A low-cost smelting process to reduce oxygen content in molten steel

Abstract

This invention discloses a low-cost smelting process for reducing the oxygen content of molten steel, primarily relating to the field of molten steel smelting equipment. It includes S1, where, during the early stages of converter quenching, oxygen is supplied to the furnace at a conventional intensity to rapidly raise the temperature and decarburize the molten steel. A secondary lance monitors the temperature and carbon content of the molten steel in real time to obtain internal furnace data. S2, when the secondary lance detects that the carbon content of the molten steel has decreased to the decarburization threshold, the oxygen supply intensity inside the furnace is reduced, and simultaneously, a bottom-blowing argon gas agitation mechanism is activated to introduce argon gas into the furnace, preventing excessive oxidation of the molten steel caused by intense oxygen blowing. The beneficial effects of this invention are: meeting the stringent requirements of specific customers for steel purity and internal quality, and fundamentally eliminating a series of defects in continuously cast billets caused by high oxygen content.

Description

Technical Field

[0001] This invention relates to the field of steel smelting equipment, specifically a low-cost smelting process for reducing the oxygen content of molten steel. Background Technology

[0002] For the converter smelting process of Q235B low-carbon structural steel, in order to optimize cost-effectiveness and production rhythm, some steel mills have adopted a "direct-to-converter" process that eliminates the secondary refining in the LF furnace and sends the molten steel directly to the continuous casting machine. However, the core technical bottleneck of this process is that the oxygen content of the final molten steel in the converter is too high, generally ranging from 150-200 ppm. Without deep deoxidation and purification in the refining process, the excessive dissolved oxygen will precipitate during the subsequent continuous casting solidification process, thereby inducing significant solidification defects in the billet, such as subcutaneous bubbles, central porosity, and macroscopic inclusions. These defects not only reduce the internal and surface quality of the billet, but also directly damage the mechanical properties (such as impact toughness and fatigue performance) and reliability of the final rolled product, limiting the application of this process in applications requiring high quality.

[0003] At the same time, if we return to the traditional approach, that is, to add an LF refining furnace to treat the molten steel, although the oxygen content can be effectively reduced to the ideal level of below 90ppm and the purity of the molten steel can be significantly improved, it will inevitably lead to a cost increase of 80-120 yuan per ton of steel and extend the production cycle by about 20-30 minutes. This fundamentally weakens the core advantages of the "direct" process in terms of cost and efficiency.

[0004] Therefore, the industry currently faces a clear and pressing technological dilemma: while maintaining the low-cost, high-speed "converter-continuous casting" direct-flow production framework, how can we achieve precise, stable, and in-depth control of the oxygen content in the final molten steel through technological innovation and breakthroughs in the converter smelting process itself? This would significantly reduce the oxygen content from the conventional 150-200 ppm level to below 90 ppm, thereby meeting the stringent requirements of specific customers for steel purity and internal quality without relying on additional refining equipment, and fundamentally eliminating a series of defects in continuously cast billets caused by high oxygen content. This requires a systematic redesign and refined management of converter endpoint control, deoxidation systems, slag system optimization, and tapping process protection—a key technical challenge connecting cost control and quality improvement. Summary of the Invention

[0005] The purpose of this invention is to provide a low-cost smelting process for reducing the oxygen content of molten steel. This process meets the stringent requirements of specific customers for steel purity and internal quality without relying on additional refining equipment, and fundamentally eliminates a series of defects in continuously cast billets caused by high oxygen content. This requires a systematic redesign and refined management of converter endpoint control, deoxidation procedures, slag system optimization, and tapping process protection, representing a key technical challenge in bridging cost control and quality improvement.

[0006] To achieve the above objectives, the present invention employs the following technical solution: A low-cost smelting process for reducing the oxygen content of molten steel includes the following steps: S1, in the early stage of converter quenching, the oxygen supply to the furnace body is carried out in a conventional intensity manner, so that the molten steel can be heated up and decarburized quickly. The temperature and carbon content of the molten steel in the furnace body are monitored in real time through the auxiliary gun to obtain data information inside the furnace body. S2, when the auxiliary gun detects that the carbon content of the molten steel in the furnace has dropped to the decarburization threshold, the oxygen supply intensity inside the furnace is reduced, and the bottom blowing argon gas weak stirring mechanism inside the furnace is turned on to introduce argon gas into the furnace to avoid the molten steel from being over-oxidized due to violent oxygen blowing. S3, when the auxiliary gun monitors in real time that the carbon content of the molten steel in the furnace is stable at the minimum decarburization threshold and the temperature reaches the maximum temperature threshold, the application of oxygen to the furnace is stopped, thereby controlling the initial carbon content of the molten steel. S4. When the temperature and carbon content of the molten steel in the furnace reach the requirements for tapping, a shield is set at the tapping position of the furnace to accurately block slag. A slag-forming agent is added to the molten steel impact area at the tapping position. When the tapping reaches the slag control threshold, alloys and auxiliary materials are added to the furnace. The intense stirring during the tapping process allows the alloys and auxiliary materials to melt quickly and form top slag, which adsorbs the floating inclusions. S5, the ladle used to load molten steel is transferred to the argon treatment station, and the bottom blowing argon soft blowing mode is turned on and kept before the steel is loaded into the continuous casting. S6 performs full-protection continuous casting of molten steel in the ladle, thereby completing the continuous casting and forging operation of molten steel.

[0007] The fully protected continuous casting method in step S6 includes the following steps: S21, the ladle is moved by a robotic arm so that argon gas is introduced into the connection between the ladle molten steel and the ladle drain to seal it and isolate it from the outside air. S22, which also features a double-layer covering agent process, receives molten steel again in the tundish, and the crystallizer is electromagnetically stirred to control the liquid level fluctuation within ±3mm. The casting speed is stabilized at 2.5-2.8m / min to avoid slag entrapment and secondary oxidation caused by liquid level fluctuation, thus ensuring the quality of the cast billet. S23. During the continuous casting process of molten steel, the cooling water is weakly cooled to ensure good atomization of the nozzles, ensure uniform cooling of the billet, and avoid internal cracks and center segregation.

[0008] The decarbonization threshold in step S2 is 0.12%.

[0009] The minimum decarbonization threshold in step S3 is 0.08-0.11%, and the maximum temperature threshold is 1640-1660℃.

[0010] The slag control threshold in step S4 is 20-30%, that is, when the outflow of molten steel from the furnace is 20-30%, alloys and auxiliary materials are added into the furnace.

[0011] The shielding object in step S4 is a slag-blocking ball. The slag-blocking ball is used to block slag during the tapping of molten steel, thereby controlling the amount of slag discharged from the molten steel to within 3 kg / t.

[0012] The deoxidation and alloying step in step S4 includes: When the steel reaches 20-30% of its capacity, alloys and auxiliary materials are added into the furnace, namely, carbon raisers, silicon manganese, silicon calcium barium, aluminum blocks, silicon calcium wire, and lime blocks. The intense stirring during the tapping process causes the alloys and auxiliary materials to melt rapidly and form top slag, which adsorbs the floating inclusions and initially reduces the oxygen content of the molten steel to 120-140 ppm.

[0013] Step S4 also includes steel ladle calcium treatment, the specific method of which is as follows: After the molten steel is tapped, the furnace temperature is adjusted and the oxygen level is stabilized. Then, 120-150 meters of silicon-calcium wire is fed in to control the free oxygen in the molten steel to within 50 ppm.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Reduced oxidation at the source: Precise control of carbon and temperature at the end of the converter and strict control of slag discharge during tapping reduce the oxygen content in the molten steel from the very beginning.

[0015] 2. The process involves "strong deoxidation and extensive removal": During tapping and ladle processing, various deoxidizers and calcium are added, and the steel is subjected to long-term argon gas soft stirring to deeply remove oxygen and impurities from the molten steel.

[0016] 3. Casting with “full protection and stable solidification”: During continuous casting, argon gas is used for sealing and covering agent to protect the molten steel throughout the process to prevent secondary oxidation. The process is optimized to ensure that the billet solidifies evenly and stably, avoiding internal defects. Attached Figure Description

[0017] Appendix Figure 1 This is a process flow diagram of the converter-continuous casting low-oxygen control process without refining, as described in this invention. Detailed Implementation

[0018] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined in this application.

[0019] A low-cost smelting process for reducing the oxygen content of molten steel includes the following steps: S1 employs a conventional oxygen supply method during the early stages of converter quenching, rapidly heating and decarburizing the molten steel. A secondary lance monitors the furnace temperature and carbon content in real-time, providing internal data. Dynamic monitoring by the secondary lance, combined with a "high-low" oxygen supply mode and weak bottom-blowing argon agitation, ensures that the final carbon content and temperature are precisely within the set range. This eliminates compensatory oxygen blowing (i.e., "supplementary blowing") required due to excessively low carbon content (over-oxidation) or substandard temperature, thus maximally suppressing excessive dissolved oxygen generation in the molten steel from the source of the metallurgical reaction and controlling the initial oxygen content at a low level. This is the prerequisite and core of achieving refining-free low-oxygen control.

[0020] S2, when the secondary lance detects that the carbon content of the molten steel in the furnace has decreased to the decarburization threshold, the oxygen supply intensity inside the furnace is reduced, and the bottom-blowing argon gas gentle stirring mechanism inside the furnace is activated. This allows argon gas to be introduced into the furnace to prevent the molten steel from over-oxidizing due to intense oxygen blowing. This method cleverly utilizes the "intense stirring kinetic energy during the tapping process" and the continuous, gentle stirring power provided by the subsequent "long-term bottom-blowing argon gas gentle blowing". This combination of "intense stirring + gentle blowing" provides sufficient opportunity and time for deoxidation products and modified inclusions to collide, aggregate, grow, and float to the top slag for absorption, thereby significantly improving the purity of the molten steel. Its effect is comparable to the stirring and refining function of an LF furnace.

[0021] S3: When the auxiliary lance detects in real-time that the carbon content of the molten steel in the furnace is stable at the minimum decarburization threshold and the temperature reaches the maximum temperature threshold, oxygen application to the furnace is stopped, thereby controlling the initial carbon content of the molten steel. Real-time feedback from the auxiliary lance ensures that the target carbon content and temperature range are reached in a single pass, and oxygen blowing is immediately stopped. This eliminates the need for "post-blowing" or "supplementary blowing" operations due to excessively low endpoint carbon content or substandard temperature, and "post-blowing" is one of the main causes of a sharp increase in the oxygen content of the molten steel. This fundamentally and precisely controls the endpoint carbon and temperature within the ideal range (e.g., carbon content 0.08~0.11%, temperature 1640~1660℃), achieving stable and precise control of the initial composition and oxidation state of the molten steel (initial carbon content and implicit oxygen content). This provides molten steel with qualified composition and temperature for subsequent refining-free processes, solving the industry problem of having to rely on subsequent refining adjustments due to inaccurate endpoint control.

[0022] S4. When the temperature and carbon content of the molten steel in the furnace reach the tapping requirements, a shield is set up at the tapping position for precise slag blocking. A slag-forming agent is added to the molten steel impact zone at the tapping position. When the tapping reaches the slag control threshold, alloys and auxiliary materials are added to the furnace. The intense stirring during tapping causes the alloys and auxiliary materials to melt rapidly and form top slag, adsorbing floating inclusions. This minimizes the entry of highly oxidizing, high-FeO-content converter final slag into the ladle, thus preventing secondary oxidation of the molten steel by the slag during tapping. Secondly, the addition of a composite slag-forming agent such as lime-silicon carbide to the steel flow impact zone rapidly forms top slag with appropriate basicity and reducing properties, pre-deoxidizing the molten steel and adsorbing early deoxidation products. Finally, when the steel is tapped to 1 / 4 to 1 / 3 of its full volume, deoxidizing alloys and auxiliary materials are added. This fully utilizes the intense stirring energy during tapping to achieve rapid alloy melting, initial composition homogenization, and preliminary deoxidation. It also initially reduces the oxygen content of the molten steel from its high post-tapping level (e.g., above 150 ppm) to 120-140 ppm. This series of operations completes the initial refining function (slag blocking, pre-deoxidation, initial alloying, and slag adsorption) during the tapping stage, solving the problems of secondary contamination and oxidation of molten steel during tapping, as well as low yield and insufficient deoxidation due to improper alloy addition timing.

[0023] In step S5, the ladle used to load molten steel is transferred to the argon treatment station, and the bottom-blowing argon soft-blowing mode is activated and maintained before the steel is loaded into the continuous casting. The bottom-blowing argon is used for prolonged soft-blowing agitation (e.g., ≥10 minutes), providing a gentle and continuous upward driving force for the fine deoxidation products (such as Al2O3) and inclusions in the molten steel. During the soft-blowing process, these tiny particles are fully allowed to collide, aggregate, grow, and float to the top slag for absorption. Prolonged soft-blowing also promotes further homogenization of the molten steel composition and temperature. This operation effectively removes non-metallic inclusions from the steel and further reduces the total oxygen content (e.g., controlling free oxygen below 50 ppm). Its purification effect can replace or partially replace the stirring and refining functions of the LF furnace, solving the technical bottleneck of how to effectively remove inclusions and deeply purify molten steel in the absence of an LF furnace.

[0024] S6 performs full-protection continuous casting of molten steel in the ladle, thereby completing the continuous casting and forging operation of molten steel.

[0025] The fully protected continuous casting method in step S6 includes the following steps: S21, the ladle is moved by a robotic arm so that argon gas is introduced into the connection between the ladle molten steel and the ladle drain to seal it and isolate it from the outside air. S22, which also features a double-layer covering agent process, receives molten steel again in the tundish, and the crystallizer is electromagnetically stirred to control the liquid level fluctuation within ±3mm. The casting speed is stabilized at 2.5-2.8m / min to avoid slag entrapment and secondary oxidation caused by liquid level fluctuation, thus ensuring the quality of the cast billet. S23. During the continuous casting process of molten steel, the cooling water is weakly cooled to ensure good atomization of the nozzles, ensure uniform cooling of the billet, and avoid internal cracks and center segregation.

[0026] By implementing a comprehensive protective casting process, including argon sealing at the long nozzle, tundish covering agent protection, and crystallizer liquid level stabilization, an inert atmosphere protective barrier was constructed from the ladle to the crystallizer. This effectively isolated the molten steel from contact with air, preventing secondary oxidation and air absorption during casting. This is a crucial step in preserving the achievements of low-oxygen control in the early stages and preventing the pure molten steel from being contaminated in the final stage. It solves the common problem of secondary oxidation of molten steel during casting due to inadequate protective casting, which renders the previous refining efforts futile. Combined with electromagnetic stirring in the crystallizer, stable casting speed, and weak cooling control in the secondary cooling stage, the internal and surface quality of the final billet was ensured, avoiding defects such as subcutaneous bubbles, inclusions, and cracks caused by poor protection and improper solidification control.

[0027] The decarbonization threshold in step S2 is 0.12%.

[0028] The minimum decarbonization threshold in step S3 is 0.08-0.11%, and the maximum temperature threshold is 1640-1660℃.

[0029] The slag control threshold in step S4 is 20-30%, that is, when the outflow of molten steel from the furnace is 20-30%, alloys and auxiliary materials are added into the furnace.

[0030] The shielding object in step S4 is a slag-blocking ball. The slag-blocking ball is used to block slag during the tapping of molten steel, thereby controlling the amount of slag discharged from the molten steel to within 3 kg / t.

[0031] The deoxidation and alloying step in step S4 includes: When the steel reaches 20-30% of its capacity, alloys and auxiliary materials are added into the furnace, namely, carbon raisers, silicon manganese, silicon calcium barium, aluminum blocks, silicon calcium wire, and lime blocks. The intense stirring during the tapping process causes the alloys and auxiliary materials to melt rapidly and form top slag, which adsorbs the floating inclusions and initially reduces the oxygen content of the molten steel to 120-140 ppm.

[0032] The S4 step also includes ladle calcium treatment, which is carried out as follows: after the molten steel is tapped, the furnace temperature is adjusted and the oxygen is fixed, and then 120-150 meters of silicon-calcium wire is fed in to control the free oxygen in the molten steel to within 50 ppm.

[0033] Therefore, a low-cost smelting process to reduce the oxygen content of molten steel is proposed. Through process innovation and technological breakthroughs in the converter smelting process itself, the oxygen content of the final molten steel can be precisely, stably, and deeply controlled, significantly reducing it from the conventional 150-200 ppm level and stabilizing it below 90 ppm. This allows for meeting the stringent requirements of specific customers for steel purity and internal quality without relying on additional refining equipment, and fundamentally eliminating a series of defects in continuously cast billets caused by high oxygen content.

Claims

1. A low-cost smelting process for reducing the oxygen content of molten steel, characterized in that: Includes the following steps: S1, in the early stage of converter quenching, the oxygen supply to the furnace body is carried out in a conventional intensity manner, so that the molten steel can be heated up and decarburized quickly. The temperature and carbon content of the molten steel in the furnace body are monitored in real time through the auxiliary gun to obtain data information inside the furnace body. S2, when the auxiliary gun detects that the carbon content of the molten steel in the furnace has dropped to the decarburization threshold, the oxygen supply intensity inside the furnace is reduced, and the bottom blowing argon gas weak stirring mechanism inside the furnace is turned on to introduce argon gas into the furnace to avoid the molten steel from being over-oxidized due to violent oxygen blowing. S3, when the auxiliary gun monitors in real time that the carbon content of the molten steel in the furnace is stable at the minimum decarburization threshold and the temperature reaches the maximum temperature threshold, the application of oxygen to the furnace is stopped, thereby controlling the initial carbon content of the molten steel. S4. When the temperature and carbon content of the molten steel in the furnace reach the requirements for tapping, a shield is set at the tapping position of the furnace to accurately block slag. A slag-forming agent is added to the molten steel impact area at the tapping position. When the tapping reaches the slag control threshold, alloys and auxiliary materials are added to the furnace. The intense stirring during the tapping process allows the alloys and auxiliary materials to melt quickly and form top slag, which adsorbs the floating inclusions. S5, the ladle used to load molten steel is transferred to the argon treatment station, and the bottom blowing argon soft blowing mode is turned on and kept before the steel is loaded into the continuous casting. S6 performs full-protection continuous casting of molten steel in the ladle, thereby completing the continuous casting and forging operation of molten steel.

2. The low-cost smelting process for reducing oxygen content in molten steel according to claim 1, characterized in that: The fully protected continuous casting method in step S6 includes the following steps: S21, the ladle is moved by a robotic arm so that argon gas is introduced into the connection between the ladle molten steel and the ladle drain to seal it and isolate it from the outside air. S22, which also features a double-layer covering agent process, receives molten steel again in the tundish, and the crystallizer is electromagnetically stirred to control the liquid level fluctuation within ±3mm. The casting speed is stabilized at 2.5-2.8m / min to avoid slag entrapment and secondary oxidation caused by liquid level fluctuation, thus ensuring the quality of the cast billet. S23. During the continuous casting process of molten steel, the cooling water is weakly cooled to ensure good atomization of the nozzles, ensure uniform cooling of the billet, and avoid internal cracks and center segregation.

3. The low-cost smelting process for reducing oxygen content in molten steel according to claim 1, characterized in that: The decarbonization threshold in step S2 is 0.12%.

4. The low-cost smelting process for reducing oxygen content in molten steel according to claim 1, characterized in that: The minimum decarbonization threshold in step S3 is 0.08-0.11%, and the maximum temperature threshold is 1640-1660℃.

5. The low-cost smelting process for reducing oxygen content in molten steel according to claim 1, characterized in that: The slag control threshold in step S4 is 20-30%, that is, when the outflow of molten steel from the furnace is 20-30%, alloys and auxiliary materials are added into the furnace.

6. The low-cost smelting process for reducing oxygen content in molten steel according to claim 5, characterized in that: The shielding object in step S4 is a slag-blocking ball. The slag-blocking ball is used to block slag during the tapping of molten steel, thereby controlling the amount of slag discharged from the molten steel to within 3 kg / t.

7. The low-cost smelting process for reducing oxygen content in molten steel according to claim 1, characterized in that: The deoxidation and alloying step in step S4 includes: When the steel reaches 20-30% of its capacity, alloys and auxiliary materials are added into the furnace, namely, carbon raisers, silicon manganese, silicon calcium barium, aluminum blocks, silicon calcium wire, and lime blocks. The intense stirring during the tapping process causes the alloys and auxiliary materials to melt rapidly and form top slag, which adsorbs the floating inclusions and initially reduces the oxygen content of the molten steel to 120-140 ppm.

8. The low-cost smelting process for reducing oxygen content in molten steel according to claim 7, characterized in that: Step S4 also includes steel ladle calcium treatment, the specific method of which is as follows: After the molten steel is tapped, the furnace temperature is adjusted and the oxygen level is stabilized. Then, 120-150 meters of silicon-calcium wire is fed in to control the free oxygen in the molten steel to within 50 ppm.

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