A method for hot rolling a 200 series stainless steel in an ultra-thin gauge

Abstract

This invention discloses a method for hot-rolling ultra-thin 200 series stainless steel, relating to the field of hot rolling forming of metallic materials. The method includes billet preparation and heating, rough rolling, finish rolling, and post-rolling cooling and coiling steps. This method enables the direct rolling of a 220mm thick continuously cast billet into an ultra-thin 1.55mm strip. The MVC1 roll shape precisely adapts to the 1 / 4 wave defect in a 1260mm cross-section, significantly improving strip shape stability. The rolled strip thickness is 1.55mm to 2.0mm, with a thickness difference of no more than ±30μm. The yield strength is no less than 300MPa, the elongation is no less than 45%, the hardness is no greater than 270HV, the grain size is no less than ASTM grade 6, and there are no obvious strip shape defects. This has driven the downstream cold-rolled ultra-thin material specifications to break through from 0.3mm to 0.26mm, and simplified the production path from three-rolling → four-rolling → 20-roll to three-rolling → 20-roll, reducing one intermediate step and lowering energy consumption and costs.

Description

Technical Field

[0001] This invention relates to the field of hot rolling forming of metallic materials, and particularly to a method for hot rolling extremely thin 200 series stainless steel. Background Technology

[0002] With the upgrading of downstream industries' demand for ultra-thin stainless steel, the traditional "hot rolling + cold rolling" two-stage production path can no longer meet the market requirements of low cost and fast delivery.

[0003] Due to the characteristics of the Cr-Mn-N alloy system, 200 series stainless steel suffers from low high-temperature strength, rapid work hardening, large width expansion, and sensitivity to "1 / 4 wave" shape defects. The thinnest rolling thickness produced by conventional hot continuous rolling production lines is only 2.0 mm, and there is a lack of precise roll shape design for specific width sections, making it difficult to mass-produce ultra-thin specifications. At the same time, downstream cold rolling enterprises need to go through multiple processes of "three-rolling → four-rolling → 20-roll" to obtain ultra-thin materials below 0.3 mm, resulting in long production cycles and high energy consumption. Summary of the Invention

[0004] The purpose of this invention is to provide a method for hot-rolling 200 series stainless steel to produce extremely thin grades, in order to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for hot-rolling 200 series stainless steel to ultra-thin gauges, comprising the following steps: S1. Billet preparation and heating: Provide 200 series stainless steel continuous casting billets and heat them to the temperature of the single-phase austenitic region to ensure that the billets are fully austenitic. S2. Rough rolling: The heated billet is rolled at high temperature and high pressure. Based on the billet characteristics and rolling process data, the roll gap is dynamically calculated and set through the rolling force model. The temperature drop of rough rolling is controlled by speed increase and reduction of passes, while suppressing the head and tail width loss, and rolling into an intermediate billet of preset thickness. S3. Finishing: The intermediate billet is rolled using a multi-stand continuous rolling mill with an inverted conical load distribution. A dynamic hardness-temperature self-learning model with short-term and long-term self-learning capabilities is used to correct the pre-set rolling force in real time. The strip shape is controlled by a combination of concave rolls, MVC roll shape of the last stand, bending rolls of work rolls and sliding rolls of intermediate stands. From the front stand to the back stand of the finishing mill, the tension value between stands gradually increases as the strip thins. The MVC roll shape of the last stand is a concave radius roll shape, which is adapted to the 1 / 4 wave-like strip shape defect of the target width section. S4. Post-rolling cooling and coiling: Control the coiling temperature by using a combination of laminar flow cooling manifold staged opening, rear section cooling and head and tail micro-cooling to regulate the cooling process. The coiler is rapidly cooled to the preset temperature to ensure that the strip grain size meets the preset grade.

[0006] Preferably, the 200 series stainless steel continuous casting billet mentioned in step S1 is a Cr-Mn-N alloy system, with a billet thickness of 200mm to 220mm, a length of 8m to 10m, and a width of not less than 1200mm; the heating temperature is 1180℃ to 1310℃, and the furnace time is not less than 200min.

[0007] Preferably, in step S2, the high-temperature high-reduction rolling passes are 5, the initial rolling temperature is not lower than 1210℃, the single-pass reduction rate is 24% to 35%, the intermediate billet thickness is 31mm to 34mm, and the roughing rolling temperature is not lower than 1150℃; the speed increase and reduction of passes specifically means breaking through the traditional transmission speed limit, reducing the number of descaling passes, and increasing the descaling and rolling speed.

[0008] Preferably, the multi-stand continuous rolling mill in step S3 is an 8-stand continuous rolling mill, with a finishing mill inlet temperature of not less than 1100℃, a finishing mill temperature of not less than 980℃, and a last stand rolling speed of not less than 14m / s.

[0009] Preferably, the inverted cone load distribution in step S3 is as follows: frame reduction rate of F1 to F3 is 50% to 40%, frame reduction rate of F4 to F7 is 30% to 15%, and frame reduction rate of F8 is ≤8%.

[0010] Preferably, the correction error of the dynamic hardness-temperature self-learning model in step S3 is ≤3%; short-term self-learning involves collecting actual rolling force, roll gap, and final rolling temperature data of the finishing mill stand after each coil of steel is rolled, comparing them with the model's predicted values, and fine-tuning the rolling force coefficient and temperature drop coefficient; long-term self-learning involves classifying and archiving production data according to steel type and specifications, accumulating it to a preset quantity, and then updating the long-term learning coefficient to form a process knowledge base.

[0011] Preferably, in step S3, the radius of the MVC roller shape of the final frame is defined by an 8th-order polynomial function, the roller body length is 1880mm, the diameter of the middle part of the roller body after grinding is smaller than the diameter of the side part, and the asymmetry deviation of the roller shape between the drive side and the operating side is ≤0.01mm; the intermediate frame is F5 to F7 frame, and its roller shifting amount is 15mm.

[0012] Preferably, the winding temperature in step S4 is 680℃~720℃, the winding completion temperature is ≤450℃, and the strip grain size is ≥ASTM6 grade; after step S4, a tension leveling process is also included: tension leveling of the ultra-thin strip to make the surface roughness Ra≤0.3μm.

[0013] Preferably, the thickness of the ultra-thin strip after rolling is 1.55mm to 2.0mm, and the thickness difference with the plate is ≤±30μm.

[0014] Preferably, the rolled strip has a yield strength ≥300MPa, elongation ≥45%, and hardness ≤270HV.

[0015] The technical effects and advantages of this invention are as follows: 1. This hot-rolled 200 series stainless steel ultra-thin specification rolling method enables direct rolling of 220mm thick continuously cast billets into 1.55mm ultra-thin strips. The MVC1 roll profile precisely adapts to the 1 / 4 wave defect of a 1260mm cross-section, significantly improving strip shape stability. The rolled strip thickness ranges from 1.55mm to 2.0mm, with a thickness difference of no more than ±30μm. The yield strength is no less than 300MPa, the elongation is no less than 45%, the hardness is no greater than 270HV, the grain size is no less than ASTM grade 6, and there are no obvious strip shape defects. This method drives downstream cold-rolled ultra-thin specifications from 0.3mm to 0.26mm, simplifying the production path from three consecutive rolling mills → four consecutive rolling mills → 20 rolls to three consecutive rolling mills → 20 rolls, reducing one intermediate rewinding process and lowering energy consumption and costs.

[0016] 2. This hot-rolled 200 series stainless steel ultra-thin specification rolling method utilizes a dynamic hardness-temperature self-learning model for continuous optimization through two key mechanisms: Short-term self-learning: After each coil is rolled, the system immediately collects actual rolling force, roll gap, and final rolling temperature data from the finishing mill stand and compares them with the model's predicted values. Based on the deviation, it quickly fine-tunes a series of core parameters (such as rolling force coefficient and temperature drop coefficient) and applies the results to the following rolled coils of the same type, achieving real-time feedback optimization. Long-term self-learning: The system categorizes and archives production data by steel type and specifications (thickness, width). When a certain number of coils of the same category accumulate, the model updates the long-term learning coefficients for that category, forming a more stable and accurate process knowledge base for that type of product. This allows the model to deeply understand the intrinsic relationship between the work hardening characteristics and temperature sensitivity of 200 series stainless steel.

[0017] 3. This hot-rolled 200 series stainless steel ultra-thin specification rolling method, based on the accurate knowledge provided by the model's self-learning, dynamically completes the real-time correction of rolling force during the strip threading process. Triggering and diagnosis: After the strip head bites into the first two finishing mill stands, the system immediately collects its actual rolling force. By comparing the measured force with the preset force, the model quickly determines whether the current "actual hardness" of the strip deviates from the prediction due to temperature or material fluctuations. Dynamic calculation and correction: Once a deviation is confirmed, the "finishing mill entry correction" function in the system is immediately activated. Based on the deviation of the first two stands, it recalculates the deformation resistance of the subsequent stands in real time and quickly corrects the roll gap setting value of the subsequent stands accordingly. This process is completed within milliseconds, ensuring that the settings of the subsequent stands are adapted to their actual state before the strip is fully threaded into the finishing mill. Closed-loop control: The entire correction process forms a closed loop with the model's self-learning. The results of real-time correction serve as new learning data, continuously enriching the model's database and making its preset settings for future strip increasingly accurate. Attached Figure Description

[0018] Fig. 1 This is a schematic diagram of the overall process of the present invention; Fig. 2 This is a schematic diagram of the roller curve of the final frame MVC1 of the present invention. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] This invention provides, for example Figs. 1-2 The method for hot-rolling 200 series stainless steel to ultra-thin gauges includes the following steps: S1. Billet preparation and heating: Provide 200 series stainless steel continuous casting billets and heat them to the temperature of the single-phase austenitic region to ensure that the billets are fully austenitic. S2. Rough rolling: The heated billet is rolled at high temperature and high pressure. Based on the billet characteristics and rolling process data, the roll gap is dynamically calculated and set through the rolling force model. The temperature drop of rough rolling is controlled by speed increase and reduction of passes, while suppressing the head and tail width loss, and rolling into an intermediate billet of preset thickness. S3. Finishing: The intermediate billet is rolled using a multi-stand continuous rolling mill with an inverted conical load distribution. A dynamic hardness-temperature self-learning model with short-term and long-term self-learning capabilities is used to correct the pre-set rolling force in real time. The strip shape is controlled by a combination of concave rolls, MVC roll shape of the last stand, bending rolls of work rolls and sliding rolls of intermediate stands. From the front stand to the back stand of the finishing mill, the tension value between stands gradually increases as the strip thins. The MVC roll shape of the last stand is a concave radius roll shape, which is adapted to the 1 / 4 wave-like strip shape defect of the target width section. S4. Post-rolling cooling and coiling: Control the coiling temperature by using a combination of laminar flow cooling manifold staged opening, rear section cooling and head and tail micro-cooling to regulate the cooling process. The coiler is rapidly cooled to the preset temperature to ensure that the strip grain size meets the preset grade.

[0021] Furthermore, the 200 series stainless steel continuous casting billet mentioned in step S1 is a Cr-Mn-N alloy system, with a billet thickness of 200mm to 220mm, a length of 8m to 10m, and a width of not less than 1200mm; the heating temperature is 1180℃ to 1310℃, and the furnace time is not less than 200min.

[0022] Furthermore, in step S2, the high-temperature high-reduction rolling has 5 passes, the initial rolling temperature is not lower than 1210℃, the single-pass reduction rate is 24% to 35%, the intermediate billet thickness is 31mm to 34mm, and the roughing rolling temperature is not lower than 1150℃; the speed increase and reduction of passes specifically means breaking through the traditional transmission speed limit, reducing the number of descaling passes, and increasing the descaling and rolling speed.

[0023] Furthermore, the multi-stand continuous rolling mill mentioned in step S3 is an 8-stand continuous rolling mill, with a finishing mill inlet temperature of not less than 1100℃, a finishing mill temperature of not less than 980℃, and a last stand rolling speed of not less than 14m / s.

[0024] Furthermore, the inverted cone load distribution in step S3 is as follows: frame reduction rate of F1 to F3 is 50% to 40%, frame reduction rate of F4 to F7 is 30% to 15%, and frame reduction rate of F8 is ≤8%.

[0025] Furthermore, the correction error of the dynamic hardness-temperature self-learning model described in step S3 is ≤3%; short-term self-learning involves collecting actual rolling force, roll gap, and final rolling temperature data of the finishing mill stand after each coil of steel is rolled, comparing them with the model's predicted values, and fine-tuning the rolling force coefficient and temperature drop coefficient; long-term self-learning involves classifying and archiving production data according to steel type and specifications, accumulating it to a preset quantity, and then updating the long-term learning coefficient to form a process knowledge base.

[0026] Furthermore, in step S3, the radius of the MVC roller shape of the final frame is defined by an 8th-order polynomial function, the roller body length is 1880mm, the diameter of the middle part of the roller body after grinding is smaller than the diameter of the side part, and the asymmetry deviation of the roller shape between the drive side and the operating side is ≤0.01mm; the intermediate frame is the F5 to F7 frame, and its roller shifting amount is 15mm.

[0027] Furthermore, in step S4, the winding temperature is 680℃~720℃, the winding completion temperature is ≤450℃, and the strip grain size is ≥ASTM6 grade; after step S4, a tension leveling process is also included: tension leveling of the extremely thin strip to make the surface roughness Ra≤0.3μm.

[0028] Furthermore, the thickness of the rolled ultra-thin strip is 1.55mm to 2.0mm, with a thickness difference of ≤±30μm from the plate.

[0029] Furthermore, the rolled strip has a yield strength ≥300MPa, elongation ≥45%, and hardness ≤270HV.

[0030] This technology enables the direct rolling of 220mm thick continuously cast billets into ultra-thin 1.55mm strip steel. The MVC1 roll profile precisely adapts to the 1 / 4 wave defect of a 1260mm cross-section, significantly improving strip shape stability. After rolling, the strip thickness ranges from 1.55mm to 2.0mm, with a thickness difference of no more than ±30μm. The yield strength is no less than 300MPa, elongation no less than 45%, hardness no greater than 270HV, grain size no less than ASTM 6 grade, and there are no obvious strip shape defects. This technology drives downstream cold-rolled ultra-thin material specifications from 0.3mm to 0.26mm, simplifying the production path from three consecutive rolling mills → four consecutive rolling mills → 20 rolls to three consecutive rolling mills → 20 rolls, reducing one intermediate rewinding process and lowering energy consumption and costs.

[0031] The dynamic hardness-temperature self-learning model is continuously optimized through two key mechanisms; Short-term self-learning: After each coil of steel is rolled, the system immediately collects data on the actual rolling force, roll gap, and final rolling temperature of the finishing mill stand and compares them with the model's predicted values. Based on the deviation, it quickly fine-tunes a series of core parameters (such as rolling force coefficient and temperature drop coefficient) and applies the results to the following rolled coils of the same type, achieving real-time feedback optimization.

[0032] Long-term self-learning: The system categorizes and archives production data by steel type, specifications (thickness, width), etc. When a certain number of steel coils of the same category accumulate, the model updates the long-term learning coefficients for that category, forming a more stable and accurate process knowledge base for that type of product. This allows the model to deeply understand the intrinsic relationship between the work hardening characteristics and temperature sensitivity of 200 series stainless steel.

[0033] Based on the accurate knowledge provided by the model's self-learning, the real-time correction of the rolling force is dynamically completed during the strip threading process; Triggering and diagnosis: After the strip head bites into the first two finishing mills (F1, F2), the system immediately collects its actual rolling force. By comparing the measured force with the preset force, the model quickly determines whether the "actual hardness" of the current strip deviates from the prediction due to temperature fluctuations or material fluctuations.

[0034] Dynamic Calculation and Correction: Once a deviation is confirmed, the "Finishing Mill Entry Correction" function within the system is immediately activated. Based on the deviations of the first two stands, it recalculates the deformation resistance of subsequent stands in real time and quickly corrects the roll gap settings of subsequent stands accordingly. This process is completed within milliseconds, ensuring that the settings of subsequent stands are adapted to their actual state before the strip fully enters the finishing mill. Closed-Loop Control: The entire correction process forms a closed loop with the model's self-learning. The results of real-time correction serve as new learning data, continuously enriching the model's database and making its pre-settings for future strip increasingly accurate.

[0035] The core technology of this invention is a four-step integrated process of high-temperature rapid rolling, ultimate rolling force model, steady-state shape control, and rapid cooling in the later stage. The specific steps are as follows: Step 1: Preparation and Heating of Billet Provide 200 series stainless steel continuous casting billets with a Cr-Mn-N alloy system, with a billet thickness of 200 mm to 220 mm, a length of 8 m to 10 m, and a width of not less than 1200 mm, preferably 1248 mm. The billets are fed into a heating furnace and heated to a single-phase austenitic temperature of 1180°C to 1310°C for at least 200 minutes to ensure complete austenitization.

[0036] Step 2: Rough rolling The heated billet is subjected to five passes of high-temperature, high-reduction fast rolling, with an initial rolling temperature of not less than 1210℃ and a single-pass reduction rate of 24% to 35%, to produce an intermediate billet with a thickness of 31mm to 34mm.

[0037] Temperature drop control: Breaking through the traditional transmission speed limit, reducing the number of descaling passes, and increasing the descaling and rolling speed, so that the roughing rolling temperature is not lower than 1150℃; Width stability: Based on billet characteristics and real-time rolling data, the roll gap is dynamically calculated and set through the rolling force model to suppress width loss at the beginning and end, with the width loss not exceeding 5mm.

[0038] Step 3: Finish rolling The intermediate billet is rolled using an 8-stand continuous rolling mill, with a finishing mill inlet temperature of not less than 1100℃, a finishing mill inlet temperature of not less than 980℃, and a last stand rolling speed of not less than 14m / s.

[0039] Load reduction distribution: an inverted cone load distribution is adopted, with the reduction rate of frames F1 to F3 being 50% to 40%, the reduction rate of frames F4 to F7 being 30% to 15%, and the reduction rate of frame F8 not exceeding 8%.

[0040] Rolling force correction: The rolling force preset is corrected in real time through a dynamic hardness-temperature self-learning model with short-term and long-term self-learning capabilities, with a correction error of no more than 3%.

[0041] Short-term self-learning involves collecting actual rolling force, roll gap, and final rolling temperature data after each coil of steel is rolled, and fine-tuning the rolling force coefficient and temperature drop coefficient. Long-term self-learning involves archiving data by steel type and specification, accumulating it to a preset quantity, and then updating the long-term learning coefficient to form a process knowledge base.

[0042] Plate shape control: The plate shape is controlled by a combination of concave rollers, MVC1 rollers on the last frame, bending rollers on the work rollers, and rollers on the F5 to F7 frames.

[0043] MVC1 Roller Shape Parameters (see attached table) Fig. 2 It is a concave radius roller shape, composed of an 8th degree polynomial. Defined as follows, where x is the axial position of the roller body, in mm. The coefficient is accurate as follows: , , , , , , , , The roller body length is 1880mm. After grinding, the diameter of the middle part of the roller body is smaller than the diameter of the side part. The asymmetry deviation of the roller shape between the drive side and the operating side is no more than 0.01mm. This roller shape is only suitable for 1 / 4 wave defects with a 1260mm width cross section. During production, the roller ticket must be marked with roller shape 238 to accommodate mixed four-foot and five-foot test lines.

[0044] Roller shifting control: The roll shifting amount from frame F5 to F7 is 15mm, and the lateral distribution of the roll gap is adjusted.

[0045] Tension control: From the front stand to the back stand of the finishing mill, the tension between stands gradually increases as the strip becomes thinner. For example, the tension between stands F1 and F2 is 5 MPa, between stands F3 and F4 is 8 MPa, between stands F5 and F6 is 12 MPa, and between stands F7 and F8 is 15 MPa, to avoid tension instability in thin strip.

[0046] Step 4: Post-rolling cooling and coiling The coiling temperature is controlled between 680℃ and 720℃, employing a combination of laminar flow cooling manifolds with staged opening, rear-stage cooling, and slight cooling at the beginning and end. The strip is rapidly cooled after entering the coiler to ensure the coiling temperature does not exceed 450℃, guaranteeing that the strip grain size is not lower than ASTM grade 6 and inhibiting carbide precipitation along the grain.

[0047] Optionally, the strip can be straightened after winding to ensure that the surface roughness Ra is no more than 0.3μm, thus meeting the requirement of direct use with heat instead of cold.

[0048] This technology enables the direct rolling of 220mm thick continuously cast billets into ultra-thin 1.55mm strip steel. The MVC1 roll profile precisely adapts to the 1 / 4 wave defect of a 1260mm cross-section, significantly improving strip shape stability. After rolling, the strip thickness ranges from 1.55mm to 2.0mm, with a thickness difference of no more than ±30μm. The yield strength is no less than 300MPa, elongation no less than 45%, hardness no greater than 270HV, grain size no less than ASTM 6 grade, and there are no obvious strip shape defects. This technology drives downstream cold-rolled ultra-thin material specifications from 0.3mm to 0.26mm, simplifying the production path from three consecutive rolling mills → four consecutive rolling mills → 20 rolls to three consecutive rolling mills → 20 rolls, reducing one intermediate rewinding process and lowering energy consumption and costs.

[0049] Example: A 200-series stainless steel continuous casting billet with a Cr-Mn-N alloy system was selected, with specific dimensions of 220 mm thickness, 1248 mm width, and 8.5 m length, and a billet temperature of 1250℃. The continuous casting billet was sent to a heating furnace, with the heating temperature set at 1250℃ and the furnace time controlled at 220 min to ensure complete austenitization of the billet.

[0050] The heated billet was subjected to five passes of high-temperature and high-reduction rolling. The initial rolling temperature was 1220℃, and the single-pass reduction rates were 35%, 32%, 30%, 28%, and 24%, respectively. The final rolled intermediate billet had a thickness of 31.516mm, a width of 1294.792mm, and a length of 62.279m. The intermediate billet temperature was 1080℃.

[0051] Temperature drop control: The transmission speed is increased to 1.2 times the traditional upper limit, one descaling pass is reduced, the descaling speed is increased by 30%, the rolling speed is increased by 25%, and the rough rolling temperature is 1160℃. Width stability: The roll gap is dynamically set by the rolling force model, and the width loss at the beginning and end of the billet is controlled within 5mm.

[0052] The intermediate billet is rolled using an 8-stand continuous rolling mill. The finishing mill inlet temperature is 1120℃, the finishing mill temperature is 990℃, and the rolling speed of the last stand is 14.5m / s.

[0053] The support roll diameter parameters for stands F1 to F3 of the 8-stand continuous rolling mill are as follows: upper support roll diameter 1428.27mm, lower support roll diameter 1415.82mm; upper support roll diameter 1467.65mm, lower support roll diameter 1464.21mm; upper support roll diameter 1463.44mm, lower support roll diameter 1448.77mm.

[0054] The specific settings for each rack are as follows: Rolling force correction: A dynamic hardness-temperature self-learning model is enabled. After each coil of steel is rolled, the parameters are finely adjusted. After the strip bites into the F1 and F2 stands, the system collects the actual rolling force within 10ms. If the deviation is 2.5%, the deformation resistance of the F3 to F8 stands is immediately recalculated and the roll gap setting is corrected. The final rolling force preset correction error is 2.8%. Plate shape control: A combination of concave rollers, MVC1 roller shape, work roller bending rollers, and F5 to F7 shifting rollers is used. The roller shape is marked as 238, and the shifting amount is 15mm. The deviation between the drive side and the operating side of the MVC1 roller shape is 0.008mm. Tension control: The tension between F1 and F2 frames is 5MPa, the tension between F3 and F4 frames is 8MPa, the tension between F5 and F6 frames is 12MPa, and the tension between F7 and F8 frames is 15MPa, gradually increasing as the strip thins.

[0055] The coiling temperature is set at 700℃, and the laminar flow cooling manifold opening is gradually increased from 30% to 80%, employing a rear-stage cooling and head-and-tail micro-cooling mode. The strip is rapidly cooled after entering the coiler, and the final coiling temperature is 430℃. The finished product specifications are a thickness of 1.55mm, a width of 1257mm, a temperature of 720℃, and a strip grain size of ASTM grade 7.

[0056] The coiled 1.56mm thick strip steel was subjected to tension leveling treatment with a tension of 20MPa and a leveling elongation of 1.2%. The surface roughness Ra of the strip steel after treatment was 0.25μm, which meets the requirements for direct use with hot steel instead of cold steel.

[0057] The 1.56mm thick strip steel obtained in this embodiment has a thickness difference of ±28μm from the plate, a yield strength of 320MPa, an elongation of 48%, and a hardness of 260HV, all of which meet the requirements. Downstream cold-rolled ultra-thin sheet specifications have been reduced to 0.26mm, and the simplified production path has reduced energy consumption by 15% and shortened the production cycle by 20%.

[0058] This technology enables the direct rolling of 220mm thick continuously cast billets into ultra-thin 1.55mm strip steel. The MVC1 roll profile precisely adapts to the 1 / 4 wave defect of a 1260mm cross-section, significantly improving strip shape stability. After rolling, the strip thickness ranges from 1.55mm to 2.0mm, with a thickness difference of no more than ±30μm. The yield strength is no less than 300MPa, elongation no less than 45%, hardness no greater than 270HV, grain size no less than ASTM 6 grade, and there are no obvious strip shape defects. This technology drives downstream cold-rolled ultra-thin material specifications from 0.3mm to 0.26mm, simplifying the production path from three consecutive rolling mills → four consecutive rolling mills → 20 rolls to three consecutive rolling mills → 20 rolls, reducing one intermediate rewinding process and lowering energy consumption and costs.

[0059] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for hot-rolling ultra-thin gauge 200 series stainless steel, characterized in that, Includes the following steps: S1. Billet preparation and heating: Provide 200 series stainless steel continuous casting billets and heat them to the temperature of the single-phase austenitic region to ensure that the billets are fully austenitic. S2. Rough rolling: The heated billet is rolled at high temperature and high pressure. Based on the billet characteristics and rolling process data, the roll gap is dynamically calculated and set through the rolling force model. The temperature drop of rough rolling is controlled by speed increase and reduction of passes, while suppressing the head and tail width loss, and rolling into an intermediate billet of preset thickness. S3. Finishing: The intermediate billet is rolled using a multi-stand continuous rolling mill with an inverted conical load distribution. A dynamic hardness-temperature self-learning model with short-term and long-term self-learning capabilities is used to correct the pre-set rolling force in real time. The strip shape is controlled by a combination of concave rolls, MVC roll shape of the last stand, bending rolls of work rolls and sliding rolls of intermediate stands. From the front stand to the back stand of the finishing mill, the tension value between stands gradually increases as the strip thins. The MVC roll shape of the last stand is a concave radius roll shape, which is adapted to the 1 / 4 wave-like strip shape defect of the target width section. S4. Post-rolling cooling and coiling: Control the coiling temperature by using a combination of laminar flow cooling manifold staged opening, rear section cooling and head and tail micro-cooling to regulate the cooling process. The coiler is rapidly cooled to the preset temperature to ensure that the strip grain size meets the preset grade.

2. The method for hot-rolling 200 series stainless steel to ultra-thin gauges according to claim 1, characterized in that, The 200 series stainless steel continuous casting billet mentioned in step S1 is a Cr-Mn-N alloy system, with a billet thickness of 200mm to 220mm, a length of 8m to 10m, and a width of not less than 1200mm; the heating temperature is 1180℃ to 1310℃, and the furnace time is not less than 200min.

3. The method for hot-rolling 200 series stainless steel to ultra-thin gauges according to claim 1, characterized in that, In step S2, the high-temperature high-reduction rolling process consists of 5 passes, with an initial rolling temperature of not less than 1210℃, a single-pass reduction rate of 24% to 35%, an intermediate billet thickness of 31mm to 34mm, and a roughing rolling temperature of not less than 1150℃.

4. The method for hot-rolling 200 series stainless steel to ultra-thin gauges according to claim 1, characterized in that, The multi-stand continuous rolling mill mentioned in step S3 is an 8-stand continuous rolling mill with a finishing mill inlet temperature of not less than 1100℃, a finishing mill temperature of not less than 980℃, and a last stand rolling speed of not less than 14m / s.

5. A method for hot-rolling 200 series stainless steel to ultra-thin gauges according to claim 1, characterized in that, The inverted cone load distribution in step S3 is as follows: frame reduction rate of F1 to F3 is 50% to 40%, frame reduction rate of F4 to F7 is 30% to 15%, and frame reduction rate of F8 is ≤8%.

6. A method for hot-rolling 200 series stainless steel to ultra-thin gauges according to claim 1, characterized in that, The correction error of the dynamic hardness-temperature self-learning model described in step S3 is ≤3%; short-term self-learning involves collecting actual rolling force, roll gap, and final rolling temperature data of the finishing mill stand after each coil of steel is rolled, comparing them with the model's predicted values, and fine-tuning the rolling force coefficient and temperature drop coefficient; long-term self-learning involves classifying and archiving production data according to steel type and specifications, accumulating it to a preset quantity, and then updating the long-term learning coefficient to form a process knowledge base.

7. A method for hot-rolling 200 series stainless steel to ultra-thin gauges according to claim 1, characterized in that, In step S3, the radius of the MVC roller shape of the final frame is defined by an 8th degree polynomial function, the roller body length is 1880mm, the diameter of the middle part of the roller body after grinding is smaller than the diameter of the side part, and the asymmetry deviation of the roller shape between the drive side and the operating side is ≤0.01mm; the intermediate frame is the F5 to F7 frame, and its roller shifting amount is 15mm.

8. A method for hot-rolling 200 series stainless steel to ultra-thin gauges according to claim 1, characterized in that, In step S4, the coiling temperature is 680℃~720℃, the coiling completion temperature is ≤450℃, and the strip grain size is ≥ASTM6 grade. After step S4, a tension leveling process is also included: tension leveling of the ultra-thin strip to make the surface roughness Ra≤0.3μm.

9. A method for hot-rolling 200 series stainless steel to ultra-thin gauges according to claim 1, characterized in that, The thickness of the rolled ultra-thin strip is 1.55mm to 2.0mm, and the thickness difference with the plate is ≤±30μm.

10. A method for hot-rolling 200 series stainless steel to ultra-thin gauges according to claim 1, characterized in that, After rolling, the strip has a yield strength ≥300MPa, elongation ≥45%, and hardness ≤270HV.

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