A processing method of large-size wide-width high-boron stainless steel plate

Abstract

The application discloses a processing method of large-size wide-width high-boron stainless steel plate material, which comprises the following steps: (1) embedding high-boron stainless steel blank (boron content 0.15-2.4 wt.%) into grooves formed by two pieces of common metal material after polishing the surface of the high-boron stainless steel blank clean, and coating metal release agent on the contact surface; (2) after grouping three groups of blanks and welding, a composite blank is formed, and the composite blank is kept at 1050-1200 DEG C for 2-12 h to homogenize the structure; (3) hot rolling or hot forging the composite blank into a slab with a required thickness and width, and separating the three slabs along the release agent interface after the steel plate is cooled, and the middle slab is the obtained high-boron stainless steel plate material. The application ingeniously introduces a special hot deformation method to ensure the deformation temperature and make the high-boron stainless steel plate material deform along a specific direction, so that the deformation coordination of hard and brittle borides and the matrix structure is enhanced, the hot plasticity is greatly improved, and the edge cracking risk is reduced.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of steel alloy materials, and particularly relates to a processing method of large-size wide-width high-boron stainless steel plate. BACKGROUND

[0002] High-boron stainless steel refers to stainless steel with a boron content greater than 0.1% (mass fraction), which has excellent thermal neutron absorption performance and gamma ray shielding comprehensive protection effect, and is often used as a neutron absorption and gamma ray shielding material for spent fuel. The solidification structure of high-boron stainless steel is composed of an austenitic or ferritic matrix and eutectic borides such as (Fe, Cr)2B that are segregated at the grain boundaries. The borides are hard, brittle and difficult to deform, resulting in poor hot plasticity of high-boron stainless steel, which is prone to edge cracking during hot deformation. Studies have shown that the edge cracking degree of high-boron stainless steel hot-rolled plate increases with the decrease of hot rolling temperature, and the hot plasticity is good when the hot working temperature is higher than 1000 ℃. However, when the hot working temperature exceeds 1200 ℃, the high-boron stainless steel exhibits zero hot plasticity, which is due to the melting of borides and austenite at the grain boundaries, forming a low-melting-point eutectic metal liquid, resulting in serious hot brittleness of the material. Therefore, the processing and preparation of high-boron stainless steel has been a world-class problem, especially for large-size wide-width plate, which has a very narrow hot working range and requires extremely high control of processing parameters.

[0003] At present, powder metallurgy is the most commonly used method for preparing high-boron stainless steel. It is a technology that uses metal powder or alloy powder prepared by rapid solidification as raw material to produce metal materials, composite materials and various types of products through blank forming and sintering. However, the powder metallurgy method has a long process flow and small product specifications, which cannot meet the needs of batch production. The main reason is that it is difficult to control the density, solidification structure size and uniform distribution of sintered blanks when preparing large-size high-boron stainless steel workpieces. With the progress of smelting, casting and processing technologies at home and abroad, forming methods based on mold casting / continuous casting have also been gradually applied to the preparation of high-boron stainless steel. For example, Baosteel in China developed a "vacuum induction melting + gas protection electroslag remelting / vacuum consumable remelting" process in 2009 to prepare 20.0Cr-13.0Ni-1.8B stainless steel slabs. However, it cannot be ignored that the high-boron stainless steel blanks prepared by mold casting method will be broken under stress during subsequent hot working deformation such as forging and hot rolling, which can easily cause cracking in the edge and surface area of the workpiece, greatly reducing the yield. Therefore, it is crucial to control the hot working process parameters and develop new hot deformation processes for manufacturing large-size, wide-width high-boron stainless steel.

[0004] According to the above research background, the application provides a processing method of large-size wide-width high-boron stainless steel plate. According to the characteristics of high hardness, high brittleness, high thermal stability and difficult deformation of borides in high-boron stainless steel compared with the matrix structure, a special hot deformation method is ingeniously introduced. By restraining the high-boron stainless steel plate during hot rolling, the deformation of the hard and brittle borides and the matrix structure is coordinated, the hot plasticity is greatly improved, and the edge cracking risk is reduced. SUMMARY

[0005] The purpose of the application is to solve the above problems, and provide a processing method of large-size wide-width high-boron stainless steel plate.

[0006] The purpose of the application is achieved by a processing method of large-size wide-width high-boron stainless steel plate, comprising the following steps: step one: preparing high-boron stainless steel blank, wherein the boron content is 0.15-2.4wt.%, the matrix microstructure is austenite or ferrite, and the surface of the high-boron stainless steel blank is polished clean for standby; step two: preparing two pieces of ordinary metal material with thickness H=(0.6-4.0)H0, width K=(1.0-4.0)K0, and length L=(1.0-4.0)L0, and polishing the surface of the two pieces of ordinary metal material clean for standby; in the formula, H0, K0 and L0 are the thickness, width and length of the high-boron stainless steel blank, respectively, and the unit is mm; step three: grooving the two pieces of ordinary metal material in step two, embedding the high-boron stainless steel blank in the groove formed by the two pieces of ordinary metal material, and coating metal release agent on the contact surface of the high-boron stainless steel blank and the two pieces of ordinary metal material; step four: after the three groups of blanks are combined and welded, a composite blank is formed, and the composite blank is kept at 1050-1200℃ for 2-12h; step five: hot rolling or hot forging the composite blank into a plate blank with the required thickness and width, and after the steel plate is cooled, the three plate blanks are separated along the metal release agent interface, and the middle plate blank is the obtained high-boron stainless steel plate.

[0007] In the above step one, the high-boron stainless steel blank includes but is not limited to continuous casting blank, electroslag casting blank or hot deformation intermediate blank.

[0008] In the above step two, the ordinary metal material can be carbon steel, stainless steel or other metal material with better hot plasticity than the coated high-boron stainless steel.

[0009] In the above step four, the welding is carried out under vacuum condition, and the maximum welding depth on one side should not reach the contact surface of the three groups of blanks.

[0010] In the above-mentioned step five, the required thickness and width dimensions should include the dimensions of the upper and lower cladding materials after hot deformation and the dimensions of the obtained high-boron stainless steel plate, the thickness of the obtained high-boron stainless steel plate is between 2-80mm, the width is not less than 80mm, the length is not less than 100mm, and there is no obvious crack on the surface and the edge.

[0011] The beneficial effects of the present application are: (1) The present application innovatively introduces a special hot deformation method aiming at the key problem of poor plasticity and serious edge cracking in the hot working process of high-boron stainless steel, enhances the deformation coordination of hard and brittle borides and matrix structure, greatly improves the hot plasticity, and provides an effective method for industrial production of large-size wide high-boron austenitic stainless steel plate.

[0012] (2) The present application adopts a new hot working process, proves that high-boron stainless steel medium plate can also be prepared by adopting hot rolling / hot forging, heat treatment and other means, breaks through the bottleneck that only small specifications and small batches can be produced in the traditional processing method of such materials such as powder metallurgy, greatly widens the application field of high-boron stainless steel, and accelerates the localization process. DETAILED DESCRIPTION

[0013] The present application innovatively introduces a special hot deformation method aiming at the key problem of poor plasticity and serious edge cracking in the hot working process of high-boron stainless steel, enhances the deformation coordination of hard and brittle borides and matrix structure, greatly improves the hot plasticity, and provides an effective method for industrial production of large-size wide high-boron austenitic stainless steel plate.

[0014] The present application adopts a new hot working process, proves that high-boron stainless steel medium plate can also be prepared by adopting hot rolling / hot forging, heat treatment and other means, breaks through the bottleneck that only small specifications and small batches can be produced in the traditional processing method of such materials such as powder metallurgy, greatly widens the application field of high-boron stainless steel, and accelerates the localization process.

[0015] The method of the present application comprises the following steps: 1. preparing high-boron stainless steel blank, wherein the boron content is 0.15-2.4wt.%, the base microstructure is austenite or ferrite, and the surface is polished clean for standby; 2. preparing two pieces of common metal material with thickness H=(0.6-4.0)H0, width K=(1.0-4.0)K0, and length L=(1.0-4.0)L0, and the surface is polished clean for standby; wherein H0, K0, and L0 are the thickness, width, and length of the high-boron stainless steel blank, respectively; 3. grooving the two pieces of common metal material in step 2 so that the high-boron stainless steel blank in step 1 can be embedded into the groove formed by the two pieces of common metal material, and coating metal release agent on the contact surface of the high-boron stainless steel blank and the two pieces of common metal material (the metal release agent has many types, which are not required here. The main function is to prevent the adhesion of the two pieces of metal); 4. after the three groups of blanks (here, the three groups of blanks refer to one piece of high-boron stainless steel and two pieces of coated common metal material) are combined and welded, a composite blank is formed, and the composite blank is kept at 1050-1200℃ for 2-12 h to homogenize the structure; 5. hot rolling or hot forging the composite blank into a slab with the required thickness and width, and after the steel plate is cooled, the three slabs are separated along the release agent interface, and the middle slab is the obtained high-boron stainless steel plate.

[0016] In step 1 above, the high-boron stainless steel blank includes but is not limited to continuous casting blank, electroslag casting blank, or hot deformed intermediate blank.

[0017] In step 2 above, the common metal material can be carbon steel, stainless steel, or other metal material with better hot plasticity than the coated high-boron stainless steel.

[0018] In step 4 above, the welding is carried out under vacuum condition, and the maximum welding depth on one side should not reach the contact surface of the three groups of blanks.

[0019] In step 5 above, the required thickness and width size should include the size after hot deformation of the upper and lower coated materials and the size of the obtained high-boron stainless steel plate. The thickness of the obtained high-boron stainless steel plate is 2-80 mm, the width is not less than 80 mm, and the length is not less than 100 mm (note: the maximum width and length size are limited by the original blank size and hot rolling equipment), and there is no obvious crack on the surface and edge.

[0020] In the embodiment of the present application, the heat treatment adopts a box-type resistance furnace, and the furnace temperature is raised to the set temperature to start timing.

[0021] In the embodiment of the present application, the common metal material is grooved in a cold machining manner, and the surface of the steel plate is polished clean by a grinding machine.

[0022] The metal release agent used in the present application is magnesium oxide. Example 1

[0023] A 304-based high-boron stainless steel electroslag ingot with a boron content of 1.95 wt.% and a size of 30 mm in thickness, 140 mm in width, and 160 mm in length is prepared. The base structure of the ingot is austenite. The surface is polished clean and then reserved.

[0024] Two 304 stainless steel (GB / T 4238-2015) plates with a size of 45 mm in thickness (H = 1.5 H0), 300 mm in width (K = 2.1 K0), and 320 mm in length (L = 2.0 L0) are prepared. The surfaces are polished clean and then grooves are formed inward from the surfaces, so that the high-boron stainless steel ingot can be embedded in the grooves formed by the two 304 stainless steel plates. In the formula, H0, K0, and L0 are the thickness, width, and length of the high-boron stainless steel ingot, respectively.

[0025] The contact surfaces of the high-boron stainless steel ingot and the two 304 stainless steel plates are coated with release agents, and the three ingots are then combined and welded to form a composite ingot. The welding is performed in a vacuum chamber, and the maximum welding depth is 50 mm on one side, without reaching the contact surface of the three ingots.

[0026] After the composite ingot is kept at 1130°C for 6 h, it is hot-rolled to a thickness of 8 mm (total thickness of the composite plate). After the plate cools, the three plate ingots are separated along the release agent interface, and the middle plate ingot is the obtained high-boron stainless steel plate. The size of the plate is 3 mm in thickness, 144 mm in width, and 830 mm in length (Note: This size only counts the length of the parallel section in the middle of the hot-rolled plate. Since the front end of the hot-rolled plate generally has a curvature, the actual length of the high-boron stainless steel plate is much greater than this statistical value). No obvious cracks are found on the surface of the plate, meeting the requirements of the present application. Example 2

[0027] The method is the same as in Example 1, except that: (1) the high-boron stainless steel ingot used is a continuous casting ingot with a grade of 06Cr19Ni10 and a boron content of 2.2 wt.%. The size of the ingot is 35 mm in thickness, 120 mm in width, and 150 mm in length; (2) the coated ordinary metal material is Q235 carbon steel with a size of 50 mm in thickness (H = 1.4 H0), 280 mm in width (K = 2.3 K0), and 300 mm in length (L = 2.0 L0). The plate is asymmetrically grooved inward from the surface, so that the high-boron stainless steel ingot can be embedded in the grooves formed by the two Q235 plates; (3) the composite ingot is kept at 1180°C for 4 h, and then hot-rolled to a thickness of 12 mm (total thickness of the composite plate) after being taken out of the furnace. After the plate cools and is separated along the release agent interface, the obtained high-boron stainless steel plate has a size of 5 mm in thickness, 123 mm in width, and 660 mm in length (Note: This size only counts the length of the parallel section in the middle of the hot-rolled plate). No obvious cracks are found on the surface of the plate, meeting the requirements of the present application. Comparative Example

[0028] The high-boron stainless steel blank and the original size are the same as those of Example 1, and the difference is that the electroslag ingot is not coated with 304 stainless steel, and is directly hot-rolled after holding at 1130℃ for 6h. When the steel plate is deformed to 16mm thick after 4 passes of hot rolling, obvious cracks appear at the edge and front end of the steel plate, the maximum crack length reaches 35mm, and the surface of the steel plate is in a fragmented state, so the hot rolling is stopped. The design requirements of the present application are not met.

[0029] The features and effects of the present application are described in more detail above through examples and comparative examples, but are not limited to only these examples, and there can be more other equivalent examples without departing from the concept of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for processing large-size, wide-width high-boron stainless steel sheets, characterized in that: Includes the following steps: Step 1: Prepare high boron stainless steel billet with a boron content of 0.15~2.4wt.% and a matrix microstructure of austenite or ferrite. Grind the surface of the high boron stainless steel billet clean and set it aside. Step 2: Prepare two pieces of ordinary metal material with thickness H=(0.6~4.0)H0, width K=(1.0~4.0)K0, and length L=(1.0~4.0)L0. Clean the surfaces of the two pieces of ordinary metal material and set them aside. In the formula, H0, K0, and L0 are the thickness, width, and length of the high boron stainless steel billet, respectively, and the units are all mm. Step 3: Hollow out the two ordinary metal materials from Step 2, so that the high boron stainless steel billet from Step 1 is embedded in the groove formed by the two ordinary metal materials, and apply a metal release agent to the contact surface of the high boron stainless steel billet and the two ordinary metal materials respectively. Step 4: After assembling and welding the three sets of billets, a composite billet is formed. The composite billet is then kept at 1050~1200℃ for 2~12 hours. Step 5: Hot roll or hot forge the composite billet into a slab of the required thickness and width. After the steel plate cools, separate the three slabs along the interface of the metal release agent. The middle slab is the high boron stainless steel plate obtained. In step five above, the required thickness and width dimensions should include the dimensions of the upper and lower cladding materials after heat deformation and the dimensions of the obtained high boron stainless steel sheet. The obtained high boron stainless steel sheet should have a thickness between 2 and 80 mm, a width of not less than 80 mm, a length of not less than 100 mm, and no obvious cracks on the surface and edges.

2. The processing method for large-size, wide-width high-boron stainless steel sheets according to claim 1, characterized in that: In step one above, the high-boron stainless steel billet includes, but is not limited to, continuously cast billets, electroslag cast billets, or hot-deformed intermediate billets.

3. The processing method for large-size, wide-width high-boron stainless steel sheets according to claim 1, characterized in that: In step two above, the ordinary metal material can be carbon steel, stainless steel, or other metal materials with better thermoplasticity than the high boron stainless steel being coated.

4. The processing method for large-size, wide-width high-boron stainless steel sheets according to claim 1, characterized in that: In step four above, welding is performed under vacuum conditions, and the maximum welding depth on one side should not reach the contact surface of the three sets of blanks.