Preparation method of superplastic high-silicon austenitic stainless steel
阅读说明：本技术 一种超塑性高硅奥氏体不锈钢的制备方法 (Preparation method of superplastic high-silicon austenitic stainless steel ) 是由 梁田 陈思含 高明 马颖澈 刘奎 于 2021-06-30 设计创作，主要内容包括：本发明公开了一种超塑性高硅奥氏体不锈钢的制备方法,属于材料热加工技术领域。该方法首先采用等温热时效方法对高硅奥氏体不锈钢锻造钢锭进行700-900℃、保温24-128小时的等温时效处理,并保证等温时效处理后其组织中的析出相体积分数达到15-30％；然后进行750-850℃等温超塑性变形。本发明方法可避免在热变形过程中产生热裂纹、断裂缺陷,且组织均匀性高,可有效解决高硅奥氏体不锈钢复杂部件的难于热变形加工等问题。(The invention discloses a preparation method of superplastic high-silicon austenitic stainless steel, and belongs to the technical field of hot working of materials. The method comprises the steps of firstly, carrying out isothermal aging treatment on a high-silicon austenitic stainless steel forging steel ingot at the temperature of 700-900 ℃ for 24-128 hours by adopting an isothermal thermal aging method, and ensuring that the volume fraction of precipitated phases in the structure of the ingot reaches 15-30% after the isothermal aging treatment; then carrying out 750-850 ℃ isothermal superplastic deformation. The method can avoid the defects of heat crack and fracture in the thermal deformation process, has high structure uniformity, and can effectively solve the problems of difficult thermal deformation processing of complex parts of high-silicon austenitic stainless steel and the like.)
1. A preparation method of superplastic high-silicon austenitic stainless steel is characterized by comprising the following steps: the method comprises the steps of firstly, carrying out isothermal aging treatment on a high-silicon austenitic stainless steel forging steel ingot by using an isothermal thermal aging method, and ensuring that the volume fraction of precipitated phases in the structure of the ingot after the isothermal aging treatment reaches 15-30%; isothermal superplastic deformation was then carried out.
2. A method of producing a superplastic high silicon austenitic stainless steel according to claim 1, characterized in that: the high silicon austenitic stainless steel has a Si content of 5.5 to 6.5 wt.%.
3. A method of manufacturing a superplastic high silicon austenitic stainless steel according to claim 2, characterized in that: the high-silicon austenitic stainless steel comprises the following chemical components in percentage by weight:
c: 0.015-0.050%; cr: 14.00 to 20.00 percent; ni: 15.00-22.00%; si:5.50 to 6.50 percent; mn: 0.50-2.00%; s is less than 0.010 percent; p is less than 0.025 percent; mo: 0.50-2.00%; cu: 0.50-1.50%; al is less than 0.10 percent; n is less than 0.02 percent; the balance of Fe.
4. A method of producing a superplastic high silicon austenitic stainless steel according to claim 1, characterized in that: the isothermal aging method comprises the following steps: the temperature of the forged steel ingot is raised to 700 and 900 ℃ in a heating furnace at the temperature raising speed of 100 and 150 ℃/h, and the isothermal heat preservation is carried out for 24 to 128 hours.
5. A method of manufacturing a superplastic high silicon austenitic stainless steel according to claim 4, characterized in that: after the forged steel ingot is subjected to isothermal aging treatment, the types of precipitated phases in the steel ingot tissues are chi, sigma and Cr3Ni5Si2Phase, and dispersed and separated out in the matrix tissue.
6. A method of producing a superplastic high silicon austenitic stainless steel according to claim 1, characterized in that: the isothermal superplastic deformation is as follows: the steel ingot is drawn at constant temperature of 750-850 ℃ with the strain rate of 0.1-1 mm/min; and after the deformation is finished, air cooling or water cooling is carried out.
7. The method of producing a superplastic high silicon austenitic stainless steel according to claim 6, characterized in that: and when the steel ingot after the isothermal aging treatment is subjected to constant-temperature stretching treatment, the elongation at break is more than 100%.
Technical Field
The invention relates to the technical field of hot working of materials, in particular to a preparation method of superplastic high-silicon austenitic stainless steel.
Background
Sulfuric acid is one of the most widely produced chemicals in the world today and has extraordinary modern uses in the chemical, agricultural, military and medical fields. However, sulfuric acid will exhibit different properties due to differences in concentration and temperature. Particularly, high-concentration sulfuric acid is highly corrosive at high temperatures, and thus corrosion of sulfuric acid plants is a major cause of equipment leakage in the sulfuric acid manufacturing process. Therefore, special attention must be paid to corrosion resistance of critical parts in sulfuric acid production.
High silicon austenitic stainless steel generally refers to austenitic stainless steel with Si content > 4%, has excellent corrosion resistance in high temperature concentrated sulfuric acid, and thus has very important application in the sulfuric acid industry, such as steel plate for preparing liner of sulfuric acid absorption tower, concentrated sulfuric acid cooler, pump, grate plate, pipeline, etc. And the higher the Si content in the high-silicon austenitic stainless steel is, the better the corrosion resistance is, and the high-silicon austenitic stainless steel can be used in a more rigorous service environment. However, the higher the Si content, the worse the hot workability of the high-silicon austenitic stainless steel. This is because if Si > 5.0 wt.%, a large amount of precipitated phases precipitate during solidification and precipitation of the alloy, and the precipitated phases cannot be completely eliminated by the high-temperature solution treatment. Particularly, some parts with complex structures can not be prepared by the conventional hot forming method, thus seriously affecting the application of the high-silicon austenitic stainless steel in the sulfuric acid industry and being not beneficial to the improvement of the corrosion resistance of key sulfuric acid production equipment.
Therefore, the development of a new process suitable for the high-silicon austenitic stainless steel is used for solving the problem that complex parts cannot be subjected to hot forming, eliminating the defects of hot cracks, low yield and the like in the hot working process, and is the key to be solved urgently for large-scale application of the high-silicon austenitic stainless steel on sulfuric acid industrial equipment.
Disclosure of Invention
The invention aims to provide a preparation method of superplastic high-silicon austenitic stainless steel, which solves the problems of hot forming, easy cracking, low yield and the like of a complex structural part of the high-silicon austenitic stainless steel, and the prepared high-silicon austenitic stainless steel has uniform tissue, good compactness and no microcrack.
In order to achieve the purpose, the technical scheme of the invention is as follows:
a preparation method of superplastic high-silicon austenitic stainless steel comprises the steps of firstly carrying out isothermal aging treatment on a high-silicon austenitic stainless steel forging steel ingot by using an isothermal thermal aging method, and ensuring that the volume fraction of precipitated phases in tissues of the high-silicon austenitic stainless steel forging ingot reaches 15-30% after the isothermal aging treatment; isothermal superplastic deformation was then carried out.
The high-silicon austenitic stainless steel comprises the following chemical components in percentage by weight:
c: 0.015-0.050%; cr: 14.00 to 20.00 percent; ni: 15.00-22.00%; si:5.50 to 6.50 percent; mn: 0.50-2.00%; s is less than 0.010 percent; p is less than 0.025 percent; mo: 0.50-2.00%; cu: 0.50-1.50%; al is less than 0.10 percent; n is less than 0.02 percent; the balance of Fe.
The isothermal aging method comprises the following steps: the temperature of the forged steel ingot is raised to 700 and 900 ℃ in a heating furnace at the temperature raising speed of 100 and 150 ℃/h, and the isothermal heat preservation is carried out for 24 to 128 hours. After the forged steel ingot is subjected to isothermal aging treatment, the types of precipitated phases in the steel ingot tissues are chi, sigma and Cr3Ni5Si2Phase, and dispersed and separated out in the matrix tissue. If the forged steel ingot subjected to isothermal aging treatment cannot be subjected to isothermal superplastic deformation immediately, the structure of the forged steel ingot needs to be preserved by water cooling.
The isothermal superplastic deformation is as follows: the steel ingot is drawn at constant temperature of 750-850 ℃ with the strain rate of 0.1-1 mm/min; after the deformation is finished, the tissue is preserved by adopting an air cooling or water cooling mode.
When the steel ingot after isothermal aging treatment is subjected to constant temperature stretching treatment, the elongation at break is more than 100%.
The invention has the following advantages:
the method can realize the molding of the high-silicon austenitic stainless steel complex part with the Si content of 5.5-6.5 wt.%, and promotes the matrix to be strongly recrystallized and refine grains in the constant-temperature deformation process under the condition that a large amount of precipitated phases exist in the steel ingot structure by using the isothermal aging method, so that the hot crack and the cracking defect can not be generated in the superplastic deformation process, and the structure after the superplastic molding is compact and uniform. The method has the advantages of wide applicability, simple operation, low equipment requirement, easy large-scale industrial production and high yield.
Drawings
FIG. 1 shows the as-forged structure of the high silicon austenitic stainless steel of example 3.
FIG. 2 shows the superplastic deformation structure of the high-silicon austenitic stainless steel in example 3.
Detailed Description
The present invention will be described in detail with reference to examples.
The invention provides a superplastic forming method suitable for 5.5-6.5 wt.% austenitic stainless steel, which comprises the following specific superplastic forming processes:
(1) preparing raw materials: selecting the chemical components (wt.%) of the austenitic stainless steel alloy ingot with high Si content: c: 0.015-0.050%; cr: 14.00 to 20.00 percent; ni: 15.00-22.00%; 5.50 to 6.50 percent of Si; 0.50 to 2.00 percent of Mn; s is less than 0.010 percent; p is less than 0.025 percent; 0.50 to 2.00 percent of Mo; 0.50 to 1.50 percent of Cu; al is less than 0.10 percent; n is less than 0.02 percent; the balance of Fe.
(2) Isothermal thermal aging treatment of steel ingots: the temperature of the forged steel ingot is firstly raised to 700-900 ℃ in a heating furnace at the temperature raising speed of 100-150 ℃/h, isothermal heat preservation is carried out for 24-128 hours, and the precipitation amount of dispersed fine precipitated phases in the tissues after isothermal aging treatment is ensured to be 15-30%. If the forged steel ingot subjected to long-term aging treatment cannot immediately realize superplastic deformation, the structure of the forged steel ingot needs to be preserved by water cooling.
(3) And (3) constant temperature deformation: the temperature of the forged rod after long-term aging needs to be rapidly raised to 750-850 ℃, and the heat preservation time is calculated according to 2.5 mm/h, so that the temperature of the forged rod is ensured to be uniform. Then stretching at constant temperature with the strain rate of 0.1-1mm/min, and preserving the superplastic deformation tissue by adopting an air cooling or water cooling mode after the deformation is finished.
Example 1
(1) Preparing raw materials: selecting the chemical composition (wt.%) of the high Si content austenitic stainless steel alloy: c: 0.034%; cr: 18.30 percent; ni: 22.10 percent; 6.10 percent of Si; 1.20 percent of Mn; s is less than 0.010 percent; p is less than 0.025 percent; 1.00 percent of Mo; 1.30 percent of Cu; al is less than 0.10 percent; n is less than 0.02 percent; the balance of Fe.
(2) Isothermal thermal aging treatment of steel ingots: firstly, the temperature of a forged steel ingot is raised to 700 ℃ in a heating furnace at the heating rate of 120 ℃/h, isothermal heat preservation is carried out for 128h, and a large amount of chi, sigma and Cr are dispersed and precipitated in the structure after isothermal heat aging treatment3Ni5Si2And the volume fraction of precipitated phase is about 18.2%, after isothermal aging heat treatment, the forged rod is subjected to water cooling treatment and then processed into a standard tensile test rod.
(3) Constant temperature superplastic deformation: and (3) rapidly heating the stretched sample after long-term aging to 750 ℃, and keeping the temperature for 15 minutes to ensure that the temperature of the stretched sample is uniform. Then stretching at constant temperature, wherein the stretching speed is 0.5mm/min, the elongation at break of the sample is about 110.5%, and after the deformation is finished, preserving the superplastic deformation tissue by adopting a water cooling mode.
Example 2
(1) Preparing raw materials: selecting the chemical composition (wt.%) of the high Si content austenitic stainless steel alloy: c: 0.034%; cr: 18.30 percent; ni: 22.10 percent; 6.10 percent of Si; 1.20 percent of Mn; s is less than 0.010 percent; p is less than 0.025 percent; 1.00 percent of Mo; 1.30 percent of Cu; al is less than 0.10 percent; n is less than 0.02 percent; the balance of Fe.
(2) Isothermal thermal aging treatment of steel ingots: the forged steel ingot is heated to 800 ℃ at a heating rate of 120 ℃/h in a heating furnace, isothermal heat preservation is carried out for 72h, and a large amount of chi, sigma and Cr are dispersed and precipitated in the structure3Ni5Si2And the volume fraction of a precipitated phase is about 24.6%, after isothermal aging heat treatment, the forged rod is subjected to water cooling treatment, and then the forged rod is processed into a standard tensile test rod.
(3) Constant temperature superplastic deformation: the temperature of the stretched sample after long-term aging needs to be rapidly raised to 850 ℃ respectively, and the heat preservation time is 15 minutes, so that the temperature of the stretched sample is ensured to be uniform. Then stretching at constant temperature, wherein the stretching speed is 0.5mm/min, the elongation at break of the sample is about 120.5%, and after the deformation is finished, preserving the superplastic deformation tissue by adopting a water cooling mode.
Example 3
(1) Preparing raw materials: selecting the chemical composition (wt.%) of the high Si content austenitic stainless steel alloy: c: 0.034%; cr: 18.30 percent; ni: 22.10 percent; 6.10 percent of Si; 1.20 percent of Mn; s is less than 0.010 percent; p is less than 0.025 percent; 1.00 percent of Mo; 1.30 percent of Cu; al is less than 0.10 percent; n is less than 0.02 percent; the balance of Fe.
(2) Isothermal thermal aging treatment of steel ingots: the forged steel ingot is heated to 800 ℃ at a heating rate of 120 ℃/h in a heating furnace, isothermal heat preservation is carried out for 72h, and a large amount of chi, sigma and Cr are dispersed and precipitated in the structure3Ni5Si2And the volume fraction of a precipitated phase is about 24.6%, after isothermal aging heat treatment, the forged rod is subjected to water cooling treatment, and then the forged rod is processed into a standard tensile test rod.
(3) Constant temperature superplastic deformation: the temperature of the stretched sample after long-term aging needs to be rapidly raised to 800 ℃ respectively, and the heat preservation time is 15 minutes, so that the temperature of the stretched sample is ensured to be uniform. Then stretching at constant temperature, wherein the stretching speed is 0.1mm/min, the elongation at break of the sample is about 273%, and after the deformation is finished, preserving the superplastic deformation tissue by adopting a water cooling mode. Metallographic analysis shows that after the alloy is subjected to superplastic deformation, a large number of precipitated phases promote strong recrystallization of the matrix in the constant-temperature deformation process, and grains are refined, as shown in figures 1 and 2.
Comparative example 1
(1) Preparing raw materials: selecting the chemical composition (wt.%) of the high Si content austenitic stainless steel alloy: c: 0.034%; cr: 18.30 percent; ni: 22.10 percent; 6.10 percent of Si; 1.20 percent of Mn; s is less than 0.010 percent; p is less than 0.025 percent; 1.00 percent of Mo; 1.30 percent of Cu; al is less than 0.10 percent; n is less than 0.02 percent; the balance of Fe.
(2) Isothermal thermal aging treatment of steel ingots: the forged steel ingot is heated to 900 ℃ in a heating furnace at a heating rate of 120 ℃/h, isothermal heat preservation is carried out for 24h at the temperature, and metallographic analysis shows that a small amount of chi, sigma and Cr are dispersed in the structure3Ni5Si2And the volume fraction of precipitated phase is about 10.4%, after isothermal aging heat treatment, the forged bar is subjected to water cooling treatment, and then processed into a standard tensile test bar.
(3) Constant temperature superplastic deformation: the tensile sample after long-term aging needs to be quickly heated to 900 ℃ for about 15 minutes, so that the temperature of the tensile sample is ensured to be uniform. Then stretching at constant temperature, wherein the strain rate is 0.5mm/min, the elongation at break of the sample is about 38%, and after the deformation is finished, preserving the superplastic deformation tissue by adopting a water cooling mode.
Comparative example 2
(1) Preparing raw materials: selecting the chemical composition (wt.%) of the high Si content austenitic stainless steel alloy: c: 0.034%; cr: 18.30 percent; ni: 22.10 percent; 6.10 percent of Si; 1.20 percent of Mn; s is less than 0.010 percent; p is less than 0.025 percent; 1.00 percent of Mo; 1.30 percent of Cu; al is less than 0.10 percent; n is less than 0.02 percent; the balance of Fe.
(2) Isothermal thermal aging treatment of steel ingots: the forged steel ingot is heated to 700 ℃ at a heating speed of 120 ℃/h in a heating furnace, isothermal heat preservation is carried out for 24h at the temperature, and metallographic analysis shows that a small amount of chi, sigma and Cr are dispersed in the structure3Ni5Si2And the volume fraction of precipitated phase is about 10.4%, after isothermal aging heat treatment, the forged bar is subjected to water cooling treatment, and then processed into a standard tensile test bar.
(3) Constant temperature superplastic deformation: the tensile sample after long-term aging needs to be quickly heated to 600 ℃ for about 15 minutes, so that the temperature of the tensile sample is ensured to be uniform. Then stretching at constant temperature, wherein the strain rate is 1mm/min, the elongation at break of the sample is about 12%, and after the deformation is finished, preserving the superplastic deformation tissue by adopting a water cooling mode.