CN115637376B - Austenitic stainless steel and heat treatment process thereof - Google Patents
Austenitic stainless steel and heat treatment process thereof Download PDFInfo
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- 229910000963 austenitic stainless steel Inorganic materials 0.000 title claims abstract description 49
- 238000000034 method Methods 0.000 title claims description 27
- 230000008569 process Effects 0.000 title claims description 24
- 238000010438 heat treatment Methods 0.000 title claims description 23
- 238000005096 rolling process Methods 0.000 claims description 38
- 238000001953 recrystallisation Methods 0.000 claims description 27
- 238000005098 hot rolling Methods 0.000 claims description 24
- 238000000137 annealing Methods 0.000 claims description 23
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 20
- 230000032683 aging Effects 0.000 claims description 18
- 230000009467 reduction Effects 0.000 claims description 17
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 15
- 238000010791 quenching Methods 0.000 claims description 14
- 230000000171 quenching effect Effects 0.000 claims description 14
- 238000004321 preservation Methods 0.000 claims description 13
- 229910000831 Steel Inorganic materials 0.000 claims description 12
- 239000010959 steel Substances 0.000 claims description 12
- 229910052757 nitrogen Inorganic materials 0.000 claims description 10
- 238000003723 Smelting Methods 0.000 claims description 4
- 238000005266 casting Methods 0.000 claims description 4
- 238000001816 cooling Methods 0.000 claims description 4
- 238000002156 mixing Methods 0.000 claims description 4
- 239000007788 liquid Substances 0.000 claims description 3
- 239000013078 crystal Substances 0.000 abstract description 29
- 239000000463 material Substances 0.000 abstract description 13
- 238000005728 strengthening Methods 0.000 description 13
- 238000005097 cold rolling Methods 0.000 description 11
- 230000000694 effects Effects 0.000 description 10
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 10
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 7
- 229910001566 austenite Inorganic materials 0.000 description 7
- 229910001220 stainless steel Inorganic materials 0.000 description 7
- 239000010935 stainless steel Substances 0.000 description 6
- 230000000930 thermomechanical effect Effects 0.000 description 6
- 230000000052 comparative effect Effects 0.000 description 5
- 238000001556 precipitation Methods 0.000 description 5
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 4
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 description 4
- 229910052799 carbon Inorganic materials 0.000 description 4
- 238000009826 distribution Methods 0.000 description 4
- 229910052748 manganese Inorganic materials 0.000 description 4
- 239000011572 manganese Substances 0.000 description 4
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- 229910052759 nickel Inorganic materials 0.000 description 3
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- 239000010949 copper Substances 0.000 description 2
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- 238000005260 corrosion Methods 0.000 description 2
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- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 2
- 238000013508 migration Methods 0.000 description 2
- 230000005012 migration Effects 0.000 description 2
- 230000035882 stress Effects 0.000 description 2
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 1
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 1
- 238000005275 alloying Methods 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 238000013459 approach Methods 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
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- 229910052742 iron Inorganic materials 0.000 description 1
- 230000000670 limiting effect Effects 0.000 description 1
- WPBNNNQJVZRUHP-UHFFFAOYSA-L manganese(2+);methyl n-[[2-(methoxycarbonylcarbamothioylamino)phenyl]carbamothioyl]carbamate;n-[2-(sulfidocarbothioylamino)ethyl]carbamodithioate Chemical compound [Mn+2].[S-]C(=S)NCCNC([S-])=S.COC(=O)NC(=S)NC1=CC=CC=C1NC(=S)NC(=O)OC WPBNNNQJVZRUHP-UHFFFAOYSA-L 0.000 description 1
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- 229910052698 phosphorus Inorganic materials 0.000 description 1
- 239000011574 phosphorus Substances 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
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- 230000002829 reductive effect Effects 0.000 description 1
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- 230000003313 weakening effect Effects 0.000 description 1
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Classifications
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
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Abstract
The application discloses austenitic stainless steel, its metallographic structure is the mixed crystal structure that has nanocrystalline, superfine crystal and coarse crystal, austenitic stainless steel comprises following element by mass percent: c:0.05-0.1%; n:0.2-0.25%; cr:16.0-18.0%; ni:2.5-3.5%; mn:5.5-6.5%; cu:1.3-2.0%; si:0.3-0.5%; mo:0.05-0.15%; s: less than or equal to 0.004%; p: less than or equal to 0.003%; o:0.0005-0.001%; ca:0.0005-0.005%; the balance being Fe. The austenitic stainless steel provided by the invention can effectively improve the yield strength of the material while ensuring the plasticity of the material, and can be prepared into austenitic stainless steel with strong plasticity at room temperature.
Description
Technical Field
The present application relates to the field of stainless steel, and in particular to austenitic stainless steel and heat treatment processes thereof.
Background
Austenitic stainless steel has been one of the most widely used structural materials with the highest development value due to its excellent corrosion resistance and toughness. But the main disadvantage of single-phase austenitic stainless steel is that its yield strength tends not to be high. Conventional approaches to increasing yield strength of austenitic stainless steels include fine grain strengthening and solution strengthening, where cold rolling deformation and recrystallization annealing by simple is the most common form of thermo-mechanical treatment. However, during room temperature rolling, a dynamic recovery process of dislocations is accompanied accordingly, thereby weakening the strengthening effect.
In order to ensure the plasticity of the material, the grain refinement is performed, and meanwhile, as many deformation mechanisms as possible, such as transformation induced plasticity (TRIP), twinning induced plasticity (TWIP) and the like, are required to be excited in the plastic deformation process of the material. However, grain refinement improves the stability of austenite, so that the occurrence of phase transformation and twinning can be significantly suppressed.
Therefore, how to obtain austenitic stainless steel with both strong plasticity is a problem to be solved.
Disclosure of Invention
The embodiment of the application provides an austenitic stainless steel, which at least solves the problem that austenite with strong plasticity is not available at present.
According to one aspect of the present application, there is provided an austenitic stainless steel having a metallographic structure of a mixed crystal structure having nanocrystalline, ultrafine grain, and coarse grain.
Further, the austenitic stainless steel is composed of the following elements in percentage by mass:
c:0.05-0.1%; n:0.2-0.25%; cr:16.0-18.0%; ni:2.5-3.5%; mn:5.5-6.5%; cu:1.3-2.0%; si:0.3-0.5%; mo:0.05-0.15%; s: less than or equal to 0.004%; p: less than or equal to 0.003%; o:0.0005-0.001%; ca:0.0005-0.005%; the balance being Fe.
Further, the austenitic stainless steel consists of the following elements in percentage by mass:
c:0.05-0.08%; n:0.2-0.24%; cr:17.0-18.0%; ni:2.5-3.0%; mn:6.0-6.5%; cu:1.5-2.0%; si:0.4-0.5%; mo:0.08-0.15%; s: less than or equal to 0.004%; p: less than or equal to 0.003%; o:0.0005-0.001%; ca:0.0005-0.005%; the balance being Fe;
or (b)
C:0.06-0.08%; n:0.21-0.24%; cr:17.0-18.0%; ni:2.7-3.0%; mn:6.0-6.3%; cu:1.5-1.8%; si:0.4-0.45%; mo:0.08-0.12%; s: less than or equal to 0.004%; p: less than or equal to 0.003%; o:0.0005-0.001%; ca:0.0005-0.005%; the balance being Fe;
or (b)
C:0.06-0.08%; n:0.22-0.24%; cr:17.0-18.0%; ni:2.7-3.0%; mn:6.0-6.3%; cu:1.5-1.7%; si:0.4-0.5%; mo:0.09-0.13%; s: less than or equal to 0.004%; p: less than or equal to 0.003%; o:0.0005-0.001%; ca:0.0005-0.005%; the balance being Fe.
In a second aspect of the present application, there is provided a heat treatment process of austenitic stainless steel, comprising the steps of:
mixing the element components according to the proportion, smelting, continuously casting a slab into an ingot, heating and preserving the heat of a steel ingot, and performing air cooling after multi-step hot rolling treatment;
and (3) rolling the air-cooled steel plate at a low temperature, naturally recovering to room temperature, cold-rolling to obtain a rolled sheet, aging the sheet, water quenching to room temperature, and finally performing recrystallization annealing and water quenching again to room temperature.
Further, the heating temperature of the steel ingot is 1100-1300 ℃.
Further, the multi-step hot rolling includes the steps of:
the first step: hot rolling temperature: 1150-1250 ℃, and the heat preservation time is as follows: 115-125 minutes;
and a second step of: hot rolling temperature: 880-970 ℃, and the heat preservation time is as follows: 65-75 minutes;
and a third step of: hot rolling temperature: 700-800 ℃, and the heat preservation time is as follows: 20-30 minutes.
Further, the low-temperature rolling is carried out in a single step at the temperature of liquid nitrogen, and the rolling reduction is 8% -12%.
Further, the cold rolling is performed in a single step at room temperature, and the rolling reduction is 70% -75%.
Further, the aging treatment temperature interval is 350-450 ℃ and the treatment time is 0.5-1.5 h.
Further, the recrystallization temperature interval is 650-750 ℃, and the heat preservation time is 10-20 min.
In the embodiment of the application, the austenitic stainless steel with a mixed crystal structure is adopted, fine crystals play a role in improving strength, and coarse crystals play a role in carrying out larger plastic deformation so as to improve the work hardening capacity of the material. The austenitic stainless steel provided by the invention can effectively improve the yield strength of the material while ensuring the plasticity of the material, and can be used for preparing the austenitic stainless steel with high plasticity at room temperature, wherein the yield strength reaches 1100-1300MPa, and the elongation reaches 30% -40%, so that the technical problem that the austenitic stainless steel cannot realize high plasticity.
Drawings
The accompanying drawings, which are included to provide a further understanding of the application, illustrate and explain the application and are not to be construed as limiting the application. In the drawings:
FIG. 1 shows two austenitic stainless steel scanning microstructure graphs 1a,1b obtained after a rolling-aging-recrystallization annealing thermo-mechanical treatment in the example of the present invention, wherein 1a is the scanning microstructure graph of example 1; 1b is a scanning microstructural map of example 2.
FIG. 2 is a scanning microstructure of an austenitic stainless steel of comparative example 1 obtained after a roll-recrystallization annealing thermo-mechanical treatment in an example of the present invention.
Fig. 3 shows a transmission electron microscope image of the deformation 10% of an austenitic stainless steel obtained after the thermo-mechanical treatment of the rolling-aging-recrystallization annealing and the rolling-recrystallization annealing in the example of the present invention. Wherein 3a is a transmission electron microscope image of the modification of example 1; 3b is a transmission electron microscope image of the modified form of comparative example 1.
Detailed Description
It should be noted that, in the case of no conflict, the embodiments and features in the embodiments may be combined with each other. The present application will be described in detail below with reference to the accompanying drawings in conjunction with embodiments.
As described in the background, the mechanism of fine grain strengthening and deformation is two aspects of obtaining the strong plasticity of austenitic stainless steel, however, the existing process and structure have contradiction to achieve both the strong plasticity, which is reflected in that dislocation dynamic recovery occurring in the room temperature rolling process of achieving fine grain strengthening weakens the strengthening effect on the one hand, and the mechanism of achieving plasticity is inhibited due to the structure of grain refinement on the other hand.
The embodiment of the invention provides austenitic stainless steel, and the metallographic structure of the austenitic stainless steel is a mixed crystal structure with nanocrystalline, superfine crystal and coarse crystal.
In the above mixed crystal structure, the sizes of the respective crystal grains are as follows: the nanocrystalline is less than 100nm, the superfine crystal is 100nm-1000nm, and the coarse crystal is more than 1000nm. In the mixed crystal structure, fine crystals play a role in improving strength, and coarse crystals play a role in improving the work hardening capacity of the material by adopting larger plastic deformation, so that the effect of considering strong plasticity is achieved.
To achieve the above organization, design elements and processing techniques are required. The raw materials containing elements such as carbon, nickel, manganese, copper, aluminum, phosphorus, sulfur, nitrogen, oxygen, iron and the like used in the following examples are all commercially available, and equipment for realizing the processes such as hot rolling treatment, water quenching, tempering and the like are also commercially available.
The austenite in the embodiment of the invention consists of the following elements in percentage by mass:
c:0.05-0.1%; n:0.2-0.25%; cr:16.0-18.0%; ni:2.5-3.5%; mn:5.5-6.5%; cu:1.3-2.0%; si:0.3-0.5%; mo:0.05-0.15%; s: less than or equal to 0.004%; p: less than or equal to 0.003%; o:0.0005-0.001%; ca:0.0005-0.005%; the balance being Fe.
Among the above-mentioned elements, have higher nitrogen and manganese and lower carbon and nickel, wherein nitrogen and manganese can be used for substituting a portion of nickel element, reduce price and development difficulty, nitrogen can substitute a portion of carbon and be used for stabilizing austenite and optimizing the solid solution strengthening effect at the same time. More importantly, the nitrogen and the manganese can promote the formation of stacking faults and dislocation density during deformation, and are beneficial to reverse transformation and recrystallization so as to form the multi-system twinned structure.
Meanwhile, the austenitic stainless steel with strong plasticity has the element composition, wherein low carbon can also ensure the welding performance of the material, a proper amount of Cu element is introduced into a precipitation strengthening effect, and the conventional content of Cr and trace Mo element is used for ensuring the corrosion resistance of the material.
As a preferred first embodiment, the austenitic stainless steel comprises the following elements in mass percent:
c:0.05-0.08%; n:0.2-0.24%; cr:17.0-18.0%; ni:2.5-3.0%; mn:6.0-6.5%; cu:1.5-2.0%; si:0.4-0.5%; mo:0.08-0.15%; s: less than or equal to 0.004%; p: less than or equal to 0.003%; o:0.0005-0.001%; ca:0.0005-0.005%; the balance being Fe.
As a preferred second embodiment, the austenitic stainless steel comprises the following elements in mass percent:
c:0.06-0.08%; n:0.21-0.24%; cr:17.0-18.0%; ni:2.7-3.0%; mn:6.0-6.3%; cu:1.5-1.8%; si:0.4-0.45%; mo:0.08-0.12%; s: less than or equal to 0.004%; p: less than or equal to 0.003%; o:0.0005-0.001%; ca:0.0005-0.005%; the balance being Fe;
as a preferred third embodiment, the austenitic stainless steel comprises the following elements in mass percent:
c:0.06-0.08%; n:0.22-0.24%; cr:17.0-18.0%; ni:2.7-3.0%; mn:6.0-6.3%; cu:1.5-1.7%; si:0.4-0.5%; mo:0.09-0.13%; s: less than or equal to 0.004%; p: less than or equal to 0.003%; o:0.0005-0.001%; ca:0.0005-0.005%; the balance being Fe.
On the basis of the above elements, in order to achieve the purpose of fine grain strengthening, various deformation channels for improving plasticity are excited and finally a mixed crystal structure is obtained, and a thermomechanical treatment mode of large deformation and subsequent partial recrystallization annealing is required to be combined, so that the embodiment of the invention provides a heat treatment process of austenitic stainless steel, which comprises the following steps:
mixing the element components according to the proportion, smelting, continuously casting a slab into an ingot, heating and preserving the heat of a steel ingot, and performing air cooling after multi-step hot rolling treatment;
and (3) rolling the air-cooled steel plate at a low temperature, naturally recovering to room temperature, cold-rolling to obtain a rolled sheet, aging the sheet, water quenching to room temperature, and finally performing recrystallization annealing and water quenching again to room temperature.
A rolling-aging-recrystallization annealing process is adopted, wherein rolling adopts a mode of combining low-temperature rolling and room-temperature cold rolling to inhibit dynamic recovery of dislocation. In the aspect of heat treatment, alloying of nitrogen and manganese reduces the fault energy to about 20 mJ/m2 at low temperature, realizes effective dispersion precipitation of nano precipitated phases in a matrix, and a large amount of dislocation in the matrix after large deformation during rolling promotes nucleation of the nano precipitated phases. And the subsequent aging process is performed by nitrogen segregation and the pinning effect of nano precipitation relative to grain boundary migration during recrystallization annealing, so as to obtain a mixed crystal structure containing nano crystals, ultrafine crystals and coarse crystals. In the uniaxial tension deformation process, the TRIP and TWIP effects of coarse-grain austenite phases are utilized for fine-grain strengthening and nano precipitation strengthening, so that good strength and plasticity are obtained, the cost is low, and the thermomechanical treatment process is simple.
By adopting the rolling-aging-recrystallization annealing process, a composite rolling mode of combining low-temperature rolling with room-temperature cold rolling is developed, and the mixed crystal structure which is effectively thinned and contains nanocrystalline, superfine crystal and coarse crystal is obtained through aging and recrystallization annealing, so that the problems that the yield strength is low and the strong plasticity of the existing austenitic stainless steel is difficult to combine are solved.
As an alternative heat treatment process, the following steps may be specifically adopted:
firstly, mixing the element components according to the proportion, smelting, continuously casting a slab into an ingot, heating the steel ingot at 1100-1300 ℃, preferably 1200 ℃, preserving heat for more than or equal to 2 hours, and performing multi-step hot rolling treatment at the initial rolling temperature of 1150-1250 ℃ and the final rolling temperature of 700-800 ℃ and then air cooling.
Specifically, the multi-step hot rolling includes the following three steps:
the first step: hot rolling temperature: 1150-1250 ℃, and the heat preservation time is as follows: 115-125 minutes;
and a second step of: hot rolling temperature: 880-970 ℃, and the heat preservation time is as follows: 65-75 minutes;
and a third step of: hot rolling temperature: 700-800 ℃, and the heat preservation time is as follows: 20-30 minutes.
The reduction rate of each hot rolling step is maintained at 20% -30%. The rolling reduction is the reduction which is commonly used in the rolling process to express relative deformation, and the rolling effect is better when the rolling reduction is maintained in a stable range as much as possible.
Step two, firstly carrying out low-temperature rolling at the liquid nitrogen temperature on the air-cooled steel plate, naturally returning to room temperature with the rolling reduction of 8% -12%, then carrying out cold rolling at the room temperature of 20 ℃ -25 ℃ with the rolling reduction of 70% -75%, obtaining a rolled sheet, carrying out aging treatment on the sheet in the temperature range of 350 ℃ -450 ℃ for 0.5h-1.5h, then carrying out water quenching to room temperature, and finally carrying out recrystallization annealing in the temperature range of 650 ℃ -750 ℃ and preferably 680 ℃ -730 ℃ for 10 min-20 min and preferably 12min-18min, and then carrying out water quenching again to room temperature, thus obtaining the austenitic stainless steel with both strong plasticity and the property.
The austenitic stainless steel was processed in accordance with the above-mentioned processing technique for the components in the first two preferred embodiments mentioned above, to obtain sample # 1 and sample # 2, respectively.
Among them, sample # 1 was prepared by using the preferred ingredients of the first example and performing the following more preferred operations:
the steel ingot is subjected to rust removal and oil removal, and is cleaned, so that the phenomenon of uneven stress in the rolling process is avoided. The ingot was subjected to multi-step hot rolling at an initial rolling temperature of 1200 ℃ and a final rolling temperature of 750 ℃ and then air-cooled. The multi-step hot rolling conditions are as follows: the rolling reduction rates are 24.2%,23.8% and 25.3% respectively and the heat preservation time is 120, 70 and 25 minutes respectively at 1200, 950 and 750 ℃ respectively.
Then, carrying out heat mechanical treatment on the austenitic stainless steel plate after hot rolling, namely, carrying out cold rolling with the rolling reduction at a low temperature of 10 percent and the cold rolling reduction at room temperature of 73 percent, carrying out aging treatment, namely, carrying out isothermal aging at 400 ℃ for 1.0h, and then carrying out water quenching to room temperature; and (3) carrying out recrystallization annealing on the stainless steel subjected to aging treatment at 700 ℃ for 15min, and finally quenching the stainless steel to room temperature by water.
Among them, sample # 2 was prepared by using the preferred ingredients of the second example and performing the following more preferred operations:
the steel ingot is subjected to rust removal and oil removal, and is cleaned, so that the phenomenon of uneven stress in the rolling process is avoided. The ingot was subjected to multi-step hot rolling at an initial rolling temperature of 1200 ℃ and a final rolling temperature of 750 ℃ and then air-cooled. The multi-step hot rolling conditions are as follows: the rolling reduction rates are 25.2%,23.6% and 24.1% respectively and the heat preservation time is 120, 70 and 25 minutes respectively at 1200, 950 and 750 ℃ respectively.
Then, carrying out heat mechanical treatment on the austenitic stainless steel plate after hot rolling, namely, carrying out cold rolling with the rolling reduction at a low temperature of 10 percent and the cold rolling reduction at room temperature of 73 percent, carrying out aging treatment, namely, carrying out isothermal aging at 400 ℃ for 1.0h, and then carrying out water quenching to room temperature; and (3) carrying out recrystallization annealing on the stainless steel subjected to aging treatment at 700 ℃ for 15min, and finally quenching the stainless steel to room temperature by water.
Sample 1 was obtained with the above-mentioned preferred first embodiment ingredients and modified processing.
The modification of the processing technology is specifically realized in that isothermal aging and water quenching are not performed after low-temperature and room-temperature rolling is completed, and the stainless steel plate is directly subjected to recrystallization annealing at 700 ℃ for 15min and finally water quenched to room temperature. The obtained austenitic stainless steel sample 1 with strong plasticity is detected under a scanning electron microscope, and a specific microstructure is shown in fig. 2.
The austenite phase and nano precipitated phase were observed by scanning electron microscopy for sample 1#, sample 2# and sample 1 respectively, and specific results are shown in fig. 1a,1b and 2.
As can be seen from fig. 1a and 1b, the structures after the rolling-aging-recrystallization annealing treatment, i.e., sample # 1 and sample # 2, show mixed crystal distribution, and the size distribution is 0.2 μm to 1.5 μm from the coverage of nanocrystalline to ultrafine to coarse crystal. As can be seen from fig. 2, the comparative sample, sample 1, subjected to the roll-recrystallization annealing also exhibits a mixed crystal distribution, and the size distribution is 0.35 μm to 1.6 μm. A large number of nano precipitated phases with different sizes are distributed in the matrix of the three samples, and the sizes are about 20nm-85 nm. Therefore, the mixed crystal structure is derived from a recrystallization annealing treatment in a relatively short time, and in addition, the precipitated phase can also play a role in pinning grain boundary migration during austenite recrystallization to inhibit growth.
Room temperature tensile test
Room temperature stretching experiments were performed on sample 1#, sample 2# and sample 1 respectively, and specific experimental results are shown in table 1. As can be seen from table 1, compared with comparative sample 1, which was not subjected to aging treatment, sample 1# and sample 2# which were subjected to rolling-aging-recrystallization annealing treatment had higher yield strength, could reach 1180-1250MPa level, and elongation was as high as 30% or more, which was mainly due to the combined effects of fine grain strengthening and precipitation strengthening, and simultaneously excited TRIP and TWIP effects during plastic deformation, thereby improving work hardening capacity and plasticity of the material. For comparative sample 1, the strength of sample 1 was reduced (about 120 MPa) compared to samples 1# and 2# because of the lack of aging step and the lack of sufficiently high density of nano-precipitates in the matrix. However, the differences in elongation between the three samples were not significant (within 3%) since they all stimulated the TRIP and TWIP effects during plastic deformation.
TABLE 1
| Sample of | Aging | Recrystallization annealing | Yield strength (MPa) | Tensile strength (MPa) | Elongation (%) |
| 1# | √ | √ | 1180-1250 | 1260-1320 | 30.2-33.5 |
| 2# | √ | √ | 1170-1245 | 1220-1290 | 31.5-34.1 |
| 1* | / | √ | 1050-1120 | 1170-1220 | 34.3-37.5 |
Note that: wherein ∈represents treated/represents untreated
Sample 1# and sample 1 x were each examined by transmission electron microscopy after 10% tensile deformation, and the specific experimental results are shown in fig. 3a, 3b. As can be seen from fig. 3, deformation twins appear in both samples, which proves that twins induce plasticity in the plastic deformation process, and the work hardening capacity of the material is improved by a dynamic fine crystal mode.
In summary, the austenitic stainless steel with strong plasticity and the heat treatment process thereof provided by the invention adopt a rolling-aging-recrystallization annealing heat treatment process to prepare the austenitic stainless steel with strong plasticity and have good strength and excellent plasticity, low Ni content, low preparation cost and simpler heat treatment process. Therefore, the invention effectively overcomes the defects in the prior production technology and has the value of further development and application.
The foregoing is merely exemplary of the present application and is not intended to limit the present application. Various modifications and changes may be made to the present application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc. which are within the spirit and principles of the present application are intended to be included within the scope of the claims of the present application.
Claims (7)
1. A heat treatment process of austenitic stainless steel is characterized in that: the method comprises the following steps:
mixing the element components according to the proportion, smelting, continuously casting a slab into an ingot, heating and preserving the heat of a steel ingot, and performing air cooling after multi-step hot rolling treatment;
firstly carrying out low-temperature rolling on the air-cooled steel plate, wherein the low-temperature rolling is carried out in a single step at the temperature of liquid nitrogen, the rolling reduction is 8% -12%, the rolling reduction is 70% -75% after naturally recovering to room temperature, the rolling is carried out in a single step at the room temperature, the rolling reduction is 70% -20%, the sheet is subjected to aging treatment and then water quenching to the room temperature, and finally, the sheet is subjected to recrystallization annealing and water quenching again to the room temperature, wherein the recrystallization temperature interval is 650 ℃ -750 ℃, and the heat preservation time is 10-20 min;
wherein, the proportion of the austenitic stainless steel comprises the following elements in percentage by mass:
c:0.05-0.1%; n:0.2-0.25%; cr:16.0-18.0%; ni:2.5-3.5%; mn:5.5-6.5%; cu:1.3-2.0%; si:0.3-0.5%; mo:0.05-0.15%; s: less than or equal to 0.004%; p: less than or equal to 0.003%; o:0.0005-0.001%; ca:0.0005-0.005%; the balance being Fe.
2. The heat treatment process of austenitic stainless steel according to claim 1, wherein: the austenitic stainless steel comprises the following elements in percentage by mass:
c:0.05-0.08%; n:0.2-0.24%; cr:17.0-18.0%; ni:2.5-3.0%; mn:6.0-6.5%; cu:1.5-2.0%; si:0.4-0.5%; mo:0.08-0.15%; s: less than or equal to 0.004%; p: less than or equal to 0.003%; o:0.0005-0.001%; ca:0.0005-0.005%; the balance being Fe.
3. The heat treatment process of austenitic stainless steel according to claim 1, wherein: the austenitic stainless steel comprises the following elements in percentage by mass:
c:0.06-0.08%; n:0.21-0.24%; cr:17.0-18.0%; ni:2.7-3.0%; mn:6.0-6.3%; cu:1.5-1.8%; si:0.4-0.45%; mo:0.08-0.12%; s: less than or equal to 0.004%; p: less than or equal to 0.003%; o:0.0005-0.001%; ca:0.0005-0.005%; the balance being Fe.
4. The heat treatment process of austenitic stainless steel according to claim 1, wherein: the austenitic stainless steel comprises the following elements in percentage by mass:
c:0.06-0.08%; n:0.22-0.24%; cr:17.0-18.0%; ni:2.7-3.0%; mn:6.0-6.3%; cu:1.5-1.7%; si:0.4-0.5%; mo:0.09-0.13%; s: less than or equal to 0.004%; p: less than or equal to 0.003%; o:0.0005-0.001%; ca:0.0005-0.005%; the balance being Fe.
5. The heat treatment process of austenitic stainless steel according to claim 1, wherein:
the heating temperature of the steel ingot is 1100-1300 ℃.
6. The heat treatment process of austenitic stainless steel according to claim 1, wherein: the multi-step hot rolling includes the steps of:
the first step: hot rolling temperature: 1150-1250 ℃, and the heat preservation time is as follows: 115-125 minutes;
and a second step of: hot rolling temperature: 880-970 ℃, and the heat preservation time is as follows: 65-75 minutes;
and a third step of: hot rolling temperature: 700-800 ℃, and the heat preservation time is as follows: 20-30 minutes.
7. The heat treatment process of austenitic stainless steel according to claim 1, wherein: the aging treatment temperature range is 350-450 ℃ and the treatment time is 0.5-1.5 h.
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