A method for simulating a continuous annealing process of ferritic stainless steel sheet equivalent

Abstract

The application discloses an experimental method for equivalent simulation of a continuous annealing process of ferrite stainless steel plate, and belongs to the field of stainless steel production and manufacturing. A box furnace is selected to perform annealing treatment on the stainless steel plate, the furnace temperature of the box furnace is set to be consistent with the plate temperature at the outlet of a continuous annealing furnace of a cold rolling mill, the annealing time t of the box furnace is t=r*d*L / TV, wherein r is a coefficient related to the thickness of the steel plate, the furnace length L of the continuous annealing furnace is L=preheating section+heating section+soaking section, and TV=d*continuous annealing line speed of the steel plate. The method can equivalently simulate the heat treatment system of a laboratory and the continuous annealing process of the cold rolling mill, the microstructure and mechanical properties of the ferrite stainless steel plate obtained are consistent, and in the development of new stainless steel products, the application of new production lines or the optimization and improvement of processes, the experimental efficiency can be greatly improved, and the cost of on-site experiments of the cold rolling mill can be reduced.

Description

Technical Field

[0001] This invention relates to the field of steel research and manufacturing, and in particular to a method for equivalently simulating a continuous annealing process for ferritic stainless steel sheets. Background Technology

[0002] Ferritic stainless steel has a body-centered cubic structure and features high strength, low tendency to work hardening, high thermal conductivity, low coefficient of thermal expansion, good oxidation resistance, and excellent resistance to stress corrosion. It is widely used in various aspects of daily life, including household appliances, building roofs, automotive exhaust systems, heat exchange pipes, and pressure vessels. Furthermore, ferritic stainless steel contains little or no nickel, making it a resource-saving type of stainless steel with low and relatively stable prices.

[0003] The properties of ferritic stainless steel are closely related to its microstructure; a good microstructure ensures excellent mechanical and corrosion resistance properties. The most important process affecting the microstructure is the finished product annealing process.

[0004] In actual production, ferritic stainless steel sheets are mostly delivered in coil form. To ensure the uniformity of the microstructure and properties of the entire coil, cold rolling mills use continuous annealing furnaces for final heat treatment, i.e., continuous annealing process. A continuous annealing furnace is generally divided into a preheating section, a heating section, and a soaking section. The furnace is not sealed; after the coil is uncoiled, the strip passes through the annealing furnace continuously at a certain speed without pausing. After exiting the furnace, it is directly cooled, pickled, and coiled. The key control parameters for the continuous annealing process are plate temperature and TV value (i.e., steel plate thickness × steel plate linear speed).

[0005] In the laboratory, a box furnace is used for heat treatment experiments, where the samples remain stationary during heating. Its advantage lies in its ability to rapidly and flexibly conduct experiments with small samples using different processes, thereby efficiently determining the appropriate annealing process.

[0006] When developing new products, applying new production lines, or optimizing and improving processes, box furnaces are first selected to conduct heat treatment experiments with different processes. Suitable process parameters are then determined through microscopic observation of the microstructure, and these parameters are applied to actual production. However, due to the completely different equipment structures in laboratories and cold rolling mills, how to match the processes between the two is a critical issue that urgently needs to be addressed.

[0007] In summary, there is a need for a method that equivalences laboratory annealing processes with continuous annealing processes in cold rolling mills. To simulate the continuous annealing process of ferritic stainless steel in a cold rolling mill in the laboratory, this invention provides a method that equivalences the two. Using this method, stainless steel sheets are annealed in the laboratory, and the resulting stainless steel sheets exhibit the same microstructure and mechanical properties as those obtained through continuous annealing in a cold rolling mill. This method can improve experimental efficiency and significantly reduce the cost of experiments in cold rolling mills when developing new stainless steel products, applying them to new production lines, or optimizing processes. Summary of the Invention

[0008] The purpose of this invention is to address the above-mentioned problems by providing a method for equivalently simulating the continuous annealing process of ferritic stainless steel sheets.

[0009] The objective of this invention is achieved as follows: a method for equivalently simulating the continuous annealing process of ferritic stainless steel plates, wherein a laboratory box furnace is selected for annealing the ferritic stainless steel plates, the furnace temperature of the box furnace is set to be consistent with the outlet plate temperature of the continuous annealing furnace in the cold rolling mill, the holding time of the box furnace is t = r × steel plate thickness d × continuous annealing furnace length L / TV, where r is a coefficient related to the steel plate thickness, the continuous annealing furnace length L = preheating section + heating section + soaking section, and TV = steel plate thickness × continuous annealing line speed.

[0010] When the steel plate thickness d < 1.0 mm, the coefficient r is 0.8 to 0.9; when the steel plate thickness 1.0 mm ≤ d < 3.0 mm, the coefficient r is 1 to 1.2; when the steel plate thickness d ≥ 3.0 mm, the coefficient r is 1.5 to 1.7.

[0011] The beneficial effects of this invention are: this method solves the problem of matching the annealing processes of the laboratory and the cold rolling mill, ensuring the consistency of the experimental material and the commercial material in terms of microstructure and properties. When developing new stainless steel products, applying them to new production lines, or optimizing and improving processes, it can significantly improve experimental efficiency and reduce the cost of experiments in the cold rolling mill. Attached Figure Description

[0012] The present invention will now be further described with reference to the accompanying drawings.

[0013] Figure 1 This is a microstructure diagram of the ferritic stainless steel sheet after laboratory annealing in Example 1.

[0014] Figure 2 This is a microstructure diagram of the ferritic stainless steel sheet after annealing in the cold rolling mill in Example 1.

[0015] Figure 3 This is a microstructure diagram of the ferritic stainless steel sheet before process optimization in the cold rolling mill in Example 2.

[0016] Figure 4 This is a microstructure diagram of the laboratory ferritic stainless steel sheet used in Example 2.

[0017] Figure 5 This is a microstructure diagram of the ferritic stainless steel sheet after process optimization in the cold rolling mill in Example 2.

[0018] Figure 6 This is a microstructure diagram of the ferritic stainless steel sheet before process optimization in the cold rolling mill in Example 3.

[0019] Figure 7 This is a microstructure diagram of the laboratory ferritic stainless steel sheet used in Example 3.

[0020] Figure 8 This is a microstructure diagram of the ferritic stainless steel sheet after process optimization in the cold rolling mill in Example 3.

[0021] Figure 9 This is a microstructure diagram of the laboratory ferritic stainless steel sheet used in Example 4.

[0022] Figure 10 This is a microstructure diagram of the ferritic stainless steel sheet after annealing in the cold rolling mill in Example 4. Detailed Implementation

[0023] This invention provides a method for equivalently simulating the continuous annealing process of a stainless steel cold rolling mill in a laboratory. The technical solution is carried out according to the following steps: a box furnace is selected in the laboratory for annealing stainless steel plates. The furnace temperature of the box furnace is set to be consistent with the outlet plate temperature of the continuous annealing furnace. The holding time of the box furnace is t = r × steel plate thickness × continuous annealing furnace length L / TV, where r is a coefficient related to the steel plate thickness, the continuous annealing furnace length L = preheating section + heating section + soaking section, and TV = steel plate thickness × continuous annealing speed of the steel plate.

[0024] When the steel plate thickness d < 1.0 mm, the coefficient r is 0.8 to 0.9; when the steel plate thickness 1.0 mm ≤ d < 3.0 mm, the coefficient r is 1 to 1.2; and when the steel plate thickness d ≥ 3.0 mm, the coefficient r is 1.5 to 1.7.

[0025] This method can make the heat treatment regime in the laboratory equivalent to the process in the cold rolling mill, and the resulting stainless steel sheet has the same microstructure, mechanical properties and corrosion properties. When developing new stainless steel products, applying them to new production lines or optimizing and improving processes, it can improve experimental efficiency and significantly reduce the cost of experiments in the cold rolling mill.

[0026] The experimental method for the equivalent simulated ferritic stainless steel sheet continuous annealing process provided by the present invention is described in detail below with reference to the embodiments. However, the specific implementation of the present invention is not limited to the following embodiments. Example 1

[0027] This embodiment describes laboratory and cold rolling mill annealing of ferritic stainless steel sheets with a thickness of 1.5 mm.

[0028] Its chemical composition by mass percentage is as follows: C: 0.009%; N: 0.008%; Si: 0.34%; Mn: 0.15%; P: 0.015%; S: 0.001%; ​​Cr: 18.11%; Ni: 0.08%; Nb: 0.41%; Ti: 0.18%. The remainder is Fe and unavoidable impurities.

[0029] When performing annealing in the laboratory, the furnace temperature was set to 1040℃ and the holding time was 1.5min. Figure 1 The microstructure of the steel plate after laboratory annealing.

[0030] According to the method provided by this invention, a continuous annealing process is adopted in a cold rolling mill. The length L of the continuous annealing furnace is 45 meters, including a 10-meter preheating section and a 35-meter heating section plus a soaking section. The outlet plate temperature is controlled at 1040℃. According to the formula: box furnace holding time t = r × steel plate thickness × continuous annealing furnace length L / TV = 1 × 1.5 × 45 / TV = 1.5 min, where r is taken as 1, and the TV value is 45. Figure 2 The microstructure of the steel plate after annealing in the cold rolling mill.

[0031] Table 1 shows the mechanical properties of steel plates after annealing in the cold rolling mill and laboratory.

[0032]

[0033] Example 2

[0034] This embodiment describes laboratory and cold rolling mill annealing of ferritic stainless steel sheets with a thickness of 3.0 mm.

[0035] Its chemical composition by mass percentage is as follows: C: 0.008%; N: 0.010%; Si: 0.19%; Mn: 0.22%; P: 0.012%; S: 0.001%; ​​Cr: 17.11%; Ni: 0.09%; Nb: 0.15%; Ti: 0.17%. The remainder is Fe and unavoidable impurities.

[0036] The cold rolling mill uses a continuous annealing process. The continuous annealing furnace is 90 meters long (L), with a 20-meter preheating section and a 70-meter heating and soaking section. The outlet plate temperature is controlled at 1000℃, and the TV value is 45 when the plate passes through the line. Figure 3 This is the microstructure of a steel sheet after annealing in a cold rolling mill. Under this process, the steel sheet has coarse grains, requiring process improvement.

[0037] According to the method provided by the present invention, the laboratory annealing process equivalent to the continuous annealing process in a cold rolling mill is as follows: furnace temperature 1000℃, box furnace holding time t = r × steel plate thickness × continuous annealing furnace length L / TV = 1.5 × 3 × 90 / 45 = 9min, where r is taken as 1.5.

[0038] The annealing process optimization was first conducted in the laboratory. When the furnace temperature was 980℃ and the holding time was 6.75 min, the grain size was considered suitable. Figure 4 As shown.

[0039] According to the method provided by the present invention, the laboratory annealing process is converted into the cold rolling mill annealing process, and the outlet plate temperature is changed to 980℃. According to the formula: box furnace holding time t = r × steel plate thickness × continuous annealing furnace length L / TV = 1.5 × 3 × 90 / TV = 6.75min, r is taken as 1, and the TV value is 60. Figure 5 The microstructure of the steel plate after annealing in the cold rolling mill is consistent with the laboratory results.

[0040] Table 2 shows the mechanical properties of the steel plates after annealing in the cold rolling mill and the laboratory.

[0041]

[0042] Example 3

[0043] This embodiment describes laboratory and cold rolling mill annealing of ferritic stainless steel sheets with a thickness of 0.8 mm.

[0044] Its chemical composition by mass percentage is as follows: C: 0.008%; N: 0.010%; Si: 0.35%; Mn: 0.19%; P: 0.012%; S: 0.001%; ​​Cr: 17.91%; Ni: 0.07%; Mo: 2.01%; Nb: 0.20%. The remainder is Fe and unavoidable impurities.

[0045] The cold rolling mill uses a continuous annealing process. The continuous annealing furnace is 90 meters long (L), with a 20-meter preheating section and a 70-meter heating and soaking section. The outlet plate temperature is controlled at 1020℃, and the TV value is 45 when the plate passes through the line. Figure 6 This is the microstructure of a steel sheet after annealing in a cold rolling mill. Under this process, the recrystallization of the steel sheet is insufficient, requiring process improvement.

[0046] According to the method provided by the present invention, the laboratory annealing process equivalent to the continuous annealing process in a cold rolling mill is as follows: furnace temperature 1020℃, box furnace holding time t = r × steel plate thickness × continuous annealing furnace length L / TV = 0.8 × 0.8 × 90 / 45 = 1.28 min, where r is 0.8.

[0047] The improvement of the annealing process was first carried out in the laboratory. When the furnace temperature was 1020℃ and the holding time was 2 minutes, the grain size was relatively suitable. Figure 7 As shown.

[0048] According to the method provided by the present invention, the laboratory annealing process is converted into the cold rolling mill annealing process, and the outlet plate temperature is changed to 1020℃. According to the formula: box furnace holding time t = r × steel plate thickness × continuous annealing furnace length L / TV = 0.8 × 0.8 × 90 / TV = 2min, r is taken as 0.8, and the TV value is 28.8. Figure 8 The microstructure of the steel plate after annealing in the cold rolling mill is consistent with the laboratory results.

[0049] Table 3 shows the mechanical properties of the steel plates after annealing in the cold rolling mill and the laboratory.

[0050]

[0051] Example 4

[0052] This embodiment describes laboratory and cold rolling mill annealing of ferritic stainless steel sheets with a thickness of 8.0 mm.

[0053] Its chemical composition by mass percentage is as follows: C: 0.008%; N: 0.009%; Si: 0.11%; Mn: 0.21%; P: 0.014%; S: 0.001%; ​​Cr: 17.84%; Ni: 0.08%; Nb: 0.43%; Ti: 0.12%. The remainder is Fe and unavoidable impurities.

[0054] When performing annealing in the laboratory, the furnace temperature was set to 980℃ and the annealing time was 10 minutes. Figure 9 The microstructure of the steel plate after laboratory annealing.

[0055] According to the method provided by this invention, a continuous annealing process is adopted in a cold rolling mill. The length L of the continuous annealing furnace is 140 meters, including a 30-meter preheating section and a 110-meter soaking section. The outlet plate temperature is controlled at 980℃. According to the formula: the holding time t of the box furnace = r × steel plate thickness × continuous annealing furnace length L / TV = 1.6 × 8 × 140 / TV = 10 min, where r is taken as 1.6, and the TV value is 180. Figure 10 The microstructure of the steel plate after annealing in the cold rolling mill.

[0056] Table 4 shows the mechanical properties of the steel plates after annealing in the cold rolling mill and the laboratory.

[0057]

[0058] The above description is only a specific embodiment of the present invention, but the structural features protected by the present invention are not limited thereto. Any changes or modifications made by those skilled in the art within the scope of the present invention are covered by the patent scope of the present invention.

Claims

1. A method for equivalently simulating a continuous annealing process for ferritic stainless steel sheets, characterized in that: A laboratory box furnace was selected for annealing ferritic stainless steel plates. The furnace temperature was set to be consistent with the outlet temperature of the continuous annealing furnace in the cold rolling mill. The holding time in the box furnace was t = r × steel plate thickness d × continuous annealing furnace length L / TV, where r is a coefficient related to the steel plate thickness, the continuous annealing furnace length L = preheating section + heating section + soaking section, and TV = steel plate thickness × continuous annealing line speed. When the steel plate thickness d < 1.0 mm, the coefficient r is 0.8 to 0.9; when the steel plate thickness 1.0 mm ≤ d < 3.0 mm, the coefficient r is 1 to 1.2; when the steel plate thickness d ≥ 3.0 mm, the coefficient r is 1.5 to 1.7.

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