Clean smelting process and production process of L485M pipeline steel

Abstract

The invention relates to the technical field of pipeline steel smelting, in particular to a clean smelting process and a production process of L485M pipeline steel. The clean smelting process at least comprises the following steps that RH refining is conducted on molten steel of pipeline steel, high-temperature molten steel is used for rinsing cold steel attached to the interior of an RH vacuum tank in the first furnace before pipeline steel production, the station entering temperature of the high-temperature molten steel in the rinsing furnace is controlled to be larger than or equal to 1610 DEG C, the vacuum pressure maintaining time is controlled to be larger than or equal to 16 minutes, and a special tank special production mode is adopted after rinsing; a pure calcium wire is fed after RH vacuum breaking, precise calcium treatment is carried out on molten pipeline steel, the Ca content of the molten pipeline steel is controlled to be 0.0015%-0.0025%, and soft blowing is carried out for 12-15 minutes after wire feeding. The method is beneficial for improving the cleanliness level of the pipeline steel, improving the flaw detection qualification rate of the steel plate and improving the order product delivery speed.

Description

Technical Field

[0001] The present invention relates to the technical field of pipeline steel smelting, and in particular to a clean smelting process and a production process of L485M pipeline steel. Background Art

[0002] Pipeline steel undergoes approximately 5-7 rounds of flaw detection during the manufacturing process. Furthermore, during pipeline construction, the steel is re-inspected within 100 mm of both ends using specialized flaw detection equipment such as phased array or TOFT. Stringent quality requirements are in place. Previously produced pipeline steel experienced quality issues, and sampling and analysis often revealed excessive levels of Class B and Class D inclusions, resulting in flaw detection results that failed to meet acceptance standards. Because aluminum (Al) is a highly deoxidizing and cost-effective metallic element, it is currently used in steelmaking as the primary and final deoxidizing element. Consequently, the primary goal of RH refining, soft blowing, and continuous casting processes is to promote the flotation of aluminum deoxidation products into the slag. Despite various process optimization measures, the removal rate of alumina and calcium aluminate inclusions remains unstable due to numerous influencing factors.

[0003] CN118291708A discloses a smelting method for hydrogen pipeline steel, comprising: performing KR desulfurization on molten iron and controlling the endpoint sulfur content of the KR desulfurization, then performing a slag skimming operation and controlling the slag skimming rate of the slag skimming operation to obtain a first molten steel; performing converter smelting on the first molten steel, performing slag dephosphorization by a double slag method in the converter smelting, controlling the process parameters of the slag dephosphorization, and then tapping the steel, taking a slag blocking operation and adding slag during the tapping, and controlling the process parameters of the slag to obtain a second molten steel; performing LF refining on the second molten steel and controlling the process parameters of the slag desulfurization stage of the LF refining to obtain a third molten steel; performing VD vacuum refining on the third molten steel and controlling the time of the VD vacuum refining and the bottom blowing argon flow rate to obtain clean molten steel; and controlling the moisture content of the alloy and raw and auxiliary materials during the entire smelting process.

[0004] CN117778864A discloses a method for preparing pipeline steel, comprising: S1, adding quicklime to liquid Fe material to form slag, supplying oxygen, then adding Al and Mn alloys, and then adding slag-forming materials and mixing to obtain smelted steel; S2, transferring the smelted steel into an LF refining furnace, adjusting the contents of Si, Mn, Cr, Ni, Mo, V, and Nb, controlling the binary basicity of the slag system to 5-10, blowing argon to remove impurities, and obtaining refined steel; S3, transferring the refined steel into a VD vacuum furnace, evacuating the furnace, and obtaining cast steel; S4, continuously casting round billets to obtain continuously cast round tube billets; S5, sequentially slitting, heating, spraying water for dephosphorization, cooling, perforating, and pipe-rolling the continuously cast round tube billets, and then sequentially cooling, heating, quenching, heating, and cooling to obtain pipeline steel.

[0005] CN116855843A discloses a smelting method for improving the purity of molten steel for acid-resistant and corrosion-resistant pipeline steel. The method comprises the following steps: subjecting the molten steel to magnesium metallurgical treatment after refining to obtain inclusions mainly composed of MgO·Al2O3 and MgO, which are then removed by floating through static stirring and sedation, thereby improving the purity of the molten steel; tapping the steel at high temperatures to reduce the sulfur content in the molten steel; and creating a low-melting-point, high-fluidity, low-oxidizing refining slag system during the refining process to enhance the adsorption of inclusions, modify and refine oxide inclusions, disperse hydrogen atom adsorption sites, utilize fine inclusions to refine grains, and hinder the expansion of microcracks, thereby achieving the hydrogen-induced cracking resistance of the acid-resistant and corrosion-resistant pipeline steel.

[0006] CN116516235A discloses a method for controlling Class B inclusions in pipeline steel, comprising converter smelting, LF refining, calcium treatment, RH vacuum refining, magnesium treatment, soft blowing, continuous casting, and rolling. During the LF refining process, the molten steel composition and slag basicity are adjusted. After the LF refining, Si-Ca alloy cored wire is fed into the molten steel for calcium treatment. After RH refining, Mg-Al alloy cored wire is fed into the molten steel for magnesium treatment. Large-sized CaO-Al2O3 inclusions are absent from the molten steel, with the main inclusions being CaO-Al2O3-MgO-CaS with a high MgO content. After hot rolling, the inclusions are dispersed small particles of magnesia-alumina spinel.

[0007] The above technical solution mainly obtains clean molten steel through magnesium metallurgical treatment of molten steel after refining molten steel, Si-Ca line calcium treatment and Mg-Al line magnesium treatment, controlling the binary basicity of the slag system to 5-10, blowing argon to remove impurities and then VD vacuum treatment, double slag method slag dephosphorization and slag blocking out of the furnace LF slag desulfurization and VD vacuum refining, mainly using conventional processes including calcium treatment, magnesium treatment, control of slag basicity, double slag method refining process to improve steel cleanliness, and does not pay attention to the influence of cold steel attached to the RH vacuum tank on cleanliness. Summary of the Invention

[0008] In response to the technical problem of poor cleanliness in pipeline steel smelting, the present invention provides a clean smelting process and production process for L485M pipeline steel. The present invention helps to improve the cleanliness level of pipeline steel, increase the steel plate flaw detection pass rate, and speed up the delivery of ordered products.

[0009] The technical solutions of the present invention are as follows: In a first aspect, the present invention provides a clean smelting process for L485M pipeline steel, comprising at least the following steps: RH refining is performed on pipeline steel molten steel. In the first heat before pipeline steel production, high-temperature molten steel is used to rinse the cold steel attached to the RH vacuum tank. The inlet temperature of the high-temperature molten steel of the rinsing heat is controlled to be ≥1610℃, and the vacuum pressure holding time is ≥16 minutes. After rinsing, a dedicated tank and dedicated production mode is adopted; After RH breaks through the air, pure calcium wire is fed into the pipeline steel molten steel for precise calcium treatment, and the Ca content of the pipeline steel molten steel is controlled at 0.0015%-0.0025%. After feeding the wire, soft blowing is carried out for 12 minutes-15 minutes.

[0010] Furthermore, during RH refining, the inlet temperature of the pipeline steel molten steel is 1595℃-1615℃; the RH vacuum degree is ≤200Pa; the pressure holding time is ≥12 minutes, and the pure degassing time is ≥7 minutes; the outlet temperature is 1560℃-1580℃, ensuring that the aluminum burn-off during the RH process is controlled at ≤0.008% and the H content is controlled below 0.0002%.

[0011] Furthermore, the pipeline steel is subjected to KR pretreatment, converter smelting and LF refining before RH refining.

[0012] Furthermore, the KR pretreatment process controls the sulfur content of the molten iron entering the converter to below 0.002%, and the slag skimming bright surface is controlled to be above 80%. The temperature of the molten iron after treatment is 1380℃-1410℃.

[0013] Furthermore, in the converter smelting process, the converter end temperature is ≥1620℃, the end oxygen content is ≤0.050%, the end sulfur content is ≤0.015%, the Als content in the steel after deoxidation is ≥0.015%, and the slag during the tapping process is aligned with the steel flow impact zone to ensure that the added ladle top slag is fully melted, so as to achieve early slag formation, and the slag sample is white slag or grayish white slag.

[0014] Furthermore, in the LF refining process, the inlet temperature is ≥1540℃, the outlet temperature is 1610℃-1630℃, the heating time is ≤30 minutes, and the LF slag system optimization target is to control the binary basicity in the range of 5.0-8.0, control the CaO / Al2O3 in the range of 1.7-1.9, ensure that the slag system has good fluidity, and control the white slag retention time to ≥15 minutes, so as to achieve the purpose of rapid adsorption and removal of inclusions in molten steel.

[0015] In a second aspect, the present invention further provides a production process for L485M pipeline steel, comprising a KR pretreatment process, a converter smelting process, an LF refining process, an RH refining process, a casting process, and a rolling process; In the RH refining process, before the production of pipeline steel, high-temperature molten steel is used to rinse the cold steel attached to the RH vacuum tank. The inlet temperature of the high-temperature molten steel of the rinsing furnace is controlled to be ≥1610℃, and the vacuum pressure holding time is ≥16 minutes. After rinsing, a dedicated tank and dedicated production mode is adopted. After RH breaks through the air, pure calcium wire is fed into the molten steel to perform precise calcium treatment, and the Ca content of the molten steel is controlled at 0.0015%-0.0025%. After feeding the wire, soft blowing is performed for 12 minutes-15 minutes.

[0016] Furthermore, the specific steps of the production process of L485M pipeline steel are as follows: (1) KR pretreatment: Using the KR hot metal deep desulfurization process, the sulfur content of the hot metal entering the converter is controlled at 0.002% or below, and the slag bright surface is controlled to be above 80%. The temperature of the hot metal after treatment is 1380℃-1410℃; (2) Converter smelting: converter endpoint temperature ≥ 1620℃, endpoint oxygen ≤ 0.050%, endpoint sulfur content ≤ 0.015%, Als in steel after deoxidation ≥ 0.015%, slag material should be aligned with the steel flow impact zone during tapping to ensure that the added ladle top slag is fully melted, so as to achieve early slag formation and the slag sample should be white slag or grayish white slag; (3) LF refining: LF refining inlet temperature ≥1540℃, outlet temperature 1610℃-1630℃, heating time ≤30 minutes, LF slag system optimization target is to control binary basicity in the range of 5.0-8.0, control CaO / Al2O3 in the range of 1.7-1.9, ensure the slag system has good fluidity, control white slag holding time ≥15 minutes, and achieve rapid adsorption and removal of inclusions in molten steel; (4) RH refining: Before the production of pipeline steel, use high-temperature molten steel to rinse the cold steel in the vacuum tank in advance. The molten steel entering the tank during the rinsing heat is ≥1610℃, and the vacuum pressure holding time is ≥16 minutes. After the rinsing heat, the dedicated tank production mode is maintained during the production of pipeline steel. The incoming temperature of pipeline steel heats is 1595-1615°C; the RH vacuum is ≤200 Pa; the pressure holding time is ≥12 minutes, and the pure degassing time is ≥7 minutes; the outgoing temperature is 1560-1580°C, ensuring that the aluminum burnout during the RH process is controlled at ≤0.008% and the H content is controlled below 0.0002%. After RH breaks through the air, pure calcium wire is fed to accurately treat the molten steel with calcium. The Ca content of the molten steel is controlled at 0.0015%-0.0025%. The soft blowing time after wire feeding is 12 minutes-15 minutes. (5) Continuous casting: Cast into ingots in a continuous casting machine. Dynamic soft reduction technology is used during the casting process to improve the internal quality of the ingots, ensuring that the low-magnification segregation C class is better than level 1.5. The cast ingots are cut into fixed lengths and slowly cooled for at least 48 hours. (6) Rolling: After cold casting and heating in a heating furnace for 4 to 6 hours, the steel plate is rolled into a thickness of 12 mm to 30 mm. The starting temperature of rough rolling is 1100℃ to 1180℃. The thickness of the intermediate billet is more than 3 times the thickness of the finished product. The finishing temperature of fine rolling is 790℃ to 830℃. The starting temperature of cold rolling is not less than 780℃. The cooling rate is 8℃ / s to 18℃ / s.

[0017] Furthermore, the flaw detection pass rate of the rolled steel plates was over 99.5%.

[0018] The beneficial effects of the present invention are: The clean smelting process provided by the present invention strengthens the rinsing process by controlling the temperature of the hot molten steel in the rinsing heat to above 1610°C and appropriately extending the rinsing time, thereby increasing the number of times the hot molten steel circulates within the RH vacuum tank. This ensures the complete removal of cold steel within the RH vacuum tank, and resolves the technical problem of poor smelting cleanliness due to the presence of cold steel. Repeated production practices have demonstrated that, using the same tightened gain inspection standards, the inspection pass rate of pipeline steel heats produced after RH rinsing is more than 10% higher than that of heats without rinsing. Furthermore, the corresponding steel plates from heats produced after rinsing exhibit virtually no defect waves, while the corresponding steel plates from heats produced without rinsing are prone to continuous defect waves.

[0019] The clean smelting process provided by the present invention can further reduce the situation in which residual cold steel with strong oxidizing properties is brought into the refined high-quality pipeline steel liquid and affects the already stable acid-soluble aluminum, thereby avoiding the re-oxidation of aluminum in the molten steel, reducing the content of regenerated Al2O3 inclusions, and providing relatively stable conditions for subsequent calcium treatment. The subsequent calcium treatment process converts the residual Al2O3 in the molten steel into 12CaO·7Al2O3, while reducing the generation of CaS inclusions, improving the cleanliness level of the molten steel, and providing process support for the production of pipeline steel.

[0020] The present invention also provides a process for producing pipeline steel L485M using the aforementioned clean smelting process. This process encompasses the entire process, from hot metal KR pretreatment to rolling, with precise parameter control at each step. In addition to achieving the benefits of a clean smelting process, this production process utilizes dynamic soft reduction technology during the continuous casting process to improve the internal quality of the ingot. Furthermore, during the rolling process, excellent steel plate microstructure and performance are achieved by controlling parameters such as heating time, start rolling temperature, finish rolling temperature, start cooling temperature, and cooling rate. DETAILED DESCRIPTION

[0021] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions in the embodiments of the present invention are clearly and completely described below. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work should fall within the scope of protection of the present invention.

[0022] The present invention first proposes a clean smelting process for L485M pipeline steel, which comprises at least the following steps: RH refining is performed on pipeline steel molten steel. In the first heat before pipeline steel production, high-temperature molten steel is used to rinse the cold steel attached to the RH vacuum tank. The inlet temperature of the high-temperature molten steel of the rinsing heat is controlled to be ≥1610℃, and the vacuum pressure holding time is ≥16 minutes. After rinsing, a dedicated tank and dedicated production mode is adopted; After RH breaks through the air, pure calcium wire is fed into the pipeline steel molten steel for precise calcium treatment, and the Ca content of the pipeline steel molten steel is controlled at 0.0015%-0.0025%. After feeding the wire, soft blowing is carried out for 12 minutes-15 minutes.

[0023] As a preferred embodiment of the present invention, during RH refining, the pipeline steel molten steel has an inlet temperature of 1595°C-1615°C, an RH vacuum of ≤200 Pa, a holding time of ≥12 minutes, and a pure degassing time of ≥7 minutes; and an outlet temperature of 1560°C-1580°C. By controlling parameters such as the inlet and outlet temperatures, RH vacuum, holding time, and pure degassing time of the pipeline steel molten steel, aluminum burn-off during the RH process is kept to a low level (≤0.008%) and the hydrogen content is also kept to an extremely low range (below 0.0002%). This helps stabilize the molten steel composition, reduce the content of impurity gases, and improve the quality of the molten steel, laying the foundation for the subsequent production of high-quality pipeline steel.

[0024] As a preferred embodiment of the present invention, multiple refining steps are combined. The molten iron first undergoes KR pretreatment for deep desulfurization, followed by smelting in a converter, followed by LF refining and RH refining, forming a complete smelting process. Pretreatment, converter smelting, LF refining, and RH refining work synergistically to produce high-quality molten steel for pipeline steel.

[0025] As a preferred embodiment of the present invention, the KR pretreatment process controls the sulfur content of the molten iron entering the converter to below 0.002%, controls the skimming finish to above 80%, and maintains a temperature of 1380°C-1410°C after treatment. Low sulfur content helps reduce the formation of sulfide inclusions in steel, improving its purity and performance. The appropriate skimming finish and molten iron temperature provide excellent conditions for subsequent converter smelting.

[0026] As a preferred embodiment of the present invention, in the converter smelting process, the converter end temperature is ≥1620°C, the end oxygen content is ≤0.050%, the end sulfur content is ≤0.015%, the Als content in the steel after tapping and deoxidation is ≥0.015%, and the slag in the tapping process is aligned with the steel flow impact zone. By controlling parameters such as the converter end temperature, end oxygen content, end sulfur content, Als content in the steel after tapping and deoxidation, and the method of adding slag in the tapping process, it is ensured that the composition of the molten steel meets the requirements. The slag can be fully melted to form white slag or grayish-white slag during tapping, which is beneficial to adsorb inclusions in the molten steel and improve the purity of the molten steel.

[0027] As a preferred embodiment of the present invention, in the LF refining process, the inlet temperature is ≥1540°C, the outlet temperature is 1610°C-1630°C, the heating time is ≤30 minutes, and the LF slag system optimization target is to control the binary basicity in the range of 5.0-8.0, control the CaO / Al2O3 in the range of 1.7-1.9, and control the white slag holding time to be ≥15 minutes. By controlling the inlet temperature, outlet temperature, heating time, binary basicity and CaO / Al2O3 ratio of the LF slag system and white slag holding time and other parameters of LF refining, the slag system performance is optimized, so that it has good fluidity, can quickly adsorb and remove inclusions in molten steel, and further improve the cleanliness of the molten steel.

[0028] The present invention also provides a process for producing L485M pipeline steel using the above-mentioned clean smelting process, which includes a KR pretreatment process, a converter smelting process, an LF refining process, an RH refining process, a casting process and a rolling process; In the RH refining process, before the production of pipeline steel, high-temperature molten steel is used to rinse the cold steel attached to the RH vacuum tank. The inlet temperature of the high-temperature molten steel of the rinsing furnace is controlled to be ≥1610℃, and the vacuum pressure holding time is ≥16 minutes. After rinsing, a dedicated tank and dedicated production mode is adopted. After RH breaks through the air, pure calcium wire is fed into the molten steel to perform precise calcium treatment, and the Ca content of the molten steel is controlled at 0.0015%-0.0025%. After feeding the wire, soft blowing is performed for 12 minutes-15 minutes.

[0029] As a preferred embodiment of the present invention, the specific steps of the L485M pipeline steel production process are as follows: (1) KR pretreatment: Using the KR hot metal deep desulfurization process, the sulfur content of the hot metal entering the converter is controlled at 0.002% or below, and the slag bright surface is controlled to be above 80%. The temperature of the hot metal after treatment is 1380℃-1410℃; (2) Converter smelting: converter endpoint temperature ≥ 1620℃, endpoint oxygen ≤ 0.050%, endpoint sulfur content ≤ 0.015%, Als in steel after deoxidation ≥ 0.015%, slag material should be aligned with the steel flow impact zone during tapping to ensure that the added ladle top slag is fully melted, so as to achieve early slag formation and the slag sample should be white slag or grayish white slag; (3) LF refining: LF refining inlet temperature ≥1540℃, outlet temperature 1610℃-1630℃, heating time ≤30 minutes, LF slag system optimization target is to control binary basicity in the range of 5.0-8.0, control CaO / Al2O3 in the range of 1.7-1.9, ensure the slag system has good fluidity, control white slag holding time ≥15 minutes, and achieve rapid adsorption and removal of inclusions in molten steel; (4) RH refining: Before the production of pipeline steel, use high-temperature molten steel to rinse the cold steel in the vacuum tank in advance. The molten steel entering the tank during the rinsing heat is ≥1610℃, and the vacuum pressure holding time is ≥16 minutes. After the rinsing heat, the dedicated tank production mode is maintained during the production of pipeline steel. The incoming temperature of pipeline steel heats is 1595-1615°C; the RH vacuum is ≤200 Pa; the pressure holding time is ≥12 minutes, and the pure degassing time is ≥7 minutes; the outgoing temperature is 1560-1580°C, ensuring that the aluminum burnout during the RH process is controlled at ≤0.008% and the H content is controlled below 0.0002%. After RH breaks through the air, pure calcium wire is fed to accurately treat the molten steel with calcium. The Ca content of the molten steel is controlled at 0.0015%-0.0025%. The soft blowing time after wire feeding is 12 minutes-15 minutes. (5) Continuous casting: Cast into ingots in a continuous casting machine. Dynamic soft reduction technology is used during the casting process to improve the internal quality of the ingots, ensuring that the low-magnification segregation C class is better than level 1.5. The cast ingots are cut into fixed lengths and slowly cooled for at least 48 hours. (6) Rolling: After cold casting and heating in a heating furnace for 4 to 6 hours, the steel plate is rolled into a thickness of 12 mm to 30 mm. The starting temperature of rough rolling is 1100℃ to 1180℃. The thickness of the intermediate billet is more than 3 times the thickness of the finished product. The finishing temperature of fine rolling is 790℃ to 830℃. The starting temperature of cold rolling is not less than 780℃. The cooling rate is 8℃ / s to 18℃ / s.

[0030] As a preferred embodiment of the present invention, by performing flaw detection on the rolled steel plates, the flaw detection pass rate is above 99.5%, which proves that the quality and performance of the pipeline steel L485M steel plates prepared using the production process of the present invention meet high standards and can meet the reliability and safety requirements of pipeline steel in practical applications.

[0031] Example 1 An L485M pipeline steel plate with a thickness of 26 mm, comprising the following chemical elements by weight: C 0.078%, Si 0.23%, Mn 1.59%, P 0.01%, S 0.0009%, Alt 0.031% (Als 0.028%), Ti 0.015%, Nb 0.056%, Cr 0.246%, Ca 0.0019%, Mo 0.12%, and the balance is Fe and inevitable impurities.

[0032] The L485M pipeline steel plate is produced according to the following production process steps: (1) KR pretreatment: KR hot metal deep desulfurization process is used, the slag bright surface is 87%, the hot metal temperature after treatment is 1395℃, and the sulfur content of hot metal entering the converter is 0.0010%; (2) 210-ton converter smelting: The converter endpoint temperature was 1635°C, the endpoint oxygen content was 0.043%, the endpoint sulfur content was 0.012%, and the Als content in the steel after deoxidation was 0.018%. During the tapping process, the slag was aligned with the steel flow impact zone, and the added ladle top slag was fully melted, resulting in a white slag sample. (3) LF refining: The LF refining inlet temperature is 1560℃, the outlet temperature is 1625℃, the heating time is 26 minutes, and the LF slag system optimization target is to control the binary basicity at 6.0 and the CaO / Al2O3 at 1.85. The slag system has good fluidity and the white slag retention time is 16 minutes, so as to achieve the purpose of rapid adsorption and removal of inclusions in molten steel. (4) RH refining: In the first furnace before pipeline steel production, high-temperature molten steel with an inlet temperature of 1625°C is used, and the vacuum pressure holding time is controlled to 16 minutes. The cold steel in the vacuum tank is rinsed clean in advance. After rinsing the tank, the dedicated tank production mode is maintained during the pipeline steel production period; The pipeline steel heat’s inlet temperature is 1610°C; the RH vacuum is 180 Pa; the pressure holding time is 16 minutes, and the pure degassing time is 10 minutes; the outlet temperature is 1568°C; the RH process aluminum loss is 0.006%, and the H content is controlled at 0.00015%. After RH breaks through the air, a pure calcium line of 175 m is fed to the molten steel for precise calcium treatment. The Ca content in the molten steel is tested to be 0.0019%. After feeding the line, soft blowing is performed for 12 minutes. (5) Continuous casting: The continuous casting machine is used to cast the ingot into a 300 mm thick ingot. The dynamic soft reduction technology is used during the casting process to improve the internal quality of the ingot and ensure that the low-magnification segregation C class is 1.0. The cast ingot is cut into fixed lengths and slowly cooled for 50 hours. (6) Rolling: After being cold cast and heated in a heating furnace for 4.8 hours, the steel plates are rolled into 26 mm thick steel plates on the 4300 production line. The starting temperature of the rough rolling is 1170 °C, the thickness of the intermediate billet is more than 3 times the thickness of the finished product, the finishing temperature of the fine rolling is 810 °C, the starting temperature of the cold rolling is not less than 795 °C, and the cooling rate is 15 °C / s.

[0033] The steel plates rolled in step (6) were inspected for flaws, and the inspection pass rate was 99.8%.

[0034] Comparative Example 1 An L485M pipeline steel plate with a thickness of 26 mm, comprising the following chemical elements by weight: C 0.071%, Si 0.25%, Mn 1.58%, P 0.01%, S 0.0010%, Alt 0.032% (Als 0.029%), Ti 0.016%, Nb 0.055%, Cr 0.238%, Ca 0.0019%, Mo 0.11%, and the balance is Fe and inevitable impurities.

[0035] The L485M pipeline steel plate is produced according to the following production process steps: (1) KR pretreatment: KR hot metal deep desulfurization process is used, the slag bright surface is 87%, the hot metal temperature after treatment is 1395℃, and the sulfur content of hot metal entering the converter is 0.0010%; (2) 210-ton converter smelting: The converter endpoint temperature was 1635°C, the endpoint oxygen content was 0.043%, the endpoint sulfur content was 0.012%, and the Als content in the steel after deoxidation was 0.018%. During the tapping process, the slag was aligned with the steel flow impact zone, and the added ladle top slag was fully melted, resulting in a white slag sample. (3) LF refining: The LF refining inlet temperature is 1560℃, the outlet temperature is 1625℃, the heating time is 26 minutes, and the LF slag system optimization target is to control the binary basicity at 6.0 and the CaO / Al2O3 at 1.85. The slag system has good fluidity and the white slag retention time is 16 minutes, so as to achieve the purpose of rapid adsorption and removal of inclusions in molten steel. (4) RH refining: The inlet temperature of the pipeline steel heat is 1610℃; the RH vacuum is 180 Pa; the pressure holding time is 16 minutes, and the pure degassing time is 10 minutes; the outlet temperature is 1568℃, the aluminum loss during the RH process is 0.006%, and the H content is controlled at 0.00015%; After RH breaks through the air, a pure calcium line of 175 m is fed to the molten steel for precise calcium treatment. The Ca content in the molten steel is tested to be 0.0019%. After feeding the line, soft blowing is performed for 12 minutes. (5) Continuous casting: The continuous casting machine is used to cast the ingot into a 300 mm thick ingot. The dynamic soft reduction technology is used during the casting process to improve the internal quality of the ingot and ensure that the low-magnification segregation C class is 1.0. The cast ingot is cut into fixed lengths and slowly cooled for 50 hours. (6) Rolling: After being cold cast and heated in a heating furnace for 4.8 hours, the steel plates are rolled into 26 mm thick steel plates on the 4300 production line. The starting temperature of the rough rolling is 1170 °C, the thickness of the intermediate billet is more than 3 times the thickness of the finished product, the finishing temperature of the fine rolling is 810 °C, the starting temperature of the cold rolling is not less than 795 °C, and the cooling rate is 15 °C / s.

[0036] The difference between Comparative Example 1 and Example 1 is that the trough was not rinsed before RH refining. Cold steel adhered to the RH vacuum tank, which affected the cleanliness of the smelting and the inclusion content of the final product. The steel plates rolled in step (6) were inspected for flaws, and the inspection pass rate was 86.2%.

[0037] Comparative Example 2 An L485M pipeline steel plate with a thickness of 26 mm, comprising the following chemical elements by weight: C 0.060%, Si 0.23%, Mn 1.55%, P 0.01%, S 0.0010%, Alt 0.032% (Als 0.028%), Ti 0.015%, Nb 0.057%, Cr 0.257%, Ca 0.0019%, Mo 0.11%, and the balance is Fe and inevitable impurities.

[0038] The L485M pipeline steel plate is produced according to the following production process steps: (1) KR pretreatment: KR hot metal deep desulfurization process is used, the slag bright surface is 87%, the hot metal temperature after treatment is 1395℃, and the sulfur content of hot metal entering the converter is 0.0010%; (2) 210-ton converter smelting: The converter endpoint temperature was 1635°C, the endpoint oxygen content was 0.043%, the endpoint sulfur content was 0.012%, and the Als content in the steel after deoxidation was 0.018%. During the tapping process, the slag was aligned with the steel flow impact zone, and the added ladle top slag was fully melted, resulting in a white slag sample. (3) LF refining: The LF refining inlet temperature is 1560℃, the outlet temperature is 1625℃, the heating time is 26 minutes, and the LF slag system optimization target is to control the binary basicity at 6.0 and the CaO / Al2O3 at 1.85. The slag system has good fluidity and the white slag retention time is 16 minutes, so as to achieve the purpose of rapid adsorption and removal of inclusions in molten steel. (4) RH refining: In the first heat before pipeline steel production, use molten steel with an inlet temperature of 1608°C, control the vacuum pressure holding time to 12 minutes, rinse the cold steel in the vacuum tank in advance, and maintain a dedicated tank dedicated production mode during pipeline steel production after rinsing the tank; The pipeline steel heat’s inlet temperature is 1610°C; the RH vacuum is 180 Pa; the pressure holding time is 16 minutes, and the pure degassing time is 10 minutes; the outlet temperature is 1568°C; the RH process aluminum loss is 0.006%, and the H content is controlled at 0.00015%. After RH breaks through the air, a pure calcium line of 175 m is fed to the molten steel for precise calcium treatment. The Ca content in the molten steel is tested to be 0.0019%. After feeding the line, soft blowing is performed for 12 minutes. (5) Continuous casting: The continuous casting machine is used to cast the ingot into a 300 mm thick ingot. The dynamic soft reduction technology is used during the casting process to improve the internal quality of the ingot and ensure that the low-magnification segregation C class is 1.0. The cast ingot is cut into fixed lengths and slowly cooled for 50 hours. (6) Rolling: After being cold cast and heated in a heating furnace for 4.8 hours, the steel plates are rolled into 26 mm thick steel plates on the 4300 production line. The starting temperature of the rough rolling is 1170 °C, the thickness of the intermediate billet is more than 3 times the thickness of the finished product, the finishing temperature of the fine rolling is 810 °C, the starting temperature of the cold rolling is not less than 795 °C, and the cooling rate is 15 °C / s.

[0039] The difference between Comparative Example 2 and Example 1 is that the molten steel temperature used in the rinsing stage is relatively low, and the vacuum holding time is different. This condition has a limited effect on removing the cold steel attached to the RH vacuum tank, thus affecting the cleanliness of the smelting and the inclusion content of the final product. The steel plates rolled in step (6) were inspected for flaws, and the inspection pass rate was 89.6%.

[0040] Example 2 An L485M pipeline steel plate with a thickness of 15 mm, comprising the following chemical elements by weight: C 0.055%, Si 0.24%, Mn 1.56%, P 0.01%, S 0.0012%, Alt 0.034% (Als 0.032%), Ti 0.016%, Nb 0.055%, Cr 0.255%, Ca 0.0015%, Mo 0.10%, and the balance is Fe and inevitable impurities.

[0041] The L485M pipeline steel plate is produced according to the following production process steps: (1) KR pretreatment: KR hot metal deep desulfurization process is used, the slag bright surface is 85%, the hot metal temperature after treatment is 1390℃, and the sulfur content of hot metal entering the converter is 0.0009%; (2) 210-ton converter smelting: The converter endpoint temperature was 1627°C, the endpoint oxygen content was 0.040%, the endpoint sulfur content was 0.014%, and the Als content in the steel after deoxidation was 0.022%. During the tapping process, the slag was aligned with the steel flow impact zone, and the added ladle top slag was fully melted, resulting in a white slag sample. (3) LF refining: The LF refining inlet temperature is 1563℃, the outlet temperature is 1625℃, the heating time is 25 minutes, and the LF slag system optimization target is to control the binary basicity at 6.6 and the CaO / Al2O3 at 1.8. The slag system has good fluidity, and the white slag retention time is 19 minutes, so as to achieve rapid adsorption and removal of inclusions in molten steel. (4) RH refining: In the first furnace before pipeline steel production, high-temperature molten steel with an inlet temperature of 1622°C is used, and the vacuum pressure holding time is controlled to 18 minutes. The cold steel in the vacuum tank is rinsed clean in advance. After rinsing the tank, the dedicated tank production mode is maintained during the pipeline steel production period; The inlet temperature of the pipeline steel heat is 1605°C; the RH vacuum is 175 Pa; the pressure holding time is 15 minutes, and the pure degassing time is 9 minutes; the outlet temperature is 1572°C, the aluminum loss during the RH process is 0.005%, and the hydrogen content is controlled at 0.00010%. After RH breaks through the air, a pure calcium line of 168 m is fed to the molten steel for precise calcium treatment. The Ca content in the molten steel is tested to be 0.0015%. After feeding the line, soft blowing is performed for 13 minutes. (5) Continuous casting: Cast into 300 mm thick ingots on a continuous casting machine. Dynamic soft reduction technology is used during the casting process to improve the internal quality of the ingots and ensure that the low-magnification segregation C class is 1.0. The cast ingots are cut into fixed lengths and slowly cooled for 48 hours. (6) Rolling: After being cold cast and heated in a heating furnace for 4.6 hours, the steel plates are rolled into 15 mm thick steel plates on the 4300 production line. The starting temperature of the rough rolling is 1165 °C, the thickness of the intermediate billet is more than 3 times the thickness of the finished product, the finishing temperature of the fine rolling is 825 °C, the starting temperature of the cold rolling is not less than 810 °C, and the cooling rate is 15 °C / s.

[0042] The steel plates rolled in step (6) were inspected for flaws, and the inspection pass rate was 99.8%.

[0043] Example 3 A 30 mm thick L485M pipeline steel plate comprising the following chemical elements by weight: C 0.056%, Si 0.23%, Mn 1.56%, P 0.01%, S 0.0008%, Alt 0.034% (Als 0.032%), Ti 0.014%, Nb 0.056%, Cr 0.258%, Ca 0.0015%, Mo 0.13%, and the balance is Fe and inevitable impurities.

[0044] The L485M pipeline steel plate is produced according to the following production process steps: (1) KR pretreatment: KR hot metal deep desulfurization process is used, the slag bright surface is 80%, the hot metal temperature after treatment is 1380℃, and the sulfur content of hot metal entering the converter is 0.002%; (2) 210-ton converter smelting: The converter endpoint temperature was 1620°C, the endpoint oxygen content was 0.050%, the endpoint sulfur content was 0.015%, and the Als content in the steel after deoxidation was 0.016%. During the tapping process, the slag was aligned with the steel flow impact zone, and the added ladle top slag was fully melted, resulting in a white slag sample. (3) LF refining: The LF refining inlet temperature is 1540℃, the outlet temperature is 1610℃, the heating time is 30 minutes, and the LF slag system optimization target is to control the binary basicity at 8.0 and the CaO / Al2O3 at 1.7. The slag system has good fluidity, and the white slag retention time is 15 minutes to achieve rapid adsorption and removal of inclusions in molten steel. (4) RH refining: In the first furnace before pipeline steel production, high-temperature molten steel with an inlet temperature of 1610°C is used, and the vacuum pressure holding time is controlled to 19 minutes. The cold steel in the vacuum tank is rinsed clean in advance. After rinsing the tank, the dedicated tank production mode is maintained during the pipeline steel production period; The inlet temperature of the pipeline steel heat is 1595°C; the RH vacuum is 200 Pa; the pressure holding time is 12 minutes, and the pure degassing time is 7 minutes; the outlet temperature is 1560°C, the aluminum loss during the RH process is 0.008%, and the hydrogen content is controlled at 0.0002%. After RH breaks through the air, pure calcium wire is fed to accurately treat the molten steel with calcium. The Ca content in the molten steel is tested to be 0.0015%. After feeding the wire, soft blowing is performed for 15 minutes. (5) Continuous casting: The continuous casting machine is used to cast the ingot into a 300 mm thick ingot. The dynamic soft reduction technology is used during the casting process to improve the internal quality of the ingot and ensure that the low-magnification segregation C class is 1.0. The cast ingot is cut into fixed lengths and slowly cooled for 50 hours. (6) Rolling: After being cold cast and heated in a heating furnace for 4 hours, the steel plates are rolled into 30 mm thick steel plates on the 4300 production line. The starting temperature of the rough rolling is 1180 °C, the thickness of the intermediate billet is more than 3 times the thickness of the finished product, the finishing temperature of the fine rolling is 830 °C, the starting temperature of the cold rolling is not less than 780 °C, and the cooling rate is 8 °C / s.

[0045] The steel plates rolled in step (6) were inspected for flaws, and the inspection pass rate was 99.6%.

[0046] Example 4 A 20 mm thick L485M pipeline steel plate comprising the following chemical elements by weight: C 0.063%, Si 0.25%, Mn 1.58%, P 0.01%, S 0.0010%, Alt 0.033% (Als 0.031%), Ti 0.012%, Nb 0.052%, Cr 0.249%, Ca 0.0025%, Mo 0.12%, and the balance is Fe and inevitable impurities.

[0047] The L485M pipeline steel plate is produced according to the following production process steps: (1) KR pretreatment: KR hot metal deep desulfurization process is used, the slag bright surface is 85%, the hot metal temperature after treatment is 1410℃, and the sulfur content of hot metal entering the converter is 0.001%; (2) 210-ton converter smelting: The converter endpoint temperature was 1650°C, the endpoint oxygen content was 0.032%, the endpoint sulfur content was 0.010%, and the Als content in the steel after deoxidation was 0.018%. During the tapping process, the slag was aligned with the steel flow impact zone, and the added ladle top slag was fully melted, resulting in a white slag sample. (3) LF refining: The LF refining inlet temperature is 1555℃, the outlet temperature is 1630℃, the heating time is 30 minutes, and the LF slag system optimization target is to control the binary basicity at 5.0 and the CaO / Al2O3 at 1.75. The slag system has good fluidity and the white slag retention time is 20 minutes to achieve rapid adsorption and removal of inclusions in molten steel. (4) RH refining: In the first furnace before pipeline steel production, high-temperature molten steel with an inlet temperature of 1630°C is used, and the vacuum pressure holding time is controlled to 18 minutes. The cold steel in the vacuum tank is rinsed clean in advance. After rinsing the tank, the dedicated tank production mode is maintained during the pipeline steel production period; The pipeline steel heat’s inlet temperature is 1615°C; the RH vacuum is 180 Pa; the pressure holding time is 15 minutes, and the pure degassing time is 9 minutes; the outlet temperature is 1580°C; the aluminum loss during the RH process is 0.006%, and the H content is controlled at 0.00010%. After RH breaks through the air, pure calcium wire is fed to accurately treat the molten steel with calcium. The Ca content in the molten steel is tested to be 0.0025%. After feeding the wire, soft blowing is performed for 12 minutes. (5) Continuous casting: The continuous casting machine is used to cast the ingot into a 300 mm thick ingot. The dynamic soft reduction technology is used during the casting process to improve the internal quality of the ingot and ensure that the low-magnification segregation C class is 1.0. The cast ingot is cut into fixed lengths and slowly cooled for 60 hours. (6) Rolling: After being cold-casted and heated in a heating furnace for 6 hours, the steel plates are rolled into 20 mm thick steel plates on the 4300 production line. The starting temperature of the rough rolling is 1100 °C, the thickness of the intermediate billet is more than 3 times the thickness of the finished product, the finishing temperature of the fine rolling is 790 °C, the starting temperature of the cold rolling is not less than 785 °C, and the cooling rate is 18 °C / s.

[0048] The steel plates rolled in step (6) were inspected for flaws, and the inspection pass rate was 99.7%.

[0049] Although the present invention has been described in detail by way of preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and substance of the present invention, persons of ordinary skill in the art may make various equivalent modifications or substitutions to the embodiments of the present invention, and such modifications or substitutions shall be within the scope of the present invention. Any changes or substitutions that can be readily conceived by persons skilled in the art within the technical scope disclosed in the present invention shall be within the scope of protection of the present invention.

Claims

1. A clean smelting process for L485M pipeline steel, characterized in that: At least the following steps are included: RH refining is performed on pipeline steel molten steel. In the first heat before pipeline steel production, high-temperature molten steel is used to rinse the cold steel attached to the RH vacuum tank. The inlet temperature of the high-temperature molten steel of the rinsing heat is controlled to be ≥1610℃, and the vacuum pressure holding time is ≥16 minutes. After rinsing, a dedicated tank and dedicated production mode is adopted; After RH breaks through the air, pure calcium wire is fed into the pipeline steel molten steel for precise calcium treatment, and the Ca content of the pipeline steel molten steel is controlled at 0.0015%-0.0025%. After feeding the wire, soft blowing is carried out for 12 minutes-15 minutes.

2. The clean smelting process for L485M pipeline steel according to claim 1, characterized in that: During RH refining, the inlet temperature of pipeline steel molten steel is 1595℃-1615℃; the RH vacuum degree is ≤200 Pa; the pressure holding time is ≥12 minutes, and the pure degassing time is ≥7 minutes; the outlet temperature is 1560℃-1580℃, and the aluminum burn-off loss in the RH process is controlled to ≤0.008%, and the H content is controlled below 0.0002%.

3. The clean smelting process for L485M pipeline steel according to claim 1, characterized in that: The pipeline steel liquid undergoes KR pretreatment, converter smelting and LF refining before RH refining.

4. The clean smelting process for L485M pipeline steel according to claim 1, characterized in that: The KR pretreatment process controls the sulfur content of the molten iron entering the converter to below 0.002%, and the slag bright surface is controlled to be above 80%. The temperature of the molten iron after treatment is 1380℃-1410℃.

5. The clean smelting process for L485M pipeline steel according to claim 1, characterized in that: In the converter smelting process, the converter endpoint temperature is ≥1620℃, the endpoint oxygen content is ≤0.050%, the endpoint sulfur content is ≤0.015%, the Als content in the steel after deoxidation is ≥0.015%, the slag is aligned with the steel flow impact zone during the tapping process, the ladle top slag is fully melted, and the slag sample is white slag or grayish white slag.

6. The clean smelting process for L485M pipeline steel according to claim 1, characterized in that: In the LF refining process, the inlet temperature is ≥1540℃, the outlet temperature is 1610℃-1630℃, the heating time is ≤30 minutes, and the optimization target of the LF slag system is to control the binary basicity in the range of 5.0-8.0, the CaO / Al2O3 in the range of 1.7-1.9, and the white slag holding time ≥15 minutes.

7. A production process for L485M pipeline steel, characterized in that: Including KR pretreatment process, converter smelting process, LF refining process, RH refining process, casting process and rolling process; In the RH refining process, before the production of pipeline steel, high-temperature molten steel is used to rinse the cold steel attached to the RH vacuum tank. The inlet temperature of the high-temperature molten steel of the rinsing furnace is controlled to be ≥1610℃, and the vacuum pressure holding time is ≥16 minutes. After rinsing, a dedicated tank and dedicated production mode is adopted. After RH breaks through the air, pure calcium wire is fed into the molten steel to perform precise calcium treatment, and the Ca content of the molten steel is controlled at 0.0015%-0.0025%. After feeding the wire, soft blowing is performed for 12 minutes-15 minutes.

8. The production process of L485M pipeline steel according to claim 7, characterized in that: The specific steps of the production process of L485M pipeline steel are as follows: (1) KR pretreatment: Using the KR hot metal deep desulfurization process, the sulfur content of the hot metal entering the converter is controlled at 0.002% or below, and the slag bright surface is controlled to be above 80%. The temperature of the hot metal after treatment is 1380℃-1410℃; (2) Converter smelting: converter endpoint temperature ≥ 1620℃, endpoint oxygen ≤ 0.050%, endpoint sulfur content ≤ 0.015%, Als in steel after deoxidation ≥ 0.015%, slag material is aligned with the steel flow impact zone during tapping, the added ladle top slag is fully melted, and the slag sample is white slag or grayish white slag; (3) LF refining: LF refining inlet temperature ≥1540℃, outlet temperature 1610℃-1630℃, heating time ≤30 minutes, LF slag system optimization target is to control binary basicity in the range of 5.0-8.0, control CaO / Al2O3 in the range of 1.7-1.9, and control white slag holding time ≥15 minutes; (4) RH refining: Before the production of pipeline steel, use high-temperature molten steel to rinse the cold steel in the vacuum tank in advance. The molten steel entering the tank during the rinsing heat is ≥1610℃, and the vacuum pressure holding time is ≥16 minutes. After the rinsing heat, the dedicated tank production mode is maintained during the production of pipeline steel. The incoming temperature of pipeline steel heats is 1595-1615°C; the RH vacuum is ≤200 Pa; the pressure holding time is ≥12 minutes, and the pure degassing time is ≥7 minutes; the outgoing temperature is 1560-1580°C; the aluminum burn-off loss during the RH process is controlled to ≤0.008%, and the H content is controlled below 0.0002%. After RH breaks through the air, pure calcium wire is fed to accurately treat the molten steel with calcium. The Ca content of the molten steel is controlled at 0.0015%-0.0025%. The soft blowing time after wire feeding is 12 minutes-15 minutes. (5) Continuous casting: The ingot is cast into a continuous casting machine. The dynamic soft reduction technology is applied during the casting process to improve the internal quality of the ingot. The low segregation C class is better than grade 1.

5. The cast ingot is cut into fixed lengths and slowly cooled for at least 48 hours. (6) Rolling: The ingot is heated in a heating furnace for 4 to 6 hours and then rolled into a steel plate with a thickness of 12 mm to 30 mm. The starting temperature of the rough rolling is 1100°C to 1180°C. The thickness of the intermediate billet is more than 3 times the thickness of the finished product. The finishing temperature of the fine rolling is 790°C to 830°C. The starting cooling temperature is not less than 780°C and the cooling rate is 8°C / s to 18°C / s.

9. The production process of L485M pipeline steel according to claim 8, characterized in that: The flaw detection pass rate of rolled steel plates is above 99.5%.