A method of reducing the wedge of a ferritic stainless steel head blank

Abstract

This invention relates to the field of metallurgical production technology, specifically disclosing a method for reducing the wedge shape of ferritic stainless steel billets, comprising the following steps: setting the crystallizer taper and thermal shrinkage ratio; pre-casting preparation: placing cold material in the crystallizer to fill the gap between the crystallizer and the ingot head before the molten steel reaches the continuous casting platform; ladle start-up operation: controlling the tundish liquid level and the timing of adding the covering agent after ladle start-up; tundish start-up control: setting the start-up casting speed and controlling the lifting speed; crystallizer water and secondary cooling water control: setting the crystallizer water flow rate, and manually controlling the secondary cooling water and secondary cooling air; slab width measurement and determination of the billet head length removal amount: after the billet is drawn out of the fan-shaped section, measuring the width of the first slab, and determining the billet head cutting length based on the width of the hot billet; removing the large wedge-shaped portion of the slab; this invention reduces the wedge shape of the billet, improves the slab grinding efficiency and transfer progress, and effectively ensures the quality of the rolled steel strip of the billet.

Description

Technical Field

[0001] This invention relates to the field of metallurgical production technology, and specifically to a method for reducing the wedge shape of ferritic stainless steel billets. Background Technology

[0002] 400 series ferritic stainless steel has excellent corrosion resistance, plasticity, and cold forming properties, making it popular among users. Its applications are wide-ranging, including kitchenware, machinery, decoration, and appliance panels. Market demand is high. However, in slab production, the first slab in each casting often exhibits a large wedge shape, resulting in low slab yield. The wedge shape can easily exceed the process requirements by 0-20mm, severely impacting the normal transfer and grinding progress of the slab. This also leads to prolonged slab dwell time. Due to the characteristics of the steel, prolonged slab storage easily causes cracks and defects. After rolling, slabs with long dwell times will exhibit surface peeling and cracks on the steel strip.

[0003] Therefore, there is an urgent need to invent a method to reduce the wedge shape of ferritic stainless steel billets, thereby reducing the amount of grinding required and solving the problem of long billet dwell time caused by the amount of grinding. Summary of the Invention

[0004] In view of the problems existing in the prior art, the purpose of this invention is to provide a method for reducing the wedge shape of ferritic stainless steel billets.

[0005] The technical solution adopted by this invention to solve its technical problem is: a method for reducing the wedge shape of ferritic stainless steel billets, comprising the following steps:

[0006] S1, settings for crystallizer taper and heat shrink ratio;

[0007] S2. Pre-casting preparation: Before the molten steel reaches the continuous casting platform, cold material is placed in the crystallizer to fill the gap between the crystallizer and the ingot head.

[0008] S3. Tundish pouring operation: control of liquid level in tundish and timing of adding covering agent after pouring.

[0009] S4, Intermediate Load Start Control: Setting the starting speed and controlling the acceleration speed;

[0010] S5. Crystallizer water and secondary cooling water control: Crystallizer water flow rate setting, secondary cooling water and secondary cooling air are manually controlled;

[0011] S6. Measurement of slab width and determination of the amount to be removed from the billet head: After the slab is pulled out into a fan-shaped section, measure the width of the first slab and determine the cutting length of the billet head to be 1.5-1.8 meters based on the width of the hot slab; remove the larger wedge-shaped part of the slab.

[0012] Specifically, in step S1, the crystallizer taper is set to 1.1%, and the heat shrinkage ratio is set to 0.968.

[0013] Specifically, the cold material in step S2 includes, but is not limited to, one or more of spring wire cold material, asbestos rope, and pins. The cold material seals the gap between the crystallizer and the ingot head, making it dense and seamless.

[0014] Specifically, in step S3, when the ladle starts pouring for 1 minute and 40 seconds, and the weight of the molten steel in the tundish reaches 8 tons, the temperature of the molten steel in the tundish is measured with a manual temperature gun and is ≥1540℃, and the liquid level in the tundish is ≥500mm. Then, tundish covering agent is added for heat preservation. After the pouring conditions are met, the tundish pouring is organized.

[0015] Specifically, when the weight of molten steel in the tundish is ≥8 tons, 120 kg of low-melting-point covering agent is added to cover the molten steel in the tundish to prevent secondary oxidation of the molten steel; when the weight of molten steel in the tundish is ≥15 tons, 180 kg of high-magnesium covering agent is added; and when changing ladles between furnaces, 20 kg of high-magnesium covering agent is added.

[0016] Specifically, in step S4, the intermediate ladle starting control starts the intermediate ladle pouring operation 1 minute and 45 seconds after the main ladle starts pouring. The crystallizer emergence time is controlled at 70-90 seconds. When the molten steel level in the crystallizer is 200-250 mm from the top of the crystallizer, the slag for the steel grade is added. After the molten steel in the crystallizer and the dummy bar have fully solidified and cooled, the casting speed is started. The starting casting speed is set at 0.6 m / min. After the start is stable for 30 seconds, the casting speed is gradually increased, and the increase speed is controlled at 0.02 m / min. The casting speed is increased once every 2 seconds. When the length of the billet is 1.5-1.8 meters, the casting speed is increased to the normal casting speed.

[0017] Specifically, the normal drawing speed is as follows: for production of four-foot cross-sections with a width ≤ 1400mm, the normal drawing speed is 1.0-1.15 m / min; for production of five-foot cross-sections with a width > 1400mm, the normal drawing speed is 0.9-0.95 m / min.

[0018] Specifically, in step S5, the crystallizer water flow rate is set to 3200-3800 liters / minute on the wide side and 400-500 liters / minute on the narrow side. The cooling water and air in the secondary cooling zone are manually controlled, and the proportion of secondary cooling water is gradually adjusted as the casting speed increases. When the casting length of the billet reaches 1.5 meters, the secondary cooling water supply reaches the normal value, and the specific water volume is controlled at 0.9-1.0 liters / minute.

[0019] Specifically, in step S6, after the billet is pulled out into a fan-shaped segment, the width between 1.0 and 1.8 meters is measured using a red billet measuring tool. The cutting length of the billet head is determined based on the width of the red billet, and the wedge amount of the head billet is controlled within 20 mm.

[0020] The present invention has the following beneficial effects:

[0021] The method for reducing the wedge shape of ferritic stainless steel billets designed in this invention solves two problems: first, it solves the problem of large wedge shape in ferritic stainless steel billets, and the large amount of grinding required increases grinding costs; second, it reduces the amount of wedge shape in the billet, further shortens the grinding time, greatly improves the grinding efficiency and transfer progress of the billet, and effectively ensures the quality of the rolled steel strip of the first billet (the first billet). Detailed Implementation

[0022] The technical solutions in the embodiments of the present invention will be described clearly, completely, and in further detail below. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0023] A method for reducing the wedge shape of ferritic stainless steel billets, taking a typical 10Cr17 steel grade as an example, includes the following steps:

[0024] Step 1) The mass fraction of molten steel for 10Cr17 grade steel shall meet the following requirements: C: 0.03-0.05%, Si: 0.35-0.55%, Mn: 0.15-0.30%, P: ≤0.035%, S: ≤0.015%, Cr: 16.0-16.5%, Ni: ≤0.20%, N: 0.020-0.055%.

[0025] Step 2) Crystallizer taper setting: The crystallizer taper setting value for continuous casting of 10Cr17 steel is 1.1%, and the thermal shrinkage ratio setting value is 0.968.

[0026] Step 3) Pre-casting preparation: 10 minutes before the molten 10Cr17 steel arrives at the continuous casting platform, spring wire, asbestos rope, nail pins and other materials are placed in the crystallizer to seal the gap between the crystallizer and the ingot head, so as to ensure that it is tight and seamless, and to ensure a stable start-up.

[0027] Step 4) Ladle pouring operation: 1 minute and 40 seconds after the ladle starts pouring, when the weight of the molten steel in the tundish reaches 8 tons, use a manual temperature gun to measure the temperature of the molten steel in the tundish. If it is ≥1540℃ and the liquid level in the tundish is ≥500mm, start adding tundish covering agent for heat preservation. After meeting the pouring conditions, organize the pouring of the tundish.

[0028] When the weight of molten steel in the tundish is ≥8 tons, add 120 kg of low-melting-point covering agent to cover the molten steel in the tundish and prevent secondary oxidation of the molten steel; when the weight of molten steel in the tundish is ≥15 tons, add 180 kg of high-magnesium covering agent. When changing ladles between furnaces, add 20 kg of high-magnesium covering agent to effectively prevent corrosion of the tundish lining.

[0029] Step 5) Tundish Start-up Control: Start tundish casting 1 minute and 45 seconds after the ladle begins pouring. Control the crystallizer emergence time to 70-90 seconds. When the molten steel level in the crystallizer is 200-250 mm from the top of the crystallizer, add the slag for the specified steel grade. Allow the molten steel in the crystallizer and the dummy bar to fully solidify and cool before starting the casting speed. Set the starting speed to 0.6 m / min. After a stable start of 30 seconds, gradually increase the speed, controlling the increase at 0.02 m / min, increasing the speed every 2 seconds. When the billet length is 1.5-1.8 meters, increase the speed to the normal speed. Normal casting speed: 1.0-1.15 m / min for producing four-foot cross-sections (width ≤ 1400 mm); 0.9-0.95 m / min for producing five-foot cross-sections (width > 1400 mm).

[0030] The crystallizer emergence time is controlled at 70-90 seconds. The molten steel in the crystallizer and the dummy bar are fully solidified and connected to prevent the occurrence of start-up pull-out or start-up steel leakage accidents. After the crystallizer starts casting, the billet shell trend is tested with a slag removal rod.

[0031] Step 6) Control of crystallizer water and secondary cooling water: Set the crystallizer water flow rate to 3200-3800 liters / minute for the wide side and 400-500 liters / minute for the narrow side; the cooling water and secondary cooling air in the secondary cooling zone are manually controlled. The proportion of secondary cooling water is gradually adjusted as the casting speed increases. Manual control is implemented when the casting length of the billet reaches 1.5 meters or less. The secondary cooling water volume is kept at the normal value: 100-110 liters / minute for the wide side of Zone 1, 180-190 liters / minute for the narrow side of Zone 1, and the water flow rate of Zones 2-4 is controlled at 270-290 liters / minute. The specific water volume is controlled at 0.9-1.0 liters / minute to ensure safe start-up of the crystallizer and sufficient thickness of the billet shell exiting the crystallizer.

[0032] Step 7) Slab Width Measurement and Cutting Length Determination: After the slab is drawn out into a fan-shaped section, measure the width of the first slab. Based on the width of the hot slab, determine the cutting length of the slab head to be 1.5-1.8 meters. Remove the portion of the slab with a large wedge shape corresponding to the initial adjustment of the drawing speed, reducing the amount of grinding required for the first slab. After the slab is drawn out into a fan-shaped section, use a hot slab measuring tool to measure the width between 1.0-1.8 meters. Determine the cutting length of the slab head based on the width of the hot slab, controlling the wedge shape of the first slab to within 20mm.

[0033] Example 1.

[0034] A method for reducing the wedge shape of ferritic stainless steel billets includes the following steps:

[0035] Step 1) The mass fraction of molten steel for 10Cr17 grade steel shall meet the following requirements: C: 0.03-0.05%, Si: 0.35-0.55%, Mn: 0.15-0.30%, P: ≤0.035%, S: ≤0.015%, Cr: 16.0-16.5%, Ni: ≤0.20%, N: 0.020-0.055%.

[0036] Step 2) Crystallizer taper setting: The crystallizer taper setting value for continuous casting of 10Cr17 steel is 1.1%, and the thermal shrinkage ratio setting value is 0.968.

[0037] Step 3) Pre-casting preparation: 10 minutes before the molten 10Cr17 steel arrives at the continuous casting platform, spring wire, asbestos rope, nail pins and other materials are placed in the crystallizer to seal the gap between the crystallizer and the ingot head, so as to ensure that it is tight and seamless, and to ensure a stable start-up.

[0038] Step 4) Ladle pouring operation: 1 minute and 40 seconds after the ladle starts pouring, when the weight of the molten steel in the tundish reaches 8 tons, use a manual temperature gun to measure the temperature of the molten steel in the tundish. If it is ≥1540℃ and the liquid level in the tundish is ≥500mm, start adding tundish covering agent for heat preservation. After meeting the pouring conditions, organize the pouring of the tundish.

[0039] Step 5) Tundish Start-up Control: Start tundish casting 1 minute and 45 seconds after the ladle begins pouring. Control the crystallizer emergence time to 70 seconds. When the molten steel level in the crystallizer is 200 mm from the top, add the slag for that steel grade. After the molten steel and the dummy bar in the crystallizer have fully solidified and cooled, prepare for the starting speed increase. Set the starting speed to 0.6 m / min. After a stable start of 30 seconds, gradually increase the speed, controlling the increase at 0.02 m / min, increasing the speed every 2 seconds. When the billet length reaches 1.5 meters, increase the speed to the normal speed.

[0040] Step 6) Control of crystallizer water and secondary cooling water: Set the crystallizer water flow rate to 3200 liters / minute for the wide side and 400 liters / minute for the narrow side; the cooling water and secondary cooling air in the secondary cooling zone are manually controlled, and the proportion of secondary cooling water is gradually adjusted as the casting speed increases. When the casting length of the billet reaches 1.5 meters, the secondary cooling water distribution reaches the normal value, and the specific water volume is controlled at 0.9 liters / minute, of which: 100 liters / minute for the wide side of zone 1, 190 liters / minute for the narrow side of zone 1, and the water flow rates of zones 2-4 are 270, 285, and 290 liters / minute, respectively, to ensure safe start-up of the crystallizer and sufficient thickness of the billet shell exiting the crystallizer.

[0041] Step 7) Slab width measurement and billet head cutting length control: After the cast billet is pulled out into a fan-shaped section, measure the width of the first billet (first slab). The wedge length of the first billet is 10mm. According to the width of the hot billet, the length of the billet head to be cut off is 1.5 meters.

[0042] Example 2.

[0043] A method for reducing the wedge shape of ferritic stainless steel billets includes the following steps:

[0044] Step 1) The mass fraction of molten steel for 10Cr17 grade steel shall meet the following requirements: C: 0.03-0.05%, Si: 0.35-0.55%, Mn: 0.15-0.30%, P: ≤0.035%, S: ≤0.015%, Cr: 16.0-16.5%, Ni: ≤0.20%, N: 0.020-0.055%.

[0045] Step 2) Crystallizer taper setting: The crystallizer taper setting value for continuous casting of 10Cr17 steel is 1.1%, and the thermal shrinkage ratio setting value is 0.968.

[0046] Step 3) Pre-casting preparation: 10 minutes before the molten 10Cr17 steel arrives at the continuous casting platform, spring wire, asbestos rope, nail pins and other materials are placed in the crystallizer to seal the gap between the crystallizer and the ingot head, so as to ensure that it is tight and seamless, and to ensure a stable start-up.

[0047] Step 4) Ladle pouring operation: 1 minute and 40 seconds after the ladle starts pouring, when the weight of the molten steel in the tundish reaches 8 tons, use a manual temperature gun to measure the temperature of the molten steel in the tundish. If it is ≥1540℃ and the liquid level in the tundish is ≥500mm, start adding tundish covering agent for heat preservation. After meeting the pouring conditions, organize the pouring of the tundish.

[0048] Step 5) Tundish Start-up Control: Start tundish casting 1 minute and 45 seconds after the ladle begins pouring. Control the crystallizer emergence time to 86 seconds. When the molten steel level in the crystallizer is 220 mm from the top of the crystallizer, add the slag for this steel grade. After the molten steel in the crystallizer and the dummy bar have fully solidified and cooled, prepare for the starting speed increase. Set the starting speed to 0.6 m / min. After a stable start of 30 seconds, gradually increase the speed, controlling the increase rate at 0.02 m / min, increasing the speed every 2 seconds. When the billet length reaches 1.6 meters, increase the speed to the normal speed.

[0049] Step 6) Control of crystallizer water and secondary cooling water: Set the crystallizer water flow rate to 3500 liters / minute for the wide side and 450 liters / minute for the narrow side; the cooling water and secondary cooling air in the secondary cooling zone are manually controlled, and the proportion of secondary cooling water is gradually adjusted as the casting speed increases. When the casting length of the billet reaches 1.5 meters, the secondary cooling water distribution reaches the normal value, and the specific water flow rate is controlled at 0.95 liters / minute. The water flow rate of the wide side of zone 1 is 110 liters / minute, the water flow rate of the narrow side of zone 1 is 180 liters / minute, and the water flow rates of zones 2-4 are 275, 280, and 288 liters / minute, respectively, to ensure safe start-up of the crystallizer and sufficient thickness of the billet shell exiting the crystallizer.

[0050] Step 7) Slab width measurement and billet head cutting length control: After the slab is pulled out into a fan-shaped section, measure the width of the first slab. The wedge length of the first slab is 17mm, and the length of the billet head to be cut off is 1.6 meters.

[0051] Example 3.

[0052] A method for reducing the wedge shape of ferritic stainless steel billets includes the following steps:

[0053] Step 1) The mass fraction of molten steel for 10Cr17 grade steel shall meet the following requirements: C: 0.03-0.05%, Si: 0.35-0.55%, Mn: 0.15-0.30%, P: ≤0.035%, S: ≤0.015%, Cr: 16.0-16.5%, Ni: ≤0.20%, N: 0.020-0.055%.

[0054] Step 2) Crystallizer taper setting: The crystallizer taper setting value for continuous casting of 10Cr17 steel is 1.1%, and the thermal shrinkage ratio setting value is 0.968.

[0055] Step 3) Pre-casting preparation: 10 minutes before the molten 10Cr17 steel arrives at the continuous casting platform, spring wire, asbestos rope, nail pins and other materials are placed in the crystallizer to seal the gap between the crystallizer and the ingot head, so as to ensure that it is tight and seamless, and to ensure a stable start-up.

[0056] Step 4) Ladle pouring operation: 1 minute and 40 seconds after the ladle starts pouring, when the weight of the molten steel in the tundish reaches 8 tons, use a manual temperature gun to measure the temperature of the molten steel in the tundish. If it is ≥1540℃ and the liquid level in the tundish is ≥500mm, start adding tundish covering agent for heat preservation. After meeting the pouring conditions, organize the pouring of the tundish.

[0057] Step 5) Tundish Start-up Control: Start tundish casting 1 minute and 45 seconds after the ladle begins pouring. Control the crystallizer emergence time to 90 seconds. When the molten steel level in the crystallizer is 250 mm from the top of the crystallizer, add the slag for that steel grade. After the molten steel in the crystallizer and the dummy bar have fully solidified and cooled, prepare for the starting speed increase. Set the starting speed to 0.6 m / min. After a stable start of 30 seconds, gradually increase the speed, controlling the increase at 0.02 m / min, increasing the speed every 2 seconds. When the billet length reaches 1.8 meters, increase the speed to the normal speed.

[0058] Step 6) Control of crystallizer water and secondary cooling water: Set the crystallizer water flow rate to 3800 liters / minute for the wide side and 500 liters / minute for the narrow side; the cooling water and secondary cooling air in the secondary cooling zone are manually controlled, and the proportion of secondary cooling water is gradually adjusted as the casting speed increases. When the casting length of the billet reaches 1.5 meters, the secondary cooling water distribution reaches the normal value, and the specific water flow rate is controlled at 1.0 liters / minute. The water flow rate of the wide side of zone 1 is 105 liters / minute, the water flow rate of the narrow side of zone 1 is 185 liters / minute, and the water flow rates of zones 2-4 are 272, 286, and 299 liters / minute, respectively, to ensure safe start-up of the crystallizer and sufficient thickness of the billet shell exiting the crystallizer.

[0059] Step 7) Slab width measurement and billet head cutting length control: After the slab is pulled out into a fan-shaped section, measure the width of the first slab (first slab). The wedge length of the first slab is 20mm, and the length of the billet head to be cut off is 1.8 meters.

[0060] This invention solves the problems of large wedge shape in the first furnace head billet of 400 series ferritic stainless steel, increased grinding amount, and long transition time, and accelerates the slab transition time and improves grinding efficiency. This invention has been applied to the production of ferritic and ultra-pure ferritic stainless steels, resulting in a significant improvement in the wedge shape of the first furnace head billet of 400 series ferritic and ultra-pure ferritic stainless steel.

[0061] This invention is not limited to the above-described embodiments. Anyone should know that any structural changes made under the guidance of this invention, and any technical solutions that are the same as or similar to this invention, fall within the protection scope of this invention.

[0062] The technologies, shapes, and structures not described in detail in this invention are all known technologies.

Claims

1. A method for reducing the wedge shape of ferritic stainless steel billets, characterized in that, Includes the following steps: S1. Crystallizer taper and heat shrink ratio settings: Crystallizer taper setting value is 1.1%, heat shrink ratio setting value is 0.968; S2. Pre-casting preparation: Before the molten steel reaches the continuous casting platform, cold material is placed in the crystallizer to fill the gap between the crystallizer and the ingot head. S3. Tundish pouring operation: control of liquid level in tundish and timing of adding covering agent after pouring. S4. Tundish Start-up Control: Setting the starting casting speed and controlling the lifting speed; Tundish start-up control begins 1 minute and 45 seconds after the ladle starts casting. The crystallizer emergence time is controlled at 70-90 seconds. When the molten steel level in the crystallizer is 200-250 mm from the top of the crystallizer, the slag for the steel grade is added. After the molten steel in the crystallizer and the dummy bar have fully solidified and cooled, the casting speed is started. The starting casting speed is set at 0.6 m / min. After stabilizing for 30 seconds, the casting speed is gradually increased, and the lifting speed is controlled at 0.02 m / min. The casting speed is increased every 2 seconds. When the billet length is 1.5-1.8 meters, the casting speed is increased to the normal casting speed. Normal casting speed: For four-foot cross-sections with a width ≤1400 mm, the normal casting speed is 1.0-1.15 m / min; for five-foot cross-sections with a width >1400 mm, the normal casting speed is 0.9-0.95 m / min. S5. Control of Crystallizer Water and Secondary Cooling Water: Crystallizer water flow rate setting; secondary cooling water and secondary cooling air are manually controlled; crystallizer water flow rate setting: wide side: 3200-3800 liters / minute, narrow side: 400-500 liters / minute; secondary cooling water and secondary cooling air are manually controlled, and the secondary cooling water ratio is gradually adjusted as the casting speed increases. When the casting length of the billet reaches 1.5 meters, the secondary cooling water distribution reaches the normal value, and the specific water volume is controlled at 0.9-1.0 liters / minute. S6. Measurement of slab width and determination of the amount to be removed from the billet head: After the slab is drawn out into a fan-shaped section, measure the width of the first slab. Use a red billet measuring tool to measure the width between 1.0 and 1.8 meters. Determine the cutting length of the billet head based on the width of the red billet. The wedge shape of the first billet should be controlled within 20 mm. The cutting length of the billet head should be between 1.5 and 1.8 meters based on the width of the slab. Remove the larger wedge-shaped part of the slab.

2. The method for reducing the wedge shape of ferritic stainless steel billets according to claim 1, characterized in that, The cold material in step S2 includes one or more of spring wire cold material, asbestos rope, and pins. The cold material seals the gap between the crystallizer and the ingot head, making it dense and seamless.

3. The method for reducing the wedge shape of ferritic stainless steel billets according to claim 1, characterized in that, In step S3, when the molten steel in the tundish reaches 8 tons after 1 minute and 40 seconds of pouring, the temperature of the molten steel in the tundish is measured with a manual temperature gun and is ≥1540℃, and the liquid level in the tundish is ≥500mm. Then, tundish covering agent is added for heat preservation. After the pouring conditions are met, the tundish pouring is organized.

4. The method for reducing the wedge shape of ferritic stainless steel billets according to claim 3, characterized in that, When the weight of molten steel in the tundish is ≥8 tons, 120 kg of low-melting-point covering agent is added to cover the molten steel in the tundish to prevent secondary oxidation of the molten steel; when the weight of molten steel in the tundish is ≥15 tons, 180 kg of high-magnesium covering agent is added; when changing ladles between furnaces, 20 kg of high-magnesium covering agent is added.