Hot rolling control method for improving surface color difference defect of 430 stainless steel thick cold plate

Abstract

The invention discloses a hot rolling control method for improving the surface chromatic aberration defect of a 430 stainless steel thick cold plate, which comprises the following steps: controlling the coiling temperature: controlling the coiling temperature of 430 stainless steel to be 650-700 DEG C; a laminar cooling process is determined, a laminar cooling valve device is adopted to cool the 430 stainless steel, the 30m-60m head of the 430 stainless steel is not cooled, and the 30m tail of the 430 stainless steel is not cooled; the time from rolling offline to charging annealing is controlled, the thicker the 430 stainless steel is, the earlier the time from rolling offline to charging annealing is, and the latest time from rolling offline to charging annealing does not exceed 24 h; and optimizing a bell-type furnace annealing process, controlling the annealing temperature to be 840 + / -10 DEG C, and controlling the heat preservation time to be 10 hours. According to the method, the structure uniformity of the annealed thick 430 stainless steel is effectively improved, the color difference defect of the thick 430 stainless steel subjected to cold rolling is remarkably improved, the reject ratio is reduced to 6% or below from 30%, the product quality is improved, the overall production efficiency is improved, and good benefits can be obtained.

Description

Technical Field

[0001] The invention belongs to the technical field of stainless steel product production, and more specifically relates to a hot rolling control method for improving the color difference defects on the surface of a 430 stainless steel thick-gauge cold plate. Background Art

[0002] Ferritic stainless steel has obvious cost advantages due to its small amount of alloy elements, no need to add expensive alloy elements such as Ni, and good corrosion resistance. In particular, medium and low chromium ferritic stainless steel cold-rolled sheets and strips with a Cr content of less than 20% are widely used in the automotive, construction, home appliances and other fields.

[0003] The manufacturing process of 430 ferritic stainless steel is: hot rolling-annealing-cold rolling. After hot rolling, the material has been hardened. In order to obtain good processing performance, the material needs to be annealed. After annealing, 430 stainless steel, especially thick 430 (thickness ≥ 4.0mm), has serious color difference defects on the surface after final cold rolling. Its macroscopic appearance is a black and white defect visible to the naked eye, and the upper and lower surfaces are penetrated, showing a completely consistent appearance, such as Figure 1 The non-conformity rate of such defects is as high as 30%, which not only affects the surface appearance quality of the material, but also causes unplanned re-rolling, resulting in great quality loss.

[0004] Therefore, it is particularly important to develop a hot rolling control method to improve the surface color difference defects of 430 stainless steel thick cold plate. Summary of the invention

[0005] In order to solve the above technical problems existing in the prior art, the present invention provides a hot rolling control method for improving the surface color difference defect of 430 stainless steel thick cold plate, comprising:

[0006] (1) Control the coiling temperature. The coiling temperature of 430 stainless steel is controlled at 650℃~700℃;

[0007] (2) Determine the laminar cooling process and use a laminar cooling valve device to cool the 430 stainless steel, wherein the head 30m to 60m of the 430 stainless steel is not cooled and the tail 30m is not cooled;

[0008] (3) Control the time from rolling off the line to loading into the furnace for annealing. The thicker the 430 stainless steel, the earlier the time from rolling off the line to loading into the furnace for annealing. The latest time from rolling off the line to loading into the furnace for annealing shall not exceed 24 hours.

[0009] (4) Optimize the bell-type furnace annealing process, control the annealing temperature to 840±10℃, and control the holding time to 10h.

[0010] Furthermore, in the above-mentioned hot rolling control method for improving the color difference defects on the surface of 430 stainless steel thick-gauge cold plate, in determining the laminar cooling process step, the laminar cooling valve device is provided with three types of upper valves, lower valves and side blowing valves, among which the upper valves and the lower valves are a group, with a total of 48 groups of valves.

[0011] Furthermore, in the above-mentioned hot rolling control method for improving the color difference defects on the surface of 430 stainless steel thick-gauge cold plate, in determining the laminar cooling process step, the laminar cooling valve device starts spraying water for cooling from the third group of valves, and the upper valve and the lower valve are opened in sequence from front to back, and the valve opening sequence is the third group, the fourth group...the 48th group, and each group opens the lower valve first and then the upper valve, wherein the water volume of the upper valve is 65% of the maximum water volume, and the water volume of the lower valve is 85% of the maximum water volume.

[0012] Furthermore, in the above-mentioned hot rolling control method for improving the surface color difference defects of 430 stainless steel thick-gauge cold plate, in the optimization of the bell-type furnace annealing process step, the annealing temperature is quickly heated before 750°C, kept at 750°C for 2 hours, and then slowly heated to 840°C for 4 hours.

[0013] The hot rolling control method for improving the color difference defects on the surface of the thick cold plate of 430 stainless steel of the present invention optimizes and strictly controls the key process parameters such as the coiling temperature control and the layer cooling strategy as well as the bell furnace loading time and the annealing process, so as to achieve the effect of improving the uniformity of the original structure and the uniformity of the structure after annealing, so as to eliminate the subsequent thick 430 cold plate surface color difference defects caused by the uneven annealing structure. Specifically, compared with the prior art, the hot rolling control method for improving the color difference defects on the surface of the thick cold plate of 430 stainless steel of the present invention has the following advantages and beneficial effects:

[0014] By optimizing the coiling temperature, changing the layer cooling strategy and controlling the furnace loading time to ensure the uniformity of the original structure of 430 stainless steel, by optimizing the bell-type furnace annealing process, adjusting the heating temperature, holding time and heating rate, ensuring the complete recrystallization of the grains, and avoiding excessive grain growth, the uniformity of the structure of thick-gauge 430 stainless steel after annealing can be effectively improved. The color difference defects of thick-gauge 430 after cold rolling are significantly improved, and the non-conformity rate is reduced from 30% to below 6%, which improves product quality and thus improves the overall production efficiency, and can achieve good benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0016] Figure 1 It is a color difference defect diagram of the surface of 430 stainless steel cold plate in the prior art;

[0017] Figure 2 It is a layout diagram of the laminar cooling valve device of the present invention. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the specific embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0019] The study shows that the surface color difference defects of 430 after cold rolling are mainly concentrated on the thick specification 430. Its cold rolling deformation rate is smaller than that of the thin specification 430, and the surface of the defective coil is normal after re-rolling. Analysis shows that this type of color difference defect is caused by uneven structural recovery / recrystallization during the annealing process of 430 stainless steel, and the uneven structural structure is related to the original grain uniformity of the steel coil, the loading time, and the annealing process.

[0020] Therefore, the coiling temperature control and layer cooling strategy, as well as the bell furnace loading time and annealing process and other key process parameters are optimized and strictly controlled to achieve the effect of improving the uniformity of the original structure and the uniformity of the structure after annealing, so as to eliminate the subsequent thick specification 430 cold plate surface color difference defects caused by the uneven annealing structure. Specifically, the hot rolling control method of improving the surface color difference defects of 430 stainless steel thick specification cold plate of the present invention includes:

[0021] (1) Control the coiling temperature. The coiling temperature of 430 stainless steel is controlled at 650℃~700℃. In the process of controlling the coiling temperature, on the one hand, the original plate shape should be guaranteed to avoid the potential stress caused by uneven cooling process and affect the plate shape control and on-site production. On the other hand, the uniformity of the structure after cooling should be guaranteed;

[0022] (2) Determine the laminar cooling process and use a laminar cooling valve device to cool the 430 stainless steel, wherein the head 30m to 60m of the 430 stainless steel is not cooled and the tail 30m is not cooled;

[0023] The laminar cooling valve device is equipped with three types of upper valves, lower valves and side-blowing valves, of which the upper valve and the lower valve are a group, with a total of 48 groups of valves;

[0024] The laminar cooling valve device starts to spray water for cooling from the third group of valves. The upper valve and the lower valve are opened from front to back in sequence. The valve opening sequence is the third group, the fourth group...the 48th group. Each group opens the lower valve first and then the upper valve. The water volume of the upper valve is 65% of the maximum water volume, and the water volume of the lower valve is 85% of the maximum water volume. In this way, during the laminar cooling process, the 430 stainless steel plate is quickly cooled to below the target temperature to ensure the uniformity of the structure. At the same time, it is also necessary to take into account the shape of the stainless steel plate and the problem of rapid temperature drop at the head and tail after the strip is off the line;

[0025] (3) Control the time from rolling off the line to loading into the furnace for annealing. The thicker the 430 stainless steel is, the earlier the time from rolling off the line to loading into the furnace for annealing. The latest time from rolling off the line to loading into the furnace for annealing should not exceed 24 hours. From the end of rolling to the charging into the bell-type furnace, 430 stainless steel has dynamic recovery, which also affects the uniformity of the organization, and then affects the color difference of the final 430 cold plate surface through the genetic effect. Therefore, the charging time of thick 430 stainless steel should be strictly controlled;

[0026] (4) Optimize the bell-type furnace annealing process. The heating temperature is one of the important factors affecting the grain size and uniformity of the structure after metal recrystallization. The higher the heating temperature, the stronger the atomic diffusion ability and the more obvious the trend of grain growth. Therefore, according to the temperature range of 430 recrystallization and the surface quality of the cold plate, the annealing temperature is controlled to 840±10℃, and the holding time will also affect the grain size and uniformity of the structure after 430 annealing, so the holding time is controlled to 10h;

[0027] The annealing temperature is quickly increased before 750°C, kept at 750°C for 2 hours, and then slowly increased to 840°C for 4 hours, thereby effectively ensuring the uniform recovery of the original grains.

[0028] Example 1

[0029] The hot rolling control method for producing 430 stainless steel with a thickness of 4.0mm to 5.0mm and improving the color difference defects on the surface of 430 stainless steel cold plate includes:

[0030] (1) Control the coiling temperature. The coiling temperature of 430 stainless steel is controlled at 650°C.

[0031] (2) Determine the laminar cooling process, and use a laminar cooling valve device to cool the 430 stainless steel, wherein the head 60m of the 430 stainless steel is not cooled, and the tail 30m is not cooled. The laminar cooling valve device starts to spray water for cooling from the third group of valves. The upper valve and the lower valve are opened from front to back in sequence. The valve opening sequence is the third group, the fourth group, ... the 48th group. In each group, the lower valve is opened first, and then the upper valve is opened. Among them, the water volume of the upper valve is 65% of the maximum water volume, and the water volume of the lower valve is 85% of the maximum water volume;

[0032] (3) Control the time from rolling off the line to loading into the furnace for annealing. The thicker the thickness of 430 stainless steel, the time from rolling off the line to loading into the furnace for annealing is controlled to be 17h~24h;

[0033] (4) Optimize the bell-type furnace annealing process, control the annealing temperature to 840±10℃, and control the holding time to 10h;

[0034] The annealing temperature is quickly increased before 750°C, kept at 750°C for 2 hours, then slowly increased to 840°C for 4 hours, and quickly cooled to the furnace exit temperature after keeping at 10 hours.

[0035] Example 2

[0036] The hot rolling control method for producing 5.0mm to 5.5mm thick 430 stainless steel and improving the surface color difference defects of 430 stainless steel cold plate includes:

[0037] (1) Control the coiling temperature. The coiling temperature of 430 stainless steel is controlled at 670°C.

[0038] (2) Determine the laminar cooling process, and use a laminar cooling valve device to cool the 430 stainless steel, wherein the head 50m of the 430 stainless steel is not cooled, and the tail 30m is not cooled. The laminar cooling valve device starts to spray water for cooling from the third group of valves. The upper valve and the lower valve are opened from front to back in sequence. The valve opening sequence is the third group, the fourth group, ... the 48th group. In each group, the lower valve is opened first, and then the upper valve is opened. Among them, the water volume of the upper valve is 65% of the maximum water volume, and the water volume of the lower valve is 85% of the maximum water volume;

[0039] (3) Control the time from rolling off the line to loading into the furnace for annealing. The thicker the thickness of 430 stainless steel, the time from rolling off the line to loading into the furnace for annealing is controlled to be 10h to 17h;

[0040] (4) Optimize the bell-type furnace annealing process, control the annealing temperature to 840±10℃, and control the holding time to 10h;

[0041] The annealing temperature is quickly increased before 750°C, kept at 750°C for 2 hours, then slowly increased to 840°C for 4 hours, and quickly cooled to the furnace exit temperature after keeping at 10 hours.

[0042] Example 3

[0043] The hot rolling control method for producing 430 stainless steel with a thickness greater than 5.5 mm and improving the surface color difference defects of 430 stainless steel cold plate includes:

[0044] (1) Control the coiling temperature. The coiling temperature of 430 stainless steel is controlled at 680°C.

[0045] (2) Determine the laminar cooling process, and use a laminar cooling valve device to cool the 430 stainless steel, wherein the head 30m of the 430 stainless steel is not cooled, and the tail 30m is not cooled. The laminar cooling valve device starts to spray water for cooling from the third group of valves. The upper valve and the lower valve are opened from front to back in sequence. The valve opening sequence is the third group, the fourth group, ... the 48th group. In each group, the lower valve is opened first, and then the upper valve is opened. Among them, the water volume of the upper valve is 65% of the maximum water volume, and the water volume of the lower valve is 85% of the maximum water volume;

[0046] (3) Control the time from rolling off the line to loading into the furnace for annealing. The thicker the 430 stainless steel, the time from rolling off the line to loading into the furnace for annealing should be controlled to less than 10 hours;

[0047] (4) Optimize the bell-type furnace annealing process, control the annealing temperature to 840±10℃, and control the holding time to 10h;

[0048] The annealing temperature is quickly increased before 750°C, kept at 750°C for 2 hours, then slowly increased to 840°C for 4 hours, and quickly cooled to the furnace exit temperature after keeping at 10 hours.

[0049] In summary, the hot rolling control method for improving the surface color difference defects of 430 stainless steel thick specification cold plate of the present invention optimizes and strictly controls the key process parameters such as coiling temperature control and layer cooling strategy, bell furnace loading time and annealing process, so as to achieve the effect of improving the uniformity of the original structure and the uniformity of the structure after annealing, so as to eliminate the subsequent thick specification 430 cold plate surface color difference defects caused by the uneven annealing structure.

[0050] Specifically, compared with the prior art, the hot rolling control method of the present invention for improving the surface color difference defects of 430 stainless steel thick cold plate has the following advantages and beneficial effects:

[0051] By optimizing the coiling temperature, changing the layer cooling strategy and controlling the furnace loading time to ensure the uniformity of the original structure of 430 stainless steel, by optimizing the bell-type furnace annealing process, adjusting the heating temperature, holding time and heating rate, ensuring the complete recrystallization of the grains, and avoiding excessive grain growth, the uniformity of the structure of thick-gauge 430 stainless steel after annealing can be effectively improved. The color difference defects of thick-gauge 430 after cold rolling are significantly improved, and the non-conformity rate is reduced from 30% to below 6%, which improves product quality and thus improves the overall production efficiency, and can achieve good benefits.

[0052] 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 including a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such article or device.

[0053] 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 hot rolling control method for improving the color difference defect on the surface of 430 stainless steel thick cold plate, characterized in that: include: (1) Control the coiling temperature. The coiling temperature of 430 stainless steel is controlled at 650℃~700℃; (2) Determine the laminar cooling process and use a laminar cooling valve device to cool the 430 stainless steel, wherein the head 30m to 60m of the 430 stainless steel is not cooled and the tail 30m is not cooled; (3) Control the time from rolling off the line to loading into the furnace for annealing. The thicker the 430 stainless steel, the earlier the time from rolling off the line to loading into the furnace for annealing. The latest time from rolling off the line to loading into the furnace for annealing shall not exceed 24 hours. (4) Optimize the bell-type furnace annealing process, control the annealing temperature to 840±10℃, and control the holding time to 10h.

2. The hot rolling control method for improving the color difference defect on the surface of 430 stainless steel thick cold plate according to claim 1 is characterized in that: In determining the laminar cooling process steps, the laminar cooling valve device is provided with three types of upper valves, lower valves and side blowing valves, wherein the upper valves and the lower valves are a group, and there are 48 groups of valves in total.

3. The hot rolling control method for improving the color difference defect on the surface of 430 stainless steel thick cold plate according to claim 2 is characterized in that: In determining the laminar cooling process steps, the laminar cooling valve device starts to spray water for cooling from the 3rd group of valves, and the upper valve and the lower valve are opened in sequence from front to back. The valve opening sequence is the 3rd group, the 4th group... the 48th group. In each group, the lower valve is opened first and then the upper valve. Among them, the water volume of the upper valve is 65% of the maximum water volume, and the water volume of the lower valve is 85% of the maximum water volume.

4. The hot rolling control method for improving the color difference defect on the surface of 430 stainless steel thick cold plate according to claim 1 is characterized in that: In the optimization of the bell-type furnace annealing process steps, the annealing temperature is quickly increased before 750°C, kept at 750°C for 2 hours, and then slowly increased to 840°C for 4 hours.

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