A control process for reducing hot edge cracking in an economic duplex stainless steel with a twin stand furnace and coil rolling mill

Abstract

The application discloses a kind of double-stand furnace roll mill control processes for reducing economic duplex stainless steel hot edge cracking, comprising: casting blank heating process control, the final heating temperature of casting blank is 1150-1260 DEG C, total residence time is 140-280 min;Control rough rolling process, using 5-7 pass rolling, in the first pass roughing scale removal is put, each pass reduction is 15-25%, rolling speed is 3-5 m / s, rough rolling outlet temperature is 1000-1100 DEG C;Control finish rolling process, using double-stand three rolling six pass rolling, in the first four passes, reduction is 25-35%, rolling speed is 6-9 m / s, in the last two passes, reduction is 10-15%, rolling speed is 2-3 mm, finish rolling outlet temperature is 900-1000 DEG C, coiling furnace heating temperature is 1000-1100 DEG C, coiling temperature is 500-700 DEG C.The application uses double-stand furnace roll mill control process, through casting blank heating process control, rough rolling process control, finish rolling process control, the width of economic duplex stainless steel hot edge cracking is reduced by more than 70% compared with prior art, effectively improve the product edge quality.

Description

Technical Field

[0001] This invention belongs to the field of special stainless steel development and application, specifically involving a control process for a double-stand hot-rolling mill to reduce edge cracking in economical duplex stainless steel. Background Technology

[0002] From the perspective of the long-term global development of stainless steel, high-performance and resource-saving stainless steel, represented by duplex stainless steel, has become one of the main development trends. Its characteristics such as high strength and toughness and low alloy cost have become important references for design and manufacturing.

[0003] Low-Ni economical duplex stainless steel, represented by S32101, has an austenitic and ferritic phase ratio close to 1:1. This structure gives the steel the dual characteristics of both austenitic and ferritic stainless steels. It has good mechanical properties at room temperature and excellent resistance to stress corrosion, crevice corrosion, comprehensive mechanical properties, and weldability. Therefore, it is widely used in the chemical industry.

[0004] The conventional production of S32101 economic duplex stainless steel hot-rolled coils employs a hot continuous rolling process. Because this steel grade consists of austenitic and ferritic two-phase structures, the high-temperature strength difference between the austenitic and ferritic phases is significant, making phase boundary deformation difficult and prone to causing cracks at the two-phase interface during rolling. Under current technological conditions, the edge crack of economic duplex stainless steel hot-rolled coils is approximately 40mm, severely affecting the edge quality of the material. Summary of the Invention

[0005] To address the aforementioned technical problems in the prior art, this invention targets the edge cracking issue of hot-rolled low-Ni economic duplex stainless steel, represented by S32101. It employs a dual-stand furnace coil mill for rolling, and by controlling the rolling process, reduces the edge crack width of the economic duplex stainless steel hot-rolled coil, thereby improving product quality.

[0006] The present invention provides a control process for a twin-stand hot-rolling mill to reduce edge cracking in economical duplex stainless steel hot-rolled coils, comprising:

[0007] (1) Control of billet heating process

[0008] The billet is heated in the heating furnace according to the process of controlling the heating temperature and holding time in the furnace in sections. The final heating temperature of the billet is controlled at 1150-1260℃ and the total holding time in the furnace is controlled at 140-280min.

[0009] (2) Rough rolling process control

[0010] Roughing is carried out in 5 to 7 passes. Roughing descaling is carried out in the first pass. The rolling reduction rate of each pass is controlled at 15 to 25%, and the rolling speed is controlled at 3 to 5 m / s. The rolling speed and rolling reduction rate increase with the number of passes. The exit temperature of the roughing mill is controlled at 1000 to 1100℃.

[0011] (3) Finishing rolling process control

[0012] The finishing mill adopts a two-stand, three-pass, six-stage rolling process. In the first four passes, the rolling reduction rate is controlled at 25-35% and the rolling speed is controlled at 6-9 m / s. The rolling speed increases with each pass, while the reduction rate decreases with each pass. In the last two passes, the rolling reduction rate is controlled at 10-15% and the rolling speed is controlled at 2-3 mm. The finishing mill exit temperature is controlled at 900-1000℃. The heating temperature of the coiling furnace of the two-stand hot platen is controlled at 1000-1100℃. Laminar flow cooling is applied during coiling, and the coiling temperature is controlled at 500-700℃.

[0013] Furthermore, in the above-mentioned control process for reducing edge cracks in hot-rolled duplex stainless steel, in the billet heating process control, in the preheating section of the heating furnace, the furnace temperature is controlled at 500–700℃ and the furnace dwell time is controlled at 50–100 min; in the first heating section of the heating furnace, the furnace temperature is controlled at 1000–1050℃ and the furnace dwell time is controlled at 30–60 min; in the second heating section of the heating furnace, the furnace temperature is controlled at 1100–1150℃ and the furnace dwell time is controlled at 30–60 min; in the third heating section of the heating furnace, the furnace temperature is controlled at 1150–1260℃ and the furnace dwell time is controlled at 30–60 min.

[0014] Furthermore, in the above-mentioned double-stand hot-rolling mill control process for reducing edge cracking of economic duplex stainless steel, the economic duplex stainless steel is a low-Ni economic duplex stainless steel, whose chemical composition by mass percentage includes: C≤0.040%, Si≤1.00%, Mn: 4.00%~6.00%, P≤0.040%, S≤0.030%, Cr: 21.00%~22.00%, Ni: 1.35%~1.70%, Mo: 0.1%~0.8%, Cu: 0.1%~0.8%, N: 0.20%~0.25%, with the remainder being Fe and unavoidable impurities.

[0015] Furthermore, in the above-mentioned control process for reducing edge cracking of hot-rolled duplex stainless steel, the grade of the economic duplex stainless steel is S32101.

[0016] The control process for reducing edge cracking in hot-rolled duplex stainless steel of the present invention via a double-stand hot-roll mill has the following advantages and beneficial effects:

[0017] This invention addresses the severe edge cracking problem in hot-rolled low-Ni economic duplex stainless steel, represented by S32101. It employs a dual-stand furnace coil mill control process. Through billet heating process control, the temperature range and heating curve of the billet heating process are designed to ensure uniform billet temperature and a pure microstructure. Through rough rolling process control, the number of rolling passes, pass reduction rate, and rolling speed are designed to ensure uniform microstructure, uniform stress, and controllable hot working plasticity temperature. Through finish rolling process control, the coiling furnace heating process, rolling passes, pass reduction rate, and rolling speed are designed, and the coiling process is designed to ensure controllable hot working temperature range, resulting in good sheet quality and precision. By combining these control methods, the width of edge cracks in economic duplex stainless steel hot-rolled coils is reduced by more than 70% compared to existing technologies, effectively improving the edge quality of the product. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0019] The dual-stand hot-rolling mill control process for reducing edge cracks in economical duplex stainless steel hot-rolled coils of this invention effectively reduces edge cracks and improves product edge quality through techniques such as billet heating process control, roughing rolling process control, and finishing rolling process control. Specifically, the dual-stand hot-rolling mill control process for reducing edge cracks in economical duplex stainless steel hot-rolled coils of this invention includes:

[0020] (1) Control of billet heating process

[0021] The billet is heated in the heating furnace according to a process of controlling the heating temperature and furnace dwell time in sections. The final heating temperature of the billet is controlled at 1150-1260℃, and the total furnace dwell time is controlled at 140-280min. Specifically, in the preheating section of the heating furnace, the heating furnace temperature is controlled at 500-700℃, and the furnace dwell time is controlled at 50-100min; in the first heating section, the heating furnace temperature is controlled at 1000-1050℃, and the furnace dwell time is controlled at 30-60min; in the second heating section, the heating furnace temperature is controlled at 1100-1150℃, and the furnace dwell time is controlled at 30-60min; in the third heating section, the heating furnace temperature is controlled at 1150-1260℃, and the furnace dwell time is controlled at 30-60min.

[0022] In the above-mentioned billet heating process control, the design and control of billet heating temperature and furnace dwell time mainly consider the high-temperature thermoplasticity of the material, ensuring that the material has good high-temperature plasticity at this temperature. Studies have shown that the high-temperature plasticity of economical duplex stainless steel increases with increasing temperature within a certain range, which is beneficial for hot working. However, above 1260℃, due to changes in the phase boundary and grain boundary properties, the material's thermoplasticity decreases. Therefore, the final heating temperature of economical duplex stainless steel billets is controlled within the optimal thermoplasticity range of 1150–1260℃.

[0023] In the above-mentioned billet heating process control, the heating temperature is increased to 500-700℃ and the holding time is increased to 50-100min in the preheating section of the heating furnace to ensure the uniformity of material heating. Then, the temperature is rapidly increased to above 1000℃ in the first heating section of the heating furnace to avoid the formation of second phases such as Cr2N phase in economic duplex stainless steel, which would affect the thermoplasticity. After that, the heating gradient is further precisely controlled in the second and third heating sections of the heating furnace to ensure that the temperature is uniformly increased to the optimal thermoplasticity range of 1150-1260℃ under the condition of high microstructure purity.

[0024] (2) Rough rolling process control

[0025] Roughing is carried out in 5 to 7 passes. Descaling is carried out in the first pass. The rolling reduction rate of each pass is controlled at 15 to 25%, and the rolling speed is controlled at 3 to 5 m / s. The rolling speed and rolling reduction rate increase with the number of passes. The exit temperature of the roughing mill is controlled at 1000 to 1100℃.

[0026] In the above rough rolling process control, by designing a first-pass descaling process instead of a multi-pass descaling process, the surface oxide scale generated by prolonged heating of the material surface is removed, avoiding the influence of surface oxides on the rolled surface. It also avoids the temperature drop caused by multi-pass descaling, preventing the impact on the thermoplasticity of the process or even causing edge cracking.

[0027] In the above roughing rolling process control, by designing the pass reduction rate, the material pass deformation rate is ensured to exceed the material's critical recrystallization deformation rate, thus avoiding edge cracking caused by non-recrystallization softening due to the microstructure being below the critical recrystallization deformation rate.

[0028] In the aforementioned roughing rolling process control, the high-temperature resistance and deformation temperature stability of the material are ensured by designing the rolling passes, rolling reduction rate, and rolling speed. The normal hot rolling process is a cooling process. By designing the rolling reduction rate and rolling speed to increase with each pass, the work hardening, dynamic recovery, and recrystallization softening processes of the material are matched, and the natural temperature drop and the temperature rise due to deformation energy are matched. This controls the deformation resistance and processing temperature stability during the rolling process, ensuring stable rolling force. This design is beneficial for ensuring uniform stress on the entire material while maintaining its thermoplasticity, thus ensuring good sheet shape and edge quality. Furthermore, by designing the rolling passes, rolling reduction rate, and rolling speed to match the natural temperature drop and the temperature rise due to deformation energy, the final roughing rolling temperature range is controlled within 1000–1100℃.

[0029] (3) Finishing rolling process control

[0030] The finishing mill adopts a two-stand, three-pass, six-stage rolling process. In the first four passes, the rolling reduction rate is controlled at 25-35% and the rolling speed is controlled at 6-9 m / s. The rolling speed increases with each pass, while the reduction rate decreases with each pass. In the last two passes, the rolling reduction rate is controlled at 10-15% and the rolling speed is controlled at 2-3 mm. The finishing mill exit temperature is controlled at 900-1000℃. The heating temperature of the coiling furnace of the two-stand hot platen is controlled at 1000-1100℃. Laminar flow cooling is applied during coiling, and the coiling temperature is controlled at 500-700℃.

[0031] In the above-mentioned finishing rolling process control, the coiling furnace of the double-stand furnace coil mill is set at a temperature of 1000-1100℃. The two coiling furnaces arranged at the mill inlet and outlet ensure the stability of the material's hot processing temperature, especially the edge temperature. This reduces the processing cracking caused by the difference in high-temperature strength between the two phases due to the edge temperature drop. The material's temperature distribution is uniform across the entire plate surface, thereby ensuring uniform rolling force, controlling the plate flatness, which is beneficial for furnace coil mill rolling and coiling, and ensuring good edge quality.

[0032] In the above-mentioned precision rolling process control, a two-stand, three-pass, six-stage rolling process is adopted. The first four passes are designed with a higher reduction rate and rolling speed to match the natural temperature drop of the material and the temperature rise due to deformation energy accumulation, ensuring the stability of hot working temperature and rolling force. The last two passes are designed with a lower reduction rate and rolling speed, which is conducive to controlling dimensional accuracy and ensuring surface and edge quality.

[0033] In the above-mentioned finishing rolling process control, laminar flow cooling is adopted during coiling. The cooling rate is controlled to ensure uniform temperature drop, reduce thermal stress, and avoid stress cracking caused by mismatch in cooling rate. The coiling temperature is controlled at 500-700℃. Cooling within this temperature range ensures that the material has a certain thermoplasticity to meet the coiling requirements, while avoiding the precipitation of the second phase caused by coiling at higher temperatures, which would affect the material properties and edge quality.

[0034] In one specific implementation, in the above-mentioned double-stand hot-rolling mill control process for reducing edge cracks in hot-rolled economic duplex stainless steel, the economic duplex stainless steel is a low-Ni economic duplex stainless steel, whose chemical composition by mass percentage includes: C≤0.040%, Si≤1.00%, Mn: 4.00%~6.00%, P≤0.040%, S≤0.030%, Cr: 21.00%~22.00%, Ni: 1.35%~1.70%, Mo: 0.1%~0.8%, Cu: 0.1%~0.8%, N: 0.20%~0.25%, with the remainder being Fe and unavoidable impurities.

[0035] In one specific implementation, in the above-mentioned control process of the double-stand furnace coil mill for reducing edge cracking of hot-rolled economic duplex stainless steel, the grade of the economic duplex stainless steel is S32101.

[0036] The following describes the control process of the dual-stand hot-rolling mill for reducing edge cracking in economical duplex stainless steel hot-rolled coils according to specific embodiments of the present invention.

[0037] Example 1

[0038] In Embodiment 1 of the present invention, the economical duplex stainless steel is S32101 economical duplex stainless steel, and its chemical composition by mass percentage is: C: 0.019%, Si: 0.63%, Mn: 5.12%, P: 0.021%, S: 0.001%, Cr: 21.52%, Ni: 1.53%, Mo: 0.13%, N: 0.20%, with the remainder being Fe and unavoidable impurities.

[0039] The specific implementation process of the dual-stand hot-rolling mill control technology for reducing edge cracking in economical duplex stainless steel hot-rolled coils in Example 1 is as follows:

[0040] (1) Control of billet heating process

[0041] The final heating temperature of the billet is controlled at 1150–1260℃, and the total furnace dwell time is controlled at 140–280 min. The heating temperature and furnace dwell time are controlled in sections according to the process parameters shown in the table below:

[0042] Heating furnace section Preheating section A section Second section Three sections Time (min) 50～100 30～60 30～60 30～60 Furnace temperature (°C) 500～700 1000～1050 1100～1150 1150～1260

[0043] (2) Rough rolling process control

[0044] The roughing process involves seven passes. Descaling is performed in the first pass. The rolling reduction rate for each pass is 15-25%, and the rolling speed is 3-5 m / s. The rolling speed and rolling reduction rate increase with each pass. The exit temperature of the roughing mill is controlled at 1076℃.

[0045] (3) Finishing rolling process control

[0046] The finishing mill adopts a two-stand, three-pass, six-stage rolling process. In the first four passes, the rolling reduction rate is 25-35% and the rolling speed is 6-9 m / s. The rolling speed increases with each pass, while the reduction rate decreases with each pass. In the last two passes, the rolling reduction rate is 10-15% and the rolling speed is 2-3 mm. The finishing mill exit temperature is controlled at 960℃. The heating temperature of the coiling furnace of the two-stand hot platen is 1000-1100℃. Laminar flow cooling is applied during coiling, and the coiling temperature is controlled at 500-700℃.

[0047] The finished S32101 economic duplex stainless steel hot-rolled coil produced in Example 1 has a specification of 5×1280×L mm. After testing, the edge crack width of the hot-rolled coil is 5-10 mm.

[0048] Example 2

[0049] In Embodiment 2 of the present invention, the economical duplex stainless steel is S32101 economical duplex stainless steel, and its chemical composition by mass percentage is: C: 0.019%, Si: 0.63%, Mn: 5.12%, P: 0.021%, S: 0.001%, Cr: 21.52%, Ni: 1.53%, Mo: 0.13%, N: 0.20%, with the remainder being Fe and unavoidable impurities.

[0050] The specific implementation process of the dual-stand hot-rolling mill control technology for reducing edge cracking in economical duplex stainless steel hot-rolled coils in Example 2 is as follows:

[0051] (1) Control of billet heating process

[0052] The final heating temperature of the billet is controlled at 1150–1260℃, and the total furnace dwell time is controlled at 140–280 min. The heating temperature and furnace dwell time are controlled in sections according to the process parameters shown in the table below:

[0053] Heating furnace section Preheating section A section Second section Three sections Time (min) 50～100 30～60 30～60 30～60 Furnace temperature (°C) 500～700 1000～1050 1100～1150 1150～1260

[0054] (2) Rough rolling process control

[0055] The roughing process uses a 5-pass rolling process. The roughing descaling is carried out in the first pass. The rolling reduction rate of each pass is 15-25%, and the rolling speed is 3-5 m / s. The rolling speed and rolling reduction rate increase with the number of passes. The exit temperature of the roughing mill is controlled at 1050℃.

[0056] (3) Finishing rolling process control

[0057] The finishing mill adopts a two-stand, three-pass, six-stage rolling process. In the first four passes, the rolling reduction rate is 25-35% and the rolling speed is 6-9 m / s. The rolling speed increases with each pass, while the reduction rate decreases with each pass. In the last two passes, the rolling reduction rate is 10-15% and the rolling speed is 2-3 mm. The finishing mill exit temperature is controlled at 935℃. The heating temperature of the coiling furnace of the two-stand hot platen is 1000-1100℃. Laminar flow cooling is applied during coiling, and the coiling temperature is controlled at 500-700℃.

[0058] The finished S32101 economic duplex stainless steel hot-rolled coil produced in Example 2 has a specification of 6×1280×L mm. After testing, the edge crack width of the hot-rolled coil is 5-10 mm.

[0059] In summary, compared with the prior art, the dual-stand hot-rolling mill control process for reducing edge cracking in economical duplex stainless steel hot-rolled coils of the present invention has the following advantages and beneficial effects:

[0060] This invention addresses the severe edge cracking problem in hot-rolled low-Ni economic duplex stainless steel, represented by S32101. It employs a dual-stand furnace coil mill control process. Through billet heating process control, the temperature range and heating curve of the billet heating process are designed to ensure uniform billet temperature and a pure microstructure. Through rough rolling process control, the number of rolling passes, pass reduction rate, and rolling speed are designed to ensure uniform microstructure, uniform stress, and controllable hot working plasticity temperature. Through finish rolling process control, the coiling furnace heating process, rolling passes, pass reduction rate, and rolling speed are designed, and the coiling process is designed to ensure controllable hot working temperature range, resulting in good sheet quality and precision. By combining these control methods, the width of edge cracks in economic duplex stainless steel hot-rolled coils is reduced by more than 70% compared to existing technologies, effectively improving the edge quality of the product.

[0061] It should be noted that, in this document, the term "comprising" or any other variation thereof is intended to cover non-exclusive inclusion, such that an article or device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or device.

[0062] It should also be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the present invention.

Claims

1. A control process for a double-stand hot-rolling mill to reduce edge cracking in economical duplex stainless steel hot-rolled coils, characterized in that, include: (1) Control of billet heating process The billet is heated in the heating furnace according to the process of controlling the heating temperature and holding time in the furnace in sections. The final heating temperature of the billet is controlled at 1150~1260℃ and the total holding time in the furnace is controlled at 140~280min. In the preheating section of the heating furnace, the furnace temperature is controlled at 500~700℃, and the furnace dwell time is controlled at 50~100min; in the first heating section, the furnace temperature is controlled at 1000~1050℃, and the furnace dwell time is controlled at 30~60min; in the second heating section, the furnace temperature is controlled at 1100~1150℃, and the furnace dwell time is controlled at 30~60min; in the third heating section, the furnace temperature is controlled at 1150~1260℃, and the furnace dwell time is controlled at 30~60min. By heating the material at a temperature of 500~700℃ for 50~100min in the preheating section of the heating furnace, the uniformity of heating is ensured. Then, the material is rapidly heated to above 1000℃ in the first heating section of the heating furnace to avoid the formation of second phases such as Cr2N phase in the economic duplex stainless steel, which would affect its thermoplasticity. Subsequently, the heating gradient is further precisely controlled in the second and third heating sections of the heating furnace. Finally, the material is uniformly heated to the temperature range of 1150~1260℃, which is the optimal temperature for thermoplasticity, while ensuring high microstructure purity. (2) Rough rolling process control Roughing is carried out in 5 to 7 passes. Roughing descaling is carried out in the first pass. The rolling reduction rate of each pass is controlled at 15 to 25%, and the rolling speed is controlled at 3 to 5 m / s. The rolling speed and rolling reduction rate increase with the number of passes. The exit temperature of the roughing mill is controlled at 1000 to 1100℃. The first descaling process removes the surface oxide scale generated by prolonged heating of the material, thus avoiding the impact of surface oxides on the rolled surface. It also avoids the temperature drop caused by multiple descaling processes, preventing the impact on the thermoplasticity of the material or even causing edge cracking. By controlling the number of rolling passes, rolling reduction rate, and rolling speed, the high-temperature resistance and deformation temperature stability of the material are ensured. (3) Finishing rolling process control The finishing mill employs a two-stand, three-pass, six-stage rolling process. In the first four passes, the rolling reduction rate is controlled at 25-35%, and the rolling speed is controlled at 6-9 m / s. This ensures that the natural temperature drop of the material and the temperature rise due to deformation energy are matched, guaranteeing stable hot working temperature and rolling force. The rolling speed increases with each pass, while the reduction rate decreases with each pass. In the last two passes, the rolling reduction rate is controlled at 10-15%, and the rolling speed is controlled at 2-3 mm. This allows for precise dimensional control, ensuring surface and edge quality. The finishing mill exit temperature is controlled at 900-1000℃. The heating temperature of the coiling furnace on the two-stand hot platen is controlled at 1000-1100℃. Laminar flow cooling is applied during coiling, and the coiling temperature is controlled at 500-700℃.

2. The control process for reducing edge cracking in economical duplex stainless steel hot-rolled coils using a double-stand hot-rolling mill as described in claim 1, characterized in that, The economical duplex stainless steel is a low-Ni economical duplex stainless steel, whose chemical composition by mass percentage includes: C≤0.040%, Si≤1.00%, Mn: 4.00%~6.00%, P≤0.040%, S≤0.030%, Cr: 21.00%~22.00%, Ni: 1.35%~1.70%, Mo: 0.1%~0.8%, Cu: 0.1%~0.8%, N: 0.20%~0.25%, with the remainder being Fe and unavoidable impurities.

3. The control process for reducing edge cracking in economical duplex stainless steel hot-rolled coils using a double-stand hot-rolling mill as described in claim 1, characterized in that, The grade of the economical duplex stainless steel is S32101.