm) at -196 ° C. Manufacturing method of high manganese steel. 9. The method of claim 8,
The slab, by weight%, further comprising 0.0005 to 0.01% of B, a method of manufacturing austenitic high manganese steel having excellent yield strength. 9. The method of claim 8,
The slab is, by weight, 1.0% or less of Cu and 5.0% or less of Cr, further comprising at least one selected from the group consisting of, a method of producing an austenitic high manganese steel excellent in yield strength. 11. The method of claim 10,
The slab has a stacking fault energy (SFE) expressed by the following Relational Equation 1, ^{which satisfies the range of 10 to 19 mJ/m 2} , a method of manufacturing an austenitic high manganese steel having excellent yield strength.
[Relational Expression 1]
Stacking Fault Energy (SFE) = -24.9 + 0.814*Mn + 44.3*C - 0.62*Si + 1.06*Cu + 7.9*Al - 0.555*Cr
(In Relation 1, Mn, C, Si, Cu, Al, and Cr mean wt% of each component content) delete

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