A processing method for reducing hot rolling edge cracks of non-oriented silicon steel

Abstract

The application discloses a processing method for reducing hot rolling edge cracks of non-oriented silicon steel, and belongs to the technical field of rolling steel. The processing method comprises the following steps: adding smelting raw materials into a smelting furnace to form silicon steel liquid; adding the silicon steel liquid into a continuous casting machine to process into continuous casting blank; transmitting the continuous casting blank to a heating furnace through a conveying device to heat; transmitting the heated continuous casting blank to a rough rolling line through the conveying device to perform rough rolling; conveying the hot coil box after uncoiling to a finishing rolling line through the conveying device to perform finishing rolling; and winding the finished rolling steel strip into a hot rolling steel strip coil. The intermediate blank thickness is controlled, the hot rolling temperature is adjusted, the descaling is fully performed, and the target hot rolling reduction rate is adjusted, so that the edge micro-cracks of the non-oriented silicon steel are reduced, and the utilization rate of the finished hot rolling silicon steel is improved.

Description

Technical Field

[0001] This invention relates to the field of steel rolling technology, and in particular to a processing method for reducing edge cracking during hot rolling of non-oriented silicon steel. Background Technology

[0002] Iron and steel smelting is a general term for the metallurgical processes of steel and iron. Industrially produced iron is divided into pig iron with a carbon content of more than 2% and steel with a carbon content of less than 2% according to its carbon content. Steelmaking mainly uses pig iron produced in blast furnaces, sponge iron produced by direct reduction ironmaking, and scrap steel as raw materials. Its basic production process is to refine iron ore into pig iron in a blast furnace, and then use pig iron as raw material to refine steel using different methods, and then cast it into steel ingots or continuously cast billets.

[0003] Silicon content has a sensitive effect on the magnetic properties of silicon steel. As the silicon content increases, the resistivity increases, eddy current loss decreases, and iron loss also decreases. However, with the increase in silicon content, the steel becomes more brittle, and edge cracks are more likely to occur during hot rolling. Non-oriented silicon steel is widely used as the core material for motors and transformers and needs to have good magnetic properties. Therefore, the silicon and aluminum alloying element content in non-oriented silicon steel is constantly increasing. However, with the increase of silicon and aluminum alloy content, the toughness of the steel strip decreases sharply while its brittleness increases, leading to micro-cracks at the edges of the steel strip during hot rolling. This is mainly because, firstly, non-oriented silicon steel has a high silicon content, and silicon's solubility in austenite is greater than in ferrite. During the austenite-ferrite transformation, silicon tends to segregate towards the grain boundaries, causing grain boundary embrittlement. Secondly, the temperature drop at the edge of the steel strip is faster during rolling, resulting in an edge elongation lower than that of the matrix. Furthermore, silicon shrinks the austenite region, easily leading to non-uniformity of the hot-rolled grains. Since edge trimming is required after hot rolling, minor edge cracks have little impact, but severe edge cracks can cause excessive trimming, significantly reducing the yield. In addition, strip breakage accidents are highly likely to occur during subsequent cold rolling, affecting the rolling efficiency and yield of cold rolling.

[0004] In the existing production process of non-oriented silicon steel, in order to reduce the strip breakage rate during rolling, a heating system is usually added before rolling to increase the temperature of the rolled piece and increase its plasticity. However, most continuous rolling mills do not have the conditions for heating the edge of the steel strip. This method of heating equipment requires a large investment, consumes a lot of energy, and significantly increases costs. Summary of the Invention

[0005] The technical problem solved by this invention is to address the issue of edge cracks appearing on both sides of non-oriented silicon steel during hot rolling in the prior art. This invention provides a processing method to reduce edge cracks in hot-rolled non-oriented silicon steel. By adopting comprehensive control processes such as controlling the thickness of the intermediate slab, adjusting the hot rolling temperature, performing thorough descaling, and adjusting the target reduction ratio during hot rolling, the micro-cracks at the edges of non-oriented silicon steel are reduced, thereby improving the finished product utilization rate of hot-rolled silicon steel.

[0006] Technical solution: The present invention provides a processing method for reducing edge cracks in hot-rolled non-oriented silicon steel, the processing method comprising the following steps:

[0007] Step 1: Add the raw materials to the smelting furnace for smelting to form molten silicon steel;

[0008] Step 2: Add molten silicon steel to a continuous casting machine and continuously cast it into a continuous casting billet with a thickness of 210-230mm;

[0009] Step 3: The continuous casting billet is conveyed to the heating furnace through the conveying device for heating. The temperature of the continuous casting billet before entering the heating furnace is controlled at 450~650℃, and the temperature of the continuous casting billet after exiting the furnace is controlled at 1135~1145℃.

[0010] Step 4: The heated continuous casting billet is conveyed to the roughing rolling line through a conveying device. After roughing, an intermediate billet with a thickness of 39~41mm is formed. The rolled intermediate billet is wound in a hot coil box and kept at a constant temperature of 1050℃.

[0011] Step 5: After the hot coil box is uncoiled, the end of the intermediate billet is cut off and conveyed to the finishing line by the conveying device. The finishing line adopts seven-stand continuous rolling. The inlet temperature of the finishing mill is controlled at 1010~1030℃ and the outlet temperature of the finishing mill is controlled at 850~880℃.

[0012] Step 6: The 2.6~2.8mm steel strip obtained by precision rolling is wound into hot-rolled steel strip coils at 660~700℃.

[0013] Preferably, in step 4, the roughing line uses two four-high rolling mills, R1 and R2, and the continuously cast billet is rolled in 4 to 6 passes to form an intermediate billet.

[0014] Preferably, in step 6, the finishing mill adopts a seven-stand four-high continuous rolling mill, and the reduction of the finishing mill stands F1 to F7 is distributed as follows: F1: 38%, F2: 38%, F3: 38%, F4: 40%, F5: 28%, F6: 22%, F7: 15%, so that the austenitic-ferrite phase transformation stand of the hot-rolled steel strip is maintained between the F2 stand and the F3 stand.

[0015] Preferably, four-stage high-pressure descaling is performed in the continuous casting process of step 2, the R1 and R2 stands of the roughing mill in step 4, and the finishing mill in step 5, respectively, with the pressure of the descaling system maintained at 18~20MPa.

[0016] Preferably, the descaling system includes a main spray pipe with a high-pressure water chamber, a plurality of spray branch pipes arranged in a row at equal intervals along the length of the main spray pipe, and spray end pipes provided at both ends of the main spray pipe. The axial direction of the spray branch pipe is at an angle of 10-20° to the vertical direction and is inclined downward toward the slab's forward direction. The outlet end of the spray end pipe is inclined inward at an angle of 10-20° to the vertical direction. A water inlet pipe is provided at the top of the main spray pipe.

[0017] Preferably, drainage collection troughs are provided on both sides of the finishing mill in step 5 along its length, and the descaling water produced by the descaling system is quickly discharged along the drainage collection troughs.

[0018] Compared with the prior art, the present invention has at least the following beneficial effects:

[0019] 1. This invention reduces edge micro-cracks in non-oriented silicon steel and improves the finished product utilization rate of hot-rolled silicon steel by adopting comprehensive control processes such as controlling the thickness of intermediate slabs, adjusting hot rolling temperature, performing thorough descaling, and adjusting the target reduction rate of hot rolling.

[0020] 2. This processing method refines the heating furnace heating process, adopts multi-stage gradual heating, uses a hot rolling box to control the temperature drop of the intermediate billet and control the uniform temperature of the intermediate billet coil, strictly controls the inlet and outlet temperatures of the intermediate billet entering the finishing rolling line, and reduces the edge crack size of hot-rolled steel strip.

[0021] 3. During the finishing rolling process, the reduction load of stands F1 to F7 is controlled respectively, and the austenite-ferrite phase transformation range is maintained within stands F2 to F3. This ensures that the phase transformation of silicon steel does not change abruptly during finishing rolling, and that the silicon steel sheet produces uniform elongation under tension, reducing edge cracks in the silicon steel sheet and thus improving the hot rolling quality.

[0022] 4. During the hot rolling process of silicon steel, four-stage high-pressure descaling is performed on the continuous casting process, the R1 and R2 stands of the roughing mill, and the finishing mill to remove the iron oxide scales generated on the surface of the silicon steel plate, improve the hot rolling quality of silicon steel, and further reduce its edge cracks. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the processing flow of the non-oriented silicon steel of the present invention;

[0024] Figure 2 Before improving the processing technology of non-oriented silicon steel, the edge crack diagram of steel strip is shown ((a) hot-rolled steel strip, (b) cold-rolled steel strip);

[0025] Figure 3 for Figure 2 Measurement diagram of microcracks at the edge of medium-hot rolled steel strip;

[0026] Figure 4To improve the processing technology of non-oriented silicon steel, the edge crack diagram of the steel strip is shown in (a) hot-rolled steel strip and (b) cold-rolled steel strip.

[0027] Figure 5 for Figure 4 End view of medium hot-rolled steel strip;

[0028] Figure 6 This is a top view of the descaling system structure;

[0029] Figure 7 for Figure 6 Right view of the structure of the descaling system;

[0030] Figure 8 for Figure 6 Schematic diagram of the AA descaling system;

[0031] Figure 9 for Figure 8 Schematic diagram of the BB descaling system.

[0032] Attached reference numerals: 1. Main sprinkler pipe; 2. Inlet pipe; 3. Branch sprinkler pipe; 4. End sprinkler pipe. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will be described in conjunction with the accompanying drawings. Figures 1-9 The technical solutions of the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention are within the scope of protection of the present invention. Example 1:

[0034] like Figure 1 As shown in the figure, an embodiment of the present invention provides a processing method for reducing edge cracks in hot-rolled non-oriented silicon steel. The processing method includes the following steps:

[0035] Step 1: Add the raw materials to the smelting furnace for smelting to form molten silicon steel;

[0036] Step 2: Add molten silicon steel to a continuous casting machine and continuously cast it into a continuous casting billet with a thickness of 210-230mm;

[0037] Step 3: The continuously cast billet is conveyed to the heating furnace via a conveying device for heating. The temperature of the continuously cast billet before entering the heating furnace is controlled at 450~650℃. The temperature in the preheating section is 1030~1070℃ for 30 minutes; the temperature in the first heating section is 1100~1140℃ for 40 minutes; the temperature in the second heating section is 1130~1150℃ for 40 minutes; the temperature in the soaking section is 1130~1150℃ for 40 minutes; the target temperature at the exit of the furnace is 1140℃, and the total time in the furnace is >150 minutes.

[0038] Step 4: The heated continuous casting billet is conveyed to the roughing rolling line by a conveying device. The roughing rolling line adopts two four-high rolling mills, R1 and R2. The four-high rolling mill consists of two sets of support rolls arranged vertically and vertically, and work rolls arranged on the inner side of the support rolls. The two sets of work rolls have high temperature resistance and smooth surface to meet the roughing requirements of the continuous casting billet. The continuous casting billet is rolled into an intermediate billet after 4 to 6 passes. After roughing, an intermediate billet with a thickness of 39 to 41 mm is formed. The rolled intermediate billet is wound in a hot coil box and kept at a constant temperature of 1050℃.

[0039] Step 5: After the hot coil box is uncoiled, the end of the intermediate billet is cut off and conveyed to the finishing line via a conveying device. The finishing line adopts a seven-stand four-high continuous rolling mill. The finishing mill stands F1 to F7 are set up sequentially along the conveying line. The reduction of the finishing mill stands F1 to F7 is distributed as follows: F1: 38%, F2: 38%, F3: 38%, F4: 40%, F5: 28%, F6: 22%, F7: 15%. By adjusting the reduction of the finishing mill stands accordingly, the austenitic-ferrite phase transformation stand of the hot-rolled steel strip is maintained between the F2 and F3 stands, so as to obtain a reasonably distributed austenitic-ferrite phase transformation hot-rolled steel strip coil. The inlet temperature of the finishing mill is controlled at 1010-1030℃, and the outlet temperature of the finishing mill is controlled at 850-880℃.

[0040] Step 6: The 2.6~2.8mm steel strip obtained by precision rolling is wound into hot-rolled steel strip coils at 660~700℃.

[0041] Example 2:

[0042] Based on Example 1, such as Figures 6-9 As shown, four stages of high-pressure descaling are performed in the continuous casting process of step 2, the R1 and R2 stands of the roughing mill in step 4, and the finishing mill in step 5. The descaling system is set up in conjunction with the corresponding continuous casting or rolling equipment. The pressure of the descaling system is maintained at 18~20MPa to achieve efficient descaling. The descaling system includes a main spray pipe 1 with a high-pressure water chamber, multiple spray branch pipes 3 arranged in a row at equal intervals along the length of the main spray pipe 1, and spray end pipes 4 set at both ends of the main spray pipe 1. The axial direction of the spray branch pipes 3 forms an angle of 10-20° with the vertical direction and is inclined downwards towards the slab's forward direction. The outlet end of the spray end pipe 4 is inclined inwards at an angle of 10-20° with the vertical direction. A water inlet pipe 2 is set at the top of the main spray pipe 1. Drainage collection tanks are set on both sides of the finishing mill along its length. The descaling water produced by the descaling system is quickly discharged along the drainage collection tanks to reduce the adverse effects of the descaling cooling water on the hot-rolled plate.

[0043] The processing methods of Examples 1 and 2 can reduce microcrack defects at the edges of non-oriented silicon steel sheets, resulting in better appearance quality of hot-rolled steel strip coils, reducing the amount of edge trimming, or even eliminating the need for trimming, thereby improving the finished product utilization rate of hot-rolled silicon steel. The hot rolling process parameters of Examples 1-3 and Comparative Example 1 are shown in Tables 1 and 2.

[0044] Table 1 Hot rolling process parameters

[0045] Example Slab loading temperature (°C) Preheating section temperature ℃ Temperature of heating section ℃ Temperature of the second heating section (°C) Temperature of the soaking zone (°C) Total time in the furnace (min) Target temperature for furnace exit (°C) Finishing mill inlet temperature (°C) Finishing mill exit temperature (°C) Example 1 480 1045 1120 1135 1141 180 1140 1010 860 Example 2 500 1052 1122 1145 1140 180 1140 1020 865 Example 3 520 1050 1118 1150 1138 180 1140 1030 870 Comparative Example 1 490 1043 1119 1144 1150 180 1130 1040 865

[0046] Table 2. Reduction parameters of finishing mill stands F1 to F7

[0047]

[0048] Compare the quality of silicon steel strips produced by the processing methods of Examples 1-3 and Comparative Example 1, such as Figures 2-3 As shown, before the improved processing technology for non-oriented silicon steel, severe microcracks existed on both sides of the hot-rolled silicon steel strip coil. After subsequent cold rolling, severe edge cracks appeared on the steel strip edges, with crack sizes reaching 2-4 mm. Figures 4-5 As shown, after improving the processing technology of non-oriented silicon steel, the edges of hot-rolled silicon steel strip coils are neat and the micro-cracks are significantly reduced. Furthermore, the steel strip coils are not trimmed before cold rolling, and the edge cracks of the steel strip are significantly reduced after cold rolling. This can effectively reduce the scrap rate and improve the utilization rate of hot-rolled silicon steel products.

[0049] The above are preferred embodiments of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A processing method for reducing hot banding cracks in non-oriented silicon steel, characterized by, The processing method includes the following steps: Step 1: Add the raw materials to the smelting furnace for smelting to form molten silicon steel; Step 2: Add molten silicon steel to a continuous casting machine and continuously cast it into a continuous casting billet with a thickness of 210-230mm; Step 3: The continuous casting billet is conveyed to the heating furnace through the conveying device for heating. The temperature of the continuous casting billet before entering the heating furnace is controlled at 450~650℃, and the temperature of the continuous casting billet after exiting the furnace is controlled at 1135~1145℃. Step 4: The heated continuous casting billet is conveyed to the roughing rolling line through a conveying device. After roughing, an intermediate billet with a thickness of 39~41mm is formed. The rolled intermediate billet is wound in a hot coil box and kept at a constant temperature of 1050℃. Step 5: After the hot coil box is uncoiled, the end of the intermediate billet is cut off and conveyed to the finishing line by a conveying device. The finishing line adopts a seven-stand continuous rolling mill. The inlet temperature of the finishing mill is controlled at 1010-1030℃, and the outlet temperature of the finishing mill is controlled at 850-880℃. Among them, the finishing line adopts a seven-stand four-high continuous rolling mill. The reduction of the finishing mill stands F1 to F7 is distributed as follows: F1: 38%, F2: 38%, F3: 38%, F4: 40%, F5: 28%, F6: 22%, F7: 15%, so that the austenite-ferrite phase transformation stand of the hot rolled steel strip is maintained between the F2 stand and the F3 stand. Step 6: The 2.6~2.8mm steel strip obtained by precision rolling is wound into hot-rolled steel strip coils at 660~700℃.

2. The processing method to reduce hot banding of non-oriented silicon steel of claim 1, wherein, In step 4, the roughing line uses two four-high rolling mills, R1 and R2, to form intermediate billets from the continuously cast billets through 4 to 6 rolling passes.

3. The processing method for reducing edge cracks in hot-rolled non-oriented silicon steel according to claim 2, characterized in that, The continuous casting process in step 2, the R1 and R2 stands in the roughing mill in step 4, and the finishing mill in step 5 are subjected to four stages of high-pressure descaling, with the pressure of the descaling system maintained at 18~20MPa.

4. The processing method for reducing edge cracks in hot-rolled non-oriented silicon steel according to claim 3, characterized in that, The descaling system includes a main spray pipe (1) with a high-pressure water chamber, a plurality of spray branch pipes (3) arranged in a row at equal intervals along the length of the main spray pipe (1), and spray end pipes (4) arranged at both ends of the main spray pipe (1). The spray branch pipes (3) are axially at an angle of 10-20° to the vertical direction and are inclined downwards towards the slab's forward direction. The outlet end of the spray end pipe (4) is inclined inwards at an angle of 10-20° to the vertical direction. A water inlet pipe (2) is provided at the top of the main spray pipe (1).

5. The processing method for reducing edge cracks in hot-rolled non-oriented silicon steel according to claim 4, characterized in that, In step 5, drainage collection troughs are provided on both sides of the finishing mill along its length, and the descaling water produced by the descaling system is quickly discharged along the drainage collection troughs.

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