Method for eliminating powder falling defect on surface of 430 ferrite stainless steel bright plate

Abstract

The invention discloses a method for eliminating the powder falling defect on the surface of a 430 ferrite stainless steel bright plate, which comprises the following process control steps in a hot-rolled coil bell-type furnace annealing process: hot charging a hot-rolled coil into a furnace, controlling the temperature of an outer ring of the steel coil to be more than 200 DEG C, and controlling the temperature of an inner ring of the steel coil to be more than 300 DEG C; the bell-type furnace is heated, the temperature is increased to 640 DEG C in the first stage, the H2 flow is controlled to be 18-24 m < 3 > / h, the temperature is increased to 840 DEG C + / -20 DEG C from 640 DEG C in the second stage, and the H2 flow is controlled to be 8-14 m < 3 > / h; and carrying out heat preservation and slow cooling in a bell-type furnace, carrying out heat preservation at 840 + / -20 DEG C, cooling to 100 DEG C or below from 840 + / -20 DEG C, discharging, and controlling the flow of N2 to be 22-28m < 3 > / h. According to the method, the charging process is adjusted to be hot-rolled coil hot charging, and the atmosphere and temperature of protective gas for bell-type furnace annealing are comprehensively regulated and controlled, so that surface intergranular carbide precipitation caused by improper bell-type furnace annealing control is eliminated, and the powder falling defect on the surface of the 430 ferrite stainless steel bright plate is eliminated; and the surface quality of the 430 ferrite stainless steel bright plate is obviously improved.

Description

Technical Field

[0001] The invention belongs to the technical field of production and manufacturing of cold-rolled stainless steel products, and particularly relates to a method for eliminating the powder falling defect on the surface of a 430 ferritic stainless steel bright plate. Background Art

[0002] 430 ferritic stainless steel has obvious cost advantages due to its low alloying element content and the fact that it can obtain good corrosion resistance without the addition of expensive alloying elements such as Ni. Therefore, its cold-rolled sheets, especially 430 ferritic stainless steel bright sheets, are widely used in home appliances, tableware, kitchen utensils, architectural decoration and other fields.

[0003] The primary manufacturing process for 430 ferritic stainless steel cold-rolled sheet is: smelting → continuous casting → hot rolling → cold rolling. After hot and cold rolling, the material is work-hardened and requires annealing to maintain good workability. Post-hot rolling annealing is performed in a bell-type furnace, followed by pickling to remove surface scale. Post-cold rolling annealing is performed in a bright furnace under a reducing atmosphere, eliminating surface oxidation and eliminating the need for pickling and dephosphorization. Subsequent surface finishing produces the finished bright sheet. The process flow from hot-rolled coil to cold-rolled product is: 430 hot-rolled coil → bell-type furnace annealing → pickling → cold rolling → bright furnace annealing → finishing → 430 cold-rolled bright sheet.

[0004] At present, after the 430 ferritic stainless steel bright plate is cold rolled and bright annealed, the surface of the finished product will have different degrees of bright spot defects under light. The density of the bright spots represents the severity of the powder loss. Figure 1 As shown in the figure, the location of the bright spot will vary depending on the angle of illumination. Powder loss is the loss of powder from the surface metal, which affects the gloss of the bright plate surface and thus affects user experience. The shed powder will also accumulate on processing equipment, further affecting product quality and causing losses. Current conventional process methods are not effective in reducing powder loss defects. Powder loss has also become a major bottleneck restricting the expansion of the application of 430 ferritic stainless steel bright plate. Summary of the Invention

[0005] In order to solve the above technical problems existing in the prior art, the present invention provides a method for eliminating the surface powder loss defect of 430 ferritic stainless steel bright plate, comprising the following process control steps in the hot rolling bell furnace annealing process:

[0006] (1) In the hot-rolled coil hot charging furnace, the outer ring temperature of the steel coil is controlled above 200°C, and the inner ring temperature of the steel coil is controlled above 300°C;

[0007] (2) The bell-type furnace is heated in two stages. H2 is used as the protective gas in the two stages and the H2 flow rate is controlled in the two stages. Specifically, the first stage is heated to 640℃, and the H2 flow rate is controlled at 18~24m 3 / h, the second stage is heated from 640℃ to 840℃±20℃, and the H2 flow rate is controlled at 8~14m 3 / h;

[0008] (3) The bell-type furnace is kept warm and slowly cooled. After being kept warm at 840℃±20℃, it is cooled from 840℃±20℃ to below 100℃ before being taken out of the furnace. N2 is used as the protective gas during the keeping warm and slow cooling stage. The N2 flow rate is controlled at 22~28m 3 / h.

[0009] Furthermore, in the above-mentioned method for eliminating the surface powder falling defect of 430 ferritic stainless steel bright plate, the composition of the 430 ferritic stainless steel is: C≤0.12%, Si≤0.75%, Mn≤1.00%, P≤0.04%, S≤0.03%, Cr≤16%~18%, Ni≤0.60%, N≤0.10%, and the rest is Fe and unavoidable impurities.

[0010] The method of eliminating the powder loss defect on the surface of 430 ferritic stainless steel bright plate of the present invention has the following advantages and beneficial effects:

[0011] The present invention eliminates the precipitation of intergranular carbides on the surface caused by improper bell-type furnace annealing control by adjusting the furnace charging process to hot charging of hot-rolled coils and comprehensively regulating the protective gas atmosphere and temperature of bell-type furnace annealing. The 430 ferritic stainless steel bright plate obtained by pickling, cold rolling, bright annealing and finishing the 430 hot-rolled coil after bell-type furnace annealing has no powder falling defects on the surface, thereby significantly improving the surface quality of the 430 ferritic stainless steel bright plate, eliminating processing quality losses, and providing a technical basis for expanding the application scenarios of the 430 ferritic stainless steel bright plate. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the embodiments or the description of the prior art. Obviously, the drawings described below are only used to further understand the embodiments of the present invention and constitute part of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work. In the drawings:

[0013] Figure 1 This is a real product photo of the powdering defect on the surface of 430 ferritic stainless steel bright plate;

[0014] Figure 2 and Figure 3 This is a scanning analysis diagram of the powder loss defect on the surface of 430 ferritic stainless steel bright plate;

[0015] Figure 4 This is a scanning analysis diagram of surface intergranular carbide precipitation caused by improper bell-type furnace annealing control after hot rolling of 430 ferritic stainless steel;

[0016] Figure 5 This is a real product photo of a 430 ferritic stainless steel bright plate with no powder falling defects on the surface after implementing the present invention. DETAILED DESCRIPTION

[0017] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0018] Scanning electron microscope observation shows that the non-adhesive area of ​​430 ferritic stainless steel bright plate rarely peels. Figure 2 As shown, the sticky area peels more, such as Figure 3 As shown in the figure, after the subsequent rolling process, the steel peels off, forming a powder loss defect. The size of the powder loss particles is mostly 50 μm, which is consistent with the grain size.

[0019] In response to the problem of powder loss on the surface of 430 ferritic stainless steel bright plate, the applicant analyzed the influence of each process from smelting to cold rolling on the surface metal structure of 430 ferritic stainless steel bright plate. After a lot of experiments and research, it was found that the main cause of powder loss defect was improper bell-type furnace annealing control, which led to carbide precipitation between the surface grains, such as Figure 4 As shown in the figure, the pickling process causes intergranular corrosion, resulting in cracks between the surface grains and the matrix of the strip. After the subsequent rolling process, the surface grains and the metal matrix of the strip further loosen or even fall off, which is the powder loss defect.

[0020] In the conventional bell-type furnace annealing process, the steel coil needs to be cooled before being loaded into the furnace. It goes through three stages: heating → insulation → cooling. A reducing atmosphere is required for protection during the entire process. After loading the furnace, N2 is first purged, and then H2 is purged before heating begins. During the heating and insulation process, carbides precipitate at the grain boundaries. The residual O2 in the gaps of the steel coil in the protective atmosphere interacts with the carbon in the inner grain boundaries, causing the grains to easily fall off.

[0021] The present invention provides a method for eliminating surface powdering defects of 430 ferritic stainless steel bright sheet by improving the bell-type furnace annealing process to effectively control the precipitation of intergranular carbides on the surface of the hot-rolled strip, thereby eliminating the surface powdering defects of the 430 ferritic stainless steel bright sheet. Specifically, the present invention includes performing the following process control steps during the bell-type furnace annealing process of the hot-rolled coil:

[0022] (1) In the hot-rolled coil hot charging furnace, the outer ring temperature of the steel coil is controlled above 200℃, and the inner ring temperature of the steel coil is controlled above 300℃.

[0023] When the charging temperature is lower than the above temperature, O2 in the air will quickly enter the gaps in the steel coils, increasing the precipitation of carbides during subsequent heating and insulation processes.

[0024] (2) The bell-type furnace is heated in two stages. H2 is used as the protective gas in the two stages and the H2 flow rate is controlled in the two stages. Specifically, the first stage is heated to 640℃, and the H2 flow rate is controlled at 18~24m 3 / h, the second stage is heated from 640℃ to 840℃±20℃, and the H2 flow rate is controlled at 8~14m 3 / h.

[0025] (3) The bell-type furnace is kept warm and slowly cooled. After being kept warm at 840℃±20℃, it is cooled from 840℃±20℃ to below 100℃ before being taken out of the furnace. N2 is used as the protective gas during the keeping warm and slow cooling stage. The N2 flow rate is controlled at 22~28m 3 / h.

[0026] For the 430 ferritic stainless steel bright plate obtained by pickling, cold rolling, bright annealing and finishing the 430 hot rolled coil after hood furnace annealing, the following process evaluation method is used to evaluate the degree of powder loss defects: a stainless steel PE protective film of a fixed area (45mm*55mm) is used to stick to the surface of the 430 ferritic stainless steel bright plate, and the density of the bright spots is observed at a vertical viewing angle and a 45-degree viewing angle. After actual testing and evaluation, by implementing the method of eliminating the powder loss defects on the surface of the 430 ferritic stainless steel bright plate of the present invention, under the comprehensive regulation of the protective gas atmosphere and temperature of the hood furnace annealing, the 430 hot rolled coil after hood furnace annealing, the 430 ferritic stainless steel bright plate obtained by pickling, cold rolling, bright annealing and finishing has no powder loss defects on the surface, such as Figure 5 shown.

[0027] As a specific embodiment, the method for eliminating the surface powder loss defect of 430 ferritic stainless steel bright plate of the present invention is applicable to the 430 ferritic stainless steel composition: C≤0.12%, Si≤0.75%, Mn≤1.00%, P≤0.04%, S≤0.03%, Cr≤16%-18%, Ni≤0.60%, N≤0.10%, and the rest is Fe and unavoidable impurities.

[0028] The method for eliminating the surface powder loss defect of 430 ferritic stainless steel bright plate of the present invention is described in detail below with reference to specific embodiments.

[0029] Example 1

[0030] 1) The composition of 430 ferritic stainless steel is: C: 0.0425%, Si: 0.245%, Mn: 0.30%, P: 0.0204%, S: 0.005%, Cr: 16.098%, Ni≤0.198%, N: 0.0412%, and the rest is Fe and unavoidable impurities; 430 hot-rolled black coil is obtained by smelting, continuous casting and hot rolling according to the above composition.

[0031] 2) Hot charging in bell-type furnace, the outer ring temperature of 430 coil is 210℃ and the inner ring temperature is 302℃.

[0032] 3) The first stage of bell-type furnace heating is to 640℃, and the flow rate of protective gas H2 is 20m 3 / h.

[0033] 4) The second stage of bell furnace heating is from 640℃ to 840℃, and the flow rate of protective gas H2 is 12m 3 / h.

[0034] 5) The bell-type furnace is kept warm and slowly cooled. After being kept warm at 840℃, it is cooled down to 100℃ before being taken out of the furnace. The flow rate of protective gas N2 is 24m 3 / h.

[0035] 6) After bell-type furnace annealing, it is made into 430 ferritic stainless steel bright plate 2B cold plate through pickling, cold rolling, bright annealing and finishing processes.

[0036] A 430 ferritic stainless steel bright plate was finally prepared by implementing Example 1 of the present invention by sticking a stainless steel PE protective film of a fixed area (45 mm*55 mm). The density of the bright spots was observed at a vertical viewing angle and a 45-degree viewing angle. Actual testing showed that there was no powder falling defect.

[0037] Example 2

[0038] 1) The composition of 430 ferritic stainless steel is: C: 0.0379%, Si: 0.275%, Mn: 0.321%, P: 0.019%, S: 0.0056%, Cr: 16.195%, Ni≤0.161%, N: 0.0372%, and the rest is Fe and unavoidable impurities; 430 hot-rolled black coil is obtained by smelting, continuous casting and hot rolling according to the above composition.

[0039] 2) Hot charging in bell-type furnace, the outer ring temperature of 430 coil is 206℃ and the inner ring temperature is 303℃.

[0040] 3) The first stage of bell-type furnace heating is to 640℃, and the flow rate of protective gas H2 is 22m 3 / h.

[0041] 4) The second stage of bell-type furnace heating is from 640℃ to 840℃, and the flow rate of protective gas H2 is 10m 3 / h.

[0042] 5) The bell-type furnace is kept warm and slowly cooled. After being kept warm at 840℃, it is cooled down to 100℃ before being taken out of the furnace. The flow rate of protective gas N2 is 25m 3 / h.

[0043] 6) After bell-type furnace annealing, it is made into 430 ferritic stainless steel bright plate 2B cold plate through pickling, cold rolling, bright annealing and finishing processes.

[0044] A 430 ferritic stainless steel bright plate was finally prepared by implementing Example 2 of the present invention by sticking a stainless steel PE protective film of a fixed area (45 mm*55 mm). The density of the bright spots was observed at a vertical viewing angle and a 45-degree viewing angle. Actual testing showed that there was no powder falling defect.

[0045] Example 3

[0046] 1) The composition of 430 ferritic stainless steel is: C: 0.042%, Si: 0.4362%, Mn: 0.0632%, P: 0.0177%, S: 0.0012%, Cr: 17.794%, Ni≤0.2689%, N: 0.0087%, and the rest is Fe and unavoidable impurities; 430 hot-rolled black coil is obtained by smelting, continuous casting and hot rolling according to the above composition.

[0047] 2) Hot charging in bell-type furnace, the outer ring temperature of 430 coil is 204℃ and the inner ring temperature is 307℃.

[0048] 3) The first stage of bell-type furnace heating is to 640℃, and the flow rate of protective gas H2 is 20m 3 / h.

[0049] 4) The second stage of bell furnace heating is from 640℃ to 840℃, and the flow rate of protective gas H2 is 12m 3 / h.

[0050] 5) The bell-type furnace is kept warm and slowly cooled. After being kept warm at 840℃, it is cooled down to 100℃ before being taken out of the furnace. The flow rate of protective gas N2 is 25m 3 / h.

[0051] 6) After bell-type furnace annealing, it is made into 430 ferritic stainless steel bright plate 2B cold plate through pickling, cold rolling, bright annealing and finishing processes.

[0052] A 430 ferritic stainless steel bright plate was finally prepared by implementing Example 3 of the present invention by sticking a stainless steel PE protective film of a fixed area (45 mm*55 mm). The density of bright spots was observed at a vertical viewing angle and a 45-degree viewing angle. Actual testing showed that there was no powder falling defect.

[0053] After the 430 hot-rolled coil is annealed in a bell furnace by the method of the present invention, it is pickled and cold-rolled, and the cold-rolled coil is bright annealed and leveled. After it is adhered with a stainless steel PE protective film, no obvious powdering defects are found on the surface.

[0054] In summary, compared with the prior art, the method of eliminating the surface powdering defect of 430 ferritic stainless steel bright plate of the present invention eliminates the precipitation of surface intergranular carbides caused by improper control of bell furnace annealing by adjusting the furnace charging process to hot charging of hot-rolled coils and comprehensively regulating the protective gas atmosphere and temperature of bell furnace annealing. The 430 ferritic stainless steel bright plate obtained by pickling, cold rolling, bright annealing and finishing the 430 hot-rolled coil after bell furnace annealing has no powdering defect on the surface, thereby significantly improving the surface quality of the 430 ferritic stainless steel bright plate, eliminating processing quality loss, and providing a technical basis for expanding the application scenarios of 430 ferritic stainless steel bright plate.

[0055] It should be noted that, in this article, the term "comprise" or any other variation thereof is intended to cover non-exclusive inclusion, so that an article or device that includes a series of elements includes not only those elements, but also includes other elements that are not explicitly listed, or also includes elements that are inherent to such article or device.

[0056] It should also be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the present invention.

Claims

1. A method for eliminating the powder loss defect on the surface of 430 ferritic stainless steel bright plate, characterized in that: The following process control steps are included in the hot rolling coil bell furnace annealing process: (1) In the hot-rolled coil hot charging furnace, the outer ring temperature of the steel coil is controlled above 200°C, and the inner ring temperature of the steel coil is controlled above 300°C; (2) The bell-type furnace is heated in two stages. H2 is used as the protective gas in the two stages and the H2 flow rate is controlled in the two stages. Specifically, the first stage is heated to 640℃, and the H2 flow rate is controlled at 18~24m 3 / h, the second stage is heated from 640℃ to 840℃±20℃, and the H2 flow rate is controlled at 8~14m 3 / h; (3) The bell-type furnace is kept warm and slowly cooled. After keeping warm at 840℃±20℃, the temperature is lowered from 840℃±20℃ to below 100℃. N2 is used as the protective gas during the keeping warm and slow cooling stage. The N2 flow rate is controlled at 22~28m 3 / h.

2. The method for eliminating the surface powder loss defect of 430 ferritic stainless steel bright plate according to claim 1, characterized in that: The composition of the 430 ferritic stainless steel is: C≤0.12%, Si≤0.75%, Mn≤1.00%, P≤0.04%, S≤0.03%, Cr≤16%-18%, Ni≤0.60%, N≤0.10%, and the rest is Fe and unavoidable impurities.

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