Production method for eliminating defects of industrial pure iron flat steel in double-furnace rolling

Abstract

The invention discloses a method for preventing steel for producing pure iron by a pusher-type heating furnace from generating cracks. The method comprises the following steps: changing a charging and discharging mode and ensuring in-furnace time; improving a heating process; the special roller is specially used; bending is controlled, and perpendicularity is improved. According to the production method for eliminating the defects of the industrial pure iron flat steel rolled by the double furnaces, the defects of the pure iron rolled by the double furnaces are eliminated, double-furnace production is carried out by adopting the pusher furnace and the stepping furnace at the same time, the yield and the product physical quality are improved, the yield is increased, the efficiency is increased, and meanwhile the product quality percent of pass reaches 97% or above.

Description

Technical Field

[0001] The invention belongs to the technical field of steel rolling, and in particular relates to a production method for eliminating defects of industrial pure iron flat steel rolled in double furnaces. Background Art

[0002] Industrial pure iron electrode flat steel is the main product of our factory after the product structure adjustment. It has certain advantages in price, but it is difficult to produce. Our factory currently has two heating furnaces, one walking beam heating furnace and one pusher type heating furnace. In one of the pusher type heating furnaces, the temperature of the transition steel before and after is not easy to control, and the slideway is heavy. When handling accidents and changing rollers, the steel billet stays in the furnace for a long time and cracks occur. Restricted by the fact that industrial pure iron is prone to cracks, we have tried to use a pusher type heating furnace to roll pure iron flat steel before the improvement, but a large number of cracks appeared and it could only be scrapped. Therefore, before the improvement, we have always used a single walking beam heating furnace for production, and have never used double furnaces for production, but the hourly output of a single furnace is low, the cost is high, the delivery time cannot be guaranteed, and the product profit margin is small.

[0003] Compared with common electrode flat steel, industrial pure iron is particularly soft, has good toughness, and has good electromagnetic properties, so it is often used as deep drawing material, electromagnetic material and pure iron flat steel. Industrial pure iron can also be used as raw material for heavy melt alloy, vacuum induction furnace and ultra-low carbon stainless steel, so industrial pure iron can also be called raw material pure iron. The microstructure of low resistivity steel designed with low carbon is basically all ferrite, while the microstructure of existing electrode steel is mostly pearlite + ferrite.

[0004] Surface cracks and shape defects have always been the main common problems in the production of industrial pure iron flat steel. Cracks are distributed in large numbers on the surface and edges of the flat steel, and the cracks are wide and deep. The austenite grains are coarse, indicating that the heating temperature is high and uneven. The higher the heating temperature, the more sulfur will be dissolved in the steel at high temperature, and the more effective sulfur can be provided to precipitate or segregate at the austenite grain boundaries during the rolling process, which has a certain promoting effect on the formation of surface cracks on the flat steel.

[0005] High heating temperature will produce corner cracks or surface cracks, and low temperature rolling will lead to irregular material shape. Pure iron has a low Mn content and a low Mn / S ratio. There is not enough Mn to fix S, which leads to an increase in iron-rich sulfides in the austenite state and the formation of intergranular microcracks at the edges and corners of the finished product. The temperature drop at the four corners is greater than that at other parts, and cracks are prone to occur at the corners. The heating system and rolling process of industrial pure iron directly affect the quality of the product. Poor matching of the two will cause surface defects of the product. Therefore, the heating system and rolling process of industrial pure iron are the key to ensuring product quality. Therefore, how to control the process to ensure product quality is a difficult problem that this patent needs to solve. Summary of the invention

[0006] The purpose of the present invention is to provide a production method for eliminating the defects of industrial pure iron flat steel rolled in double furnaces, eliminating the defects of pure iron rolled in double furnaces, realizing double furnace production using a pusher furnace and a walking furnace at the same time, improving the output and the physical quality of the product, achieving increased production and efficiency, and at the same time the product quality qualification rate reaches more than 97%.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0008] The present invention discloses a production method for eliminating defects of industrial pure iron flat steel rolled in double furnaces, comprising:

[0009] 1) Change the loading and unloading method and ensure the time in the furnace

[0010] 1.1) The spacing between the 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 alternately tap steel at a rate of 1-5;

[0012] 1.3) To reduce corner cracks, the first steel grade on the 1# furnace reaches the pure iron in the soaking section and starts to load steel, or there is an empty step before loading pure iron;

[0013] 1.4) Ensure that the time in the furnace is more than 2 hours and 30 minutes.

[0014] 2) Improve the 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 is not allowed to exceed 1100℃. The preheating section of the double furnace production is below 800℃, the heating section I is below 1050℃, and the heating section II and soaking section are between 950 and 1100℃; the total heating time is more than 2h30min; the soaking time of the continuous casting billet is ≥30min, and the continuous casting billet is heated slowly, and overburning or overheating is 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℃, and the temperature should be kept constant every 5 to 8 minutes;

[0017] 3) Realize special roller for special purpose

[0018] 3.1) For the rolling of pure iron flat steel, the Ø850mm roller is used for special purpose, and the II hole is configured with a groove bottom of 250mm and a groove mouth of 275mm. By reducing the size of the II hole and increasing the side wall clamping, the purpose of flattening the material shape is achieved. The groove bottom width of the III hole is widened, and the groove bottom width of the hole type is changed from 220mm to 230mm to reduce wire drawing and realize the smooth rolling of industrial pure iron flat steel;

[0019] 3.2) Reduce the overall reduction of the continuous rolling unit, increase the overall hole type of the continuous rolling Φ700mm-3V by 2mm, and increase the double slope or chamfer angle of the Φ500-4H finished hole to prevent the feed size from being enlarged and the finished product from drawing;

[0020] 4) Control bending and improve verticality

[0021] 4.1) Uniform rolling is adopted, and the production hourly count of a single furnace is controlled at 23-25 ​​pieces / hour, and the production hourly count of a double furnace is controlled at 40-42 pieces / hour;

[0022] 4.2) If the curvature of the hot-rolled state exceeds 5 mm / m by visual inspection, the furnace time must be increased;

[0023] 4.3) Strictly implement the technical standards for pre-assembly of rollers and guides. In order to reduce the adjustment time of pure iron, the installation quality of rollers and guide plates must be guaranteed before the rollers are put into operation. It is strictly forbidden to have axial movement of rollers or guide wheels, misalignment, left-right looseness or severe wear of guide plates; ensure that the bending is ≤3mm.

[0024] Furthermore, the above 1.3) also includes: when a type of steel is finished on the 3# furnace, ordinary carbon raw materials need to be loaded into the top furnace and then pure iron raw materials are loaded.

[0025] Furthermore, the above 1) also includes: 1.5) reducing shift change time and equipment accidents, and strictly implementing the waiting-to-roll cooling system when rolling is stopped.

[0026] Furthermore, it is applicable to slabs with a cross section of 230×(137-480) mm.

[0027] Furthermore, the above 2.2) also includes: if some pulse burners do not turn off after reaching the set temperature and remain in the normally open state, the heating worker must manually intervene.

[0028] Compared with the prior art, the beneficial technical effects of the present invention are:

[0029] This solution has been used on site many times to produce industrial pure iron in two furnaces. The product quality meets the requirements and achieves the effect of optimizing process operations.

[0030] 1. Increased hourly output

[0031] Before the improvement, only single furnace production was available, with an hourly output of 23-25 ​​pieces per hour (average hourly output of 55.2 tons). After the improvement, double furnace production was realized, increasing to 40-42 pieces per hour (average hourly output can be increased to 94.3 tons), an average increase of 17 pieces / hour, an increase of 39.1 tons per hour, an average shift increase of 17 pieces / hour × 2.3 tons / piece × 11.5 hours = 449.65 tons / shift, and a daily increase of 899.3 tons. After the change to double furnace production, according to the current average monthly output of 7,700 tons, 3,193 tons are the increased output of double furnace production, and the benefit of pure iron flat steel per ton is calculated at 177 yuan. The value of saving due to improved work efficiency = 3,193 × 177 × 12 = 6.782 million yuan.

[0032] 2. Reduced corner crack rate

[0033] Before the improvement, only a single furnace could be used for production. The scrap rate of intermediate rolling caused by cracks was 3.0%. The products could only be repaired, re-rolled or scrapped, which increased production costs and caused secondary metal loss. The average loss of unqualified products was 500-1500 yuan / ton. After the improvement, the average scrap rate of intermediate rolling caused by cracks was 0.35%. According to the current monthly output of 7,700 tons, the qualified rate increased by 2.65%, and 204 tons of unqualified products could be reduced per month. The annual savings and efficiency increase due to the optimization of the pure iron rolling process of the double-furnace production process = 1000 × 7700 × 2.65% × 12 = 2.4486 million yuan.

[0034] The project is expected to generate annual revenue of 678.2+244.86=923.06 million yuan

[0035] Through the research on the double-furnace rolling pure iron process, stable rolling is achieved, which not only improves the hourly output and the physical quality of the product (quality problems such as bending and corner cracks are significantly reduced), but also ensures the delivery time. The product qualification rate reaches more than 97.5%, creating good economic benefits for the enterprise, reaching the target value, and achieving a balance. DETAILED DESCRIPTION

[0036] A production method for eliminating defects of industrial pure iron flat steel rolled in double furnaces, the specific technical scheme is as follows:

[0037] 1. Change the loading and unloading method and ensure the time in the furnace

[0038] 1) The spacing between the 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 produce steel alternately at a rate of 1-5.

[0040] 3) To reduce corner cracks, when a type of steel on the 1# furnace reaches the soaking section, pure iron begins to be loaded, or there is an empty step before loading pure iron. When a type of steel on the 3# furnace is finished, ordinary carbon raw materials need to be loaded into the top furnace before pure iron raw materials are loaded.

[0041] 4) Taking a pure iron slab with a cross-section of 230×320mm as an example, the guaranteed time is more than 2 hours and 30 minutes.

[0042] 5) Reduce shift change time and equipment accidents, and strictly implement the cooling system when rolling is stopped.

[0043] 2. Improve the heating process

[0044] 1) Industrial pure iron generally uses slabs with a cross-section of 230×(137-480)mm. Due to changes in the furnace time in double-furnace production, the heating system needs to be optimized. Taking slabs of 230×(137-480)mm as an example, the maximum heating temperature of the heating section II and the soaking section of the push-steel heating furnace for industrial pure iron production is not allowed to exceed 1100℃. The preheating section of double-furnace production is below 800℃, the heating section I is below 1050℃, and the heating section II and soaking section are between 950 and 1100℃. The total heating time is more than 2h30min. The soaking time of the continuous casting billet is ≥30min, and the continuous casting billet is heated slowly. Overburning or overheating is prohibited to ensure uniform temperature inside and outside the continuous casting billet.

[0045] 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℃, and the insulation process should be stepped on once every 5 to 8 minutes. If some pulse burners do not turn off after reaching the set temperature and remain in the normally open state, the heating worker must intervene manually.

[0046] 3. Realize special roller for special purpose

[0047] 1) For the rolling of pure iron flat steel, the Ф850mm roller is used for special purpose. The II hole is configured with a groove bottom of 250mm and a groove mouth of 275mm. By reducing the size of the II hole and increasing the side wall clamping, the purpose of material flatness is achieved. 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 and realize the smooth rolling of industrial pure iron flat steel.

[0048] 2) Reduce the overall reduction of the continuous rolling unit, increase the overall hole size of the continuous rolling Φ700mm-3V by 2mm, and increase the double slope (or chamfer angle) of the Φ500-4H finished hole to prevent the feed size from being enlarged and wire drawing from occurring in the finished product.

[0049] 4. Control bending and improve verticality

[0050] 1) The heating temperature is low and the rolling force increases, causing the blanking machine to bend for continuous rolling feeding, affecting the bending of the finished product.

[0051] 2) Strictly control the curvature of the hot-rolled state. If the hot-rolled curvature exceeds the standard, the rolling rhythm must be controlled to ensure the time in the furnace. Uniform rolling is adopted. The hourly production number of a single furnace is controlled at 23-25 ​​pieces / hour, and the hourly production number of a double furnace is controlled at 40-42 pieces / hour.

[0052] 3) If the curvature in the hot-rolled state exceeds 5 mm / m (visual inspection), the furnace time must be increased.

[0053] 4) Strictly implement the technical standards for pre-assembly of rollers and guides. To reduce the adjustment time of pure iron, the installation quality of rollers and guides must be guaranteed before the rollers are put on line. It is strictly forbidden to have axial movement of rollers or guide wheels, misalignment, left-right looseness or severe wear of guides. Ensure that the bending is ≤3mm.

[0054] This solution has been used many times on site to produce industrial pure iron in two furnaces. The product quality meets the requirements and achieves the effect of optimizing process operation. The specific application results are as follows:

[0055] 1. Increased hourly output

[0056] Before the improvement, only single furnace production was available, with an hourly output of 23-25 ​​pieces per hour (average hourly output of 55.2 tons). After the improvement, double furnace production was realized, increasing to 40-42 pieces per hour (average hourly output can be increased to 94.3 tons), an average increase of 17 pieces / hour, an increase of 39.1 tons per hour, an average shift increase of 17 pieces / hour × 2.3 tons / piece × 11.5 hours = 449.65 tons / shift, and a daily increase of 899.3 tons. After the change to double furnace production, according to the current average monthly output of 7,700 tons, 3,193 tons are the increased output of double furnace production, and the benefit of pure iron flat steel per ton is calculated at 177 yuan. The value of saving due to improved work efficiency = 3,193 × 177 × 12 = 6.782 million yuan.

[0057] 2. Reduced corner crack rate

[0058] Before the improvement, only a single furnace could be used for production. The scrap rate of intermediate rolling caused by cracks was 3.0%. The products could only be repaired, re-rolled or scrapped, which increased production costs and caused secondary metal loss. The average loss of unqualified products was 500-1500 yuan / ton. After the improvement, the average scrap rate of intermediate rolling caused by cracks was 0.35%. According to the current monthly output of 7,700 tons, the qualified rate increased by 2.65%, and 204 tons of unqualified products could be reduced per month. The annual savings and efficiency increase due to the optimization of the pure iron rolling process of the double-furnace production process = 1000 × 7700 × 2.65% × 12 = 2.4486 million yuan.

[0059] The project is expected to generate annual revenue of 678.2+244.86=923.06 million yuan

[0060] Through the research on the double-furnace rolling pure iron process, stable rolling is achieved, which not only improves the hourly output and the physical quality of the product (quality problems such as bending and corner cracks are significantly reduced), but also ensures the delivery time. The product qualification rate reaches more than 97.5%, creating good economic benefits for the enterprise, reaching the target value, and achieving a balance.

[0061] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A production method for eliminating defects of industrial pure iron flat steel rolled in double furnaces, characterized by comprising: 1) Change the loading and unloading method and ensure the time in the furnace 1.1) The spacing between the 1# heating furnace 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 alternately tap steel at a rate of 1-5; 1.3) To reduce corner cracks, the first steel grade on the 1# furnace reaches the pure iron in the soaking section and starts to load steel, or there is an empty step before loading pure iron; 1.4) Ensure that the time in the furnace 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 soaking section of the pusher type heating furnace for producing industrial pure iron is not allowed to exceed 1100℃. The preheating section of the double furnace production is below 800℃, the heating section I is below 1050℃, and the heating section II and soaking section are between 950 and 1100℃; the total heating time is more than 2h30min; the soaking time of the continuous casting billet is ≥30min, and the continuous casting billet is heated slowly, and overburning or overheating is prohibited to ensure uniform temperature inside and outside the continuous casting billet; 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℃, and the temperature should be kept constant every 5 to 8 minutes; 3) Realize special roller for special purpose 3.1) For the rolling of pure iron flat steel, the Ø850mm roller is used for special purpose, and the II hole is configured with a groove bottom of 250mm and a groove mouth of 275mm. By reducing the size of the II hole and increasing the side wall clamping, the purpose of flattening the material shape is achieved. The groove bottom width of the III hole is widened, and the groove bottom width of the hole type is changed from 220mm to 230mm to reduce wire drawing and realize the smooth rolling of industrial pure iron flat steel; 3.2) Reduce the overall reduction of the continuous rolling unit, increase the overall hole type of the continuous rolling Φ700mm-3V by 2mm, and increase the double slope or chamfer angle of the Φ500-4H finished hole to prevent the feed size from being enlarged and the finished product from drawing; 4) Control bending and improve verticality 4.1) Uniform rolling is adopted, and the production hourly count of a single furnace is controlled at 23-25 ​​pieces / hour, and the production hourly count of a double furnace is controlled at 40-42 pieces / hour; 4.2) If the curvature 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 rollers and guides. In order to reduce the adjustment time of pure iron, the installation quality of rollers and guide plates must be guaranteed before the rollers are put into operation. It is strictly forbidden to have axial movement of rollers or guide wheels, misalignment, left-right looseness or severe wear of guide plates; ensure that the bending is ≤3mm.

2. The production method for eliminating defects of industrial pure iron flat steel rolled in double furnaces according to claim 1 is characterized in that, in the above 1.3), it also includes: when a type of steel on the 3# furnace is finished, ordinary carbon raw materials need to be loaded into the top furnace and then pure iron raw materials are loaded.

3. The production method for eliminating defects of double-furnace rolled industrial pure iron flat steel according to claim 1, characterized in that: The above 1) also includes: 1.5) reducing shift change time and equipment accidents, and strictly implementing the waiting-for-rolling cooling system during rolling stops.

4. The production method for eliminating defects of 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 of 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 turn off after reaching the set temperature and remain in the normally open state, the heating operator must intervene manually.