Vacuum electron beam welding method for large-thickness 304 stainless steel

Abstract

A vacuum electron beam welding method for large-thickness 304 stainless steel comprises the steps that two pieces of 304 stainless steel to be welded with the thickness of 20-150 mm are mechanically polished and put into a vacuum chamber, the vacuumizing degree of the vacuum chamber is controlled to be 10 <-2 > Pa to 10 <-3 > Pa, the welding distance between the two pieces of 304 stainless steel to be welded is controlled to be within 0.2 mm, common welding is conducted on the welding distance through a focused electron beam, and then the welding distance is controlled to be within 0.2 mm; defocusing electron beams are adopted to conduct modification welding on the welding distance, after electron beam welding is completed under the vacuum condition, the welded 304 stainless steel is placed in a vacuum chamber to be naturally cooled for 10 min, then the vacuum degree of the vacuum chamber is removed, the welded 304 stainless steel is taken out, the welding seam quality meets the GJB1718-2005I level requirement, the single-face welding and double-face forming process without beveling of the to-be-welded face can be achieved, and the welding efficiency is improved. Welding efficiency is remarkably improved, welding heat input is small, welding deformation is small, and welding precision can be effectively controlled.

Description

Technical Field

[0001] The invention belongs to the technical field of welding, and in particular relates to a vacuum electron beam welding method for thick 304 stainless steel. Background Art

[0002] 304 stainless steel is a medium carbon quenched and tempered steel. The carbon equivalent of 304 stainless steel is relatively high, and it has a high tendency to cold cracking during welding. At the same time, it is very sensitive to heat and has a tendency to be brittle. It has very strict requirements on heat input, a narrow range of welding process parameters, a high tendency to produce thermal cracks, and it is very difficult to control the welding quality.

[0003] At present, the commonly used welding methods for 304 stainless steel are mainly TIG, MIG and MAG. These welding methods have relatively large heat input, large welding deformation, coarse weld structure and poor welding quality. Especially for thick 304 stainless steel, beveling is required for multi-layer and multi-pass welding, which has low welding efficiency and poor overall joint performance.

[0004] Chen Guoqing et al. conducted vacuum electron beam welding on 2 mm thick 304 stainless steel and obtained a welded joint without metallurgical defects. They also studied the joint structure and properties (Chen Guoqing, Zhang Binggang, Wang Zhenbing, et al. Vacuum electron beam welding of 304 stainless steel [J]. Journal of the China Welding Society, 2011, 32(9): 33-36.). This study was mainly aimed at 2 mm thick 304 stainless steel sheets and is not applicable to 304 stainless steel thicker than 5 mm.

[0005] Up to now, there is no report on the electron beam welding method for 20 to 150 mm thick 304 stainless steel. Summary of the invention

[0006] In order to solve the above problems, the present invention provides a vacuum electron beam welding method for thick 304 stainless steel. The method utilizes the characteristics of electron beam welding, such as strong penetration ability, small heat input, fast welding speed, high weld purity under vacuum conditions, finer weld and heat affected zone structure than arc welding, small welding deformation and residual stress, etc., and can weld 304 stainless steel with a thickness of 20 to 150 mm, with high welding efficiency, stable welding performance, and guaranteed welding quality.

[0007] In order to achieve the above-mentioned invention object, the present invention adopts the following technical scheme:

[0008] A vacuum electron beam welding method for thick 304 stainless steel, wherein the thick 304 stainless steel has a wall thickness ranging from 20 to 150 mm, and the 304 stainless steel is either a plate, a casting, or a forging. The characteristics of the invention are as follows:

[0009] First, the two 304 stainless steel surfaces to be welded are mechanically polished respectively, and then the surfaces to be welded are degreased with acetone, alcohol and ultrasound after mechanical polishing, and then dried for use;

[0010] The two dried and ready-to-be-welded 304 stainless steels are placed in a vacuum chamber, and the welding distance between the two 304 stainless steels is adjusted by a fixture, and the welding distance is controlled within 0.2 mm, and the electron beam is accurately aligned with the midpoint of either end of the welding distance, and then the vacuum chamber is evacuated, and the vacuum degree of the vacuum chamber is controlled at 10-2Pa to 10-3Pa;

[0011] First, general welding is performed on the welding interval by using a focused electron beam, at which the acceleration voltage of the focused electron beam is controlled at 150 KV, the welding speed is controlled at 200 to 800 mm / min, the beam current of the focused electron beam is controlled at 30 to 200 mA, the vertical distance between the muzzle of the focused electron beam and the two surfaces of the 304 stainless steel to be welded is controlled at 500 to 1300 mm, the defocus amount of the focused electron beam is 0, and the general welding is performed from either end of the welding interval to the other end thereof;

[0012] Then, a defocused electron beam is used to perform modification welding on the welding interval, wherein the acceleration voltage of the defocused electron beam is controlled at 150KV, the welding speed is controlled at 250-350mm / min, the beam current of the defocused electron beam is controlled at 20-30mA, the vertical distance between the muzzle of the defocused electron beam and the surfaces of the two 304 stainless steels to be welded is controlled at 500-1300mm, the defocus amount of the defocused electron beam is controlled at 0.3-0.8mm, and the modification welding is performed from the other end of the welding interval to either end thereof, thereby completing the vacuum electron beam welding of the two 304 stainless steels to be welded;

[0013] After electron beam welding is completed under vacuum conditions, the welded 304 stainless steel is placed in a vacuum chamber to cool naturally for 10 minutes. After that, the vacuum degree of the vacuum chamber is removed and the welded 304 stainless steel is taken out. Samples are taken from the weld joints for strength testing, and the strength coefficient of the weld joints is required to be ≥ 0.90.

[0014] Due to the adoption of the above technical solution, the present invention produces the following positive effects:

[0015] 1. Whether the present invention adopts focused electron beam welding or defocused electron beam welding, the electron beam has concentrated energy, small heat input, strong penetration ability, high energy conversion rate and good controllability, so that the whole welding process time is shortened, the heat affected zone is reduced, and the weld quality meets the GJB 1718-2005 I level requirements.

[0016] 2. The electron beam welding process of the present invention is carried out in a vacuum chamber. The evacuation of the vacuum chamber can effectively avoid the influence of harmful gases in the atmosphere on the weld and effectively improve the bonding strength of the weld.

[0017] 3. The electron beam welding of the present invention can realize a single-sided welding and double-sided forming process without a groove on the welded surface, which significantly improves the welding efficiency and avoids the problem of reduced weld performance and quality caused by multi-layer and multi-pass welding in the prior art.

[0018] 4. The electron beam welding of the present invention has a small welding heat input and a small welding deformation, and can effectively control the welding manufacturing accuracy of 304 stainless steel. DETAILED DESCRIPTION

[0019] The invention discloses a vacuum electron beam welding method for thick 304 stainless steel. The thick 304 stainless steel refers to 304 stainless steel with a wall thickness ranging from 20 to 150 mm. The 304 stainless steel is either a plate, a casting or a forging.

[0020] The invention firstly performs mechanical grinding on the welding surfaces of two 304 stainless steels to be welded respectively, and then uses acetone, alcohol and ultrasonic waves to remove oil stains on the welding surfaces after mechanical grinding, and then dries them for standby use.

[0021] The two dried and ready-to-be-welded 304 stainless steels are placed in a vacuum chamber, and the welding distance between the two 304 stainless steels is adjusted by a fixture, and the welding distance is controlled within 2 mm. The electron beam is accurately aligned with the midpoint of either end of the welding distance, and then the vacuum chamber is evacuated, and the vacuum degree of the vacuum chamber is controlled at 10-2Pa to 10-3Pa.

[0022] First, general welding is performed on the welding interval by using a focused electron beam, at which the acceleration voltage of the focused electron beam is controlled at 150 KV, the welding speed is controlled at 200 to 800 mm / min, the beam current of the focused electron beam is controlled at 30 to 200 mA, the vertical distance between the muzzle of the focused electron beam and the two surfaces of the 304 stainless steel to be welded is controlled at 500 to 1300 mm, the defocus amount of the focused electron beam is 0, and the general welding is performed from either end of the welding interval to the other end thereof;

[0023] A defocused electron beam is then used to perform modification welding on the welding interval, wherein the acceleration voltage of the defocused electron beam is controlled at 150 KV, the welding speed is controlled at 250 to 350 mm / min, the beam current of the defocused electron beam is controlled at 20 to 30 mA, the vertical distance between the muzzle of the defocused electron beam and the surfaces of the two 304 stainless steels to be welded is controlled at 500 to 1300 mm, and the defocus amount of the defocused electron beam is controlled at 0.3 to 0.8 mm. The modification welding is performed from the other end of the welding interval to either end thereof, thereby completing the vacuum electron beam welding of the two 304 stainless steels to be welded;

[0024] Electron beam welding may cause surface collapse defects during normal welding, while modified welding can repair the collapse defects and make the welding surface smoother and brighter. No other welding materials are added for either normal welding or modified welding.

[0025] After electron beam welding is completed under vacuum conditions, the welded 304 stainless steel is placed in a vacuum chamber to cool naturally for 10 minutes. After that, the vacuum degree of the vacuum chamber is removed and the welded 304 stainless steel is taken out. Samples are taken from the weld joints for strength testing, and the strength coefficient of the weld joints is required to be ≥ 0.90.

[0026] In the present invention, the heat input of electron beam welding is small, the welding speed is fast, the purity of the weld is high under vacuum conditions, the weld and heat-affected zone structure are finer than those of ordinary arc welding, the welding deformation and residual stress are small, and the performance comparison with tungsten inert gas arc welding is shown in the table below.

[0027] Welding methods Average tensile strength (MPa) Average elongation A (%) Strength coefficient Electron beam welding 1970 7.1 0.98 Tungsten Inert Gas Welding 1830 5.2 0.91 304 Stainless Steel 2020 8.1 0.1

[0028] Taking the butt welding of two 304 stainless steel plates with a size of 300×150×25mm as an example, the welding efficiency is shown in the table below.

[0029] Welding methods Welding time (minutes) Beveling processing time (minutes) Assembly time (minutes) Total working hours (minutes) Electron beam welding 60 -- 60 120 Tungsten Inert Gas Welding 300 120 10 430

[0030] The above two tables fully illustrate that the present invention is significantly superior to tungsten inert gas arc welding in terms of average tensile strength, average elongation, strength coefficient and welding efficiency.

Claims

1. A vacuum electron beam welding method for thick 304 stainless steel, wherein the thick 304 stainless steel has a wall thickness of 20 to 150 mm, and the 304 stainless steel is a plate, a casting, or a forging, and is characterized by: First, the two 304 stainless steel surfaces to be welded are mechanically polished respectively, and then the surfaces to be welded are degreased with acetone, alcohol and ultrasound after mechanical polishing, and then dried for use; The two dried and ready-to-be-welded 304 stainless steels are placed in a vacuum chamber, and the welding distance between the two 304 stainless steels is adjusted by a fixture, and the welding distance is controlled within 0.2 mm. The electron beam is accurately aligned with the midpoint of either end of the welding distance, and then the vacuum chamber is evacuated, and the vacuum degree of the vacuum chamber is controlled at 10-2Pa to 10-3Pa; First, general welding is performed on the welding interval by using a focused electron beam, at which the acceleration voltage of the focused electron beam is controlled at 150 KV, the welding speed is controlled at 200 to 800 mm / min, the beam current of the focused electron beam is controlled at 30 to 200 mA, the vertical distance between the muzzle of the focused electron beam and the two surfaces of the 304 stainless steel to be welded is controlled at 500 to 1300 mm, the defocus amount of the focused electron beam is 0 mm, and the general welding is performed from either end of the welding interval to the other end thereof; A defocused electron beam is then used to perform modification welding on the welding interval, wherein the acceleration voltage of the defocused electron beam is controlled at 150 KV, the welding speed is controlled at 250 to 350 mm / min, the beam current of the defocused electron beam is controlled at 20 to 30 mA, the vertical distance between the muzzle of the defocused electron beam and the surfaces of the two 304 stainless steels to be welded is controlled at 500 to 1300 mm, and the defocus amount of the defocused electron beam is controlled at 0.3 to 0.8 mm. The modification welding is performed from the other end of the welding interval to either end thereof, thereby completing the vacuum electron beam welding of the two 304 stainless steels to be welded; After electron beam welding is completed under vacuum conditions, the welded 304 stainless steel is placed in a vacuum chamber to cool naturally for 10 minutes. After that, the vacuum degree of the vacuum chamber is removed and the welded 304 stainless steel is taken out. Samples are taken from the weld joints for strength testing, and the strength coefficient of the weld joints is required to be ≥ 0.90.