Austenitic steel with high toughness, low temperature resistance and low density and preparation method thereof

Abstract

The invention relates to austenitic steel with high toughness, low temperature resistance and low density and a preparation method of the austenitic steel, and the austenitic steel comprises the following components in percentage by weight: 0.51 to 0.69 percent of C, 1.5 to 3 percent of Si, 4.1 to 5.9 percent of Al, 22.1 to 24.9 percent of Mn, 3 to 5 percent of Cr, 0 to 0.002 percent of S, 0 to 0.002 percent of P, 0 to 0.008 percent of N and the balance of iron and inevitable impurities. The austenitic steel provided by the invention has relatively low density, has relatively high yield strength, tensile strength and elongation within a temperature range of 27-293 K, shows good crack resistance and bearing capacity in a low-temperature environment, and meets performance requirements of low-temperature engineering structural members.

Description

Technical Field

[0001] The present invention relates to the technical field of steel alloy materials, and in particular to a high-toughness, low-temperature-resistant, low-density austenitic steel and a preparation method thereof. Background Art

[0002] In recent years, with the development of polar scientific expeditions, energy storage and transportation, deep-sea exploration and aerospace technology, the demand for high-performance low-temperature resistant metal materials has been growing. Different from the strengthening and toughening mechanism at room temperature, the mechanical properties of metal materials in low-temperature environments often change significantly. For example, some steel materials even show strong low-temperature embrittlement characteristics, which poses a severe challenge to the safety and economy of engineering structures. Therefore, the development of low-temperature resistant metal materials with excellent strength and toughness has important practical engineering significance for improving the crack resistance and bearing capacity of engineering structural metal materials in low-temperature environments.

[0003] In the past few decades, Ni-based low-temperature steels (such as 9Ni steel, 5Ni steel, etc.) have gradually replaced traditional low-temperature materials such as austenitic stainless steel, invar alloy, etc. with their excellent low-temperature performance and many advantages. Although these low-temperature steel materials have made breakthroughs in low-temperature performance, strength and corrosion resistance, providing more options for the design and manufacture of low-temperature equipment, they are faced with the problem of soaring metal Ni prices and domestic Ni resource shortages. At present, the preparation of high-manganese austenitic steel with Mn instead of Ni has become an important direction for the development of low-temperature steel. Although the existing high-manganese austenitic steel has good strength and toughness at room temperature, its low-temperature toughness still needs to be further improved to meet the performance requirements of lightweight engineering structures in low-temperature environments.

[0004] Therefore, how to break the dependence on Ni resources and develop an austenitic steel with high strength, toughness, low temperature resistance and low density is a technical problem that needs to be solved in this field. Summary of the invention

[0005] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a high-strength, low-temperature-resistant, low-density austenitic steel and a preparation method thereof. Compared with the prior art, the austenitic steel provided by the present invention has a lower density, higher yield strength, tensile strength and elongation in the temperature range of 27-293K, exhibits good crack resistance and load-bearing capacity in low-temperature environments, and can meet the performance requirements of low-temperature engineering structural parts.

[0006] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a high-strength, low-temperature-resistant, low-density austenitic steel, wherein the austenitic steel comprises, by weight percentage: 0.51-0.69% C, 1.5-3% Si, 4.1-5.9% Al, 22.1-24.9% Mn, 3-5% Cr, 0-0.002% S, 0-0.002% P, 0-0.008% N, and the remainder is iron and unavoidable impurities.

[0008] In the austenitic steel provided by the present invention, elements such as C, Si, Al, Mn, and Cr are introduced to improve its mechanical properties. The addition of Si can refine the grains, increase the grain boundary density, and reduce the grain boundary spacing, thereby improving the plastic deformation ability and low-temperature toughness. In addition, grain refinement can also effectively hinder dislocation movement and grain boundary sliding, and improve the strength and fatigue resistance of the material. Cr can be dissolved in the steel matrix in the form of a solid solution element, producing a solid solution strengthening effect, improving the tensile strength and hardness of the material, and improving the mechanical properties. At the same time, Cr also exists in the steel in the form of carbides, such as Cr 23 C6, which can play a role in precipitation strengthening. In addition, Cr, as a corrosion-resistant element, can promote the formation of Cr2O3 protective film at the grain boundary, thereby inhibiting the occurrence of intergranular corrosion. Al, as a light metal element, can reduce the density of steel and play a role in solid solution strengthening. It can also form a high-density nanoscale (Fe, Mn)3AlC-type carbide precipitation phase with C, Mn, Fe, etc., greatly improving the strength of steel through precipitation strengthening effect.

[0009] On the other hand, the present invention can improve the corrosion resistance of austenitic steel and form an appropriate amount of Cr-rich carbide to improve the mechanical properties of the steel by preferably controlling the weight percentage range of Cr; by controlling the weight percentage range of Si, the mechanical properties of the steel can be strengthened and the density can be reduced, thereby avoiding the increase in material brittleness caused by excessive addition of Si; by controlling the weight percentage range of C, carbides can be formed in the steel matrix to improve the strength of the steel and reduce the tendency of intergranular carbide formation, thereby avoiding low-temperature intergranular cracking of the steel.

[0010] In the present invention, the austenitic steel comprises, by weight percentage: 0.51-0.69% C, for example, 0.51%, 0.53%, 0.55%, 0.57%, 0.59%, 0.61%, 0.63%, 0.65%, 0.67% or 0.69%; 1.5-3% Si, for example, 1.5%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.6%, 2.8% or 3%; 4.1-5.9% Al, for example, 4.1%, 4.3%, 4.5%, 4.7%, 4.9%, 5.1%, 5.3%, 5.5%, 5.7% or 5.9%; 22. 1-24.9% Mn may be, for example, 22.1%, 22.6%, 23.1%, 23.6%, 24.1%, 24.6% or 24.9%; 3-5% Cr may be, for example, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.2%, 4.5%, 4.8% or 5%; 0-0.002% S may be, for example, 0.002% or 0.001%; ​​0-0.002% P may be, for example, 0.002% or 0.001%; ​​0-0.008% N may be, for example, 0.008% or 0.007%, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0011] Preferably, the weight percentage of C in the austenitic steel is 0.55-0.65%.

[0012] Preferably, the weight percentage of Al in the austenitic steel is 4.8-5.2%.

[0013] In the present invention, by further preferably controlling the weight percentage of C and Al within a specific range, when Fe and Mn are added in excess, it is possible to promote the formation of an appropriate amount of (Fe, Mn)3AlC type carbides in the crystal, while avoiding the problem of intergranular embrittlement caused by the precipitation of excessive carbides at the grain boundaries, thereby strengthening the steel matrix while avoiding the intergranular embrittlement phenomenon.

[0014] Preferably, the weight percentage of Cr in the austenitic steel is 3.2-3.7%.

[0015] In the present invention, by further preferably controlling the weight percentage of Cr within a specific range, the formation of chromium carbide between Cr and part of C in the matrix can be further promoted, thereby playing a role in strengthening the steel matrix.

[0016] In the present invention, the unavoidable impurities include, for example, oxygen and / or calcium, and the weight percentage range of the impurities is generally O<0.008%, Ca<0.002%.

[0017] Preferably, annealing twins exist inside the grains of the austenitic steel.

[0018] In the present invention, the annealing twins exist inside the grains of the austenitic steel, which can hinder the movement of dislocations during the deformation process, thereby playing a role in strengthening the austenitic steel.

[0019] Preferably, the density of the austenitic steel is 6.8-7.2 g / cm 3 , for example, it can be 6.8 g / cm 3 、6.9g / cm 3 , 7.0g / cm 3 , 7.1g / cm 3 or 7.2g / cm 3 , but not limited to the listed values, other unlisted values ​​within the numerical range are also applicable.

[0020] Preferably, the yield strength of the austenitic steel at 293K is 468-512 MPa, for example, 468 MPa, 474 MPa, 484 MPa, 494 MPa, 504 MPa or 512 MPa, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0021] Preferably, the tensile strength of the austenitic steel at 293K is 864-889 MPa, for example, 864 MPa, 867 MPa, 870 MPa, 873 MPa, 876 MPa, 879 MPa, 882 MPa, 885 MPa or 889 MPa, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0022] Preferably, the total elongation of the austenitic steel at 293K is 65-74%, for example, 65%, 67%, 69%, 71% or 74%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0023] Preferably, the yield strength of the austenitic steel at 77K is 849-895 MPa, for example, 849 MPa, 859 MPa, 869 MPa, 879 MPa, 889 MPa or 895 MPa, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0024] Preferably, the tensile strength of the austenitic steel at 77K is 1224-1274 MPa, for example, it may be 1224 MPa, 1229 MPa, 1234 MPa, 1239 MPa, 1244 MPa, 1249 MPa, 1254 MPa, 1259 MPa, 1264 MPa, 1269 MPa or 1274 MPa, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0025] Preferably, the total elongation of the austenitic steel at 77K is 63-70%, for example, it can be 63%, 64%, 65%, 66%, 67%, 68%, 69% or 70%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0026] Preferably, the yield strength of the austenitic steel at 27K is 972-1005 MPa, for example, it may be 972 MPa, 977 MPa, 982 MPa, 987 MPa, 992 MPa, 997 MPa or 1005 MPa, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0027] Preferably, the tensile strength of the austenitic steel at 27K is 1312-1378 MPa, for example, it may be 1312 MPa, 1322 MPa, 1332 MPa, 1342 MPa, 1352 MPa, 1362 MPa, 1372 MPa or 1378 MPa, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0028] Preferably, the total elongation of the austenitic steel at 27K is 60-67%, for example, it can be 60%, 61%, 62%, 63%, 64%, 65%, 66% or 67%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0029] In a second aspect, the present invention provides a method for preparing the high-toughness, low-temperature-resistant, low-density austenitic steel as described in the first aspect of the present invention, the preparation method comprising the following steps:

[0030] (1) subjecting the raw materials to vacuum induction melting to obtain molten steel according to the composition and weight percentage of austenitic steel, and then casting and cooling to obtain an ingot;

[0031] (2) subjecting the ingot obtained in step (1) to a first heat treatment and a forging treatment in sequence, and then cooling the ingot to obtain a forging blank;

[0032] (3) subjecting the forging blank obtained in step (2) to a second heat treatment and a hot rolling treatment in sequence, and then cooling the forging blank to obtain a hot-rolled plate;

[0033] (4) The hot-rolled sheet obtained in step (3) is annealed and then cooled to obtain austenitic steel.

[0034] In the preparation method provided by the present invention, firstly, through the steps of the first heat treatment and forging treatment, the internal organizational structure of the ingot can be improved, and the density and uniformity of the internal organization can be improved; then, through the second heat treatment and hot rolling treatment, the steel can be rolled to a desired shape, the grains can be refined and the strength of the steel can be improved; finally, through the annealing treatment, the internal stress of the steel during the processing can be eliminated and a precipitation phase can be formed in the matrix to obtain a stable austenite organization, and finally a good match between the yield strength, the tensile strength and the elongation can be achieved, thereby obtaining excellent comprehensive mechanical properties.

[0035] In the present invention, the cooling method in steps (1), (2) and (4) can be, for example, air cooling, and the cooling method in step (3) can be, for example, water cooling. In order to avoid defects such as pores, the ingot obtained in step (1) generally needs to be cut off before the first heat treatment. In the present invention, the hot rolling treatment can be conventional operations in the art, for example, it can be carried out on a two-roll reversible hot rolling experimental unit, and the number of hot rolling can be, for example, 1 time, 2 times, 3 times, 5 times or 7 times, which can be selected according to needs.

[0036] Preferably, the temperature of the vacuum induction melting in step (1) is 1450-1550°C, for example, 1450°C, 1470°C, 1490°C, 1510°C, 1530°C or 1550°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0037] Preferably, the vacuum induction melting time is 60-80 min, for example, 60 min, 65 min, 70 min, 75 min or 80 min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0038] Preferably, the temperature of the first heat treatment in step (2) is 1190-1210°C, for example, it can be 1190°C, 1192°C, 1194°C, 1196°C, 1198°C, 1200°C, 1202°C, 1204°C, 1206°C, 1208°C or 1210°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0039] Preferably, the time of the first heat treatment is 110-130 min, for example, it can be 110 min, 112 min, 114 min, 116 min, 120 min, 122 min, 124 min, 126 min, 128 min or 130 min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0040] Preferably, the initial forging temperature of the forging process is 1185-1215°C, for example, it can be 1185°C, 1186°C, 1188°C, 1190°C, 1192°C, 1194°C, 1196°C, 1198°C, 1200°C, 1202°C, 1204°C, 1206°C, 1208°C, 1210°C, 1212°C or 1215°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0041] Preferably, the final forging temperature of the forging treatment is 880-920°C, for example, it can be 880°C, 882°C, 884°C, 886°C, 888°C, 890°C, 892°C, 894°C, 896°C, 898°C, 900°C, 902°C, 904°C, 906°C, 908°C, 910°C, 912°C, 914°C, 916°C, 918°C or 920°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0042] Preferably, the deformation amount of the forging process is 15-25%, for example, it can be 15%, 17%, 19%, 21%, 23% or 25%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0043] Preferably, the temperature of the second heat treatment in step (3) is 1190-1210°C, for example, it can be 1190°C, 1192°C, 1194°C, 1196°C, 1198°C, 1200°C, 1202°C, 1204°C, 1206°C, 1208°C or 1210°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0044] Preferably, the time of the second heat treatment is 1.5-2.5 h, for example, 1.5 h, 1.6 h, 1.8 h, 2 h, 2.1 h, 2.2 h, 2.4 h or 2.5 h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0045] Preferably, the starting temperature of the hot rolling treatment is 1160-1200°C, for example, it can be 1160°C, 1165°C, 1170°C, 1175°C, 1180°C, 1185°C, 1190°C, 1195°C or 1200°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0046] Preferably, the final rolling temperature of the hot rolling treatment is 850-950°C, for example, it can be 850°C, 860°C, 870°C, 880°C, 890°C, 900°C, 910°C, 920°C, 930°C, 940°C or 950°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0047] Preferably, the total reduction ratio of the hot rolling treatment is 85-90%, for example, it can be 85%, 86%, 87%, 88%, 89% or 90%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0048] In the present invention, by preferably controlling the total reduction ratio of the hot rolling process within a specific range, it is possible to achieve a large plastic deformation of the forging blank, thereby refining the grains and eliminating defects such as pores.

[0049] Preferably, the temperature of the annealing treatment in step (4) is 950-1040°C, for example, it can be 950°C, 970°C, 980°C, 1000°C, 1020°C or 1040°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0050] In the present invention, by preferably controlling the temperature of the annealing treatment within a specific range, the hot-rolled grains can be fully recrystallized within this temperature range, and the grain size can be controlled within an appropriate range; if the temperature of the annealing treatment is too low, it will lead to difficulty in recrystallization or the recrystallized grains will be too small, which is not conducive to improving the plasticity of the steel; if the temperature of the annealing treatment is too high, the grains will grow abnormally, and the strength of the steel will be greatly reduced.

[0051] Preferably, the annealing time is 30-50 min, for example, it can be 30 min, 32 min, 34 min, 36 min, 38 min, 40 min, 42 min, 44 min, 46 min, 48 min or 50 min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0052] As a preferred technical solution provided in the second aspect of the present invention, the preparation method comprises the following steps:

[0053] (1) According to the composition and weight percentage of austenitic steel, the raw materials are subjected to vacuum induction melting at 1450-1550° C. for 60-80 min to obtain molten steel, which is then cast and cooled to obtain an ingot;

[0054] (2) subjecting the ingot obtained in step (1) to a first heat treatment at 1190-1210° C. for 110-130 min, and then subjecting the ingot to a forging treatment, wherein the initial forging temperature is 1185-1215° C., the final forging temperature is 880-920° C., the deformation amount of the forging treatment is 15-25%, and then cooling to obtain a forging blank;

[0055] (3) subjecting the forged blank obtained in step (2) to a second heat treatment at 1190-1210° C. for 1.5-2.5 h, and then to hot rolling, with the starting rolling temperature being 1160-1200° C., the final rolling temperature being 850-950° C., and the total reduction ratio being 85-90%, and then cooling to obtain a hot-rolled plate;

[0056] (4) The hot-rolled sheet obtained in step (3) is annealed at 950-1040° C. for 30-50 min, and then cooled to obtain austenitic steel.

[0057] Compared with the prior art, the present invention has the following beneficial effects:

[0058] (1) The austenitic steel provided by the present invention can control its elemental composition and weight percentage so that each element can synergistically strengthen the performance of the alloy, avoid the formation of low-temperature brittle phases, improve the yield strength, tensile strength and total elongation of the austenitic steel, and obtain excellent low-temperature mechanical properties.

[0059] (2) The preparation method of austenitic steel provided by the present invention, such as through forging, hot rolling and annealing operations, can improve the density and uniformity of the internal structure of the material, so that it can obtain good strength and plasticity and meet the mechanical property requirements of low-temperature engineering structural parts.

[0060] (3) Under optimal conditions, the austenitic steel provided by the present invention can achieve a yield strength of more than 468 MPa, a tensile strength of more than 864 MPa, and a total elongation of more than 65% at 293 K; at 77 K, the yield strength can reach more than 849 MPa, the tensile strength can reach more than 1224 MPa, and the total elongation can reach more than 63%; at 27 K, the yield strength can reach more than 972 MPa, the tensile strength can reach more than 1312 MPa, and the total elongation can reach more than 60%. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 is the microstructure morphology of the austenitic steel provided in Example 1 of the present invention;

[0062] Figure 2 is a grain orientation distribution diagram of austenitic steel provided in Example 1 of the present invention;

[0063] Figure 3is the tensile curve of the austenitic steel provided in Example 1 of the present invention at 293K, 77K and 27K;

[0064] Figure 4 is the tensile fracture morphology of the austenitic steel provided in Example 1 of the present invention at 27K, 77K and 293K, Figure 4 Middle: (a) shows the tensile fracture morphology at 27K; (b) shows the tensile fracture morphology at 77K; (c) shows the tensile fracture morphology at 293K. DETAILED DESCRIPTION

[0065] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0066] In the following examples, the scanning electron microscope used to observe the microstructure morphology and grain orientation distribution of austenitic steel is a Verios 5UC electron microscope; the quasi-static tensile test is carried out on a temperature-controlled microcomputer-controlled electronic universal testing machine; and the fracture morphology of the tensile sample is observed under a ZEISS / Gemini 300 electron microscope.

[0067] Example 1

[0068] This embodiment provides a high-toughness, low-temperature-resistant, low-density austenitic steel, which includes, by weight percentage, 0.6% C, 2% Si, 5% Al, 24% Mn, 3.5% Cr, 0.0018% S, 0.0012% P, 0.005% N, and the remainder is iron and unavoidable impurities. The austenitic steel is observed by scanning electron microscopy, and its microstructure is as follows: Figure 1 The grain orientation distribution diagram is shown in Figure 2 As shown, from Figure 1 and Figure 2 It can be seen that its microstructure is austenite, and there are a large number of annealing twins in the austenite grains ( Figure 1 The green line in the middle is the annealing twin boundary), and the grain orientation is random, which is conducive to showing good comprehensive mechanical properties.

[0069] This embodiment also provides a method for preparing the above-mentioned high-toughness, low-temperature-resistant, low-density austenitic steel, the preparation method comprising the following steps:

[0070] (1) According to the composition and weight percentage of austenitic steel, the raw materials are vacuum induction melted at 1480° C. for 70 min to obtain molten steel, which is then cast and air-cooled to 25° C. to obtain an ingot. In order to avoid defects such as pores, the head and tail of the ingot are removed;

[0071] (2) subjecting the ingot obtained in step (1) to a first heat treatment at 1200° C. for 120 min, and then subjecting the ingot to a forging treatment, wherein the initial forging temperature is 1200° C., the final forging temperature is 920° C., the deformation amount is 20%, and then air-cooling to 25° C. to obtain a forging blank;

[0072] (3) subjecting the forged blank obtained in step (2) to a second heat treatment at 1200° C. for 2 h, and then to hot rolling with a starting rolling temperature of 1180° C., a finishing rolling temperature of 900° C., and a total reduction ratio of 90%, and then water cooling to 25° C. to obtain a hot-rolled plate;

[0073] (4) The hot-rolled sheet obtained in step (3) is annealed at 1020° C. for 40 min, and then cooled to obtain austenitic steel. The austenitic steel generally needs to be pickled and machined to obtain a smooth surface.

[0074] Taking Example 1 as an example, the tensile curves of austenitic steel at 293K, 77K and 27K were obtained by quasi-static tensile test. Figure 3 As shown. Figure 3 It can be seen that as the experimental temperature decreases, the yield strength and tensile strength of the austenitic steel gradually increase, but the elongation does not decrease significantly. The tensile strength at 27K exceeds 1350MPa, and the elongation still reaches 63%. The tensile fracture morphology of the obtained austenitic steel at 27K, 77K and 293K is shown in Figure 2. Figure 4 As shown, from Figure 4 It can be seen that the fracture surfaces at the three experimental temperatures all contain a large number of dimples, that is, they are all plastic fractures.

[0075] Example 2

[0076] The present embodiment provides an austenitic steel with high strength, toughness, low temperature resistance and low density. The austenitic steel comprises, by weight percentage, 0.55% C, 1.5% Si, 4.8% Al, 24.9% Mn, 3.2% Cr, 0.0017% S, 0.0013% P, 0.006% N, and the remainder is iron and unavoidable impurities.

[0077] This embodiment also provides a method for preparing the above-mentioned high-toughness, low-temperature-resistant, low-density austenitic steel, the preparation method comprising the following steps:

[0078] (1) According to the composition and weight percentage of austenitic steel, the raw materials are vacuum induction melted at 1550° C. for 60 min to obtain molten steel, which is then cast and air-cooled to 25° C. to obtain an ingot. In order to avoid defects such as pores, the head and tail of the ingot are removed;

[0079] (2) subjecting the ingot obtained in step (1) to a first heat treatment at 1190° C. for 130 min, and then subjecting the ingot to a forging treatment with an initial forging temperature of 1185° C., a final forging temperature of 880° C., a deformation amount of 15%, and then air cooling to 25° C. to obtain a forging blank;

[0080] (3) subjecting the forging blank obtained in step (2) to a second heat treatment at 1190° C. for 2.5 h, and then to hot rolling with a starting rolling temperature of 1160° C., a finishing rolling temperature of 950° C., and a total reduction ratio of 85%, and then water cooling to 25° C. to obtain a hot-rolled plate;

[0081] (4) The hot-rolled sheet obtained in step (3) is annealed at 1000° C. for 50 min, and then cooled to obtain austenitic steel. The austenitic steel generally needs to be pickled and machined to obtain a smooth surface.

[0082] Example 3

[0083] The present embodiment provides an austenitic steel with high strength, toughness, low temperature resistance and low density. The austenitic steel comprises, by weight percentage, 0.65% C, 3% Si, 5.2% Al, 22.1% Mn, 3.7% Cr, 0.0016% S, 0.0015% P, 0.007% N, and the remainder is iron and unavoidable impurities.

[0084] This embodiment also provides a method for preparing the above-mentioned high-toughness, low-temperature-resistant, low-density austenitic steel, the preparation method comprising the following steps:

[0085] (1) According to the composition and weight percentage of austenitic steel, the raw materials are vacuum induction melted at 1450° C. for 80 min to obtain molten steel, which is then cast and air-cooled to 25° C. to obtain an ingot. In order to avoid defects such as pores, the head and tail of the ingot are removed;

[0086] (2) subjecting the ingot obtained in step (1) to a first heat treatment at 1210° C. for 110 min, and then subjecting the ingot to a forging treatment, wherein the initial forging temperature is 1215° C., the final forging temperature is 900° C., the deformation amount is 25%, and then air-cooling to 25° C. to obtain a forging blank;

[0087] (3) subjecting the forging blank obtained in step (2) to a second heat treatment at 1210° C. for 1.5 h, and then to hot rolling with a starting rolling temperature of 1200° C., a finishing rolling temperature of 850° C., and a total reduction ratio of 88%, and then water cooling to 25° C. to obtain a hot-rolled plate;

[0088] (4) The hot-rolled sheet obtained in step (3) is annealed at 1040° C. for 30 min, and then cooled to obtain austenitic steel. The austenitic steel generally needs to be pickled and machined to obtain a smooth surface.

[0089] Example 4

[0090] This embodiment provides a high-strength, low-temperature-resistant, low-density austenitic steel. The only difference compared with Embodiment 1 is that only the contents of Fe and C are adjusted so that the weight percentage of C is 0.51%.

[0091] Example 5

[0092] This embodiment provides a high-strength, low-temperature-resistant, low-density austenitic steel. The only difference compared with Embodiment 1 is that only the contents of Fe and C are adjusted so that the weight percentage of C is 0.69%.

[0093] Example 6

[0094] This embodiment provides a high-strength, low-temperature-resistant, low-density austenitic steel. The only difference compared with Embodiment 1 is that only the contents of Fe and Al are adjusted so that the weight percentage of Al is 4.1%.

[0095] Example 7

[0096] This embodiment provides a high-strength, low-temperature-resistant, low-density austenitic steel. The only difference compared with Embodiment 1 is that only the contents of Fe and Al are adjusted so that the weight percentage of Al is 5.9%.

[0097] Example 8

[0098] This embodiment provides an austenitic steel with high strength, low temperature resistance and low density. The difference compared with the embodiment 1 is that only the contents of Fe and Cr are adjusted so that the weight percentage of Cr is 3%.

[0099] Example 9

[0100] This embodiment provides an austenitic steel with high strength, low temperature resistance and low density. The difference compared with the embodiment 1 is that only the contents of Fe and Cr are adjusted so that the weight percentage of Cr is 4%.

[0101] Example 10

[0102] This embodiment provides a method for preparing austenitic steel with high toughness, low temperature resistance and low density. The only difference compared with Example 1 is that the total reduction rate of the hot rolling process is 80%.

[0103] Embodiment 11

[0104] This embodiment provides a method for preparing austenitic steel with high strength, toughness, low temperature resistance and low density. The only difference compared with the embodiment 1 is that the total reduction rate of the hot rolling process is 95%.

[0105] Example 12

[0106] This embodiment provides a method for preparing austenitic steel with high strength, toughness, low temperature resistance and low density. The only difference compared with Example 1 is that the annealing temperature is 900°C.

[0107] Embodiment 13

[0108] This embodiment provides a method for preparing austenitic steel with high strength, toughness, low temperature resistance and low density. The only difference compared with Example 1 is that the annealing temperature is 1100°C.

[0109] Comparative Example 1

[0110] This comparative example provides a high-strength, low-temperature-resistant, low-density austenitic steel, which is different from Example 1 in that the contents of Fe and Si are adjusted so that the weight percentage of Si is 1%.

[0111] Comparative Example 2

[0112] This comparative example provides a high-strength, low-temperature-resistant, low-density austenitic steel, which is different from Example 1 in that the contents of Fe and Si are adjusted so that the weight percentage of Si is 4%.

[0113] Comparative Example 3

[0114] This comparative example provides an austenitic steel with high toughness, low temperature resistance and low density. The only difference compared with Example 1 is that only the contents of Fe and Cr are adjusted so that the weight percentage of Cr is 2%.

[0115] Comparative Example 4

[0116] This comparative example provides a high-strength, low-temperature-resistant, low-density austenitic steel, which is different from Example 1 in that the contents of Fe and Cr are adjusted so that the weight percentage of Cr is 6%.

[0117] The yield strength and tensile strength of the austenitic steels prepared in Examples 1-13 and Comparative Examples 1-4 were tested by quasi-static tensile test, the total elongation was tested by an extensometer with a gauge length of 10 mm, and the density was measured by the Archimedes drainage method. The results are shown in Table 1.

[0118] Table 1

[0119]

[0120]

[0121] From the data in Table 1, we can see the following points:

[0122] (1) It can be seen from the data of Examples 1-3 that, under optimal conditions, the austenitic steel provided by the present invention can achieve a yield strength of more than 468 MPa, a tensile strength of more than 864 MPa, and a total elongation of more than 65% at 293 K; at 27 K, the yield strength can reach more than 972 MPa, the tensile strength can reach more than 1312 MPa, and the total elongation can reach more than 60%.

[0123] (2) Comprehensively comparing the data of Example 1 and Comparative Examples 1-4, it can be seen that the difference between Comparative Examples 1-2 and Example 1 is that the weight percentage of Si is not within the range defined by the present invention, and the difference between Comparative Examples 3-4 and Example 1 is that the weight percentage of Cr is not within the range defined by the present invention. The yield strength and tensile strength of Example 1 are significantly better than those of Comparative Examples 1 and 3, and the total elongation is significantly better than that of Comparative Examples 2 and 4. It can be seen that the present invention can improve the mechanical properties while avoiding the increase of the brittleness of the material by controlling the weight percentage of Si and Cr.

[0124] Furthermore, a comprehensive comparison of the data of Example 1 and Examples 8-9 shows that the only difference between Example 8-9 and Example 1 is that the weight percentage of Cr is not within the preferred range of the present invention. The yield strength and tensile strength of Example 1 are significantly better than those of Example 8, and the total elongation is significantly better than that of Example 9. It can be seen that the present invention can further promote the formation of chromium carbide between Cr and part of the C in the matrix by preferably controlling the weight percentage of Cr, thereby playing a role in strengthening the steel matrix.

[0125] (3) Comprehensive comparison of the data of Example 1 and Examples 4-7 shows that the difference between Example 4-5 and Example 1 is only that the weight percentage of C is not within the preferred range of the present invention, and the difference between Examples 6-7 and Example 1 is only that the weight percentage of Al is not within the preferred range of the present invention. The yield strength and tensile strength of Example 1 are significantly better than those of Examples 4 and 6, and the total elongation is significantly better than that of Examples 5-7. It can be seen that the present invention can further promote the formation of an appropriate amount of (Fe, Mn)3AlC type carbides in the crystal by preferably controlling the weight percentage of C and Al, while avoiding the problem of intergranular embrittlement caused by the precipitation of excessive carbides at the grain boundaries, thereby strengthening the steel matrix while avoiding the intergranular embrittlement phenomenon.

[0126] (4) Comprehensive comparison of the data of Example 1 and Examples 10-11 shows that the only difference between Examples 10-11 and Example 1 is that the total reduction ratio of the hot rolling treatment is not within the preferred range of the present invention. The strength of Example 1 is significantly better than that of Example 10, and the total elongation is significantly better than that of Example 11. It can be seen that the present invention can further improve the comprehensive mechanical properties of austenitic steel by optimally controlling the total reduction ratio of the hot rolling treatment.

[0127] (5) A comprehensive comparison of the data of Example 1 and Examples 12-13 shows that the only difference between Examples 12-13 and Example 1 is that the temperature of the annealing treatment is not within the preferred range of the present invention. The strength of Example 1 is significantly better than that of Example 13, and the total elongation is significantly better than that of Example 12. It can be seen that the present invention can further improve the comprehensive mechanical properties of austenitic steel by preferentially controlling the temperature of the annealing treatment.

[0128] In summary, the austenitic steel provided by the present invention has a low density, high yield strength, tensile strength and elongation in the temperature range of 27-293K, exhibits good crack resistance and bearing capacity in low temperature environments, and can meet the performance requirements of low-temperature engineering structural parts.

[0129] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A high-toughness, low-temperature-resistant, low-density austenitic steel, characterized in that: The austenitic steel comprises, by weight percentage, 0.51-0.69% C, 1.5-3% Si, 4.1-5.9% Al, 22.1-24.9% Mn, 3-5% Cr, 0-0.002% S, 0-0.002% P, 0-0.008% N, and the balance is iron and unavoidable impurities.

2. The austenitic steel according to claim 1, characterized in that: Annealing twins exist inside the grains of the austenitic steel; Preferably, the density of the austenitic steel is 6.8-7.2 g / cm 3 ; Preferably, the weight percentage of C in the austenitic steel is 0.55-0.65%; Preferably, the weight percentage of Al in the austenitic steel is 4.8-5.2%; Preferably, the weight percentage of Cr in the austenitic steel is 3.2-3.7%.

3. The austenitic steel according to claim 1 or 2, characterized in that: The yield strength of the austenitic steel at 293K is 468-512MPa; Preferably, the tensile strength of the austenitic steel at 293K is 864-889MPa; Preferably, the total elongation of the austenitic steel at 293K is 65-74%.

4. The austenitic steel according to any one of claims 1 to 3, characterized in that: The yield strength of the austenitic steel at 77K is 849-895MPa; Preferably, the tensile strength of the austenitic steel at 77K is 1224-1274MPa; Preferably, the total elongation of the austenitic steel at 77K is 63-70%.

5. The austenitic steel according to any one of claims 1 to 4, characterized in that: The yield strength of the austenitic steel at 27K is 972-1005MPa; Preferably, the tensile strength of the austenitic steel at 27K is 1312-1378 MPa; Preferably, the total elongation of the austenitic steel at 27K is 60-67%.

6. A method for preparing austenitic steel with high toughness, low temperature resistance and low density as claimed in any one of claims 1 to 5, characterized in that: The preparation method comprises the following steps: (1) subjecting the raw materials to vacuum induction melting to obtain molten steel according to the composition and weight percentage of austenitic steel, and then casting and cooling to obtain an ingot; (2) subjecting the ingot obtained in step (1) to a first heat treatment and a forging treatment in sequence, and then cooling the ingot to obtain a forging blank; (3) subjecting the forging blank obtained in step (2) to a second heat treatment and a hot rolling treatment in sequence, and then cooling the forging blank to obtain a hot-rolled plate; (4) The hot-rolled sheet obtained in step (3) is annealed and then cooled to obtain austenitic steel.

7. The preparation method according to claim 6, characterized in that: The temperature of the vacuum induction melting in step (1) is 1450-1550°C; Preferably, the vacuum induction melting time is 60-80 min; Preferably, the temperature of the first heat treatment in step (2) is 1190-1210°C; Preferably, the first heat treatment time is 110-130 min; Preferably, the initial forging temperature of the forging process is 1185-1215°C; Preferably, the final forging temperature of the forging process is 880-920°C; Preferably, the deformation amount of the forging process is 15-25%.

8. The preparation method according to claim 6 or 7, characterized in that: The temperature of the second heat treatment in step (3) is 1190-1210°C; Preferably, the second heat treatment time is 1.5-2.5h; Preferably, the hot rolling process starts at a temperature of 1160-1200°C; Preferably, the final rolling temperature of the hot rolling treatment is 850-950°C; Preferably, the total reduction ratio of the hot rolling process is 85-90%.

9. The preparation method according to any one of claims 6 to 8, characterized in that: The temperature of the annealing treatment in step (4) is 950-1040°C; Preferably, the annealing treatment time is 30-50 minutes.

10. The preparation method according to any one of claims 6 to 9, characterized in that: The preparation method comprises the following steps: (1) According to the composition and weight percentage of austenitic steel, the raw materials are subjected to vacuum induction melting at 1450-1550° C. for 60-80 min to obtain molten steel, which is then cast and cooled to obtain an ingot; (2) subjecting the ingot obtained in step (1) to a first heat treatment at 1190-1210° C. for 110-130 min, and then subjecting the ingot to a forging treatment, wherein the initial forging temperature is 1185-1215° C., the final forging temperature is 880-920° C., the deformation amount of the forging treatment is 15-25%, and then cooling to obtain a forging blank; (3) subjecting the forged blank obtained in step (2) to a second heat treatment at 1190-1210° C. for 1.5-2.5 h, and then to hot rolling, with the starting rolling temperature being 1160-1200° C., the final rolling temperature being 850-950° C., and the total reduction ratio being 85-90%, and then cooling to obtain a hot-rolled plate; (4) The hot-rolled sheet obtained in step (3) is annealed at 950-1040° C. for 30-50 min, and then cooled to obtain austenitic steel.

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