A smelting-rolling method for optimizing the cold upsetting performance of SAE10B33A steel

Abstract

The present application relates to the technical fields of metallurgical metal materials, and discloses a smelting-rolling method for optimizing the cold upsetting performance of SAE10B33A steel, which comprises the following steps: step 1, a smelting process; step 2, the coordinated connection of the smelting and rolling processes; and step 3, a rolling process.The step 1, the smelting process, comprises the following steps: step 1.1, pre-treatment of molten iron; step 1.2, converter smelting; step 1.3, LF furnace refining; and step 1.4, continuous casting.The step 3, the rolling process, comprises the following steps: step 3.1, slow cooling treatment of the casting blank; step 3.2, blank heating; step 3.3, high-pressure water descaling; step 3.4, wire rod rolling; step 3.5, post-rolling controlled cooling; and step 3.6, online defect detection and judgment.The method can reduce the original defects of the casting blank, reduce the proportion of surface cracks of the finished product, reduce the free nitrogen content of the molten steel by controlling the continuous casting pouring, the drawing speed and the cooling parameters, and reduce the generation of longitudinal cracks and subcutaneous pinholes on the surface of the casting blank.The wire rod after rolling is detected by a thermal eye, and the transmission of the casting blank defects to the finished product is controlled.

Description

Technical Field

[0001] This invention relates to the field of metallurgical materials technology, specifically to a smelting-rolling method for optimizing the cold heading performance of SAE10B33A steel. Background Technology

[0002] Medium-carbon boron-containing cold heading steel SAE10B33A relies on boron to improve hardenability and has controllable production costs. It is a core raw material for fastener manufacturers producing high-strength bolts and nuts, and is widely used in the production of high-end fasteners in the automotive, machinery, and construction industries, with the industry's annual demand remaining at a high level. This type of steel requires pickling, wire drawing, and large deformation cold heading, with clear requirements for the surface quality, internal structure uniformity, and cold heading performance of the wire rod. The industry standard is that the wire rod has no obvious surface cracks, banded structure ≤2 grade, and no cracking during 1 / 4 cold heading upsetting.

[0003] In conventional industrial production, SAE10B33A exhibits common quality issues in the smelting and rolling processes. Continuous casting is prone to surface longitudinal cracks and subcutaneous pinholes, some of which are quite deep and accompanied by decarburization and oxidation. These original defects in the cast billet can be transferred to the finished wire rod during rolling. Simultaneously, steel produced by conventional processes tends to have a higher banded microstructure grade, making it prone to cracking during cold heading and forging, resulting in cold heading performance that fails to meet application requirements. In downstream processing, fasteners made from this type of wire rod are prone to batch cracking, affecting product performance.

[0004] The core causes of these problems are: fluctuations in casting speed and uneven distribution of secondary cooling during continuous casting; high nitrogen content in molten steel leading to precipitates at grain boundaries and reducing the surface quality of the billet; and insufficient matching between steel composition and rolling process, resulting in excessive banding structure which further reduces cold heading performance. Conventional production processes struggle to control the transfer of billet defects to the finished product and cannot optimize internal microstructure uniformity, making it difficult to meet the requirements for large-scale production and stable use of high-end fasteners. Therefore, it is necessary to optimize the corresponding smelting and rolling methods. Summary of the Invention

[0005] (a) Technical problems to be solved To address the shortcomings of existing technologies, this invention provides a smelting-rolling method for optimizing the cold heading performance of SAE10B33A steel. This method has advantages such as reducing the original defects of the billet and lowering the proportion of surface cracks in the finished product, and solves the problems of surface longitudinal cracks and subcutaneous pinhole defects.

[0006] (II) Technical Solution To achieve the above-mentioned goals of reducing the original defects of the billet and lowering the proportion of surface cracks in the finished product, the present invention provides the following technical solution: a smelting-rolling method for optimizing the cold heading performance of SAE10B33A steel, comprising step 1: smelting process, step 2: synergistic connection of smelting and rolling processes, and step 3: rolling process. The smelting process in step 1 includes step 1.1: hot metal pretreatment, step 1.2: converter smelting, step 1.3: LF furnace refining, and step 1.4: continuous casting forming. Step 3: Rolling process includes Step 3.1: Slow cooling treatment of billet, Step 3.2: Billet heating, Step 3.3: High-pressure water descaling, Step 3.4: Wire rolling, Step 3.5: Post-rolling controlled cooling and Step 3.6: Online defect detection and judgment.

[0007] Preferably, step 1.1 involves pretreatment of molten iron. The molten iron from the blast furnace is introduced into a desulfurization pretreatment tank, and a magnesium-based composite desulfurizing agent is injected into the molten iron. The injection pressure is controlled at 0.3~0.5MPa, and the mixture is continuously stirred for 8~12 minutes. After stirring, the mixture is allowed to stand for 5 minutes, and the desulfurization slag on the surface of the molten iron is thoroughly removed with a slag remover until no slag is exposed. The sulfur content of the molten iron is sampled and tested to ensure that the final sulfur content is ≤0.012wt%. Any unqualified molten iron is returned to the tank for reprocessing.

[0008] Preferably, step 1.2 involves converter smelting; The feed should be prepared according to a molten iron consumption of ≥810kg / t, the proportion of scrap steel should be reduced, and the surface of scrap steel should be derusted and impurities removed in advance. The converter adopts a top and bottom combined blowing process. Iron ore is added in 2 to 3 batches during the blowing process, with each batch containing 500 to 800 kg, to help reduce carbon and nitrogen emissions. Precise temperature control is required at the end of the blowing process, with an endpoint temperature of 1610~1630℃ and an endpoint carbon content of ≥0.055wt%. Overblowing with low carbon content is strictly prohibited. When tapping steel, the slag-blocking plug and slag-blocking cap are opened simultaneously. When the steel is tapped to 1 / 3 full, the slag detection is turned off to prevent slag from entering the ladle. The tapping time is controlled within 3 to 5 minutes.

[0009] Preferably, step 1.3 involves refining in an LF furnace; After the ladle is placed in the LF station, lime and pre-melted slag are added to form slag. The temperature is raised by electricity for 3-5 minutes. After the slag melts, the basicity is adjusted to 3.0-5.2 to maintain the white slag state (FeO≤1.0%). Add the alloy precisely according to the composition range: first add ferromanganese and ferrosilicon to adjust the basic composition, then add ferrotitanium (0.018~0.062wt%) to fix nitrogen, and finally add ferroboron at the end of refining, controlling the boron content to 0.0014~0.0026wt%, and stir evenly throughout the process. In the later stage of refining, pure calcium wire is fed in at a rate of 150~200m / min for 140~160m / furnace. After the wire is fed, argon gas is gently blown in for ≥14min. The argon gas flow rate is controlled at 50~80L / min to ensure that the inclusions float to the surface. Gases and components are sampled and tested to ensure that free nitrogen is ≤50ppm, the outlet temperature is 1550~1580℃, and the temperature fluctuation is ≤±5℃. After passing the test, the steel ladle is hoisted out.

[0010] Preferably, step 1.4 involves continuous casting. Full-process protective pouring: The ladle is covered and sealed, and an asbestos gasket is installed between the long nozzle and the ladle outlet for sealing. Argon gas purging is started simultaneously (flow rate 30~50L / min); a covering agent + carbonized rice husks are spread inside the tundish, with a thickness of 30~50mm, to prevent the molten steel from being exposed. The intermediate ladle should be preheated for more than 4 hours, with an inner wall temperature ≥1000℃. It should be purged with argon gas before pouring. The superheat of the intermediate ladle should be controlled at 20~38℃, and the liquid level should be stable at ≥600mm. The crystallizer uses large-beveled copper tubes. After installation, the water flow rate is adjusted to 108~114t / h, the vibration frequency is set to 28~32 times / min, the amplitude is 0.24~0.28mm, and the negative slip time is controlled at 0.07~0.09s. Add medium carbon steel special protective slag evenly into the crystallizer, maintain the slag layer thickness at 10-15mm, and replenish it every 5 minutes to avoid the slag layer being exposed; The pulling speed is dynamically adjusted according to the superheat: when the superheat is <20℃, the pulling speed is 2.2~2.6m / min; when the superheat is >20℃, the pulling speed is 1.7~2.1m / min. The pulling speed is constant throughout the process, and the liquid level fluctuation in the crystallizer is controlled at ±3~±6mm. The secondary cooling process employs a weak cooling technique, automatically adjusting the specific water volume to 0.26~0.62L / kg, optimizing the nozzle angle, and adjusting the water volume at the corners to 80%~85% of that at the center. After the billet is cut to length, the unsteady billets in the pouring section, ladle changing section, and liquid level fluctuation section are cut and removed separately, with each section having a cut length of ≥10m. Qualified billets are then hoisted to the slow cooling area.

[0011] Preferably, step 2 involves the coordinated integration of smelting and rolling processes; Smelting is the source of quality, while rolling solidifies performance. The two are seamlessly connected through billet transfer, defect control, microstructure regulation, stress release, and parameter matching, resulting in no quality gaps. Defect inheritance closed loop connection: Smelting eliminates original cracks, pinholes and decarburization defects in the billet through weak cooling, constant pulling speed and large chamfer crystallizer, thus preventing defect inheritance from the source; rolling removes minor defects left over from smelting through high-pressure water descaling and hot-eye online detection, forming a closed loop of "source control of defects - process elimination of defects - finished product without defects"; Synergistic integration of microstructure and performance: Smelting refines the grain size of the billet and reduces the tendency of banded structure through component ratio and electromagnetic stirring; Rolling optimizes the original microstructure of the billet into uniform ferrite + pearlite through controlled rolling and controlled cooling and segmented weak cooling, and stabilizes the banded structure to level ≤2, which directly improves cold heading plasticity; Internal stress release connection: After the smelting billet comes off the production line, it is immediately cooled slowly to release the solidification stress. The rolling process adopts segmented low temperature homogenization to avoid the superposition of heating stress and billet residual stress and prevent crack initiation during rolling and cold heading processes. Purity-Deformation Capacity Connection: Smelting reduces inclusions and gas content through calcium treatment, soft blowing, and protective casting, thereby improving the plasticity of the steel; Rolling adopts twist-free uniform deformation and U-shaped roll forming, allowing the high plasticity imparted by smelting to be fully utilized in cold heading with large deformation; Precise matching of process parameters: smelting uniform billets with low superheat and constant casting speed is matched with low temperature rolling and slow cooling processes; smelting high-purity steel billets is matched with high-precision rolling forming, with all process parameters corresponding one-to-one.

[0012] Preferably, step 3.1 involves slow cooling of the cast billet; Qualified continuous casting billets are hoisted to the slow cooling pit by overhead crane and stacked neatly according to the furnace number, with a 50-80mm gap between each pile. After all the billets are in the pit, they are completely covered and sealed with insulation cotton. The temperature inside the pit is controlled at 600-700℃, and the slow cooling time is ≥28h. After the slow cooling is completed, the temperature is measured to ≤200℃ before being hoisted to the rolling billet area. It is forbidden to directly load the billet into the furnace at high temperature.

[0013] Preferably, step 3.2 involves heating the billet. A walking beam furnace is used, and the billets are loaded into the furnace in batches according to the furnace number, with a spacing of 80~100mm between them to avoid stacking during heating; Precise temperature control in three stages: preheating stage temperature ≤660℃, heating time 25~30min; heating stage temperature 1100~1130℃, heating time 30~35min; heat spread stage temperature 1080~1110℃, heat spread time 30~40min. The billet should be in the furnace for a total time of ≥85 minutes. Temperature should be measured before it is removed from the furnace to ensure that the overall temperature difference of the billet is ≤±30℃. It should be removed from the furnace after being uniformly fired.

[0014] Preferably, step 3.3 involves high-pressure water descaling; After the billet exits the furnace, it immediately enters the descaling box at the roughing mill inlet. High-pressure water descaling is started, with the pressure adjusted to ≥18MPa and the descaling speed at 1.0~1.5m / s. The descaling is repeated twice to completely remove the iron oxide scale from the surface. The intermediate rolling section adopts descaling rolling, and the roll gap is adjusted in advance to be 0.2~0.3mm smaller than that of conventional rolling. The residual iron oxide scale is further broken up by rolling pressure to avoid pressing into the billet and forming defects.

[0015] Preferably, step 3.4 involves wire rolling; The process employs a twist-free high-speed rolling technology, with each stage of the roughing, intermediate, pre-finishing, and finishing mills compressing the material, and the total compression ratio is controlled between 80 and 120 to ensure uniform deformation. Replace all U-shaped rolls on the rolling mill. After installation, adjust the roll gap accuracy to ≤ ±0.05mm to reduce scratches on the wire rod surface. Real-time monitoring of the final rolling temperature; by adjusting the mill speed and the water volume in the water cooling section, the final rolling temperature is controlled at 880~920℃; if the temperature exceeds the standard, the speed is immediately reduced and the temperature is lowered. Step 3.5: Post-rolling controlled cooling; After the wire is precision rolled, it enters the wire spinning machine. The speed and temperature of the wire spinning machine are adjusted to control the spinning temperature at 890~910℃. The wire rod enters the Stellmore cooling line, where the fan air volume and roller speed are adjusted in stages: the roller speed in the first stage is 0.14~0.16m / s, and the fan air volume is adjusted to 60%~70%; the fan air volume in the second stage is adjusted to 30%~40% to slow down the cooling rate. After cooling, the wire rods are allowed to air-cool to room temperature before being coiled and bundled. The bundling pressure is controlled at 7 to 12 tons to avoid scratching the wire rods. Step 3.6: Online defect detection and judgment; Before the wire rods are coiled, they are scanned one by one by a thermal online inspection device to detect surface cracks, scars, pits and other defects, and the location of the defects is automatically marked. Billets with long surface cracks and a depth > 0.5 mm are directly cut and rejected; billets with short cracks are sampled and acid-washed for verification, and only those that pass the verification can proceed to the next process. Finished products are sampled according to furnace number and subjected to 1 / 3, 1 / 4, and 1 / 5 cold forging tests, banded structure rating, decarburized layer detection, and inclusion rating in sequence. Once all tests are qualified, the products are put into storage, and unqualified products are isolated and treated as whole furnaces.

[0016] (III) Beneficial Effects Compared with the prior art, the present invention provides a smelting-rolling method for optimizing the cold heading performance of SAE10B33A steel, which has the following beneficial effects: 1. The smelting-rolling method for optimizing the cold heading performance of SAE10B33A steel reduces the original defects of the billet and the proportion of surface cracks in the finished product. By controlling the continuous casting pouring, casting speed, and cooling parameters, the free nitrogen content in the molten steel is reduced, thereby reducing the generation of longitudinal cracks and subcutaneous pinholes on the billet surface. After rolling, the wire rod is inspected by hot-eye, and the crack rejection rate is reduced to below 1%, the surface defect depth is controlled within 0.1 mm, and the transmission of billet defects to the finished product is controlled.

[0017] 2. The smelting-rolling method for optimizing the cold heading performance of SAE10B33A steel improves the cold heading processing performance and adapts to the processing requirements of large deformation. By precisely controlling the steel composition and cooperating with the cooling process after rolling, the strip structure of the wire rod is controlled to level 2 or below, and the grain size reaches level 10 or above. The qualified upsetting ratio of 1 / 4 cold heading of wire rod is increased to over 98%, and there are no straight or oblique cracks during processing. It can meet the processing requirements of large deformation cold heading and cold extrusion of high-strength fasteners.

[0018] 3. The smelting-rolling method for optimizing the cold heading performance of SAE10B33A steel optimizes the internal structure and improves the stability of product performance. Through full-process temperature control, descaling treatment and rolling processing, the internal structure of the wire rod is uniform ferrite + pearlite, the decarburized layer thickness is controlled within 0.05mm, and the non-metallic inclusion rating is ≤1.0. The hardness fluctuation range of the wire rod is controlled within ±2HRB, and the mechanical property data dispersion is small, making it suitable for mass production of fasteners.

[0019] 4. The smelting-rolling method for optimizing the cold heading performance of SAE10B33A steel stabilizes product quality, reduces the failure rate during customer use, and ensures that all parameters of smelting and rolling are matched to each other, forming a complete quality control process from billet production to finished product rolling. The cold heading performance, banded structure, and decarburized layer indicators of the finished product all meet the requirements. During customer use, the failure rate of bolt cracking has been reduced from 8‰ to below 0.5‰, which can meet the supply requirements of large fastener companies. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0021] This solution provides a technical approach, specifically a smelting-rolling method for optimizing the cold heading performance of SAE10B33A steel, comprising the following steps: Step 1: Smelting process; (including detailed operations throughout the entire process). Step 1.1: Hot metal pretreatment; The molten iron from the blast furnace is introduced into a desulfurization pretreatment tank, and a magnesium-based composite desulfurizing agent is injected into the molten iron. The injection pressure is controlled at 0.3~0.5MPa, and the mixture is continuously stirred for 8~12 minutes. After stirring, the mixture is allowed to stand for 5 minutes. The desulfurization slag on the surface of the molten iron is then thoroughly removed with a slag remover until no slag is exposed. The sulfur content of the molten iron is sampled and tested to ensure that the final sulfur content is ≤0.012wt%. Any unqualified molten iron is returned to the tank for reprocessing. Step 1.2: Converter smelting; The feed should be prepared according to a molten iron consumption of ≥810kg / t, the proportion of scrap steel should be reduced, and the surface of scrap steel should be derusted and impurities removed in advance. The converter adopts a top and bottom combined blowing process. Iron ore is added in 2 to 3 batches during the blowing process, with each batch containing 500 to 800 kg, to help reduce carbon and nitrogen emissions. Precise temperature control is required at the end of the blowing process, with an endpoint temperature of 1610~1630℃ and an endpoint carbon content of ≥0.055wt%. Overblowing with low carbon content is strictly prohibited. When tapping steel, the slag-blocking plug and slag-blocking cap are opened simultaneously. When the steel is tapped to 1 / 3 of its length, the slag detection is closed to prevent slag from entering the ladle. The tapping time is controlled within 3 to 5 minutes. Step 1.3: LF furnace refining; After the ladle is placed in the LF station, lime and pre-melted slag are added to form slag. The temperature is raised by electricity for 3-5 minutes. After the slag melts, the basicity is adjusted to 3.0-5.2 to maintain the white slag state (FeO≤1.0%). Add the alloy precisely according to the composition range: first add ferromanganese and ferrosilicon to adjust the basic composition, then add ferrotitanium (0.018~0.062wt%) to fix nitrogen, and finally add ferroboron at the end of refining, controlling the boron content to 0.0014~0.0026wt%, and stir evenly throughout the process. In the later stage of refining, pure calcium wire is fed in at a rate of 150~200m / min for 140~160m / furnace. After the wire is fed, argon gas is gently blown in for ≥14min. The argon gas flow rate is controlled at 50~80L / min to ensure that the inclusions float to the surface. Sampling and testing of gas and composition, ensuring free nitrogen ≤50ppm, outlet temperature 1550~1580℃, temperature fluctuation ≤±5℃, and steel ladle is hoisted out after passing the test; Step 1.4: Continuous casting; Full-process protective pouring: The ladle is covered and sealed, and an asbestos gasket is installed between the long nozzle and the ladle outlet for sealing. Argon gas purging is started simultaneously (flow rate 30~50L / min); a covering agent + carbonized rice husks are spread inside the tundish, with a thickness of 30~50mm, to prevent the molten steel from being exposed. The intermediate ladle should be preheated for more than 4 hours, with an inner wall temperature ≥1000℃. It should be purged with argon gas before pouring. The superheat of the intermediate ladle should be controlled at 20~38℃, and the liquid level should be stable at ≥600mm. The crystallizer uses large-beveled copper tubes. After installation, the water flow rate is adjusted to 108~114t / h, the vibration frequency is set to 28~32 times / min, the amplitude is 0.24~0.28mm, and the negative slip time is controlled at 0.07~0.09s. Add medium carbon steel special protective slag evenly into the crystallizer, maintain the slag layer thickness at 10-15mm, and replenish it every 5 minutes to avoid the slag layer being exposed; The pulling speed is dynamically adjusted according to the superheat: when the superheat is <20℃, the pulling speed is 2.2~2.6m / min; when the superheat is >20℃, the pulling speed is 1.7~2.1m / min. The pulling speed is constant throughout the process, and the liquid level fluctuation in the crystallizer is controlled at ±3~±6mm. The secondary cooling process employs a weak cooling technique, automatically adjusting the specific water volume to 0.26~0.62L / kg, optimizing the nozzle angle, and adjusting the water volume at the corners to 80%~85% of that at the center. After the billet is cut to length, the unstable billets in the pouring section, ladle changing section, and liquid level fluctuation section are cut and removed separately, with each section having a cut length of ≥10m. Qualified billets are then hoisted to the slow cooling area. Step 2: Coordinated integration of smelting and rolling processes; (closed-loop connection throughout the entire process) Smelting is the source of quality, while rolling solidifies performance. The two are seamlessly connected through billet transfer, defect control, microstructure regulation, stress release, and parameter matching, resulting in no quality gaps. Defect inheritance closed loop connection: Smelting eliminates original cracks, pinholes and decarburization defects in the billet through weak cooling, constant pulling speed and large chamfer crystallizer, thus preventing defect inheritance from the source; rolling removes minor defects left over from smelting through high-pressure water descaling and hot-eye online detection, forming a closed loop of "source control of defects - process elimination of defects - finished product without defects"; Synergistic integration of microstructure and performance: Smelting refines the grain size of the billet and reduces the tendency of banded structure through component ratio and electromagnetic stirring; Rolling optimizes the original microstructure of the billet into uniform ferrite + pearlite through controlled rolling and controlled cooling and segmented weak cooling, and stabilizes the banded structure to level ≤2, which directly improves cold heading plasticity; Internal stress release connection: After the smelting billet comes off the production line, it is immediately cooled slowly to release the solidification stress. The rolling process adopts segmented low temperature homogenization to avoid the superposition of heating stress and billet residual stress and prevent crack initiation during rolling and cold heading processes. Purity-Deformation Capacity Connection: Smelting reduces inclusions and gas content through calcium treatment, soft blowing, and protective casting, thereby improving the plasticity of the steel; Rolling adopts twist-free uniform deformation and U-shaped roll forming, allowing the high plasticity imparted by smelting to be fully utilized in cold heading with large deformation; Precise matching of process parameters: smelting uniform billets with low superheat and constant casting speed is matched with low temperature rolling and slow cooling processes; smelting high-purity steel billets is matched with high-precision rolling forming, with all process parameters corresponding one-to-one. Step 3: Rolling process; (including detailed operation of the entire process) Step 3.1: Slow cooling treatment of the cast billet; Qualified continuous casting billets are hoisted to the slow cooling pit by overhead crane and stacked neatly according to the furnace number, with a 50-80mm gap between each pile. After all the billets are in the pit, they are completely covered and sealed with insulation cotton. The temperature inside the pit is controlled at 600-700℃, and the slow cooling time is ≥28h. After the slow cooling is completed, the temperature is measured to ≤200℃ before being hoisted to the rolling billet area. It is forbidden to directly load the furnace at high temperature. Step 3.2: Heating the billet; A walking beam furnace is used, and the billets are loaded into the furnace in batches according to the furnace number, with a spacing of 80~100mm between them to avoid stacking during heating; Precise temperature control in three stages: preheating stage temperature ≤660℃, heating time 25~30min; heating stage temperature 1100~1130℃, heating time 30~35min; heat spread stage temperature 1080~1110℃, heat spread time 30~40min. The total time the billet spends in the furnace is ≥85 minutes. The temperature is measured before the billet is removed from the furnace to ensure that the overall temperature difference of the billet is ≤±30℃. The billet is removed from the furnace after being uniformly fired. Step 3.3: High-pressure water descaling; After the billet exits the furnace, it immediately enters the descaling box at the roughing mill inlet. High-pressure water descaling is started, with the pressure adjusted to ≥18MPa and the descaling speed at 1.0~1.5m / s. The descaling is repeated twice to completely remove the iron oxide scale from the surface. The intermediate rolling section adopts descaling rolling, and the roll gap is adjusted in advance to be 0.2~0.3mm smaller than that of conventional rolling. The residual iron oxide scale is further broken up by rolling pressure to avoid pressing into the billet and forming defects. Step 3.4: Wire rolling; The process employs a twist-free high-speed rolling technology, with each stage of the roughing, intermediate, pre-finishing, and finishing mills compressing the material, and the total compression ratio is controlled between 80 and 120 to ensure uniform deformation. Replace all U-shaped rolls on the rolling mill. After installation, adjust the roll gap accuracy to ≤ ±0.05mm to reduce scratches on the wire rod surface. Real-time monitoring of the final rolling temperature; by adjusting the mill speed and the water volume in the water cooling section, the final rolling temperature is controlled at 880~920℃; if the temperature exceeds the standard, the speed is immediately reduced and the temperature is lowered. Step 3.5: Post-rolling controlled cooling; After the wire is precision rolled, it enters the wire spinning machine. The speed and temperature of the wire spinning machine are adjusted to control the spinning temperature at 890~910℃. The wire rod enters the Stellmore cooling line, where the fan air volume and roller speed are adjusted in stages: the roller speed in the first stage is 0.14~0.16m / s, and the fan air volume is adjusted to 60%~70%; the fan air volume in the second stage is adjusted to 30%~40% to slow down the cooling rate. After cooling, the wire rods are allowed to air-cool to room temperature before being coiled and bundled. The bundling pressure is controlled at 7 to 12 tons to avoid scratching the wire rods. Step 3.6: Online defect detection and judgment; Before the wire rods are coiled, they are scanned one by one by a thermal online inspection device to detect surface cracks, scars, pits and other defects, and the location of the defects is automatically marked. Billets with long surface cracks and a depth > 0.5 mm are directly cut and rejected; billets with short cracks are sampled and acid-washed for verification, and only those that pass the verification can proceed to the next process. Finished products are sampled according to furnace number and subjected to 1 / 3, 1 / 4, and 1 / 5 cold heading and upsetting tests, banded structure rating, decarburized layer detection, and inclusion rating in sequence. Once all tests are qualified, the products are put into storage, and unqualified products are isolated and treated as whole furnaces. Furthermore, this method reduces the original defects of the billet and lowers the proportion of surface cracks in the finished product. By controlling the continuous casting pouring, casting speed, and cooling parameters, the free nitrogen content in the molten steel is reduced, thus reducing the generation of longitudinal cracks and subcutaneous pinholes on the billet surface. After rolling, the wire rod is inspected by hot-eye testing, and the crack rejection rate is reduced to below 1%, the surface defect depth is controlled within 0.1 mm, and the transmission of billet defects to the finished product is controlled. Furthermore, this method improves the cold heading performance and adapts to the processing requirements of large deformation. By precisely controlling the steel composition and cooperating with the cooling process after rolling, the strip structure of the wire rod is controlled to level 2 or below, and the grain size reaches level 10 or above. The qualified upsetting ratio of 1 / 4 cold heading of wire rod is increased to over 98%, and there are no straight or oblique cracks during the processing. It can meet the processing requirements of large deformation cold heading and cold extrusion of high-strength fasteners. Furthermore, this method optimizes the internal structure and improves the stability of product performance. Through full-process temperature control, descaling and rolling, the internal structure of the wire rod is uniform ferrite + pearlite, the decarburized layer thickness is controlled within 0.05mm, and the non-metallic inclusion rating is ≤1.0. The hardness fluctuation range of the wire rod is controlled within ±2HRB, and the mechanical property data dispersion is small, making it suitable for mass production of fasteners. Furthermore, this method stabilizes product quality, reduces the failure rate during customer use, and ensures that various parameters of smelting and rolling are matched with each other, forming a complete quality control process from billet production to finished product rolling. The cold heading performance, banded structure, and decarburization layer indicators of the finished product all meet the requirements. During customer use, the failure rate of bolt cracking has been reduced from 8‰ to below 0.5‰, which can meet the supply requirements of large fastener companies.

[0022] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A smelting-rolling method for optimizing the cold heading performance of SAE10B33A steel, comprising step 1: smelting process, step 2: synergistic connection of smelting and rolling processes, and step 3: rolling process, characterized in that: Step 1: The smelting process includes Step 1.1: Hot metal pretreatment, Step 1.2: Converter smelting, Step 1.3: LF furnace refining and Step 1.4: Continuous casting. Step 3: Rolling process includes Step 3.1: Slow cooling treatment of billet, Step 3.2: Billet heating, Step 3.3: High-pressure water descaling, Step 3.4: Wire rolling, Step 3.5: Post-rolling controlled cooling and Step 3.6: Online defect detection and judgment.

2. The smelting-rolling method for optimizing the cold heading performance of SAE10B33A steel according to claim 1, characterized in that: Step 1.1: Hot metal pretreatment; The molten iron from the blast furnace is introduced into a desulfurization pretreatment tank, and a magnesium-based composite desulfurizing agent is injected into the molten iron. The injection pressure is controlled at 0.3~0.5MPa, and the mixture is continuously stirred for 8~12 minutes. After stirring, the mixture is allowed to stand for 5 minutes, and the desulfurization slag on the surface of the molten iron is thoroughly removed with a slag remover until no slag is exposed. The sulfur content of the molten iron is sampled and tested to ensure that the final sulfur content is ≤0.012wt%. Any unqualified molten iron is returned to the tank for reprocessing.

3. The smelting-rolling method for optimizing the cold heading performance of SAE10B33A steel according to claim 1, characterized in that: Step 1.2: Converter smelting; The feed should be prepared according to a molten iron consumption of ≥810kg / t, the proportion of scrap steel should be reduced, and the surface of scrap steel should be derusted and impurities removed in advance. The converter adopts a top and bottom combined blowing process. Iron ore is added in 2 to 3 batches during the blowing process, with each batch containing 500 to 800 kg, to help reduce carbon and nitrogen emissions. Precise temperature control is required at the end of the blowing process, with an endpoint temperature of 1610~1630℃ and an endpoint carbon content of ≥0.055wt%. Overblowing with low carbon content is strictly prohibited. When tapping steel, the slag-blocking plug and slag-blocking cap are opened simultaneously. When the steel is tapped to 1 / 3 full, the slag detection is turned off to prevent slag from entering the ladle. The tapping time is controlled within 3 to 5 minutes.

4. The smelting-rolling method for optimizing the cold heading performance of SAE10B33A steel according to claim 1, characterized in that: Step 1.3: LF furnace refining; After the ladle is placed in the LF station, lime and pre-melted slag are added to form slag. The temperature is raised by electricity for 3-5 minutes. After the slag melts, the basicity is adjusted to 3.0-5.2 to maintain the white slag state (FeO≤1.0%). Add the alloy precisely according to the composition range: first add ferromanganese and ferrosilicon to adjust the basic composition, then add ferrotitanium (0.018~0.062wt%) to fix nitrogen, and finally add ferroboron at the end of refining, controlling the boron content to 0.0014~0.0026wt%, and stir evenly throughout the process. In the later stage of refining, pure calcium wire is fed in at a rate of 150~200m / min for 140~160m / furnace. After the wire is fed, argon gas is gently blown in for ≥14min. The argon gas flow rate is controlled at 50~80L / min to ensure that the inclusions float to the surface. Gases and components are sampled and tested to ensure that free nitrogen is ≤50ppm, the outlet temperature is 1550~1580℃, and the temperature fluctuation is ≤±5℃. After passing the test, the steel ladle is hoisted out.

5. The smelting-rolling method for optimizing the cold heading performance of SAE10B33A steel according to claim 1, characterized in that: Step 1.4: Continuous casting; Full-process protective pouring: The ladle is covered and sealed, and an asbestos gasket is installed between the long nozzle and the ladle outlet for sealing. Argon gas purging is started simultaneously (flow rate 30~50L / min); a covering agent + carbonized rice husks are spread inside the tundish, with a thickness of 30~50mm, to prevent the molten steel from being exposed. The intermediate ladle should be preheated for more than 4 hours, with an inner wall temperature ≥1000℃. It should be purged with argon gas before pouring. The superheat of the intermediate ladle should be controlled at 20~38℃, and the liquid level should be stable at ≥600mm. The crystallizer uses large-beveled copper tubes. After installation, the water flow rate is adjusted to 108~114t / h, the vibration frequency is set to 28~32 times / min, the amplitude is 0.24~0.28mm, and the negative slip time is controlled at 0.07~0.09s. Add medium carbon steel special protective slag evenly into the crystallizer, maintain the slag layer thickness at 10-15mm, and replenish it every 5 minutes to avoid the slag layer being exposed; The pulling speed is dynamically adjusted according to the superheat: when the superheat is <20℃, the pulling speed is 2.2~2.6m / min; when the superheat is >20℃, the pulling speed is 1.7~2.1m / min. The pulling speed is constant throughout the process, and the liquid level fluctuation in the crystallizer is controlled at ±3~±6mm. The secondary cooling process employs a weak cooling technique, automatically adjusting the specific water volume to 0.26~0.62L / kg, optimizing the nozzle angle, and adjusting the water volume at the corners to 80%~85% of that at the center. After the billet is cut to length, the unsteady billets in the pouring section, ladle changing section, and liquid level fluctuation section are cut and removed separately, with each section having a cut length of ≥10m. Qualified billets are then hoisted to the slow cooling area.

6. The smelting-rolling method for optimizing the cold heading performance of SAE10B33A steel according to claim 1, characterized in that: Step 2: Coordination and integration of smelting and rolling processes; Smelting is the source of quality, while rolling solidifies performance. The two are seamlessly connected through billet transfer, defect control, microstructure regulation, stress release, and parameter matching, resulting in no quality gaps. Defect inheritance closed loop connection: Smelting eliminates original cracks, pinholes and decarburization defects in the billet through weak cooling, constant pulling speed and large chamfer crystallizer, thus preventing defect inheritance from the source; rolling removes minor defects left over from smelting through high-pressure water descaling and hot-eye online detection, forming a closed loop of "source control of defects - process elimination of defects - finished product without defects"; Synergistic integration of microstructure and performance: Smelting refines the grain size of the billet and reduces the tendency of banded structure through component ratio and electromagnetic stirring; Rolling optimizes the original microstructure of the billet into uniform ferrite + pearlite through controlled rolling and controlled cooling and segmented weak cooling, and stabilizes the banded structure to level ≤2, which directly improves cold heading plasticity; Internal stress release connection: After the smelting billet comes off the production line, it is immediately cooled slowly to release the solidification stress. The rolling process adopts segmented low temperature homogenization to avoid the superposition of heating stress and billet residual stress and prevent crack initiation during rolling and cold heading processes. Purity-Deformation Capacity Connection: Smelting reduces inclusions and gas content through calcium treatment, soft blowing, and protective casting, thereby improving the plasticity of the steel; Rolling adopts twist-free uniform deformation and U-shaped roll forming, allowing the high plasticity imparted by smelting to be fully utilized in cold heading with large deformation; Precise matching of process parameters: smelting uniform billets with low superheat and constant casting speed is matched with low temperature rolling and slow cooling processes; smelting high-purity steel billets is matched with high-precision rolling forming, with all process parameters corresponding one-to-one.

7. The smelting-rolling method for optimizing the cold heading performance of SAE10B33A steel according to claim 1, characterized in that: Step 3.1: Slow cooling treatment of the cast billet; Qualified continuous casting billets are hoisted to the slow cooling pit by overhead crane and stacked neatly according to the furnace number, with a 50-80mm gap between each pile. After all the billets are in the pit, they are completely covered and sealed with insulation cotton. The temperature inside the pit is controlled at 600-700℃, and the slow cooling time is ≥28h. After the slow cooling is completed, the temperature is measured to ≤200℃ before being hoisted to the rolling billet area. It is forbidden to directly load the billet into the furnace at high temperature.

8. The smelting-rolling method for optimizing the cold heading performance of SAE10B33A steel according to claim 1, characterized in that: Step 3.2: Heating the billet; A walking beam furnace is used, and the billets are loaded into the furnace in batches according to the furnace number, with a spacing of 80~100mm between them to avoid stacking during heating; Precise temperature control in three stages: preheating stage temperature ≤660℃, heating time 25~30min; heating stage temperature 1100~1130℃, heating time 30~35min; heat spread stage temperature 1080~1110℃, heat spread time 30~40min. The billet should be in the furnace for a total time of ≥85 minutes. Temperature should be measured before it is removed from the furnace to ensure that the overall temperature difference of the billet is ≤±30℃. It should be removed from the furnace after being uniformly fired.

9. The smelting-rolling method for optimizing the cold heading performance of SAE10B33A steel according to claim 1, characterized in that: Step 3.3: High-pressure water descaling; After the billet exits the furnace, it immediately enters the descaling box at the roughing mill inlet. High-pressure water descaling is started, with the pressure adjusted to ≥18MPa and the descaling speed at 1.0~1.5m / s. The descaling is repeated twice to completely remove the iron oxide scale from the surface. The intermediate rolling section adopts descaling rolling, and the roll gap is adjusted in advance to be 0.2~0.3mm smaller than that of conventional rolling. The residual iron oxide scale is further broken up by rolling pressure to avoid pressing into the billet and forming defects.

10. The smelting-rolling method for optimizing the cold heading performance of SAE10B33A steel according to claim 1, characterized in that: Step 3.4: Wire rolling; The process employs a twist-free high-speed rolling technology, with each stage of the roughing, intermediate, pre-finishing, and finishing mills compressing the material, and the total compression ratio is controlled between 80 and 120 to ensure uniform deformation. Replace all U-shaped rolls on the rolling mill. After installation, adjust the roll gap accuracy to ≤ ±0.05mm to reduce scratches on the wire rod surface. Real-time monitoring of the final rolling temperature; by adjusting the mill speed and the water volume in the water cooling section, the final rolling temperature is controlled at 880~920℃; if the temperature exceeds the standard, the speed is immediately reduced and the temperature is lowered. Step 3.5: Post-rolling controlled cooling; After the wire is precision rolled, it enters the wire spinning machine. The speed and temperature of the wire spinning machine are adjusted to control the spinning temperature at 890~910℃. The wire rod enters the Stellmore cooling line, where the fan air volume and roller speed are adjusted in stages: the roller speed in the first stage is 0.14~0.16m / s, and the fan air volume is adjusted to 60%~70%; the fan air volume in the second stage is adjusted to 30%~40% to slow down the cooling rate. After cooling, the wire rods are allowed to air-cool to room temperature before being coiled and bundled. The bundling pressure is controlled at 7 to 12 tons to avoid scratching the wire rods. Step 3.6: Online defect detection and judgment; Before the wire rods are coiled, they are scanned one by one by a thermal online inspection device to detect surface cracks, scars, pits and other defects, and the location of the defects is automatically marked. Billets with long surface cracks and a depth > 0.5 mm are directly cut and rejected; billets with short cracks are sampled and acid-washed for verification, and only those that pass the verification can proceed to the next process. Finished products are sampled according to furnace number and subjected to 1 / 3, 1 / 4, and 1 / 5 cold forging tests, banded structure rating, decarburized layer detection, and inclusion rating in sequence. Once all tests are qualified, the products are put into storage, and unqualified products are isolated and treated as whole furnaces.