Method for stably controlling surface quality of low-carbon low-alloy peritectic steel continuous casting round billet

Abstract

The invention discloses a method for stably controlling the surface quality of a low-carbon low-alloy peritectic steel continuous casting round billet, which is suitable for 10Mn / 1 series peritectic steel with the specification of phi 200-220mm. According to the method, through the integrated design of refining purification, parameter collaboration, dynamic regulation and control and efficient slow cooling, low-aluminum calcium treatment and LF furnace white slag refining are adopted in the refining stage, and T [O] in the steel is controlled to be less than or equal to 20ppm; the low-fluorine environment-friendly casting powder is customized to adapt to the characteristics of a small-section slag channel; a component-temperature-pulling speed association rule is established, the degree of superheat of a tundish is reduced by 2-3 DEG C every time the C content is increased by 0.01%, and the amount of cold water is adjusted by 5-8 m / h every time the section diameter is changed by 20 mm; and a dynamic compensation mechanism that the pulling speed is adjusted by 0.05 m / min when the temperature fluctuates by 5 DEG C is adopted for the temperature drop fluctuation working condition. The qualified rate of casting blanks reaches 99.9% or above, the crack rate is reduced to 0.1% or below, and compared with a traditional process, the casting powder consumption is reduced by 25%.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steel metallurgy continuous casting, in particular to a method for controlling the surface quality of a low-carbon low-alloy peritectic steel continuous casting round billet with a specification of φ200-220 mm and adapted to multiple component intervals, which is especially suitable for the industrial production of 10Mn / 1 series peritectic steel for oil well pipes and engineering machinery. BACKGROUND

[0002] Low-carbon low-alloy peritectic steel (C content 0.07%-0.15%) has excellent strength and toughness matching, and is in high demand in the high-end equipment manufacturing field. The φ200-220 mm small-specification round billet is the core billet for producing thick-walled pipes. However, this type of steel faces multiple technical bottlenecks during continuous casting: first, peritectic transformation has inherent defects. When solidifying, the δ-Fe→γ-Fe phase transition is accompanied by about 4% volume shrinkage, which easily forms an air gap between the billet shell and the mold, leading to deteriorated heat transfer and a weak billet shell. Second, the small cross-section characteristics amplify the risk. The large specific surface area accelerates the cooling rate, and the low static pressure of the molten steel makes it difficult to close the air gap, resulting in a significant increase in the rate of leakage and concave cracks. Third, there is a problem in the adaptation of components and specifications. Existing processes are mostly designed for a single specification. When the C and Mn contents fluctuate or the cross-section is adjusted, the contradictions of "too thin billet shell" or "shrinkage concentration" easily occur.

[0003] The existing technology has many shortcomings: the traditional protective slag has a high fluorine content (3-5 wt%), which pollutes the environment and makes it difficult to adapt to the small cross-section narrow slag channel; it only relies on fixed parameters for production, without considering the temperature drop difference between heats and component fluctuations, and has poor working condition adaptability; there are no targeted inclusion control measures during the refining stage, and Al2O3 inclusions caused by low Al content easily induce cracks; the slow cooling process takes a long time (≥78 h), and has high energy consumption and site cost. Therefore, developing a surface quality control method that is "multi-specification adaptable, multi-working condition compensating, and environmentally friendly and efficient" is of great significance to break through the production bottleneck of small cross-section peritectic steel. SUMMARY

[0004] In view of the poor adaptability, high surface defect rate, and insufficient environmental protection of existing processes in the production of peritectic steel with multiple specifications and components, an integrated control method is provided, which integrates refining purification, dynamic parameter regulation, environmentally friendly protective slag, and efficient slow cooling, to realize the stable improvement of the surface quality of φ200-220 mm peritectic steel round billets.

[0005] To achieve the above-mentioned purpose, the present application provides the following technical solutions: 1. Refining treatment: Low-carbon, low-alloy peritectic steel molten steel is subjected to low-aluminum-calcium treatment. The calcium feeding line controls the Ca content to 0.001%-0.003%. The argon blowing flow rate is controlled in stages: 600-900 L / min in the early stage, 250-450 L / min in the middle stage, and 70-150 L / min in the later stage. The subsequent LF furnace white slag refining is carried out, and the white slag holding time is ≥20 min. The total oxygen content T[O] in the steel is controlled to be ≤20 ppm. 2. Casting control: The superheat of the tundish for the first heat of refined steel is 26~36℃, and for subsequent heats it is 16~26℃. For every 0.01% increase in C content, the superheat of the tundish decreases by 2-3℃. After the start of casting, protective slag is added. The standard casting speed is 1.80~1.90m / min. For every 5℃ fluctuation in the tundish steel temperature, the casting speed is adjusted by 0.05m / min. 3. Cooling control: The primary cooling water volume is adapted to the billet diameter. For the φ200mm standard specification, it is controlled at 90-95m³ / h. For every 20mm change in cross-sectional diameter, the primary cooling water volume increases by 5-8m³ / h. The secondary cooling water volume is 0.29-0.30L / kg. The crystallizer vibration parameters are set as A1:8, A2:0, f1:95, f2:80, As:0.28, where A1 is the stroke constant parameter 1, A2 is the stroke constant parameter 2, f1 is the frequency constant parameter 1, f2 is the frequency constant parameter 2, and As is the non-sinusoidal factor. 4. Slow cooling treatment: After the billet is cut, it is placed in a sheltered, windproof stack for cooling. The temperature after unpacking is ≤200℃, and the slow cooling time is controlled at 65-72h.

[0006] Preferably, the protective slag composition, by mass percentage, includes: 33-39 wt% CaO, 28-30 wt% SiO2, 5-7 wt% Al2O3, 2.5-3.5 wt% MgO, 0-1 wt% F, 7-11 wt% TC, viscosity 0.9-1.0 Pa·S, basicity R=1.10-1.30, melting point 1080-1130℃, and moisture ≤0.25%.

[0007] Preferably, the consumption of the protective slag is controlled at 0.85-0.95 kg / t, and the thickness of the liquid slag layer is maintained at 12.5-14 mm.

[0008] Preferably, the chemical composition of the low-carbon low-alloy peritectic steel, by mass percentage, includes: C 0.07%-0.15%, Si 0.17%-0.52%, Mn 0.40%-0.80%, Al≤0.012%, P≤0.015%, S≤0.003%, with the remainder being Fe and unavoidable impurities.

[0009] Preferably, the continuously cast round billet is φ200mm in size, and the cooling water flow rate is 90-95m³ / h; the continuously cast round billet is φ220mm in size, and the cooling water flow rate is 97-102m³ / h.

[0010] Preferably, the amount of calcium wire fed is matched with the Al content in the steel: when the Al content is ≤0.005%, the amount of calcium wire fed is 0.15-0.20 kg / t; when the Al content is 0.005%-0.012%, the amount of calcium wire fed is 0.20-0.25 kg / t.

[0011] The beneficial effects of this invention are as follows: The core technical solution of this invention is a full-process control system of "front-end purification - process control - back-end protection". It adopts a combination process of "calcium treatment + LF furnace white slag refining". Through precise matching of calcium wire feed rate and Al content, Al2O3 inclusions are converted into low-melting-point calcium aluminate. Combined with the step-by-step control of LF furnace argon blowing flow rate, the removal rate of >20μm inclusions is ≥95%, and T[O] in steel is ≤20ppm, reducing the induction of cracks from the source. With gun crystal crystalline phase as the target, a low-fluorine (≤1wt%), high-MgO (2.5-3.5wt%) protective slag composition system is designed to reduce viscosity to 0.9-1.0Pa·S, which not only ensures the fluidity of small cross-section slag channels, but also reduces fluoride volatilization pollution. The thickness of the liquid slag layer is controlled at 12.5-14mm to ensure continuous filling of the air gap by the slag film; multi-dimensional parameter dynamic coordination: establish a correlation model of "composition-temperature-pulling speed-cooling", reduce the superheat by 2-3℃ for every 0.01% increase in C content, and adjust the cooling water flow rate by 5-8m³ / h for every 20mm change in cross-section; design a dynamic compensation mechanism for pulling speed for temperature drop fluctuations, with a pulling speed adjustment of 0.05m / min corresponding to a 5℃ temperature fluctuation, to ensure that the thickness of the billet shell exiting the crystallizer is stable within the safe range of 12-15mm; efficient slow cooling optimization: replace the traditional slow cooling pit with a windproof stacking cooling enclosure, and shorten the slow cooling time from ≥78h to 65-72h by controlling the stacking density and windproof measures, while ensuring that the unpacking temperature is ≤200℃, suppressing hydrogen-induced cracking and reducing energy consumption. Detailed Implementation

[0012] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below through examples.

[0013] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0014] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments. Example 1

[0015] This embodiment provides a method for stable control of the surface quality of φ200mm low-carbon low-alloy peritectic steel 09Mn series continuously cast round billets.

[0016]

[0017] The method is as follows: 1. Refining process: The Al content of the molten steel is 0.008%, the calcium feed line is 0.22 kg / t, the white slag in the LF furnace is maintained for 25 min, the argon blowing flow rate is controlled in stages: 750 L / min in the early stage, 300 L / min in the middle stage, and 100 L / min in the later stage. For a 200t ladle, the T[O] of the molten steel leaving the station is 8 ppm. Before leaving the station after refining, the loading temperature is determined according to the condition of the ladle and the temperature drop during the process to ensure that the superheat of the tundish meets the standard.

[0018] 2. Preparations before continuous casting: ① Parameter confirmation: Set the primary cooling water flow rate to 92 m³ / h (weak cooling process), and the secondary cooling water specific flow rate to 0.295 L / kg; set the crystallizer vibration parameters to A1:8, A2:0, f1:95, f2:80, As:0.28 (A1 - stroke constant parameter 1, A2 - stroke constant parameter 2, f1 - frequency constant parameter 1, f2 - frequency constant parameter 2, As - non-sinusoidal factor); ② Preparation of protective slag: The composition is as follows: CaO 36wt%, SiO2 29wt%, Al2O3 6wt%, MgO 3wt%, F 0.5wt%, TC 9wt% configuration, viscosity 0.95Pa·S, basicity 1.24, melting point 1100℃, moisture 0.20%; ③ Equipment inspection: confirm that the ingot does not slide down and the sealing is good, clean the debris from the tundish nozzle, install the tundish argon blowing pipe and blow argon for ≥10min, turn on the argon gas 4min before shutting down, and wait for pouring after aligning the tank.

[0019] 3. Casting Operation: ① Ladle Casting: Pull the ladle open to the position in one go, and after receiving the guide sand, control the flow to fall into the ladle by 150-300mm. If the steel overturning in the impact zone is severe, reduce the opening degree of the ladle cylinder. After the steel overturning is reduced, open it fully; ② Tundish Casting: The superheat of the tundish for the first heat is 30℃, and for subsequent heats it is 20℃. When the weight of the molten steel in the tundish reaches 22t, the pressure bar starts casting. Before casting, the pulling speed is set to 0.8m / min; after the molten steel has passed the side hole of the nozzle, push the protective slag into the crystallizer at an addition rate of 0.9kg / t, and control the thickness of the liquid slag layer to 13mm.

[0020] 4. Casting speed control and liquid level stabilization: After the pressure bar is turned on, raise the liquid level in the crystallizer to 180mm from the top within 10-20 seconds, start the straightening machine, vibration system and casting speed, and gradually raise the liquid level to 90-110mm from the top; within 30 seconds, steadily increase the casting speed to 1.28m / min (1.6 times the starting casting speed), manually control the bar to stabilize the liquid level for more than 10 seconds, and then put into automatic liquid level control; after all the casting streams are turned on, drop them into the tundish, and gradually adjust the casting speed to 1.85m / min. During the process, if the temperature fluctuation of the molten steel in the tundish is monitored to be 5℃, adjust the casting speed to 1.80m / min.

[0021] 5. Cooling and slow cooling: Maintain a primary cooling water flow rate of 92m³ / h. 3 / h, secondary cooling water ratio 0.295L / kg; after the billet is cut to length, it is quickly hoisted to the enclosure area for windproof cooling, slow cooling time 70h, and stacking temperature 180℃.

[0022] 6. Quality Inspection and Indicators: The cast billet, after shot blasting, showed no dents or cracks; the pass rate was 99.95%, and the content of inclusions >20μm was 0.5 particles / mm², passing the inspection on the first attempt. Example 2

[0023] This embodiment provides a method for stable control of the surface quality of φ220mm low-carbon low-alloy peritectic steel 09Mn series continuously cast round billets.

[0024]

[0025] The method is as follows: 1. Refining process: The Al content of the molten steel is 0.005%, the calcium feed line is 0.19 kg / t, the white slag in the LF furnace is maintained for 20 min, the argon blowing flow rate is controlled in a step-by-step manner: 700 L / min in the early stage, 300 L / min in the middle stage, and 90 L / min in the later stage. For a 200t ladle, the T[O] of the molten steel leaving the station is 8 ppm. Before refining and leaving the station, the loading temperature is determined according to the condition of the ladle and the temperature drop during the process to ensure that the superheat of the tundish meets the standard.

[0026] 2. Preparations before continuous casting: ① Parameter confirmation: Set the primary cooling water flow rate to 100 m³ / h (weak cooling process), and the secondary cooling water specific flow rate to 0.29 L / kg; set the crystallizer vibration parameters to A1:8, A2:0, f1:95, f2:80, As:0.28 (A1 - stroke constant parameter 1, A2 - stroke constant parameter 2, f1 - frequency constant parameter 1, f2 - frequency constant parameter 2, As - non-sinusoidal factor); ② Preparation of protective slag: The composition is as follows: CaO 38wt%, SiO2 28wt%, Al2O3 7wt%, MgO 2.5wt%, F 0.5wt%, TC 10wt% configuration, viscosity 0.98Pa·S, basicity 1.22, melting point 1120℃, moisture 0.20%; ③ Equipment inspection: confirm that the ingot does not slide down and the sealing is good, clean the debris from the tundish nozzle, install the tundish argon blowing pipe and blow argon for ≥10min, turn on the argon gas 4min before the fire is shut down, and wait for the pouring to begin after the tank is aligned.

[0027] 3. Casting Operation: ① Ladle Casting: Pull the ladle open to the position in one go, and after receiving the guide sand, control the flow to fall into the ladle by 150-300mm. If the steel overturning in the impact zone is severe, reduce the opening degree of the ladle cylinder. After the steel overturning is reduced, open it fully; ② Tundish Casting: The superheat of the tundish for the first heat is 35℃, and for subsequent heats it is 25℃. When the weight of the molten steel in the tundish reaches 22t, start casting with the pressure bar. Before casting, set the pulling speed to 0.8m / min; after the molten steel has passed the side hole of the nozzle, push the protective slag into the crystallizer at an addition rate of 0.95kg / t, and control the thickness of the liquid slag layer to 14mm.

[0028] 4. Casting speed control and liquid level stabilization: Within 20 seconds, raise the liquid level in the crystallizer to 180mm from the top, and after starting the relevant system, gradually adjust it to 100mm; within 30 seconds, increase the casting speed to 1.28m / min (1.6 times the initial casting speed), and after stabilizing the liquid level, put it into automatic control; after the casting flow stabilizes, gradually increase the casting speed to 1.85m / min, with a temperature fluctuation of 5℃ during the process, and adjust the casting speed to 1.80m / min.

[0029] 5. Cooling and slow cooling: Maintain a primary cooling water flow rate of 100 m³ / h and a secondary cooling water ratio of 0.29 L / kg; after the billet is cut to length, quickly hoist it to the sheltered area for wind-proof stacking and slow cooling for 68 hours, with an unstacking temperature of 190℃.

[0030] 6. Quality Inspection and Indicators: The cast billet was shot blasted and the surface was inspected. There were no dents or cracks. The pass rate was 99.97%. The content of inclusions >20μm was 0.4 per mm². The billet passed the inspection on the first attempt.

Claims

1. A method for stable control of the surface quality of continuously cast round billets of low-carbon, low-alloy peritectic steel, characterized in that, It includes four core processes: refining, casting control, cooling regulation, and slow cooling. The specific steps are as follows: (1) Refining treatment: Low-carbon low-alloy peritectic steel molten steel is subjected to low aluminum and calcium treatment. The calcium feeding line controls the Ca content to 0.001%-0.003%. The argon blowing flow rate is controlled in a stepwise manner: 600-900L / min in the early stage, 250-450L / min in the middle stage, and 70-150L / min in the later stage. The subsequent LF furnace white slag refining is carried out. The white slag holding time is ≥20min. The total oxygen content T[O] in the steel is controlled to be ≤20ppm. (2) Casting control: The superheat of the tundish for the first heat of refined steel is 26~36℃, and for subsequent heats it is 16~26℃. For every 0.01% increase in C content, the superheat of the tundish decreases by 2-3℃. After the start of casting, protective slag is added. The standard value of casting speed is 1.85m / min. For every 5℃ fluctuation in the temperature of the tundish steel, the casting speed is adjusted by 0.05m / min. (3) Cooling control: The amount of primary cooling water is adapted to the diameter of the billet. For every 20mm change in cross-sectional diameter, the amount of primary cooling water increases by 5-8m³ / h; the amount of secondary cooling water is 0.29-0.30L / kg; the crystallizer vibration parameters are set as A1:8, A2:0, f1:95, f2:80, As:0.28, where A1 is the stroke constant parameter 1, A2 is the stroke constant parameter 2, f1 is the frequency constant parameter 1, f2 is the frequency constant parameter 2, and As is the non-sinusoidal factor. (4) Slow cooling treatment: After the billet is cut, it is stacked in a sheltered manner to avoid wind and cool. The temperature of the stack is ≤200℃ and the slow cooling time is controlled at 65-72h.

2. The method for stable control of surface quality of low-carbon, low-alloy peritectic steel continuously cast round billets according to claim 1, characterized in that, The protective slag composition, by mass percentage, includes: 33-39 wt% CaO, 28-30 wt% SiO2, 5-7 wt% Al2O3, 2.5-3.5 wt% MgO, 0-1 wt% F, 7-11 wt% TC, viscosity 0.9-1.0 Pa·S, basicity R=1.10-1.30, melting point 1080-1130℃, and moisture ≤0.25%.

3. The method for stable control of surface quality of low-carbon, low-alloy peritectic steel continuously cast round billets according to claim 2, characterized in that, The consumption of protective slag is controlled at 0.85-0.95 kg / t, and the thickness of the liquid slag layer is maintained at 12.5-14 mm.

4. The method for stable control of surface quality of low-carbon, low-alloy peritectic steel continuously cast round billets according to claim 1, characterized in that, The chemical composition of the low-carbon low-alloy peritectic steel, by mass percentage, includes: C 0.07%-0.15%, Si 0.17%-0.52%, Mn 0.40%-0.80%, Al≤0.012%, P≤0.015%, S≤0.003%, with the remainder being Fe and unavoidable impurities.

5. The method for stable control of surface quality of low-carbon, low-alloy peritectic steel continuously cast round billets according to claim 1, characterized in that, The continuously cast round billet is φ200mm in size, and the cooling water flow rate is 90-95m³ / h; the continuously cast round billet is φ220mm in size, and the cooling water flow rate is 97-102m³ / h.

6. The method for stable control of surface quality of low-carbon, low-alloy peritectic steel continuously cast round billets according to claim 1, characterized in that, The amount of calcium wire fed should be matched with the Al content in the steel: when the Al content is ≤0.005%, the amount of calcium wire fed should be 0.15-0.20 kg / t; when the Al content is 0.005%-0.012%, the amount of calcium wire fed should be 0.20-0.25 kg / t.

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