A method for controlling sulfur smelting of welding wire steel ER50-6S
By employing the KR desulfurization, converter smelting, and LF refining process, combined with the addition of alloys during converter tapping and the adjustment of the slag system during LF refining, the problem of sulfur content control in welding wire steel ER50-6S was solved, achieving low-cost and stable sulfur content control, and improving welding performance and molten steel quality.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- CHANGSHU LONGTENG SPECIAL STEEL CO LTD
- Filing Date
- 2023-12-28
- Publication Date
- 2026-05-12
AI Technical Summary
Controlling the sulfur content in welding wire steel ER50-6S is difficult, as it affects welding performance and quality. In particular, desulfurization is severe in the later stages of LF smelting, requiring the addition of sulfur lines for adjustment, which is both difficult to control and costly.
The process involves KR desulfurization, converter smelting, LF refining, and continuous casting. By strictly controlling KR hot metal desulfurization, the total sulfur content in the converter, and the slag basicity, combined with alloy additions during converter tapping and slag system adjustments before LF refining, the sulfur content of molten steel can be precisely controlled, avoiding the need for traditional calcium feeding lines or sulfur-added iron adjustments.
Stable control of sulfur content in welding wire steel ER50-6S was achieved, reducing smelting costs, improving steel quality and continuous casting speed, reducing labor and smelting time, and avoiding the defects of traditional methods.
Abstract
Description
[0001] This invention relates to a controlled sulfur smelting method for welding wire steel ER50-6S, belonging to the technical field of welding wire steel smelting. Background Technology
[0002] Sulfur is typically considered a harmful element and must be controlled during steelmaking. It is almost insoluble in steel, but forms compounds with iron, existing as FeS. FeS forms a low-melting-point eutectic with Fe (melting point 985°C). When steel is hot-worked at around 1200°C, the low-melting-point eutectic distributed at the grain boundaries will melt and crack, a phenomenon known as hot brittleness. Excessive sulfur in welding steel can easily cause segregation in the weld, forming low-melting-point eutectic and promoting crack formation or embrittlement in the weld.
[0003] The sulfur content in molten steel ER50-6S welding wire needs to be controlled between 0.008% and 0.015%. Too low a sulfur content results in poor molten pool fluidity during welding, while too high a sulfur content causes hot brittleness at the weld site, affecting welding performance and quality. The limited range of sulfur content in the steel makes control extremely difficult. In particular, severe desulfurization occurs in the later stages of the LF smelting process, necessitating the addition of sulfur to maintain the appropriate sulfur ratio. The smelting process technology designed and developed in this invention solves the key technical problem of controlling the stability of sulfur content in ER50-6S welding wire. Summary of the Invention
[0004] To address the aforementioned problems, this invention discloses a controlled-sulfur smelting method for welding wire steel ER50-6S, the specific technical solution of which is as follows:
[0005] A controlled sulfur smelting method for welding wire steel ER50-6S, wherein the chemical composition of the welding wire steel, by mass percentage, includes: C: 0.06-0.09%, Si: 0.8-1.0%, Mn: 1.4-1.7%, P≤0.02%, S: 0.008-0.015%, Alt≤0.005%, T.Ca≤0.0008%, and other unavoidable components;
[0006] The smelting process includes KR desulfurization, converter smelting, LF refining, and continuous casting, and production is carried out according to the following steps:
[0007] Step 1: KR desulfurization. After KR desulfurization, the molten iron obtained has C: 4.1-4.5%, S: 0.003-0.008%, and a temperature of 1300-1360℃.
[0008] Step 2: Converter smelting. Desulfurized molten iron and high-quality scrap steel are added to the converter for smelting. The scrap steel ratio is 15-20%. The final molten steel composition at the converter smelting point is: C: 0.03-0.06%, O: 0.040-0.075%, P≤0.018%, S≤0.015%, temperature above 1630℃, and the final slag basicity of the converter is CaO / SiO2=2.5-3.0, T.Fe: 13-18%.
[0009] Step 3: Converter tapping. When the sulfur content in the molten steel is 0.010-0.015%, after tapping 25% of the steel, add alloys in the order of ferrosilicon and high-silicon ferromanganese. All alloys should be added before the end of tapping. When the sulfur content in the molten steel is ≤0.010%, add sulfur-containing slag and alloys in the order of sulfur-containing slag, ferrosilicon, and high-silicon ferromanganese. All sulfur-containing slag and alloys should be added before the end of tapping. Then add calcium silicate synthetic slag. The ladle should be bottom blown and stirred throughout the tapping process. After the synthetic slag is added, stir for another 3-5 minutes. The resulting slag has a basicity of CaO / SiO2 = 0.4-0.7 and a T.Fe+MnO content of 3-5%. Then it is transported to LF refining treatment.
[0010] Step 4: LF Refining. Upon arrival at the LF refining station, samples are taken to measure the chemical composition of the molten steel and slag. Bottom blowing and stirring are initiated in the ladle. After the composition of the molten steel and slag is analyzed, low-titanium, low-aluminum ferrosilicon and metallic manganese are added to adjust the molten steel composition according to the target composition of the steel grade. Then, lime and silicon carbide are added to adjust the slag composition, achieving a slag basicity of CaO / SiO2 = 0.9-1.2 and a T.Fe+MnO content of 2.5-4.5%. Electricity is then applied to raise the temperature until the molten steel reaches the target value. The bottom blowing in the ladle is then switched to soft stirring mode. After soft stirring is completed, the molten steel is transported to the continuous casting station for pouring.
[0011] Step 5: Continuous casting protective pouring.
[0012] Furthermore, in step 1, during the KR desulfurization process, molten iron samples are taken at 3-5 minute intervals to analyze the S content. When the S content is between 0.003-0.008%, desulfurization is stopped and slag removal is performed, with a slag removal rate ≥95%.
[0013] Furthermore, in step 2, the high-quality scrap steel has an S content of 0.005-0.015%, a P content of ≤0.02%, and the remainder is Fe and other unavoidable components.
[0014] Furthermore, in step 3, the alloy composition, by mass percentage, is as follows: ferrosilicon: Si: 70-75%, P≤0.025%, S≤0.015%, with the remainder being Fe and other unavoidable components; high-silicon manganese ferrosilicon: Si: 25-30%, Mn: 62-67%, P≤0.015%, S≤0.01%, with the remainder being Fe and other unavoidable components; sulfur-containing slag: S: 2.5-5.5%, CaO / SiO2=0.3-0.5, and other unavoidable components, with a particle size of 3-10mm accounting for ≥90%, and a maximum not exceeding 20mm; calcium silicate synthetic slag: CaO: 45-55%, SiO2: 35-45%, MgO: 5-10%, with the remainder being unavoidable components.
[0015] Furthermore, in step 3, during the tapping process, 4.5-5.5 kg / t of ferrosilicon, 17-19 kg / t of high-silicon manganese ferrosilicon, 2.5-3.5 kg / t of sulfur-containing slag, and 10-15 kg / t of calcium silicate synthetic slag are added. During the tapping process, the bottom blowing flow rate of the ladle is 400-500 L / min, and the bottom blowing flow rate at the end of tapping is 300-400 NL / min.
[0016] Furthermore, in step 4, the lime contains ≥95% CaO and other unavoidable components; the silicon carbide contains ≥98% SiC and other unavoidable components.
[0017] Furthermore, in step 4, the LF refining inlet temperature is ≥1560℃, the ladle bottom blowing flow rate is 100-150NL / min during the non-operation stage of the LF refining process, the ladle bottom blowing flow rate is 200-250NL / min during the alloying stage, the ladle bottom blowing flow rate is 150-200NL / min during the stage of adding lime and silicon carbide to adjust the slag composition, the ladle bottom blowing flow rate is 200-250NL / min during the power-on heating stage, and the ladle bottom blowing flow rate is 50-100NL / min during the soft stirring stage, with a soft stirring time ≥20min.
[0018] The working principle of this invention is:
[0019] This invention provides a method for precisely controlling the sulfur content of welding wire steel ER50-6S. According to the method described in this invention, the sulfur content of welding wire steel ER50-6S can be controlled at the target level without feeding calcium wire.
[0020] First, by strictly controlling the sulfur content after KR hot metal desulfurization, combined with measures such as controlling the composition of scrap steel in the converter, the total sulfur content in the converter reaches the target. At the same time, by further controlling the basicity and oxidizing properties of the slag at the end of the converter, reducing the sulfur capacity of the slag, and further stabilizing the sulfur content of the molten steel at the end of the converter, the S content in the molten steel at the end of the converter smelting is controlled at a reasonable level.
[0021] Secondly, when the sulfur content in the converter steel is low, low-basicity sulfur-containing slag is added, while lime and fluorite are not added for slag formation. The deoxidation product is mainly SiO2, which further reduces the basicity of the slag. Under the action of the oxidizing properties of the molten steel and the ultra-low basicity slag, a large amount of sulfur element in the sulfur-containing slag will return to the molten steel, increasing the sulfur content of the molten steel. After desulfurization is completed, low-basicity slag system is added again, while the relatively weak bottom blowing of the ladle is controlled to avoid further desulfurization of the slag.
[0022] Finally, in the early stage of LF refining, an innovative design was adopted to add lime and slag-forming materials without adding alloys or slag-forming materials. The slag composition was adjusted after the steel composition met the standards. This avoided the desulfurization caused by bottom blowing and stirring when adjusting alloys after the slag composition was adjusted in advance. In addition, the slag basicity was generally low and had a slight oxidizing property during the refining process. The bottom blowing of the ladle was weak and the slag had almost no desulfurization effect, thus achieving precise control of the sulfur content in the steel.
[0023] The beneficial effects of this invention are:
[0024] This invention innovatively designs technical measures for precise control of sulfur content in molten steel during the KR and converter processes, stabilizing the sulfur content of molten steel at the converter endpoint. At the same time, by utilizing the formation conditions of ultra-low basicity slag at converter tapping and combining it with sulfur-containing slag, a low-cost sulfur-increasing effect is achieved, further enhancing the stability of sulfur content in molten steel.
[0025] This invention provides a precise design process for controlling ultra-low basicity and variable basicity, and weakly oxidizing slag system during the process from converter tapping to LF refining. Combined with low-intensity bottom blowing control technology in the ladle, it significantly reduces the desulfurization effect of slag.
[0026] This invention breaks with traditional thinking by eliminating the traditional approach of adjusting the sulfur content in molten steel using sulfur-feeding lines or sulfur-added iron. It has advantages such as lower cost and stronger control stability.
[0027] This invention 1. reduces smelting time and smelting cost; 2. improves steel quality, soft blowing time and continuous pouring speed; 3. reduces worker labor output and eliminates the need for additional sulfur. Detailed Implementation
[0028] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that the following specific embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.
[0029] The process requirements for welding wire steel ER50-6S of this invention are as follows: S: 0.008%-0.015%, C: ≤0.05% at converter tapping, lime addition at converter tapping controlled at 300Kg, argon gas control at 280-320NL / min in the early stage of LF, 240-260NL / min in the middle stage, and 220-240NL / min in the later stage, bypass smelting is prohibited throughout the process, total lime consumption in LF does not exceed 200Kg, fluorite ball addition is 100Kg-150Kg, deoxidizer ferrosilicon powder and 95% silicon carbide are used for diffusion deoxidation, and should not be added to the argon port to prevent carbon increase in molten steel. Ferrosilicon powder is added in small amounts and multiple times in the later stage of refining to maintain a reducing atmosphere, and the final slag basicity is controlled at 1.5-1.9.
[0030] The smelting process of this invention includes KR desulfurization, converter smelting, LF refining, and continuous casting, and is carried out according to the following steps:
[0031] Step 1: KR desulfurization. After KR desulfurization, the molten iron obtained has C: 4.1-4.5%, S: 0.003-0.008%, and temperature 1300-1360℃. During KR desulfurization, molten iron samples are taken every 3-5 minutes to analyze the S content. When the S content is 0.003-0.008%, desulfurization is stopped, and slag removal is performed with a slag removal rate ≥95%.
[0032] Step 2: Converter smelting. Desulfurized molten iron and high-quality scrap steel are added to the converter for smelting. The scrap steel ratio is 15-20%. The final molten steel composition at the converter smelting point is: C: 0.03-0.06%, O: 0.040-0.075%, P≤0.018%, S≤0.015%, temperature above 1630℃. The final slag basicity of the converter is CaO / SiO2=2.5-3.0, T.Fe: 13-18%. The high-quality scrap steel has an S content of 0.005-0.015%, a P content ≤0.02%, and the remainder is Fe and other unavoidable components.
[0033] Step 3: Converter tapping. When the sulfur content in the molten steel is 0.010-0.015%, after tapping 25% of the steel, add alloys in the order of ferrosilicon and high-silicon ferromanganese, ensuring all alloys are added before the end of tapping. When the sulfur content in the molten steel is ≤0.010%, add sulfur-containing slag and alloys in the order of sulfur-containing slag, ferrosilicon, and high-silicon ferromanganese, ensuring all sulfur-containing slag and alloys are added before the end of tapping. Then add calcium silicate synthetic slag. Throughout the tapping process, bottom blowing and stirring are maintained in the ladle. After adding the synthetic slag, stir for another 3-5 minutes. The resulting slag has a basicity of CaO / SiO2 = 0.4-0.7 and a T.Fe+MnO content of 3-5%, and is then transported to the LF refining plant. Alloy composition is expressed as a percentage by mass. Ferrosilicon: Si: 70-75%, P≤0.025%, S≤0.015%, the remainder being Fe and other unavoidable components; High-silicon manganese ferrosilicon: Si: 25-30%, Mn: 62-67%, P≤0.015%, S≤0.01%, the remainder being Fe and other unavoidable components; Sulfur-containing slag: S: 2.5-5.5%, CaO / SiO2=0.3-0.5, and other unavoidable components, with a particle size of 3-10mm accounting for ≥90%, and a maximum not exceeding 20mm; Calcium silicate synthetic slag: CaO: 45-55%, SiO2: 35-45%, MgO: 5-10%, the remainder being unavoidable components.
[0034] Step 4: LF Refining. Upon arrival at the LF refining station, samples are taken to measure the chemical composition of the molten steel and slag. Bottom blowing and stirring are initiated in the ladle. After the composition of the molten steel and slag is analyzed, low-titanium, low-aluminum ferrosilicon and metallic manganese are added to adjust the molten steel composition according to the target steel grade. Then, lime and silicon carbide are added to adjust the slag composition, achieving a slag basicity of CaO / SiO2 = 0.9-1.2 and a T.Fe+MnO content of 2.5-4.5%. Electricity is then applied to raise the temperature of the molten steel to the target value. The bottom blowing in the ladle is then switched to soft stirring mode. After soft stirring, the molten steel is transported to the continuous casting station for pouring. Lime: CaO ≥ 95%, and other unavoidable components; Silicon carbide: SiC ≥ 98%, and other unavoidable components. The LF refining inlet temperature is ≥1560℃. During the non-operational stage of the LF refining process, the ladle bottom blowing flow rate is 100-150NL / min. During the alloying stage, the ladle bottom blowing flow rate is 200-250NL / min. During the stage of adding lime and silicon carbide to adjust the slag composition, the ladle bottom blowing flow rate is 150-200NL / min. During the power-on heating stage, the ladle bottom blowing flow rate is 200-250NL / min. During the soft stirring stage, the ladle bottom blowing flow rate is 50-100NL / min, and the soft stirring time is ≥20min.
[0035] Step 5: Continuous casting protective pouring.
[0036] The technical means disclosed in this invention are not limited to those disclosed above, but also include technical solutions composed of any combination of the above technical features.
[0037] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.
Claims
1. A controlled-sulfur smelting method for welding wire steel ER50-6S, characterized in that, The chemical composition of the welding wire steel, by mass percentage, includes: C: 0.06-0.09%, Si: 0.8-1.0%, Mn: 1.4-1.7%, P≤0.02%, S: 0.008-0.015%, Alt≤0.005%, T.Ca≤0.0008%, and other unavoidable components; The smelting process includes KR desulfurization, converter smelting, LF refining, and continuous casting, and production is carried out according to the following steps: Step 1: KR desulfurization. After KR desulfurization, the molten iron obtained has C: 4.1-4.5%, S: 0.003-0.008%, and a temperature of 1300-1360℃. Step 2: Converter smelting. Desulfurized molten iron and high-quality scrap steel are added to the converter for smelting. The scrap steel ratio is 15-20%. The final molten steel composition at the converter smelting point is: C: 0.03-0.06%, O: 0.040-0.075%, P≤0.018%, S≤0.015%, temperature above 1630℃, and the final slag basicity of the converter is CaO / SiO2=2.5-3.0, T.Fe: 13-18%. Step 3: Converter tapping. When the sulfur content in the molten steel is 0.010-0.015%, after tapping 25% of the steel, add alloys in the order of ferrosilicon and high-silicon ferromanganese. All alloys should be added before the end of tapping. When the sulfur content in the molten steel is ≤0.010%, add sulfur-containing slag and alloys in the order of sulfur-containing slag, ferrosilicon, and high-silicon ferromanganese. All sulfur-containing slag and alloys should be added before the end of tapping. Then add calcium silicate synthetic slag. The ladle should be bottom blown and stirred throughout the tapping process. After the synthetic slag is added, stir for another 3-5 minutes. The resulting slag has a basicity of CaO / SiO2 = 0.4-0.7 and a T.Fe+MnO content of 3-5%. Then it is transported to LF refining treatment. Step 4: LF Refining. Upon arrival at the LF refining station, samples are taken to measure the chemical composition of the molten steel and slag. Bottom blowing and stirring are initiated in the ladle. After the composition of the molten steel and slag is analyzed, low-titanium, low-aluminum ferrosilicon and metallic manganese are added to adjust the molten steel composition according to the target composition of the steel grade. Then, lime and silicon carbide are added to adjust the slag composition, achieving a slag basicity of CaO / SiO2 = 0.9-1.2 and a T.Fe+MnO content of 2.5-4.5%. Electricity is then applied to raise the temperature until the molten steel reaches the target value. The bottom blowing in the ladle is then switched to soft stirring mode. After soft stirring is completed, the molten steel is transported to the continuous casting station for pouring. Step 5: Continuous casting protective pouring.
2. The controlled sulfur smelting method for welding wire steel ER50-6S according to claim 1, characterized in that, In step 1, during the KR desulfurization process, molten iron samples are taken every 3-5 minutes to analyze the sulfur content. When the sulfur content is between 0.003-0.008%, desulfurization is stopped and slag removal is performed, with a slag removal rate of ≥95%.
3. The controlled sulfur smelting method for welding wire steel ER50-6S according to claim 1, characterized in that, In step 2, the high-quality scrap steel has an S content of 0.005-0.015%, a P content of ≤0.02%, and the remainder is Fe and other unavoidable components.
4. The controlled sulfur smelting method for welding wire steel ER50-6S according to claim 1, characterized in that, In step 3, the alloy composition, by mass percentage, is as follows: ferrosilicon: Si: 70-75%, P≤0.025%, S≤0.015%, with the remainder being Fe and other unavoidable components; high-silicon manganese ferrosilicon: Si: 25-30%, Mn: 62-67%, P≤0.015%, S≤0.01%, with the remainder being Fe and other unavoidable components; sulfur-containing slag: S: 2.5-5.5%, CaO / SiO2=0.3-0.5, and other unavoidable components, with a particle size of 3-10mm accounting for ≥90%, and a maximum not exceeding 20mm; calcium silicate synthetic slag: CaO: 45-55%, SiO2: 35-45%, MgO: 5-10%, with the remainder being unavoidable components.
5. The controlled sulfur smelting method for welding wire steel ER50-6S according to claim 1, characterized in that, In step 3, during the tapping process, 4.5-5.5 kg / t of ferrosilicon, 17-19 kg / t of high-silicon manganese ferrosilicon, 2.5-3.5 kg / t of sulfur-containing slag, and 10-15 kg / t of calcium silicate synthetic slag are added. The bottom blowing rate of the ladle during the tapping process is 400-500 L / min, and the bottom blowing flow rate at the end of the tapping process is 300-400 NL / min.
6. The controlled sulfur smelting method for welding wire steel ER50-6S according to claim 1, characterized in that, In step 4, the lime contains ≥95% CaO and other unavoidable components; the silicon carbide contains ≥98% SiC and other unavoidable components.
7. The controlled sulfur smelting method for welding wire steel ER50-6S according to claim 1, characterized in that, In step 4, the LF refining inlet temperature is ≥1560℃. During the non-operational stage of the LF refining process, the ladle bottom blowing flow rate is 100-150NL / min. During the alloying stage, the ladle bottom blowing flow rate is 200-250NL / min. During the stage of adding lime and silicon carbide to adjust the slag composition, the ladle bottom blowing flow rate is 150-200NL / min. During the power-on heating stage, the ladle bottom blowing flow rate is 200-250NL / min. During the soft stirring stage, the ladle bottom blowing flow rate is 50-100NL / min, and the soft stirring time is ≥20min.