A continuous annealing method of a cold hard sheet

Abstract

The application relates to the technical field of steel production, in particular to a continuous annealing method of cold hard plate. The method comprises the following steps: continuously annealing a cold hard plate with a set chemical composition and controlling the atmosphere composition of the annealing; wherein the continuous annealing comprises the following steps: heating the cold hard plate, then homogenizing, and setting the heating temperature and the homogenizing temperature according to the annealing time. By adopting the control strategy of matching different annealing temperatures with different annealing times, that is, matching a lower annealing temperature when the continuous annealing speed is low and the continuous annealing time is long, and matching a higher annealing temperature when the continuous annealing speed is high and the continuous annealing time is short, the denitrogenation amount and the grain size stability control are realized, and the mechanical property fluctuation of the finished product is reduced. The high-nitrogen continuous annealing plate produced by the method can realize the denitrogenation amount control of + / -0.0002% by weight during the annealing process, and meanwhile, the grain size fluctuation control is + / -0.5 levels.

Description

Technical Field

[0001] This application relates to the field of steel preparation technology, and in particular to a continuous annealing method for cold-hardened steel sheets. Background Technology

[0002] High nitrogen content is a common chemical composition of tin-plated and chrome-plated sheets used in metal packaging. The nitrogen content is usually above 0.006% by weight. However, during continuous annealing in a nitrogen-hydrogen mixed atmosphere, the nitrogen content of such high nitrogen steel will decrease, which is called denitrification. That is, the nitrogen content in the steel after annealing is lower than before annealing. This often leads to fluctuations in the nitrogen content of the finished product, sometimes exceeding 0.001% by weight. At the same time, there are often differences in grain size, resulting in fluctuations in the mechanical properties of the finished product. Summary of the Invention

[0003] This application provides a continuous annealing method for cold-rolled steel sheets to solve the technical problem of large fluctuations in nitrogen content during the continuous annealing process of existing high-nitrogen cold-rolled steel sheets.

[0004] In a first aspect, this application provides a continuous annealing method for cold-rolled steel sheets, the method comprising:

[0005] A cold-hardened sheet with a predetermined chemical composition is subjected to continuous annealing, and the composition of the annealing atmosphere is controlled; wherein, the continuous annealing includes:

[0006] The cold-hardened plate is heated and then homogenized, and the heating temperature and homogenization temperature are set according to the annealing time.

[0007] Optionally, setting the heating temperature and the homogenization temperature based on the annealing time includes: if the annealing time is 60-120s, then the heating temperature and the homogenization temperature are 650-670℃.

[0008] Optionally, setting the heating temperature and the homogenization temperature based on the annealing time includes: if the annealing time is 40-59 seconds, then the heating temperature and the homogenization temperature are 670-690°C.

[0009] Optionally, setting the heating temperature and the homogenization temperature based on the annealing time includes: if the annealing time is 30-39 seconds, then the heating temperature and the homogenization temperature are 690-710°C.

[0010] Optionally, the annealing atmosphere composition includes hydrogen and nitrogen; wherein the hydrogen content is 3-6% by weight.

[0011] Optionally, the specified chemical composition includes: N, Al, Nb, V, Ti, and B; wherein,

[0012] The N content is 0.008–0.020% by weight, the Al content is ≤0.05% by weight, and the total content of Nb, V, Ti, and B is ≤0.01% by weight.

[0013] Optionally, the process of heating the cold-hardened plate, then homogenizing it, and setting the annealing heating temperature and homogenizing temperature according to the annealing time, further includes: rapidly cooling the homogenized cold-hardened plate under a first set temperature.

[0014] Optionally, the first set temperature is 380–420°C.

[0015] Optionally, the rapid cooling of the heated and hardened plate further includes aging the rapidly cooled plate at a second set temperature.

[0016] Optionally, the second set temperature is 320–360°C.

[0017] The technical solutions provided in this application have the following advantages compared with the prior art:

[0018] The continuous annealing method for the cold-hardened steel sheet provided in this application embodiment addresses the issue of nitrogen-based solid solution strengthening to enhance product performance. Therefore, ensuring the stability of the nitrogen content in the finished product is crucial. Simultaneously, controlling the grain size and minimizing fluctuations in grain size are essential for achieving stable microstructure and properties in the final product. To address the issue of coordinated control of denitrification and grain size during continuous annealing in a nitrogen-hydrogen mixed atmosphere for high-nitrogen cold-hardened steel sheets, a control strategy matching different annealing times with different annealing temperatures is employed. Based on the thermodynamic and kinetic conditions of the denitrification process, a lower annealing temperature is used for longer annealing times to avoid increased denitrification while ensuring complete recrystallization and the formation of a suitable grain size. Conversely, a higher annealing temperature is used for shorter annealing times to avoid significant differences in denitrification between short and long annealing times. Considering the impact of heating rate on recrystallization temperature, a higher annealing temperature is used to form a suitable grain size. This achieves stable control of denitrification amount and grain size under different annealing time conditions, ultimately ensuring stable microstructure and properties of the finished product. The high-nitrogen continuous annealing plate produced by this method can achieve nitrogen removal control of ±0.0002% by weight during the annealing process, while grain size fluctuation can be controlled at ±0.5 grade. Attached Figure Description

[0019] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0020] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 A schematic flowchart of a continuous annealing method for a cold-rolled steel sheet provided in an embodiment of this application;

[0022] Figure 2 The temperature change curve in a continuous annealing method for a cold-hardened sheet provided in this application embodiment; wherein, 1-heating temperature, 2-soaking temperature, 3-rapid cooling temperature, 4-aging temperature. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0024] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0025] In this application, unless otherwise stated, directional terms such as "upper" and "lower" specifically refer to the drawing directions in the accompanying drawings. Furthermore, in the description of this application, terms such as "comprising" and "including" mean "including but not limited to." In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this document, "and / or" describes the relationship between related objects, indicating that three relationships can exist; for example, A and / or B can represent: A alone, A and B simultaneously, or B alone. A and B can be singular or plural. In this document, "at least one" means one or more, and "more than one" means two or more. "At least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c" or "at least one of a, b, and c" can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be a single or multiple.

[0026] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0027] Firstly, this application provides a continuous annealing method for cold-rolled steel sheets; please refer to [link to relevant documentation]. Figure 1 The method includes:

[0028] S1. Continuously annealing a cold-hardened sheet with a predetermined chemical composition, and controlling the composition of the annealing atmosphere; wherein, the continuous annealing includes:

[0029] The cold-hardened plate is heated and then homogenized, and the heating temperature and homogenization temperature are set according to the annealing time.

[0030] The continuous annealing method for the cold-hardened steel sheet provided in this application embodiment mainly improves product performance through nitrogen solid solution strengthening. Therefore, ensuring the stability of the nitrogen content in the finished product is crucial. Simultaneously, it is also necessary to control the grain size and minimize fluctuations in grain size to achieve stable microstructure and properties in the final product. Therefore, to address the issue of coordinated control of denitrification and grain size during continuous annealing of high-nitrogen cold-hardened steel sheets in a nitrogen-hydrogen mixed atmosphere, a control strategy of matching different annealing times with different annealing temperatures is adopted. Based on the thermodynamic and kinetic conditions of the denitrification process, a lower annealing temperature is used for longer annealing times to avoid increased denitrification during prolonged annealing while ensuring complete recrystallization and the formation of a suitable grain size. A higher annealing temperature is used for shorter annealing times to avoid significant differences in denitrification between short and long annealing times. Considering the effect of heating rate on recrystallization temperature, a higher annealing temperature is used to form a microstructure with a suitable grain size. (See also...) Figure 2 This reveals the temperature variations during the annealing process. This allows for stable control of denitrification and grain size under different annealing times, ultimately ensuring stable microstructure and properties of the finished product. High-nitrogen continuously annealed plates produced using this method can achieve denitrification control of ±0.0002 wt% and grain size fluctuation control of ±0.5 grade during the annealing process.

[0031] In some embodiments, setting the heating temperature and the homogenization temperature based on the annealing time includes: if the annealing time is 60 to 120 seconds, then the heating temperature and the homogenization temperature are 650 to 670°C.

[0032] In some embodiments, setting the heating temperature and the homogenization temperature based on the annealing time includes: if the annealing time is 40 to 59 seconds, then the heating temperature and the homogenization temperature are 670 to 690°C.

[0033] In some embodiments, setting the heating temperature and the homogenization temperature based on the annealing time includes: if the annealing time is 30 to 39 seconds, then the heating temperature and the homogenization temperature are 690 to 710°C.

[0034] In this embodiment, a control strategy of matching different annealing times with different annealing temperatures is adopted. Specifically, a lower annealing temperature is matched when the continuous annealing speed is low and the continuous annealing time is long; a higher annealing temperature is matched when the continuous annealing speed is high and the continuous annealing time is short. This achieves stable control of denitrification and grain size, reducing fluctuations in the mechanical properties of the finished product. Under different annealing time conditions, an excessively low annealing temperature is, to some extent, detrimental to the complete recrystallization of the microstructure; an excessively high annealing temperature, to some extent, makes the microstructure prone to significant coarsening and increases the amount of denitrification. Specifically, if the annealing time is 60s, 80s, 100s, 120s, etc., then the heating temperature and the homogenization temperature during annealing are 650℃, 660℃, 670℃, etc.; if the annealing time is 40s, 42s, 44s, 46s, 48s, 49s, etc., then the heating temperature and the homogenization temperature during annealing are 670℃, 680℃, 690℃, etc.; if the annealing time is 30s, 32s, 34s, 36s, 38s, 39s, etc., then the heating temperature and the homogenization temperature during annealing are 690℃, 700℃, 710℃, etc.

[0035] In some embodiments, the annealing atmosphere comprises hydrogen and nitrogen; wherein the hydrogen content is 3-6% by weight.

[0036] The positive effects of controlling the hydrogen content in the nitrogen-hydrogen mixture to 3–6% by weight include: achieving high surface quality in the strip steel under low-cost atmospheric conditions and ensuring that the rapid cooling rate meets the strip steel's cooling requirements. If the hydrogen content is too high, it will lead to increased costs to some extent; if the hydrogen content is too low, oxidation may easily occur to some extent. Specifically, the hydrogen content can be 3%, 4%, 5%, 6%, etc.

[0037] In some embodiments, the specified chemical composition includes: N, Al, Nb, V, Ti, and B; wherein,

[0038] The N content is 0.008–0.020% by weight, the Al content is ≤0.05% by weight, and the total content of Nb, V, Ti, and B is ≤0.01% by weight.

[0039] This method is based on the above chemical composition. The specific steps of this method can be referred to the above embodiments. In addition, the cold-rolled rigid sheet meets the technical requirements of GB / T 2520 and GB / T 24180 for the content of other elements.

[0040] In some embodiments, the process of heating the cold-hardened plate, followed by homogenization, and setting the annealing heating temperature and homogenization temperature according to the annealing time, further includes: rapidly cooling the homogenized cold-hardened plate under a first set temperature.

[0041] In some embodiments, the first set temperature is 380–420°C.

[0042] The "first set temperature" refers to the rapid cooling temperature. Controlling the rapid cooling temperature to 380–420°C has the positive effect of promoting the fine, dispersed precipitation of interstitial atoms. If the rapid cooling temperature is too high, it may lead to excessively coarse precipitated carbides; if the rapid cooling temperature is too low, it may hinder carbide precipitation. Specifically, the rapid cooling temperature can be 380°C, 390°C, 400°C, 410°C, 420°C, etc.

[0043] In some embodiments, the rapid cooling of the homogenized cold-hardened plate is further included by aging the rapidly cooled cold-hardened plate at a second set temperature.

[0044] In some embodiments, the second set temperature is 320–360°C.

[0045] The "second set temperature" refers to the aging temperature. Controlling the aging temperature to 320–360℃ has the following positive effects: establishing a reasonable temperature gradient between the rapid cooling temperature and the aging temperature facilitates the precipitation of interstitial atoms, improving the stability of the strip steel during high-speed operation. If the aging temperature is too high, the small temperature difference between the rapid cooling and aging temperatures may hinder carbide precipitation. If the aging temperature is too low, the large temperature difference between it and the rapid cooling temperature may cause warping. Specifically, the rapid cooling temperature can be 320℃, 330℃, 340℃, 350℃, 360℃, etc.

[0046] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards. If there is no corresponding national standard, then general international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0047] Example 1

[0048] A 0.22mm thick chilled steel sheet with an N content of 0.0099%, an Al content of 0.04%, and an Nb+V+Ti+B content of 0.007% was obtained using conventional methods. The strip then underwent degreasing, preheating, heating, homogenization, rapid cooling, aging, final cooling, and leveling to obtain continuously annealed steel coils or plates. During continuous annealing, the annealing time was 100 seconds, the annealing heating and homogenization temperatures were 660℃, the rapid cooling temperature was 405℃, and the aging temperature was 350℃.

[0049] Example 2

[0050] The difference from Example 1 is that the annealing time during the continuous annealing process is 52s, the annealing heating temperature and the soaking temperature are 675℃, the rapid cooling temperature is 385℃, and the aging temperature is 340℃.

[0051] Example 3

[0052] The difference from Example 1 is that the annealing time during the continuous annealing process is 35s, the annealing heating temperature and the soaking temperature are 699℃, the rapid cooling temperature is 380℃, and the aging temperature is 338℃.

[0053] Example 4

[0054] A 0.20mm thick cold-rolled steel sheet with an N content of 0.0167%, an Al content of 0.013%, and an Nb+V+Ti+B content of 0.005% was obtained using conventional methods. The strip then underwent degreasing, preheating, heating, homogenization, rapid cooling, aging, final cooling, and secondary cold rolling to obtain continuously annealed steel coils or sheets. During continuous annealing, the annealing time was 65 seconds, the annealing heating and homogenization temperatures were 666℃, the rapid cooling temperature was 400℃, and the aging temperature was 352℃.

[0055] Example 5

[0056] The difference from Example 4 is that the annealing time during the continuous annealing process is 45s, the annealing heating temperature and the soaking temperature are 680℃, the rapid cooling temperature is 383℃, and the aging temperature is 330℃.

[0057] Example 6

[0058] The difference from Example 4 is that the annealing time during the continuous annealing process is 38s, the annealing heating temperature and the soaking temperature are 692℃, the rapid cooling temperature is 388℃, and the aging temperature is 327℃.

[0059] Comparative Example 1

[0060] The difference from Example 4 is that the nitrogen content is 0.0255%.

[0061] Comparative Example 2

[0062] The difference from Example 4 is that the annealing heating temperature and the homogenization temperature during the continuous annealing process are 710°C.

[0063] Comparative Example 3

[0064] The difference from Example 4 is that the annealing time during the continuous annealing process is 170 seconds.

[0065] Table 1 Results of continuous annealing performance of cold-rolled steel sheets

[0066]

[0067]

[0068] In Examples 1-3, the denitrification amount fluctuation under different annealing processes was 0.0002 wt%, and the grain size fluctuation was 0.5 grade. In Examples 4-6, the denitrification amount fluctuation under different annealing processes was 0.0003 wt%, and the grain size fluctuation was 0 grade. In Comparative Examples 1-3, the denitrification amount fluctuation under different annealing processes was 0.0025 wt%, and the grain size fluctuation was 1.5 grade. The embodiments of this application employ a control method that matches different annealing times with different annealing temperatures to achieve denitrification amount fluctuation control within ±0.0002 wt% and grain size fluctuation control within ±0.5 grade under different annealing time conditions. This results in high-nitrogen continuously annealed plates with stable microstructure and properties, effectively reducing the performance fluctuations of the finished product caused by large fluctuations in denitrification amount and changes in microstructure and grain size, thus meeting the requirements of high-speed metal packaging processing.

[0069] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A continuous annealing method for high-nitrogen cold-hardened steel sheets, characterized in that, The method includes: A cold-hardened sheet with a predetermined chemical composition is subjected to continuous annealing, and the composition of the annealing atmosphere is controlled; wherein, the continuous annealing includes: The cold-hardened plate is heated, then homogenized, and the heating temperature and homogenization temperature are set according to the annealing time. The heated plate is then rapidly cooled, with the rapid cooling temperature controlled at 380~420℃. The rapidly cooled cold-hardened sheet is then aged, with the aging temperature controlled at 320~360℃. The annealing atmosphere comprises hydrogen and nitrogen; wherein the hydrogen content is 3-6% by weight. The specified chemical composition includes: N, Al, Nb, V, Ti, and B; the content of N is 0.008~0.020% by weight, the content of Al is ≤0.05% by weight, and the total content of Nb, V, Ti, and B is ≤0.01% by weight. The step of setting the heating temperature and the homogenization temperature based on the annealing time includes: If the annealing time is 60~120s, then the heating temperature and the homogenization temperature are 650~670℃; If the annealing time is 40~59s, then the heating temperature and the homogenization temperature are 670~690℃; If the annealing time is 30~39s, then the heating temperature and the homogenization temperature are 690~710℃.

Images