Method for controlling mountain scale defects of 409 ultra-pure ferritic stainless steel

Abstract

The invention discloses a 409 ultra-pure ferrite stainless steel mountain scale defect control method, which comprises the control of a heating furnace heating procedure, the heating furnace heating procedure comprises a first heating section, a second heating section and a soaking section, the upper furnace temperature of the first heating section is controlled to be 1070 + / -10 DEG C, the lower furnace temperature of the first heating section is controlled to be 1050 + / -10 DEG C, and the temperature of the second heating section is controlled to be 1070 + / -10 DEG C; the upper furnace temperature of the second heating section is controlled to be 1090 + / -10 DEG C, the lower furnace temperature of the second heating section is controlled to be 1070 + / -10 DEG C, the upper furnace temperature of the soaking section is controlled to be 1180 + / -10 DEG C, and the lower furnace temperature of the soaking section is controlled to be 1170 + / -10 DEG C. By optimizing the ultrapure ferrite 409L heating process, adjusting the furnace temperature of each section of the heating furnace, reducing the furnace temperature of the primary heating furnace and the furnace temperature of the secondary heating furnace and improving the furnace temperature of the soaking section, the scale in the plate blank water beam cushion block is easy to remove, and the M mountain scale defect is effectively controlled.

Description

Technical Field

[0001] This invention relates to the field of iron and steel smelting processes, and in particular to a method for controlling scale defects in 409 ultrapure ferritic stainless steel. Background Technology

[0002] In walking beam furnaces, the water beam pads can cause deep, flaky iron oxide scale, approximately 1 meter in length and width, to be pressed into the lower surface of 409 ultrapure ferrite hot-rolled steel, forming M-scale defects. These M-scale defects easily damage the rolls, significantly impacting downstream production. The hazards of these M-scale defects are mainly reflected in three aspects: 1) Economic loss: These M-scale defects directly lead to non-compliance with the quality requirements of cold-rolled finished products; 2) Production efficiency: Damage to the rolls results in approximately 0.5 hours of downtime for roll replacement; 3) Safety and management: Roll replacement increases unsafe risk factors.

[0003] Chinese Patent No. 202210063638.4 discloses a method for eliminating surface streak defects in ultrapure ferritic stainless steel. This method optimizes the billet grinding process, regulates the furnace heating regime, controls the high-pressure water descaling process, increases the first-pass deformation by ≥40% during the finishing rolling process, employs a high-temperature fast rolling process, and performs EPS (Eco-Enhanced Polystyrene) surface pretreatment on the hot-rolled stainless steel coils, optimizing the pickling concentration and temperature to ultimately eliminate surface streak defects in ultrapure ferritic stainless steel cold-rolled sheets. This solution utilizes lower furnace temperature to increase the strength of the slab in the furnace, thereby reducing the pits on the lower surface of the slab caused by furnace pads. However, this furnace temperature control scheme does not significantly improve the M-scale defects on the lower surface of ultrapure ferritic hot-rolled sheets. Summary of the Invention

[0004] The purpose of this invention is to provide a method for controlling scale-like defects in 409 ultrapure ferritic stainless steel.

[0005] The technical solution to achieve the purpose of this invention is: a method for controlling scale-like defects in ultrapure ferritic stainless steel, which includes controlling the heating process of a heating furnace. The heating process of the heating furnace includes a first heating stage, a second heating stage, and a soaking stage. The upper furnace temperature of the first heating stage is controlled at 1070±10℃, the lower furnace temperature of the first heating stage is controlled at 1050±10℃, the upper furnace temperature of the second heating stage is controlled at 1090±10℃, the lower furnace temperature of the second heating stage is controlled at 1070±10℃, the upper furnace temperature of the soaking stage is controlled at 1180±10℃, and the lower furnace temperature of the soaking stage is controlled at 1170±10℃.

[0006] Furthermore, it also includes the control of the hot rolling process, which includes the control of the roughing descaling passes and the control of the roughing rolling passes. The number of roughing descaling passes is increased from 1 pass to 3 passes. With the slab thickness remaining unchanged at 195-200 mm and the roughing exit thickness remaining unchanged at 30-34 mm, the control of the roughing rolling passes includes controlling the reduction rate of the first pass at 15%-17%, the reduction rate of the second pass at 30%-33%, the reduction rate of the third pass at 23%-25%, the reduction rate of the fourth pass at 14-18%, and the reduction rate of the fifth pass at 11%-13%. The purpose of adding roughing descaling passes in the hot rolling process is to enhance the descaling capacity. The control of roughing passes is to reduce the reduction rate of the first pass and distribute the reduced reduction amount of the first pass to the second to fourth roughing passes, thereby improving the scale breaking effect of the first pass and improving the pressing of iron oxide scale into the pit, thus enhancing the descaling effect.

[0007] Traditional industry practice holds that lowering the furnace temperature can indeed improve the strength of the slab in the furnace and reduce pits on the lower surface of the slab caused by furnace pads, but it has no effect on improving M-scale defects. The inventors have overcome this technical bottleneck by proposing a solution that first lowers the furnace temperature in the first and second heating stages, and then raises the temperature in the soaking zone. This significantly reduces the retention rate of M-scale defects. The underlying principle is that the first and second heating stages require lower furnace temperature control, and the temperature difference between the upper and lower furnace sections should be increased to 20°C to reduce the water-beam pad marks caused by the slab in the second heating stage and before. The heating load is mainly shifted to the soaking zone, raising its temperature to the target 1180±10°C to increase the surface temperature of the steel strip, which facilitates the removal of iron oxide scale within the water-beam pad marks, thereby effectively controlling M-scale defects. Attached Figure Description

[0008] Figure 1 A photograph of the white sheet obtained by pickling 409 ultrapure ferritic stainless steel treated in Comparative Example 1 of the present invention. Figure 2 This is a photograph of a white sheet obtained by pickling 409 ultrapure ferritic stainless steel after processing in Example 3 of the present invention. Detailed Implementation

[0009] The preferred embodiments of the present invention will be described in detail below. Example 1

[0010] A method for controlling scale defects in 409 ultrapure ferritic stainless steel includes controlling the heating process in a heating furnace and controlling the hot rolling process. The heating process in the heating furnace includes a first heating stage, a second heating stage, and a soaking stage. The upper furnace temperature of the first heating stage is controlled at 1070±10℃, the lower furnace temperature of the first heating stage is controlled at 1050±10℃, the upper furnace temperature of the second heating stage is controlled at 1090±10℃, the lower furnace temperature of the second heating stage is controlled at 1070±10℃, the upper furnace temperature of the soaking stage is controlled at 1180±10℃, and the lower furnace temperature of the soaking stage is controlled at 1170±10℃.

[0011] The control of the hot rolling process includes the control of the roughing descaling passes and the control of the roughing rolling passes. The number of roughing descaling passes is increased from one to three. With the slab thickness remaining unchanged at 195-200 mm and the roughing exit thickness remaining unchanged at 30-34 mm, the control of the roughing rolling passes includes controlling the reduction rate of the first pass at 17%, the reduction rate of the second pass at 17%, the reduction rate of the third pass at 16%, the reduction rate of the fourth pass at 16%, and the reduction rate of the fifth pass at 25%.

[0012] Examples 2-4 Examples 2-4 use the same control method as Example 1, the difference being the specific process parameters. This invention also provides a conventional control method for reducing the temperature of the heating furnace as Comparative Example 1, with specific process parameters shown in Table 1. Table 1

[0013] Table 2 shows the M scale retention rates of 409 ultrapure ferritic stainless steel treated according to Examples 1-4 and Comparative Example 1, respectively: Table 2

[0014] Figure 1 The image shows a photograph of the white sheet obtained after pickling of 409 ultrapure ferritic stainless steel treated in Comparative Example 1. Numerous M-scale scales are still visible to the naked eye. Figure 2 The image shows a photograph of a white sheet roll obtained after pickling of 409 ultrapure ferritic stainless steel treated in Example 3. The white sheet roll has a smooth surface and is free of scale. (Refer to Table 2...) Figure 1 and Figure 2As can be seen, this invention optimizes the heating process of ultra-pure ferrite 409L, adjusts the furnace temperature of each section of the heating furnace, reduces the furnace temperature of the first and second heating sections, and improves the control of the furnace temperature in the soaking section. This makes it easier to remove the iron oxide scale in the slab water beam pad block. Furthermore, by increasing the number of rough rolling descaling passes from one to three and controlling the reduction rate of the rough rolling passes, the descaling effect on the iron oxide scale in the pits is improved. The retention rate of M-scale in ultra-pure ferrite 409L is reduced from 33.0% in Comparative Example 1 to 1.5-5.8% in this example, which can significantly improve the M-scale of ultra-pure ferrite 409L. The above description is only an embodiment of this invention and does not limit the patent scope of this invention. Any equivalent process transformations made based on the content of this specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this invention.

Claims

1. A method for controlling scale-like defects in 409 ultrapure ferritic stainless steel, characterized in that: It includes the control of the heating process of the heating furnace, which includes a first heating stage, a second heating stage, and a soaking stage. The upper furnace temperature of the first heating stage is controlled at 1070±10℃, the lower furnace temperature of the first heating stage is controlled at 1050±10℃, the upper furnace temperature of the second heating stage is controlled at 1090±10℃, the lower furnace temperature of the second heating stage is controlled at 1070±10℃, the upper furnace temperature of the soaking stage is controlled at 1180±10℃, and the lower furnace temperature of the soaking stage is controlled at 1170±10℃.

2. The method for controlling scale-like defects in 409 ultrapure ferritic stainless steel according to claim 1, characterized in that: It also includes the control of the hot rolling process, which includes the control of the roughing descaling passes and the control of the roughing rolling passes. The number of roughing descaling passes is increased from 1 pass to 3 passes. With the slab thickness of 195-200 mm and the roughing exit thickness of 30-34 mm remaining unchanged, the control of the roughing rolling passes includes controlling the reduction rate of the first pass at 15%-17%, the reduction rate of the second pass at 30%-33%, the reduction rate of the third pass at 23%-25%, the reduction rate of the fourth pass at 14-18%, and the reduction rate of the fifth pass at 11%-13%.

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