Process for the phased melting through of the cold steel of the furnace bottom of an electric furnace

Abstract

The present application relates to a kind of electric furnace bottom cold steel stage penetration process, belong to steel smelting technical field.To achieve the purpose of the present application, the process includes the following steps:A. arc heating to bottom cold steel, until initial molten pool is formed on the surface of cold steel;B. continue heating, while blowing oxygen and spraying carbon, until the molten pool area expands to cover the entire cold steel surface;C. discharge the slag formed in the furnace, and add lime 35-40 kg / t molten steel to the furnace to re-slag;D. heating, while blowing oxygen and spraying carbon, when the molten pool temperature rises to 1670-1680 ℃, stop power supply, measure the molten pool temperature after 5 minutes of standing;E. if the molten pool temperature decreases by more than 50 ℃ after 5 minutes of standing, repeat step D until the temperature drop is less than or equal to 50 ℃ after 5 minutes of standing, and the bottom cold steel is completely penetrated.The process of the present application is efficient and thorough, reliable in quality, energy saving, furnace lining protection, and strong operability.

Description

Technical Field

[0001] This invention relates to a staged melting process for cold steel at the bottom of an electric furnace, belonging to the field of steel smelting technology. Background Technology

[0002] In electric arc furnace steelmaking, unexpected situations such as equipment failure (e.g., electrode breakage, hydraulic system malfunction), unplanned shutdowns (e.g., power outages, crane malfunctions), or abnormal production scheduling may cause molten steel to solidify completely at the bottom of the furnace due to the inability to drain it in time. This results in a layer of cold steel with complex composition and uneven thickness, including solidified steel and slag, hereinafter referred to as "cold steel". This phenomenon is particularly common in heavy casting and forging steel plants with relatively slow production pace and long smelting cycles.

[0003] The cold-rolled steel layer has significant physical properties that make it difficult to process: 1. Formation of "false furnace bottom": Cold steel forms a solid metal-slag mixture layer on the refractory material of the furnace bottom, raising the actual working surface of the furnace bottom and encroaching on the effective molten pool volume of the electric furnace.

[0004] 2. Uneven melting: Due to uneven thickness and poor thermal conductivity, traditional heating methods can easily cause the upper molten steel to overheat to boiling, while the lower cold steel remains solidified, creating an awkward situation of "liquid on top and solid on the bottom".

[0005] Traditionally, the industry has lacked efficient and specialized solutions for dealing with cold steel at the bottom of the furnace, relying mainly on passive and extensive methods. This involves attempting to gradually melt the steel in subsequent normal smelting heats, typically more than 10 heats, by increasing the tapping temperature and extending the smelting time. This traditional process has a series of drawbacks: High energy consumption: In order to melt the huge cold steel, each furnace requires an additional large amount of electrical and chemical energy, resulting in a significant increase in the unit product's electricity consumption, oxygen consumption, and carbon powder consumption, thus increasing production costs.

[0006] Disruption of production rhythm: The abnormally long smelting cycle disrupted the normal production organization order, resulting in a decrease in equipment utilization, waiting for subsequent continuous casting or refining processes, and affecting the efficiency of the entire production line.

[0007] Fluctuations in molten steel quality and output: Uncontrolled melting of cold steel leads to instability in the furnace thermal regime, affecting dephosphorization and decarburization effects, and causing fluctuations in steel composition and temperature. Simultaneously, the reduction in actual charge volume due to the erosion of effective volume results in a decrease and instability in single-furnace steel output, posing challenges to production management.

[0008] Furnace lining safety and lifespan risks: To melt the cold steel at the bottom, operators are often forced to use high-power electricity for extended periods, causing the electric arc to continuously approach or even directly act on the furnace bottom area. This results in the furnace lining refractory material being subjected to abnormally high-temperature loads and arc erosion, accelerating its erosion rate and significantly shortening the furnace lining lifespan.

[0009] Operational safety risks: Due to the presence of a "false furnace bottom," operators may misjudge the actual depth of the molten pool. In subsequent heats, if scrap steel is added at the normal capacity, the molten steel level may actually rise to a dangerous height, causing a "steel run" accident that spills from the furnace door or furnace cover gaps, threatening the safety of personnel and equipment.

[0010] Although the problem of cold steel melting at the furnace bottom has long plagued some electric arc furnace steelmaking plants, to date, no systematic and mature process reports have been found in publicly available patent literature and non-patent technology materials that can proactively and completely solve this problem within a single heat. Existing technologies are mostly based on localized operational experience, such as simply increasing power or extending smelting time, without offering a complete solution from a systemic perspective, addressing aspects such as phased control of energy input, slag condition management, and verification of melt penetration. Therefore, developing a dedicated cold steel melting process that is efficient, reliable, and equipment-friendly has become an urgent technical challenge in this field. Summary of the Invention

[0011] The purpose of this invention is to provide a staged melting process for cold steel at the bottom of an electric furnace.

[0012] To achieve the objective of this invention, the process includes the following steps: A. Initiate arc heating on the cold steel at the bottom of the furnace until an initial molten pool forms on the surface of the cold steel; B. Continue heating while blowing oxygen and spraying carbon until the molten pool area expands to cover the entire surface of the cold steel; C. Remove the slag formed in the furnace and add 35-40 kg / t of lime to the furnace to re-form slag; D. Heat the furnace while blowing oxygen and spraying carbon. When the temperature of the molten pool reaches 1670-1680°C, stop the power supply and let it stand for 5 minutes before measuring the temperature of the molten pool. E. If the temperature drop of the molten pool is greater than 50°C after standing for 5 minutes, repeat step D until the power supply is stopped, and the temperature drop after standing for 5 minutes is less than or equal to 50°C, and the cold steel at the bottom of the furnace is completely melted.

[0013] In one specific embodiment, the arc-initiating heating in step A adopts a power supply system with an electrode voltage of 190-200V and an electrode current of 45-50kA.

[0014] In one specific embodiment, the continued heating in step B uses a power supply system with an electrode voltage of 240-250V and an electrode current of 45-50kA.

[0015] In one specific embodiment, the oxygen flow rate of the oxygen blowing in step B is 1150-1250 Nm³ / h.

[0016] In one specific embodiment, the carbon injection rate in step B is 75–85 kg / min.

[0017] In one specific embodiment, the heating in step D uses a power supply system with an electrode voltage of 300-310V and an electrode current of 38-40kA.

[0018] In one specific embodiment, the oxygen flow rate of the oxygen blowing in step D is 1250-1350 Nm³ / h.

[0019] In one specific embodiment, the carbon injection rate in step D is 95–105 kg / min.

[0020] In one specific embodiment, after the cold steel at the bottom of the furnace is completely melted, the process further includes step F. Adding 8-12 kg / t of lime, 7-9 kg / t of carbon powder, and 300-400 kg / t of low-density briquetted scrap steel to the furnace, and using a power supply system of 300-310V electrode voltage and 38-40kA electrode current for melting, while blowing oxygen and injecting carbon, and after the scrap steel is basically melted, it is transferred to conventional smelting.

[0021] In one specific embodiment, the oxygen flow rate in step F is 1050–1150 Nm³ / h; the carbon injection rate is 75–85 kg / min.

[0022] Beneficial effects: 1. High efficiency and thoroughness: Through phased and refined control and an innovative "melting penetration verification" mechanism, the cold steel is thoroughly melted in a single heat.

[0023] 2. Reliable quality: By removing slag and re-forming slag, the adverse effects of peroxide slag on the quality of molten steel (especially phosphorus content) are avoided.

[0024] 3. Energy saving and consumption reduction: "Fusion verification" avoids blind heating and achieves precise heating.

[0025] 4. Furnace lining protection: It eliminates highly fluid slag and avoids prolonged high-temperature loads on the furnace body refractory materials.

[0026] 5. High operability: The process flow is clear, the parameters are specific, and it is easy to standardize the operation on site. Attached Figure Description

[0027] Figure 1 This is a process flow diagram for the first stage of the embodiment; Figure 2This is a process flow diagram for the second stage of the embodiment; Figure 3 This is a process flow diagram for the third stage of the embodiment; Figure 4 This is a process flow diagram for the fourth stage of the embodiment; Figure 5 This is a process flow diagram for the fifth stage of the embodiment. Detailed Implementation

[0028] To achieve the objective of this invention, the process includes the following steps: A. Initiate arc heating on the cold steel at the bottom of the furnace until an initial molten pool forms on the surface of the cold steel; B. Continue heating while blowing oxygen and spraying carbon until the molten pool area expands to cover the entire surface of the cold steel; C. Remove the slag formed in the furnace and add 35-40 kg / t of lime to the furnace to re-form slag; D. Heat the furnace while blowing oxygen and spraying carbon. When the temperature of the molten pool reaches 1670-1680°C, stop the power supply and let it stand for 5 minutes before measuring the temperature of the molten pool. E. If the temperature drop of the molten pool is greater than 50°C after standing for 5 minutes, repeat step D until the power supply is stopped, and the temperature drop after standing for 5 minutes is less than or equal to 50°C, and the cold steel at the bottom of the furnace is completely melted.

[0029] The process of this invention is specifically designed for processing large lumps of cold steel formed at the bottom of an electric furnace due to the complete solidification of molten steel.

[0030] In one specific embodiment, the arc-initiating heating in step A adopts a power supply system with an electrode voltage of 190-200V and an electrode current of 45-50kA.

[0031] Step A utilizes the voltage and current regime of this invention to achieve rapid arc initiation and penetrating heating, while ensuring high energy utilization.

[0032] In one specific embodiment, the continued heating in step B uses a power supply system with an electrode voltage of 240-250V and an electrode current of 45-50kA.

[0033] In one specific embodiment, the oxygen flow rate of the oxygen blowing in step B is 1150-1250 Nm³ / h.

[0034] In one specific embodiment, the carbon injection rate in step B is 75–85 kg / min.

[0035] In one specific embodiment, the heating in step D uses a power supply system with an electrode voltage of 300-310V and an electrode current of 38-40kA.

[0036] In one specific embodiment, the oxygen flow rate of the oxygen blowing in step D is 1250-1350 Nm³ / h.

[0037] In one specific embodiment, the carbon injection rate in step D is 95–105 kg / min.

[0038] In one specific embodiment, after the cold steel at the bottom of the furnace is completely melted, the process further includes step F. Adding 8-12 kg / t of lime, 7-9 kg / t of carbon powder, and 300-400 kg / t of low-density briquetted scrap steel to the furnace, and using a power supply system of 300-310V electrode voltage and 38-40kA electrode current for melting, while blowing oxygen and injecting carbon, and after the scrap steel is basically melted, it is transferred to conventional smelting.

[0039] In one specific embodiment, the oxygen flow rate in step F is 1050–1150 Nm³ / h; the carbon injection rate is 75–85 kg / min.

[0040] The specific embodiments of the present invention will be further described below with reference to examples, but the present invention is not limited to the scope of the embodiments described herein.

[0041] Example 1

[0042] The process of this invention was applied in four industrial trials on an 80-ton electric arc furnace at a casting and forging company to treat cold steel from the furnace bottom caused by equipment failure. In each of the four trials, the weight of solidified cold steel was approximately 40 tons, and the amount of slag was approximately 4 tons.

[0043] The specific application parameters are as follows: like Figure 1 As shown, the first stage (stable arc initiation) uses a power supply of 196V and 47kA. This operation continues until an initial molten pool forms on the surface of the cold steel.

[0044] like Figure 2 As shown, the second stage (expanding the molten pool): The power supply is adjusted to 241V and 47kA. Simultaneously, the oxygen flow rate is increased to 1200Nm³, and the carbon injection rate is maintained at 80kg / min. This operation continues until the molten pool area expands to cover the entire surface of the cold steel.

[0045] like Figure 3 As shown, the third stage (slag discharge and slag formation): The molten slag formed in the previous stage is discharged from the furnace door, and then 1.5 tons of lime (about 37.5 kg / t) is added into the furnace to re-form slag.

[0046] like Figure 4As shown, the fourth stage (melt penetration verification) involved adjusting the power supply to 306V and 39kA. Simultaneously, the oxygen flow rate was increased to 1300 Nm³, and the carbon injection rate was increased to 100 kg / min. When the molten pool temperature reached 1670℃, the power supply was stopped. After standing for 5 minutes, the temperature drop was measured at 67℃. This heating and temperature measurement process was repeated three times. On the fourth attempt, after power was cut off and the pool was left to stand for 5 minutes, the temperature drop was 27℃, confirming complete melt penetration.

[0047] like Figure 5 As shown, the fifth stage (transition to normal smelting) involves adding 450 kg of lime, 300 kg of carbon powder, and 16 tons of low-density briquetted scrap steel. The power supply is adjusted to 308V and 39kA, supplemented with 1100 Nm³ of oxygen and 80 kg / min of carbon powder for melting. After the scrap steel is melted, the process transitions to normal operation.

[0048] Application Results: All four applications achieved consistent and excellent results. Approximately 40 tons of cold steel from the furnace bottom were completely melted within a single smelting cycle. The phosphorus content of the final molten steel remained stable at 0.002%, with minimal fluctuations each time, fully meeting smelting requirements. The entire process demonstrated significant protection for the electric furnace refractory materials, with only slight erosion of the furnace lining as seen under normal production conditions. This proves that the process of this invention possesses extremely high reliability, stability, and repeatability.

[0049] Comparative Example 1

[0050] This comparative example omits the third stage of slag removal and the addition of 1.5 tons of lime; instead, 1 ton of lime is added only after the second stage. Other operating parameters are the same as in Example 1.

[0051] Application: It was carried out 3 times in total, with each time the weight of cold steel processed was about 43 tons and the amount of slag was about 4 tons.

[0052] Results: In all three smelting processes, the excessive fluidity of the unremoved slag caused severe erosion and corrosion of the refractory material along the electric arc furnace slag line. Although the cold steel was eventually completely melted, the unstable composition and severe over-oxidation of the slag led to large fluctuations in the phosphorus content of the final molten steel (ranging from a high of 0.0032% to a low of 0.0015%), indicating unstable dephosphorization. Conclusion: The lack of a slag removal and re-slag-forming stage leads to unstable slag control, jeopardizing furnace lining safety and posing risks to molten steel quality.

[0053] Comparative Example 2

[0054] After completing the third stage, this comparative example directly begins the fifth stage operation, omitting the fourth stage's deep melting and penetration verification process. Otherwise, it is the same as Example 1.

[0055] Application details: Approximately 45 tons of cold steel and 4 tons of slag were produced. Five heats were subsequently produced.

[0056] Results: Inspection after five heats revealed a large amount of unmelted cold steel remaining at the furnace bottom. The presence of this cold steel reduced the actual volume of the molten pool, leading to significant fluctuations in tapping temperature (highest at 1720℃, lowest at 1685℃). Unable to accurately assess the molten pool condition, operators added scrap steel in the normal amount during the fifth stage, resulting in two heats experiencing near-miss incidents of molten steel overflowing from the furnace door due to overfilling of the molten pool. Conclusion: The lack of a full-melting verification stage prevented confirmation of complete melting of the cold steel, leading to unstable production, safety risks, and low production efficiency (multiple heats still showed unmelted steel).

[0057] Comparative Example 3

[0058] This comparative example modifies the power supply parameters for the first stage, using a higher voltage and current: 306V and 52kA. Other stage parameters are the same as in Example 1.

[0059] Application: A total of 3 implementations were carried out, each time processing approximately 41 tons of cold steel and 4 tons of slag.

[0060] Results: The average power consumption per furnace in the three implementations increased by 13% compared to the example. Due to the excessively high input power, a large amount of energy was dissipated in the furnace through radiation and convection, resulting in reduced thermal efficiency, significantly increased energy consumption, and increased thermal load on the refractory materials of the furnace cover and walls. Conclusion: The excessively high energy input in the first stage not only failed to accelerate melting but also led to a sharp increase in energy consumption and could potentially damage the equipment, demonstrating the superiority of the parameter range set in this invention.

Claims

1. A staged melting process for cold steel at the bottom of an electric furnace, characterized in that, The process includes: A. Initiate arc heating on the cold steel at the bottom of the furnace until an initial molten pool forms on the surface of the cold steel; B. Continue heating while blowing oxygen and spraying carbon until the molten pool area expands to cover the entire surface of the cold steel; C. Remove the slag formed in the furnace and add 35-40 kg / t of lime to the furnace to re-form slag; D. Heat the furnace while blowing oxygen and spraying carbon. When the temperature of the molten pool reaches 1670-1680°C, stop the power supply and let it stand for 5 minutes before measuring the temperature of the molten pool. E. If the temperature drop of the molten pool is greater than 50°C after standing for 5 minutes, repeat step D until the power supply is stopped, and the temperature drop after standing for 5 minutes is less than or equal to 50°C, and the cold steel at the bottom of the furnace is completely melted. The arc-initiating heating described in step A uses a power supply system with an electrode voltage of 190-200V and an electrode current of 45-50kA.

2. The staged melting process for cold steelmaking at the bottom of an electric furnace according to claim 1, characterized in that, Step B describes the continued heating using a power supply system with an electrode voltage of 240–250V and an electrode current of 45–50kA.

3. The staged melting process for cold steelmaking at the bottom of an electric furnace according to claim 1 or 2, characterized in that, The oxygen flow rate for oxygen blowing in step B is 1150–1250 Nm³ / h.

4. The staged melting process for cold steelmaking at the bottom of an electric furnace according to claim 1 or 2, characterized in that, The carbon injection rate in step B is 75–85 kg / min.

5. The staged melting process for cold steelmaking at the bottom of an electric furnace according to claim 1 or 2, characterized in that, The heating described in step D uses a power supply system with an electrode voltage of 300-310V and an electrode current of 38-40kA.

6. The staged melting process for cold steelmaking at the bottom of an electric furnace according to claim 1 or 2, characterized in that, The oxygen flow rate for oxygen blowing in step D is 1250–1350 Nm³ / h.

7. The staged melting process for cold steelmaking at the bottom of an electric furnace according to claim 1 or 2, characterized in that, The carbon injection rate in step D is 95–105 kg / min.

8. The staged melting process for cold steelmaking at the bottom of an electric furnace according to claim 1 or 2, characterized in that, After the cold steel at the bottom of the furnace is completely melted, the process also includes step F. Adding 8-12 kg / t of lime, 7-9 kg / t of carbon powder, and 300-400 kg / t of low-density briquetted scrap steel to the furnace, and using an electrode voltage of 300-310V and an electrode current of 38-40kA for melting, while blowing oxygen and injecting carbon, and after the scrap steel is basically melted, it is transferred to conventional smelting.

9. The staged melting process for cold steelmaking at the bottom of an electric furnace according to claim 8, characterized in that, The oxygen flow rate in step F is 1050–1150 Nm³ / h; the carbon injection rate is 75–85 kg / min.

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