A composite steel billet rolling connection method

Abstract

The invention discloses a composite steel billet rolling connection method. First, the connection part of two 150x150mm short billets is processed into a step shape, and the contact surfaces of the two short billets are processed into a serrated shape; the processed short billets are butt-jointed, and then the butt joint part is wrapped and welded on four sides with thin steel plates, and the wrapped part is vacuumed; the reduction of the 1#, 3#, and 5# rolling mills is increased, and the short billets are connected according to the above steps. After the length reaches 7m, they are put into a furnace for heating, with a heating section of 1160-1200°C, a soaking section of 1080-1160°C, and a rolling start temperature of 1040-1080°C; the heating time is controlled to be no less than 140 minutes; the tapping temperature is controlled according to an upper limit, and the temperature difference between the head and tail of the billet is controlled within a range of 30°C. After the composite steel billet is heated, it is directly transported to a roughing mill unit by a discharge roller with a heat insulation cover for rolling.

Description

Technical Field

[0001] The invention relates to a method for rolling and connecting composite steel billets. Background Art

[0002] With the rapid development of my country's high-end manufacturing industry, demand for high-end, specialized bar and wire rod is increasing. These high-end, specialized steel bars and wire rods are highly specialized and highly priced, often requiring only a few hundred kilograms. When producing these orders, due to the high alloy costs, smelting often involves only a few hundred kilograms to reduce costs, and casting can only produce short billets of 1-2 meters. Furthermore, special steel mills often cast short billets during the experimental phase of new product development to reduce scrap. The moving beams of domestic bar and wire rod production lines are typically spaced 3 meters apart in the heating furnaces. Billets must be supported on three beams to ensure proper stepping within the furnace. Therefore, billets shorter than 7 meters cannot be properly heated in the furnace. The spacing between the 5# and 6# rolling mills in a bar and wire rod continuous rolling line is 6.5 meters. If the billet is too short, the tail of the rolled piece will not enter the 6# rolling mill before the head enters the 5# rolling mill, making continuous rolling impossible. Therefore, producing short billets in bar and wire rod continuous rolling lines has been an unresolved challenge.

[0003] Retrieved literature: (1) Butt welding technology for steel billets in bar and wire mills, THAusten, “Steel” (2) Analysis of the causes of fracture in the explosive welding of cladding for long continuous casting steel billets, Chen Jianmei, Chen Yunxiang (3) Research on the welding process for forged steel billets, Jiang Lili, Yan Jiawei, Xiaoming The above-mentioned literature search shows that the current method for connecting steel billets for bar and wire mills is mainly through welding. This method requires that the two steel billets to be welded are of the same or similar material. In addition, the metal thermal stress at the weld is easily concentrated during the welding process, affecting the plasticity of the material, and it is very easy to cause fracture accidents during the subsequent rolling process. Summary of the Invention

[0004] The present invention aims to provide a method for rolling and joining composite steel billets. This method utilizes the rolling force of a rolling mill to combine two different steel grades into one, addressing the problem of continuous bar and wire rod rolling lines being unable to produce billets that are too short. This method achieves this goal without changing the existing heating and rolling equipment in the continuous bar and wire rod rolling line. The resulting billets are joined to a length exceeding 7 meters, enabling normal heating and rolling of short billets in the continuous bar and wire rod rolling line.

[0005] The technical solution adopted by the present invention is a method for rolling and connecting composite steel billets, which is implemented according to the following steps: 1) First, the connection part of two 150x150mm short billets is processed into a step shape, and the contact surface of the two short billets is processed into a serrated shape. The height of the contact surface is 75mm and the length is 100mm to increase the contact area. The smoothness of the contact surface must reach level ▽6 or above to facilitate easier rolling during subsequent rolling; the processed short billets are butt-jointed, and then the butt joint is wrapped on all four sides with thin steel plates, and the thin steel plates and the billets are welded together using a full welding process. 1. Welding is performed, and finally, the wrapped area is vacuumed. This prevents oxidation at the connecting portion of the billets during the subsequent heating process, preventing the formation of oxide scale on the contact surface that could affect the rolling effect. 2. The reduction deformation process model for the bar and wire roughing mills is redesigned, increasing the reduction of the 1#, 3#, and 5# mills. This increases the rolling force and deformation of the metal in the contact area, facilitating the rolling of the two billets. 3. Once the short billets are connected according to the above steps and reach a length of 7m, they are placed in the furnace, stepped in, and removed from the furnace to complete the heating process. During heating in the furnace, the connecting portion is vacuumed, preventing the formation of oxide scale on the contact surface of the two billets, maintaining a smooth surface. The heating temperature of composite steel billets needs to be increased by about 20°C compared with ordinary steel grades. The furnace temperature of each heating section and the heating time of the billet in each heating section need to be strictly controlled. The heating control requirements are as follows: heating section 1160-1200°C, soaking section 1080-1160°C, and rolling start temperature 1040-1080°C; 4) Heating time control, the experimental steel in the furnace time control: ≥140min, preheating section time: ≥60min; heating section time: ≥45min; soaking section time: ≥35min, the time in the furnace is not less than 140min; the steel tapping temperature is controlled according to the upper limit, and the temperature difference between the head and tail of the billet is controlled within 30°C.

[0006] 1. After heating, the composite steel billet is transported directly to the roughing mill by a roller conveyor with a heat-insulating cover. When rolling to the billet joint, the jagged contact surface of the rolled piece is subjected to tremendous downward pressure from the rollers. At this point, the contact surface is very smooth and the temperature is very high (around 1050°C). Under such high pressure, the two contact surfaces of the rolled pieces are rolled and welded together, achieving a high-strength connection. During subsequent continuous rolling, the joint becomes increasingly tight.

[0007] 2. To improve the rolling effect of the rolling process, the conventional rough rolling process is optimized. Under the condition that the total reduction rate remains unchanged, the reduction of the 1#, 3#, and 5# flat rolling mills is increased, and the reduction of the 2#, 4#, and 6# vertical rolling mills is reduced accordingly, as follows:

[0008] 1# run, the pass shape is shallow groove pass, the rolled piece width is 176, the rolled piece height is 95, the roll gap value is 80, the area is 16965, and the reduction rate is 36.8%;

[0009] 2# batch, the pass shape is shallow groove pass, the rolled piece width is 114, the rolled piece height is 120, the roll gap value is 82, the area is 12675, and the reduction rate is 31.8%;

[0010] 3# run, the pass shape is elliptical, the rolled piece width is 135, the rolled piece height is 66, the roll gap value is 13, the area is 9009, and the reduction rate is 42.1%;

[0011] For the 4# batch, the pass shape is round, the width of the rolled piece is 85, the height of the rolled piece is 92, the roll gap value is 12, the area is 6638, and the reduction rate is 31.8%;

[0012] 5#, the hole shape is elliptical, the rolled piece width is 96, the rolled piece height is 48, the roll gap value is 15, the area is 4961, and the reduction rate is 43.5%;

[0013] For the 6# batch, the hole shape is round, the width of the rolled piece is 65, the height of the rolled piece is 67, the roll gap value is 9, the area is 3420, and the reduction rate is 30.2%.

[0014] The present invention is suitable for connecting composite steel billets of various materials, and is particularly suitable for connecting billets of highly specialized high-end special materials. The process adjustment of the present invention is simple, no additional investment is required, and it has good promotional potential. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a schematic structural diagram of the short blank connection portion of the present invention;

[0016] Figure 2 It is a schematic diagram of the structure after two short billets are connected in the present invention. DETAILED DESCRIPTION

[0017] A composite steel billet rolling connection method is implemented according to the following steps: 1) Figure 1 、 2As shown in the figure, first, the connection part of two 150x150mm short billets is processed into a step shape, and the contact surface of the two short billets is processed into a serrated shape with a contact surface height of 75mm and a length of 100mm to increase the contact area. The contact surface finish should reach level ▽6 or above to facilitate easier rolling during subsequent rolling. The processed short billets are butt-jointed, and then the butt joint is wrapped on all four sides with thin steel plates. The thin plates and the billets are welded using a full welding process. Finally, the wrapped parts are vacuumed. In this way, during the subsequent heating process, the connection part of the billets will not oxidize, avoiding the formation of iron oxide scale on the contact surface that affects the rolling effect. 2) The reduction deformation process model of the bar and wire roughing mill is redesigned, and the reduction of the 1#, 3#, and 5# rolling mills is increased, which correspondingly increases the rolling force and the deformation of the metal in the contact area, which is conducive to the rolling of the two billets. 3) After the short billets are connected according to the above steps and the length reaches 7m, they are put into the furnace, stepped, and taken out of the furnace to complete the heating process. During heating in the heating furnace, the connection parts are vacuumed, and the contact surfaces of the two billets do not produce iron oxide scale, and remain smooth. The heating temperature of composite steel billets needs to be increased by about 20°C compared to ordinary steel grades. The furnace temperature and heating time of each heating section must also be strictly controlled. The heating control requirements are as follows: heating section 1160-1200°C, soaking section 1080-1160°C, and rolling temperature 1040-1080°C; 4) Heating time control, the experimental steel in the furnace time control: ≥140min, preheating section time: ≥60min; heating section time: ≥45min; soaking section time: ≥35min, the furnace time is not less than 140min; the tapping temperature is controlled according to the upper limit, and the temperature difference between the head and tail of the billet is controlled within 30°C.

[0018] 1. After heating, the composite steel billet is transported directly to the roughing mill by a roller conveyor with a heat-insulating cover. When rolling to the billet joint, the jagged contact surface of the rolled piece is subjected to tremendous downward pressure from the rollers. At this point, the contact surface is very smooth and the temperature is very high (around 1050°C). Under such high pressure, the two contact surfaces of the rolled pieces are rolled and welded together, achieving a high-strength connection. During subsequent continuous rolling, the joint becomes increasingly tight.

[0019] 2. To improve the rolling effect of the rolling process, the conventional rough rolling process is optimized. Under the condition that the total reduction rate remains unchanged, the reduction of the 1#, 3#, and 5# flat rolling mills is increased, and the reduction of the 2#, 4#, and 6# vertical rolling mills is reduced accordingly, as follows:

[0020] 1# run, the pass shape is shallow groove pass, the rolled piece width is 176, the rolled piece height is 95, the roll gap value is 80, the area is 16965, and the reduction rate is 36.8%;

[0021] 2# batch, the pass shape is shallow groove pass, the rolled piece width is 114, the rolled piece height is 120, the roll gap value is 82, the area is 12675, and the reduction rate is 31.8%;

[0022] 3# run, the pass shape is elliptical, the rolled piece width is 135, the rolled piece height is 66, the roll gap value is 13, the area is 9009, and the reduction rate is 42.1%;

[0023] For the 4# batch, the pass shape is round, the width of the rolled piece is 85, the height of the rolled piece is 92, the roll gap value is 12, the area is 6638, and the reduction rate is 31.8%;

[0024] 5#, the hole shape is elliptical, the rolled piece width is 96, the rolled piece height is 48, the roll gap value is 15, the area is 4961, and the reduction rate is 43.5%;

[0025] For the 6# batch, the hole shape is round, the width of the rolled piece is 65, the height of the rolled piece is 67, the roll gap value is 9, the area is 3420, and the reduction rate is 30.2%.

Claims

1. A composite steel billet rolling connection method, characterized in that Follow these steps to implement: 1) First, the connection part of two 150x150mm short billets is processed into a step shape, and the contact surface of the two short billets is processed into a serrated shape. The height of the contact surface is 75mm and the length is 100mm. The surface finish of the contact surface must reach level ▽6 or above. The processed short billets are connected, and then the connecting part is wrapped with thin steel plates on all four sides. The thin steel plates and the billets are welded using a full welding process. Finally, the wrapped part is vacuumed. 2) Redesign the reduction deformation process model of the bar and wire roughing mill. While keeping the total reduction ratio unchanged, increase the reduction of the 1#, 3#, and 5# flat mills, and correspondingly reduce the reduction of the 2#, 4#, and 6# vertical mills. This will increase the rolling force of the flat mill and the deformation of the metal in the contact area. 3) After the short billets are connected according to the above steps and the length reaches 7m, they are put into the furnace, stepped into the furnace, and taken out of the furnace to complete the heating process. The heating control requirements are as follows: heating section 1160-1200℃, soaking section 1080-1160℃, and rolling start temperature 1040-1080℃; 4) Heating time control, the experimental steel is kept in the furnace for a period of ≥140 min, preheating period: ≥60 min; heating period: ≥45 min; soaking period: ≥35 min, and the time in the furnace is not less than 140 min; the tapping temperature is controlled according to the upper limit, and the temperature difference between the head and tail of the billet is controlled within 30 ° C. After heating, the composite steel billet is directly transported to the rough rolling unit for rolling by the discharge roller with an insulation cover. The contact surfaces of the two rolled pieces will be rolled and welded into one, achieving a high-strength connection.

2. The method for rolling and connecting composite steel billets according to claim 1, characterized in that The conventional rough rolling process is optimized. Under the condition that the total reduction rate remains unchanged, the reduction rate of the 1#, 3#, and 5# flat rolling mills is increased, and the reduction rate of the 2#, 4#, and 6# vertical rolling mills is reduced accordingly. The details are as follows: 1# run, the pass shape is shallow groove pass, the rolled piece width is 176, the rolled piece height is 95, the roll gap value is 80, the area is 16965, and the reduction rate is 36.8%; 2# batch, the pass shape is shallow groove pass, the rolled piece width is 114, the rolled piece height is 120, the roll gap value is 82, the area is 12675, and the reduction rate is 31.8%; 3# run, the pass shape is elliptical, the rolled piece width is 135, the rolled piece height is 66, the roll gap value is 13, the area is 9009, and the reduction rate is 42.1%; For the 4# batch, the pass shape is round, the width of the rolled piece is 85, the height of the rolled piece is 92, the roll gap value is 12, the area is 6638, and the reduction rate is 31.8%; 5#, the hole shape is elliptical, the rolled piece width is 96, the rolled piece height is 48, the roll gap value is 15, the area is 4961, and the reduction rate is 43.5%; For the 6# batch, the hole shape is round, the width of the rolled piece is 65, the height of the rolled piece is 67, the roll gap value is 9, the area is 3420, and the reduction rate is 30.2%.

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