Online demagnetization process for cold-rolled stainless steel strip

Abstract

The present invention provides an online demagnetization process method for cold-rolled stainless steel strip, comprising: performing continuous rough rolling for multiple passes after annealing and softening of the cold-rolled stainless steel strip to obtain a rough-rolled strip, wherein the total reduction rate of the continuous rough rolling is 60% to 70%; performing continuous finish rolling for multiple passes after high-temperature annealing of the rough-rolled strip to obtain a finished strip, wherein the total reduction rate of the continuous finish rolling is 20% to 30%; performing straightening and leveling on the finished strip, wherein the straightening and leveling has a reduction rate of 0.5% to 2%; performing low-temperature annealing on the finished strip after straightening and leveling to obtain a low-permeability strip. The online demagnetization process method for cold-rolled stainless steel strip provided by the present invention obtains a low-permeability strip that meets the mechanical performance requirements by adopting a low-temperature annealing treatment after straightening and leveling, and can complete online demagnetization during the entire cold rolling process, thereby improving the production and processing efficiency of the low-permeability strip.

Description

Technical Field

[0001] The invention belongs to the technical field of cold-rolled strip steel, and in particular relates to an online demagnetization process method for stainless steel cold-rolled strip steel. Background Art

[0002] Austenitic stainless steel and martensitic stainless steel are common stainless steels with obvious differences in magnetic conductivity. The crystal phase of austenitic stainless steel is a non-magnetic austenite structure, while the crystal phase of martensitic stainless steel is a magnetic martensite structure. In the field of electronics and electrical engineering, stainless steel is a common material with high requirements for its magnetic permeability, so austenitic stainless steel is mostly used. During the cold rolling process of stainless steel strip, some unstable austenite will undergo phase transformation to form martensite, resulting in the magnetic permeability of the finished strip product failing to meet the requirements.

[0003] At present, in order to meet the requirements of non-magnetic or low-magnetic stainless steel strip products, it is usually necessary to demagnetize the strip by heating it to above the Curie point (basically around 1050°C) after rolling. However, the high heating temperature of the stainless steel strip will cause a serious decline in its mechanical properties, thus affecting its application. Moreover, this demagnetization method requires a long period of heat preservation after heating to the target temperature to stabilize the austenite morphology, resulting in extremely low production efficiency. In view of this, there is an urgent need to develop an efficient demagnetization solution that can ensure the mechanical properties of stainless steel strip. Summary of the invention

[0004] The embodiment of the present invention provides an online demagnetization process method for cold-rolled stainless steel strip, which aims to reduce the magnetic permeability of the stainless steel strip while ensuring the mechanical properties of the stainless steel strip and improve production efficiency.

[0005] To achieve the above object, the technical solution adopted by the present invention is: to provide an online demagnetization process method for cold-rolled stainless steel strip, comprising:

[0006] After annealing and softening, the stainless steel cold-rolled strip is subjected to continuous rough rolling for multiple passes to obtain a rough-rolled strip steel, and the total reduction rate of the continuous rough rolling is 60% to 70%;

[0007] After high temperature annealing treatment of the rough rolled strip, continuous finishing rolling is performed for multiple passes to obtain the finished strip, and the total reduction rate of the continuous finishing rolling is 20% to 30%;

[0008] The finished rolled strip is leveled and flattened, with a reduction rate of 0.5% to 2%;

[0009] The finished rolled strip steel after drawing and leveling is subjected to low temperature annealing treatment to obtain a low magnetic permeability strip steel.

[0010] In a possible implementation, the temperature of the high temperature annealing treatment is a first temperature, and the first temperature is 1075° C. to 1120° C.

[0011] In some embodiments, the high temperature annealing treatment adopts a bright annealing furnace, which includes a heating section, a constant temperature section and a cooling section connected in sequence; the rough-rolled strip is heated to a first temperature at a first speed in the heating section and then enters the constant temperature section, the rough-rolled strip is kept warm in the constant temperature section for 180S to 240S and then enters the cooling section, and the rough-rolled strip is cooled to a second temperature at a second speed in the cooling section and then taken out of the furnace; wherein the second speed is greater than the first speed, and the second temperature is 80℃ to 85℃.

[0012] Exemplarily, the first speed is 30°C / S to 40°C / S, and the second speed is 50°C / S to 80°C / S.

[0013] For example, during the straightening and flattening, hot air with a third temperature is used to blow and heat the finished rolled strip, and the third temperature is 5° C. to 10° C. higher than the second temperature.

[0014] For example, the protective atmosphere of the bright annealing furnace is hydrogen.

[0015] In a possible implementation, the temperature of the low temperature annealing treatment is 380° C. to 420° C.

[0016] In some embodiments, the reduction ratio of each finishing pass of the continuous finishing rolling is 6% to 10%.

[0017] Exemplarily, the annealing temperature of the annealing softening treatment is 740°C to 780°C.

[0018] For example, the weight percentage of the components of stainless steel cold-rolled strip is: C: 0.03~0.07%, Si: 0.4~0.9%, Mn≤1.4%, Cr: 17.9~19.7%, Ni: 8.3~10.2%; N: 0.05~0.1%, P≤0.04%, S≤0.02%, Mo: 0.25~0.4%, and the rest is Fe and unavoidable impurities.

[0019] The beneficial effect of the online demagnetization process method for stainless steel cold-rolled strip provided by the present invention is that: compared with the prior art, the online demagnetization process method for stainless steel cold-rolled strip provided by the present invention performs annealing and softening treatment on the stainless steel cold-rolled strip before rough rolling, so that the total reduction rate of continuous rough rolling can reach 60% to 70% to obtain the rough-rolled strip, and by performing high-temperature annealing treatment on the rough-rolled strip, on the one hand, the martensitic phase transformation induced by large deformation during continuous rough rolling can be eliminated, thereby achieving demagnetization of the rough-rolled strip, and on the other hand, the rough-rolled strip can be softened to facilitate subsequent finishing rolling; then, by controlling the total reduction rate of continuous finishing rolling to 20% to 30%, the reduction amount of the rough-rolled strip after each finishing pass can be reduced, thereby avoiding the continuous finishing process due to deformation. The martensite formation caused by the transformation-induced phase transformation is reduced, thereby reducing the magnetic permeability of the finished strip, and the reduction rate of the finished strip during the drawing, straightening and flattening process is controlled at 0.5% to 2%, thereby avoiding the influence of the drawing, straightening and flattening process on the magnetic permeability. On this basis, the magnetic permeability is further reduced by performing low-temperature annealing on the finished strip after drawing, straightening and flattening. After the high-temperature annealing treatment, the finished strip can regain good mechanical properties through multiple passes of continuous finishing rolling, and the low-temperature annealing treatment after drawing, straightening and flattening has almost no negative impact on the mechanical properties, thereby obtaining a low-permeability strip that can meet the mechanical property requirements, and can complete online demagnetization during the entire cold rolling process, thereby improving the production and processing efficiency of the low-permeability strip. DETAILED DESCRIPTION

[0020] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0021] It should be noted that the terms "first", "second" and "third" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first", "second" and "third" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "multiple" and "several" is two or more, unless otherwise clearly and specifically defined.

[0022] The online demagnetization process method for cold-rolled stainless steel strip provided by the present invention is now described. The online demagnetization process method for cold-rolled stainless steel strip comprises:

[0023] Step S100, annealing and softening the stainless steel cold-rolled strip and then performing a plurality of continuous rough rolling passes to obtain a rough-rolled strip, wherein the total reduction ratio of the continuous rough rolling is 60% to 70%.

[0024] It should be noted that the stainless steel cold-rolled strip is annealed and softened before rough rolling, so that the total reduction rate of continuous rough rolling can reach 60% to 70% to obtain rough-rolled strip. By subjecting the rough-rolled strip to high-temperature annealing treatment, on the one hand, the martensitic phase transformation induced by the large deformation during continuous rough rolling can be eliminated, thereby achieving demagnetization of the rough-rolled strip. On the other hand, the rough-rolled strip can be softened to facilitate subsequent finishing rolling.

[0025] Specifically, in the present embodiment, each rough rolling pass of the continuous rough rolling can adopt a four-roll mill or a six-roll mill, and three to five rough rolling passes can be arranged in sequence. The reduction rate of each rough rolling pass is the same or decreases sequentially, but the reduction rate of each rough rolling pass is in the range of 20% to 35%; by annealing and softening the stainless steel cold-rolled strip in advance, the pressure of each rough rolling pass is appropriately increased. It should be noted that when the deformation of stainless steel exceeds 10%, phase transformation will be induced and martensite will appear, thereby leading to an increase in magnetic permeability. Therefore, the continuous rough rolling process in the present embodiment aims to reduce the number of rough rolling passes by a relatively large reduction, thereby improving efficiency.

[0026] Step S200, after high temperature annealing treatment of the rough-rolled steel strip, continuous finishing rolling is performed for multiple passes to obtain a finished steel strip, and the total reduction rate of the continuous finishing rolling is 20% to 30%.

[0027] First of all, it should be explained that the high temperature annealing treatment in this embodiment can be an annealing temperature that exceeds the Curie point of the rough-rolled strip. On the one hand, the high temperature annealing treatment can eliminate the martensitic phase transformation in the continuous rough rolling process and restore the martensitic structure to a stable austenitic structure, thereby reducing or even eliminating the magnetic permeability of the rough-rolled strip. On the other hand, the high temperature annealing treatment can soften the rough-rolled strip to facilitate the subsequent continuous finishing of the rough-rolled strip.

[0028] On the basis of the above, controlling the total reduction rate of continuous finishing rolling at 20% to 30% can reduce the reduction amount of the rough-rolled strip after each finishing pass; the continuous finishing rolling can specifically be three to five passes of a four-roll or six-roll mill, and the reduction rate of each finishing pass is as consistent as possible and controlled below 10%, thereby avoiding the formation of martensite caused by deformation-induced phase transformation during continuous finishing rolling, thereby reducing the magnetic permeability of the finished strip.

[0029] The finished rolled strip is leveled and flattened, and the leveling and flattening has a reduction rate of 0.5% to 2%. There is cold deformation in the leveling and flattening process. Excessive cold deformation is likely to induce martensitic phase transformation and lead to an increase in magnetic permeability. Therefore, in this embodiment, the reduction rate of the leveling and flattening is controlled within the range of 0.5% to 2%, and the martensitic phase transformation caused by cold deformation is reduced while ensuring the flatness of the finished strip, thereby ensuring the low magnetic permeability of the finished strip.

[0030] The finished rolled strip after drawing and leveling is subjected to low temperature annealing to obtain a low magnetic permeability strip. Finally, the low temperature annealing is performed to control the temperature below the Ms point (the temperature at which martensite transformation begins), thereby avoiding the increase in magnetic permeability caused by martensite transformation during the annealing process. On this basis, low temperature annealing is beneficial to reducing magnetic permeability while avoiding affecting the mechanical properties of the finished strip (here, the mechanical properties include microhardness HV, tensile strength and yield strength).

[0031] Compared with the prior art, the online demagnetization process method for cold-rolled stainless steel strip provided in the present embodiment performs annealing and softening treatment on the cold-rolled stainless steel strip before rough rolling, so that the total reduction rate of continuous rough rolling can reach 60% to 70% to obtain the rough-rolled strip, and high-temperature annealing treatment of the rough-rolled strip can eliminate the martensitic phase transformation induced by large deformation during continuous rough rolling, thereby achieving demagnetization of the rough-rolled strip, and soften the rough-rolled strip to facilitate subsequent finishing rolling; then, by controlling the total reduction rate of continuous finishing rolling to 20% to 30%, the reduction amount of the rough-rolled strip after each finishing pass can be reduced, thereby avoiding the martensitic phase transformation caused by deformation-induced phase transformation during continuous finishing rolling. The magnetic permeability of the finished strip is reduced, and the reduction rate of the finished strip during the drawing, straightening and flattening process is controlled at 0.5% to 2%, thereby avoiding the influence of the drawing, straightening and flattening process on the magnetic permeability. On this basis, the magnetic permeability is further reduced by performing low-temperature annealing on the finished strip after drawing, straightening and flattening. After the high-temperature annealing treatment, the finished strip can regain good mechanical properties through multiple passes of continuous finishing rolling, and the low-temperature annealing treatment after drawing, straightening and flattening has almost no negative impact on the mechanical properties, thereby obtaining a low-permeability strip that can meet the mechanical property requirements, and can complete online demagnetization during the entire cold rolling process, thereby improving the production and processing efficiency of the low-permeability strip.

[0032] In some embodiments, the temperature of the high temperature annealing treatment is a first temperature, and the first temperature is 1075° C. to 1120° C. The temperature of the high temperature annealing treatment of the rough-rolled steel strip is controlled at about 1100° C., specifically in the range of 1075° C. to 1120° C., so that all the martensitic phase transformations generated during the continuous rough rolling process can be transformed back into austenite under high temperature conditions, thereby eliminating the magnetic conductivity of the rough-rolled steel strip and meeting the process requirements for softening the rough-rolled steel strip.

[0033] In some possible implementations, the high temperature annealing treatment adopts a bright annealing furnace, which includes a heating section, a constant temperature section and a cooling section connected in sequence; the rough rolled strip is heated to a first temperature at a first speed in the heating section and then enters the constant temperature section, the rough rolled strip is kept in the constant temperature section for 180S to 240S and then enters the cooling section, and the rough rolled strip is cooled to a second temperature at a second speed in the cooling section and then discharged; wherein the second speed is greater than the first speed, and the second temperature is 80℃ to 85℃. Specifically, the above-mentioned first speed is 30℃ / S to 40℃ / S, and the second speed is 50℃ / S to 80℃ / S.

[0034] The purpose of using a bright annealing furnace here is to eliminate the hardening of the rough-rolled strip caused by the continuous rough rolling process and to obtain a metallographic structure that meets the conditions, or it can be understood that a fully hard rough-rolled strip is obtained after continuous rough rolling, and the fully hard rough-rolled strip is softened to less than half the hardness through bright annealing to facilitate subsequent finishing processing. On this basis, the temperature of the rough-rolled strip is heated to 1075℃~1120℃ through the heating section, and then kept warm in the constant temperature section to allow all carbides to dissolve in the austenite structure. At the same time, the martensitic phase transformation structure caused by continuous rough rolling is transformed back into austenite, thereby obtaining a single-phase austenite, and then entering the cooling section to achieve furnace cooling. At the same time, the cooling rate is controlled to be greater than the heating rate, which is beneficial to inhibit the martensitic phase transformation during the cooling process, thereby inhibiting the magnetic permeability.

[0035] In some possible implementations, hot air blowing with a third temperature is used to heat the finished steel strip during the stretching and leveling, and the third temperature is 5°C to 10°C higher than the second temperature. Here, the finished steel strip is deformed at a third temperature 5°C to 10°C higher than the second temperature by blowing hot air to heat the finished steel strip during the stretching and leveling. Since a high deformation temperature is conducive to promoting the stabilization of the austenite structure, the stretching and leveling at the third temperature of 85°C to 90°C can avoid the martensitic phase transformation caused by the deformation of the finished steel strip during the stretching and leveling process, thereby suppressing the magnetic permeability.

[0036] Optionally, the protective atmosphere of the bright annealing furnace in this embodiment is hydrogen. Using hydrogen as a protective atmosphere due to its reducing property can suppress the surface oxidation reaction of the rough rolled steel strip during bright annealing, thereby ensuring the surface quality of the rough rolled steel strip after bright annealing.

[0037] In some embodiments, the temperature of the low temperature annealing treatment is 380° C. to 420° C. This temperature range is below the Ms point of stainless steel, which can avoid the increase of magnetic permeability caused by martensitic phase transformation during annealing, and can also ensure that the mechanical properties of the finished steel strip are not affected. At the same time, the low magnetic permeability of the finished steel strip is further reduced by this temperature.

[0038] It should be noted that the reduction ratio of each finishing pass of the above continuous finishing rolling is 6% to 10%. By controlling the reduction ratio of each finishing pass to be below 10%, the martensitic phase transformation caused by excessive cold deformation during the finishing rolling process can be avoided, thereby ensuring the low magnetic permeability of the finished rolled strip.

[0039] For example, the annealing temperature of the annealing softening treatment is 740°C to 780°C. Since the stainless steel cold-rolled strip itself has a high hardness, equivalent to the half hardness state, in order to meet the large reduction rate requirement of continuous rough rolling, the stainless steel cold-rolled strip is annealed and softened before continuous rough rolling to reduce its hardness, thereby increasing the total reduction rate of continuous rough rolling and improving processing efficiency.

[0040] It should be noted that the weight percentage of the components of the above-mentioned stainless steel cold-rolled strip is:

[0041] C: 0.03-0.07%, promotes the formation of austenite, is beneficial to improve the strength of the material, and improves the stabilization of the austenite structure.

[0042] Si: 0.4-0.9%. Silicon element is beneficial to improving the strength performance of stainless steel strip.

[0043] Mn≤1.4%. Manganese is beneficial to improving the strength performance of the stainless steel strip. At the same time, the solid solubility of manganese decreases during the cooling stage of annealing treatment and is enriched near the grain boundary, thereby promoting the TRIP effect (a phenomenon in which the residual austenite in the material is transformed into martensite during plastic deformation, thereby improving the plasticity and strength of the material). Considering that this embodiment is intended to inhibit the martensitic phase transformation and reduce the magnetic permeability, the manganese content is controlled below 1.4%.

[0044] Cr: 17.9~19.7%. Chromium is mainly used to improve the antioxidant and anti-corrosion properties and promote the stability of the crystal phase structure. By appropriately increasing the chromium content, the stabilization of the austenite structure can be promoted, thereby inhibiting the martensitic phase transformation during continuous rough rolling and continuous finishing rolling, and further inhibiting the increase in magnetic permeability.

[0045] Ni: 8.3-10.2%; the nickel element plays a significant role in forming stable austenite.

[0046] N: 0.05-0.1%. Nitrogen can produce an effect close to that of nickel. Since nickel is expensive, adding an appropriate amount of nitrogen to replace nickel can improve the stabilization of austenite.

[0047] P≤0.04%, phosphorus element should be controlled to the minimum under process conditions.

[0048] S≤0.02%, sulfur element should be controlled to the minimum under process conditions.

[0049] Mo: 0.25-0.4%. The cost of molybdenum is relatively high. Adding a small amount of molybdenum helps to improve the corrosion resistance of stainless steel cold-rolled strip.

[0050] The rest is Fe and unavoidable impurities.

[0051] The following table shows the relevant process experimental parameters of the low magnetic permeability strip steels of different specifications obtained by the online demagnetization process for cold-rolled stainless steel strip provided in this embodiment, as well as the performance comparison between the low magnetic permeability strip steel products of different specifications and the existing process strip steel products:

[0052] Table 1, Processing parameters of 0.55mm low magnetic permeability strip steel products:

[0053]

[0054] Table 2, Processing parameters of 0.33mm low magnetic permeability strip products:

[0055]

[0056] Table 3, Processing parameters of 0.6mm low magnetic permeability strip steel products:

[0057]

[0058] Table 4, Comparison of magnetic permeability and mechanical properties between low magnetic permeability strip products and existing process strip products:

[0059]

[0060] Through comparison of the above experimental data, it can be found that the low magnetic permeability strip obtained by the online demagnetization process method for stainless steel cold-rolled strip provided by the present invention can reduce the magnetic permeability to below 1.04 while basically not affecting the mechanical properties (including microhardness HV, tensile strength, yield strength and elongation) of the existing process products, and adopts an online demagnetization method during the cold rolling process, thereby saving post-processing time, thereby greatly improving production efficiency.

[0061] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. An online demagnetization process for cold-rolled stainless steel strip, characterized in that: include: After annealing and softening the stainless steel cold-rolled strip, a plurality of continuous rough rolling passes are performed to obtain a rough-rolled strip steel, wherein the total reduction rate of the continuous rough rolling is 60% to 70%; After high temperature annealing treatment of the rough-rolled steel strip, continuous finishing rolling is performed for multiple passes to obtain a finished steel strip, wherein the total reduction ratio of the continuous finishing rolling is 20% to 30%; the temperature of the high temperature annealing treatment is a first temperature, and the first temperature is 1075° C. to 1120° C.; The finished rolled steel strip is subjected to straightening and flattening, wherein the straightening and flattening has a reduction rate of 0.5% to 2%; The finished rolled steel strip after drawing and leveling is subjected to low temperature annealing treatment to obtain a low magnetic permeability steel strip.

2. The online demagnetization process for cold-rolled stainless steel strip according to claim 1, characterized in that: The high temperature annealing treatment adopts a bright annealing furnace, which includes a heating section, a constant temperature section and a cooling section connected in sequence; the rough-rolled strip is heated to the first temperature at a first speed in the heating section and then enters the constant temperature section, the rough-rolled strip is kept in the constant temperature section for 180S to 240S and then enters the cooling section, and the rough-rolled strip is cooled to a second temperature at a second speed in the cooling section and then discharged from the furnace; wherein, the second speed is greater than the first speed, and the second temperature is 80°C to 85°C.

3. The online demagnetization process for cold-rolled stainless steel strip according to claim 2, characterized in that: The first speed is 30°C / S to 40°C / S, and the second speed is 50°C / S to 80°C / S.

4. The online demagnetization process for cold-rolled stainless steel strip according to claim 2, characterized in that: During the straightening and flattening, hot air with a third temperature is used to blow and heat the finished rolled steel strip, and the third temperature is 5° C. to 10° C. higher than the second temperature.

5. The online demagnetization process for cold-rolled stainless steel strip according to claim 2, characterized in that: The protective atmosphere of the bright annealing furnace is hydrogen.

6. The online demagnetization process for cold-rolled stainless steel strip according to claim 1, characterized in that: The temperature of the low temperature annealing treatment is 380°C to 420°C.

7. The online demagnetization process for cold-rolled stainless steel strip according to claim 1, characterized in that: The reduction rate of each finishing pass of the continuous finishing rolling is 6% to 10%.

8. The online demagnetization process for cold-rolled stainless steel strip according to claim 1, characterized in that: The annealing temperature of the annealing and softening treatment is 740°C to 780°C.

9. The online demagnetization process for cold-rolled stainless steel strip according to any one of claims 1 to 8, characterized in that: The components of the stainless steel cold-rolled strip are as follows by weight: C: 0.03-0.07%, Si: 0.4-0.9%, Mn≤1.4%, Cr: 17.9-19.7%, Ni: 8.3-10.2%; N: 0.05-0.1%, P≤0.04%, S≤0.02%, Mo: 0.25-0.4%, and the rest are Fe and unavoidable impurities.

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