TWI715852B - Austenitic alloy steel - Google Patents

Abstract

The present invention provides an austenitic alloy steel comprising 25wt% to 31wt% of manganese, 7wt% to 10wt% of aluminum, 1.2wt% to 1.6wt% of carbon, less than 6wt% of molybdenum, and a balance of iron. The austenitic alloy steel of the invention has high strength, high ductility and high temperature strength, and has a density of 6.8 g/cm ³ , which is 14% lighter than traditional die steel.

Description

Austenitic alloy steel

The invention relates to a kind of austenitic alloy steel, in particular to a kind of austenitic alloy steel suitable for making hot processing tools.

Matian bulk steel has excellent mechanical properties such as hardness and toughness, so it is often used as a material for making hot working tools. However, Matian bulk steel has poor ductility, which may cause cracks in the finished hot working tools.

AISI H13 steel is one of the matian bulk steels used to make hot working tools. It contains 0.32wt% to 0.45wt% carbon, 0.8wt% to 1.2wt% silicon, 0.20wt% to 0.50wt% manganese, 4.75wt% % To 5.5% by weight of chromium, 1.10% to 1.75% by weight of molybdenum, 0.8% to 1.2% by weight of vanadium, no more than 0.03% by weight of phosphorus, no more than 0.03% by weight of sulfur, and a balance of iron. The AISI H13 steel has a maximum room temperature hardness of 55 to 58, and an elongation of 3% to 5%. Due to the low elongation, it is easy to be brittle in use, so the hardness of the steel will be reduced to 42 in general use. To 50, the elongation is increased to between 5% to 8%, the impact toughness is between 5 joules to 10 joules, and the high temperature hardness (Rockwell C hardness, HRc) is between 33 to 41.

QRO 90 steel is another Matian bulk steel used to make hot working tools. It contains 0.38wt% carbon, 0.30wt% silicon, 0.75wt% manganese, 2.60wt% chromium, 2.25wt% molybdenum, 0.9wt% % Vanadium, and balance iron. The QRO 90 steel has a room temperature hardness of 45, an elongation rate of 11%, an impact toughness of 10 Joules, and a high temperature hardness (Rockwell C hardness, HRc) of 26 to 41.

On the other hand, Austenite steel has application potential due to its high mechanical strength and high ductility, so it has been extensively studied in the past few decades.

When the carbon content in the conventional steel alloy exceeds about 1.2wt.%, the ductility of the alloy will be seriously degraded or embrittlement. Therefore, in the previous technology of studying the austenitic alloy system, the amount of carbon in the alloy will be controlled between 0.54-1.3wt.%. The iron-manganese-aluminum-carbon steel with this carbon content increases the mechanical strength by adding molybdenum, niobium, and/or tungsten. However, the addition of the above elements can increase the mechanical strength of conventional iron-manganese-aluminum-carbon steel Strength, but also because this kind of alloy is easy to precipitate coarse carbides on the grain boundaries of the austenitic body during aging treatment, which causes the problem of ductility (that is, elongation) decline, making the use of hot working tools made of this type of steel to be useful It is easy to crack during use.

Applicant's US Patent No. 9,528,177 discloses an iron-manganese-aluminum-carbon quaternary alloy with a specific content of iron, manganese, aluminum, and carbon. The iron-manganese-aluminum-carbon quaternary alloy uses the carbon content to be controlled between 1.4wt. % To 2.2wt.% so that the iron-manganese-aluminum-carbon quaternary alloy can form a high density in the base phase of the austenitic body through the spinodal decomposition mechanism during the quenching after the solution treatment (SHT) And the fine κ'-carbide makes the iron-manganese-aluminum-carbon quaternary alloy have excellent ductility and high mechanical strength. However, the addition of strong carbide forming elements, such as chromium, titanium, and molybdenum, to the iron-manganese-aluminum-carbon quaternary alloy cannot significantly affect the formation of high-density and fine-grained κ'-carbides in the base phase of the austenitic body. Therefore, it is not recommended to add these strong carbide forming elements to the iron-manganese-aluminum-carbon quaternary alloy.

Therefore, the object of the present invention is to provide an Austenite alloy steel that has excellent mechanical properties at room temperature without affecting ductility, and also has excellent strength at high temperatures.

Therefore, the austenitic alloy steel of the present invention contains 25wt% to 31wt% of manganese, 7wt% to 10wt% of aluminum, 1.2wt% to 1.6wt% of carbon, greater than 0wt% and less than 6wt% of molybdenum, and a balance Of iron.

The effect of the present invention is: by adding less than 6wt% molybdenum to the iron-aluminum-manganese-carbon austenitic alloy steel of specific composition, the austenitic alloy steel has excellent mechanical properties at room temperature, and the limit Tensile strength, and can also have good strength performance at high temperature (~500℃).

The present invention discloses an Austenite alloy steel with high strength and high ductility. The Austenite alloy steel can be applied to general steel plates (such as automobile steel plates), parts (such as gears) or hot die steels.

The alloy composition of the austenitic alloy steel includes 25wt% to 31wt% manganese, 7wt% to 10wt% aluminum, 1.2wt% to 1.6wt% carbon, greater than 0wt% and less than 6wt% of molybdenum, and a balance amount Of iron.

Manganese is a strengthening element for the austenitic field. Because the austrian field is a face-center-cubic (FCC) structure and has more slip systems, it is compared with body-centered cubic (body-center- Cubic (BCC) structure or hexagonal close packed (HCP) structure has better ductility. In order to obtain a complete austenitic structure at room temperature, the manganese content in the austenitic alloy steel of the present invention is 25wt% to 31wt%. In some embodiments, the manganese content of the austenitic alloy steel is between 26 wt% and 30 wt%. In some embodiments, the manganese content of the austenitic alloy steel is between 27 wt% and 29 wt%.

Aluminum is not only a strengthening element for the austenitic field, but also the main element for the formation of (Fe,Mn) ₃ AlC _x carbides (ie κ'-carbides). The aluminum content in the austenitic alloy steel of the present invention is 7wt% To 10wt%. In some embodiments, the aluminum content of the austenitic alloy steel is between 8wt% and 10wt%. In some embodiments, the aluminum content of the austenitic alloy steel is between 8 wt% and 9 wt%.

The carbon content in the austenitic alloy steel of the present invention is 1.2wt% to 1.6wt%, which is higher than the carbon content of the conventional iron-manganese-aluminum-carbon austenitic steel containing molybdenum, niobium, and/or tungsten (that is, the highest 1.0wt%). In some embodiments, the carbon content of the austenitic alloy steel is 1.3 wt% to 1.6 wt%.

Molybdenum is a strong carbide-forming element. In the austenitic alloy steel of the present invention, the content of molybdenum is greater than 0wt% and less than 6wt%. In some embodiments, the molybdenum content of the austenitic alloy steel is between 2wt% and 6wt%.

In some embodiments, the austenitic alloy steel further contains chromium, which is also a strong carbide forming element, and the content of chromium is less than 6 wt%.

In some embodiments, the austenitic alloy steel further contains cobalt, which is also a strong carbide forming element, and the content of cobalt is less than 5 wt%.

It should be noted that the content of low-melting elements (such as manganese and aluminum) in the austenitic alloy steel will be caused by volatilization during the smelting process. The amount of addition during smelting is different, however, the difference between the two is not large, and within the allowable error range without affecting the properties of the final austenitic alloy.

With reference to FIG. 1, the manufacturing method of the austenitic alloy steel includes steps 91 to 95.

The step 91 is to smelt the alloy composition of the aforementioned austenitic alloy steel into a casting in a high-frequency melting furnace under the atmosphere.

Then, step 92 is performed to perform a hot work treatment (such as hot rolling, hot forging, etc.) on the casting at 1100° C. to 950° C. to a predetermined shape to become a hot work piece.

Then proceed to step 93, the hot work piece is water quenched for the first time and cooled to room temperature.

Then proceed to step 94. In step 94, the hot work piece after the first water quenching treatment is subjected to aging treatment at 480°C to 600°C.

In detail, when the temperature of the aging treatment is between 480°C and 500°C, the time of the aging treatment (Aging time) is 5 to 12 hours; when the temperature of the aging treatment is greater than 500°C, the time of the aging treatment is 1 to 4 hours.

Finally, step 95 is performed to perform a second water quenching of the hot work piece after the aging treatment and cool it to room temperature to complete the production of the austenitic alloy steel.

The manufacturing process of the austenitic alloy steel of the present invention is different from the conventional iron-manganese-aluminum-carbon alloy steel with low carbon content and strong carbide-forming elements, and the conventional iron-manganese-aluminum with low carbon content and strong carbide-forming elements After the carbon alloy steel is hot processed, it needs to undergo a solution heat treatment to re-dissolve the coarse carbide precipitated on the grain boundary in the base phase to improve the ductility of the iron-manganese-aluminum-carbon alloy steel. Although the composition of field alloy steel has a relatively high content of carbon and strong carbide forming elements, however, the present invention uses hot work treatment (hot rolling or hot forging) temperature control (1100°C to 950°C), so it can avoid The iron-manganese-aluminum-carbon alloy composition precipitates coarse carbides on the grain boundaries during the hot working treatment, so the conventional solution heat treatment step is not required after the hot working treatment to make the austenitic body obtained Alloy steel has both strength and ductility.

In addition, it should be noted that the aforementioned step 95 can also be performed depending on the manufacturing process, that is, the hot work piece can be naturally cooled to room temperature after the aging treatment, without performing a second water quenching. Furthermore, the present invention uses the control of the heat treatment temperature to effectively avoid the precipitation of coarse carbides and affect the ductility of the alloy steel. Therefore, the conventional hot solution step can be omitted, and the overall process time can be effectively reduced. However, after the hot work treatment and the first water quenching, you can also choose to perform the hot solution step. This process does not affect the overall characteristics of the alloy steel in this case.

In particular, the austenitic alloy steel produced by using the austenitic ferroalloy composition of the present invention and the production method of this case is a complete austenitic phase, and its yield strength (YS) at room temperature (25°C) is 1200MPa To 1400MPa, Rockwell C hardness (HRc) between 45 to 55, ultimate tensile strength between 1200MPa to 1500MPa, and elongation (El) between 20% to 40%, and at the same time can be at high temperature (< 700℃) has good yield strength (YS) and ultimate tensile strength (UTS). Therefore, the austenitic alloy steel in this case can be used as general steel plates (such as automobile steel plates) and parts (such as gears), and is more suitable for hot work die steel.

In addition, it should be noted that the density of the general iron-aluminum-manganese-carbon alloy is about 6.6~6.8g/cm ³ , which is 14% lighter than the general mold steel (density about 7.8~7.9g/cm ³ ). Therefore, in addition to high strength and high ductility, the austenitic alloy steel of the present invention can also have the advantages of light weight.

The conventionally known high carbon content (1.4wt.% to 2.2wt.%) iron-aluminum-manganese-carbon alloys can be obtained through process control (heat treatment/solution/quenching) to obtain a complete austenitic phase, and There are very dense and fine nano-sized (Fe,Mn) ₃ AlC _x carbides (κ'-carbides) in the austenitic bulk phase base, which can avoid the precipitation of coarse carbides on the grain boundaries. Therefore, the The iron-aluminum-manganese-carbon alloy has basically good mechanical properties and elongation at room temperature. However, the present invention found that when the content of carbide strengthening elements (molybdenum, chromium, cobalt) is added to a specific proportion of iron-manganese-aluminum-carbon alloy composition with a content of 2-6wt%, and the heat treatment temperature is controlled, it can be effective Avoid the disadvantages of coarse carbide precipitation on the grain boundaries that would greatly reduce the ductility of the material. Therefore, in addition to maintaining the ductility of the iron-aluminum-manganese-carbon alloy steel produced at room temperature, it can also be further improved The iron-aluminum-manganese-carbon alloy steel has room temperature and high-temperature strength. In addition, because the iron-aluminum-manganese-carbon alloy steel in this case does not require a solution treatment step, it can effectively reduce the overall process time.

The following specific examples 1 to 11 and comparative examples 1 to 3 are used to make test specimens and then perform related physical property tests to more specifically illustrate the characteristics of the austenitic alloy steel of the present invention.

It should be noted that the following specific examples are intended to illustrate and demonstrate the austenitic alloy steel of the present invention, and should not be used to limit the scope of the present invention.

Specific example 1

1. The alloy composition containing 30wt% of manganese, 8.5wt% of aluminum, 1.45wt% of carbon, 6% of molybdenum, and a balance of iron is melted in a high-frequency smelting furnace under the atmosphere to produce a thickness of 2 cm casting.

2. Heat the casting in a furnace at 1100°C for 20 minutes, and then perform hot rolling at 1100°C to 950°C to a thickness of at least less than 25% of the thickness of the casting to obtain a test piece.

3. Perform the first water quenching of the test piece to room temperature, then grind to remove the oxide layer, then perform aging treatment at 500°C, and finally perform the second water quenching of the test piece to room temperature stand-by.

Specific examples 2 to 11

The manufacturing method of the test specimens of the specific examples 2 to 11 is the same as the test specimens of the specific example 1, except for the content of each element in the alloy.

Comparative example 1~3

The preparation method of the test specimens of Comparative Examples 1 to 3 is the same as that of Specific Example 1, except for the content of each element in the alloy.

The alloy composition element contents of these specific examples and comparative examples are summarized as shown in Table 1.

Table 1

Then, the test specimens prepared in the foregoing specific examples and comparative examples were tested for yield strength (YS), ultimate tensile strength (UTS), elongation (El), and hardness (HRc).

The yield strength, ultimate tensile strength, elongation, and hardness of the test specimens were measured at room temperature using the following test methods. The measurement results are shown in Table 2.

In addition, the test specimens of the specific examples 4, 7 and 9 and comparative examples 1 to 3 were tested for yield strength and ultimate tensile strength at 300°C, 500°C, and 700°C. The results are shown in Table 3.

Test method of each characteristic:

1. Tensile test

Yield Strength (Yield Strength, YS): The stress when the tensile curve is parallel to the elastic line by 0.2% strain.

Ultimate Tensile Strength (UTS): The maximum stress in the tensile curve.

Elongation (Elongation, El): The tensile curve uses the breaking point to draw the amount of strain parallel to the elastic line.

The aforementioned yield strength, ultimate tensile strength, and elongation are obtained by testing with an Instron tensile testing machine at room temperature (25° C.) at a tensile rate of 10 ^-3 /sec. Among them, the specifications of the test specimens refer to the ASTM E8/E8M specifications. In the high temperature test, the high temperature furnace is installed in the tensile testing machine, and the tensile test is performed after heating to a predetermined temperature.

2. Hardness test (HRc)

A Rockwell Hardness machine is used to test with a load of 150kgf. The indenter is a diamond cone.

Table 2

table 3

As shown in Table 2, the room temperature yield strength of the test specimens prepared in specific examples 1 to 11 is between 1230 MPa and 1350 MPa, the room temperature ultimate tensile strength is between 1280 MPa and 1386 MPa, and the room temperature elongation is between 20% and 37. %, and the hardness (HRc) is between 45.0 and 47.7. Compared with the characteristic data of Comparative Example 1 and Comparative Example 2, it is shown that the austenitic alloy steel of the present invention does have high strength and good ductility. Sex. In particular, by controlling the molybdenum content in the austenitic alloy steel at 2wt% to 6wt%, compared with Comparative Examples 1 to 3, and the two conventional hot working alloys of AISI H13 and QRO 90, The austenitic alloy steel of the present invention not only maintains excellent room temperature strength and room temperature elongation, but also has a certain strength at high temperatures, showing that the austenitic alloy steel of the present invention has good ductility and can also be used as The use of a new type of hot work alloy steel can avoid the cracking of the manufactured hot work tool during use.

Preferably, the carbon content of the austenitic alloy steel is between 1.42wt% and 1.5wt%, and the molybdenum content is between 3.5wt% and 5wt%, and the ultimate tensile strength of the austenitic alloy steel can reach 1353MPa To 1386MPa, the yield strength can reach 1310MPa to 1340MPa, and the hardness can reach 47 to 47.7.

More preferably, the carbon content of the austenitic alloy steel is between 1.42wt% and 1.45wt%, and the molybdenum content is between 3.5wt% and 4wt%, and the elongation of the austenitic alloy steel can reach 25%.

Preferably, the manganese content of the austenitic alloy steel is between 27.7wt% and 30wt%, and the aluminum content is between 8.2wt% and 8.5wt%, and the ultimate tensile strength of the austenitic alloy steel is up to 1280MPa To 1386MPa, the yield strength can reach 1250MPa to 1350MPa, the hardness can reach 46.7 to 47.7, and the elongation rate can reach 20% to 32%.

Preferably, the manganese content of the austenitic alloy steel is between 27wt% and 29wt%, the aluminum content is between 8.0wt% and 8.5wt%, and the molybdenum content is between 3.0wt% and 6wt%. The elongation of alloy steel can be greater than 20%, the ultimate tensile strength at room temperature can be greater than 1280MPa, the yield strength can be greater than 1230MPa, and the ultimate tensile strength and yield strength at 300°C can be greater than 1000MPa.

Preferably, the austenitic alloy steel has a molybdenum content of 3.0wt% and contains 3wt% chromium or 2wt% cobalt, and the ultimate tensile strength of the austenitic alloy steel at room temperature can reach 1280MPa to At 1344MPa, the yield strength can reach 1230MPa to 1300MPa, the hardness can reach 45 to 46.8, and the elongation rate can reach 24% to 37%.

In addition, it should be noted that from the mechanical strength data in Table 2, it can be seen that the aging time of the specific examples 1 to 11 is between 5 to 12 hours and has no significant effect on the final mechanical strength, which shows that the present invention uses heat treatment temperature The control can effectively avoid the precipitation of coarse carbides. Therefore, the aging treatment time can have greater flexibility, and it will not be caused by the longer the aging time of conventional iron-manganese-aluminum-carbon steels, the more significant the precipitation of coarse carbides. The problem of reduced ductility.

Refer to Figures 2 to 4. Figures 2 to 4 are optical microscope photos of the specific examples 1, 3, and 8 after heat treatment, and Figures 5 to 7 are the specific examples 1, 3, and 8 after heat treatment and Optical microscope photograph after aging treatment. It can be seen from Figures 2 to 4 that when the hot work temperature is controlled at 1100°C to 950°C, coarse carbides are not easy to precipitate at the grain boundaries after the hot work treatment. Therefore, after further treatment with different aging time, with reference to Figures 5-7, it is not easy to produce coarse carbides. However, referring to Figures 8 and 9, Figures 8 and 9 are optical micrographs of the comparative examples 1 and 2 after heat treatment. It can be seen from Figures 8 and 9 that when the strong carbide forming elements are excessively added, the thermal work is controlled The treatment temperature will still precipitate a large amount of coarse carbides, which is not conducive to the ductility of the iron-manganese-aluminum-carbon alloy.

In addition, from the high-temperature tensile strength results in Table 3 above, it can be seen that the yield strength of the iron-aluminum-manganese-carbon-worth field alloy steel produced by the present invention at 300°C is between 970 MPa and 1030 MPa, and the ultimate tensile strength is between 1022 MPa and 1070 MPa. The yield strength at 500°C is between 650MPa and 700MPa, the ultimate tensile strength is between 719MPa and 786MPa, the yield strength at 700°C is between 410MPa and 420MPa, and the ultimate tensile strength is between 440MPa and 449MPa. Although Comparative Example 3 has good ductility at room temperature, the yield strength and ultimate tensile strength at room temperature and high temperature (300°C, 500°C) are still inferior to the present invention. In comparison, the present invention Sitati alloy steel not only has good strength performance at room temperature, but also has good mechanical strength at 300°C and 500°C, so it can be used as a new type of medium and low temperature hot work alloy steel.

In summary, according to the prior art, in the conventional iron-manganese-aluminum-carbon alloy with a carbon content of less than 1wt%, strong carbide-forming elements such as molybdenum and tungsten (for example: Fe-29Mn-9Al- 0.9C-0.6Mo, Fe-29Mn-9Al-0.9C-0.4Mo-0.6W and other iron-manganese-aluminum-carbon alloys) can improve the ductility of the alloy, but cannot significantly increase the strength of the alloy, and the low-carbon content of iron Manganese-aluminum-carbon alloys are added with more content of these strong carbide forming elements (for example: Fe-27.9Mn-8.6Al-1.0C-0.51Mo-0.73W-0.55Nb iron-manganese-aluminum-carbon alloy), although it can increase the alloy Strength but cannot maintain good ductility. The aforementioned US Patent No. 9,528,177 also discloses that adding these strong carbide forming elements to high-carbon iron-manganese-aluminum-carbon alloys cannot effectively improve the ductility of the alloy. Therefore, it is not recommended for high-carbon iron-manganese-aluminum-carbon alloys. These strong carbide-forming elements are added to it. However, the austenitic alloy steel of the present invention controls the content of each element in the high-carbon iron-manganese-aluminum-carbon alloy composition within a specific range and matches a specific heat treatment temperature to make the austenitic steel finally produced Alloy steel has excellent mechanical strength and ductility at the same time at room temperature, and can maintain proper strength at high temperature, and is light in weight and good in performance. It can be used as a steel for mechanical parts and heat treatment tools. Invented austenitic alloy steel can not only be used as general steel, but also as hot-work alloy steel, so it can indeed achieve the purpose of the invention.

However, the above are only examples of the present invention. When the scope of implementation of the present invention cannot be limited by this, all simple equivalent changes and modifications made in accordance with the scope of the patent application of the present invention and the content of the patent specification still belong to This invention patent covers the scope.

91~95‧‧‧Step

Other features and effects of the present invention will be clearly presented in the embodiments with reference to the drawings, in which: Figure 1 is a block diagram of the production process of the austenitic alloy steel of the present invention; Figure 2 is the austenitic alloy steel of the present invention An optical microscope photograph of specific example 1 of alloy steel after hot work treatment; Figure 3 is an optical microscope photograph of specific example 3 of the austenitic alloy steel of the present invention after hot work treatment; Fig. 4 is an optical microscope photograph of austenitic alloy steel of the present invention after hot work Optical microscope photograph of specific example 8 of alloy steel after hot work treatment; Fig. 5 is an optical microscope photograph of specific example 1 of austenitic alloy steel of the present invention after aging treatment; Fig. 6 is an optical microscope photograph of austenitic alloy steel of the present invention after aging treatment; The optical microscope photograph of concrete example 3 of steel after aging treatment; Figure 7 is the optical microscope photograph of concrete example 8 of the austenitic alloy steel of the present invention after aging treatment; Fig. 8 is the optical microscope photograph of the austenitic alloy steel of the present invention after aging treatment The optical microscope photograph of Comparative Example 1 after the hot work treatment; and FIG. 9 is the optical microscope photograph of Comparative Example 2 of the austenitic alloy steel of the present invention after the hot work treatment.

Claims (17)

A kind of austenitic alloy steel, containing 25wt% to 31wt% manganese, 7wt% to 10wt% aluminum, 1.4wt% to 1.6wt% carbon, 2wt% to 6wt% molybdenum, and a balance of iron . The austenitic alloy steel according to claim 1, wherein the proportion of the manganese is between 26wt% and 30wt%, and the proportion of the aluminum is between 8wt% and 10wt%. The austenitic alloy steel of claim 2, wherein the proportion of the manganese is between 27wt% and 29wt%, and the proportion of the molybdenum is between 2wt% and 6wt%. The austenitic alloy steel according to claim 3, wherein the proportion of the aluminum is 8wt% to 9wt%. The austenitic alloy steel described in claim 1 further contains chromium in a proportion of less than 6wt%. The austenitic alloy steel described in claim 1 further contains cobalt in a proportion of less than 5wt%. The austenitic alloy steel according to claim 1, wherein the austenitic alloy steel is a complete austenitic phase, has an elongation of 20 to 40% at 25°C, and an ultimate tensile strength greater than 1250MPa, and the ultimate tensile strength at 300°C is greater than 1000MPa. A manufacturing method of austenitic alloy steel, comprising: step (a): smelting the composition of austenitic alloy steel as described in claim 1 into a casting; step (b): treating the austenitic alloy steel at 1100°C to 950°C The casting is hot-worked to become a hot-worked part; Step (c): the hot-worked part is subjected to the first water treatment Quenching; and step (d): aging the hot work piece after the first water quenching at 480°C to 600°C. The method for manufacturing austenitic alloy steel according to claim 8, wherein the temperature of the aging treatment is 480°C to 500°C, the time of the aging treatment is 5 to 12 hours, and the temperature of the aging treatment When it is greater than 500°C to 600°C, the aging treatment time is 1 to 4 hours. The manufacturing method of austenitic alloy steel according to claim 8 further includes a step (e) of subjecting the aging-treated casting to a second water quenching. The method for manufacturing austenitic alloy steel according to claim 8, wherein the step (b) is to heat the casting to a thickness of at least less than 25% of the thickness of the casting. An austenitic alloy steel produced by the manufacturing method according to claim 8, wherein the austenitic alloy steel is a complete austenitic phase, and has very dense and fine particles in the austenitic phase base. The nano-sized (Fe,Mn) ₃ AlC _x carbide (κ'-carbide) has an elongation of 20 to 40% at room temperature and an ultimate tensile strength greater than 1000 MPa at 300°C. The austenitic alloy steel according to claim 12, wherein the yield strength of the austenitic alloy steel at room temperature is between 1230 and 1350 MPa, and the ultimate tensile strength is between 1280 and 1386 MPa. The austenitic alloy steel according to claim 12, wherein the Rockwell hardness of the austenitic alloy steel at room temperature is between 45 and 48. The austenitic alloy steel according to claim 12, wherein the yield strength of the austenitic alloy steel at 300°C is greater than 970MPa. The austenitic alloy steel according to claim 12, wherein the yield strength of the austenitic alloy steel at 500°C is greater than 650 MPa, and the ultimate tensile strength is greater than 700 MPa. The austenitic alloy steel according to claim 12, wherein the yield strength of the austenitic alloy steel at 700°C is between 410 and 420 MPa, and the ultimate tensile strength is between 440 and 449 MPa.

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