A straightening process for duplex stainless steel sheets

Abstract

The application discloses a straightening process method of duplex stainless steel plate, compared with the traditional process, the duplex stainless steel plate is subjected to pressure processing, the process of first shot blasting and then straightening is adopted, and the generation of defects such as surface rough surface, pitting, scratch and the like of the hot-rolled duplex stainless steel plate can be greatly reduced. In the straightening process, the surface roughness Ra of the work rolls of the three roller tables before and after the straightening machine is 3-6 mu m, the temperature of the steel plate entering the straightening machine is controlled in the range of 180-280 DEG C, the generation of defects such as surface rough surface, pitting, scratch and the like of the hot-rolled duplex stainless steel plate is further reduced, the workload of manual grinding after pickling is reduced, and the re-acidification rate of the hot-rolled duplex stainless steel plate is reduced.

Description

Technical Field

[0001] This invention relates to the field of stainless steel pressure processing technology, and in particular to a straightening process method for duplex stainless steel plates. Background Technology

[0002] In the processing of duplex stainless steel plates, straightening machines are used to eliminate warping and wave defects generated during the cooling process after solution heat treatment of the steel plate, in order to improve the flatness and residual stress of the plate, so that the product meets national standards or user requirements. Among ordinary austenitic stainless steel plate products, the pressure processing of 300 series stainless steels such as 304, 316 and 321 is the most representative. The strength of duplex stainless steel is about twice that of conventional austenitic stainless steel. The straightening pressure processing of duplex stainless steel plates is more difficult and the technical control is more complex. Therefore, the flatness, factory standards or technical agreements of duplex stainless steel plates have specific regulations. Among duplex stainless steel plate products, grades such as S32750, S32205, S32304 and S32101 are the most representative. Among them, the S32205 series of duplex stainless steel has both the good mechanical properties of ferritic stainless steel and the excellent corrosion resistance of austenitic stainless steel, and has been widely used in pipeline transportation, bridges, chemical industry, shipbuilding industry and other industries.

[0003] S32205 duplex stainless steel is designed with high chromium, high nitrogen, and high molybdenum content. Currently, well-known domestic and international companies use hot-rolled S32205 series duplex stainless steel plates. Regarding the pressure processing methods related to the quality of the straightening process, there are two main approaches, and the corresponding processes and technologies are attached. Figure 1 As shown.

[0004] Process 1: Solution heat treatment → Straightening → Shot blasting → Pickling → Manual grinding → Packaging, etc. Among these, solution heat treatment, straightening, and shot blasting are crucial. The solution heat treatment process is key to determining the surface quality and flatness of duplex stainless steel plates for chemical tankers and other industrial plates. After heat treatment and holding, the steel plates are cooled using a roller-bottom quenching machine, with continuous cooling and a plate temperature ≤150℃. In the straightening process, a fifteen-roll combination straightener is designed for duplex stainless steel plates, expanding the thickness range of the straightened products. For thinner specifications, a parallel straightening process is generally used. The parallel straightening process places the steel plate in a state of high reverse curvature and large deformation within a small roller system, resulting in a more uniform residual curvature. After straightening, the steel plate is shot blasted, achieving a surface quality of A and BSa2.5.

[0005] The characteristics of this process are: after heat treatment and heat preservation, the steel plate is cooled using a roller hearth quenching machine, requiring the steel plate temperature to be ≤150℃. During the straightening process, thin and thick products are straightened on a single straightening machine. In the shot blasting process, the straightened steel plate is shot blasted, resulting in a surface quality of A and BSa2.5. The entire process utilizes advanced equipment and is highly automated.

[0006] Process 2: Solution heat treatment → Straightening → Shot blasting → Pickling → Manual grinding → Packaging, etc. Among these, solution heat treatment, straightening, and shot blasting determine the surface quality and flatness of the industrial plate. The solution heat treatment process is crucial; after heat treatment and holding, the steel plate is cooled using a roller-bottom quenching machine for continuous cooling, with the plate temperature ≤100℃. In the straightening process, thin and thick products are straightened on a single straightening machine using two sets of rollers. After straightening, the steel plate is shot blasted, achieving a surface quality of A and BSa2.5.

[0007] The characteristics of this process are: after heat treatment and heat preservation, the steel plate is cooled using a roller bottom quenching machine, requiring the steel plate temperature to be ≤100℃. During the straightening process, thin and thick products are straightened on a single straightening machine by changing the roller system. In the shot blasting process, the steel plate is shot-blasted after straightening, achieving a surface quality of A and BSa2.5. The entire process utilizes advanced equipment and technology with a high degree of automation.

[0008] Processes 1 and 2 share a common drawback: in the process selection for duplex stainless steel plates, solution heat treatment is performed first, followed by straightening, and then shot blasting. Since the strength of duplex stainless steel is approximately twice that of conventional austenitic stainless steel, greater straightening pressure is required to straighten the steel plate. Furthermore, after solution heat treatment, a thin layer of iron oxide scale forms on the surface of the steel plate. During the straightening process, some of this scale falls off and into the bottom of the lower support roller of the straightener, while some adheres to the surface of the working and support rollers. In actual straightening, this causes defects such as pitting, scratches, and other imperfections on the steel plate surface. These defects are exposed during subsequent pickling, increasing the workload of the grinding process and also leading to a higher re-acidification rate. Summary of the Invention

[0009] The main objective of this invention is to provide a straightening process for duplex stainless steel plates, which can effectively solve the problems in the background art.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0011] A straightening process for duplex stainless steel plates includes the following steps:

[0012] S1. The solution heat treatment process of the duplex stainless steel plate involves water quenching of the plate through spraying and water bath cooling. The temperature of the quenched duplex stainless steel plate is 200-300℃, and the flatness is ≤20mm / m. S2. The quenched duplex stainless steel plate is conveyed to a shot blasting machine via roller conveyors for shot blasting. The temperature of the steel plate entering the shot blasting machine is 190-290℃, and high-carbon steel shot of type S260-S280 is used. The surface finish of the steel plate after shot blasting is ASa2.5. S3. The shot-blasted duplex stainless steel plate is straightened using a straightening machine. The surface roughness Ra of the first three roller conveyors and the last three roller conveyors of the straightening machine is 3μm-6μm, and the temperature of the steel plate entering the straightening machine is 180-280℃.

[0013] As a preferred embodiment, in step S2, shot blasting is performed using a shot blasting machine in conjunction with high-carbon steel shot, the high-carbon steel shot being of type S280.

[0014] As a preferred embodiment, in step S2, the surface cleanliness of the duplex stainless steel plate after shot blasting meets ASa2.5.

[0015] As a preferred embodiment, in step S3, the flatness of the duplex stainless steel plate after straightening is ≤5mm / m.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] In this invention, duplex stainless steel plates are pressure processed using a process of shot blasting followed by straightening. This process can improve the surface quality of the upper and / or lower surfaces of each steel plate. During the straightening process, three working rollers (with a surface roughness Ra of 3μm-6μm) are used to straighten the steel plates before and after the straightening machine. The optimized temperature control technology, which keeps the temperature of the steel plates entering the straightening machine between 180 and 280°C, significantly reduces the generation of defects such as pitting, scratches, etc. on the surface of hot-rolled duplex stainless steel plates. This also reduces the amount of manual grinding required in the subsequent pickling process and lowers the re-acidification rate of hot-rolled duplex stainless steel plates. Attached Figure Description

[0018] Figure 1 A table showing the straightening process for traditional duplex stainless steel sheets;

[0019] Figure 2 This is a schematic diagram of a straightening process for a duplex stainless steel plate according to the present invention.

[0020] Figure 3 This is an illustration of an embodiment of the straightening process for duplex stainless steel plates according to the present invention. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. The terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Furthermore, unless otherwise explicitly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0023] Example 1: Straightening process of hot-rolled S32205 duplex stainless steel plate under pressure processing. The duplex stainless steel plate has a thickness of 14mm, a width of 2200mm, and a length of 8720mm.

[0024] First, the hot-rolled duplex stainless steel sheet undergoes solution heat treatment. During this process, the sheet is water-quenched using a spray and water bath cooling method. The spray system quenches the sheet at a pressure of 0.4 MPa, followed by water bath cooling. This process continues until the steel sheet temperature reaches 290℃ and the flatness reaches 15 mm / m. Next, shot blasting is performed. The steel sheet temperature entering the shot blasting machine is 280℃, using high-carbon steel shot (S280). After shot blasting, the surface finish reaches ASa2.5. Following this, straightening is performed. The surface roughness Ra of the three working rollers on the front and rear roller conveyors of the straightening machine is 3μm-6μm. The steel sheet temperature entering the straightening machine is 260℃. Finally, pickling and manual inspection (grinding) are conducted. The surface finish of the steel sheet after pickling and manual inspection (grinding) meets the standards and user requirements, ultimately reducing the re-acidification rate of the duplex stainless steel sheet by 15%.

[0025] Example 2: Straightening process of hot-rolled S31803 duplex stainless steel plate during pressure processing. The steel plate has a thickness of 16mm, a width of 2000mm, and a length of 6300mm.

[0026] First, the hot-rolled duplex stainless steel sheet undergoes solution heat treatment. During this process, the sheet is water-quenched using a spray and water bath cooling method. The spray system quenches the sheet at a pressure of 0.4 MPa, followed by water bath cooling. This process continues until the steel sheet temperature drops to 260℃ and the flatness reaches 15 mm / m. Next, shot blasting is performed. The steel sheet temperature entering the shot blasting machine is 251℃, using high-carbon steel shot (S280). After shot blasting, the surface finish is ASa2.5. Following this, a straightening process is performed. The surface roughness Ra of the three working rollers on the front and back of the straightening machine is 3μm-6μm. The steel sheet temperature entering the straightening machine is 241℃. Finally, pickling and manual inspection (grinding) are performed. The surface finish of the steel sheet after pickling and manual inspection (grinding) meets the standards and user requirements, ultimately reducing the re-acidification rate of the duplex stainless steel sheet by 12%.

[0027] In the above implementation scheme, the quenching process of the solution heat treatment process adopts spray and water tank cooling to control the temperature of the steel plate after quenching, creating conditions for the steel plate to be straightened with temperature during the straightening process, and at the same time controlling the size of the unevenness of the steel plate after quenching, so as to ensure that the steel plate can pass through the shot blasting process smoothly.

[0028] Similarly, during the shot blasting process, the temperature of the steel plate entering the shot blasting machine naturally decreases. This clarifies the use of high-carbon steel shot particle size control technology and also clarifies the surface quality of the steel plate after shot blasting, as well as the surface finish of the duplex stainless steel plate.

[0029] Furthermore, during the straightening process, the surface roughness control requirements of the working rolls of the front and rear (3) roller conveyors of the straightener were proposed, and the temperature range of the steel plate entering the straightener was clarified, so that the strength of the straightened steel plate was reduced by about one-quarter compared with the strength at room temperature.

[0030] It should be noted that the present invention is a straightening process for duplex stainless steel plates, including the following steps: S1, the duplex stainless steel plate solution heat treatment process, wherein the duplex stainless steel plate is water-cooled and quenched by spraying and water tank cooling, and the temperature of the duplex stainless steel plate after quenching is 200~300℃, and the flatness is ≤20mm / m.

[0031] S2. The quenched duplex stainless steel plate is conveyed to the shot blasting machine via roller conveyor for shot blasting treatment. The temperature of the steel plate entering the shot blasting machine is 190-290℃. High carbon steel shot is used, with shot type S260-S280. After shot blasting, the surface quality of the steel plate is ASa2.5. The shot blasting is performed by using a shot blasting machine with high carbon steel shot of type S280. The surface cleanliness of the duplex stainless steel plate after shot blasting meets ASa2.5.

[0032] S3. The duplex stainless steel plate after shot blasting is straightened by a straightening machine. There are requirements for the surface roughness of the rollers before and after the straightening machine. The surface roughness Ra of the working rollers of the three rollers before and after the straightening machine is 3μm-6μm. The temperature of the steel plate entering the straightening machine is 180~280℃.

[0033] This invention performs pressure processing on duplex stainless steel sheets, employing a process of shot blasting followed by straightening. This process can significantly improve the surface quality of the upper and / or lower surfaces of each steel sheet. During the straightening process, the surface roughness Ra of the working rollers on the front and rear (3) roller conveyors of the straightener is set to 3μm-6μm, and the temperature of the steel sheet entering the straightener is kept between 180 and 280℃. This optimized control technology greatly reduces the generation of defects such as pitting, scratches, etc. on the surface of hot-rolled duplex stainless steel sheets, reduces the amount of manual grinding work in the subsequent pickling process, and lowers the re-acidification rate of hot-rolled duplex stainless steel sheets.

[0034] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A straightening process for duplex stainless steel plates, characterized in that, Includes the following steps, S1. The solution heat treatment process of the duplex stainless steel plate involves water quenching of the duplex stainless steel plate through spraying and water tank cooling. The spray pipe quenches the steel plate with water, and the water supply pressure is selected as 0.4MPa. Then, the plate is cooled in a water tank. The temperature of the duplex stainless steel plate after quenching is 200-300℃, and the flatness is ≤20mm / m. S2. The quenched duplex stainless steel plate is conveyed to the shot blasting machine through a roller conveyor for shot blasting treatment. The temperature of the steel plate entering the shot blasting machine is 190-290℃. High carbon steel shot is used, and the shot type is S280. The surface quality and cleanliness of the steel plate after shot blasting is ASa2.

5. S3. The duplex stainless steel plate after shot blasting is straightened by a straightening machine. Roller tracks are set in front of and behind the straightening machine. The surface roughness Ra of the working rollers in the three roller tracks in front of and behind the straightening machine is 3μm-6μm. The temperature of the steel plate entering the straightening machine is 180-280℃. The flatness of the duplex stainless steel plate after straightening is ≤5mm / m.

Images