Manufacturing method of ultra-low temperature high-strength non-magnetic austenitic stainless steel bar

Abstract

The application discloses a manufacturing method of an ultra-low-temperature high-strength non-magnetic austenitic stainless steel rod, which comprises the following steps: forming a fine-grain protective layer on the surface of a steel ingot by radial forging, small-deformation high-frequency forging and breaking down, so as to reduce the cracking risk in the fast forging process; increasing the forging ratio by fast forging, upsetting and elongating; and making the structure of the center of the steel ingot recrystallize to a certain extent; and finally, forming the steel rod by radial forging, large-deformation low-frequency forging and breaking down, so that dynamic recrystallization occurs in the whole cross-section of the steel rod, and uniform equiaxed crystals are formed, thereby solving the problems of multiple forging times, easy surface cracking and poor structure uniformity of the ultra-low-temperature high-strength non-magnetic austenitic stainless steel rod.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of steel materials, in particular to a manufacturing method of an ultra-low-temperature high-strength non-magnetic austenitic stainless steel bar. BACKGROUND

[0002] The technical route of thermonuclear fusion mainly includes magnetic confinement and inertial confinement, and the current mainstream technical route is the magnetic confinement route, mainly taking the tokamak as the main body, such as the international thermonuclear experimental reactor (ITER) and the like. However, with the progress of low-temperature superconducting technology, the magnetic field strength and current required by the design of a large superconducting fusion experimental device are significantly improved compared with the ITER, and the requirements for the materials of the magnet structure and the coil armor are higher. In order to achieve higher strength, the material design contains higher N, Cr, Mn and other elements, and due to the pure austenitic structure, there are problems such as poor high-temperature forgeability and difficulty in recrystallization. The traditional fast forging process is prone to cracking, the forging times are many, and the yield and production efficiency are low, and the core structure is coarse and non-recrystallized by using the traditional radial forging process.

[0003] The engineering design of a large superconducting fusion experimental device in China, the magnetic field strength and current of the magnet system are significantly improved, and the electromagnetic load borne by the superconducting magnet is greatly improved compared with the international thermonuclear fusion experimental reactor (ITER) device. At present, the ultra-low-temperature structural material in the ITER device cannot meet the bearing requirements of the fusion engineering experimental reactor in China. Therefore, it is urgent to develop an ultra-low-temperature high-strength non-magnetic austenitic stainless steel to meet the bearing requirements of the superconducting magnet of the fusion engineering experimental reactor in China. Compared with the original 316LN, the ultra-low-temperature high-strength non-magnetic austenitic stainless steel has higher Cr, N and Mn contents, higher high-temperature strength and poorer hot workability, and has the problems of difficulty in recrystallization and easy cracking in the forging process.

[0004] The application creatively proposes a process route of "radial forging small deformation high-frequency forging breakdown + fast forging secondary breakdown + radial forging large deformation low-frequency forging" to produce the ultra-low-temperature high-strength non-magnetic austenitic stainless steel. The problems of easy cracking, many forging times and uneven structure in the production of low-temperature high-strength non-magnetic austenitic stainless steel by using the fast forging process or the radial forging process are solved.

[0005] By radial forging small deformation high-frequency forging breakdown, a fine-grained layer is formed on the surface of the steel ingot, the risk of surface cracking in the fast forging upsetting process is reduced, then the fast forging upsetting is used to increase the forging ratio and make the center of the steel ingot recrystallize to a certain extent, and finally radial forging large deformation low-frequency forging is used to make the dynamic recrystallization occur in the whole cross-section of the steel bar and form uniform equiaxed grains. SUMMARY

[0006] The present application aims at the above-mentioned problems, and provides a manufacturing method of an ultra-low-temperature high-strength non-magnetic austenitic stainless steel rod.

[0007] The present application is achieved in the following way: an ultra-low-temperature high-strength non-magnetic austenitic stainless steel rod, the chemical elements of the ultra-low-temperature high-strength non-magnetic austenitic stainless steel rod are as follows in percentage by weight: C≤0.03%, Si 0.2%-0.5%, Mn: 1.2%-7.0%, Cr: 16.0%-24.0%, Ni: 10.0%-16.0%, Mo: 1.8%-3.0%, P≤0.035%, S≤0.005%, Nb≤0.3%, V≤0.3%, N: 0.20%-0.45%.

[0008] A manufacturing method of an ultra-low-temperature high-strength non-magnetic austenitic stainless steel rod, comprising the following steps: Step 1: obtaining a required electroslag ingot by a method of smelting-mold casting-electroslag; Step 2: steel ingot heating: the heating temperature target is 1190-1210 DEG C, and the holding time is 3-4 hours; Step 3: radial forging breakdown: the electroslag ingot after heating is discharged is subjected to breakdown in a radial forging machine, the total deformation amount of the breakdown is controlled to be 26%-30%, the single pass deformation amount is 5-6%, the forging frequency is 200-220 times / minute, and a first intermediate round billet is obtained; Step 4: first intermediate round billet heating: the heating temperature is 1190-1210 DEG C, and the holding time is 1-3 hours; Step 5: fast forging secondary breakdown: the first intermediate round billet after heating is subjected to secondary breakdown after fast forging, the upsetting compression amount of the fast forging is controlled to be 25%-35%, the upsetting compression amount is controlled to be 10%-15% in 2-3 passes, the fast forging elongation deformation amount is 20-30%, and a second intermediate round billet is obtained; Step 6: second intermediate round billet heating: the heating target temperature is 1190-1210 DEG C, and the holding time is 1-3 hours; Step 7: radial forging into finished product: the second intermediate round billet after heating is subjected to radial forging into finished product, the total compression ratio in the radial forging process is 3-8, the forging is performed in 3-10 passes, the single pass deformation amount is 10%-20%, and the forging frequency is 30-40 times / minute; and Step 8: finished product rod solid solution treatment: the solid solution treatment temperature is 1050-1060 DEG C, the holding time is 1-1.5 hours, and water cooling is performed to room temperature.

[0009] The present application has the following beneficial effects: the manufacturing process route of "radial forging small deformation amount high-frequency forging breakdown + fast forging secondary breakdown + radial forging large deformation amount low-frequency forging into finished product" proposed by the present application, compared with the existing fast forging process, has a large reduction in forging times, is not prone to surface cracking, improves production efficiency and yield, and compared with the existing radial forging process, forms uniform equiaxed crystals in the whole cross-section of the steel rod, greatly improves the uniformity of the structure, and meets the structure requirements of the product. DETAILED DESCRIPTION

[0010] The ultra-low temperature high-strength non-magnetic austenitic stainless steel is pure austenitic structure, and has the characteristics of narrow hot working process window, high high-temperature strength, poor forgeability and difficult recrystallization, etc. When the fast forging process is adopted, the steel ingot needs to be forged for multiple times due to the narrow hot working process window, high high-temperature strength and poor forgeability, and cracks are easily generated on the surface of the steel ingot, thereby affecting the yield rate. When the radial forging process is adopted, the surface of the steel ingot is formed with uniform equiaxed crystals due to the characteristic of difficult recrystallization, and the center and the surrounding position of the steel ingot are still in the as-cast structure.

[0011] To solve the cracking problem in the fast forging process, the application creatively proposes to perform radial forging small-deformation high-frequency forging breakdown, so that a fine-grain protective layer is formed on the surface of the steel ingot, the cracking risk in the fast forging process is reduced, the fast forging upsetting and elongation are used to increase the forging ratio, the recrystallization of the structure in the center of the steel ingot is caused to a certain degree, and finally the radial forging large-deformation low-frequency forging is performed to form the steel bar, so that the dynamic recrystallization occurs in the whole cross-section range of the steel bar, and uniform equiaxed crystals are formed.

[0012] The application proposes a manufacturing method of "radial forging small-deformation high-frequency forging breakdown + fast forging secondary breakdown + radial forging large-deformation low-frequency forging to form the material" to solve the problems of multiple forging times, surface cracking and poor structure uniformity of the ultra-low temperature high-strength non-magnetic austenitic stainless steel bar, and the obtained steel bar has good surface quality and structure uniformity, and the specific technical scheme is as follows: (1) the required electroslag ingot is obtained by the method of smelting-mold casting-electroslag.

[0013] (2) Steel ingot heating: the target heating temperature is 1190-1210 DEG C, and the holding time is 3-4 hours.

[0014] (3) Radial forging breakdown: the total deformation amount of the breakdown is controlled to be 26%-30%, the single-pass deformation amount is 5-6%, the forging frequency is 200-220 times per minute, and the first intermediate round billet is obtained.

[0015] (4) First intermediate round billet heating: the target heating temperature is 1190-1210 DEG C, and the holding time is 1-3 hours.

[0016] (5) Fast forging secondary breakdown: the upsetting reduction amount of the fast forging is controlled to be 25%-35%, the upsetting reduction amount is controlled to be 10%-15% in 2-3 passes, the fast forging elongation deformation amount is 20-30%, and the second intermediate round billet is obtained.

[0017] (6) Second intermediate round billet heating: the target heating temperature is 1190-1210 DEG C, and the holding time is 1-3 hours.

[0018] (7) Radial forging to form the material: the total compression ratio of the radial forging process is greater than 3-8. The forging is performed in 3-10 passes, the single-pass deformation amount is 10%-20%, and the forging frequency is 30-40 times per minute.

[0019] (8) Solution treatment: solution treatment target temperature 1050-1060℃, holding time 1-1.5 hours, water cooling to room temperature.

[0020] The chemical elements of the ultra-low temperature high-strength non-magnetic austenitic stainless steel bar are as follows in terms of percentage by weight: C≤0.03%, Si 0.2%-0.5%, Mn 1.2%-7.0%, Cr 16.0%-24.0%, Ni 10.0%-16.0%, Mo 1.8%-3.0%, P≤0.035%, S≤0.005%, Nb≤0.3%, V≤0.3%, and N 0.20%-0.45%.

[0021] The specific implementation of the method will be described in detail below in conjunction with examples, but the specific implementation of the present application is not limited to the examples described below. Example One

[0022] According to the process of the present application, the steps of the method for producing the φ220mm ultra-low temperature high-strength non-magnetic austenitic stainless steel bar are as follows: (1) obtaining a φ500mm electroslag ingot by the method of smelting-mold casting-electroslag, and the chemical composition of the ingot is as follows in terms of percentage by mass: C: 0.013%, Si: 0.32%, Mn: 5.3%, Cr: 21.20%, Ni: 15.2%, Mo: 1.82%, P: 0.012%, S: 0.001%, Nb: 0.12%, V: 0.15%, and N: 0.33%.

[0023] (2) Ingot heating: target heating temperature 1190℃, holding time 4 hours.

[0024] (3) Upsetting and blooming: total deformation amount of blooming is controlled to be 30%, single-pass deformation amount 6%, and forging frequency 220 times / minute, to obtain a first intermediate round billet.

[0025] (4) First intermediate round billet heating: target heating temperature 1210℃, holding time 2 hours.

[0026] (5) Fast forging secondary blooming: fast forging upsetting reduction amount is controlled to be 30%, in 3 passes, single-pass reduction amount is controlled to be 10%, fast forging elongation deformation amount is 22%, to obtain a second intermediate round billet.

[0027] (6) Second intermediate round billet heating: target heating temperature 1210℃, holding time 2 hours.

[0028] (7) Upsetting and blooming: total compression ratio of upsetting and blooming is 3.8. The upsetting and blooming is performed in 8 passes, single-pass deformation amount is 15%, and forging frequency is 40 times / minute.

[0029] (8) Solution treatment: solution treatment target temperature 1050℃, holding time 1 hour, water cooling to room temperature.

[0030] After the steps are implemented, the surface grain size of the steel bar is grade 7, and the grain size of the core of the steel bar is grade 5. Example 2

[0031] According to the process of the application, the steps of the method for producing φ190mm ultra-low temperature high-strength non-magnetic austenitic stainless steel bar are as follows: (1) Obtain φ410mm electroslag ingot by smelting-mold casting-electroslag method, and the chemical composition is as follows: C: 0.025%, Si: 0.32%, Mn: 5.8%, Cr: 21.20%, Ni: 15.2%, Mo: 1.82%, P: 0.012%, S: 0.001%, Nb: 0.18%, V: 0.19%, N: 0.42%.

[0032] (2) Steel ingot heating: target heating temperature is 1190℃, holding time is 3 hours.

[0033] (3) Radial forging breakdown: the total deformation amount is controlled to be 30%, the single pass deformation amount is 6%, the forging frequency is 220 times / minute, and the first intermediate round billet is obtained.

[0034] (4) First intermediate round billet heating: target heating temperature is 1210℃, holding time is 1.5 hours.

[0035] (5) Fast forging secondary breakdown: the fast forging upsetting reduction amount is controlled to be 30%, which is divided into 3 passes, the single pass reduction amount is controlled to be 10%, the fast forging elongation deformation amount is 20%, and the second intermediate round billet is obtained.

[0036] (6) Second intermediate round billet heating: target heating temperature is 1210℃, holding time is 1.5 hours.

[0037] (7) Radial forging into finished product: the total radial forging compression ratio is 3.8. The forging is divided into 7 passes, the single pass deformation amount is 17%, and the forging frequency is 40 times / minute.

[0038] (8) Solution treatment: solution treatment target temperature 1050℃, holding time 1 hour, water cooling to room temperature.

[0039] After the steps are implemented, the surface grain size of the steel bar is grade 8, and the grain size of the core of the steel bar is grade 5.

[0040] The above only describes specific embodiments of the application, but the structural features of the scope of protection of the application are not limited thereto, and any person skilled in the art can make changes or modifications in the field of the application, which are all covered by the patent scope of the application.

Claims

1. A method of manufacturing an ultra-low temperature high-strength non-magnetic austenitic stainless steel bar, characterized by: The chemical elements of the ultra-low temperature high-strength non-magnetic austenitic stainless steel rod are as follows in percentage by weight: C≤0.03%, Si 0.2%-0.5%, Mn: 1.2%-7.0%, Cr: 16.0%-24.0%, Ni: 10.0%-16.0%, Mo: 1.8%-3.0%, P≤0.035%, S≤0.005%, Nb≤0.3%, V≤0.3%, N: 0.20%-0.45%; A manufacturing method of an ultra-low temperature high-strength non-magnetic austenitic stainless steel rod comprises the following steps: Step one: obtaining the required electroslag ingot by the method of smelting-mold casting-electroslag; Step two: steel ingot heating: the heating temperature target is 1190-1210 DEG C, and the holding time is 3-4 hours; Step three: radial forging breakdown: the electroslag ingot after heating is discharged is broken down in a radial forging machine, the total deformation amount of the breakdown is controlled to be 26%-30%, the single pass deformation amount is 5-6%, the forging frequency is 200-220 times per minute, and a first intermediate round billet is obtained; Step four: first intermediate round billet heating: the heating temperature is 1190-1210 DEG C, and the holding time is 1-3 hours; Step five: fast forging second breakdown: the first intermediate round billet after heating is fast forged to perform the second breakdown, the upsetting compression amount of the fast forging is controlled to be 25%-35%, the fast forging is divided into 2-3 passes, the single pass compression amount is controlled to be 10%-15%, the fast forging elongation deformation amount is 20-30%, and a second intermediate round billet is obtained; Step six: second intermediate round billet heating: the heating target temperature is 1190-1210 DEG C, and the holding time is 1-3 hours; Step seven: radial forging into finished product: the second intermediate round billet after heating is radially forged into a finished product, the total compression ratio of the radial forging process is 3-8, the forging is divided into 3-10 passes, the single pass deformation amount is 10%-20%, and the forging frequency is 30-40 times per minute; Step eight: finished product rod solid solution treatment: the solid solution treatment temperature is 1050-1060 DEG C, the holding time is 1-1.5 hours, and the water cooling is to room temperature.