Cold rolling method for a 20-high rolling mill of super ferritic stainless steel

Abstract

The invention discloses a cold rolling method for a 20-high rolling mill of super ferritic stainless steel, comprising: determining the rolling passes and allocating the rolling deformation rate of each pass according to the raw material thickness specification and the finished product thickness specification, wherein the rolling deformation rate of the first pass is controlled at 5-8%; the starting tension of the first pass is controlled at 125-280 KN, the normal rolling tension is set starting from the second pass, and AFC is enabled; in the first pass and the second pass, constant pressure rolling is carried out at a rolling pressure of 380-400 KN, and after two passes of constant pressure rolling, AGC is enabled to carry out automatic rolling; after rolling starts, uniform acceleration rolling is carried out, the acceleration is controlled at 40-60 m / min, and before rolling ends, uniform deceleration rolling is carried out, the acceleration is controlled at -40 to -60 m / min. By using the cold rolling method for the 20-high rolling mill of super ferritic stainless steel of the invention, the frequency of brittle strip breakage of the super ferritic stainless steel material during rolling is significantly reduced, the stable rolling of the super ferritic stainless steel is realized, and the industrial mass production requirements of the super ferritic stainless steel material are fully met.

Description

Technical Field

[0001] The present invention belongs to the technical field of stainless steel rolling, and more particularly relates to a cold rolling method for a 20-high rolling mill of super ferritic stainless steel. Background Art

[0002] In super ferritic stainless steels such as S44660 and S44735, the chromium alloy content reaches 24% - 30%, and the molybdenum alloy content reaches 3% - 4.5%. Because of its excellent corrosion resistance in many harsh corrosive media, it can replace titanium metal and is mainly used in projects such as coastal power plants and seawater desalination.

[0003] Due to the high content of alloying elements, super ferritic stainless steel has high strength but great brittleness. As a conventional cold rolling raw material, the thickness of super ferritic stainless steel before rolling is generally 3.5 - 5 mm. However, affected by the thickness effect of the brittleness of ferritic stainless steel, when the thickness specification before rolling > 3.5 mm, the brittleness is more obvious. During the rolling process, brittle breakage of the strip is likely to occur. Therefore, the conventional cold rolling process of super ferritic stainless steel in the prior art cannot meet the cold rolling requirements of super ferritic stainless steel, seriously restricting the industrial production of super ferritic stainless steel materials. Summary of the Invention

[0004] In order to solve the above technical problems existing in the prior art, the present invention provides a new cold rolling method for a 20-high rolling mill of super ferritic stainless steel, overcomes the deficiencies of the existing cold rolling process of super ferritic stainless steel, reduces the risk of brittle breakage of the strip, and realizes the industrial batch production of super ferritic stainless steel.

[0005] The cold rolling method for a 20-high rolling mill of super ferritic stainless steel of the present invention includes:

[0006] According to the thickness specification of the raw material and the thickness specification of the finished product, determine the rolling passes and allocate the rolling reduction rate for each pass, wherein the rolling reduction rate of the first pass is controlled to be 5 - 8%;

[0007] The starting tension of the first pass is controlled to be 125 - 280 KN, and starting from the second pass, the normal rolling tension is set and AFC is enabled;

[0008] In the first pass and the second pass, constant pressure rolling is performed with a rolling pressure of 380 - 400 KN. After two passes of constant pressure rolling, AGC is enabled to perform automatic rolling;

[0009] After rolling starts, accelerate uniformly, with the acceleration controlled to be 40 - 60 m / min, and before rolling ends, decelerate uniformly, with the acceleration controlled to be -40 - -60 m / min.

[0010] As a specific implementation manner, in the cold rolling method of the twenty-high rolling mill for super ferritic stainless steel of the present invention, the starting tension in the first pass is first controlled to be 130 KN, and is gradually increased to 260 KN after the strip state is stable.

[0011] As a specific implementation manner, in the cold rolling method of the twenty-high rolling mill for super ferritic stainless steel of the present invention, the starting tension in the first pass is first controlled to be 130 KN, and is gradually increased to 260 KN after the strip is rolled to 50 m.

[0012] As a specific implementation manner, in the cold rolling method of the twenty-high rolling mill for super ferritic stainless steel of the present invention, the acceleration of uniform acceleration rolling after the rolling starts is controlled to be 50 m / min, and the acceleration of uniform deceleration rolling before the rolling ends is controlled to be -50 m / min.

[0013] The cold rolling method of the twenty-high rolling mill for super ferritic stainless steel of the present invention has the following advantages and beneficial effects:

[0014] Through the rolling process design in four aspects: adopting a first-pass deformation rate of 5-8%, a small starting tension of 130 KN in the first pass, constant-pressure rolling of the first two passes with a rolling pressure of 380-400 KN, and uniform acceleration and deceleration of the head and tail, the frequency of brittle strip breakage during the rolling of super ferritic stainless steel materials is significantly reduced, and the brittle fracture probability is reduced from the existing 30% to less than 5%, realizing the stable rolling of super ferritic stainless steel and fully meeting the industrial mass production requirements of super ferritic stainless steel materials. Specific implementation manner

[0015] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0016] The cold rolling method of the twenty-high rolling mill for super ferritic stainless steel of the present invention includes:

[0017] According to the raw material thickness specification and the finished product thickness specification, determine the rolling passes and allocate the rolling deformation rate for each pass, wherein the rolling deformation rate in the first pass is controlled to be 5-8%;

[0018] The starting tension in the first pass is controlled to be 125-280 KN, and starting from the second pass, the normal rolling tension is set, and AFC (automatic flatness control) is enabled;

[0019] In the first pass and the second pass, constant-pressure rolling is carried out at a rolling pressure of 380 - 400 KN. After two passes of constant-pressure rolling, AGC (Automatic Gauge Control) is enabled to perform automatic rolling.

[0020] After rolling starts, the rolling is carried out with uniform acceleration, and the acceleration is controlled at 40 - 60 m / min. Before rolling ends, the rolling is carried out with uniform deceleration, and the acceleration is controlled at -40 - -60 m / min.

[0021] As a specific implementation manner, in the cold rolling method of a 20-high rolling mill for super ferritic stainless steel of the present invention, the starting tension in the first pass is first controlled at 130 KN, and is gradually increased to 260 KN after the strip state is stable. For example, it is gradually increased to 260 KN after the strip is rolled to 50 m.

[0022] As a specific implementation manner, in the cold rolling method of a 20-high rolling mill for super ferritic stainless steel of the present invention, the acceleration of the uniform acceleration rolling after rolling starts is controlled at 50 m / min, and the acceleration of the uniform deceleration rolling before rolling ends is controlled at -50 m / min.

[0023] The thickness of the super ferritic stainless steel before rolling is generally 3.5 - 5 mm, and the temperature of the steel coil before rolling is at room temperature (-20 - 30 °C), and it is brittle. According to the conventional ferritic rolling method in the prior art, rolling at a first-pass deformation rate of 23% is extremely likely to cause brittle breakage of the strip. Therefore, in the cold rolling method of a 20-high rolling mill for super ferritic stainless steel of the present invention, the first-pass rolling deformation rate is controlled at 5 - 8%, which can achieve two effects: (1) reducing the deformation amount, and correspondingly reducing the rolling pressure by more than 60%, reducing the risk of strip breakage; (2) after the first-pass rolling, the temperature of the strip can reach 70 - 80 °C, reducing the brittleness of the strip and further reducing the risk of strip breakage.

[0024] The yield strength of the super ferritic is about 500 - 600 MPa. According to the characteristics of ordinary stainless steel, the starting tension in the first pass should be about 180 - 400 KN. However, due to the brittle characteristics of the super ferritic, excessive tension is likely to break the strip. Therefore, it is more reasonable to reduce the tension to about 70% of the conventional tension. In the cold rolling method of a 20-high rolling mill for super ferritic stainless steel of the present invention, the starting tension in the first pass is controlled at 130 KN, and the tension is gradually increased to 260 KN after the strip state is stable when it is rolled to about 50 m, thereby effectively reducing the risk of strip breakage.

[0025] The prerequisite for the stable rolling of brittle materials is a stable state. Since the annealing state and thickness fluctuation of the incoming material are unknown, in the cold rolling method of the 20-high rolling mill for super ferritic stainless steel in the present invention, constant-pressure rolling is adopted in the first pass and the second pass, which can ensure the stable state during the rolling process. After two passes of constant-pressure rolling, AGC is enabled in a timely manner according to the thickness fluctuation to perform automatic rolling, ensuring that the thickness of the finished product has no obvious fluctuation and meeting the requirements of the finished product specifications.

[0026] During the rolling process, the speed needs to be increased and decreased at the head and tail. The AGC and AFC will be closed during the speed increase and decrease process. Since the stress state of the steel strip will fluctuate during the speed increase and decrease process, uniform speed increase and decrease should be adopted, and the speed cannot increase or decrease suddenly to avoid brittle fracture caused by unstable state. Therefore, in the cold rolling method of the 20-high rolling mill for super ferritic stainless steel in the present invention, the rolling starts with uniform acceleration rolling, and the acceleration is controlled at 40 - 60 m / min. Before the rolling ends, uniform deceleration rolling is carried out, and the acceleration is controlled at -40 - -60 m / min.

[0027] Therefore, by using the cold rolling method of the 20-high rolling mill for super ferritic stainless steel in the present invention, the brittle fracture probability of super ferritic stainless steel is effectively reduced. Through actual measurement, the brittle fracture probability is reduced from 30% in the prior art to less than 5%, realizing the stable rolling of super ferritic stainless steel and fully meeting the industrialized mass production requirements of super ferritic stainless steel materials.

[0028] The following describes the cold rolling method of the 20-high rolling mill for super ferritic stainless steel in the present invention in combination with specific embodiments.

[0029] Example 1: The steel grade is super ferritic stainless steel S44660, the raw material thickness specification is 4.0 mm, the finished product thickness specification is 1.2 mm, and the width is 1219 mm.

[0030] Example 2: The steel grade is super ferritic stainless steel S44735, the raw material thickness specification is 4.0 mm, the finished product thickness specification is 1.2 mm, and the width is 1219 mm.

[0031] The specific parameters in the cold rolling method of the 20-high rolling mill for super ferritic stainless steel in Example 1 and Example 2 are as follows:

[0032]

[0033] According to the cold rolling methods of the 20-high rolling mill for super ferritic stainless steel in Example 1 and Example 2, more than 30 coils (with an average of 12 tons / coil) of S44660 and S44735 were rolled. The cold rolling process was stable, and no rolling breakage occurred.

[0034] In summary, the cold rolling method of the 20-high rolling mill for super ferritic stainless steel according to the present invention targets the material characteristics of super ferritic stainless steel. Through the rolling process design in four aspects, namely, adopting a first-pass deformation rate of 5-8%, a small starting tension of 130 KN in the first pass, constant-pressure rolling of the first pass and the second pass with a rolling pressure of 380-400 KN, and uniform acceleration and deceleration at the head and tail, the frequency of brittle strip breakage during the rolling of super ferritic stainless steel materials is significantly reduced, and the brittle fracture probability is reduced from the existing 30% to less than 5%. The stable rolling of super ferritic stainless steel is achieved, fully meeting the industrial mass production requirements of super ferritic stainless steel materials.

[0035] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. These modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the present invention.

Claims

1. A cold rolling method for a 20-high rolling mill of super ferritic stainless steel, characterized in that, During the acceleration and deceleration at the head and tail of the rolling process, AGC and AFC are closed during the acceleration and deceleration process. The method includes: Determine the rolling passes according to the raw material thickness specification and the finished product thickness specification, and allocate the rolling deformation rate for each pass. The rolling deformation rate of the first pass is controlled at 5-8% to reduce the deformation amount and the brittleness of the steel strip. The starting tension of the first pass is controlled at 125-280 KN. Starting from the second pass, the normal rolling tension is set and AFC is enabled. In the first pass and the second pass, constant pressure rolling is carried out at a rolling pressure of 380-400 KN. After two passes of constant pressure rolling, AGC is enabled to adopt automatic rolling. After the rolling starts, it is rolled with uniform acceleration, and the acceleration is controlled at 40-60 m / min. Before the rolling ends, it is rolled with uniform deceleration, and the acceleration is controlled at -40 to -60 m / min.

2. The cold rolling method of a 20-high rolling mill for super ferritic stainless steel according to claim 1, characterized in that, The starting tension of the first pass is first controlled at 130 KN and gradually increased to 260 KN after the steel strip state is stable.

3. The cold rolling method of the 20-high rolling mill for super ferritic stainless steel according to claim 1, characterized in that, The starting tension of the first pass is first controlled at 130 KN and gradually increased to 260 KN after the steel strip is rolled to 50 m.

4. The cold rolling method of a 20-high rolling mill for super ferritic stainless steel according to claim 1, characterized in that The acceleration of uniform acceleration rolling after the rolling starts is controlled at 50 m / min, and the acceleration of uniform deceleration rolling before the rolling ends is controlled at -50 m / min.

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