HIGH-ENTROPY AUSTENITIC STAINLESS STEEL AND PREPARATION METHOD THEREOF

Abstract

A high-entropy austenitic stainless steel and a preparation method thereof are provided. The elemental composition of the stainless steels developed by the invention is as follows: Cr: 5-30%; Ni: 5-50%; Ti: 1-15%; Al: 1-15%; the rest are Fe and inevitable impurities; preferably, the composition is Cr: 5-19%; Ni: 5-29%; Ti: 6-15%; Al: 5-15%; the rest element is Fe. By adjusting the atomic ratio of each element, the nano-sized precipitates are generated as much as possible, and the strength is maximized while maintaining a high plasticity. The stainless steels provided by this invention have only five alloying components, a low manufacturing cost, and high-strength and high-plasticity. They can be widely used in many industrial fields such as aviation, aerospace, marine, and nuclear power with broad market prospects.

Claims

1. A high-entropy austenitic stainless steel, comprising an elemental composition expressed with an atomic percentage content as follows: 5-30% of Cr; 5-50% of Ni; 1-15% of Ti; 1-15% of Al; and a balance of Fe.

2. The high-entropy austenitic stainless steel according to claim 1, wherein the elemental composition expressed with the atomic percentage content is as follows: 5-19% of the Cr; 5-29% of the Ni; 6-15% of the Ti; 5-15% of the Al; and the balance of the Fe.

3. The high-entropy austenitic stainless steel according to claim 1, wherein a size of each of nano-sized precipitates in the high-entropy austenitic stainless steel is ?30 nm, and a number density of each of the nano-sized precipitates is ?5.0?10.sup.21 m.sup.?3.

4. A preparation method for a high-entropy austenitic stainless steel, comprising steps of: mixing raw materials according to atomic percentage content to obtain a resulting mixture; melting and casting the resulting mixture in a vacuum argon arc furnace to obtain an ingot; performing solution/homogenization treatment on the ingot to obtain a first resulting product; performing a first process by cold rolling and recrystallizing the first resulting product to obtain a second resulting product or performing a second process by hot rolling, cold rolling, and recrystallizing the first resulting product to obtain a second resulting product; carrying out an aging treatment on the second resulting product to obtain the high-entropy austenitic stainless steel.

5. The preparation method according to claim 4, wherein the cold rolling in the first process is as follows: a reduction in thickness per pass is no more than 0.2 mm, and a total reduction in thickness is 60%-70%.

6. The preparation method according to claim 4, wherein the hot rolling and the cold rolling in the second process is as follows: carrying out the hot rolling at a temperature of 800-1150? C., wherein a reduction in thickness per pass of the hot rolling is no more than 0.5 mm, and the temperature is guaranteed to be within a range of 800-1150? C. during the hot rolling; when the temperature decreases during the hot rolling, the first resulting product is put back into a furnace and remained within the range of 800-1150? C. for 5-15 min; after a total reduction in thickness during the hot rolling is 50%-60%, carrying out the cold rolling, wherein a reduction in thickness per pass during the cold rolling is no more than 0.2 mm, and a total reduction in thickness is 60%-70%.

7. The preparation method according to claim 4, wherein an operation of the recrystallizing is as follows: remaining the first resulting product rolled by the first process or the second process at 1140-1160? C. for 1-3 min; a heating rate of the recrystallizing is 10-20? C./min.

8. The preparation method according to claim 4, wherein vacuuming the vacuum argon arc furnace to a pressure better than 5.0?10.sup.?3 Pa to obtain a first resulting furnace and then filling argon into the first resulting furnace to a pressure of 5.0?10.sup.3 Pa to obtain a second resulting furnace, removing oxygen with pure Ti in the second resulting furnace, starting the melting when an oxygen content and a nitrogen content in the second resulting furnace are lower than 0.002% within 180 min; the melting is repeated at least four times.

9. The preparation method according to claim 4, wherein an operation of the solution/homogenization treatment is as follows: heating the ingot to 1140-1160? C. under a vacuum with a pressure better than 1.0?10.sup.?3 Pa to obtain a heated ingot, remaining the heated ingot at 1140-1160? C. for 1-2.5 h, and then quenching the heated ingot in water or cooling the heated ingot in air to obtain the first resulting product; a heating rate of the solution/homogenization treatment is 10-20? C./min.

10. The preparation method according to claim 4, wherein an operation of the aging treatment is as follows: ageing the second resulting product at 500-600? C. for 0.5-1.5 h to obtain a third resulting product and then quenching the third resulting product in water or cooling the third resulting product in air to obtain the high-entropy austenitic stainless steel; a heating rate of the aging treatment is 5-15? C./min.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] FIG. 1 is an X-ray diffraction pattern of the high-entropy austenitic stainless steel Fe.sub.47Cr.sub.16Ni.sub.26Ti.sub.6Al.sub.5.

[0038] FIG. 2 is a transmission electron microscopy and element distribution image of the high-entropy austenitic stainless steel Fe.sub.47Cr.sub.16Ni.sub.26Ti.sub.6Al.sub.5.

[0039] FIG. 3 is an engineering stress-strain curve of the high-entropy austenitic stainless steel measured at room temperature.

[0040] FIG. 4 is a comparison of the yield strength Re and the fracture elongation E of commercial stainless steels and the FeCrNiTiAl high-entropy austenitic stainless steels.

[0041] FIG. 5 is a comparison of the tensile strength R.sub.m and the fracture elongation E of commercial stainless steels and the FeCrNiTiAl high-entropy austenitic stainless steels.

[0042] FIG. 6 is a comparison of the yield strength and the product of strength and plasticity [ultimate tensile strength (UTS)?fracture elongation] of commercial stainless steels and the FeCrNiTiAl high-entropy austenitic stainless steels.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0043] In order to understand the invention more clearly, the invention is further described with reference to the following embodiments and drawings. The embodiments are only used to explain without limiting the invention in any way. In the embodiments, each raw reagent material is commercially available, and the unspecified experimental method and condition are those well known in the field, or according to those recommended by the instrument manufacturers.

Embodiment 1

[0044] This embodiment provides a high-entropy austenitic stainless steel with a chemical composition of Fe.sub.47Cr.sub.16Ni.sub.26Ti.sub.6Al.sub.5 (atomic ratio) or Fe.sub.48.56Cr.sub.15.39Ni.sub.28.24Ti.sub.5.32Al.sub.2.5 (weight ratio). The influence of the introduction of unavoidable and very few impurity elements (C, N, O, etc.) during the melting process and heat treatment process on the properties of the material can be ignored.

[0045] The preparation steps of the high-entropy austenitic stainless steels are as follows:

[0046] According to the design proportion of elements, the raw elemental materials with a purity?99.9% were weighed and mixed. The argon arc furnace was vacuumed to a pressure below 5.0?10.sup.?3 Pa and then filled with argon to a pressure of 5.0?10.sup.3 Pa. When the oxygen content and nitrogen content in the furnace were lower than 0.002% within 180 min, 30 g of pure Ti was melted first to remove oxygen and then the arc melting was started. A 60?10?5 mm.sup.3 flake ingot was obtained by the arc melting for 6 times.

[0047] The ingot was placed in a furnace for solution and homogenization treatment. The ingot was heated to 1150? C. at a rate of 15? C./min, remained at 1150? C. for 120 min, and then quenched in water. Cold rolling deformation was performed for the ingot after the solution/homogenization treatment. The rolling process was as follows: the reduction in thickness per pass was no more than 0.2 mm, and the total reduction in thickness was 66.7%. The rolled ingot was heated to 1150? C. at a rate of 10? C./min and recrystallized at 1150? C. for 1.5 min. The recrystallized ingot was heated to 600? C. at a rate of 10? C./min, remained at 600? C. for 1 h, and then quenched in water to complete the aging treatment.

[0048] The conventional Cu K? radiation was used as the X-ray source for x-ray diffraction. The diffraction pattern was shown in FIG. 1, where the diffraction peaks can be indexed as the (111), (200), (220), (311), (222) diffraction peaks of a face-centered structure, so the obtained structure was austenitic. Because the size of the nano-sized precipitates was too small, they did not exhibit any visible diffraction peak on the X-ray diffraction patterns.

Embodiment 2

[0049] This embodiment provides a high-entropy austenitic stainless steel with a chemical composition of Fe.sub.47Cr.sub.16Ni.sub.26Ti.sub.6Al.sub.5 (atomic ratio) or Fe.sub.48.36Cr.sub.15.39Ni.sub.28.24Ti.sub.5.32Al.sub.2.5 (weight ratio). The influence of the introduction of unavoidable and very few impurity elements (C, N, O, etc.) during the melting process and heat treatment process on the properties of the material can be ignored.

[0050] The preparation steps of the high-entropy austenitic stainless steel are as follows:

[0051] According to the design proportion of elements, the raw elemental materials with a purity?99.9% were weighed and mixed. The argon arc furnace was vacuumed to a pressure below 5.0?10.sup.?3 Pa and then filled with argon to a pressure of 5.0?10.sup.3 Pa. When the oxygen content and nitrogen content in the furnace were lower than 0.002% within 180 min, 30 g of pure Ti was melted first to remove oxygen and then the arc melting was started. A 60?10?5 mm.sup.3 flake ingot was obtained by the arc melting for 6 times.

[0052] The ingot was placed in a furnace for solution and homogenization treatment. The ingot wash heated to 1150? C. at a rate of 15? C./min, remained at 1150? C. for 120 min, and then cooled in air. After the solution/homogenization treatment, hot rolling and the subsequent cold rolling were performed. The rolling process was as follows: the hot rolling temperature was 1150? C., and the temperature was guaranteed to be in the range of 800-1150? C. during the hot rolling process. If the temperature was reduced during the hot rolling, the ingot can be put back into the furnace and remained at the desired rolling temperature for 5-15 min. The reduction in thickness per rolling pass was no more than 0.5 mm, and the total reduction in thickness was 50% during the hot rolling. Then, cold rolling was performed. The reduction in thickness per rolling pass was no more than 0.2 mm, and the total reduction in thickness was 66.7%. The rolled ingot was heated to 1140? C. at a rate of 15? C./min and recrystallized at 1140? C. for 1.5 min. The recrystallized ingot was heated to 550? C. at a rate of 15? C./min, remained at 550? C. for 1.5 h, and then cooled in the air to complete the aging treatment.

[0053] The material was characterized by transmission electron microscopy. The transmission electron microscopy and element distribution image was shown in FIG. 2. A large number of spherical nano-sized precipitates were distributed in the stainless steel matrix, whose composition was NiTiAl. The crystal structure was face-centered cubic. The average size and number density of the nano-sized precipitates were 14.4 nm and 1.68?10.sup.22 m.sup.?3, respectively.

Embodiment 3

[0054] This embodiment provides a high-entropy austenitic stainless steel with a chemical composition of Fe.sub.39Cr.sub.20Ni.sub.30Ti.sub.6Al.sub.5 (atomic ratio) or Fe.sub.40.33Cr.sub.19.25Ni.sub.32.6Ti.sub.5.32Al.sub.2.5 (weight ratio). The influence of the introduction of unavoidable and very few impurity elements (C, N, O, etc.) during the melting process and heat treatment process on the properties of the material can be ignored.

[0055] The preparation steps of the high-entropy austenitic stainless steel are as follows:

[0056] According to the design proportion of elements, the raw elemental materials with a purity?99.9% were weighed and mixed. The argon arc furnace was vacuumed to a pressure below 5.0?10.sup.?3 Pa and then filled with argon to a pressure of 5.0?10.sup.3 Pa. When the oxygen content and nitrogen content in the furnace were lower than 0.002% within 180 min, 35 g of pure Ti was melted first to remove oxygen and then the arc melting was started. A 60?10?5 mm.sup.3 flake ingot was obtained by the arc melting for 5 times.

[0057] The ingot was placed in a furnace for solution/homogenization treatment. The ingot was heated to 1150? C. at a rate of 15? C./min, remained at 1150? C. for 120 min, and then quenched in water. After the solution/homogenization treatment, cold rolling was performed. The cold rolling process was as follows: the reduction in thickness per rolling pass was no more than 0.2 mm, and the total reduction in thickness was 66.7%. The cold-rolled ingot was heated to 1145? C. at a rate of 18? C./min and recrystallized at 1145? C. for 1.5 min. The recrystallized ingot was heated to 600? C. at a rate of 12? C./min, remained at 600? C. for 1 h, and then quenched in water to complete the aging treatment.

Embodiment 4

[0058] This embodiment provides a high-entropy austenitic stainless steel with a chemical composition of Fe.sub.31Cr.sub.24Ni.sub.34Ti.sub.6Al.sub.5 (atomic ratio) or Fe.sub.32.08Cr.sub.23.12Ni.sub.36.98Ti.sub.5.32Al.sub.2.5 (weight ratio). The influence of the introduction of unavoidable and very few impurity elements (C, N, O, etc.) during the melting process and heat treatment process on the properties of the material can be ignored.

[0059] The preparation steps of the high-entropy austenitic stainless steel are as follows:

[0060] According to the design proportion of elements, the raw elemental materials with a purity?99.9% were weighed and mixed. The argon arc furnace was vacuumed to a pressure below 5.0?10.sup.?3 Pa and then filled with argon to a pressure of 5.0?10.sup.3 Pa. When the oxygen content and nitrogen content in the furnace were lower than 0.002% within 180 min, 40 g of pure Ti was melted first to remove oxygen and then the arc melting was started. A 60?10?5 mm.sup.3 flake ingot was obtained by the arc melting for 5 times.

[0061] The ingot was placed in a furnace for solution/homogenization treatment. The ingot was heated to 1150? C. at a rate of 15? C./min, remained at 1150? C. for 120 min, and then quenched in water. After the solution/homogenization treatment, cold rolling deformation was performed for the ingot. The cold rolling process was as follows: the reduction in thickness per pass was no more than 0.2 mm, and the total reduction in thickness was 66.7%. The cold-rolled ingot was heated to 1155? C. at a rate of 10? C./min and recrystallized at 1155? C. for 1.5 min. The recrystallized ingot was heated to 600? C. at a rate of 10? C./min, remained at 600? C. for 1 h, and then quenched in water to complete the aging treatment.

Embodiment 5

[0062] This embodiment of the invention provides a high-entropy austenitic stainless steel with a chemical composition of Fe.sub.42Cr.sub.16Ni.sub.28Ti.sub.7Al.sub.7 (atomic ratio) or Fe.sub.43.88Cr.sub.15.56Ni.sub.30.75Ti.sub.6.27Al.sub.3.53 (weight ratio). The influence of the introduction of unavoidable and very few impurity elements (C, N, O, etc.) during the melting process and heat treatment process on the properties of the material can be ignored.

[0063] The preparation steps of the high-entropy austenitic stainless steel are as follows:

[0064] According to the design proportion of elements, the raw elemental materials with a purity?99.9% were weighed and mixed. The argon arc furnace was vacuumed to a pressure below 5.0?10.sup.?3 Pa and then filled with argon to a pressure of 5.0?10.sup.3 Pa. When the oxygen content and nitrogen content in the furnace were lower than 0.002% within 180 min, 35 g of pure Ti was melted first to remove oxygen and then the arc melting was started. A 60?10?5 mm.sup.3 flake ingot was obtained by the arc melting for 6 times.

[0065] The ingot was placed in a furnace for solution and homogenization treatment. The ingot was heated 1150? C. at a rate of 15? C./min, remained at 1150? C. for 120 min, and then quenched in water. After the solution/homogenization treatment, cold rolling deformation was performed for the ingot. The cold rolling process was as follows: the reduction in thickness per pass was no more than 0.2 mm, and the total reduction in thickness was 66.7%. The cold-rolled ingot was heated to 1160? C. at a rate of 20? C./min and recrystallized at 1160? C. for 1.5 min. The recrystallized ingot was heated to 600? C. at a rate of 10? C./min, remained at 600? C. for 1 h, and then quenched in water to complete the aging treatment.

Embodiment 6

[0066] The embodiment of the invention provides a high-entropy austenitic stainless steel with a chemical composition of Fe.sub.49Cr.sub.16Ni.sub.28Ti.sub.4Al.sub.3 (atomic ratio) or Fe.sub.49.9Cr.sub.15.17Ni.sub.29.98Ti.sub.3.49A.sub.1.48 (weight ratio). The influence of the introduction of unavoidable and very few impurity elements (C, N, O, etc.) during the melting process and heat treatment process on the properties of the material can be ignored.

[0067] The preparation steps of the high-entropy austenitic stainless steel are as follows:

[0068] According to the design proportion of elements, the raw elemental materials with a purity?99.9% were weighed and mixed. The argon arc furnace was vacuumed to a pressure below 5.0?10.sup.?3 Pa and then filled with argon to a pressure of 5.0?10.sup.3 Pa. When the oxygen content and nitrogen content in the furnace were lower than 0.002% within 180 min, 30 g of pure Ti was melted first to remove oxygen and then the arc melting was started. A 60?10?5 mm.sup.3 flake ingot was obtained by the arc melting for 6 times.

[0069] The ingot was placed in a furnace for solution and homogenization treatment. The ingot was heated to 1150? C. at a rate of 15? C./min, remained at 1150? C. for 120 min, and then quenched in water. After solution/homogenization treatment, cold rolling deformation was performed for the ingot. The cold rolling process was as follows: the reduction in thickness per pass was no more than 0.2 mm, and the total reduction in thickness was 66.7%. The cold-rolled ingot was heated to 1150? C. at a rate of 10? C./min and recrystallized at 1150? C. for 1.5 min. The recrystallized ingot was heated to 600? C. at a rate of 10? C./min, remained at 600? C. for 1 h, and then quenched in water to complete the aging treatment.

Experimental Example

[0070] The statistical analysis results of yield strength R.sub.eL, ultimate tensile strength R.sub.m, fracture elongation E, and yield ratio (R.sub.eL/R.sub.m) of the materials prepared by Embodiments 1-6 are shown in Table 1. Each sample in the table was tested three times, and sample was randomly selected.

TABLE-US-00001 TABLE 1 Alloy performance data of Embodiments 1-6. Measured properties Name of ReL Rm E Yield ratio material (MPa) (MPa) (%) (ReL/Rm) Embodiment 1 820 ? 10 1220 ? 15 35.5 ? 2.6 0.67 Embodiment 2 810 ? 5 1215 ? 12 33.2 ? 3.5 0.67 Embodiment 3 980 ? 22 1340 ? 24 22.4 ? 4.5 0.73 Embodiment 4 1210 ? 18 1510 ? 22 10.2 ? 1.6 0.80 Embodiment 5 1050 ? 20 1425 ? 35 16.7 ? 1.5 0.74 Embodiment 6 680 ? 20 1165 ? 30 37.8 ? 2.2 0.56

[0071] It can be seen from Table 1 that the yield strength, tensile strength, and fracture elongation of the high-entropy austenitic stainless steels prepared by Embodiments 1-3 of the invention maintain a high level, and the yield ratio is within a reasonable range of 0.67-0.73. In Embodiments 4-5, brittle intermetallic compounds are formed due to the excessive content of Ti and Al. As a result, although the strength is improved, the plasticity is significantly degraded. In Embodiment 6, the precipitation strengthening cannot be maximized due to the insufficient content of Ti and Al, which results in low strength.

[0072] FIG. 3 is an engineering stress-strain curve of high-entropy austenitic stainless steel measured at room temperature at a strain rate of 1?10.sup.?3 s.sup.?1. The yield strength, tensile strength, and fracture elongation of the high-entropy austenitic stainless steel are shown in Table 1. FIG. 3 shows that the yield strength, ultimate tensile strength, and fracture elongation of the optimized high-entropy austenitic stainless steel are 820 MPa, 1220 MPa, and 37%, respectively.

[0073] FIG. 4 is a comparison of the yield strength R.sub.eL and fracture elongation E of commercial stainless steels and the high-entropy austenitic stainless steels of the invention. FIG. 4 shows that the high-entropy austenitic stainless steels of the invention have yield strength higher than those of most commercial stainless steels and maintain a high plasticity. The product of yield strength and fracture elongation is 14.5-30.3 GPa %, which is higher than those (2.62-17.2 GPa %) of commercial stainless steels.

[0074] FIG. 5 is a comparison of the tensile strength R.sub.m and the fracture elongation E of commercial stainless steels and the high-entropy austenitic stainless steels of the invention. FIG. 5 shows that the high-entropy austenitic stainless steels of the invention maintain a high plasticity and high tensile strength. The product of tensile strength and fracture elongation is 18.0-46.1 GPa %, which is higher than those (2.9-42.8 GPa %) of commercial stainless steels.

[0075] FIG. 6 is a comparison of the yield strength and the product of strength and plasticity [ultimate tensile strength (UTS)?fracture elongation] of commercial stainless steels and the high-entropy austenitic stainless steels of the invention. FIG. 6 shows that the yield strength and the product of strength and elongation of the high-entropy austenitic stainless steels of the invention are higher than those of commercial stainless steels. The high-entropy austenitic stainless steels maintain a high plasticity and high-strength, and their comprehensive performance is better than that of commercial stainless steels.

[0076] Obviously, the above embodiments are only examples for a clear explanation, not a limitation on the implementation methods. For ordinary technical personnel in their field, other different forms of change or modification can be made based on the above description. There is no need and no way to exhaust all the implementation methods. The obvious changes or modifications thus extended are still within the protection scope of the invention.