A method for manufacturing a non-acid-washed nickel-saving austenitic steel strip for cold-rolling and direct-rolling applications

Abstract

This invention discloses a method for preparing nickel-saving austenitic steel strip for cold-rolled direct rolling applications without pickling, relating to the technical field of nickel-saving austenitic stainless steel material preparation. This method involves controlling the residual oxygen content in the high-temperature zone of the heating furnace to 2%–5%, the air-fuel ratio (air to fuel gas volume flow ratio) to 9.5–20, combined with a double descaling water pressure of 28.5–30.0 MPa, a roll cycle of ≤160 rolls for high-speed finishing steel, and laminar flow cooling water Cl. ‑ By controlling multiple parameters in synergistic manner, such as a rust content ≤50mg / L and a coiling temperature of 680~720℃, a uniform rust layer structure was obtained in hot-rolled black steel strip. This avoided folding and covering caused by uneven rust layer during cold rolling and calendering, resulting in no residual rust spots on the surface of the finished cold-rolled steel strip. This solved the technical problem of embedded rust spots distributed across the entire surface of the strip after cold rolling in the existing black direct rolling process, and met the surface quality requirements for mirror panel processing.

Description

Technical Field

[0001] This invention relates to the field of nickel-saving austenitic stainless steel material preparation technology, specifically a method for preparing nickel-saving austenitic steel strip for non-acid-washed cold-rolled direct rolling applications. Background Technology

[0002] Nickel-saving austenitic stainless steel, by reducing nickel content and increasing manganese content, lowers raw material costs while maintaining good overall performance. It is increasingly widely used in fields such as construction decoration, transportation, and home appliance manufacturing. The conventional production process of this type of stainless steel hot-rolled strip is generally as follows: continuous casting slab → hot rolling (including heating, rough rolling, and finish rolling) → laminar flow cooling → coiling → annealing → hot pickling (to remove surface oxide scale) → cold rolling → finished product. Among them, the annealing and hot pickling processes are used to soften the deformed structure after hot rolling and remove the dense oxide scale (i.e., "black scale") attached to the surface of the steel strip to obtain a clean "white scale" steel coil for cold rolling. This process is mature and stable and can guarantee the surface quality of the cold-rolled finished product.

[0003] In recent years, in order to shorten the process flow, reduce energy consumption and production costs, the industry has begun to explore the process route of directly cold rolling hot-rolled black steel strip. That is, to skip the annealing and hot pickling processes, the hot-rolled steel coil with oxide rust scale is directly sent to the cold rolling mill for rolling deformation, followed by rust removal treatment. This technical direction has been initially explored for some steel grades. For example, there have been studies on the pickling-free direct rolling process of martensitic stainless steel, which achieves direct cold rolling of black strip by optimizing the pre-descaling process. There are also literature reports on attempts to directly cold roll hot-rolled black strip of stainless steel. However, in actual production, it has been found that when the above approach is directly applied to the direct rolling of black strip of nickel-saving austenitic stainless steel, the cold-rolled steel strip has embedded rust spots distributed throughout the entire coil and surface, which cannot be removed even after subsequent rust removal treatment, resulting in the surface quality not meeting the requirements of high-end surface processing such as mirror finish.

[0004] Analysis revealed the following formation mechanism of embedded rust spots: The oxide rust layer on the surface of hot-rolled black steel strip exhibits unevenness in thickness and structure. When the black steel strip is directly subjected to cold rolling, areas that were originally loose or locally deeply corroded fold and cover under the strong rolling deformation. The dense rust layer is pressed into the surface of the steel strip, forming embedded defects. Subsequent conventional rust removal treatments can only remove surface rust and cannot remove the rust spots pressed into the steel strip matrix, ultimately forming embedded rust spot defects distributed across the entire surface. Current technologies lack a systematic approach to controlling this defect through the hot rolling process. To improve the uniformity of the rust layer on black steel strips and thus adapt them to subsequent cold-rolling and direct-rolling processes, no effective technical solution has yet been provided. Furthermore, due to its high-manganese, low-nickel composition, nickel-saving austenitic stainless steel exhibits different oxidation behavior during high-temperature heating compared to conventional austenitic stainless steel, making it more sensitive to the heating atmosphere. Existing conventional hot-rolling process parameters are insufficient to directly meet the rust layer uniformity requirements of black steel strip direct rolling. The pitting corrosion effect of chloride ions on the surface of black steel strips during cooling and the influence of the sensitization temperature range on the material's corrosion resistance have also not been adequately considered in existing technologies. To address the shortcomings of existing technologies, this invention provides a method for preparing nickel-saving austenitic steel strips for non-acid-washed cold-rolled and direct-rolling applications, thereby solving the aforementioned problems. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for preparing nickel-saving austenitic steel strip for non-acid-washed cold-rolled direct rolling applications, thereby solving the problems mentioned in the background section.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing nickel-saving austenitic steel strip for non-pickled cold-rolled direct rolling applications, the method comprising the following steps: Step S1: Provide a nickel-saving austenitic stainless steel slab, the chemical composition of which, by mass percentage, is: C: 0.06%–0.30%, Si≤0.5%, Cr: 12%–15%, Ni: 0.5%–1.5%, Mn: 8%–11%, Cu: 0.1%–1.6%, S≤0.003%, P≤0.05%, with the balance being Fe and unavoidable impurities; Step S2: The slab is fed into a continuous heating furnace for heating. A zoned temperature control method is adopted, with the highest heating zone temperature greater than 1200℃ and the total heating time greater than 180 minutes. The residual oxygen content in the high-temperature zone of the heating furnace is controlled within the range of 2% to 5%, and the air-fuel ratio is controlled within the range of 9.5 to 20. The air-fuel ratio is the volume flow ratio of combustion air to fuel gas. Step S3: Perform double descaling on the heated slab, which includes post-furnace descaling and rough rolling descaling, with the descaling water pressure controlled at 28.5-30.0 MPa; Step S4: The descaled slab is finished rolled. The work rolls of the finishing mill are high-speed steel rolls. The number of rolls continuously rolled by a single high-speed steel roll shall not exceed 160 rolls to obtain hot-rolled steel strip. Step S5: The hot-rolled steel strip after finishing is subjected to laminar flow cooling. After cooling to the coiling temperature, it is coiled into a steel coil. The coiling temperature is 680-720℃. The concentration of Cl in the laminar flow cooling water is controlled. - The content shall not exceed 50 mg / L; Step S6: After air cooling the coiled steel coil to ≤180℃, directly perform cold rolling on the steel coil to obtain cold-rolled finished steel strip.

[0007] Preferably, in step S2, the continuous heating furnace includes at least a preheating section, a first heating section, a second heating section, and a soaking section. The temperature of the preheating section is 750–900°C, the temperature of the first heating section is 1000–1200°C, the temperature of the second heating section is 1160–1280°C, and the temperature of the soaking section is 1270–1310°C.

[0008] Preferably, in step S2, the residual oxygen content in the high-temperature zone of the heating furnace is controlled by adjusting the combustion air supply and fuel supply of the heating furnace to maintain the air-to-gas volume flow ratio in the high-temperature zone at 9.5 to 20, so as to control the residual oxygen volume percentage in the high-temperature zone at 2% to 5%.

[0009] Preferably, in step S5, the air-cooling time of the coiled steel coil is 48 to 60 hours.

[0010] Preferably, in step S5, the Cl of the laminar cooling water is controlled. - The method for ensuring that the concentration does not exceed 50 mg / L is as follows: Water quality monitoring is performed on laminar flow cooling water, and when the Cl content is... - When the concentration exceeds 50 mg / L, replace the cooling water source or dechlorinate the cooling water.

[0011] Preferably, in step S3, the double descaling process includes: performing a first descaling pass immediately after the slab exits the furnace, with a descaling water pressure of 28.5–30.0 MPa; and performing a second descaling pass at the inlet of the roughing mill, with a descaling water pressure of 28.5–30.0 MPa, wherein the spray direction of each descaling pass is perpendicular to the slab running direction.

[0012] Preferably, in step S3, both the descaling after the furnace and the descaling during rough rolling are carried out using high-pressure water descaling. The distance between the descaling nozzle and the slab surface is 80-150 mm, and the pressure fluctuation of the descaling water jet does not exceed ±0.5 MPa.

[0013] Preferably, in step S4, the finishing mill unit includes multiple finishing mill stands, and the work rolls of each finishing mill stand are made of high-speed steel rolls. The surface hardness of the high-speed steel rolls is HS75~85, and the surface roughness Ra≤0.8μm.

[0014] Preferably, in step S2, the residual oxygen content in the high-temperature zone of the heating furnace is controlled at 3.0% to 4.5%, and the air-fuel ratio is controlled at 10 to 15.

[0015] Preferably, in step S5, the laminar cooling adopts a segmented cooling method, with multiple sets of cooling spray devices set along the running direction of the hot-rolled steel strip. The cooling water flow rate of each set of cooling spray devices is independently controlled, so that the temperature drop rate of the hot-rolled steel strip during the laminar cooling process is controlled at 5 to 15℃ / s, and the coiling temperature is 690 to 710℃.

[0016] The technical effects and advantages of this invention are as follows: This method for preparing nickel-saving austenitic steel strip for cold-rolled direct rolling without pickling involves controlling the residual oxygen content in the high-temperature zone of the heating furnace to 2%–5%, the air-fuel ratio (air to fuel gas volume flow ratio) to 9.5–20, combined with a double descaling water pressure of 28.5–30.0 MPa, a roll cycle of ≤160 rolls for high-speed finishing rolling, and laminar flow cooling water Cl. - By controlling multiple parameters such as rust content ≤50mg / L and coiling temperature 680~720℃, a uniform rust layer structure of hot-rolled black steel strip was obtained, avoiding folding and covering caused by uneven rust layer during cold rolling and calendering. This resulted in no residual rust spots on the surface of the finished cold-rolled steel strip, solving the technical problem of embedded rust spots distributed across the entire surface of the strip after cold rolling in the existing black direct rolling process, and meeting the surface quality requirements for mirror panel processing.

[0017] This invention avoids the jagged, uneven oxide rust layer caused by excess oxygen and the incomplete combustion of fuel gas caused by insufficient oxygen by strictly controlling the residual oxygen content and air-fuel ratio in the high-temperature zone of the heating furnace. It ensures the uniformity of the oxide rust layer on the surface of the hot-rolled steel strip from the source, providing a uniform rust layer foundation for subsequent cold rolling and direct rolling. At the same time, the initial iron oxide scale on the surface of the steel billet is removed by combining the post-furnace and roughing double-pass high-pressure descaling, further reducing the risk of uneven rust layer thickness.

[0018] This invention controls the laminar flow cooling water Cl -With a content not exceeding 50 mg / L, chloride ions are prevented from penetrating the rust layer and causing chloride pitting corrosion on the steel substrate, ensuring the integrity of the rust layer structure and the steel strip itself. At the same time, the coiling temperature is controlled at 680-720℃, and the temperature drop rate is controlled at 5-15℃ / s through segmented temperature control of laminar flow cooling. Combined with slow cooling to below 180℃ for 48-60 hours after coiling, the continuous precipitation and aggregation of carbides along the grain boundaries are effectively inhibited, avoiding the decrease in corrosion resistance caused by sensitization. The quality integrity of the rust layer structure and the steel strip itself is ensured from the cooling stage.

[0019] This invention eliminates the annealing and hot pickling processes in traditional processes, enabling direct cold rolling of hot-rolled black steel strip. This shortens the process flow, reduces energy consumption and production costs, while ensuring the surface quality of the finished cold-rolled steel strip. It has good industrial application prospects and economic benefits. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a flowchart of the overall preparation method of the present invention; Figure 2 This is a schematic diagram of the temperature control of the heating furnace in this invention, showing the temperature of different sections. Figure 3 This is a flowchart of the dual descaling process of the present invention; Figure 4 This is a diagram showing the connection between the finishing rolling and coiling processes of this invention; Figure 5 This is a diagram showing the adjustment of air-fuel ratio and residual oxygen in the heating furnace of the present invention. Detailed Implementation

[0022] 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.

[0023] This embodiment discloses a method for preparing nickel-saving austenitic steel strip for non-pickled cold-rolled direct rolling applications, according to the attached... Figure 1 To be continued Figure 5 As shown, it includes the following steps: We provide nickel-saving austenitic stainless steel slabs. The chemical composition of the slabs, by mass percentage, is as follows: C: 0.06%~0.30%, Si≤0.5%, Cr: 12%~15%, Ni: 0.5%~1.5%, Mn: 8%~11%, Cu: 0.1%~1.6%, S≤0.003%, P≤0.05%, with the balance being Fe and unavoidable impurities. The slab is fed into a continuous heating furnace for sectional temperature-controlled heating. The residual oxygen content in the high-temperature zone of the heating furnace is controlled within the range of 2% to 5%, and the air-fuel ratio is controlled within the range of 9.5 to 20. The air-fuel ratio is the volumetric flow ratio of combustion air to fuel gas. The heated slab is subjected to double descaling treatment, with the descaling water pressure controlled at 28.5–30.0 MPa; The descaled slab is then finished rolled. The finishing mill uses high-speed steel rolls as its work rolls, and the number of rolls continuously rolled by a single high-speed steel roll does not exceed 160 rolls, in order to obtain hot-rolled steel strip. The hot-rolled steel strip after finishing rolling is subjected to laminar flow cooling. After cooling to a coiling temperature of 680–720°C, it is coiled into a steel coil. The Cl of the laminar flow cooling water is controlled. - The content shall not exceed 50 mg / L; After the coiled steel coil is air-cooled to ≤180℃, it is directly cold-rolled to obtain cold-rolled finished steel strip.

[0024] Furthermore, due to its lower nickel content (0.5%–1.5%), nickel-saving austenitic stainless steel has lower austenitic structural stability than traditional 18-8 type austenitic stainless steel. With a high manganese content (8%–11%) and low nickel composition, this steel grade is more sensitive to the furnace atmosphere during hot rolling. When the residual oxygen content in the furnace is too high, the oxidation reaction on the billet surface intensifies, forming an uneven, interlocking oxide rust layer. This uneven rust layer is pressed into the steel strip surface during subsequent cold rolling and... This results in folded coverage; when the residual oxygen content is too low, the combustion of the gas is incomplete, the heating efficiency decreases, and a reducing atmosphere may be generated, which is also not conducive to obtaining a uniform oxide rust layer structure. In this embodiment, the residual oxygen content in the high-temperature zone of the heating furnace is controlled at 2% to 5%, and the air-fuel ratio (air / gas volume ratio) is controlled at 9.5 to 20. This avoids both the jagged and uneven oxidation caused by excess oxygen and the incomplete combustion of gas caused by insufficient oxygen, thus ensuring the uniformity of the thickness and structure of the oxide rust layer on the steel billet surface.

[0025] Furthermore, chloride ions (Cl) in the cooling water -It possesses extremely strong penetrating power, capable of penetrating the oxide and rust layer on the surface of the steel strip to reach the surface of the steel substrate. During the cooling process of the steel coil, it easily forms point-like or pit-like chloride pitting corrosion. For deformed black steel strips with rust adhering to them, once this pitting corrosion forms, it will be folded and covered during subsequent cold rolling deformation, forming embedded rust spots that cannot be removed by conventional rust removal methods. In this embodiment, the Cl- in the laminar flow cooling water... - The chloride content is controlled to not exceed 50 mg / L to avoid chloride pitting corrosion caused by residual cooling water. For cooling water quality control, this embodiment preferably uses online water quality monitoring of laminar flow cooling water. - If the concentration exceeds 50 mg / L, immediately replace the cooling water source or dechlorinate the cooling water to ensure the cooling water's chloride content is within acceptable limits. - The content consistently meets the control requirements.

[0026] Furthermore, nickel-saving austenitic stainless steel has a sensitization temperature range (approximately 450℃ to 800℃). This application sets the coiling temperature at 680℃ to 720℃. Although this temperature is within the sensitization temperature range, by strictly controlling the temperature drop rate (5℃ to 15℃ / s) during the laminar flow cooling process and combining it with slow air cooling for 48 to 60 hours after coiling, the continuous precipitation of grain boundary carbides can be effectively suppressed. At the same time, the internal temperature of the steel coil is uniform, which is convenient for subsequent production line production. It should be particularly emphasized that when the coiling temperature is below 680℃, the steel strip strength is too high and the plasticity is reduced, which is not conducive to coiling and forming and is prone to plate shape defects. When the coiling temperature is above 720℃, the steel strip remains at a high temperature for a longer period of time after coiling, which increases the risk of grain coarsening and carbide aggregation and growth, affecting the corrosion resistance of the final product.

[0027] Furthermore, high-pressure water descaling is an effective means of removing iron oxide scale from the surface of hot-rolled steel billets. Under conventional descaling water pressure of 18-20 MPa, it is still not enough to completely remove the iron oxide scale from the surface of austenitic stainless steel billets. In this embodiment, a dual-pass high-pressure water descaling method of post-furnace descaling and rough rolling descaling is adopted, with the descaling water pressure controlled at 28.5-30.0 MPa. This water pressure range ensures sufficient descaling force to remove the iron oxide scale from the surface of the steel billet, while avoiding excessive impact and cooling on the surface of the steel billet caused by excessively high water pressure (such as exceeding 30 MPa), which would affect the stability of the hot rolling temperature regime. The distance between the descaling nozzle and the slab surface is preferably 80-150 mm, and the fluctuation range of the descaling water spray pressure does not exceed ±0.5 MPa to ensure the uniformity and stability of the descaling effect.

[0028] Furthermore, the material and rolling cycle of the work rolls in the finishing rolling process have a significant impact on the surface quality of hot-rolled steel strip. High-speed steel rolls have high red hardness and wear resistance, and can maintain a good roll surface condition under high-temperature rolling conditions. When the number of rolls continuously used by a single high-speed steel roll exceeds 160, the roll surface wear intensifies, the roll surface roughness increases, and tiny roll marks are easily formed on the surface of the hot-rolled steel strip. These marks may become the cause of uneven rust accumulation in the subsequent cold rolling process. In this embodiment, the number of rolls continuously used by a single high-speed steel roll is controlled to not exceed 160, ensuring the stability of the steel strip surface quality in the finishing rolling stage. The roll surface hardness of the high-speed steel roll is preferably HS75~85, and the roll surface roughness Ra≤0.8μm.

[0029] Specifically disclosed is the sectional temperature control method of the continuous heating furnace in the heating process. The continuous heating furnace includes at least a preheating section, a first heating section, a second heating section, and a soaking section. After the slab enters the heating furnace, it is heated through each section in sequence. The temperature of the preheating section is preferably 750-900℃, the temperature of the first heating section is preferably 1000-1200℃, the temperature of the second heating section is preferably 1160-1280℃, and the temperature of the soaking section is preferably 1270-1310℃. The total heating time is greater than 180 minutes to ensure that the core temperature of the steel billet is uniform and has good thermoplasticity. The temperature of the highest heating section is greater than 1200℃ to meet the high-temperature plasticity requirements of nickel-saving austenitic stainless steel during hot rolling deformation. The purpose of sectional temperature control is to accurately control the temperature distribution of each section according to the heat absorption characteristics and oxidation behavior of the steel billet at different heating stages, and to avoid abnormal oxidation and rust layers caused by local overheating or burning.

[0030] Specifically disclosed, the laminar flow cooling adopts a segmented cooling method, with multiple sets of cooling spray devices set along the running direction of the hot-rolled steel strip. The cooling water flow rate of each set of cooling spray devices is independently controlled. Through segmented cooling, the temperature drop rate of the hot-rolled steel strip during the laminar flow cooling process can be precisely controlled. In this embodiment, the temperature drop rate is preferably controlled at 5-15℃ / s. If the temperature drop rate is too low, the steel strip will stay in the sensitization temperature range for too long, increasing the risk of carbide precipitation. If the temperature drop rate is too high, it may cause an excessive temperature difference between the surface and the core of the steel strip, resulting in thermal stress and strip shape problems. The coiling temperature is preferably controlled at 690-710℃ (this range falls within the overall range of 680-720℃ and is more consistent with the specific embodiment).

[0031] It is particularly important to emphasize that the core innovation of this embodiment lies in: eliminating the traditional annealing and hot pickling processes, and achieving superior performance through control of the heating atmosphere (residual oxygen content 2%–5%, air-fuel ratio 9.5–20), dual descaling water pressure control (28.5–30.0 MPa), control of the finishing roll cycle (≤160 rolls), and control of cooling water Cl during the hot rolling process. -The systematic operation method of content control (≤50mg / L) and laminar flow cooling and coiling temperature control (680~720℃) achieves uniformity of rust layer on hot-rolled black steel strip. The control parameters have synergistic effects: the heating atmosphere affects the initial structure and thickness uniformity of the oxide rust layer; double descaling removes surface iron oxide scale and avoids the early-formed thick oxide scale being pressed in; the control of the finishing rolls avoids secondary damage to the steel strip surface caused by the deterioration of the roll surface condition; the cooling water quality control avoids the generation of chloride pitting corrosion; although the laminar flow cooling and coiling temperature control are in the sensitization range, the combination of cooling rate and air cooling system avoids the formation of a continuous network of harmful precipitates. It is this multi-dimensional and systematic parameter synergistic control that solves the technical problem of embedded rust spots on the surface of non-pickled black steel strip after direct cold rolling, so that the surface of the cold-rolled finished plate is uniform and free of residual rust spots, which can meet the processing requirements of mirror plate.

[0032] The workflow of this application will be described in detail below with reference to specific embodiments: Example 1: This example uses low-copper, nickel-saving austenitic stainless steel as an example, combined with the attached... Figure 1 To be continued Figure 5 Provide a detailed description of the workflow.

[0033] The chemical composition of the slab, by mass percentage, is: C 0.138%, Si 0.377%, Mn 8.795%, P 0.045%, S 0.0013%, Cr 13.19%, Ni 1.18%, Cu 0.172%, with the balance being Fe and unavoidable impurities.

[0034] The above-mentioned slabs were fed into a continuous heating furnace for heating. The total heating time was 193 minutes, with the preheating section temperature at 829°C, the first heating section temperature at 1170°C, the second heating section temperature at 1278°C, and the soaking section temperature at 1300°C. The residual oxygen content in the high-temperature zone of the heating furnace was controlled at 3.71%, and the air-fuel ratio (air / fuel volume ratio) was controlled at 9.6.

[0035] The heated slab undergoes a double descaling process: two descaling passes after the furnace with a descaling water pressure of 29.2 MPa; two descaling passes during rough rolling with a descaling water pressure of 29.2 MPa. The distance between the descaling nozzle and the slab surface is 100 mm, and the fluctuation range of the descaling water pressure is controlled within ±0.4 MPa.

[0036] After descaling, the slab enters the finishing mill for finishing rolling. The work rolls of the finishing mill are made of high-speed steel rolls with a surface hardness of HS80 and a surface roughness of Ra of 0.6μm. The number of rolls that can be rolled continuously by a single high-speed steel roll is 159 (not exceeding 160).

[0037] After finishing, the hot-rolled steel strip undergoes laminar flow cooling, employing a segmented cooling method. Six sets of cooling spray devices are installed along the running direction of the hot-rolled steel strip, with independent control of the cooling water flow rate for each set. The temperature drop rate of the steel strip is controlled at 10℃ / s. After cooling to a coiling temperature of 694℃, the strip is coiled into a steel coil. The Cl- content of the laminar flow cooling water... - The concentration was controlled at 48 mg / L (not exceeding 50 mg / L), and monitored in real time using an online water quality monitor. - When the concentration approaches 50 mg / L, replenish with fresh water promptly to dilute it.

[0038] After being air-cooled for 54 hours, the temperature of the coil drops below 180°C. The coil is then directly cold-rolled to obtain cold-rolled finished steel strip.

[0039] Testing revealed that the cold-rolled finished steel strip had a uniform surface with no residual rust spots, meeting the surface quality requirements for subsequent mirror panel processing.

[0040] Example 2: This example uses semi-copper nickel-retaining austenitic stainless steel as an example, combined with the attached... Figure 1 To be continued Figure 5 Provide a detailed description of the workflow.

[0041] The chemical composition of the slab, by mass percentage, is: C 0.08%, Si 0.446%, Mn 9.23%, P 0.041%, S 0.0015%, Cr 14.05%, Ni 1.22%, Cu 0.83%, with the balance being Fe and unavoidable impurities.

[0042] The above-mentioned slabs were fed into a continuous heating furnace for heating. The total heating time was 191 minutes, with the preheating section temperature at 859°C, the first heating section temperature at 1143°C, the second heating section temperature at 1242°C, and the soaking section temperature at 1277°C. The residual oxygen content in the high-temperature zone of the heating furnace was controlled at 3.98%, and the air-fuel ratio (air / fuel volume ratio) was controlled at 10.31.

[0043] The heated slab undergoes a double descaling process: two descaling passes after the furnace with a descaling water pressure of 28.92 MPa; two descaling passes during rough rolling with a descaling water pressure of 28.92 MPa. The distance between the descaling nozzle and the slab surface is 120 mm, and the fluctuation range of the descaling water pressure is controlled within ±0.5 MPa.

[0044] After descaling, the slab enters the finishing mill for finishing rolling. The work rolls of the finishing mill are made of high-speed steel rolls with a surface hardness of HS78 and a surface roughness of Ra of 0.7μm. The continuous rolling capacity of a single high-speed steel roll is 160 rolls.

[0045] The hot-rolled steel strip after finishing rolling undergoes laminar flow cooling. This laminar flow cooling employs a segmented cooling method, with six sets of cooling spray devices installed along the running direction of the hot-rolled steel strip. The cooling water flow rate of each set is independently controlled, and the temperature drop rate of the steel strip is controlled at 8℃ / s. After cooling to the coiling temperature of 708℃, the strip is coiled into a steel coil. The Cl- content of the laminar flow cooling water... - The content is controlled at 49 mg / L (not exceeding 50 mg / L), and is monitored in real time by an online water quality monitor and a full analysis of the cooling water is performed regularly.

[0046] After being air-cooled for 56 hours, the temperature of the coil drops below 180°C. The coil is then directly cold-rolled to obtain cold-rolled finished steel strip.

[0047] Testing revealed that the cold-rolled finished steel strip had a uniform surface with no residual rust spots, meeting the surface quality requirements for subsequent mirror panel processing.

[0048] 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 preparing nickel-saving austenitic steel strip for non-pickled cold-rolled direct rolling applications, characterized in that, The preparation method includes the following steps: Step S1: Provide a nickel-saving austenitic stainless steel slab, the chemical composition of which, by mass percentage, is: C: 0.06%–0.30%, Si≤0.5%, Cr: 12%–15%, Ni: 0.5%–1.5%, Mn: 8%–11%, Cu: 0.1%–1.6%, S≤0.003%, P≤0.05%, with the balance being Fe and impurities; Step S2: The slab is fed into a continuous heating furnace for heating. A zoned temperature control method is adopted, with the highest heating zone temperature greater than 1200℃ and the total heating time greater than 180 minutes. The residual oxygen content in the high-temperature zone of the heating furnace is controlled within the range of 2% to 5%, and the air-fuel ratio is controlled within the range of 9.5 to 20. The air-fuel ratio is the volume flow ratio of combustion air to fuel gas. Step S3: Perform double descaling on the heated slab, which includes post-furnace descaling and rough rolling descaling, with the descaling water pressure controlled at 28.5-30.0 MPa; Step S4: The descaled slab is finished rolled. The work rolls of the finishing mill are high-speed steel rolls. The number of rolls continuously rolled by a single high-speed steel roll shall not exceed 160 rolls to obtain hot-rolled steel strip. Step S5: The hot-rolled steel strip after finishing is subjected to laminar flow cooling. After cooling to the coiling temperature, it is coiled into a steel coil. The coiling temperature is 680-720℃. The concentration of Cl in the laminar flow cooling water is controlled. - The content shall not exceed 50 mg / L; Step S6: After air cooling the coiled steel coil to ≤180℃, directly perform cold rolling on the steel coil to obtain cold-rolled finished steel strip.

2. The method for preparing non-pickled, cold-rolled, direct-rolling nickel-saving austenitic steel strip according to claim 1, characterized in that, In step S2, the continuous heating furnace includes at least a preheating section, a first heating section, a second heating section, and a soaking section. The temperature of the preheating section is 750–900°C, the temperature of the first heating section is 1000–1200°C, the temperature of the second heating section is 1160–1280°C, and the temperature of the soaking section is 1270–1310°C.

3. The method for preparing non-pickled, cold-rolled, direct-rolling nickel-saving austenitic steel strip according to claim 2, characterized in that, In step S2, the residual oxygen content in the high-temperature zone of the heating furnace is controlled by adjusting the supply of combustion air and fuel in the heating furnace to maintain the air-to-gas volume flow ratio in the high-temperature zone at 9.5-20, so as to control the residual oxygen volume percentage in the high-temperature zone at 2%-5%.

4. The method for preparing non-pickled, cold-rolled, direct-rolling nickel-saving austenitic steel strip according to claim 1, characterized in that, In step S5, the air cooling time of the coiled steel coil is 48 to 60 hours.

5. The method for preparing non-pickled, cold-rolled, direct-rolling nickel-saving austenitic steel strip according to claim 4, characterized in that, In step S5, the Cl of the laminar cooling water is controlled. - The method for ensuring that the concentration does not exceed 50 mg / L is as follows: Water quality monitoring is performed on laminar flow cooling water, and when the Cl content is... - When the concentration exceeds 50 mg / L, replace the cooling water source or dechlorinate the cooling water.

6. The method for preparing nickel-saving austenitic steel strip for non-pickled cold-rolled direct rolling applications according to claim 1, characterized in that, In step S3, the double descaling process includes: performing a first descaling pass immediately after the slab exits the furnace, with a descaling water pressure of 28.5–30.0 MPa; and performing a second descaling pass at the inlet of the roughing mill, with a descaling water pressure of 28.5–30.0 MPa, wherein the spray direction of each descaling pass is perpendicular to the slab running direction.

7. The method for preparing non-pickled, cold-rolled, direct-rolling nickel-saving austenitic steel strip according to claim 6, characterized in that, In step S3, both the post-furnace descaling and rough rolling descaling adopt high-pressure water descaling. The distance between the descaling nozzle and the slab surface is 80-150mm, and the pressure fluctuation of the descaling water jet does not exceed ±0.5MPa.

8. The method for preparing non-pickled, cold-rolled, direct-rolling nickel-saving austenitic steel strip according to claim 1, characterized in that, In step S4, the finishing mill unit includes multiple finishing mill stands, and the work rolls of each finishing mill stand are made of high-speed steel rolls. The surface hardness of the high-speed steel rolls is HS75~85, and the surface roughness Ra≤0.8μm.

9. The method for preparing non-pickled, cold-rolled, direct-rolling nickel-saving austenitic steel strip according to claim 1, characterized in that, In step S2, the residual oxygen content in the high-temperature zone of the heating furnace is controlled at 3.0% to 4.5%, and the air-fuel ratio is controlled at 10 to 15.

10. The method for preparing non-pickled, cold-rolled, direct-rolling nickel-saving austenitic steel strip according to claim 1, characterized in that, In step S5, the laminar cooling adopts a segmented cooling method, with multiple sets of cooling spray devices set along the running direction of the hot-rolled steel strip. The cooling water flow rate of each set of cooling spray devices is independently controlled, so that the temperature drop rate of the hot-rolled steel strip during the laminar cooling process is controlled at 5-15℃ / s, and the coiling temperature is 690-710℃.

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