A method for controlling grain size of typical austenitic stainless steel under low compression ratio condition

Abstract

The present application relates to the technical field of austenitic stainless steel, in particular to a method for controlling grain size of typical austenitic stainless steel under low compression ratio condition. The production process of the austenitic stainless steel comprises smelting, continuous casting, heating, rolling, cooling, straightening and solid solution treatment. The present application adopts the process means of controlled rolling and controlled cooling + solid solution treatment, reasonably controls the deformation temperature, deformation rate and deformation amount of each pass for two-stage rolling, so as to achieve the purpose of uniformly distributing the dynamic and static recrystallization ratio. Through the coupling design of rolling process, post-rolling cooling process and solid solution process, the uniform distribution of internal energy storage of the steel plate is realized, and the purpose of 5-6 grade and uniform grain size of 60-90mm S30408 austenitic stainless steel super-thick plate is achieved.

Description

Technical Field

[0001] This invention relates to the field of austenitic stainless steel technology, and specifically to a method for controlling the grain size of typical austenitic stainless steel under low compression ratio conditions. Background Technology

[0002] S30408 ​​austenitic stainless steel has excellent corrosion resistance and is widely used in industrial equipment, containers, pipelines, heat exchangers and other fields such as petroleum, chemical, nuclear energy and nuclear power.

[0003] Due to the high alloy element content in austenitic stainless steel, it exhibits strong deformation resistance during rolling. Compared to carbon steel, under a given rolling force, the reduction per pass for stainless steel is relatively small, making it difficult to reach the critical deformation condition for dynamic recrystallization. Furthermore, as the temperature decreases during rolling, a larger reduction per pass is required for dynamic recrystallization. However, under low compression ratio conditions, the small total deformation makes it difficult to ensure uniform deformation distribution along the thickness direction. This can lead to uneven grain size distribution along the thickness direction or even mixed grains, severely affecting material properties, particularly low-temperature impact toughness at large grains. Additionally, austenitic stainless steel has a single austenitic structure, making it difficult to improve the mixed grain structure through heat treatment phase transformation. Therefore, the production of thick austenitic stainless steel plates often employs continuous casting electroslag remelting technology to obtain large-section remelted billets, followed by forging, rolling, and solution treatment to achieve grain size control of austenitic stainless steel plates under high compression ratio conditions. This process is cumbersome, costly, has a long delivery cycle, and involves many uncontrollable factors, making it unsuitable for large-scale production.

[0004] Patent CN202010371442.2 discloses a method for controlling the grain size of medium-thick plates of high-carbon austenitic stainless steel. The method uses a three-stage temperature gradient holding process to control the grain size of high-carbon austenitic stainless steel. Under this process, alloy carbides will precipitate during the holding process. Due to the non-uniformity of the carbide precipitation, their distribution and size are irregular. The pinning forces generated by these non-uniform carbides are different, which will increase the degree of non-uniformity of the recrystallized grain size during solid solution treatment.

[0005] Patent CN202110713344.7 discloses a method for controlling the grain size of extra-thick high-carbon austenitic stainless steel plates. This method employs a "two-stage controlled rolling + solution treatment" approach to control the grain size of high-carbon austenitic stainless steel. This design is suitable for production conditions with a relatively high compression ratio (≥5). Although the total compression ratio involved in Example 1 of this patent is low, the rough rolling stage cannot guarantee that deformation penetrates to the core, easily leading to a mixed-grain structure after rolling. Furthermore, the lack of controlled cooling after rolling results in a significant release of stored energy within the steel plate, preventing complete static recrystallization during solution treatment, thus easily leading to mixed-grain phenomena. Additionally, air cooling after rolling results in a slow cooling rate for thick steel plates, satisfying the thermal and kinetic conditions for carbide precipitation. Since carbide precipitation is non-uniform, the differential pinning behavior generated during subsequent solution treatment further exacerbates the non-uniformity of grain size.

[0006] Patent CN202110725388.1 discloses a method for producing medium-thick plates of austenitic stainless steel. It uses continuously cast slabs and electroslag billets as raw materials. The total compression ratio involved is large, the laminar cooling final cooling temperature is too high, and the deformation energy storage release rate is fast, resulting in a long solution time. In addition, the laminar cooling final cooling temperature is located in the carbide precipitation temperature range, and the non-uniform precipitation of carbides will cause uneven grain size during solution treatment. Its overall design concept is suitable for grain size control under high compression ratio conditions. It achieves the absence of mixed grain structure in the rolled steel plate through controlled rolling and controlled cooling. The solution treatment is to dissolve the carbides. Summary of the Invention

[0007] The purpose of this invention is to provide a method for controlling the grain size of typical austenitic stainless steel under low compression ratio conditions. By strictly controlling the continuous casting process to obtain a higher proportion of equiaxed crystal slabs, and combining it with a two-stage rolling process to ensure dynamic recrystallization in as many parts as possible, a full-thickness mixed-grain structure steel plate with a higher degree of recrystallization in the core than on the surface is obtained. For the mixed-grain structure after rolling, deformation energy is preserved by reducing the final rolling temperature and water cooling after rolling. The overall design of controlled rolling and cooling and solution treatment processes reduces the difference in deformation energy storage between the core and the upper and lower surfaces in the thickness direction of the steel plate. This results in the phenomenon that the rolled steel plate exhibits a high degree of recrystallization in the core and a low degree of recrystallization on the surface with a high degree of deformation energy storage. By using this complementary design of "one positive and one negative", the steel plate obtains uniform and fine austenitic grains during the solution treatment and heat preservation process, so as to ensure that uniform and fine austenitic grains are obtained throughout the thickness under low compression ratio conditions.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows:

[0009] A method for controlling the grain size of typical austenitic stainless steel under low compression ratio conditions, wherein the compression ratio of the austenitic stainless steel is 2.8 to 3.4, and the production process is as follows: smelting—continuous casting—heating—rolling—cooling—straightening—solution treatment, wherein...

[0010] The smelting process is as follows: the molten steel obtained by smelting contains the following components by weight percentage: C≤0.08%, Si≤1.00%, Mn≤2.00%, Ni: 8.00%~11.00%, Cr: 18.00%~20.00%, P: ≤0.045%, S: ≤0.030%, Re: 0.1%~0.3%, with the remainder being Fe and unavoidable impurities; the addition of rare earth element Re can reduce the heterogeneous nucleation work during the solidification of molten steel, increase the number of equiaxed crystal nuclei in the core, limit and interrupt the development of columnar crystals earlier, thereby expanding the equiaxed crystal region, and shortening and refining the columnar crystal region. In this invention, the Re content is controlled at 0.1%~0.3%;

[0011] The continuous casting process is as follows: during the pouring of molten steel, the superheat is controlled at 15-20℃, the casting speed is controlled at 1.10-1.20m / min, and electromagnetic stirring with a current intensity of 600-800A is used for continuous stirring for 30-60s during the secondary cooling stage. The total reduction under heavy pressure at the end of solidification is 20-30mm to ensure that the equiaxed grain ratio of the continuous casting billet is higher than 90%. Since the superheat, casting speed, electromagnetic stirring and the heavy pressure at the end of solidification have a great influence on the equiaxed grain ratio and internal defects of the continuous casting billet, achieving an equiaxed grain ratio of higher than 90% in the austenitic stainless steel continuous casting billet through the control of the above parameters will be beneficial to the dynamic recrystallization behavior during the rolling process, resulting in grain refinement and improved internal quality of the steel plate.

[0012] The heating process is as follows: after surface grinding and spraying, the continuously cast billet is sent to a walking beam furnace for heating, and then passes through a preheating section, a heating section and a soaking section before exiting the furnace. The temperature range of the preheating section is 750-1000℃ and the preheating time is 1-1.5h. The temperature range of the heating section is 1150-1240℃ and the heating time is 1-1.5h. The temperature range of the soaking section is 1180-1220℃ and the soaking time is 1-2h. After exiting the furnace, the billet is cooled.

[0013] The rolling process is as follows: a rolling-water cooling coupled process is adopted, which allows deformation to penetrate into the core of the steel plate during rolling, thereby increasing the recrystallization ratio. The surface temperature of the rough rolling is 970-1000℃, and the reduction rate of each pass in the rough rolling stage is guaranteed to be 18-23%. The surface temperature of the finish rolling is 820-840℃, and the reduction rate of each pass in the finish rolling stage is 8-13%. The purpose is to increase the energy storage of the rolled steel plate. The final rolling temperature is controlled at 800±20℃. When the steel plate is rolled to 1.5-2 times the thickness of the finished steel plate, the waiting time begins. During the waiting time, cooling water is used first, and then the plate is rolled on the roller table to ensure that the total waiting time is 2-3 minutes, thereby reducing the temperature difference between the inside and outside of the steel plate after cooling.

[0014] The cooling process is as follows: after the steel plate is rolled, it is cooled three times. The first cooling starts at a temperature of 750-800℃, ends at a temperature of 450-500℃, and has a cooling rate of 20-30℃ / s. Then, the second cooling is performed immediately, with a cooling rate of 5-10℃ / s and an ending temperature of 350-400℃. Then, the third cooling is performed immediately, with a cooling rate of 10-15℃ / s and an ending temperature of 150-200℃.

[0015] The solution treatment process is as follows: after straightening, the steel plate is shot-blasted and then fed into a quenching unit for solution heat treatment. The furnace is loaded at the required temperature, with the heating rate controlled at 10-20℃ / min for the heating section below 900℃, and the heating rate controlled at 5-8℃ / min for the temperature rise from 900℃ to the solution temperature of 1050±20℃. The net holding time at the solution temperature is 0.5-0.8 min / mm. After removal from the furnace, the plate is immediately quenched to room temperature. The heating rate below 900℃ is controlled at 10-20℃ / min because this temperature range meets the thermodynamic conditions for carbide precipitation. Rapid heating is used to reduce the kinetic conditions for carbide precipitation and avoid uneven grain size during solid solution treatment caused by differential pinning behavior resulting from uneven carbide precipitation. On the other hand, since the energy stored in the core of the steel plate is lower than that near the surface after controlled rolling and cooling, the surface temperature of the steel plate is higher than that in the core when heating is faster, resulting in a greater release of energy stored on the surface than in the core, which achieves the purpose of uniformly distributing the energy stored inside the steel plate. The heating rate from 900℃ to the solution temperature of 1050±20℃ is controlled at 5~8℃ / min. Slowing down the heating rate is to ensure the temperature uniformity of the steel plate throughout its thickness.

[0016] In the above technical solution, further, in the heating process, the temperature difference between the surface and the core is ensured not to exceed 20°C when the product is taken out of the furnace, so as to avoid the situation where the surface temperature is higher than the core temperature.

[0017] In the above technical solution, the continuous casting billet is further cooled at a rate of 10-15℃ / s after being heated and taken out of the furnace, and the cooling time does not exceed 20s, so as to ensure that the temperature difference between the surface and the core of the continuous casting billet is 80-150℃ after cooling. After cooling, it is quickly sent to the rolling mill, and the interval between cooling and the start of rolling is controlled within 30s. After exiting the furnace, rapid cooling is carried out to increase the temperature difference between the surface and the core of the continuous casting billet when rolling begins, so that deformation penetrates into the core.

[0018] In the above technical solution, further, in the rolling process, since the steel plate experiences a temperature rebound after the first two rolling passes, it needs to be cooled before the third rough rolling pass. The cooling rate is 5-10℃ / s, and the cooling time does not exceed 10s. The cooling is to reduce the surface temperature.

[0019] In the above technical solution, further, in the rolling process, it is ensured that the recrystallization ratio of the surface after rolling is not less than 50%, and the recrystallization ratio of 1 / 4T and the core is not less than 60%.

[0020] In the above technical solution, the water flow rate in the manifold during the first cooling is further 260–290 m³ / h. 3 The rolling speed is 0.6–0.8 m / s, and the surface temperature of the steel plate is 450–500℃ after the first cooling; the water flow rate in the manifold is 140–180 m³ / h during the second cooling. 3 / h, roller speed 0.8~1.0m / s; during the third cooling, the manifold water flow rate is 200~230m³ / h. 3 The rolling speed is 1.0–1.2 m / s; the cooling water temperature is controlled at 20–30℃, the laminar cooling time is 90–120 s, and the final cooling temperature is 150–200℃. Thick steel plates exhibit significant differences in cooling rate along their thickness direction, resulting in uneven plate temperature. This invention employs a staged cooling process, using a larger volume of water at higher temperatures to enhance cooling capacity and reduce microstructure recovery. After cooling, the steel plate exhibits a certain degree of reddening. A smaller volume of water is then used for further cooling to ensure a more uniform temperature distribution. This serrated cooling method reduces the temperature difference between the inside and outside of the steel plate, improves the uneven distribution of energy storage along the thickness direction, and ensures that a large portion of the post-rolling energy is retained. This provides a greater driving force for static recrystallization during the solution treatment process, thereby reducing the solution treatment time.

[0021] In the above technical solution, further, in the solution treatment process, the grain size of the steel plate after solution treatment is grade 5 to 6, and there is no difference in grain size across the entire thickness of the plate, with uniform and fine grains.

[0022] In the above technical solution, the thickness of the continuously cast billet is 200-250 mm, and the thickness of the finished steel plate is 60-90 mm.

[0023] Compared with existing technologies, the beneficial effects are as follows:

[0024] (1) This invention adopts the process of controlled rolling and cooling + solution treatment. It rationally controls the deformation temperature, deformation rate and deformation amount of each pass in the two-stage rolling process to achieve the purpose of uniformly distributing the dynamic and static recrystallization ratio. Through the coupled design of rolling process, post-rolling cooling process and solution treatment process, the uniform distribution of energy storage inside the steel plate is achieved, and the grain size of 60-90mm S30408 ​​austenitic stainless steel extra-thick plate is 5-6 grade and uniform.

[0025] (2) By designing the overall process of smelting + continuous casting + heating + controlled rolling and cooling + solution treatment, a new method for controlling the grain size of S30408 ​​austenitic stainless steel under low compression ratio conditions was established.

[0026] (3) The present invention can shorten the solution heat preservation time of austenitic stainless steel products with a thickness of 60-90mm to 0.5-0.8min / mm, reduce production costs and improve the product's profitability.

[0027] (4) The present invention adopts a production mode of direct heating and rolling of continuous casting billets, which eliminates the need to remelt and forge the continuous casting billets by electroslag remelting and then heating them, thereby reducing production processes, shortening delivery cycle and reducing production costs.

[0028] (5) The steel plate production process is simple, stable, efficient and easy to operate. Attached Figure Description

[0029] Figure 1 The grain size after rolling in Examples 1-4;

[0030] Figure 2 The grain size after solution treatment in Examples 1-4;

[0031] Figure 3 For the evaluation of intergranular corrosion bending in Examples 1-4, a is the upper surface of Example 1, b is the lower surface of Example 1, c is the upper surface of Example 2, d is the lower surface of Example 2, e is the upper surface of Example 3, f is the lower surface of Example 3, g is the upper surface of Example 4, and h is the lower surface of Example 4. Detailed Implementation

[0032] The following embodiments are merely some preferred implementations of the present invention and do not limit the scope and technical means of the invention in any way.

[0033] A method for controlling the grain size of typical austenitic stainless steel under low compression ratio conditions, wherein the compression ratio of the austenitic stainless steel is 2.8–3.4, and the production process is as follows: smelting—continuous casting—heating—rolling—cooling—straightening—solution treatment, wherein...

[0034] The smelting process is as follows: the molten steel obtained by smelting contains the following components by weight percentage: C≤0.08%, Si≤1.00%, Mn≤2.00%, Ni: 8.00%~11.00%, Cr: 18.00%~20.00%, P: ≤0.045%, S: ≤0.030%, Re: 0.1%~0.3%, with the remainder being Fe and unavoidable impurities;

[0035] The continuous casting process is as follows: the superheat of molten steel is controlled at 15-20℃ during casting, the casting speed is controlled at 1.10-1.20m / min, and electromagnetic stirring with a current intensity of 600-800A is used for continuous stirring for 30-60s during the secondary cooling stage. The total reduction under heavy pressure at the end of solidification is 20-30mm to ensure that the proportion of equiaxed crystals in the continuous casting billet is higher than 90%.

[0036] The heating process is as follows: After surface grinding and spraying, the continuously cast billet is sent to a walking beam furnace for heating, and then goes through a preheating section, a heating section and a soaking section before exiting the furnace. The temperature range of the preheating section is 750-1000℃ and the preheating time is 1-1.5h. The temperature range of the heating section is 1150-1240℃ and the heating time is 1-1.5h. The temperature range of the soaking section is 1180-1220℃ and the soaking time is 1-2h. After exiting the furnace, the billet is cooled, and the temperature difference between the surface and the core is ensured to be no more than 20℃ when exiting the furnace.

[0037] The rolling process is as follows: a rolling-water cooling coupled process is adopted to allow deformation to penetrate into the core of the steel plate during rolling, thereby increasing the recrystallization ratio. The surface temperature of the rough rolling is 970-1000℃, and three passes of rough rolling are performed. During the rough rolling stage, the reduction rate of each pass is guaranteed to be 18-23%. Cooling is required before the third pass of rough rolling, with a cooling rate of 5-10℃ / s and a cooling time not exceeding 10s. After rough rolling, four passes of finish rolling are performed. The surface temperature of the finish rolling is 820-840℃, and the reduction rate of each pass in the finish rolling stage is 8-13%. The final rolling temperature is controlled at 800±20℃. When the steel plate is rolled to 1.5-2 times the thickness of the finished steel plate, the waiting time begins. During the waiting time, cooling water is used first, and then the plate is rolled on the roller table to ensure that the total waiting time is 2-3 minutes. This ensures that the recrystallization ratio of the surface after rolling is not less than 50%, and the recrystallization ratio of 1 / 4T and the core is not less than 60%.

[0038] The cooling process is as follows: After rolling, the steel plate undergoes three cooling processes. The first cooling begins at a temperature of 750–800℃, ends at 450–500℃, and has a cooling rate of 20–30℃ / s. Immediately following, a second cooling process is performed at a cooling rate of 5–10℃ / s, ending at 350–400℃. Then, a third cooling process is performed immediately afterward at a cooling rate of 10–15℃ / s, ending at 150–200℃. During the first cooling process, the water flow rate in the manifold is 260–290 m³ / s. 3 The rolling speed is 0.6–0.8 m / s, and the surface temperature of the steel plate is 450–500℃ after the first cooling; the water flow rate in the manifold is 140–180 m³ / h during the second cooling. 3 / h, roller speed 0.8~1.0m / s; during the third cooling, the manifold water flow rate is 200~230m³ / h. 3 / h, roller speed 1.0~1.2m / s; cooling water temperature controlled at 20~30℃, laminar flow cooling time 90~120s, final cooling temperature 150~200℃;

[0039] The solution treatment process is as follows: After straightening, the steel plate is shot blasted and then sent to the quenching unit for solution heat treatment. The furnace is loaded with steel plates at the solution temperature. The heating rate in the heating section below 900℃ is controlled at 10-20℃ / min. The heating rate from 900℃ to the solution temperature of 1050±20℃ is controlled at 5-8℃ / min. The net holding time at the solution temperature is 0.5-0.8min / mm. After being taken out of the furnace, the steel plate is immediately quenched to room temperature.

[0040] Examples 1-8

[0041] Table 1 lists the components involved in Examples 1-8; Table 2 lists the continuous casting process parameters for Examples 1-8; Table 3 lists the heating process for Examples 1-8; Table 4 lists the rolling process parameters for Examples 1-8; Table 5 lists the pass information for Examples 1-8; Table 6 lists the post-rolling cooling process parameters for Examples 1-8; Table 7 lists the solution treatment process parameters for Examples 1-8; and Table 8 lists the various properties of the steel plates from Examples 1-8. Figure 1 The post-rolling metallographic images of Examples 1-4 are shown. Figure 2 The metallographic images after solution treatment in Examples 1-4 are as follows. Figure 3 This is an evaluation of intergranular corrosion bending in Examples 1-4.

[0042] Table 1. Chemical composition (wt.%) of steels from Examples 1-8

[0043] Example 1 0.057 0.50 1.52 8.01 18.25 0.033 0.0039 0.23 Example 2 0.059 0.53 1.53 8.04 18.12 0.035 0.0058 0.18 Example 3 0.056 0.42 1.46 8.16 18.05 0.034 0.0052 0.28 Example 4 0.061 0.49 1.56 8.05 18.19 0.033 0.0046 0.21 Example 5 0.071 0.45 1.42 8.25 18.29 0.031 0.0069 0.11 Example 6 0.063 0.62 1.58 8.16 18.31 0.029 0.0038 0.13 Example 7 0.052 0.58 1.49 8.06 18.06 0.038 0.0049 0.26 Example 8 0.069 0.55 1.52 8.12 18.18 0.032 0.0051 0.19

[0044] Table 2 Continuous casting process parameters for Examples 1-8

[0045]

[0046] Table 3 Heating process parameters for Examples 1-8

[0047]

[0048]

[0049] Table 4 Rolling process parameters for Examples 1-8

[0050]

[0051] Table 5 Rolling Passes in Examples 1-8

[0052]

[0053]

[0054]

[0055] Table 6 Post-rolling cooling process parameters for Examples 1-8

[0056]

[0057] Table 7 Solution treatment process parameters for Examples 1-8

[0058]

[0059] From the rolled microstructure, the steel underwent partial dynamic recrystallization, with elongated original austenite grains and fine dynamically recrystallized grains, exhibiting a classic "chain-like structure." Generally, austenitic stainless steel is a low-stack-fault-energy metal, making it more prone to dynamic recrystallization during hot working. Due to its low stacking fault energy, cross-slip is difficult to occur, recovery is slower, and therefore the dislocation density is higher, making dynamic recrystallization more likely. The partial recrystallization observed in this experiment was entirely due to insufficient deformation, i.e., an inadequate total compression ratio. Furthermore, the degree of recrystallization gradually increases from the top surface to the center of the steel plate. This is because thermal radiation and conduction cause the center temperature of the steel plate to be higher than the outer surface during rolling. Dynamic recrystallization is a thermally activated process; the higher the temperature, the easier it is for dynamic recrystallization to occur.

[0060] Figure 1 The grain size after rolling in Examples 1-4 is shown. Figure 2 The following are the grain sizes after solution treatment in Examples 1-4. The grain size grades after solution treatment in Examples 1-4 are 6, 5.5, 5.5 and 5, respectively, and the average grain sizes are 42.5, 50.7, 45.6 and 56.4 μm, respectively.

[0061] Table 8. Various indicators of steel plates in Examples 1-8

[0062]

[0063]

[0064] The solid solution-treated samples underwent bending tests after intergranular etching according to GB / T4334-2020. The test results are as follows: Figure 3 As shown, the tensile surface condition of the bent portion of the sample is good, and no bending cracks are observed.

Claims

1. A method for controlling the grain size of typical austenitic stainless steel under low compression ratio conditions, characterized in that, The austenitic stainless steel has a compression ratio of 2.8 to 3.4, and its production process is as follows: smelting—continuous casting—heating—rolling—cooling—straightening—solution treatment, wherein... The smelting process is as follows: the molten steel obtained by smelting contains the following components by weight percentage: C≤0.08%, Si≤1.00%, Mn≤2.00%, Ni: 8.00%~11.00%, Cr: 18.00%~20.00%, P: ≤0.045%, S: ≤0.030%, Re: 0.1%~0.3%, with the remainder being Fe and unavoidable impurities; The continuous casting process is as follows: the superheat is controlled at 15~20℃ during the pouring of molten steel, the casting speed is controlled at 1.10~1.20m / min, and electromagnetic stirring with a current intensity of 600~800A is used for continuous stirring for 30~60s during the secondary cooling stage. The total reduction under heavy pressure at the end of solidification is 20~30mm to ensure that the equiaxed crystal ratio of the continuously cast billet is higher than 90%. The heating process is as follows: after surface grinding and spraying, the continuously cast billet is sent to a walking beam furnace for heating, and then passes through a preheating section, a heating section and a soaking section before exiting the furnace. The temperature range of the preheating section is 750~1000℃ and the preheating time is 1~1.5h. The temperature range of the heating section is 1150~1240℃ and the heating time is 1~1.5h. The temperature range of the soaking section is 1180~1220℃ and the soaking time is 1~2h. After exiting the furnace, the billet is cooled. The rolling process is as follows: a rolling-water cooling coupled process is adopted. The surface temperature of the rough rolling is 970~1000℃. The reduction rate of each pass in the rough rolling stage is 18~23%. The surface temperature of the finish rolling is 820~840℃. The reduction rate of each pass in the finish rolling stage is 8~13%. The final rolling temperature is controlled at 800±20℃. When the steel plate is rolled to 1.5~2 times the thickness of the finished steel plate, the waiting time begins. During the waiting time, cooling water is used first, and then the plate is rolled on the roller table to wait for the temperature to be reached. The total waiting time is 2~3 minutes. The cooling process is as follows: after the steel plate is rolled, it is cooled three times. The first cooling starts at a temperature of 750~800℃, ends at a temperature of 450~500℃, and has a cooling rate of 20~30℃ / s. The second cooling has a cooling rate of 5~10℃ / s and ends at a temperature of 350~400℃. The third cooling has a cooling rate of 10~15℃ / s and ends at a temperature of 150~200℃. The solution treatment process is as follows: after straightening, the steel plate is shot blasted and then sent to the quenching unit for solution heat treatment. The furnace is loaded with steel plates at the solution temperature. The heating rate is controlled at 10~20℃ / min in the heating section below 900℃, and the heating rate is controlled at 5~8℃ / min from 900℃ to the solution temperature of 1050±20℃. The net holding time at the solution temperature is 0.5~0.8min / mm. After being taken out of the furnace, the steel plate is immediately quenched to room temperature. In the solution treatment process, the grain size of the steel plate after solution treatment is grade 5 to 6, and there is no grade difference in grain size for the entire thickness of the plate. The grains are uniform and fine. The thickness of the continuously cast billet is 200~250mm, and the thickness of the finished steel plate is 60~90mm.

2. The method for controlling the grain size of typical austenitic stainless steel under low compression ratio conditions according to claim 1, characterized in that, In the heating process, the temperature difference between the surface and the core is guaranteed to be no more than 20°C when the product is taken out of the furnace.

3. The method for controlling the grain size of typical austenitic stainless steel under low compression ratio conditions according to claim 1, characterized in that, After the continuously cast billet is heated and taken out of the furnace, the cooling rate is 10~15℃ / s, the cooling time does not exceed 20s, the temperature difference between the surface and the core of the continuously cast billet after cooling is 80~150℃, and the interval between cooling and starting rolling is controlled within 30s.

4. The method for controlling the grain size of typical austenitic stainless steel under low compression ratio conditions according to claim 1, characterized in that, In the rolling process, cooling is required before the third pass of rough rolling, with a cooling rate of 5~10℃ / s and a cooling time not exceeding 10s.

5. The method for controlling the grain size of typical austenitic stainless steel under low compression ratio conditions according to claim 1, characterized in that, In the rolling process, the recrystallization ratio of the surface after rolling is ensured to be no less than 50%, and the recrystallization ratio of 1 / 4T and the core is no less than 60%.

6. The method for controlling the grain size of typical austenitic stainless steel under low compression ratio conditions according to claim 1, characterized in that, In the cooling process, the water flow rate in the manifold during the first cooling operation is 260~290m³. 3 The rolling speed is 0.6~0.8 m / s, and the surface temperature of the steel plate is 450~500℃ after the first cooling; the water flow rate in the manifold is 140~180 m³ / h during the second cooling. 3 / h, roller speed 0.8~1.0m / s; during the third cooling, the manifold water flow rate is 200~230m³ / h. 3 Roller speed 1.0~1.2m / s; cooling water temperature controlled at 20~30℃, laminar flow cooling time 90~120s, final cooling temperature 150~200℃.

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