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

Abstract

The processing method comprises the following steps: (1) polishing the surface of a high-boron stainless steel blank (the boron content is 0.15-2.4 wt.%), embedding the high-boron stainless steel blank into a groove formed by two common metal materials, and coating a metal isolating agent on the contact surface; (2) assembling and welding the three groups of blanks to form a composite blank, and preserving heat at 1050-1200 DEG C for 2-12 hours to homogenize the structure; and (3) the composite blank is subjected to hot rolling or hot forging to form plate blanks with the needed thickness and width, after the steel plate is cooled, the three plate blanks are separated along the parting agent interface, and the middle plate blank is the obtained high-boron stainless steel plate. In order to solve the key technical problems that the high-boron stainless steel large-size wide plate is poor in thermoplasticity and difficult to machine, a special thermal deformation method is ingeniously introduced, the high-boron stainless steel large-size wide plate is deformed in the specific direction while the deformation temperature is guaranteed, the deformation coordination of hard and brittle boride and a matrix structure is enhanced, the thermoplasticity is greatly improved, and the edge crack risk is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of steel alloy materials, and in particular relates to a processing method of a large-size and wide-width high-boron stainless steel plate. Background Art

[0002] High-boron stainless steel refers to stainless steel with a boron content greater than 0.1% (mass fraction). It has excellent thermal neutron absorption performance and gamma-ray shielding comprehensive protection effect, and is often used as neutron absorption and gamma-ray shielding materials for spent fuel. The solidification structure of high-boron stainless steel is composed of austenite or ferrite matrix and eutectic borides concentrated at the grain boundaries, such as (Fe, Cr) 2 B, borides have high hardness, great brittleness and are difficult to deform, resulting in poor thermoplasticity of high-boron stainless steel, and edge cracks are very likely to occur during thermal deformation. Studies have shown that the degree of edge cracking of high-boron stainless steel hot-rolled plates increases with the decrease of hot rolling temperature, and the thermoplasticity is better when the hot working temperature is higher than 1000 ℃. However, when the hot working temperature exceeds 1200 ℃, the thermoplasticity of high-boron stainless steel will be zero. This is because the boride and austenite at the grain boundary melt to form a low-melting-point eutectic metal liquid, which makes the material severely hot brittle. Therefore, the processing and preparation of high-boron stainless steel has always been a world-class problem, especially for large-size and wide-width plates, whose hot working range is very narrow and the requirements for processing technology control are extremely high.

[0003] At present, powder metallurgy is the most commonly used method for preparing high-boron stainless steel. It is a technical method that uses metal powder or alloy powder prefabricated by rapid solidification as raw material, and undergoes blanking molding and sintering to produce metal materials, composite materials and various types of products. However, the process flow of preparing high-boron stainless steel by powder metallurgy is long and the product specifications are small, which makes it difficult to meet the needs of mass production. This is mainly because when preparing large-sized high-boron stainless steel workpieces, it is difficult to control the density, solidification structure size and uniform distribution of the sintered blank. With the advancement of smelting, casting and processing technology at home and abroad, molding methods based on die casting / continuous casting have gradually been applied to the preparation of high-boron stainless steel. For example, in 2009, Baosteel of China developed the process of "vacuum induction melting + gas shielded electroslag remelting / vacuum consumable remelting" for the preparation of 20.0Cr-13.0Ni-1.8B stainless steel ingots. However, it cannot be ignored that during the subsequent hot working deformation process of high-boron stainless steel billets prepared by die casting under different conditions such as forging and hot rolling, the coarse, hard and brittle boride will break under stress, which can easily lead to cracking of the edges and surface areas of the workpiece, greatly reducing the yield rate. Therefore, it is very important to control the hot working process parameters and develop new hot deformation processes for the manufacture of large-size and wide-width high-boron stainless steel.

[0004] Based on the above research background, the present invention provides a processing method for large-size and wide high-boron stainless steel sheets. In view of the characteristics of high-boron stainless steel that the boride is harder, more brittle, more thermally stable and difficult to deform compared with the matrix structure, a special thermal deformation method is cleverly introduced to constrain the high-boron stainless steel sheet during hot rolling, so that it can be deformed along a specific direction while ensuring the thermal deformation temperature, thereby enhancing the deformation coordination between the hard and brittle boride and the matrix structure, greatly improving the thermoplasticity, and reducing the risk of edge cracking. Summary of the invention

[0005] The purpose of the present invention is to provide a processing method for large-size and wide-width high-boron stainless steel plates in view of the above problems.

[0006] The object of the present invention is achieved in this way: a processing method for a large-size wide-width high-boron stainless steel plate comprises the following steps: step 1: preparing a high-boron stainless steel blank, wherein the boron content is 0.15-2.4wt.%, and the matrix microstructure is austenite or ferrite, and the surface of the high-boron stainless steel blank is polished and set aside; step 2: preparing two pieces of ordinary metal materials with a thickness of H=(0.6-4.0)H0, a width of K=(1.0-4.0)K0, and a length of L=(1.0-4.0)L0, and the surfaces of the two pieces of ordinary metal materials are polished and set aside; wherein H0, K0, and L0 are the thickness of the high-boron stainless steel blank, respectively. , width, length, all in mm; Step 3: groove the two ordinary metal materials in Step 2, so that the high boron stainless steel billet in Step 1 is embedded in the groove formed by the two ordinary metal materials, and metal isolation agent is coated on the contact surfaces of the high boron stainless steel billet and the two ordinary metal materials respectively; Step 4: assemble and weld the three groups of billets to form a composite billet, and keep the composite billet at 1050~1200℃ for 2~12h; Step 5: hot roll or hot forge the composite billet into a slab of required thickness and width, and after the steel plate is cooled, separate the three slabs along the metal isolation agent interface, and the middle slab is the obtained high boron stainless steel plate.

[0007] In the above step 1, the high-boron stainless steel billet includes but is not limited to a continuous casting billet, an electroslag casting billet or a hot-deformed intermediate billet.

[0008] In the above step 2, the common metal material may be carbon steel, stainless steel or other metal materials having better thermoplasticity than the coated high-boron stainless steel.

[0009] In the above step 4, welding is performed under vacuum conditions, and the maximum welding depth of one side should not reach the contact surface of the three sets of blanks.

[0010] In the above step 5, the required thickness and width dimensions should include the dimensions of the upper and lower cladding materials after thermal deformation and the dimensions of the obtained high-boron stainless steel sheet. The obtained high-boron stainless steel sheet has a thickness of 2 to 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.

[0011] The beneficial effects of the present invention are as follows: (1) The present invention aims to solve the key problems of poor plasticity and severe edge cracking in the hot working process of high-boron stainless steel, innovatively introduces a special hot deformation method, enhances the deformation coordination between hard and brittle borides and matrix structure, greatly improves hot plasticity, and provides an effective method for the industrial production of large-size and wide-width high-boron austenitic stainless steel plates.

[0012] (2) The present invention adopts a new type of hot processing technology, which proves that medium and thick high-boron stainless steel plates can also be prepared by hot rolling / hot forging, heat treatment and other means. It breaks through the bottleneck that traditional processing methods of this type of material such as powder metallurgy can only produce small specifications and small batches, greatly broadens the application field of high-boron stainless steel, and accelerates the localization process. DETAILED DESCRIPTION

[0013] The present invention aims to solve the key problems of poor plasticity and severe edge cracking in the hot working process of high-boron stainless steel, innovatively introduces a special hot deformation method, enhances the deformation coordination between hard and brittle borides and matrix structure, greatly improves hot plasticity, and provides an effective method for the industrial production of large-size and wide-width high-boron austenitic stainless steel plates.

[0014] The present invention adopts a new type of thermal processing technology, which proves that medium and thick high-boron stainless steel plates can also be prepared by hot rolling / hot forging, heat treatment and other means, breaking through the bottleneck that traditional processing methods of this type of material such as powder metallurgy can only produce small specifications and small batches, greatly broadening the application field of high-boron stainless steel and accelerating the localization process.

[0015] The method of the present invention comprises the following steps: 1. preparing a high-boron stainless steel blank, wherein the boron content is 0.15-2.4wt. % (mass fraction), and the matrix microstructure is austenite or ferrite. 1. Grind its surface clean and set aside; 2. Prepare two pieces of ordinary metal materials with thickness H=(0.6~4.0) H0, width K=(1.0~4.0) K0, and length L=(1.0~4.0) L0, grind their surfaces clean and set aside; where H0, K0, and L0 are the thickness, width, and length of the high-boron stainless steel blank, respectively; 3. Dig grooves in the two pieces of ordinary metal materials in step 2 so that the high-boron stainless steel blank in step 1 can be embedded in the groove formed by the two pieces of ordinary metal materials, and apply metal isolation agents on the contact surfaces of the high-boron stainless steel blank and the two pieces of ordinary metal materials (there are many kinds of metal isolation agents, which are not required here. The main function is to prevent the two pieces of metal from sticking together); 4. Assemble and weld the three groups of blanks (the three groups of blanks here refer to: a piece of high-boron stainless steel and two coated ordinary metal materials) to form a composite blank. And keep the composite billet at 1050~1200℃ for 2~12 h to homogenize the structure; 5. Hot roll or hot forge the composite billet into a slab of required thickness and width. After the steel plate is cooled, separate the three slabs along the isolation agent interface. The middle slab is the obtained high-boron stainless steel plate.

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

[0017] In the above step 2, the common metal material may be carbon steel, stainless steel or other metal materials having better thermoplasticity than the coated high-boron stainless steel.

[0018] In the above step 4, welding is performed under vacuum conditions, and the maximum welding depth of one side should not reach the contact surface of the three sets of blanks.

[0019] In the above step 5, the required thickness and width dimensions should include the dimensions of the upper and lower cladding materials after thermal deformation and the dimensions of the obtained high-boron stainless steel sheet. The obtained high-boron stainless steel sheet has a thickness of 2-80 mm, a width of not less than 80 mm, and a length of not less than 100 mm (Note: the maximum width and length dimensions are limited by the original billet size and hot rolling equipment), and there are no obvious cracks on the surface and edges.

[0020] In the embodiment of the present invention, a box-type resistance furnace is used for heat treatment, and timing starts after the furnace temperature rises to a set temperature.

[0021] In the embodiment of the present invention, the common metal material is grooved by cold machining, and the surface of the steel plate is cleaned by a grinder.

[0022] The metal separator used in the present invention is magnesium oxide. Example 1

[0023] Prepare 304-based high-boron stainless steel electroslag casting billets with a boron content of 1.95 wt.%, with dimensions of 30 mm thick, 140 mm wide, and 160 mm long. The billet matrix structure is austenite, and the surface is polished and cleaned for use.

[0024] Prepare two 304 stainless steel (GB / T 4238-2015) steel plates with a size of 45 mm thick (H=1.5 H0), 300 mm wide (K=2.1 K0), and 320 mm long (L=2.0 L0). After the surface is polished clean, grooves are dug from the surface to the inside so that the high-boron stainless steel blank can be embedded in the grooves formed by the two 304 stainless steel plates; where H0, K0, and L0 are the thickness, width, and length of the high-boron stainless steel blank, respectively; An isolating agent was coated on the contact surfaces of the high-boron stainless steel blank and two pieces of 304 stainless steel respectively, and the three groups of blanks were assembled and welded to form a composite blank; the welding was carried out in a vacuum chamber, and the maximum single-side welding depth was 50 mm, which did not reach the contact surfaces of the three groups of blanks.

[0025] After the composite blank is kept at 1130℃ for 6 hours, it is hot rolled to 8mm thick (total thickness of the composite plate). After the steel plate is cooled, the three slabs are separated along the interface of the separator, and the middle slab is the obtained high-boron stainless steel plate. Its dimensions are 3mm thick, 144mm wide, and 830mm long (Note: This dimension 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 is generally curved, the actual length of the high-boron stainless steel plate is much larger than this statistical value). No obvious cracks are found on the surface of the steel plate, which meets the requirements of the present invention. Example 2

[0026] The method is the same as that in Example 1, except that: (1) the high-boron stainless steel billet used is a continuous casting billet with a grade of 06Cr19Ni10 and a boron content of 2.2 wt.%, and the billet dimensions are 35 mm thick, 120 mm wide, and 150 mm long; (2) the coated ordinary metal material is Q235 carbon steel with dimensions of 50 mm thick (H=1.4 H0), 280 mm wide (K=2.3 K0), and 300 mm long (L=2.0 L0); the steel plate is asymmetrically grooved from the surface to the inside so that the high-boron stainless steel billet can be embedded in the groove formed by the two pieces of Q235; (3) the composite billet is kept at 1180°C for 4 h, and then taken out of the furnace and hot rolled to a thickness of 12 mm (total thickness of the composite plate). After the steel plate is cooled and separated along the interface of the separator, the obtained high-boron stainless steel plate has a thickness of 5 mm, a width of 123 mm, and a length of 660 mm (Note: this size only counts the length of the parallel section in the middle of the hot-rolled plate), and no obvious cracks are found on the surface of the steel plate, which meets the requirements of the present invention. Comparative Example

[0027] The high-boron stainless steel billet and original size are the same as those in Example 1, except that the electroslag cast billet is not coated with 304 stainless steel, and is directly hot-rolled after being kept at 1130°C for 6 hours. After 4 hot rolling passes and deformation to a thickness of 16 mm, obvious cracks appear at the edge and front end of the steel plate, with the maximum crack length reaching 35 mm. The surface of the steel plate is in the form of fragments, so hot rolling is stopped. The design requirements of the present invention are not met.

[0028] The above embodiments and comparative examples are used to illustrate the features and effects of the present invention in detail, but are not limited to these embodiments. Without departing from the concept of the present invention, there may be more other equivalent embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for processing large-size, wide-width, high-boron stainless steel sheets, characterized in that: The following steps are involved: Step 1: prepare a high-boron stainless steel blank, wherein the boron content is 0.15-2.4wt.%, and the matrix microstructure is austenite or ferrite. Grind the surface of the high-boron stainless steel blank clean and set aside; Step 2: Prepare two pieces of common metal materials with thickness H=(0.6~4.0)H0, width K=(1.0~4.0)K0, and length L=(1.0~4.0)L0, and polish the surfaces of the two pieces of common metal materials for use; where H0, K0, and L0 are the thickness, width, and length of the high-boron stainless steel blank, respectively, and the unit is mm; Step 3: dig grooves in the two ordinary metal materials in step 2, so that the high-boron stainless steel blank in step 1 is embedded in the grooves formed by the two ordinary metal materials, and metal isolation agents are respectively coated on the contact surfaces of the high-boron stainless steel blank and the two ordinary metal materials; Step 4: Assemble and weld the three groups of billets to form a composite billet, and keep the composite billet at 1050-1200°C for 2-12 hours; Step 5: hot-roll or hot-forge the composite billet into a slab of required thickness and width. After the steel plate is cooled, separate the three slabs along the metal separator interface. The middle slab is the obtained high-boron stainless steel plate.

2. The method for processing a large-size, wide-width, high-boron stainless steel sheet according to claim 1, characterized in that: In the above step 1, the high-boron stainless steel billet includes but is not limited to a continuous casting billet, an electroslag casting billet or a hot-deformed intermediate billet.

3. The method for processing a large-size, wide-width, high-boron stainless steel sheet according to claim 1, characterized in that: In the above step 2, the common metal material may be carbon steel, stainless steel or other metal materials having better thermoplasticity than the coated high-boron stainless steel.

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

5. The method for processing a large-size, wide-width, high-boron stainless steel sheet according to claim 1, characterized in that: In the above step 5, the required thickness and width dimensions should include the dimensions of the upper and lower cladding materials after thermal deformation and the dimensions of the obtained high-boron stainless steel sheet. The obtained high-boron stainless steel sheet has a thickness of 2 to 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.