A hot rolling method for improving the edge and surface quality of 6%mo type high alloy austenitic stainless steel coil plate

Abstract

The application discloses a hot rolling method for improving the edge and surface quality of 6%MO type high-alloy austenitic stainless steel coil plate, which comprises the following steps: S1, casting blank surface pretreatment; S2, spraying an anti-oxidation coating; S3, first fire heating treatment, and the heating temperature is controlled to be 1200-1230 DEG C; S4, phosphorus removal and initial rolling and cogging; S5, intermediate blank overall grinding and edge chamfering; S6, second fire heating treatment, and the heating temperature is controlled to be 1210-1240 DEG C; S7, rough rolling; S8, finish rolling; S9, cooling and coiling; S10, plate inspection; and the heating temperature of the second fire heating treatment is higher than that of the first fire heating treatment. The application can eliminate the edge crack and surface crack defects of the hot rolled coil plate, thereby improving the product quality.

Description

Technical Field

[0001] This invention belongs to the field of stainless steel production technology, specifically relating to a hot rolling method for improving the edge and surface quality of 6% MO type high alloy austenitic stainless steel coils. Background Technology

[0002] 6%Mo type super austenitic stainless steel is the most widely used category in the super austenitic stainless steel family, with S31254 being a typical grade. This steel is synergistically strengthened through a high molybdenum content of 6.0%-6.5%, a nickel content of 17.5%-18.5%, and a nitrogen content of 0.18%-0.22%. Its PREN (pitting equivalent number) can reach over 42, and its resistance to localized corrosion is 3-5 times that of 316L. It also possesses yield strength more than 50% higher than ordinary austenitic stainless steel. It is widely used in key areas such as flue gas desulfurization units, seawater desalination heat exchangers, petrochemical reaction vessels, and pulp bleaching equipment, and market demand continues to grow rapidly.

[0003] However, the extremely high alloy content also presents significant challenges to the hot working of this steel, mainly in the following three aspects: (1) Extremely high resistance to hot deformation. Due to the large amount of elements such as Mo, Cr, and Ni dissolved in the austenitic matrix, the interatomic bonding force is significantly improved. The deformation resistance at high temperature is 3 times that of ordinary 304 stainless steel, which puts extremely high requirements on the load capacity of the rolling mill. Conventional hot rolling mills are difficult to achieve large reduction rolling, resulting in low production efficiency and easy equipment overload accidents.

[0004] (2) Extremely narrow thermoplastic range. The optimal thermoplastic temperature window for this steel grade is only about 150℃. If the temperature is too high, grain boundary overheating and liquefaction cracking are likely to occur. If the temperature is below 950℃, intermetallic compounds such as σ phase will precipitate rapidly, leading to material embrittlement. Surface cracks and edge tears are very likely to occur during rolling. According to conventional processes, edge cracks can extend to more than 40mm from the edge, seriously affecting the product yield.

[0005] (3) High sensitivity to compositional segregation. Under as-cast conditions, Mo is prone to dendritic segregation, and the thermoplasticity of the segregated region decreases significantly, becoming the core source of crack initiation. Conventional hot rolling processes cannot completely eliminate the influence of as-cast segregation.

[0006] Currently, existing technologies have not yet formed a complete production plan for 6%Mo type super austenitic stainless steel hot-rolled coils. In particular, there is a lack of systematic prevention and control technologies for edge cracks and surface cracks. This results in low yield, large quality fluctuations, and high production costs during the industrial production of this type of product, which seriously restricts its industrial promotion and application. Summary of the Invention

[0007] In order to solve all or part of the above problems, the purpose of this invention is to provide a hot rolling method for improving the edge and surface quality of 6%MO type high alloy austenitic stainless steel coils, which can eliminate edge cracks and surface crack defects of hot-rolled coils, thereby improving product quality.

[0008] This invention provides a hot rolling method for improving the edge and surface quality of 6% MO type high-alloy austenitic stainless steel coils, comprising the following steps: S1, Pretreatment of the billet surface; S2, apply an anti-oxidation coating; S3, the first heating treatment, with the heating temperature controlled at 1200-1230℃; S4, descaling and initial rolling; S5, intermediate blank fully ground and edge chamfered; S6, second heating treatment, with the heating temperature controlled at 1210-1240℃; S7, rough rolling; S8, precision rolling; S9, cooling and curling; S10, Sheet metal inspection; The heating temperature of the second heating treatment is higher than that of the first heating treatment.

[0009] Optionally, in S1, a manual surface inspection is performed on the billet before it enters the furnace to remove obvious scabs and heavy scale defects from the billet surface.

[0010] Optionally, in S2, the dry film thickness of the coating is controlled to be 0.3-0.5 mm.

[0011] Optionally, in S3, the heating process is divided into three stages: a preheating stage, a heating stage, and a homogenizing stage. The heating rate in the preheating stage is controlled at 60-80℃ / h, the heating stage is rapidly heated to the target temperature, and the holding time in the homogenizing stage is extended to 4-6h.

[0012] Optionally, in S4, the billet is immediately subjected to high-pressure water descaling after exiting the furnace, with a descaling pressure ≥18MPa. Subsequently, it is rolled in multiple passes on the primary rolling mill, with the total reduction rate controlled at 28%-44%, the single-pass reduction at 8-15mm, and the final rolling temperature ≥960℃.

[0013] Optionally, in S5, the grinding process is divided into two stages: rough grinding and fine grinding. Rough grinding uses 14#-18# coarse grinding wheels, and fine grinding uses 20#-28# fine grinding wheels, controlling the overall grinding rate to 2%-3%. During the grinding process, the edges are chamfered, and the right-angled edges on both sides of the width direction of the intermediate billet are processed into a chamfered structure with a smooth transition. The chamfer depth is controlled to be 8-12mm, the angle between the chamfered bevel and the side is 35°-45°, and the radius of the chamfer transition arc is ≥5mm. During grinding, the grinding amount on both sides of the width direction of the intermediate billet is controlled to be symmetrical and balanced, and the metal removal amount deviation on both sides is ≤0.5mm.

[0014] Optionally, in S6, the total furnace dwell time is controlled to be 190-240 min, and the heat soaking time in the soaking zone is not less than 60 min.

[0015] Optionally, in S7, the roughing rolling adopts 7 passes, controlling the target exit temperature of the roughing rolling mill at 1080±20℃, the single pass reduction of the first 3 passes at 12-18mm, and the reduction of the last 4 passes gradually decreasing. During the roughing rolling process, the front and rear coiling furnaces are kept in a heated state, and the furnace temperature is controlled at 1150-1180℃ so that the strip is kept warm in the furnace after being coiled.

[0016] Optionally, in S8, the finishing mill adopts 9 passes of rolling, and the finishing mill exit temperature is controlled to be ≥1000℃ for the entire length except for the first 15m of the strip. The strip is coiled and kept warm in the coiling furnace between passes to ensure that the transverse temperature difference of the strip is ≤15℃. The maximum linear speed during the stable rolling stage is controlled at 8-10m / s, and the rolling force of a single stand does not exceed 85% of the rated value of the equipment.

[0017] Optionally, in S9, after finishing rolling, the strip immediately enters the coiler for coiling, and is slowly cooled using the strip's own residual heat, while controlling the coiling temperature to ≥900℃.

[0018] As can be seen from the above technical solution, the hot rolling method for improving the edge and surface quality of 6% MO type high alloy austenitic stainless steel coils provided by the present invention has the following advantages: This hot rolling method can eliminate network cracks, strip cracks and grain boundary oxidation defects on the surface of the sheet, and the surface quality reaches the same level as ordinary austenitic stainless steel. Moreover, the product can be delivered without additional large-scale edge trimming and deep surface grinding, which fully meets the stringent requirements of high-end fields such as petrochemicals, environmental protection, and seawater desalination.

[0019] Other features and advantages of the present invention will be set forth in the following description. Attached Figure Description

[0020] The accompanying drawings are provided to further understand the technical solutions of the present invention and constitute a part of the specification. They are used together with the embodiments of the present invention to explain the technical solutions of the present invention, and do not constitute a limitation on the technical solutions of the present invention.

[0021] Figure 1 This is a flowchart of a hot rolling method for improving the edge and surface quality of 6% MO high-alloy austenitic stainless steel coils in an embodiment of the present invention. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present invention can be arbitrarily combined with each other.

[0023] like Figure 1 The illustration shows an embodiment of the present invention, which discloses a hot rolling method for improving the edge and surface quality of 6% MO type high-alloy austenitic stainless steel coils, comprising the following steps: S1, Pretreatment of the billet surface; S2, apply an anti-oxidation coating; S3, first heat treatment; S4, descaling and initial rolling; S5, intermediate blank fully ground and edge chamfered; S6, second heating treatment; S7, rough rolling; S8, precision rolling; S9, cooling and curling; S10, Inspection of sheet metal.

[0024] The rolling method in this embodiment employs a two-pass rolling process. The first pass focuses on high-temperature homogenization of the billet, comprehensive defect removal, and optimization of the billet corner morphology, eliminating inherited defects from the as-cast structure and optimizing the corner morphology of the billet. The second pass focuses on full-process temperature control and optimization of the hot-rolling mill passes, ensuring that the material remains within its optimal thermoplastic range throughout the rolling process, ultimately achieving a fundamental improvement in edge and surface quality.

[0025] In S1, the billet undergoes a manual surface inspection before being placed into the furnace to remove obvious macroscopic defects such as scale and heavy scale.

[0026] In S2, a high-temperature resistant and anti-oxidation coating is uniformly sprayed on the upper surface, lower surface and four sides of the billet, and the dry film thickness of the coating is controlled to be 0.3-0.5 mm.

[0027] The anti-oxidation coating in this embodiment uses glassy silicate as the main component, supplemented with inert fillers such as alumina and chromium oxide. At temperatures above 1200℃, it can form a dense, molten protective film. On one hand, this effectively isolates the oxidizing atmosphere inside the furnace, preventing excessive oxidation of the billet surface and oxidation within grain boundaries, thus reducing the initiation points of surface cracks from the source. On the other hand, it reduces the temperature drop rate during heating, improving the temperature uniformity of the billet cross-section. The anti-oxidation coating can be removed along with the iron oxide scale during subsequent rolling, leaving no residue on the product surface.

[0028] In S3, a walking beam furnace is used for heating, with the heating temperature controlled at 1200-1230℃. The heating process is divided into three stages: preheating, heating, and soaking. The heating rate in the preheating stage is controlled at 60-80℃ / h to avoid thermal stress causing cracking of the billet; the heating stage rapidly raises the temperature to the target level; and the soaking stage extends the holding time to 4-6 hours, significantly longer than that of ordinary austenitic stainless steel. This prolonged high-temperature holding promotes the diffusion of elements such as Mo and Cr, reduces dendrite segregation in the billet, homogenizes the composition, fundamentally improves the high-temperature thermoplasticity of the material, and reduces microcracks induced by segregation zones.

[0029] In S4, the billet undergoes high-pressure water descaling immediately after exiting the furnace, with a descaling pressure ≥18MPa, to remove surface oxide scale. It is then rolled in multiple passes on the primary rolling mill, with a total reduction controlled at 28%-44%. The initial rolling employs a strategy of large reduction and slow pace, controlling the reduction per pass to 8-15mm, and no descaling is performed between passes. The lubricating effect of the surface oxide layer reduces rolling force and minimizes surface scratches. The final rolling temperature is controlled at ≥960℃ to ensure the material remains in the austenitic single-phase region throughout the rolling process, preventing the precipitation of brittle phases. Simultaneously, the rolled intermediate billets are rapidly stacked and slowly cooled to reduce thermal stress during the cooling process.

[0030] In S5, the intermediate slab after the first firing undergoes full-surface grinding, a crucial process for eliminating inherited surface defects and preventing the propagation of rolling cracks in the second firing. The grinding process is divided into two stages: rough grinding and fine grinding. Rough grinding uses 14#-18# coarse grinding wheels to remove the surface oxide layer, micro-cracks, and rolling defects, while fine grinding uses 20#-28# fine grinding wheels to ensure uniform surface finish. Simultaneously, the overall grinding rate is controlled at 2%-3%.

[0031] During the grinding process, an edge chamfering process is implemented to process the right-angled edges on both sides of the width direction of the intermediate blank into a chamfered structure with a smooth transition. The chamfering depth is controlled to be 8-12mm, the angle between the chamfered bevel and the side is 35°-45°, and the radius of the chamfer transition arc is ≥5mm.

[0032] By chamfering, the stress concentration effect of right-angled edges is eliminated. In other words, during the rolling process, the edge metal is subjected to triaxial compressive stress. The right-angle shape will cause the peak value of the additional tensile stress at the corner to exceed the high-temperature strength limit of the material, which is the mechanical root cause of edge cracking. Smooth chamfering can make the stress evenly distributed and significantly reduce the tendency of edge cracking.

[0033] During chamfering and grinding, the grinding amount on both sides of the intermediate billet width direction must be strictly controlled to be symmetrical and balanced, with a metal removal deviation of ≤0.5mm on both sides. This ensures the strip runs in the center during the second finishing rolling process and prevents additional tensile stress on one side caused by deviation. At the same time, after grinding, all surfaces are subjected to PT penetrant testing. Only after confirming the absence of defects such as cracks and inclusions can the next process be carried out.

[0034] In S6, a walking beam furnace is used to heat the intermediate billet, with the heating temperature controlled at 1210-1240℃. Simultaneously, the heating temperature of the second heat treatment is higher than that of the first heat treatment to compensate for surface heat loss after grinding and ensure sufficient temperature margin in the finishing rolling stage. The total furnace dwell time is controlled at 190-240 minutes, and the soaking time is no less than 60 minutes. Due to the reduced thickness of the intermediate billet and its clean, ground surface, the heating uniformity is significantly better than that of the cast billet, providing a stable temperature base for subsequent hot rolling. Furthermore, the descaling system is not used in the second heat rolling to avoid surface temperature drop and thermal stress cracking caused by high-pressure water impact.

[0035] In the S7 mill, a two-stand, four-high reversible hot roll mill is used for roughing. The strip is kept warm throughout the entire process using both front and rear coiling furnaces to minimize temperature loss during rolling. The roughing process involves seven passes, with the target exit temperature controlled at 1080±20℃. The first three passes have a reduction of 12-18mm per pass, utilizing the material's good plasticity at high temperatures for rapid thinning. The reduction is gradually reduced in the last four passes to control deformation uniformity. Furthermore, the front and rear coiling furnaces are kept heated during roughing, with the furnace temperature controlled at 1150-1180℃ to ensure the strip remains warm after coiling and to guarantee temperature recovery between passes.

[0036] In S8, a two-stand four-roll reversible hot rolling mill is used for finishing rolling. The strip is kept warm throughout the process using front and rear coiling furnaces to minimize temperature loss during rolling. At the same time, the finishing rolling is carried out in 9 passes, and the finishing mill exit temperature is controlled at ≥1000℃ for the entire length of the strip except for the first 15m. This ensures that the final rolling temperature is much higher than the σ phase precipitation temperature, avoiding low-temperature embrittlement and cracking.

[0037] During the finishing rolling process, a hydraulic HGC roll gap control system, a CVC roll shape adjustment system, and a hydraulic bending roll system are employed to achieve precise control of strip shape and thickness. The AGC thickness control system implements feedforward and feedback closed-loop control to ensure thickness accuracy. Between passes, the strip is coiled and kept warm in the coiling furnace to ensure that the transverse temperature difference of the strip is ≤15℃, avoiding excessively rapid temperature drop at the edges that could lead to a decrease in edge plasticity.

[0038] The finishing mill employs a strategy of low-speed threading, high-speed rolling, and low-speed tail-end rolling. The maximum linear speed during the stable rolling stage is controlled at 8-10 m / s, balancing production efficiency and rolling stability. Due to the high deformation resistance of this steel grade, rolling force changes are monitored in real time during the rolling process. The rolling force of a single mill stand does not exceed 85% of the equipment's rated value, leaving a safety margin to prevent steel pile-up accidents.

[0039] In S9, the strip immediately enters the coiler for coiling after finishing rolling. The laminar flow cooling system is not used; instead, the strip's own residual heat is used for slow cooling to avoid thermal stress cracks caused by rapid cooling, and the coiling temperature is controlled to ≥900℃. Simultaneously, during coiling, the coiling side guide employs a combined position and pressure control mode to ensure the strip is centered during coiling and that the mandrel tension is established smoothly, preventing edge damage caused by sudden tension changes. After coiling, a ring-shaped reinforcement is installed on the coil to prevent loosening and edge damage during hoisting. Furthermore, the coil is cooled to room temperature using a slow cooling method; water cooling or forced air cooling is prohibited.

[0040] The hot rolling method in this embodiment can reduce the width of edge cracks on the finished coil from over 40mm in traditional processes to below 3mm, eliminating edge cracking defects and surface defects such as network cracks and strip cracks, achieving a surface quality equivalent to that of ordinary austenitic stainless steel. Furthermore, this hot rolling method enables stable mass production of S31254 hot-rolled coils with a thickness of 5-6mm, increasing the overall yield by more than 15%. The process is compatible with dual-stand furnace coil mill production lines, requiring no large-scale equipment modifications, and has industrial-scale application value.

[0041] The present invention is further illustrated below by way of embodiments, but the present invention is not limited to the scope of the embodiments described herein, and the experimental methods in the following embodiments that do not specify specific conditions are in accordance with conventional methods and conditions.

[0042] Example 1 The composition of the S31254 continuously cast billet, which measures 180mm thick, 1280mm wide, and 8000mm long, is as follows: C: 0.012%, Si: 0.45%, Mn: 0.50%, P: 0.022%, S: 0.002%, Cr: 20.10%, Mo: 6.15%, Ni: 18.20%, N: 0.20%, Cu: 0.70%.

[0043] S1, Pretreatment of the surface of the billet.

[0044] The surface of the billet is pretreated by manual inspection and removal of scale on the billet surface.

[0045] S2, apply an anti-oxidation coating.

[0046] The upper and lower surfaces and four sides of the billet are uniformly sprayed with an anti-oxidation coating with a dry film thickness of 0.4 mm.

[0047] S3, first heat treatment.

[0048] The billet is fed into a walking beam furnace for heating. The preheating section has a heating rate of 70℃ / h, the heating section rapidly heats up to the target temperature of 1215℃, and the soaking section holds the temperature for 5 hours. The temperature difference between the core and surface of the billet is ≤18℃.

[0049] S4, descaling and initial rolling.

[0050] After exiting the furnace, the billet is descaled using 18MPa high-pressure water, and then rolled in 7 passes on the primary rolling mill, from 180mm to 120mm thick intermediate billet, with the total reduction rate controlled at 32%, the single-pass reduction at 12mm, and the final rolling temperature at 975℃.

[0051] S5, intermediate blank fully ground and edge chamfered.

[0052] The entire surface of the intermediate billet is ground. A 16# coarse grinding wheel is used for rough grinding and a 24# fine grinding wheel is used for fine grinding, with a total grinding rate of 3%. During the grinding process, the edges are chamfered with a depth of 10mm, an angle of 40° between the chamfer bevel and the side, and a chamfer transition radius of 6mm. During grinding, the grinding amount on both sides of the width direction of the intermediate billet is controlled to be symmetrical and balanced, and the grinding amount deviation on both sides is 0.3mm.

[0053] S6, second heat treatment.

[0054] The intermediate billet is fed into a walking beam furnace for heating. The heating section is rapidly heated to the target temperature of 1225℃, and the furnace stay time is 210 minutes, followed by a heat soaking and holding for 70 minutes.

[0055] S7, rough rolling.

[0056] The roughing process was carried out in 7 passes using a double-stand four-roll reversible furnace coil mill. The target exit temperature of the roughing mill was 1085℃. The reduction per pass in the first 3 passes was 15mm, and the reduction was gradually reduced in the last 4 passes to roll the intermediate billet from 120mm to 28mm, while controlling the furnace temperature at 1165℃.

[0057] S8, precision rolling.

[0058] Nine passes of finishing rolling were performed using a double-stand four-roll reversible hot rolling mill to roll the intermediate billet from 28mm to a finished thickness of 6mm, with a finishing exit temperature of 1015℃ (except for the first and last 15m).

[0059] S9, cooling and curling.

[0060] After finishing rolling, the strip immediately enters the coiler for coiling at a temperature of 920℃. After coiling, the coil is fitted with an annular reinforcement device.

[0061] S10, Inspection of sheet metal.

[0062] The maximum edge crack width on a single side of the finished coil is 2.1mm, far lower than the over 40mm level of traditional processes. After pickling, the surface is inspected and found to be free of surface defects such as network cracks and strip cracks, achieving a surface quality grade of A. The mechanical properties and corrosion resistance of the steel plate both meet the requirements of ASTM A240 standard. The overall yield is 16.2% higher than that of the traditional single-fire process.

[0063] Example 2 The composition of the S31254 continuously cast billet, which measures 180mm thick, 1280mm wide, and 8500mm long, is as follows: C: 0.012%, Si: 0.45%, Mn: 0.50%, P: 0.022%, S: 0.002%, Cr: 20.10%, Mo: 6.15%, Ni: 18.20%, N: 0.20%, Cu: 0.70%.

[0064] S1, Pretreatment of the surface of the billet.

[0065] The surface of the billet is pretreated by manual inspection and removal of scale on the billet surface.

[0066] S2, apply an anti-oxidation coating.

[0067] The upper and lower surfaces and four sides of the billet are uniformly sprayed with an anti-oxidation coating, and the dry film thickness is 0.35mm.

[0068] S3, first heat treatment.

[0069] The billet is fed into a walking beam furnace for heating. The preheating section has a heating rate of 65℃ / h, the heating section rapidly heats up to the target temperature of 1205℃, and the soaking section holds the temperature for 4.5 hours. The temperature difference between the core and surface of the billet is ≤18℃.

[0070] S4, descaling and initial rolling.

[0071] After exiting the furnace, the billet is descaled using 18MPa high-pressure water, and then rolled in 7 passes on the primary rolling mill, from 180mm to 110mm thick intermediate billet, with the total reduction rate controlled at 31%, the single-pass reduction at 11mm, and the final rolling temperature at 968℃.

[0072] S5, intermediate blank fully ground and edge chamfered.

[0073] The entire surface of the intermediate billet is ground. A 16# coarse grinding wheel is used for rough grinding and a 24# fine grinding wheel is used for fine grinding, with a total grinding rate of 2.4%. During the grinding process, the edges are chamfered with a depth of 9mm, an angle of 38° between the chamfer bevel and the side, and a chamfer transition radius of 5mm. During grinding, the grinding amount on both sides of the width direction of the intermediate billet is controlled to be symmetrical and balanced, with a grinding amount deviation of 0.4mm on both sides.

[0074] S6, second heat treatment.

[0075] The intermediate billet is fed into a walking beam furnace for heating. The heating section is rapidly heated to the target temperature of 1215℃, and the furnace stay time is 200 minutes, followed by heat soaking for 65 minutes.

[0076] S7, rough rolling.

[0077] The roughing process was carried out in 7 passes using a double-stand four-roll reversible hot rolling mill with a target exit temperature of 1075℃. The reduction per pass in the first 3 passes was 14mm, and the reduction was gradually reduced in the last 4 passes to roll the intermediate billet from 110mm to 26mm, while controlling the furnace temperature at 1160℃.

[0078] S8, precision rolling.

[0079] Nine finishing mills were used to roll the intermediate billet from 28mm to 5mm in thickness, with a finishing mill exit temperature of 1005℃ (except for the first and last 15m).

[0080] S9, cooling and curling.

[0081] After finishing rolling, the strip immediately enters the coiler for coiling at a temperature of 910℃. After coiling, the coil is fitted with an annular reinforcement device.

[0082] S10, Inspection of sheet metal.

[0083] The finished coil has a maximum edge crack width of 1.8mm on one side, no visible cracks or defects on the surface, good flatness, thickness tolerance controlled within ±0.08mm, good shape, and all performance indicators meet the standard requirements. The edge cutting loss is greatly reduced, and the yield rate is increased by 14.8%.

[0084] Example 3 The composition of the S31254 continuously cast billet, which measures 180mm thick, 1219mm wide, and 7500mm long, is as follows: C: 0.012%, Si: 0.45%, Mn: 0.50%, P: 0.022%, S: 0.002%, Cr: 20.10%, Mo: 6.15%, Ni: 18.20%, N: 0.20%, Cu: 0.70%.

[0085] S1, Pretreatment of the surface of the billet.

[0086] The surface of the billet is pretreated by manual inspection and removal of scale on the billet surface.

[0087] S2, apply an anti-oxidation coating.

[0088] The upper and lower surfaces and four sides of the billet are uniformly sprayed with an anti-oxidation coating, and the dry film thickness is 0.45mm.

[0089] S3, first heat treatment.

[0090] The billet is fed into a walking beam furnace for heating. The preheating section has a heating rate of 75℃ / h, the heating section rapidly heats up to the target temperature of 1225℃, and the soaking section holds the temperature for 5.5 hours. The temperature difference between the core and surface of the billet is ≤18℃.

[0091] S4, descaling and initial rolling.

[0092] After exiting the furnace, the billet is descaled using 20MPa high-pressure water, and then rolled in 7 passes on the primary rolling mill, from 180mm to 100mm thick intermediate billet, with a total reduction rate of 38%, a single-pass reduction of 13mm, and a final rolling temperature of 980℃.

[0093] S5, intermediate blank fully ground and edge chamfered.

[0094] The entire surface of the intermediate billet is ground. A 16# coarse grinding wheel is used for rough grinding and a 24# fine grinding wheel is used for fine grinding, with a total grinding rate of 3%. During the grinding process, the edges are chamfered with a depth of 12mm, an angle of 42° between the chamfer bevel and the side, and a chamfer transition radius of 7mm. During grinding, the grinding amount on both sides of the width direction of the intermediate billet is controlled to be symmetrical and balanced, and the grinding amount deviation on both sides is 0.25mm.

[0095] S6, second heat treatment.

[0096] The intermediate billet is fed into a walking beam furnace for heating. The heating section is rapidly heated to the target temperature of 1235℃, and the furnace stay time is 230 minutes, followed by 80 minutes of heat soaking.

[0097] S7, rough rolling.

[0098] The roughing process was carried out in 7 passes using a double-stand four-roll reversible hot rolling mill with a target exit temperature of 1090℃. The reduction per pass in the first 3 passes was 16mm, and the reduction was gradually reduced in the last 4 passes to roll the intermediate billet from 110mm to 25mm, while controlling the furnace temperature at 1175℃.

[0099] S8, precision rolling.

[0100] Nine finishing rolling passes were performed using a double-stand four-roll reversible hot rolling mill to roll the intermediate billet from 25mm to a finished thickness of 5mm, with a finishing exit temperature of 1020℃ (except for the first and last 15m).

[0101] S9, cooling and curling.

[0102] After finishing rolling, the strip immediately enters the coiler for coiling at a temperature of 930℃. After coiling, the coil is fitted with an annular reinforcement device.

[0103] S10, Inspection of sheet metal.

[0104] The maximum edge crack width on a single side of the coil is 2.5mm. There is no severe tearing at the edge, which is common in products. There are no crack defects across the entire width of the surface. The quality of the edge and the middle is consistent. The overall yield is 17.1% higher than that of traditional processes.

[0105] As can be seen from the above process, this hot rolling method has the following advantages: 1. A fundamental breakthrough has been achieved in the quality of product edges and surfaces.

[0106] By combining techniques such as anti-oxidation coating on cast billets, chamfering of intermediate billet edges, and full-process temperature control, efforts are made simultaneously from both the source of crack initiation and mechanical causes. This allows the width of single-sided cracks in finished hot-rolled coils to be stably controlled from over 40mm in traditional processes to within 3mm, completely eliminating surface network cracks, strip cracks, and grain boundary oxidation defects. The surface quality reaches the same level as ordinary austenitic stainless steel. The products can be delivered without extensive additional edge trimming and deep surface grinding, fully meeting the stringent requirements of high-end fields such as petrochemicals, environmental protection, and seawater desalination.

[0107] 2. Production stability and process adaptability are significantly improved.

[0108] The two-fire rolling process adopted in this invention is fully compatible with the existing double-stand hot roll mill production line configuration, without the need for large-scale equipment modification and fixed asset investment. The first fire for billet preparation combined with long-term homogenization heating effectively improves the compositional segregation in the as-cast state and enhances the overall thermoplasticity of the material. It significantly reduces the production risks of steel piling, strip breakage, and sudden cracking during the second fire for finishing rolling. The rolling production smoothness rate has been increased from less than 60% to more than 95%, realizing the leap from small-batch trial production to stable mass production of this high-alloy steel.

[0109] 3. The yield rate has been greatly improved. The significant reduction in edge cutting losses and the elimination of surface rework processes directly lead to an increase in the overall product yield of over 15%, while reducing grinding consumables, energy consumption, and labor costs, resulting in a reduction of approximately 12% in unit product production costs. The production cycle is shortened by more than 40% compared to traditional remedial processes, significantly improving production efficiency and order delivery capabilities, giving the product a strong competitive edge in the market.

[0110] It should be noted that, unless otherwise stated, the technical or scientific terms used in this invention should have the ordinary meaning as understood by one of ordinary skill in the art.

[0111] Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly defined.

[0112] Finally, it should 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 or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. The present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A hot rolling method for improving the edge and surface quality of 6% MO type high-alloy austenitic stainless steel coils, characterized in that, Includes the following steps: S1, Pretreatment of the billet surface; S2, apply an anti-oxidation coating; S3, the first heating treatment, with the heating temperature controlled at 1200-1230℃; S4, descaling and initial rolling; S5, intermediate blank fully ground and edge chamfered; S6, second heating treatment, with the heating temperature controlled at 1210-1240℃; S7, rough rolling; S8, precision rolling; S9, cooling and curling; S10, Sheet metal inspection; The heating temperature of the second heating treatment is higher than that of the first heating treatment.

2. The hot rolling method according to claim 1, characterized in that, In S1, the billet undergoes a manual surface inspection before entering the furnace to remove obvious scabs and heavy scale defects from the billet surface.

3. The hot rolling method according to claim 1, characterized in that, In S2, the dry film thickness of the coating is controlled to be 0.3-0.5 mm.

4. The hot rolling method according to claim 1, characterized in that, In S3, the heating process is divided into three stages: preheating section, heating section and soaking section. The heating rate of the preheating section is controlled at 60-80℃ / h, the heating section is rapidly heated to the target temperature, and the soaking section is kept warm for 4-6 hours.

5. The hot rolling method according to claim 1, characterized in that, In S4, the billet is immediately subjected to high-pressure water descaling after exiting the furnace, with a descaling pressure ≥18MPa. Subsequently, it is rolled in multiple passes on the primary rolling mill, with the total reduction rate controlled at 28%-44%, the single-pass reduction at 8-15mm, and the final rolling temperature ≥960℃.

6. The hot rolling method according to claim 1, characterized in that, In S5, the grinding process is divided into two stages: rough grinding and fine grinding. Rough grinding uses 14#-18# coarse grinding wheels, and fine grinding uses 20#-28# fine grinding wheels, controlling the overall grinding rate to 2%-3%. During the grinding process, the edges are chamfered, and the right-angled edges on both sides of the width direction of the intermediate billet are processed into a chamfered structure with a smooth transition. The chamfer depth is controlled to be 8-12mm, the angle between the chamfered bevel and the side is 35°-45°, and the radius of the chamfer transition arc is ≥5mm. During grinding, the grinding amount on both sides of the width direction of the intermediate billet is controlled to be symmetrical and balanced, and the metal removal amount deviation on both sides is ≤0.5mm.

7. The hot rolling method according to claim 1, characterized in that, In S6, the total furnace dwell time is controlled at 190-240 min, and the heat soaking time in the heat soaking section is not less than 60 min.

8. The hot rolling method according to claim 1, characterized in that, In S7, the roughing rolling adopts 7 passes, and the target temperature of the roughing mill exit is controlled at 1080±20℃. The single pass reduction of the first 3 passes is 12-18mm, and the reduction of the last 4 passes is gradually reduced. During the roughing rolling process, the front and rear coiling furnaces are kept in a heated state, and the furnace temperature is controlled at 1150-1180℃ so that the strip is kept warm in the furnace after being coiled.

9. The hot rolling method according to claim 1, characterized in that, In S8, the finishing mill adopts 9 passes of rolling, and the finishing mill exit temperature is controlled to be ≥1000℃ for the entire length except for the first 15m of the strip. The strip is coiled and kept warm in the coiling furnace between passes to ensure that the transverse temperature difference of the strip is ≤15℃. The maximum linear speed during the stable rolling stage is controlled at 8-10m / s, and the rolling force of a single stand does not exceed 85% of the rated value of the equipment.

10. The hot rolling method according to claim 1, characterized in that, In S9, after finishing rolling, the strip immediately enters the coiler for coiling, and is slowly cooled by the residual heat of the strip itself, while the coiling temperature is controlled to be ≥900℃.

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