Continuous casting method for improving internal quality of low-alloy steel slab

Abstract

The invention discloses a continuous casting method for improving the internal quality of a low-alloy steel slab, and belongs to the technical field of metallurgy. The specific method comprises the steps that continuous casting is conducted, constant-pulling-speed production is adopted, casting is conducted at the low superheat degree of 8-25 DEG C, the roll gap shrinkage amount of each bending section is set to be 0.2-0.4 mm, the roll gap shrinkage amount of a first straightening section is set to be 1.2-1.5 mm, the roll gap shrinkage amount of a tail section is set to be 0-0.2 mm, the specific water flow of secondary cooling water of an inner arc of a horizontal section is controlled to be 0.85-0.95 L / kg, the total specific water flow is 0.80-0.90 L / kg, the solid phase rate of a tail end soft reduction interval is 0.2-0.8, and the reduction amount is 6-8 mm. According to the method, through reasonable process and equipment parameter design, the internal quality of the low-alloy steel plate blank is effectively improved, and a good base material foundation is laid for the subsequent rolling process.

Description

Technical Field

[0001] The invention belongs to the technical field of steel smelting, and in particular relates to a continuous casting method for improving the internal quality of a low alloy steel slab. Background Art

[0002] Low alloy steel is widely used in construction, automobile manufacturing, shipbuilding, machinery manufacturing and other industries due to its low alloy cost, good weldability and excellent mechanical properties. Low alloy steel is mainly peritectic steel, which is prone to serious defects such as center segregation and middle cracks in the actual continuous casting process. These defects are generally difficult to eliminate in the subsequent rolling process, which seriously affects the mechanical properties of the finished steel plate. In severe cases, it will cause defects such as bending cracking and delamination, causing huge economic losses to enterprises and users.

[0003] As the last step of the steelmaking process, continuous casting plays an indescribable role in the quality of the ingot. The continuous casting process is a process in which high-temperature molten steel releases its latent heat and gradually solidifies into ingots. Due to the different solubility of various alloy elements in the solid and liquid phases during the solidification process, the ingots have different degrees of central segregation. The influence of element segregation can be effectively reduced through a reasonable continuous casting process. The molten steel is accompanied by a certain volume shrinkage during the solidification process. Reasonable roll gap settings can effectively compensate for the volume shrinkage and prevent defects such as bulging and cracks. Pressing down at the end of solidification can also effectively reduce defects such as central segregation and looseness.

[0004] The patent application with publication number CN 111774546 A discloses a method for improving the center segregation and surface cracks of the medium and thick slabs of peritectic steel continuous casting. The method reduces the cooling intensity of the front stage of solidification and strengthens the cooling intensity of the last stage of solidification to achieve the improvement of the center segregation and surface cracks of the medium and thick slabs of peritectic steel continuous casting. The method only considers the influence of the secondary cooling water volume on the segregation, fails to consider the influence of other factors, and the adjustment of the water volume alone cannot achieve a good effect on the intermediate cracks.

[0005] The patent application with publication number CN 114054710 A discloses a method for improving the center quality of large-section rectangular continuous casting billets. The method sets different partitions for the width and narrow sides of the billet, configures different water distribution schemes for each partition, and cooperates with electromagnetic stirring, induction heating, and soft pressure to improve the center quality of the slab. For the various types of low-alloy steel, the application of electromagnetic stirring, induction heating, etc. to low-grade steel will increase production costs, and this method is only designed for secondary cooling water distribution, without considering the overall nature of continuous casting production, and lacks pertinence for center segregation and middle crack defects. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a continuous casting method for improving the internal quality of low alloy steel slabs, so as to improve the internal quality of the slabs and provide a parent material with good internal quality for subsequent rolling.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is: a continuous casting method for improving the internal quality of low alloy steel slabs, the continuous casting method comprising the following steps: (1) Continuous casting is produced at a constant casting speed; (2) Low superheat casting is adopted, and the superheat of the tundish is controlled at 8-25°C; (3) The shrinkage of the roller gap in each section of the bending section is set to 0.2-0.4 mm, the shrinkage of the roller gap in the first straightening section is set to 1.2-1.5 mm, and the shrinkage of the roller gap in the last section is set to 0-0.2 mm; (4) The water volume of the secondary cooling water in the horizontal section is controlled at 0.85-0.95 L / kg, and the total water volume is 0.80-0.90 L / kg; (5) The final gentle pressure reduction range is 0.2-0.8 solid phase ratio and 6-8 mm reduction.

[0008] In the step (1) of the present invention, the casting is produced at a constant pulling speed, the pulling speed is controlled at 1.0-1.2 m / min, and the steelmaking scheduling is based on ensuring the continuous casting constant pulling speed casting and organizing the production.

[0009] In step (2) of the present invention, the preceding process ensures that the temperature of the molten steel meets the casting requirement of superheat of 8 to 25° C. When the temperature is too high, it is promptly cooled by increasing the net blow and adding cold materials such as iron ore.

[0010] In step (3) of the present invention, the accuracy of the roll gap of the continuous casting machine is regularly calibrated to ensure that the roll gap accuracy is within ±0.5 mm.

[0011] In step (3) of the present invention, the roller gap shrinkage of each subsequent straightening section and horizontal section except the end is set to 0-0.3 mm.

[0012] The proportion of the slab sulfur print center segregation rating C1.0 or above obtained by the continuous casting method of the present invention reaches ≥87%.

[0013] The slab obtained by the continuous casting method of the present invention has no middle cracks and triangular cracks, and the elongation qualified rate of the rolled steel plate is ≥99.5%.

[0014] The present invention is applicable to the continuous casting process of low alloy steel slabs. At present, defects such as central segregation and middle cracks of low alloy steel seriously affect the performance of steel plates. Domestic steel mills generally adopt measures such as optimizing superheat, electromagnetic stirring, and end pressure reduction to address this problem. There is a lack of continuous casting control methods that comprehensively consider multiple factors from the combination of equipment (roller gap, light pressure reduction) and process (pulling speed, superheat, secondary cooling water volume). The present application can effectively improve the internal quality of low alloy steel slabs by coordinating the continuous casting equipment and process designed by comprehensively considering multiple factors.

[0015] The beneficial effect of adopting the above technical scheme is that: the present invention can effectively improve the proportion of equiaxed crystals in the solidification process of low-alloy steel liquid, reduce the segregation of alloy elements, and prevent the generation of intermediate cracks through the comprehensive design of process parameters such as pulling speed, temperature, casting machine roll gap, water volume, and light pressure during continuous casting. The proportion of low-multiple center segregation grade C1.0 and above in the sulfur print center segregation rating of the slab reaches ≥87%, there are no intermediate cracks and triangular cracks, the qualified rate of elongation of steel plates after rolling is ≥99.5%, the performance stability of the finished product after rolling is improved, and the generation of quality objections such as bending cracking and delamination is reduced. DETAILED DESCRIPTION

[0016] The present invention is further described in detail below in conjunction with specific embodiments.

[0017] The continuous casting process for increasing the hot charging and hot delivery temperature of slabs comprises the following steps: (1) Continuous casting adopts constant pulling speed production, and the pulling speed is controlled at 1.0~1.2m / min. Scheduling is based on ensuring constant pulling speed casting for continuous casting, and production is organized. The pulling speed can be adjusted within the range of ±0.1m / min.

[0018] (2) Low superheat casting is adopted, and the superheat of the tundish is controlled at 8-25°C. The previous process ensures that the molten steel temperature meets the casting requirement of superheat of 8-25°C. When the temperature is too high, it is timely cooled by increasing the net blow and adding cold materials such as iron ore to ensure the casting temperature.

[0019] (3) The roll gap shrinkage of each section in the bending section is set to 0.2-0.4mm, the roll gap shrinkage of the first straightening section is set to 1.2-1.5mm, the roll gap shrinkage of each section except the end is set to 0.3mm, and the roll gap shrinkage of the last section is set to 0-0.2mm. The roll gap of the continuous casting machine is regularly calibrated to ensure that the roll gap accuracy is within ±0.5mm.

[0020] (4) The secondary cooling water volume in the horizontal section is controlled at 0.85-0.95 L / kg, and the total water volume is 0.80-0.90 L / kg.

[0021] (5) The final light pressure reduction range is 0.2-0.8 solid phase ratio and 6-8 mm reduction. The actual reduction can be slightly adjusted according to the steel type and equipment conditions. Example 1

[0022] A steel plant produces 260mm*1900mm low alloy steel Q355B using this continuous casting method. The continuous casting method for improving the internal quality of low alloy steel slabs is described as follows: (1) Produced at a constant pulling speed of 1.15 m / min; (2) Superheat is controlled in the range of 8-23℃; (3) The roll gap shrinkage of each section of the bending section is set to 0.3mm, the roll gap shrinkage of the first straightening section is set to 1.5mm, the roll gap shrinkage of each section of the subsequent straightening section and horizontal section except the end is set to 0.2mm, and the roll gap shrinkage of the last section is set to 0mm. The roll gap of the continuous casting machine is calibrated every 2 weeks to ensure that the roll gap accuracy is within ±0.3mm; (4) The water volume of the secondary cooling water in the horizontal section is controlled at 0.85 L / kg, and the total water volume is 0.80 L / kg; (5) The final gentle pressure reduction range is 0.2-0.4 solid phase ratio and the reduction amount is 6.5 mm.

[0023] Under this process, the proportion of slab sulfur print center segregation rating C1.0 or above reaches more than 87%, there are no middle cracks and triangular area cracks, and the qualified rate of steel plate elongation after rolling is ≥99.5%. Example 2

[0024] A steel plant produces 230mm*1700mm low alloy container steel Q345R using this continuous casting method. The continuous casting method for improving the internal quality of low alloy steel slabs is described as follows: (1) Produced at a constant pulling speed of 1.1 m / min; (2) Superheat is controlled within the range of 10-21°C; (3) The roll gap shrinkage of each section of the bending section is set to 0.4mm, the roll gap shrinkage of the first straightening section is set to 1.4mm, the roll gap shrinkage of each section of the subsequent straightening section and horizontal section except the end is set to 0.1mm, and the roll gap shrinkage of the last section is set to 0.1mm. The roll gap of the continuous casting machine is calibrated every week to ensure that the roll gap accuracy is within ±0.5mm; (4) The water volume of the secondary cooling water in the horizontal section is controlled at 0.89 L / kg, and the total water volume is 0.87 L / kg; (5) The final gentle pressure reduction range is 0.4-0.8 solid phase ratio and the reduction amount is 7.0 mm.

[0025] Under this process, the proportion of slab sulfur print center segregation rating C1.0 or above reaches more than 91%, there are no middle cracks and triangular area cracks, and the qualified rate of steel plate elongation after rolling is ≥99.7%. Example 3

[0026] A steel plant produces 260mm*1900mm low alloy container steel Q460MC using this continuous casting method. The continuous casting method for improving the internal quality of low alloy steel slabs is described as follows: (1) Produced at a constant pulling speed of 1.0 m / min; (2) Superheat is controlled within the range of 12-20℃; (3) The roll gap shrinkage of each section of the bending section is set to 0.4mm, the roll gap shrinkage of the first straightening section is set to 1.2mm, the roll gap shrinkage of each section of the subsequent straightening section and horizontal section except the end is set to 0.3mm, and the roll gap shrinkage of the last section is set to 0.1mm. The roll gap of the continuous casting machine is calibrated every week to ensure that the roll gap accuracy is within ±0.4mm; (4) The secondary cooling water volume in the horizontal section is controlled at 0.93 L / kg, and the total water volume is 0.88 L / kg; (5) The final gentle pressure reduction range is 0.3-0.6 solid phase ratio and the reduction amount is 7.5 mm.

[0027] Under this process, the proportion of slab sulfur print center segregation rating above C1.0 reaches more than 93%, there are no middle cracks and triangular area cracks, and the qualified rate of steel plate elongation after rolling is ≥99.8%. Example 4

[0028] A steel plant produces 230mm*1700mm low alloy container steel NM400 using this continuous casting method. The continuous casting method for improving the internal quality of low alloy steel slabs is specifically described as follows: (1) Produced at a constant pulling speed of 1.2 m / min; (2) Superheat is controlled in the range of 13-25℃; (3) The roll gap shrinkage of each section in the bending section is set to 0.2 mm, the roll gap shrinkage of the first straightening section is set to 1.2 mm, the roll gap shrinkage of each section in the subsequent straightening section and horizontal section except the end is set to 0.25 mm, and the roll gap shrinkage of the last section is set to 0.2 mm. The roll gap of the continuous casting machine is calibrated every week to ensure that the roll gap accuracy is within ±0.2 mm; (4) The water volume of the secondary cooling water in the horizontal section is controlled at 0.95 L / kg, and the total water volume is 0.85 L / kg; (5) The final gentle pressure reduction range is 0.5-0.8 solid phase ratio and the reduction amount is 6.0 mm.

[0029] Under this process, the proportion of slab sulfur print center segregation rating above C1.0 reaches more than 93%, there are no middle cracks and triangular area cracks, and the qualified rate of steel plate elongation after rolling is ≥99.8%.

[0030] The above embodiments are only used to illustrate rather than limit the technical solutions of the present invention. Although the present invention is described in detail with reference to the above embodiments, those skilled in the art should understand that the present invention can still be modified or replaced by equivalents. Any modification or partial replacement that does not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A continuous casting method for improving the internal quality of low alloy steel slabs, characterized in that: The continuous casting method comprises the following steps: (1) Continuous casting is produced by constant casting speed; (2) Low superheat casting is adopted, and the superheat of the tundish is controlled at 8-25℃; (3) The shrinkage of the roller gap in each section of the bending section is set to 0.2-0.4 mm, the shrinkage of the roller gap in the first straightening section is set to 1.2-1.5 mm, and the shrinkage of the roller gap in the last section is set to 0-0.2 mm; (4) The water volume of the secondary cooling water in the horizontal section is controlled at 0.85-0.95 L / kg, and the total water volume is 0.80-0.90 L / kg; (5) The final gentle pressure reduction range is 0.2-0.8 solid phase ratio and 6-8 mm reduction.

2. A continuous casting method for improving the internal quality of low alloy steel slabs according to claim 1, characterized in that: In the step (1), the casting is produced at a constant pulling speed, and the pulling speed is controlled at 1.0-1.2 m / min.

3. A continuous casting method for improving the internal quality of low alloy steel slab according to claim 1, characterized in that: In the step (2), the preceding process ensures that the temperature of the molten steel meets the casting requirement of an overheat degree of 8-25°C. When the temperature is too high, it is promptly cooled by increasing the net blow and adding cold materials such as iron ore.

4. A continuous casting method for improving the internal quality of low alloy steel slabs according to claim 1, characterized in that: The step (3) is to regularly calibrate the accuracy of the roll gap of the continuous casting machine to ensure that the roll gap accuracy is within ±0.5 mm.

5. A continuous casting method for improving the internal quality of low alloy steel slab according to claim 1, characterized in that: In the step (3), the roller gap shrinkage of each subsequent straightening section and horizontal section except the end is set to 0-0.3 mm.

6. A continuous casting method for improving the internal quality of a low alloy steel slab according to any one of claims 1 to 5, characterized in that: The proportion of the slab sulfur print center segregation rating of low center segregation grade C1.0 or above obtained by the continuous casting method reaches ≥87%.

7. A continuous casting method for improving the internal quality of a low alloy steel slab according to any one of claims 1 to 5, characterized in that: The slab obtained by the continuous casting method has no middle cracks and triangular cracks, and the qualified rate of elongation of the rolled steel plate is ≥99.5%.