Ultrahigh-plasticity hot-rolled austenitic stainless steel and preparation method thereof

Abstract

The invention discloses ultrahigh-plasticity hot-rolled austenitic stainless steel and a preparation method thereof, and belongs to the technical field of austenitic stainless steel production and manufacturing. The preparation method comprises the following steps: smelting and pouring according to a certain mass percent of chemical components to obtain a steel billet, homogenizing the steel billet, and forging the steel billet into a square billet; performing multi-pass hot rolling on the square billet to obtain a hot-rolled plate, performing interrupted solution treatment on the hot-rolled plate, and performing water cooling to room temperature; by controlling element selection of C, Cr, Mn, Ni and N and cooperating with a multi-pass hot rolling-solid solution interruption preparation method, an austenite structure after complete recrystallization is regulated and controlled firstly, then part of austenite is recrystallized again through low-temperature solid solution, and high mechanical stability and excellent strong plasticity are obtained based on two recrystallization behaviors.

Description

Technical Field

[0001] The invention belongs to the technical field of austenitic stainless steel production and manufacturing, and relates to ultra-high plasticity hot-rolled austenitic stainless steel and a preparation method thereof. Background Art

[0002] The demand for stainless steel in the fields of construction, chemical industry, food processing, medical treatment, energy, transportation, etc. is growing continuously, which has led to a high growth in demand for hot-rolled stainless steel, but the growth in demand for industrial products and household kitchen appliances is lower than expected. With the increasing global awareness of sustainable development and environmental protection and the advancement of science and technology driving the development of new materials and technologies, the future development prospects of hot-rolled stainless steel are full of potential.

[0003] Ultra-high plasticity austenitic stainless steel is expected to become a key material for the next generation of transportation structures and new energy vehicles based on certain strength, high plasticity and long life. Among them, regulating the proportion of recrystallized austenite through different heat treatment systems, increasing the volume fraction of recrystallized austenite, and increasing the proportion of high-angle grain boundaries of austenite are important strengthening and plasticization mechanisms of metastable austenitic stainless steel. In addition, the performance indicators of the test steel are improved through the coordinated microstructure of grain refinement theory, and industrial production and industrial application are completed.

[0004] Chinese patent CN 108531817 B discloses a nano / ultrafine grain structure ultra-high strength and plasticity austenitic stainless steel and its preparation method, which is to perform ingot forging after smelting in a vacuum induction furnace, hot rolling of forgings, cold rolling annealing twice after solution treatment, and obtain nano / ultrafine grain composite structure by utilizing strain-induced reverse transformation of martensite and recrystallization of deformed austenite. Ultra-high strength and plasticity of stainless steel are comprehensively achieved through fine grain strengthening, back stress strengthening, deformation-induced twinning effect and deformation-induced martensite effect.

[0005] Chinese patent CN 116219286 B discloses a nickel-saving high-strength and plastic bimodal austenitic stainless steel and its preparation method, the process route is: hot forging-solid solution-multiple hot rolling-solid solution-high pressure cold rolling-rapid annealing. The nickel-saving high-strength and plastic bimodal austenitic stainless steel of the invention first regulates the proportion of controllable deformation-induced martensite and deformed austenite, and then uses the difference in nucleation rate between the two during annealing to obtain a bimodal scale nano / ultrafine grain austenite structure. Summary of the invention

[0006] The present invention overcomes the shortcomings of the prior art and provides an ultra-high plasticity hot-rolled austenitic stainless steel and a preparation method thereof; the present invention is achieved through the following technical solutions: A super-high plasticity hot-rolled austenitic stainless steel, the chemical composition of which is calculated by mass percentage as follows: C: 0.01 wt.%~0.015 wt.%, Mn: 1.50 wt.%~1.80 wt.%, Cr: 14.5 wt.%~17.5 wt.%, Ni: 10.5 wt.%~12.5wt.%, P: 0.05 wt.%~0.07 wt.%, S≤0.001 wt.%, Mo: 1.5wt.%~2.5 wt.%, and the rest is Fe.

[0007] Preferably, the chemical composition by mass percentage is C: 0.014 wt.%, Mn: 1.71 wt.%, Cr: 16.5 wt.%, Ni: 11.5 wt.%, P: 0.053 wt.%, S≤0.001 wt.%, Mo: 1.98 wt.%, and the rest is Fe.

[0008] A method for preparing ultra-high plasticity hot-rolled austenitic stainless steel comprises the following steps: S1. Smelting a cast billet according to the mass percentage of chemical composition, obtaining a steel billet by melting and pouring, and forging the steel billet into a square billet after homogenizing the steel billet; S2, homogenizing the square billet and removing the surface iron oxide scale, roughing and finishing the square billet after the oxide scale is removed, performing multiple hot rolling to obtain a hot-rolled plate, and cooling the hot-rolled plate to room temperature by water cooling; S3. The hot-rolled plate is subjected to an interrupted solid solution treatment and then water-cooled to room temperature; the interrupted solid solution treatment method is to rapidly heat the hot-rolled plate to 900-1100 °C at a heating rate of 10 °C / s-30 °C / s, keep the temperature for 3-7 min, and then cool the hot-rolled plate to 650-750 °C at a cooling rate of ≥45 °C / s and keep the temperature for 3-7 min.

[0009] Preferably, the temperature of the homogenization treatment in step S1 is 1200°C-1250°C, and the holding time is 10 h-15 h.

[0010] Preferably, the starting rolling temperature of the multi-pass hot rolling in step S2 is 1100°C-1150°C, the finishing rolling temperature is 920°C-980°C, and the coiling temperature is 700°C-720°C.

[0011] More preferably, the thickness of the hot-rolled plate obtained by multiple hot-rolling passes is 3.3 mm-4.4 mm.

[0012] More preferably, the interrupted solution treatment method is to quickly heat the hot-rolled plate to 1000°C at a heating rate of 20°C / s, keep it at that temperature for 5 minutes, and then cool it to 700°C at a cooling rate of ≥45°C / s and keep it at that temperature for 5 minutes.

[0013] The beneficial effects of the present invention compared with the prior art are as follows: The present invention is based on low-cost component design. The low C content reduces the risk of precipitation of Cr-containing carbides and increases the corrosion resistance of the material near the welding area. Ni is an austenite-forming element, which regulates the stability of austenite and ensures the austenite content. In addition, the addition of Cr and Mo better forms a thicker passivation film, improves crevice corrosion, pitting resistance, high temperature creep and fatigue resistance.

[0014] Increasing the proportion of recrystallized austenite is conducive to promoting the density of metastable austenite grain boundary areas, which makes it easier to promote martensite nucleation during deformation and induce the TRIP effect; a high proportion of large-angle grain boundaries can effectively disperse stress concentration and reduce local plastic deformation unevenness, thereby improving the plastic deformation capacity of the entire material and helping to improve plasticity; by introducing large-angle grain boundaries and a high proportion of recrystallized austenite through interrupted solution treatment, the grain size of austenite is ultra-refined, smaller grains reflect more grain boundary area, and grain boundaries hinder dislocation movement, thereby improving the tensile strength of austenitic stainless steel, while maintaining good plastic deformation to improve elongation after fracture.

[0015] Therefore, by improving the process conditions, regulating and increasing the proportion of ultrafine grains, recrystallized austenite and large-angle grain boundaries, and combining the TRIP effect to enhance the plasticization mechanism, the material can undergo continuous plastic deformation and the elongation after fracture is significantly improved, thus possessing excellent comprehensive mechanical properties.

[0016] In summary, the present invention controls the element selection of C, Cr, Mn, Ni, and N, and cooperates with the preparation method of multi-pass hot rolling-interrupted solid solution, first adjusts the austenite structure after complete recrystallization, and then uses low-temperature solid solution to make part of the austenite recrystallize again, and obtains higher mechanical stability and excellent strength and plasticity based on the two recrystallization behaviors. The matching problem of strength and plasticity is solved by using the method of multi-pass hot rolling-interrupted annealing, which improves production efficiency and is conducive to the large-scale production and application of austenitic stainless steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The process roadmap of the method for preparing ultra-high plasticity hot-rolled austenitic stainless steel according to an embodiment of the present invention; Figure 2 This is the EBSD recrystallized grain ratio distribution diagram of Comparative Example 1 of the present invention; Figure 3 This is the EBSD recrystallized grain ratio distribution diagram of Example 1 of the present invention; Figure 4 This is the EBSD high-angle grain boundary proportion distribution diagram of Comparative Example 1 of the present invention; Figure 5This is the EBSD high-angle grain boundary proportion distribution diagram of Example 1 of the present invention; Figure 6 This is the EBSD grain size distribution diagram of Comparative Example 1 of the present invention; Figure 7 This is the EBSD grain size distribution diagram of Example 1 of the present invention. DETAILED DESCRIPTION

[0018] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer, the present invention is further described in detail in conjunction with the embodiments and the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. The technical solutions of the present invention are described in detail below in conjunction with the embodiments and the accompanying drawings, but the scope of protection is not limited thereto.

[0019] Example 1 This embodiment is an ultra-high plasticity hot-rolled austenitic stainless steel, and its chemical composition, by mass percentage, is C: 0.014 wt.%, Mn: 1.71 wt.%, Cr: 16.5 wt.%, Ni: 11.5 wt.%, P: 0.053 wt.%, S≤0.001 wt.%, Mo: 1.98 wt.%, and the rest is Fe.

[0020] A preparation method based on the ultra-high plasticity austenitic stainless steel, such as Figure 1 As shown, the preparation process steps of an ultra-high strength and ductility hot-rolled austenitic stainless steel are as follows: (1) The ingot was smelted according to the above chemical composition mass percentage, and the steel billet was obtained by melting and pouring. The steel billet was subjected to homogenization treatment at 1220°C for 11 h and then forged into a square billet. The size of the square billet was 120 mm×90 mm×90 mm.

[0021] (2) After homogenizing the square billet in step (1), the surface iron oxide scale is removed; the square billet after the iron oxide scale is removed is subjected to multiple hot rolling such as rough rolling and finishing rolling; the starting rolling temperature of the multiple hot rolling is 1120°C, the final rolling temperature is 950°C, the coiling temperature is 710°C, and then cooled to room temperature by water cooling, and the thickness of the hot rolled plate is 3.3 mm-4.4 mm.

[0022] (3) The hot-rolled plate produced in step (2) is subjected to an interrupted solid solution treatment. The interrupted solid solution treatment is performed by rapidly heating the hot-rolled plate to 1000°C at a heating rate of 20°C / s, keeping the temperature for 5 min, then placing the hot-rolled plate in a furnace at 700°C for 5 min (cooling rate of 50°C / s), and finally cooling the hot-rolled plate to room temperature with water to obtain a final interrupted solid solution hot-rolled plate.

[0023] (4) The ultra-high plasticity hot-rolled austenitic stainless steel prepared by (1)-(3) was sampled by wire cutting, and then the longitudinal and transverse surfaces of the samples were polished with 240#-5000# sandpaper in sequence and then electrolytically polished with 20% perchloric acid alcohol. The electrolytically polished samples were subjected to EBSD analysis, and the austenite recrystallization volume fraction was 87%, the high-angle grain boundary ratio was 93.6%, and the average austenite grain size was 13.3 μm, as shown in Figure 2. Figure 2 , Figure 3 , Figure 4 shown.

[0024] Example 2 This embodiment is an ultra-high plasticity hot-rolled austenitic stainless steel, whose chemical composition is the same as that of Example 1. The preparation method is different from that of Example 1 in that the interrupted solid solution method is to quickly heat the hot-rolled plate to 900°C at a heating rate of 10°C / s, and the rest are the same.

[0025] Example 3 This embodiment is an ultra-high plasticity hot-rolled austenitic stainless steel, whose chemical composition is the same as that of Example 1. The preparation method is different from that of Example 1 in that the interrupted solid solution method is to quickly heat the hot-rolled plate to 1100°C at a heating rate of 30°C / s, and the rest are the same.

[0026] Comparative Example 1 This example proposes an ultra-high plasticity hot-rolled austenitic stainless steel, whose chemical composition, by mass percentage, is C: 0.014 wt.%, Mn: 1.71 wt.%, Cr: 16.5 wt.%, Ni: 11.5 wt.%, P: 0.053 wt.%, S≤0.001 wt.%, Mo: 1.98 wt.%, and the rest is Fe.

[0027] A preparation method based on the ultra-high plasticity hot-rolled austenitic stainless steel, the preparation method specifically comprises the following steps: (1) The ingot was smelted according to the above chemical composition mass percentage, and the steel billet was obtained by melting and pouring. The steel billet was subjected to homogenization treatment at 1220°C for 11 h and then forged into a square billet. The size of the square billet was 120 mm×90 mm×90 mm.

[0028] (2) After the square billet in step (1) is homogenized, the surface iron oxide scale is homogenized and removed, and the square billet with the iron oxide scale removed is subjected to multiple hot rolling such as rough rolling and finishing rolling; the starting rolling temperature of the multiple hot rolling is 1120°C, the final rolling temperature is 950°C, the coiling temperature is 710°C, and then cooled to room temperature by water cooling. The thickness of the hot rolled plate is 3.3 mm-4.4 mm.

[0029] (3) The hot-rolled plate produced in step (2) is subjected to a low-temperature solution treatment at 700°C, kept at this temperature for 1 hour, and then water-cooled to room temperature, and the iron oxide scale is removed to obtain the final solution hot-rolled plate.

[0030] (4) The ultra-high plasticity hot-rolled austenitic stainless steel prepared by (1)-(3) was sampled by wire cutting, and then the longitudinal and transverse surfaces of the samples were polished with 240#-5000# sandpaper in sequence and then electrolytically polished with 20% perchloric acid alcohol. The electrolytically polished samples were subjected to EBSD analysis, and the volume fraction of austenite recrystallized grains was 61.3%, the proportion of high-angle grain boundaries was 81.7%, and the average austenite grain size was 14.2μm; Figure 2 , Figure 3 , Figure 4 shown.

[0031] Comparative Example 2 This example is an ultra-high plasticity austenitic stainless steel, and the chemical composition of the ultra-high plasticity austenitic stainless steel is calculated as follows: The chemical composition of Example 2 is calculated as follows: C: 0.014 wt.%, Mn: 1.71 wt.%, Cr: 16.5 wt.%, Ni: 11.5 wt.%, P: 0.053 wt.%, S≤0.001 wt.%, Mo: 1.98 wt.%, and the rest is Fe.

[0032] A preparation method based on the ultra-high strength and ductility austenitic stainless steel, the process steps are as follows: (1) The ingot was smelted according to the above chemical composition mass percentage, and the steel billet was obtained by melting and pouring. The steel billet was subjected to homogenization treatment at 1220°C for 11 h and then forged into a square billet. The size of the square billet was 120 mm×90 mm×90 mm.

[0033] (2) After the square billet in step (1) is homogenized, the surface iron oxide scale is homogenized and removed, and the square billet after the oxide scale is removed is subjected to multiple hot rolling such as rough rolling and finishing rolling. The starting rolling temperature of the multiple hot rolling is 1120°C, the final rolling temperature is 950°C, and the coiling temperature is 710°C. It is then cooled to room temperature by water cooling. The thickness of the hot rolled plate is 3.3 mm-4.4 mm.

[0034] (3) The hot-rolled plate produced in step (2) is subjected to medium-temperature solution treatment at 900°C, kept at this temperature for 1 hour, and then water-cooled to room temperature, and the iron oxide scale is removed to obtain the final annealed hot-rolled plate.

[0035] (4) The ultra-high plasticity hot-rolled austenitic stainless steel prepared by (1)-(3) was sampled by wire cutting, and then the longitudinal and transverse surfaces of the samples were polished with 240#-5000# sandpaper in sequence and then electrolytically polished with 20% perchloric acid alcohol. The electrolytically polished samples were subjected to EBSD analysis, and the austenite recrystallization volume fraction was found to be 21.1%, the high-angle grain boundary ratio was 65.2%, and the average austenite grain size was 17.8 μm.

[0036] Comparative Example 3 This example is an ultra-high plasticity austenitic stainless steel, and its chemical composition is as follows by mass percentage: C: 0.014wt.%, Mn: 1.71wt.%, Cr: 16.5wt.%, Ni: 11.5wt.%, P: 0.053wt.%, S≤0.001wt.%, Mo: 1.98wt.%, and the rest is Fe.

[0037] A preparation method of the ultra-high plasticity austenitic stainless steel, the process steps are as follows: (1) The ingot was smelted according to the above chemical composition mass percentage, and the steel billet was obtained by melting and pouring. The steel billet was subjected to homogenization treatment at 1220°C for 11 h and then forged into a square billet. The size of the square billet was 120 mm×90 mm×90 mm.

[0038] (2) After the square billet in step (1) is homogenized, the surface iron oxide scale is homogenized and removed, and the square billet with the oxide scale removed is subjected to multiple hot rolling such as rough rolling and finishing rolling. The starting rolling temperature of the multiple hot rolling is 1120°C, the final rolling temperature is 950°C, and the coiling temperature is 710°C. It is then cooled to room temperature by water cooling. The thickness of the hot rolled plate is 3.3 mm-4.4 mm.

[0039] (3) The hot-rolled plate produced in step (2) is subjected to a high-temperature solution treatment at 1000°C, kept at this temperature for 1 hour, and then water-cooled to room temperature, and the iron oxide scale is removed to obtain the final annealed hot-rolled plate.

[0040] (4) The ultra-high plasticity hot-rolled austenitic stainless steel prepared by (1)-(3) was sampled by wire cutting, and then the longitudinal and transverse surfaces of the samples were polished with 240#-5000# sandpaper in sequence and then electrolytically polished with 20% perchloric acid alcohol. The electrolytically polished samples were subjected to EBSD analysis, and the austenite recrystallization volume fraction was 86.8%, the high-angle grain boundary ratio was 89.7%, and the average austenite grain size was 25.8μm.

[0041] The stretching results of Example 1 and Comparative Examples 1-3 are shown in Table 1. The thickness of an ultra-high plasticity hot-rolled austenitic stainless steel prepared in Example 1 is 3.3 mm, and the microstructure in the steel is a high-proportion recrystallized austenite structure, wherein the volume fraction of austenite recrystallization after interrupted solid solution is high, the proportion of high-angle grain boundaries is large, and a certain grain refinement effect is obtained. The mechanical properties of a high-plasticity hot-rolled austenitic stainless steel prepared in Example 1 are as follows: yield strength is 433MPa, tensile strength is 680MPa, and elongation after fracture is 94.3%. Compared with the low-temperature solid solution phase, the tensile strength of the high-strength plasticity hot-rolled austenitic stainless steel prepared in Example 1 is increased by 16.8%, and the elongation after fracture is increased by 17.2%.

[0042] The above content is a further detailed description of the present invention in combination with a specific preferred embodiment. It cannot be determined that the specific embodiments of the present invention are limited to this. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the present invention, which should be regarded as belonging to the present invention and the scope of patent protection determined by the submitted claims.

Claims

1. An ultra-high plasticity hot-rolled austenitic stainless steel, characterized in that: The chemical composition by mass percentage is C: 0.01wt.%~0.015 wt.%, Mn: 1.50 wt.%~1.80wt.%, Cr: 14.5 wt.%~17.5 wt.%, Ni: 10.5 wt.%~12.5 wt.%, P: 0.05 wt.%~0.07 wt.%, S≤0.001 wt.%, Mo: 1.5 wt.%~2.5 wt.%, and the rest is Fe.

2. The ultra-high plasticity hot-rolled austenitic stainless steel according to claim 1, characterized in that: The chemical composition by mass percentage is C: 0.014 wt.%, Mn: 1.71 wt.%, Cr: 16.5 wt.%, Ni: 11.5 wt.%, P: 0.053 wt.%, S≤0.001 wt.%, Mo: 1.98 wt.%, and the rest is Fe.

3. A method for preparing ultra-high plasticity hot-rolled austenitic stainless steel according to claim 1 or 2, characterized in that: The following steps are involved: S1. Smelting a cast billet according to the mass percentage of chemical composition, obtaining a steel billet by melting and pouring, and forging the steel billet into a square billet after homogenizing the steel billet; S2, homogenizing the square billet and removing the surface iron oxide scale, roughing and finishing the square billet after the oxide scale is removed, performing multiple hot rolling to obtain a hot-rolled plate, and cooling the hot-rolled plate to room temperature by water cooling; S3. The hot-rolled plate is subjected to an interrupted solid solution treatment and then water-cooled to room temperature; the interrupted solid solution treatment method is to rapidly heat the hot-rolled plate to 900-1100°C at a heating rate of 10°C / s-30°C / s, keep the temperature for 3-7 minutes, and then cool to 650-750°C at a cooling rate of ≥45°C / s and keep the temperature for 3-7 minutes.

4. The method for preparing ultra-high plasticity hot-rolled austenitic stainless steel according to claim 3, characterized in that: The temperature of the homogenization treatment in step S1 is 1200°C-1250°C, and the insulation time is 10 h-15 h.

5. The method for preparing ultra-high plasticity hot-rolled austenitic stainless steel according to claim 3, characterized in that: The starting rolling temperature of the multi-pass hot rolling in step S2 is 1100°C-1150°C, the finishing rolling temperature is 920°C-980°C, and the coiling temperature is 700°C-720°C.

6. A method for preparing ultra-high plasticity hot-rolled austenitic stainless steel according to claim 5, characterized in that: The thickness of the hot rolled plate obtained after multiple hot rolling passes is 3.3 mm-4.4 mm.

7. A method for preparing ultra-high plasticity hot-rolled austenitic stainless steel according to claim 5, characterized in that: The interrupted solution treatment method is to quickly heat the hot-rolled plate to 1000°C at a heating rate of 20°C / s, keep the temperature for 5 minutes, and then cool the hot-rolled plate to 700°C at a cooling rate of ≥45°C / s and keep the temperature for 5 minutes.

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