Control method for reducing annealing marks of ferritic stainless steel bell-type furnace

Abstract

The invention discloses a control method for reducing annealing marks of ferritic stainless steel in a bell-type furnace. The technical problem that the annealing marks appear on the edge of strip steel is solved. The control method comprises the following steps: S1, adding protective gases H2, N2 and Ar into a bell-type furnace; s2, the coil type of the stainless steel coil is controlled; s3, the annealing heat preservation temperature and heat preservation time of the stainless steel coil are controlled; and S4, the tapping temperature of the stainless steel coil is controlled, and in S1, the ratio of protective gas H2 to N2 to Ar is (1-5%): (45-55%): (40-50%). The method can effectively solve the problem that annealing marks appear on the edge of the strip steel, reduce the process cost and improve the production efficiency.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy, and in particular relates to a control method for reducing ferritic stainless steel bell-type furnace annealing marks. Background Art

[0002] Ferritic stainless steel, as a stainless steel material with excellent corrosion resistance and mechanical properties, is widely used in automobiles, home appliances, construction and other fields.

[0003] During the production of ferritic stainless steel, due to various factors such as the bell-type furnace protective gas, heating temperature, holding time, and coil shape, the edges of the strip will produce varying degrees of annealing marks, which require secondary rewashing to reduce. This not only increases process costs, but also affects production efficiency and needs to be improved. Summary of the Invention

[0004] In order to solve all or part of the above problems, the purpose of the present invention is to provide a control method for reducing annealing marks of ferritic stainless steel in a bell-type furnace, which can effectively improve the problem of annealing marks on the edges of the strip, reduce process costs, and improve production efficiency.

[0005] The present invention provides a control method for reducing ferritic stainless steel bell-type furnace annealing marks, comprising the following steps:

[0006] S1, adding protective gases H2, N2 and Ar into the bell-type furnace;

[0007] S2, controls the coil shape of stainless steel coil;

[0008] S3, controlling the annealing holding temperature and holding time of the stainless steel coil;

[0009] S4, controls the temperature of the stainless steel coil out of the furnace;

[0010] Among them, in S1, the protective gas H2:N2:Ar=(1-5%):(45-55%):(40-50%).

[0011] Optionally, in S2, controlling the coil shape of the stainless steel coil includes:

[0012] Plate convexity ≤ 1.2% of steel strip thickness;

[0013] Wedge shape ≤ 1% of the thickness of the steel strip;

[0014] Sickle ≤ 4mm / 2m;

[0015] There is no loose coil in the steel coil;

[0016] Tower shape ≤50mm.

[0017] Optionally, S3 includes:

[0018] S31, controlling the stainless steel coil to be rapidly heated in a bell-type furnace to a recrystallization temperature of 650-750°C and holding the temperature for 2-4 hours;

[0019] S32, control the temperature of the stainless steel coil in the bell-type furnace to rise to the annealing temperature of 820-870℃, and keep it at this temperature for 10-24 hours.

[0020] Optionally, in S32, the stainless steel coil is controlled to be heated to the annealing and holding temperature in the bell-type furnace for 4-6 hours.

[0021] Optionally, if the strip thickness is 2.5 mm ≤ and less than 3.0 mm, the annealing holding temperature is controlled to 850-870° C. and kept warm for 20-24 hours.

[0022] Optionally, if the strip thickness is 3.0 mm ≤ and less than 5.0 mm, the annealing temperature is controlled to be 840-850° C. and kept warm for 16-18 hours.

[0023] Optionally, if the strip thickness is ≥5.0 mm, the annealing holding temperature is controlled to 820-830° C. and kept warm for 10-12 hours.

[0024] Optionally, in S4, the temperature of the stainless steel coil out of the furnace is controlled to be 260-300°C.

[0025] As can be seen from the above technical solution, the control method for reducing ferritic stainless steel bell-type furnace annealing marks provided by the present invention has the following advantages:

[0026] This control method can effectively improve the problem of annealing marks on the edge of the strip, which can not only reduce process costs but also improve production efficiency.

[0027] Other features and advantages of the present invention will be set forth in the description that follows. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings are used to provide a further understanding of the technical solution of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the technical solution of the present invention and do not constitute a limitation to the technical solution of the present invention.

[0029] Figure 1 Schematic diagram of a flow chart of an embodiment of the present invention;

[0030] Figure 2 Schematic diagram of annealing holding temperature and holding time in an embodiment of the present invention. DETAILED DESCRIPTION

[0031] To make the purpose, technical solutions and advantages of the present invention more clearly understood, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that, in the absence of conflict, the embodiments of the present invention and the features therein can be combined with each other in any manner.

[0032] After analyzing the defects of annealing marks on the edge of the strip, it is found that the color difference defects on the surface of ferritic stainless steel are mainly caused by uneven oxidation of the strip surface. Therefore, to solve the problem of annealing marks on the strip surface, the main thing is to solve the cause of uneven oxidation of the strip surface.

[0033] like Figure 1 、 Figure 2 FIG. 1 is an embodiment of the present invention, which discloses a control method for reducing ferritic stainless steel bell-type furnace annealing marks, comprising the following steps:

[0034] S1, adding protective gases H2, N2 and Ar into the bell furnace.

[0035] S2, controls the coil shape of stainless steel coil.

[0036] S3, controls the annealing holding temperature and holding time of the stainless steel coil.

[0037] S4, controls the temperature of the stainless steel coil out of the furnace.

[0038] During stainless steel production, hydrogen penetrates the oxide film on the strip surface, causing a reduction reaction and damage to the Cr2O3 oxide film. Locally, FeO / Fe3O4 mixed oxides form in the damaged areas, resulting in color differences. Therefore, adding N2 and Ar to the H2 shielding gas in the bell-type furnace inhibits hydrogen permeation. Furthermore, in S1, the shielding gas ratio is H2:N2:Ar = (1-5%):(45-55%):(40-50%).

[0039] If the stainless steel coil has a poor coil shape, with loose coils or overflowing coils on the inner and outer coils, the loose coils or overflowing coils will heat up faster in the bell-type furnace, taking longer to oxidize than other parts, resulting in uneven oxidation at the head and tail. Therefore, in S2, the coil shape of the stainless steel coil is controlled as shown in Table 1.

[0040] Table 1 Coil shape control requirements for stainless steel coils

[0041]

[0042]

[0043] S3 includes:

[0044] S31, controlling the stainless steel coil to be rapidly heated in a bell-type furnace to a recrystallization temperature of 650-750°C and holding the temperature for 2-4 hours;

[0045] S32, control the stainless steel coil to slowly heat up to the annealing temperature of 820-870℃ in the bell-type furnace over 4-6 hours, and keep it at this temperature for 10-24 hours.

[0046] like Figure 2 As shown in the figure, the temperature difference between the inner and outer coils of the stainless steel coil is too large during the heating process in the bell-type furnace. Therefore, the stainless steel coil is quickly heated to the recrystallization temperature of 650-750℃ in the bell-type furnace and kept at this temperature for 2-4 hours. Then, the temperature is slowly raised to the annealing temperature of 820-870℃ over 4-6 hours and kept at this temperature for 10-24 hours to make the inner and outer temperatures of the stainless steel coil uniform and prevent uneven oxidation of the strip due to uneven temperature.

[0047] Stainless steel coils require high annealing temperatures and long holding times. Excessively high annealing temperatures can exacerbate surface oxidation and phase transformation, leading to annealing marks. Therefore, annealing temperatures and holding times vary for different thicknesses of strip, as shown in Table 2.

[0048] Table 2 Strip thickness, annealing holding temperature and holding time control requirements

[0049] thickness Annealing holding temperature Holding time 2.5mm≤Strip thickness<3.0mm 850-870℃ 20-24h 3.0mm≤Strip thickness<5.0mm 840-850℃ 16-18h Strip thickness ≥5.0mm 820-830℃ 10-12h

[0050] The temperature of the stainless steel coil out of the furnace is high, and the strip will be oxidized again after being taken out of the furnace. Therefore, in S5, the temperature of the stainless steel coil out of the furnace is controlled to be 260-300℃.

[0051] The control method for reducing ferritic stainless steel bell-type annealing marks in this embodiment can effectively reduce the occurrence of ferritic stainless steel bell-type annealing marks, making the strip surface color uniform and meeting user requirements. The ferritic stainless steel bell-type annealing marks can be reduced from 8% to below 2%.

[0052] In order to more clearly illustrate the present application, the specific embodiments are as follows:

[0053] Example 1

[0054] Steel type: SUS430 hot rolled thickness: 3.0mm

[0055] S1, during the bell-type furnace annealing process, the protective gas ratio is H2:N2:Ar=3%:50%:47%.

[0056] S2, coil shape control is:

[0057] Roll-type projects Control requirements Plate convexity 0.9% of strip thickness Wedge 0.6% of strip thickness Sickle 3mm / 2m Loose roll none Tower 15mm

[0058] S3, the stainless steel coil is rapidly heated to 700℃ in a bell-type furnace and kept at this temperature for 3h.

[0059] S4, slowly heating to annealing temperature of 840°C over 4 hours and keeping the temperature for 16 hours.

[0060] S5, the furnace temperature of stainless steel coil is 280℃.

[0061] Through the above method, the generation of ferritic stainless steel bell furnace annealing marks is effectively reduced, the surface color of the strip is made uniform, and the ferritic stainless steel bell furnace annealing marks are reduced to 1.6%.

[0062] Example 2

[0063] Steel type: SUS430 hot rolled thickness: 5.0mm

[0064] S1, during the bell-type furnace annealing process, the protective gas ratio is H2:N2:Ar=5%:52%:43%.

[0065] S2, coil shape control is:

[0066]

[0067]

[0068] S3, the stainless steel coil is rapidly heated to 720℃ in a bell-type furnace and kept at this temperature for 2h.

[0069] S4, slowly raising the temperature to the annealing temperature of 850°C over 5 hours and keeping the temperature for 20 hours.

[0070] S5, the furnace temperature of stainless steel coil is 300℃.

[0071] Through the above method, the generation of ferritic stainless steel bell furnace annealing marks is effectively reduced, the surface color of the strip is made uniform, and the ferritic stainless steel bell furnace annealing marks are reduced to 1.2%.

[0072] It should be noted that, unless otherwise specified, the technical or scientific terms used in the present invention should have the common meanings understood by those skilled in the art to which the present invention belongs.

[0073] In addition, the terms "first," "second," etc. are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. In the description of the present invention, "plurality" means more than two, unless otherwise specifically defined.

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and description of the present invention. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. The present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A control method for reducing ferritic stainless steel bell-type furnace annealing marks, characterized in that: The steps include: S1, adding protective gases H2, N2 and Ar into the bell-type furnace; S2, controls the coil shape of stainless steel coil; S3, controlling the annealing holding temperature and holding time of the stainless steel coil; S4, controls the temperature of the stainless steel coil out of the furnace; Among them, in S1, the protective gas H2:N2:Ar=(1-5%):(45-55%):(40-50%).

2. The control method according to claim 1, characterized in that: In S2, the coil shape of stainless steel coils is controlled by: Plate convexity ≤ 1.2% of steel strip thickness; Wedge shape ≤ 1% of the thickness of the steel strip; Sickle ≤ 4mm / 2m; There is no loose coil in the steel coil; Tower shape ≤50mm.

3. The control method according to claim 1, characterized in that S3 include: S31, controlling the stainless steel coil to be rapidly heated in a bell-type furnace to a recrystallization temperature of 650-750°C and holding the temperature for 2-4 hours; S32, control the temperature of the stainless steel coil in the bell-type furnace to rise to the annealing temperature of 820-870℃, and keep it at this temperature for 10-24 hours.

4. The control method according to claim 3, characterized in that: In S32, the stainless steel coil is controlled to be heated to the annealing holding temperature in the bell-type furnace for 4-6 hours.

5. The control method according to claim 3, characterized in that: If the strip thickness is 2.5mm≤<3.0mm, control the annealing holding temperature to 850-870℃ and keep it warm for 20-24h.

6. The control method according to claim 3, characterized in that: If the strip thickness is 3.0mm≤<5.0mm, control the annealing holding temperature to 840-850℃ and keep it warm for 16-18h.

7. The control method according to claim 3, characterized in that: If the strip thickness is ≥5.0mm, control the annealing holding temperature to 820-830℃ and keep it warm for 10-12h.

8. The control method according to claim 1, characterized in that: In S4, the temperature of the stainless steel coil out of the furnace is controlled to be 260-300°C.

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