A processing method for improving surface cracks of high-strength 316L stainless steel

Abstract

This invention discloses a processing method for improving surface cracks in high-strength 316L stainless steel. The steps are as follows: S1, Product smelting: Low-sulfur raw materials are selected during the electric furnace charging stage. After electric furnace roughing, pre-desulfurization treatment, AOD refining, and calcium wire modification, the raw materials are sent to the continuous casting platform for casting to obtain slabs; S2, Slab surface grinding: The two surfaces of the slab are ground in two passes respectively; S3, Hot rolling: Rough rolling and fine rolling. This invention achieves the following: First, by increasing the chromium content, the slab maintains a reasonable ferrite content, preventing excessive austenite grain growth during electric furnace heating and smelting; second, by reducing the content of harmful elements oxygen and sulfur, the precipitation of sulfides between grains is reduced, improving intergranular bonding; third, the surface of the slab is ground to eliminate the poor quality parts of the slab surface; fourth, a hot rolling light pressing process is used to refine the surface grains of the slab. Through the above means, crack defects are avoided, and the surface quality of the final product is improved.

Description

Technical Field

[0001] This invention relates to the field of stainless steel processing technology, and in particular to a method for improving surface cracks in high-strength 316L stainless steel. Background Technology

[0002] High-strength 316L stainless steel refers to a type of high-strength 316L stainless steel with a nitrogen content of 0.07% to 0.1%, obtained through nitrogen alloying. Compared with ordinary 316L stainless steel, its tensile strength can be increased by 25%, and it is widely used in the equipment transportation industry, playing a decisive role in reducing equipment weight.

[0003] However, during the production of high-strength 316L stainless steel, the final product often exhibits numerous surface cracks and defects, such as... Figure 1 As shown, this does not meet the downstream customers' requirements for product surface quality. Currently, the common method to improve surface crack defects in stainless steel is to reduce the heating temperature of the slab in the heating furnace during the hot rolling stage. However, high-strength 316L stainless steel is a high-strength steel and requires higher temperatures for rolling. Therefore, the above-mentioned common methods are not suitable for high-strength 316L stainless steel. The presence of surface crack defects in high-strength 316L stainless steel has always been a technical problem that has troubled those skilled in the art and urgently needs to be solved. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for improving surface cracks in high-strength 316L stainless steel. The high-strength 316L stainless steel processed by this method has a smooth and clean surface, which meets the surface quality requirements of the product.

[0005] In the past, during the production of high-strength 316L stainless steel, the final product often had numerous surface cracks and defects, such as... Figure 1 As shown, existing technologies can only improve product strength, but cannot change surface cracks and defects, resulting in poor product surface quality.

[0006] The main reasons for this type of crack defect are as follows:

[0007] First, high-strength 316L stainless steel has a higher nitrogen content than ordinary 316L stainless steel. The increased nitrogen content leads to a decrease in the ferrite content in the slab that prevents austenite grain growth. During the electric furnace heating and smelting process, the austenite grains grow excessively, and the coarse grains are prone to intergranular cracking during rolling.

[0008] Second, the presence of harmful sulfide phases at grain boundaries leads to a decrease in intergranular bonding strength.

[0009] Third, excessive single-pass reduction in the roughing mill leads to intergranular cracking in the slab microstructure.

[0010] This invention addresses several key aspects: First, by increasing the chromium content, the slab maintains a reasonable ferrite content, preventing excessive austenite grain growth during electric furnace smelting. Second, by reducing the content of harmful elements such as oxygen and sulfur, intergranular sulfide precipitation is reduced, improving intergranular bonding. Third, the slab surface is ground to eliminate defective parts of the slab surface. Fourth, a hot rolling and light pressing process is used to refine the slab surface grains. Through these methods, crack defects are avoided, and the surface quality of the final product is improved.

[0011] The technical solution adopted in this invention is: a processing method for improving surface cracks in high-strength 316L stainless steel, the specific processing steps of which are as follows:

[0012] S1. Product smelting:

[0013] (a) Steelmaking raw materials are fed into the electric furnace for rough refining; the steelmaking raw materials include: general scrap steel, molybdenum-containing scrap steel, ferronickel, ferrochrome and ferrosilicon, and the general scrap steel, molybdenum-containing scrap steel, ferronickel, ferrochrome and ferrosilicon are mixed in the proportions of their components;

[0014] (b) The molten steel from the electric furnace is transported to the pre-desulfurization station via a ladle, where quicklime, fluorite, and ferrosilicon are added. Considering economic costs, nitrogen gas, which does not readily react with the molten steel, is selected as the stirring gas. Nitrogen gas is blown in to stir the molten steel and perform pre-desulfurization treatment until the sulfur content in the molten steel is reduced to below 0.1%. After the pre-desulfurization treatment, slag is removed.

[0015] (c) The pre-desulfurized molten steel is fed into an AOD refining furnace for refining; the refining process is divided into two stages:

[0016] The first stage is the oxidation stage, in which quicklime and fluorite are added to the molten steel, and oxygen is first blown in to decarburize and desulfurize the molten steel. Considering economic costs, nitrogen gas, which does not easily react with molten steel, is selected as the stirring gas and is blown in to stir until the carbon content in the molten steel is reduced to below 0.0015% and the sulfur content is reduced to below 0.003%. After the first stage of refining is completed, slag is removed.

[0017] The second stage is the reduction stage, in which ferrosilicon, ferromolybdenum, and ferrosilicon-manganese alloy are added to the molten steel. Pure nickel and ferrochromium are added as needed to adjust the composition of the molten steel according to the target composition requirements. Argon gas is blown in for stirring until the sulfur content in the molten steel is reduced to below 0.002%. After the second stage of refining is completed, slag is removed.

[0018] Considering that the nitrogen composition in the molten steel has already been adjusted in this step, if nitrogen is used for stirring here, it will affect the nitrogen composition in the molten steel. Therefore, argon is chosen as the stirring gas here.

[0019] (d) The molten steel from the AOD refining furnace is transported to the ladle station via a ladle. Calcium wire is added to improve the inclusions in the molten steel, so that the composition of the inclusions is changed from the poorly ductile Al-Mg-O system to the well-ductile Ca-Si-O and Ca-Si-Al-O type inclusions. After the molten steel is allowed to stand for a set time, the slag is removed and then it is sent to the continuous casting platform for casting to obtain slabs.

[0020] S2. Slab surface grinding: Grind the two surfaces of the slab in two passes respectively.

[0021] S3, Hot Rolling:

[0022] (a) Rough rolling: The slab is heated and then rolled for the first time, which is done in 2 passes; then the slab is heated a second time and then rolled for the second time, which is done in 9 passes.

[0023] (b) Fine rolling: The slab is rolled in 5 passes to finally obtain a black sheet of the target thickness.

[0024] Furthermore, in the aforementioned processing method for improving surface cracks in high-strength 316L stainless steel, in step (a) of step S1, the proportions of each raw material are as follows: general scrap steel accounts for 30% to 45%, molybdenum-containing scrap steel accounts for 30% to 45%, nickel iron accounts for 10% to 12%, chromium iron accounts for 12% to 15%, and silicon iron accounts for 0.5% to 1.5%.

[0025] Furthermore, in the aforementioned processing method for improving surface cracks in high-strength 316L stainless steel, in step (b) of step S1, the amount of quicklime added is 1 to 2.5 tons, the amount of fluorite added is 500 to 1000 kg, and the amount of ferrosilicon added is 500 to 1000 kg.

[0026] Furthermore, in the aforementioned processing method for improving surface cracks in high-strength 316L stainless steel, in step (b) of step S1, the nitrogen blowing rate is 50-100 mg / L. 3 The electric furnace smelting time is controlled at 50-60 minutes, the electric furnace smelting temperature is controlled at 1500-1550℃, and the stirring time is controlled at 10-20 minutes.

[0027] Furthermore, in the aforementioned processing method for improving surface cracks in high-strength 316L stainless steel, in step (c) of step S1, during the oxidation stage, the amount of quicklime added is 10-20 tons, the amount of fluorite added is 2-4 tons, and the amount of oxygen blown in is 3000-5000 mg / m³. 3 The nitrogen injection rate is 2000–4000 m³. 3 The oxidation stage duration is controlled at 50-60 minutes, and the molten steel temperature is controlled at 1600-1700℃.

[0028] Furthermore, in the aforementioned processing method for improving surface cracks in high-strength 316L stainless steel, in step (c) of step S1, during the reduction stage, the amount of ferrosilicon added is 5-10 tons, the amount of ferromolybdenum added is 4-6 tons, the amount of silicon-manganese alloy added is 5-10 tons, and the amount of argon gas blown in is 500-1000 mg / L. 3 The duration of the reduction stage is controlled at 10-15 minutes, and the temperature of the molten steel is controlled at 1600-1700℃.

[0029] Furthermore, in the aforementioned processing method for improving surface cracks in high-strength 316L stainless steel, in step (d) of step S1, the amount of calcium wire added is 30-50 kg, and the settling time is controlled at 10-15 min.

[0030] Furthermore, in the aforementioned processing method for improving surface cracks in high-strength 316L stainless steel, in step S2, the first pass is rough grinding, using a 20-mesh coarse grinding wheel with a grinding amount of 1±0.05mm; the second pass is fine grinding, using a 30-mesh fine grinding wheel with a grinding amount of 0.5±0.05mm.

[0031] Furthermore, in the aforementioned processing method for improving surface cracks in high-strength 316L stainless steel, in step S3, the reduction rate per pass is controlled at 4% to 6% in the first rolling of the rough rolling process; the reduction rate per pass is controlled at 10% to 26% in the second rolling of the rough rolling process; and the reduction rate per pass is controlled at 20% to 25% in the fine rolling process.

[0032] The beneficial effects of this invention are: while ensuring product strength, it also ensures product surface quality, and the product has the advantages of both high strength and no surface cracks or defects. Attached Figure Description

[0033] Figure 1 This is a photo of the surface of a high-strength 316L stainless steel product before the improvement.

[0034] Figure 2 These are surface photographs of high-strength 316L stainless steel products processed using the method described in this invention for improving surface cracks in high-strength 316L stainless steel. Detailed Implementation

[0035] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and preferred embodiments.

[0036] The present invention discloses a processing method for improving surface cracks in high-strength 316L stainless steel, the processing method comprising the following steps:

[0037] S1. Product smelting:

[0038] (a) Raw materials for steelmaking are fed into the electric furnace for rough refining. These raw materials include: general scrap steel, molybdenum-containing scrap steel, ferronickel, ferrochrome, and ferrosilicon. The general scrap steel referred to in this invention is scrap 300 series stainless steel that does not contain molybdenum, mainly sourced from social acquisitions and scrap such as edge wire and end-cut waste generated during subsequent production. The general scrap steel, molybdenum-containing scrap steel, ferronickel, ferrochrome, and ferrosilicon are mixed according to the following proportions: general scrap steel 30%–45%, molybdenum-containing scrap steel 30%–45%, ferronickel 10%–12%, ferrochrome 12%–15%, and ferrosilicon 0.5%–1.5%.

[0039] This embodiment provides an actual workshop steelmaking example, which is distinguished by the steelmaking furnace number SF17685, SF17689, and SF18474. The raw materials used for steelmaking and the input of each raw material are shown in Table 1.

[0040] Table 1. Raw materials used in steelmaking and their composition ratios and input amounts (unit: tons)

[0041]

[0042] During the roughing process, the electric furnace smelting time is controlled at 50-60 minutes, and the electric furnace smelting temperature is controlled at 1500-1550℃. The main parameters of SF17685, SF17689, and SF18474 in the electric furnace roughing stage are shown in Table 2. The content of harmful element sulfur in the molten steel after roughing is about 0.15%.

[0043] Table 2. Main parameters of the electric furnace refining stage

[0044] Steelmaking furnace number Power-on time (min) Molten steel temperature (°C) Steel output (tons) Sulfur content SF17685 58 1505 128 0.18％ SF17689 52 1546 130 0.14％ SF18474 54 1523 124 0.16％

[0045] (b) After the electric furnace roughing and melting is completed, the molten steel is transported to the pre-desulfurization station through a steel ladle. The steel ladle contains 150 tons of molten steel. Quicklime, fluorite, and ferrosilicon are added, and nitrogen is blown in to stir and pre-desulfurize the molten steel until the content of the harmful element sulfur in the molten steel is reduced to below 0.1%.

[0046] The input amounts are as follows: quicklime 1–2.5 tons, fluorite 500–1000 kg, ferrosilicon 500–1000 kg, and nitrogen 50–100 m³. 3 The stirring time should be controlled between 10 and 20 minutes.

[0047] After pre-desulfurization treatment, slag is removed.

[0048] Table 3 shows the raw materials and their component ratios for SF17685, SF17689, and SF18474 during the pre-desulfurization stage. Pre-desulfurization reduces the sulfur content (a harmful element) in the molten steel from approximately 0.15% to below 0.10%, preparing the steel for further desulfurization in the next AOD refining stage.

[0049] Table 3. Raw materials and their composition ratios for the pre-desulfurization stage (unit: tons)

[0050]

[0051] The main parameters of SF17685, SF17689, and SF18474 during the pre-desulfurization stage are shown in Table 4. As can be seen from Table 4, after 10 to 20 minutes of pre-desulfurization treatment, the sulfur content in the molten steel is reduced to below 0.1%.

[0052] Table 4. Main parameters of the pre-desulfurization stage

[0053] Steelmaking furnace number Processing time (min) <![CDATA[Nitrogen injection volume (m 3 )]]> Sulfur content SF17685 14 93 0.10％ SF17689 14 58 0.07％ SF18474 20 63 0.08％

[0054] (c) The pre-desulfurized molten steel is fed into an AOD refining furnace for refining; the refining process is divided into two stages:

[0055] The first stage is the oxidation stage, in which quicklime and fluorite are added to the molten steel, oxygen is first blown in to decarburize and desulfurize the molten steel, and then nitrogen is blown in to stir it.

[0056] During this stage, the amount of quicklime added is 10–20 tons, the amount of fluorite added is 2–4 tons, and the amount of oxygen blown in is 3000–5000 m³. 3 The nitrogen injection rate is 2000–4000 m³. 3 The oxidation stage lasts for 50–60 minutes. During the oxidation stage, the carbon content in the molten steel is reduced from 1.5% to below 0.0015%, and the sulfur content is reduced from 0.10% to below 0.003%.

[0057] After the first stage of refining is completed, the slag is removed.

[0058] The second stage is the reduction stage, in which ferrosilicon, ferromolybdenum, and ferrosilicon-manganese alloy are added to the molten steel. The composition of the molten steel is compared with the target composition requirements, and pure nickel and ferrochrome are added as needed to fine-tune the composition of the molten steel so that the composition of the molten steel is within the range of the target composition. Argon gas is then blown in to stir the mixture.

[0059] During this stage, the input of ferrosilicon is 5-10 tons, ferromolybdenum is 4-6 tons, and ferrosilicon manganese alloy is 5-10 tons. In addition, pure nickel and ferrochrome are added to fine-tune the composition of the molten steel, ensuring it falls within the target range. If the molten steel already contains sufficient pure nickel and ferrochrome, they do not need to be added; they can be supplemented as needed. The argon gas blowing rate is 500-1000 m³. 3 The duration of the reduction stage is controlled at 10–15 minutes. The reduction stage further reduces the sulfur content in the molten steel to below 0.002%.

[0060] After the second stage of refining is completed, the slag is removed.

[0061] The temperature of the molten steel during the oxidation and reduction stages is controlled at 1600–1700℃. The basicity of the slag is controlled at 2.2–2.5. After the two stages of treatment (oxidation and reduction), the composition of the molten steel falls within the target range, as shown in Table 7.

[0062] The raw materials and their composition ratios for SF17685, SF17689, and SF18474 during the AOD refining stage are shown in Table 5.

[0063] Table 5. Raw materials and their composition ratios for the AOD refining stage (unit: tons)

[0064]

[0065] Table 6 shows the main parameters of SF17685, SF17689, and SF18474 during the AOD refining stage. As can be seen from Table 6, after the oxidation and reduction stages, the sulfur content in the molten steel is reduced to below 0.002%. This reduction in sulfur content decreases the precipitation of sulfides between grains, thus reducing crack defects caused by intergranular cracking during the rolling stage.

[0066] Table 6. Key parameters during the AOD refining stage

[0067]

[0068] Table 7 Target Composition of High-Strength 316L (wt%)

[0069]

[0070] (d) The molten steel from the AOD refining furnace is transported to the ladle station via a ladle, where a calcium wire is added to improve the inclusions in the molten steel, so that the composition of the inclusions is changed from the poorly ductile Al-Mg-O system to the well-ductile Ca-Si-O and Ca-Si-Al-O type inclusions.

[0071] The steel ladle contains 150 tons of molten steel, with 30-50 kg of calcium wire added. Besides fine-tuning the inclusion composition in the molten steel, the calcium wire also prevents harmful elements from rebounding, further reducing the probability of crack defects. After the molten steel is allowed to stand for 10-15 minutes, slag is removed, and then it is sent to the continuous casting platform for casting to obtain qualified slabs.

[0072] During the casting process, samples were taken from the tundish to analyze the composition of SF17685, SF17689, and SF18474 slabs. The composition table is shown in Table 8.

[0073] Table 8. Slab Composition (wt%)

[0074]

[0075] Compared to regular 316L stainless steel, the nitrogen content in high-strength 316L stainless steel increases from 0.03% to approximately 0.09%. While this significantly improves the material's strength, it also leads to a decrease in ferrite content. Ferrite plays a role in preventing austenite grain growth during the slab heating stage. A decrease in ferrite content can cause excessive austenite grain growth, resulting in intergranular cracking during rolling.

[0076] Before improvement, the high-strength 316L stainless steel had a Cr content of approximately 16.5% and a ferrite content of approximately 4.0%. This invention increases the Cr content to approximately 17.6%, which corresponds to an increase in the ferrite content to approximately 8.0%. Sufficient ferrite content can prevent excessive austenite grain growth, thereby effectively improving crack defects.

[0077] S2. Slab surface grinding;

[0078] The molten steel is then used in a continuous casting machine to produce slabs with a thickness of about 200 mm and a width of 1000-1600 mm. The slabs are then sent to a grinding machine where the two surfaces of the slabs are ground in two passes.

[0079] The first pass is rough grinding, using a 20-grit coarse grinding wheel with a grinding depth of 1 ± 0.05 mm to minimize vibration marks. Since the grinding marks from the coarse wheel are relatively deep, the second pass is fine grinding, using a 30-grit fine grinding wheel with a grinding depth of 0.5 ± 0.05 mm. This eliminates residual vibration marks as well as the deeper grinding marks remaining from the first pass. After two passes of grinding, the defective parts of the slab surface can be eliminated.

[0080] The slabs produced by continuous casting of SF17685, SF17689, and SF18474 have a thickness of 200mm. The slabs are ground in the finishing workshop. The first grinding is 1.05mm and the second grinding is 0.45mm. Both the top and bottom surfaces of the slabs are ground, and the final slab thickness is 197mm. The ground slabs are then sent to the hot rolling mill for rolling.

[0081] S3, Hot Rolling:

[0082] (a) Coarse rolling:

[0083] Generally, stainless steel is hot rolled once, but this invention designs a two-stage hot rolling process. The two-stage hot rolling process can refine the surface grains of the slab and avoid intergranular cracking caused by excessive reduction, which is one of the main causes of surface cracks.

[0084] In the first rolling pass of the roughing mill, two light reductions are used to roll the slab thickness from approximately 197 mm to 180 mm, with the reduction rate controlled between 4% and 6%, preferably 5%. The purpose of the light reduction is to deform and recrystallize the large grains on the surface of the slab into smaller grains, creating conditions for the second rolling pass. The slab after the first rolling pass is then fed back into the heating furnace for a second heating, followed by a second rolling pass. During the second rolling pass, the roughing mill uses nine rolling passes, ultimately resulting in a semi-finished slab thickness of approximately 23 mm after rough rolling, with the reduction rate controlled between 10% and 26%. The reduction schedule for each pass of the roughing mill is shown in Table 9.

[0085] Table 9. Setting of Reduction Procedures for Each Pass of the Roughing Mill

[0086]

[0087] According to Table 9, the roughing mill reduction schedules for each pass were set for SF17685, SF17689, and SF18474. The actual reduction schedule data for each pass after roughing are shown in Table 10.

[0088] Table 10 Actual Rough Rolling Reduction Procedures for Each Pass

[0089]

[0090]

[0091] (b) Fine calendering:

[0092] After rough rolling, the semi-finished slab enters the finishing mill for further rolling. After five rolling passes, the final black coil of the target thickness is obtained. The coil furnace temperature of the finishing mill is controlled at 1000–1020℃, and the target thickness is usually 3.0–7.0 mm. The target thickness may vary depending on the orders received by the manufacturer. Taking a target thickness of 6.8 mm as an example, the reduction schedule for each pass of the finishing mill is given, with the reduction rate controlled at 20%–25% per pass, as shown in Table 11.

[0093] Table 11 Setting of Reduction Procedures for Each Pass of Finishing Mill

[0094] path 1 2 3 4 5 Slab thickness (mm) 19.0 15.0 11.6 8.8 6.8 Indentation (mm) 5.0 4.0 3.4 2.8 2.0 Compression ratio (%) 20.8 21.1 22.7 24.1 22.7

[0095] According to Table 11, the roughing mill reduction schedule is set for each pass. SF17685, SF17689, and SF18474 are subjected to fine rolling. The actual reduction schedule data for each pass after fine rolling is shown in Table 12.

[0096] Table 12 Rolling Procedures for Each Pass in Fine Calendering

[0097]

[0098]

[0099] The 6.8mm thick black coils, after hot rolling, are sent to an annealing and pickling plant for pickling. After pickling, they are cold rolled to obtain a 4.5mm thick product. Subsequent processes are basically the same as those for ordinary 316L steel. Since this invention does not involve the subsequent process from annealing and pickling to cold rolling, this process will not be described here. Through improvements to the preceding product smelting, slab surface grinding, and hot rolling processes, the surface crack defects of the product are ultimately improved. The product is sent to a laboratory for material performance testing. The main performance parameters are shown in Table 13. The performance is qualified, ensuring both product strength and surface quality. The product combines the advantages of high strength and a crack-free surface, meeting the customer's requirements for both surface quality and performance.

[0100] Table 13 Main Performance Parameters of Products

[0101] Number <![CDATA[YS 0.2 (MPa)]]> TS (MPa) Elongation (%) Hardness (HV) SF17685 327 647 53 171 SF17689 324 646 54 170 SF18474 331 641 53 168

[0102] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other way. Any modifications or equivalent changes made based on the technical essence of the present invention shall still fall within the scope of protection claimed by the present invention.

Claims

1. A processing method for improving surface cracks in high-strength 316L stainless steel, characterized in that: The processing method comprises the following steps: S1. Product smelting: (a) Raw materials for steelmaking are fed into the electric furnace for rough refining; the raw materials for steelmaking include: general scrap steel, molybdenum-containing scrap steel, ferronickel, ferrochrome and ferrosilicon, and the general scrap steel, molybdenum-containing scrap steel, ferronickel, ferrochrome and ferrosilicon are mixed in the following proportions; the proportions of each raw material are as follows: general scrap steel accounts for 30% to 45%, molybdenum-containing scrap steel accounts for 30% to 45%, ferronickel accounts for 10% to 12%, ferrochrome accounts for 12% to 15%, and ferrosilicon accounts for 0.5% to 1.5%; (b) The molten steel tapped from the electric furnace is transported to the pre-desulfurization station via a ladle, where quicklime, fluorite, and ferrosilicon are added, and nitrogen is blown in for stirring to pre-desulfurize the molten steel until the sulfur content in the molten steel is reduced to below 0.1%; after the pre-desulfurization treatment, slag is removed. (c) The pre-desulfurized molten steel is fed into an AOD refining furnace for refining; the refining process is divided into two stages: The first stage is the oxidation stage, in which quicklime and fluorite are added to the molten steel, oxygen is first blown in to decarburize and desulfurize the steel, and then nitrogen is blown in to stir until the carbon content in the molten steel is reduced to below 0.0015% and the sulfur content is reduced to below 0.003%. After the first stage of refining is completed, slag is removed. The second stage is the reduction stage, in which ferrosilicon, ferromolybdenum, and ferrosilicon-manganese alloy are added to the molten steel. Pure nickel and ferrochromium are added as needed to adjust the composition of the molten steel according to the target composition requirements. Argon gas is blown in for stirring until the sulfur content in the molten steel is reduced to below 0.002%. After the second stage of refining is completed, slag is removed. (d) The molten steel from the AOD refining furnace is transported to the ladle station via a ladle. Calcium wire is added to improve the inclusions in the molten steel, so that the composition of the inclusions is changed from the poorly ductile Al-Mg-O system to the well-ductile Ca-Si-O and Ca-Si-Al-O type inclusions. After the molten steel is allowed to stand for a set time, the slag is removed and then it is sent to the continuous casting platform for casting to obtain slabs. S2. Slab surface grinding: Grind the two surfaces of the slab in two passes respectively. S3, Hot Rolling: (a) Rough rolling: The slab is heated and then rolled for the first time, which is done in 2 passes; then the slab is heated a second time and rolled for the second time, which is done in 9 passes; in the first rolling of rough rolling, the reduction rate per pass is controlled at 4% to 6%; in the second rolling of rough rolling, the reduction rate per pass is controlled at 10% to 26%; in finish rolling, the reduction rate per pass is controlled at 20% to 25%. (b) Fine rolling: The slab is rolled in 5 passes to finally obtain a black sheet of the target thickness.

2. The processing method for improving surface cracks in high-strength 316L stainless steel according to claim 1, characterized in that: In step (b) of step S1, the amount of quicklime added is 1 to 2.5 tons, the amount of fluorite added is 500 to 1000 kg, and the amount of ferrosilicon added is 500 to 1000 kg.

3. The processing method for improving surface cracks in high-strength 316L stainless steel according to claim 2, characterized in that: In step (b) of step S1, the nitrogen blowing rate is 50–100 m³. 3 The electric furnace smelting time is controlled at 50-60 minutes, the electric furnace smelting temperature is controlled at 1500-1550℃, and the stirring time is controlled at 10-20 minutes.

4. The processing method for improving surface cracks in high-strength 316L stainless steel according to claim 1, characterized in that: In step (c) of step S1, during the oxidation stage, the amount of quicklime added is 10–20 tons, the amount of fluorite added is 2–4 tons, and the amount of oxygen blown in is 3000–5000 m³. 3 The nitrogen blowing rate is 2000–4000 m³. 3 The oxidation stage duration is controlled at 50-60 minutes, and the molten steel temperature is controlled at 1600-1700℃.

5. A processing method for improving surface cracks in high-strength 316L stainless steel according to claim 1 or 4, characterized in that: In step (c) of step S1, during the reduction stage, the amount of ferrosilicon added is 5–10 tons, the amount of ferromolybdenum added is 4–6 tons, the amount of ferrosilicon alloy added is 5–10 tons, and the amount of argon gas blown in is 500–1000 m³. 3 The duration of the reduction stage is controlled at 10-15 minutes, and the temperature of the molten steel is controlled at 1600-1700℃.

6. The processing method for improving surface cracks in high-strength 316L stainless steel according to claim 1, characterized in that: In step (d) of step S1, the amount of calcium thread added is 30-50 kg, and the settling time is controlled at 10-15 min.

7. The processing method for improving surface cracks in high-strength 316L stainless steel according to claim 1, characterized in that: In step S2, the first pass is rough grinding, using a 20-grit coarse grinding wheel with a grinding amount of 1 ± 0.05 mm; the second pass is fine grinding, using a 30-grit fine grinding wheel with a grinding amount of 0.5 ± 0.05 mm.

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