UNS S32615 high-silicon stainless steel and hot working method thereof

Abstract

According to the UNS S32615 high-silicon stainless steel and the hot working method thereof, the alloy has excellent high-temperature concentrated sulfuric acid corrosion resistance and nitric acid corrosion resistance, and the problems of composition segregation, precipitated phase increase, hot crack risk and the like in the casting and hot working process of the high-silicon alloy are solved. The performance of the material is improved through the following processes of diffusion annealing treatment, slow heating and soaking, high-temperature rapid water quenching, staged deformation forging and repeated remelting heating. By optimizing the diffusion annealing temperature, the forging deformation amount and the heating and heat preservation process, precipitation of an intermediate phase is remarkably reduced, the organization structure is homogenized, and the hot working plasticity and the yield of the alloy are improved. The yield of the UNS S32615 high-silicon stainless steel prepared through the method reaches 95% or above, the grain size of a forge piece is uniform and reaches 2-4 levels, the phenomena of carbide and segregation do not exist, the manufacturing requirement of high-end chemical equipment is met, and wide application prospects and remarkable economic benefits are achieved.

Description

Technical Field

[0001] The invention relates to the technical field of alloy preparation, and in particular to a UNS S32615 high-silicon stainless steel and a hot working method thereof. Background Art

[0002] UNS S32615 is a high-silicon austenitic stainless steel that has received extensive attention in the field of chemical equipment manufacturing due to its excellent corrosion resistance and low alloy cost. Its corrosion resistance is particularly reflected in its resistance to strong corrosive environments such as high-temperature concentrated sulfuric acid and nitric acid, thanks to the high silicon (Si) content in the material. The high silicon content forms a composite passivation film with SiO2 and Cr2O3 as the main components on the surface of the steel, which significantly improves the base material's resistance to uniform corrosion and intergranular corrosion.

[0003] However, although the high silicon content brings excellent corrosion resistance to UNS S32615, it faces many technical challenges in actual industrial production and hot processing:

[0004] Casting defects and composition segregation problems: High silicon content can easily cause segregation during the casting process, resulting in uneven composition. High silicon concentrations are often accompanied by intermediate phases (such as Cr3Si, Cr 23 C6) precipitation. These intermediate phases will be enriched along the grain boundaries, increasing the brittleness of the material, further affecting the uniformity of the ingot and the feasibility of subsequent hot working.

[0005] Risk of hot working cracks: High silicon content significantly reduces the hot working performance of the material, which is mainly manifested in increased sensitivity to hot cracks. During the hot working process, the material grains generate thermal stress due to high temperature diffusion and uneven deformation, which may lead to the formation of cracks, thereby reducing the yield rate. This problem significantly limits the promotion and application of UNS S32615 in actual production.

[0006] Intermediate phase precipitation affects hot working properties: Although the increase in silicon content can improve corrosion resistance, it also leads to a decrease in the size of the austenite unit cell and a decrease in the solubility of carbon, which in turn promotes the precipitation of intermediate phases (such as Cr 23 C6, σ phase, carbonitride, etc. These intermediate phases will not only weaken the high temperature strength of the material, but also significantly increase the resistance to hot deformation, further limiting the hot processing performance of the material.

[0007] Narrow thermal processing window: UNS S32615 has very strict process requirements on heating temperature, deformation and holding time during thermal processing. Any deviation from the parameters may lead to cracking, surface defects or internal structural inhomogeneity, thus reducing the quality of the finished product and increasing the difficulty of production.

[0008] In the existing technology, the research and process development for hot processing of UNS S32615 are mostly focused on general temperature control and deformation methods, and a systematic and effective hot processing process has not yet been formed to solve the process bottleneck caused by high silicon content. In particular, how to reduce component segregation and inhibit the precipitation of intermediate phases during hot processing, and how to improve the processing plasticity and yield rate of materials by optimizing the hot deformation process are still technical problems that need to be solved in this field.

[0009] In summary, the current hot working technology for UNS S32615 high silicon stainless steel has problems such as severe component segregation, intermediate phase precipitation affecting processing performance, high risk of hot working cracks, and narrow process window. These problems greatly limit the industrial application and mass production of materials, and need to be overcome by optimizing the hot working process to improve the material yield and performance stability. Summary of the invention

[0010] The technical problem to be solved by the present invention is to provide a hot working method for UNS S32615 high silicon stainless steel, so as to solve the problems of poor hot working performance, low yield, serious casting defects and intermediate phase precipitation existing in the conventional method in the prior art.

[0011] In order to overcome the above defects of the prior art, the present invention provides a heat treatment method of UNS S32615 high silicon stainless steel, comprising the following steps:

[0012] S1: Heating: Take UNS S32615 high silicon stainless steel block and put it into the heating furnace, heat it to 600±10℃ for the first time, and keep it warm for the first time, then heat it to 900℃±10℃ for the second time, keep it warm for the second time, and then heat it to 1100-1150℃ for the third time;

[0013] S2: Diffusion annealing: The UNS S32615 high silicon stainless steel block is kept at 1100-1150° C. for the third time to perform diffusion annealing;

[0014] S3: Cooling and heat preservation of steel ingot: cooling the alloy block treated in step S2 to 950±10° C., then heating it to 1060±10° C. for the fourth time, and heat preservation for the fourth time;

[0015] S4: Steel ingot blanking: After the fourth heat preservation in step S3 is completed, the alloy block is taken out of the furnace and blanked to obtain a blanked steel ingot;

[0016] S5: initial reheating: the steel ingot after the blanking in step S4 is reheated for the fifth time, and then kept warm for the fifth time;

[0017] S6: Forging: Forging the steel ingot after being processed in step S5;

[0018] S7: Returning to the furnace for heating again: The steel ingot forged in step S6 is returned to the furnace for heating for the sixth time, and then heat-insulated for the sixth time to obtain UNS S32615 high-silicon stainless steel after heat treatment.

[0019] Compared with the prior art, the thermal processing method of UNS S32615 high silicon stainless steel in this application has the following advantages:

[0020] Significantly improved hot working properties: By precisely controlling the temperature at 1100-1150°C during the diffusion annealing stage (S2), efficient homogenization of segregated elements is achieved, and carbides within the grain boundaries are effectively dissolved back into the grains, thereby reducing the deformation resistance of the material, significantly improving the plasticity and hot working properties, and solving the problem of poor hot working properties of high silicon alloys due to the precipitation of intermediate phases in the prior art;

[0021] Reduce the risk of ingot cracking: During the process of ingot blanking and forging (S4, S6), by optimizing the temperature range and deformation mode, not only the surface grains can be broken, but also the core of the ingot can be fully compacted, reducing the concentration of thermal stress and avoiding material cracking;

[0022] Improve the yield rate and material uniformity: Through multiple heating, cooling and remelting treatments (S5, S7), combined with precisely controlled heating and holding time, the dendrite structure and component segregation are effectively eliminated, and the microstructure uniformity of the material is improved. The method of the present invention can increase the yield rate from 85% to 95%, meeting the high-quality industrial needs, as verified by ultrasonic flaw detection and metallographic analysis;

[0023] Synergy of each step: The present invention rationally designs the heating, heat preservation, cooling and deformation processes in steps S1-S7, and associates the defects of high silicon alloy such as brittleness, precipitation phase and difficulty in hot working with the requirements of material plasticity and strength, and finally achieves the goal of efficiently producing high-performance UNS S32615 high silicon stainless steel;

[0024] The heat treatment method of the present invention, through the introduction of high-temperature diffusion annealing (S2), dissolves the precipitated phase and homogenizes the component segregation, so that the material has a lower resistance to thermal deformation; and the multiple precise temperature-controlled reheating and forging processes (S5-S7) fully guarantee the uniformity of the internal grains of the alloy and the optimal plasticity range, and solve the problems of cracking, uneven deformation and low yield rate in the hot working process in the prior art. In summary, the hot working method provided by the present invention, through the optimized design of the above-mentioned process steps, effectively solves the problems of poor hot working performance, casting defects and intermediate phase precipitation mentioned in the background technology part, and provides an innovative solution for the industrial production of high-performance UNS S32615 high-silicon stainless steel, which has significant technical advancement and industrial application value.

[0025] In a possible implementation, in step S1, the first heating time is 2 hours, and the first insulation time is 4 hours; the second heating time is 4 hours, and the second insulation time is 3 hours; and the third heating time is 7 hours.

[0026] Compared with the prior art, the above technical solution makes the temperature gradient inside the alloy tend to be uniform through the slow heating (2h) and heat preservation (4h) of the first heating (20℃ to 600℃), avoiding the large temperature difference between the surface and the core caused by rapid heating, thereby reducing the thermal stress concentration; and in the second heating (600℃ to 900℃) stage, the residual stress in the grains is released through a longer heating (4h) and heat preservation (3h), while reducing the brittleness of the material and optimizing the organizational state; the third heating (900℃ to 1100℃) 1150℃) stage, and then further raised to the diffusion annealing temperature to ensure the diffusion and homogenization of segregated elements, while the precipitated phase dissolves back into the crystal to create conditions for subsequent diffusion annealing; the first and second insulation times (4h and 3h respectively) ensure that the material fully completes thermal equilibrium in each temperature range to avoid the accumulation of thermal stress, and the third heating time is longer (7h), so that the material temperature is stabilized in the transition range before the diffusion annealing temperature, thereby reducing the risk of overburning or local overheating caused by high temperature for a short time. Ultimately, the synergistic effect greatly reduces the internal stress of UNS S32615 high silicon stainless steel, reduces deformation resistance, and ultimately lays the foundation for the production of high-quality alloy materials.

[0027] In a possible implementation manner, in step S2, the third insulation time is 20 hours.

[0028] Compared with the prior art, the above technical solution is adopted, because the purpose of the diffusion annealing process in step S2 is to promote the uniform diffusion of elements in the alloy and reduce component segregation. In this process, long-term heat preservation (20 hours) can significantly increase the diffusion rate of each element (such as Cr, Ni, Si, etc.) in the high-silicon alloy, so that the concentration difference between the elements is gradually reduced, thereby improving the overall performance of the alloy. In the temperature range of 1100-1150°C, the intermediate phases (such as σ phase, Cr23C6, etc.) that may precipitate in the alloy can be dissolved back into the matrix, thereby eliminating the negative effects of these phases. Long-term heat preservation helps these phases to completely dissolve back, avoiding the formation of harmful phases in subsequent processing, resulting in cracking or performance degradation. The extended heat preservation time helps to reduce the deformation resistance of the material through the dissolution process, improve its plasticity and processability, and provide a more favorable material state for subsequent thermal deformation processes.

[0029] In a possible implementation, in step S3, the cooling method is: cooling by opening the furnace door of the heating furnace, and the fourth heating method is: passing through the heating furnace again after closing the furnace door, and the alloy block is heated to 1060±10°C with the furnace, and the fourth insulation time is 5h.

[0030] Compared with the prior art, the above technical solution is adopted. In step S3, cooling by opening the furnace door of the heating furnace is a natural cooling method, which is usually used to gradually reduce the material temperature to avoid thermal stress caused by too fast temperature changes. This cooling method can ensure that the temperature difference of the material is small during the cooling process, reducing the generation of defects such as cracks, and by closing the furnace door and then heating, the alloy block can be heated to 1060±10℃ with the furnace without drastic changes in the external temperature. This method ensures the uniformity of the material temperature and avoids thermal cracks caused by excessive temperature difference between the surface and the core during heating. In the above-mentioned combination of heating and heat preservation, the elements in the alloy can have enough time to diffuse, reduce the precipitation phases such as carbides at the grain boundaries, and improve the intrinsic quality of the alloy.

[0031] In a possible implementation, in step S4, the method of blanking is: blanking the steel ingot at a temperature between 1060°C and 950°C, and blanking is performed using a WHF deformation process, by gently tapping the four sides of the steel ingot to round them and then flattening them in one direction.

[0032] Compared with the prior art, the above technical scheme is adopted, and the quality of the steel ingot during the blanking process can be significantly improved by adopting the above technical scheme, and the uniformity and plasticity of the material can be ensured. By optimizing the blanking temperature and adopting the WHF deformation process, the common defects in the traditional method (such as cracks, uneven structure, etc.) can be effectively avoided, and the yield rate of the alloy material during the hot working process is improved, and its hot working performance and reliability in the subsequent use process are improved. Finally, the hot working method of the present invention solves various technical problems of high-silicon stainless steel during the hot working process, and improves its actual effect in the application field.

[0033] In a possible embodiment, in step S4, the final forging temperature of the blank is greater than 850°C.

[0034] Compared with the prior art, the above technical solution can significantly improve the yield rate of high-silicon stainless steel alloy during the forging process, reduce the generation of cracks and defects, and by setting the final forging temperature to be greater than 850°C, not only the plasticity of the alloy is improved, but also the fluidity and uniformity of the alloy during the forging process are effectively optimized, ensuring the quality and consistency of the final product. This can better meet the application needs of high-silicon stainless steel in high-demand fields such as chemical equipment.

[0035] In a possible implementation, in step S5, the fifth heating temperature is 1100±10° C., and the fifth insulation time is 1.5 h.

[0036] Compared with the prior art, the above technical solution can significantly improve the uniformity and plasticity of UNS S32615 high-silicon stainless steel during hot working by setting the fifth heating temperature to 1100±10°C and keeping it warm for 1.5 hours, so that the alloy can show better processing performance in the subsequent forging process. In addition, this setting effectively avoids material cracks and defects caused by uneven or too low temperature, improves the yield rate, and ultimately ensures the quality and reliability of high-silicon stainless steel alloys in various high-demand applications.

[0037] In a possible implementation manner, in the step S6, the deformation amount of the forging is 20-30%.

[0038] Compared with the prior art, the above technical solution can effectively control the plasticity and processing properties of the material by setting the forging deformation to 20-30%, while ensuring the good mechanical properties of the alloy and avoiding the problems of cracks and defects in the material. In addition, a reasonable deformation amount can also refine the grains, improve the tensile strength and yield resistance of the alloy, so that the quality and yield rate of the material are further improved. The above forging process significantly improves the production efficiency and product quality of UNS S32615 high-silicon stainless steel, and is particularly suitable for application fields with high requirements on material properties.

[0039] In a possible implementation, in step S5, the temperature of the sixth heating is 1100±10° C., and the time of the sixth insulation is 1.5 h.

[0040] Compared with the prior art, the above technical solution can effectively improve the uniformity of the alloy, reduce the thermal stress caused by the temperature difference, improve the plasticity of the alloy, and provide better hot working performance for subsequent forging by setting the sixth heating temperature to 1100±10℃ and maintaining the holding time for 1.5 hours. It ensures the overall quality of the steel ingot, makes the production of the alloy more stable, avoids the possible cracks and defects, and thus improves the quality and yield rate of the final product.

[0041] Another technical problem to be solved by the present invention is to provide a hot working method for UNS S32615 high silicon stainless steel to solve the problems of casting defects, component segregation, increased precipitation phase and hot cracks existing in conventional alloys in the prior art.

[0042] In order to overcome the above defects of the prior art, the present invention provides a UNS S32615 high-silicon stainless steel, which is prepared by the preparation method.

[0043] Compared with the prior art, the present application of a UNS S32615 high silicon stainless steel has the following advantages: Improved uniformity of the alloy: The present invention realizes the homogenization of segregated elements at high temperature through a diffusion annealing process, making the composition inside the alloy more uniform, avoiding the performance inconsistency problem caused by component segregation, and further improving the corrosion resistance of the alloy: Reduced influence of precipitated phase: The high temperature diffusion annealing process and rapid cooling in the present invention avoid the precipitation of intermediate phases (such as Cr23C6, σ phase, Cr3Si, etc.), thereby improving the intergranular corrosion resistance of the alloy and ensuring that the alloy has better plasticity and strength during the subsequent hot deformation process; Significantly improved hot working performance: The hot working method of the present invention optimizes the hot deformation characteristics of the alloy through reasonable heating, heat preservation and reheating processes, making it easier to operate during the forging process and reducing the generation of hot cracks. This method enhances the forgeability of the alloy by strictly controlling the temperature and heat preservation time, avoiding defects caused by excessive heating or cooling; Improved yield rate: After being processed by the hot working method of the present invention, the forging quality of the alloy is improved. By adopting the WHF deformation process for blanking and forging, the quality of the final product is optimized, and after ultrasonic flaw detection, the qualified rate of forgings is improved, thereby increasing the yield rate from 85% to 95%, greatly reducing the generation of waste; uniform grain size and improved performance: the alloy blank forged by the method of the present invention has uniform grain size, and metallographic analysis shows that dendrites disappear, carbides and element segregation are basically eliminated, so that the mechanical properties and corrosion resistance of the alloy are significantly improved. The performance of the UNS S32615 high-silicon stainless steel provided by the present invention is significantly improved after heat treatment, especially in terms of operability, crack resistance, corrosion resistance and yield rate during the heat treatment process, which meets the application requirements of high-end chemical equipment and high sulfuric acid and nitric acid environments, and has broader market prospects and technological advancement. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is a phase change curve diagram of UNS S32615 high silicon stainless steel of the present invention;

[0045] Figure 2 is a heat treatment curve diagram of the steel ingot in the preparation method of the present invention;

[0046] Figure 3 It is a graph of the steel ingot reheating in the preparation method of the present invention;

[0047] Figure 4 The alloy spectrum comparison report obtained in Example 1 of the present invention;

[0048] Figure 5 The alloy spectrum comparison report obtained in Example 2 of the present invention;

[0049] Figure 6 This is a comparison report of the alloy spectrum obtained in Example 3 of the present invention.

[0050] Figure 7 The present invention is a flow chart of the preparation method. DETAILED DESCRIPTION

[0051] First, those skilled in the art should understand that these implementations are only used to explain the technical principles of the embodiments of the present application, and are not intended to limit the protection scope of the embodiments of the present application. Those skilled in the art can make adjustments to them as needed to adapt to specific application scenarios.

[0052] The present invention provides a thermal processing method of UNS S32615 high silicon stainless steel. Figure 7 Flow chart of the hot working method of the present invention, wherein the heat treatment of the steel ingot is as follows Figure 2 As shown, Figure 2 is the heat treatment curve of the steel ingot in the preparation method of the present invention Figure 2 As shown, Figure 2 The processing curve diagram of steps S1-S3 includes the following steps:

[0053] S1: Heating: Take UNS S32615 high silicon stainless steel block and put it into the heating furnace, heat it to 600±10℃ for the first time, and keep it warm for the first time, then heat it to 900℃±10℃ for the second time, keep it warm for the second time, and then heat it to 1100-1150℃ for the third time;

[0054] S2: Diffusion annealing: The UNS S32615 high silicon stainless steel block is kept at 1100-1150°C for the third time for diffusion annealing. Considering that the steel ingot may be over-burned at high temperature for a long time, refer to the phase diagram, as shown in FIG. Figure 1 As shown, the temperature should be set at: 1100℃~1150℃;

[0055] S3: Cooling and heat preservation of steel ingot: cooling the alloy block treated in step S2 to 950±10° C., then heating it to 1060±10° C. for the fourth time, and heat preservation for the fourth time;

[0056] S4: Steel ingot blanking: After the fourth heat preservation in step S3 is completed, the alloy block is taken out of the furnace and blanked to obtain a blanked steel ingot;

[0057] S5: Initial reheating: The steel ingot after the billeting in step S4 is reheated for the fifth time, and then kept warm for the fifth time. Figure 3 As shown;

[0058] S6: Forging: Forging the steel ingot after being processed in step S5;

[0059] S7: Returning to the furnace for heating again: The steel ingot forged in step S6 is returned to the furnace for heating for the sixth time, and then heat-insulated for the sixth time to obtain UNS S32615 high-silicon stainless steel after heat treatment.

[0060] As a preferred solution, in step S1, the first heating time is 2 hours, and the first insulation time is 4 hours; the second heating time is 4 hours, and the second insulation time is 3 hours; and the third heating time is 7 hours.

[0061] As a preferred solution, in step S2, the third insulation time is 20 hours.

[0062] As a preferred solution, in step S3, the cooling method is: cooling by opening the furnace door of the heating furnace, and the fourth heating method is: passing through the heating furnace again after closing the furnace door, and the alloy block is heated to 1060±10°C with the furnace, and the fourth insulation time is 5h.

[0063] As a preferred solution, in step S4, the method of blanking is: blanking the steel ingot at a temperature between 1060°C and 950°C, and the blanking is performed using a WHF deformation process, by gently tapping the four sides of the steel ingot to round them and then flattening them in one direction.

[0064] As a preferred solution, in step S4, the final forging temperature of the blank is greater than 850°C.

[0065] As a preferred solution, in step S5, the temperature of the fifth heating is 1100±10°C, and the time of the fifth insulation is 1.5h.

[0066] As a preferred solution, in step S6, the deformation amount of forging is 20-30%.

[0067] As a preferred solution, in step S5, the temperature of the sixth heating is 1100±10°C, and the time of the sixth insulation is 1.5h.

[0068] The present invention also provides UNS S32615 high-silicon stainless steel, which is prepared by the preparation method.

[0069] In combination with the above technical solution, an embodiment specifically combined with actual data is given below to further expand the content of the invention of the present invention:

[0070] Example 1: This example provides a UNS S32615 high silicon stainless steel and a hot working method thereof, specifically a UNS S32615 high silicon stainless steel block 250mm×250mm×2000mm forged, the preparation method comprising the following steps:

[0071] Step S1: Heating

[0072] A UNS S32615 high silicon stainless steel block (diameter 480 mm) was placed in a heating furnace and heated as follows: the first heating was to 600°C for 2 hours and kept warm for 4 hours; then the second heating was to 900°C for 4 hours and kept warm for 3 hours; finally the third heating was to 1150°C for 7 hours.

[0073] Step S2: Diffusion annealing

[0074] The UNS S32615 high silicon stainless steel block was kept at 1150° C. for 20 hours to complete diffusion annealing.

[0075] Step S3: Cooling and heat preservation of steel ingot

[0076] After diffusion annealing, the ingot was cooled to 950°C by opening the door of the heating furnace; then the door was closed, the heating furnace was heated to 1060°C, and kept at this temperature for 5 hours.

[0077] Step S4: Steel ingot blanking

[0078] After the fourth heat preservation, the ingot is taken out of the furnace and the blanking operation is carried out in the temperature range of 1000℃-950℃. The WHF deformation process is adopted to gently tap and round the four sides of the ingot and then flatten it in one direction. The final forging temperature is greater than 850℃. The specifications of the ingot after blanking are 420mm×480mm×L.

[0079] Step S5: Initial reheating

[0080] The steel ingot is returned to the furnace and heated to 1100°C for 1.5 hours.

[0081] Step S6: Forging

[0082] The steel ingot after the heat preservation in step S5 is taken out of the furnace for forging, and the deformation amount is controlled at 20-30%. The specifications of the steel ingot after forging are 200mm×420mm×L.

[0083] Step S7: Return to the furnace for heating again

[0084] The steel ingot forged in step S6 is returned to the furnace for heating at 1100°C for 1.5 hours, and then taken out of the furnace for forging into a square billet of 250mm×250mm×2000mm, and air-cooled after forging.

[0085] Performance analysis: The forgings are qualified after ultrasonic testing, and the spectrum comparison report is as follows Figure 4 As shown, metallographic analysis shows that dendrites disappear, no carbide precipitation, element segregation is basically eliminated, and the grain size is uniform, reaching level 2-4.

[0086] Example 2: This example provides a UNS S32615 high silicon stainless steel and a hot working method thereof, specifically forging a UNS S32615 high silicon stainless steel round bar with a diameter of 280 mm. The preparation method comprises the following steps:

[0087] Step S1: Heating

[0088] A UNS S32615 high silicon stainless steel block (diameter 480 mm) was placed in a heating furnace and heated as follows: the first heating was to 590°C for 2 hours and kept warm for 4 hours; then the second heating was to 890°C for 4 hours and kept warm for 3 hours; finally the third heating was to 1100°C for 7 hours.

[0089] Step S2: Diffusion annealing

[0090] The UNS S32615 high silicon stainless steel block was kept at 1100° C. for 20 hours to complete diffusion annealing.

[0091] Step S3: Cooling and heat preservation of steel ingot

[0092] After diffusion annealing, the ingot was cooled to 940°C by opening the door of the heating furnace; then the door was closed, the heating furnace was heated to 1050°C, and kept at this temperature for 5 hours.

[0093] Step S4: Steel ingot blanking

[0094] After the fourth heat preservation, the ingot is taken out of the furnace and the blanking operation is carried out in the temperature range of 980℃-950℃. The WHF deformation process is adopted to gently pat the four sides of the ingot for rounding and then flatten it in one direction. The final forging temperature is greater than 950℃. The specifications of the ingot after blanking are 420mm×480mm×L.

[0095] Step S5: Initial reheating

[0096] The steel ingot after being opened is returned to the furnace and heated to 1090°C for 1.5 hours.

[0097] Step S6: Forging

[0098] The steel ingot after the heat preservation in step S5 is taken out of the furnace for forging, the deformation is controlled at 20-30%, the specifications of the steel ingot after forging are 280mm×280mm×L, and the final forging temperature is greater than 980°C.

[0099] Step S7: Return to the furnace for heating again

[0100] The steel ingot forged in step S6 is returned to the furnace for heating at 1090°C for 1.5 hours, and then taken out of the furnace for forging into a round bar with a diameter of 280 mm, and air-cooled after forging.

[0101] Performance analysis: The forgings are qualified after ultrasonic testing, and the spectrum comparison report is as follows Figure 5 As shown, metallographic analysis shows that dendrites disappear, no carbide precipitation, element segregation is basically eliminated, and the grain size is uniform, reaching level 2-4.

[0102] Embodiment 3:

[0103] This embodiment provides a UNS S32615 high silicon stainless steel and a hot working method thereof, specifically forging a UNS S32615 high silicon stainless steel block of 250 mm×250 mm×2000 mm, the preparation method comprising the following steps:

[0104] Step S1: Heating

[0105] A UNS S32615 high silicon stainless steel block (diameter 480 mm) was placed in a heating furnace and heated as follows: the first heating was to 610°C for 2 hours and kept warm for 4 hours; then the second heating was to 910°C for 4 hours and kept warm for 3 hours; finally the third heating was to 1125°C for 7 hours.

[0106] Step S2: Diffusion annealing

[0107] The UNS S32615 high silicon stainless steel block was kept at 1125° C. for 20 hours to complete diffusion annealing.

[0108] Step S3: Cooling and heat preservation of steel ingot

[0109] After diffusion annealing, the ingot was cooled to 960°C by opening the door of the heating furnace; then the door was closed, the heating furnace was heated to 1070°C, and kept at this temperature for 5 hours.

[0110] Step S4: Steel ingot blanking

[0111] After the fourth heat preservation, the ingot is taken out of the furnace and the blanking operation is carried out in the temperature range of 1030℃-980℃. The WHF deformation process is adopted to gently pat the four sides of the ingot for rounding and then flatten it in one direction. The final forging temperature is greater than 850℃. The specifications of the ingot after blanking are 420mm×480mm×L.

[0112] Step S5: Initial reheating

[0113] The steel ingot after blooming is returned to the furnace and heated to 1110°C for 1.5 hours.

[0114] Step S6: Forging

[0115] The steel ingot after the heat preservation in step S5 is taken out of the furnace for forging, and the deformation amount is controlled at 20-30%. The specifications of the steel ingot after forging are 200mm×420mm×L.

[0116] Step S7: Return to the furnace for heating again

[0117] The steel ingot forged in step S6 is returned to the furnace for heating at 1110°C for 1.5 hours, and then taken out of the furnace for forging into a square billet of 250mm×250mm×2000mm, and air-cooled after forging.

[0118] Performance analysis: The forgings are qualified after ultrasonic testing, and the spectrum comparison report is as follows Figure 6 As shown, metallographic analysis shows that dendrites disappear, no carbide precipitation, element segregation is basically eliminated, and the grain size is uniform, reaching level 2-4.

[0119] In summary, as further demonstrated by the above embodiments, the present invention provides a UNS S32615 high silicon stainless steel and a hot working method thereof. The present invention effectively solves the problems of casting defects, component segregation and intermediate phase precipitation of UNS S32615 high silicon stainless steel during hot working by precisely controlling the heating, heat preservation, cooling and forging processes during hot working, especially by adopting a treatment method of multiple diffusion annealing and reheating. By reasonably adjusting the hot working temperature and deformation method, the present invention greatly improves the plasticity and hot working properties of the alloy, significantly reduces the risk of cracking in ingot forging, and improves the yield rate and quality stability of the product.

[0120] At the same time, the method of the present invention ensures the uniformity of the internal structure of the material through the optimized WHF deformation process and the precise temperature control strategy. Microscopic analysis shows that the internal grains of the alloy are refined, the dendrites completely disappear, and the element segregation is effectively eliminated, forming a high-quality forging suitable for subsequent processing. The technical method provided by the present invention provides a reliable basis for the industrial production of UNS S32615 high-silicon stainless steel, opens up a new direction for the optimization of the processing technology of high-silicon stainless steel, and has important technical value and broad application prospects.

[0121] In the description of the present application, the description with reference to the terms "one embodiment", "some embodiments", "in the present embodiment", "specific example", or "some examples" etc. means that the specific features, mechanisms, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, mechanisms, materials or characteristics described may be combined in a suitable manner in any one or more embodiments or examples. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0122] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A thermal processing method for UNS S32615 high silicon stainless steel, characterized in that: The following steps are involved: S1: Heating: Take UNS S32615 high silicon stainless steel block and put it into the heating furnace, heat it to 600±10℃ for the first time, and keep it warm for the first time, then heat it to 900℃±10℃ for the second time, keep it warm for the second time, and then heat it to 1100-1150℃ for the third time; S2: Diffusion annealing: The UNS S32615 high silicon stainless steel block is kept at 1100-1150° C. for the third time to perform diffusion annealing; S3: Cooling and heat preservation of steel ingot: cooling the alloy block treated in step S2 to 950±10° C., then heating it to 1060±10° C. for the fourth time, and heat preservation for the fourth time; S4: Steel ingot blanking: After the fourth heat preservation in step S3 is completed, the alloy block is taken out of the furnace and blanked to obtain a blanked steel ingot; S5: initial reheating: the steel ingot after the blanking in step S4 is reheated for the fifth time, and then kept warm for the fifth time; S6: Forging: Forging the steel ingot after being processed in step S5; S7: Returning to the furnace for heating again: The steel ingot forged in step S6 is returned to the furnace for heating for the sixth time, and then heat-insulated for the sixth time to obtain UNS S32615 high-silicon stainless steel after heat treatment.

2. The hot working method of UNS S32615 high silicon stainless steel according to claim 1, characterized in that: In the step S1, the first heating time is 2 hours, and the first insulation time is 4 hours; the second heating time is 4 hours, and the second insulation time is 3 hours; the third heating time is 7 hours.

3. The hot working method of UNS S32615 high silicon stainless steel according to claim 1, characterized in that: In step S2, the third insulation time is 20 hours.

4. The hot working method of UNS S32615 high silicon stainless steel according to claim 1, characterized in that: In step S3, the cooling method is: cooling by opening the furnace door of the heating furnace, and the fourth heating method is: passing through the heating furnace again after closing the furnace door, and the alloy block is heated to 1060±10°C with the furnace, and the fourth insulation time is 5h.

5. The hot working method of UNS S32615 high silicon stainless steel according to claim 1, characterized in that: In step S4, the method of blanking is: blanking the steel ingot at a temperature between 1060° C. and 950° C., and the blanking adopts a WHF deformation process, by gently tapping the four sides of the steel ingot to round it and then flattening it in one direction.

6. The hot working method of UNS S32615 high silicon stainless steel according to claim 5, characterized in that: In the step S4, the final forging temperature of the blank is greater than 850°C.

7. The hot working method of UNS S32615 high silicon stainless steel according to claim 1, characterized in that: In the step S5, the temperature of the fifth heating is 1100±10° C., and the time of the fifth insulation is 1.5 h.

8. The hot working method of UNS S32615 high silicon stainless steel according to claim 1, characterized in that: In the step S6, the deformation amount of the forging is 20-30%.

9. The hot working method of UNS S32615 high silicon stainless steel according to claim 1, characterized in that: In the step S5, the temperature of the sixth heating is 1100±10° C., and the time of the sixth insulation is 1.5 h.

10. A UNS S32615 high silicon stainless steel, characterized in that: The stainless steel is prepared by the preparation method according to any one of claims 1 to 9.

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