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

Abstract

The application discloses a kind of hot rolling control methods for improving the surface color difference defect of thick specification 430 stainless steel cold plate, comprising: control coiling temperature, 430 stainless steel coiling temperature is controlled as 650~700 DEG C;Determine laminar flow cooling process, 430 stainless steel is cooled using laminar flow cooling valve device, wherein 430 stainless steel head 30m~60m is not cooled, tail 30m is not cooled;Control rolling off line to furnace annealing time, wherein the thicker the thickness of 430 stainless steel, the earlier the rolling off line to furnace annealing time, the latest rolling off line to furnace annealing time does not exceed 24h;Optimize cover furnace annealing process, annealing temperature is controlled as 840±10 DEG C, and holding time is controlled as 10h.The application effectively improves the uniformity of thick specification 430 stainless steel after annealing, the color difference defect of thick specification 430 after cold rolling is significantly improved, the non-conformance rate is reduced from 30% to less than 6%, the product quality is improved, thereby improving the overall production efficiency, and good benefits can be achieved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of stainless steel product production, and more particularly to a hot rolling control method for improving surface color difference defects of thick specification cold plates of 430 stainless steel. BACKGROUND

[0002] Ferritic stainless steel has obvious cost advantage due to less alloying element content and no need to add expensive alloying elements such as Ni, and has good corrosion resistance, and especially, low-chromium ferritic stainless steel cold-rolled plate strip with a Cr content lower than 20% is widely used in the fields of automobiles, buildings, home appliances and the like.

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

[0004] Therefore, it is particularly important to develop a hot rolling control method for improving surface color difference defects of thick specification cold plates of 430 stainless steel. SUMMARY

[0005] To solve the above technical problems in the prior art, the application provides a hot rolling control method for improving surface color difference defects of thick specification cold plates of 430 stainless steel, which comprises the following steps:

[0006] (1) controlling the coiling temperature, and controlling the coiling temperature of the 430 stainless steel to be 650-700℃;

[0007] (2) determining a laminar cooling process, and cooling the 430 stainless steel by using a laminar cooling valve device, wherein the head part of the 430 stainless steel is not cooled for 30-60m, and the tail part is not cooled for 30m;

[0008] (3) controlling the rolling off-line to furnace annealing time, wherein the thicker the thickness of the 430 stainless steel is, the earlier the rolling off-line to furnace annealing time is, and the rolling off-line to furnace annealing time is not more than 24h at the latest;

[0009] (4) optimizing the cover furnace annealing process, and controlling the annealing temperature to be 840±10℃ and the holding time to be 10h.

[0010] ​Further, in the hot rolling control method for improving surface color difference defects of thick gauge 430 stainless steel cold plate described above, in the determining laminar cooling process step, the laminar cooling valve device is provided with three kinds of upper valve, lower valve and side blowing valve, wherein the upper valve and the lower valve are a group, and there are 48 groups of valves in total.

[0011] Further, in the hot rolling control method for improving surface color difference defects of thick gauge 430 stainless steel cold plate described above, in the determining laminar cooling process step, the laminar cooling valve device is provided with three kinds of upper valve, lower valve and side blowing valve, wherein the upper valve and the lower valve are a group, and there are 48 groups of valves in total.

[0012] Further, in the hot rolling control method for improving surface color difference defects of thick gauge 430 stainless steel cold plate described above, in the optimizing cover furnace annealing process step, the annealing temperature is rapidly raised to 750 DEG C, and then kept for 2 hours, and then slowly raised to 840 DEG C for 4 hours.

[0013] The hot rolling control method for improving surface color difference defects of thick gauge 430 stainless steel cold plate provided by the present application optimizes and strictly controls the coiling temperature control, the laminar cooling strategy, the cover furnace loading time and the annealing process, so as to improve the uniformity of the original structure and the uniformity of the structure after annealing, so as to eliminate the surface color difference defects of the subsequent thick gauge 430 cold plate caused by the non-uniform annealing structure. Specifically, compared with the prior art, the hot rolling control method for improving surface color difference defects of thick gauge 430 stainless steel cold plate provided by the present application has the following advantages and beneficial effects:

[0014] By optimizing the coiling temperature, changing the laminar cooling strategy and controlling the loading time, the uniformity of the original structure of the 430 stainless steel is ensured, by optimizing the cover furnace annealing process, adjusting the heating temperature, the holding time and the heating rate, the grain recrystallization is completely ensured, and the grain is also prevented from growing too much, the uniformity of the structure of the thick gauge 430 stainless steel after annealing is effectively improved, the color difference defects of the thick gauge 430 after cold rolling are significantly improved, the non-conformity rate is reduced from 30% to less than 6%, the product quality is improved, the overall production efficiency is improved, and good benefits can be obtained. BRIEF DESCRIPTION OF DRAWINGS

[0015] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creating any creative labor.

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

[0017] Figure 2 is a laminar cooling valve device arrangement of the present application. DETAILED DESCRIPTION

[0018] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described clearly and completely below in combination with specific embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0019] Research shows that the surface color difference defects of 430 after cold rolling are mainly concentrated on thick gauge 430, the cold rolling deformation rate of which is smaller than that of thin gauge 430, and the surface of the defect coil is normal after re-rolling. It is analyzed that such color difference defects are caused by uneven organization recovery / re-crystallization of 430 stainless steel during annealing, and the uneven organization is related to the original grain uniformity of the coil, the furnace loading time and the annealing process.

[0020] Therefore, the key process parameters such as the coiling temperature control, the laminar cooling strategy, the cover furnace loading time and the annealing process are optimized and strictly controlled, so as to improve the original organization uniformity and the uniformity of the annealed organization, so as to eliminate the subsequent surface color difference defects of thick gauge 430 cold plate caused by uneven annealing organization. Specifically, the hot rolling control method for improving the surface color difference defects of thick gauge 430 stainless steel cold plate of the present application comprises:

[0021] (1) controlling the coiling temperature, the coiling temperature of 430 stainless steel is controlled to be 650-700℃, in the process of controlling the coiling temperature, on the one hand, the original plate shape is ensured to avoid the potential stress generated by uneven cooling process to affect the plate shape control and the field production, on the other hand, the uniformity of the organization after cooling is ensured;

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

[0023] The laminar cooling valve device is provided with three kinds of upper valve, lower valve and side blowing valve, wherein the upper valve and the lower valve are a group, and there are 48 groups of valves in total;

[0024] The laminar flow cooling valve device starts to spray water cooling from the third group of valves, and both the upper valve and the lower valve adopt the valve opening mode from front to back in turn, and the valve opening sequence is the third group, the fourth group,..., the forty-eighth group, the lower valve is opened first and then the upper valve is opened in each group, wherein the water quantity of the upper valve is 65% of the maximum water quantity, and the water quantity of the lower valve is 85% of the maximum water quantity, so that in the laminar flow cooling process, the 430 stainless steel plate is rapidly cooled below the target temperature to ensure the uniformity of the organization, and at the same time, the shape state of the stainless steel plate and the problem of rapid temperature drop of the head and tail of the strip after the strip is discharged also need to be considered;

[0025] (3) Controlling the rolling offline to furnace annealing time, the thicker the 430 stainless steel, the earlier the rolling offline to furnace annealing time, and the latest rolling offline to furnace annealing time should not exceed 24h, and before the furnace is loaded before the end of rolling, the 430 stainless steel exists dynamic recovery, which also affects the uniformity of the organization, and then affects the final 430 cold plate surface color difference through the genetic effect. Therefore, the furnace loading time of thick specification 430 stainless steel should be strictly controlled;

[0026] (4) Optimizing the annealing process of the cover furnace, the heating temperature is one of the important factors affecting the grain size and the uniformity of the organization after the metal is recrystallized. 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, the annealing temperature is controlled to be 840±10℃ combined with the cold plate surface quality, and the holding time also affects the grain size and the uniformity of the organization after the 430 is annealed, so the holding time is controlled to be 10h;

[0027] The annealing temperature is rapidly raised to 750℃, and then the temperature is kept for 2h, and then the temperature is slowly raised to 840℃ for 4h, so as to effectively ensure the uniform recovery of the original grain.

[0028] Example 1

[0029] The hot rolling control method for improving the surface color difference defects of the 430 stainless steel cold plate includes:

[0030] (1) Controlling the coiling temperature, the coiling temperature of the 430 stainless steel is controlled to be 650℃;

[0031] (2) Determining the laminar flow cooling process, the 430 stainless steel is cooled by using the laminar flow cooling valve device, wherein the head 60m of the 430 stainless steel is not cooled, and the tail 30m is not cooled, the laminar flow cooling valve device starts to spray water cooling from the third group of valves, and both the upper valve and the lower valve adopt the valve opening mode from front to back in turn, and the valve opening sequence is the third group, the fourth group,..., the forty-eighth group, the lower valve is opened first and then the upper valve is opened in each group, wherein the water quantity of the upper valve is 65% of the maximum water quantity, and the water quantity of the lower valve is 85% of the maximum water quantity;

[0032] (3) Control the time from rolling off line to loading into the annealing furnace, the thicker the 430 stainless steel, the longer the time from rolling off line to loading into the annealing furnace is controlled to be 17h-24h;

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

[0034] The annealing temperature is rapidly increased to 750℃, then held for 2h, then slowly increased to 840℃ for 4h, and then rapidly cooled to the discharge temperature after holding for 10h.

[0035] Example 2

[0036] The hot rolling control method for improving the surface color difference defect of 430 stainless steel with a thickness of 5.0mm-5.5mm includes:

[0037] (1) Control the coiling temperature, the coiling temperature of the 430 stainless steel is controlled to be 670℃;

[0038] (2) Determine the laminar cooling process, the 430 stainless steel is cooled by using a laminar cooling valve device, the head of the 430 stainless steel is not cooled for 50m, the tail of the 430 stainless steel is not cooled for 30m, 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 both used in a way of sequentially opening from front to back, the opening sequence is the third group, the fourth group,..., the forty-eighth group, each group first opens the lower valve and then opens the upper valve, among them, the water amount of the upper valve is 65% of the maximum water amount, and the water amount of the lower valve is 85% of the maximum water amount;

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

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

[0041] The annealing temperature is rapidly increased to 750℃, then held for 2h, then slowly increased to 840℃ for 4h, and then rapidly cooled to the discharge temperature after holding for 10h.

[0042] Example 3

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

[0044] (1) Control the coiling temperature, the coiling temperature of the 430 stainless steel is controlled to be 680℃;

[0045] (2) determine the laminar cooling process, using laminar cooling valve device for cooling 430 stainless steel, wherein the head 30m 430 stainless steel is not cooled, the tail 30m is not cooled, the laminar cooling valve device starts to spray water cooling from the third group of valves, the upper valve and the lower valve are sequentially opened from front to back, the opening sequence is the third group, the fourth group, the 48th group, the lower valve is opened first, and then the upper valve is opened, wherein the water quantity of the upper valve is 65% of the maximum water quantity, and the water quantity of the lower valve is 85% of the maximum water quantity;

[0046] (3) control the rolling off-line to furnace annealing time, the thicker the thickness of the 430 stainless steel, the longer the rolling off-line to furnace annealing time is controlled to be less than 10h;

[0047] (4) optimize the bell furnace annealing process, the annealing temperature is controlled to be 840±10℃, and the holding time is controlled to be 10h;

[0048] The annealing temperature is rapidly increased to 750℃, then held for 2h, then slowly increased to 840℃ for 4h, and then rapidly cooled to the furnace outlet temperature after holding for 10h.

[0049] In summary, the hot rolling control method for improving the surface color difference defect of the thick specification cold plate of the 430 stainless steel optimizes and strictly controls the key process parameters such as the coiling temperature control, the laminar cooling strategy, the bell furnace loading time and the annealing process, so that the uniformity of the original structure and the uniformity of the structure after annealing are improved, and the purpose of eliminating the subsequent surface color difference defect of the thick specification 430 cold plate due to the uneven annealing structure is achieved.

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

[0051] By optimizing the coiling temperature, changing the laminar cooling strategy and controlling the loading time, the uniformity of the original structure of the 430 stainless steel is ensured, by optimizing the bell furnace annealing process, adjusting the heating temperature, holding time and heating rate, under the premise of ensuring complete grain recrystallization, the grain is also prevented from growing too much, the uniformity of the structure of the thick specification 430 stainless steel after annealing is effectively improved, the color difference defect of the thick specification 430 after cold rolling is significantly improved, the non-conformity rate is reduced from 30% to less than 6%, the product quality is improved, the overall production efficiency is improved, and good benefits can be achieved.

[0052] It should be noted that in this text, the term "includes" or any other variant thereof is intended to cover non-exclusive inclusion, so that the article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or includes elements inherent to such article or device.

[0053] It should be further noted that the above-mentioned embodiments are only used to explain the technical solutions of the present application, but not to limit the present application; even though the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that the technical solutions recorded in the foregoing embodiments can be modified, or some technical features thereof can be replaced equivalently; and these modifications or replacements do not cause the corresponding technical solutions to deviate from the scope of the present application.

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: Thick cold plate refers to cold plate with thickness ≥4.0mm, including: (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~60m of the 430 stainless steel is not cooled and the tail 30m is not cooled; In determining the laminar cooling process steps, the laminar cooling valve device starts spraying water cooling from the third group of valves. The upper and lower valves are opened in sequence from front to back. The valve opening order 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. (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; In the optimized bell-type furnace annealing process steps, the annealing temperature is rapidly increased before 750°C, kept at 750°C for 2 hours, and then slowly increased to 840°C for 4 hours.

2. The hot rolling control method for improving the surface color difference defect of 430 stainless steel thick gauge 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 form a group, and there are 48 groups of valves in total.

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