A production method for eliminating defects of double-furnace rolled industrial pure iron flat steel
By using a dual-furnace rolling method, adjusting the charging and uncharting process, improving the heating process, and using dedicated rollers, the problems of cracking and bending in the production of industrial pure iron flat steel were solved, achieving efficient and stable production, improving product quality and output, reducing costs, and achieving good economic benefits.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- BAOTOU IRON & STEEL (GROUP) CO LTD
- Filing Date
- 2024-11-28
- Publication Date
- 2026-05-19
AI Technical Summary
In existing technologies, the production of industrial pure iron flat steel suffers from surface cracks and shape defects. In particular, it is difficult to control the heating temperature and rolling process during the double-furnace rolling process, resulting in substandard product quality, low production efficiency, high costs, and inability to guarantee delivery time.
By adopting a dual-furnace rolling method, measures such as adjusting the charging and uncharting methods, improving the heating process, using dedicated rolls, and controlling the curvature are taken to ensure the uniformity of heating temperature and the stability of the rolling process. These measures include controlling the spacing between heating furnaces, alternating steel tapping, ensuring the installation quality of dedicated rolls and guide equipment, and optimizing rolling parameters to reduce cracks and bending defects.
It has achieved efficient production of industrial pure iron flat steel, with a product quality qualification rate of over 97.5%, increased hourly output by 17 pieces/hour, generated annual profits of 6.782 million yuan, reduced corner cracking rate and production costs, and ensured the stability of delivery time.
Abstract
Description
Technical Field
[0001] This invention belongs to the field of steel rolling technology, and in particular relates to a production method for eliminating defects in industrial pure iron flat steel produced by double-furnace rolling. Background Technology
[0002] Industrial pure iron electrode flat steel is a major product after our factory's product structure adjustment. It has a certain price advantage, but its production is difficult. Our factory currently has two heating furnaces: one walking beam furnace and one pusher furnace. In the pusher furnace, the transition steel temperature is difficult to control, and there is uneven printing on the slide. When handling accidents or changing rolls, the billets spend a long time in the furnace, resulting in cracks. Due to the tendency of industrial pure iron to crack, we previously tried using a pusher furnace to roll pure iron flat steel, but this resulted in numerous cracks, forcing the steel to be scrapped. Therefore, before the improvement, we always used a single walking beam furnace for production, never using dual furnaces. However, single-furnace production has low hourly output, high costs, and unreliable delivery times, resulting in low profit margins.
[0003] Compared to ordinary electrode flat steel, industrial pure iron is particularly soft, has good toughness, and possesses better electromagnetic properties. Therefore, it is often used as a deep-drawing material, electromagnetic material, and pure iron flat steel. Industrial pure iron can also be used as a raw material for heavy-melting alloys, vacuum induction furnaces, and ultra-low carbon stainless steel. Therefore, industrial pure iron can also be called raw material pure iron. The microstructure of low-resistivity steel designed with low carbon is almost entirely ferrite, while the microstructure of existing electrode steel is mostly pearlite + ferrite.
[0004] Surface cracks and shape defects have always been common major problems in the production of industrial pure iron flat steel. Cracks are widely distributed on the surface and edges of the flat steel, with wide and deep openings. This manifests as coarse austenite grains, indicating that the heating temperature is too high and uneven. Higher heating temperatures result in more sulfur dissolving in the steel at high temperatures, providing more effective sulfur for precipitation or segregation at the austenite grain boundaries during rolling, thus promoting the formation of surface cracks in the flat steel.
[0005] High heating temperatures cause corner or surface cracks, while low-temperature rolling leads to misshapen materials. The low Mn content and low Mn / S ratio in pure iron result in insufficient Mn to fix the S, leading to an increase in iron-rich sulfides in the austenitic state, forming intergranular microcracks at the edges and corners of the finished product. The temperature drop at the four corners is greater than in other areas, making them prone to cracking. The heating regime and rolling process of industrial pure iron directly affect product quality; a poor match between the two can cause surface defects. Therefore, the heating regime and rolling process of industrial pure iron are crucial for ensuring product quality. Thus, how to control the process to guarantee product quality is a challenge that this patent aims to solve. Summary of the Invention
[0006] The purpose of this invention is to provide a production method for eliminating defects in the double-furnace rolling of industrial pure iron flat steel. This method eliminates defects in the double-furnace rolling of pure iron, enables the simultaneous use of a pusher furnace and a walking beam furnace for double-furnace production, improves output and product quality, increases production efficiency, and achieves a product quality qualification rate of over 97%.
[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:
[0008] This invention discloses a production method for eliminating defects in double-furnace rolled industrial pure iron flat steel, comprising:
[0009] 1) Change the charging and uncharging method and ensure the time spent in the furnace.
[0010] 1.1) The loading spacing of the No. 1 heating furnace is controlled at 40-80mm to ensure uniform heating temperature and reduce temperature stress;
[0011] 1.2) To reduce corner cracks, the two heating furnaces must alternate tapping steel in batches of 1-5.
[0012] 1.3) To reduce corner cracks, the steel grade should be charged from the time it reaches the soaking zone for pure iron in furnace #1, or the empty step distance should be set before charging pure iron.
[0013] 1.4) Ensure that the furnace time is more than 2 hours and 30 minutes.
[0014] 2) Improve heating process
[0015] 2.1) The maximum heating temperature of the heating section II and soaking section of the pusher-type heating furnace for producing industrial pure iron shall not exceed 1100℃. For dual-furnace production, the preheating section shall be below 800℃, the heating section I below 1050℃, and the heating section II and soaking section between 950℃ and 1100℃. The total heating time shall be more than 2 hours and 30 minutes. The soaking time of the continuous casting billet shall be ≥30 minutes. The continuous casting billet shall be heated slowly, and overheating or burning shall be prohibited to ensure uniform temperature inside and outside the continuous casting billet.
[0016] 2.2) During the adjustment period of rolling pure iron, the temperature of heating section II and soaking section must be reduced to between 970 and 1050°C, and the temperature should be maintained by stepping back to the starting position every 5 to 8 minutes.
[0017] 3) Achieve dedicated use of special rollers
[0018] 3.1) For the rolling of pure iron flat steel, a dedicated roll is used for the Ф850mm roll. The II hole is configured with a groove bottom of 250mm and a groove opening of 275mm. By reducing the size of the II hole and increasing the side wall clamping, the material shape is flattened. The groove bottom width of the III hole is widened, and the groove bottom width is changed from 220mm to 230mm to reduce wire drawing, so as to achieve the smooth rolling of industrial pure iron flat steel.
[0019] 3.2) Reduce the overall reduction of the continuous rolling mill, and increase the overall diameter of the Φ700mm-3V roll pass by 2mm, and increase the double bevel or chamfer of the Φ500-4H finished roll pass to prevent the feed size from being enlarged and the finished product from being stringy;
[0020] 4) Control the curvature and improve verticality
[0021] 4.1) Uniform rolling is adopted, and the number of pieces produced per hour in a single furnace is controlled at 23-25 pieces / hour, while the number of pieces produced per hour in a double furnace is controlled at 40-42 pieces / hour.
[0022] 4.2) If the bending of the hot-rolled product is visually measured to exceed 5 mm / m, the furnace time must be increased;
[0023] 4.3) Strictly implement the technical standards for pre-assembly of rolls and guides. In order to reduce the adjustment time of pure iron, the installation quality of rolls and guide plates must be ensured before the rolls are put into service. Axial movement of rolls or guide wheels, misalignment of guide plates, looseness on the left and right or severe wear are strictly prohibited; ensure that the bending is ≤3mm.
[0024] Furthermore, 1.3) also includes: when finishing a steel grade on furnace #3, ordinary carbon raw materials need to be loaded into the top furnace before pure iron raw materials are loaded.
[0025] Furthermore, 1) also includes: 1.5) reducing shift handover time and equipment accidents, and strictly implementing the waiting-for-rolling-cooling system during rolling mill shutdown.
[0026] Furthermore, it is applicable to slabs with a cross section of 230×(137-480)mm.
[0027] Furthermore, 2.2) also includes: if some pulse burners do not shut off after reaching the set temperature and remain in the constantly open state, the heating operator must manually intervene.
[0028] Compared with the prior art, the beneficial technical effects of the present invention are as follows:
[0029] This solution has been used multiple times on-site to produce industrial pure iron using two furnaces, and the product quality meets the requirements, achieving the effect of optimizing process operation.
[0030] 1. Increased hourly output
[0031] Before the improvement, production was limited to a single furnace, with an hourly output of 23-25 pieces (average hourly output of 55.2 tons). After the improvement, dual-furnace production was implemented, increasing the output to 40-42 pieces per hour (average hourly output increased to 94.3 tons), an average increase of 17 pieces / hour, or 39.1 tons per hour. The average shift output increased by 17 pieces / hour × 2.3 tons / piece × 11.5 hours = 449.65 tons / shift, resulting in a daily output increase of 899.3 tons. Based on the current average monthly output of 7700 tons, 3193 tons of this increased output is attributed to the dual-furnace production. Assuming a profit of 177 yuan per ton for pure iron flat steel, the savings due to increased efficiency amount to 3193 × 177 × 12 = 6.782 million yuan.
[0032] 2. Reduced corner cracking rate
[0033] Before the improvement, production was limited to a single furnace, resulting in a 3.0% scrap rate from intermediate rolling due to cracks. This necessitated grinding, re-rolling, or rejection, increasing production costs and causing secondary metal loss. The average loss per ton of steel from defective products was 500-1500 yuan. After the improvement, the average scrap rate from intermediate rolling due to cracks is 0.35%. Based on the current monthly output of 7700 tons, the pass rate increases by 2.65%, reducing defective products by 204 tons per month. The annual savings and efficiency gains from the optimized pure iron rolling process using a dual-furnace production method are calculated as follows: 1000 × 7700 × 2.65% × 12 = 2.4486 million yuan.
[0034] The project is expected to generate annual profits of 678.2 + 244.86 = 923.06 million yuan.
[0035] Through research on the double-furnace rolling process for pure iron, stable rolling was achieved, which not only improved hourly output and product quality (significantly reduced quality problems such as bending and corner cracks), but also ensured delivery time. The product qualification rate reached over 97.5%, creating good economic benefits for the enterprise, achieving the target value, and realizing a balance. Detailed Implementation
[0036] A production method for eliminating defects in double-furnace rolled industrial pure iron flat steel, the specific technical solution of which is as follows:
[0037] 1. Change the loading and unloading method and ensure the time spent in the furnace.
[0038] 1) The loading spacing of the No. 1 heating furnace is controlled at 40-80mm to ensure uniform heating temperature and reduce temperature stress.
[0039] 2) To reduce corner cracks, the two heating furnaces must alternate tapping steel in 1-5 batches.
[0040] 3) To reduce corner cracks, for steel grades in furnace #1, charging should begin when the pure iron is loaded into the soaking zone, or the empty step distance should be maintained before loading pure iron. When finishing a steel grade in furnace #3, ordinary carbon raw materials should be loaded into the top furnace before loading pure iron raw materials.
[0041] 4) Taking a pure iron slab with a cross-section of 230×320mm as an example, the time should be guaranteed to be more than 2 hours and 30 minutes.
[0042] 5) Reduce shift handover time and equipment accidents, and strictly implement the waiting-for-rolling-cooling system when the rolling mill stops.
[0043] 2. Improve the heating process
[0044] 1) Industrial pure iron typically uses slabs with a cross-section of 230×(137-480)mm. Due to variations in furnace time during dual-furnace production, the heating regime needs optimization. Taking a 230×(137-480)mm slab as an example, the maximum heating temperature in the heating section II and soaking section of a pusher-type heating furnace for industrial pure iron production should not exceed 1100℃. In dual-furnace production, the preheating section should be below 800℃, heating section I below 1050℃, and heating sections II and soaking section between 950 and 1100℃. The total heating time should be at least 2 hours and 30 minutes. The soaking time for continuously cast slabs should be ≥30 minutes. Continuously cast slabs should be heated slowly, avoiding overheating or burning, to ensure uniform temperature throughout the slab.
[0045] 2) During the shutdown adjustment period of pure iron rolling, the temperature of heating section II and soaking section must be reduced to between 970 and 1050℃, and the temperature should be maintained at the same level every 5 to 8 minutes. If some pulse burners do not shut off after reaching the set temperature and remain in the constantly open state, the heating operator must intervene manually.
[0046] 3. Achieve dedicated use of special rollers
[0047] 1) For the rolling of pure iron flat steel, a dedicated roll is used for the Ф850mm roll. The II hole is configured with a groove bottom of 250mm and a groove opening of 275mm. By reducing the size of the II hole and increasing the side wall clamping, the material shape is flattened. The groove bottom width of the III hole is widened, and the groove bottom width is changed from 220mm to 230mm to reduce wire drawing, so as to achieve the smooth rolling of industrial pure iron flat steel.
[0048] 2) Reduce the overall reduction of the continuous rolling mill and increase the overall diameter of the Φ700mm-3V roll pass by 2mm, and increase the double bevel (or chamfer) of the Φ500-4H finished roll pass to prevent the feed size from being enlarged and the finished product from being stringy.
[0049] 4. Control the curvature and improve verticality
[0050] 1) Low heating temperature and increased rolling force cause the billet mill to bend during continuous rolling, affecting the bending of the finished product.
[0051] 2) Strictly control the curvature of the hot-rolled state. If the curvature of the hot-rolled state exceeds the standard by visual inspection, the rolling rhythm must be controlled to ensure the time in the furnace. Uniform rolling should be adopted. The number of pieces produced per hour in a single furnace should be controlled at 23-25 pieces / hour, and the number of pieces produced per hour in a double furnace should be controlled at 40-42 pieces / hour.
[0052] 3) If the curvature of the hot-rolled product exceeds 5 mm / m (visually), the furnace time must be increased.
[0053] 4) Strictly adhere to the pre-assembly technical standards for rolls and guides. To reduce the adjustment time for pure iron, the installation quality of the rolls and guide plates must be ensured before the rolls are put into service. Axial movement of the rolls or guide wheels, misalignment of the guide plates, looseness to the left or right, or severe wear are strictly prohibited. Ensure that the bending is ≤3mm.
[0054] This dual-furnace production method has been used multiple times on-site to produce industrial pure iron, and the product quality meets requirements, achieving the effect of optimizing process operation. Specific application results are as follows:
[0055] 1. Increased hourly output
[0056] Before the improvement, production was limited to a single furnace, with an hourly output of 23-25 pieces (average hourly output of 55.2 tons). After the improvement, dual-furnace production was implemented, increasing the output to 40-42 pieces per hour (average hourly output increased to 94.3 tons), an average increase of 17 pieces / hour, or 39.1 tons per hour. The average shift output increased by 17 pieces / hour × 2.3 tons / piece × 11.5 hours = 449.65 tons / shift, resulting in a daily output increase of 899.3 tons. Based on the current average monthly output of 7700 tons, 3193 tons of this increased output is attributed to the dual-furnace production. Assuming a profit of 177 yuan per ton for pure iron flat steel, the savings due to increased efficiency amount to 3193 × 177 × 12 = 6.782 million yuan.
[0057] 2. Reduced corner cracking rate
[0058] Before the improvement, production was limited to a single furnace, resulting in a 3.0% scrap rate from intermediate rolling due to cracks. This necessitated grinding, re-rolling, or rejection, increasing production costs and causing secondary metal loss. The average loss per ton of steel from defective products was 500-1500 yuan. After the improvement, the average scrap rate from intermediate rolling due to cracks is 0.35%. Based on the current monthly output of 7700 tons, the pass rate increases by 2.65%, reducing defective products by 204 tons per month. The annual savings and efficiency gains from the optimized pure iron rolling process using a dual-furnace production method are calculated as follows: 1000 × 7700 × 2.65% × 12 = 2.4486 million yuan.
[0059] The project is expected to generate annual profits of 678.2 + 244.86 = 923.06 million yuan.
[0060] Through research on the double-furnace rolling process for pure iron, stable rolling was achieved, which not only improved hourly output and product quality (significantly reduced quality problems such as bending and corner cracks), but also ensured delivery time. The product qualification rate reached over 97.5%, creating good economic benefits for the enterprise, achieving the target value, and realizing a balance.
[0061] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.
Claims
1. A production method for eliminating defects in double-furnace rolled industrial pure iron flat steel, characterized in that, include: (1) Change the charging and uncharging method and ensure the time spent in the furnace. (1.1) The spacing between the furnace loads in furnace #1 is controlled at 40-80mm to ensure uniform heating temperature and reduce temperature stress; (1.2) To reduce corner cracks, the two heating furnaces must alternate tapping steel in batches of 1-5. (1.3) To reduce corner cracks, steel grade 1 steel is loaded into the soaking section of the heat exchanger when it reaches the pure iron stage; (1.4) Ensure that the furnace time is more than 2 hours and 30 minutes; (2) Improve the heating process (2.1) The maximum heating temperature of the heating section II and the soaking section of the No. 3 furnace for producing industrial pure iron shall not exceed 1100℃. The preheating section of the double furnace shall be below 800℃, the heating section I shall be below 1050℃, and the heating section II and the soaking section shall be between 950℃ and 1100℃. The total heating time shall be more than 2 hours and 30 minutes. The soaking time of the continuous casting billet shall be ≥30 minutes. The continuous casting billet shall be heated slowly. Overheating or overheating shall be prohibited to ensure that the temperature inside and outside of the continuous casting billet is uniform. (2.2) During the adjustment period of rolling pure iron, the temperature of heating section II and soaking section must be reduced to between 970 and 1050°C, and the temperature should be maintained by stepping in place every 5 to 8 minutes. (3) Achieve dedicated use of special rollers (3.1) For the rolling of pure iron flat steel, the Ф850mm roll is used for special purposes. The II hole is configured with a groove bottom of 250mm and a groove opening of 275mm. By reducing the size of the II hole and increasing the side wall clamping, the material shape is flattened. The groove bottom width of the III hole is widened and the groove bottom width of the hole is changed from 220mm to 230mm to reduce wire drawing and achieve smooth rolling of industrial pure iron flat steel. (3.2) Reduce the overall reduction of the continuous rolling mill and increase the overall diameter of the Φ700mm-3V roll pass by 2mm, and increase the double bevel of the Φ500-4H finished product pass to prevent the feed size from being enlarged and the finished product from being stringy; (4) Control the curvature and improve the verticality (4.1) Uniform rolling is adopted. The number of pieces produced per hour in a single furnace is controlled at 23-25 pieces / hour, and the number of pieces produced per hour in a double furnace is controlled at 40-42 pieces / hour. (4.2) If the bending of the hot-rolled state exceeds 5 mm / m by visual inspection, the furnace time must be increased; (4.3) Strictly implement the technical standards for pre-assembly of rolls and guides. In order to reduce the adjustment time of pure iron, the installation quality of rolls and guide plates must be ensured before the rolls are put into service. Axial movement of rolls or guide wheels, misalignment of guide plates, loosening of left and right or severe wear are strictly prohibited. Ensure that the bending is ≤3 mm.
2. The production method for eliminating defects in double-furnace rolled industrial pure iron flat steel according to claim 1, characterized in that, As mentioned in (1.3), when finishing a steel grade on furnace #3, it is necessary to load ordinary carbon raw materials into the top furnace before loading pure iron raw materials.
3. The production method for eliminating defects in double-furnace rolled industrial pure iron flat steel according to claim 1, characterized in that, The above (1) also includes: (1.5) reducing shift handover time and equipment accidents, and strictly implementing the waiting-for-rolling cooling system when the rolling mill is stopped.
4. The production method for eliminating defects in double-furnace rolled industrial pure iron flat steel according to claim 1, characterized in that, Applicable to slabs with a cross section of 230×(137-480)mm.
5. The production method for eliminating defects in double-furnace rolled industrial pure iron flat steel according to claim 1, characterized in that, The above (2.2) also includes: if some pulse burners do not shut off after reaching the set temperature and remain in the constantly open state, the heating operator must manually intervene.