Thin-wall ultrahigh-strength steel D506A electron beam welding method

Abstract

The invention discloses an electron beam welding method for thin-wall ultrahigh-strength steel D506A. The electron beam welding method comprises the specific steps of part cleaning, assembling, demagnetizing, welding, post-welding treatment and inspection. Wherein the welding steps comprise positioned welding, preheating, deep penetration welding, first modification welding and second modification welding in sequence, and all the steps are completed in a vacuum electron beam welding machine. According to the thin-wall ultrahigh-strength steel D506A electron beam welding method, by optimizing electron beam welding parameters and controlling the interlayer temperature, the cooling speed of welding is reduced; meanwhile, the defocusing electron beam is used for preheating the to-be-welded position for a certain time, cold cracks can be avoided, the hardness of a heat affected zone can be reduced, and the plasticity of a connector can be improved; and moreover, a deep penetration welding bead is covered through two modification welding processes for surface covering, so that the forming quality of a welding seam is ensured, the problem that cracks are easily generated in thin-wall ultrahigh-strength steel D506A electron beam welding is solved, and the use requirement of a solid rocket engine is ensured.

Description

Technical Field

[0001] The invention relates to the technical field of welding, and in particular to an electron beam welding method for thin-walled ultra-high strength steel D506A. Background Art

[0002] The combustion chamber shell accounts for a large proportion of the mass of a solid missile engine. Selecting materials with characteristics such as light weight, high strength, and high rigidity to manufacture the combustion chamber shell is one of the effective ways to achieve lightweight and high quality ratio of missile engines. D506A is a new generation of economical low-alloy ultra-high strength steel for shells. The tensile strength of this ultra-high strength steel can reach more than 1800MPa, but because this ultra-high strength steel has added more alloy elements, the carbon equivalent exceeds 1.7%, which is a material with a high carbon equivalent. It has poor weldability and is prone to hardened structure after welding, thereby increasing the risk of cold cracks. In addition, excessive welding heat input can cause hot cracks during welding. This is because rapid cooling may cause low-melting-point impurities to produce liquid films at the grain boundaries, increasing the risk of hot cracks.

[0003] The existing welding sequence of ultra-high strength steel electron beam welding is positioning welding, deep penetration welding, and finishing welding. The specific parameters of electron beam welding are as follows:

[0004] (1) Positioning welding: electron beam I w =7-10mA, working distance w=250mm, welding speed v=35-40mm / s;

[0005] (2) Deep penetration welding: electron beam I w =80-90mA, working distance w=250mm, welding speed v=35-40mm / s;

[0006] (3) Modification welding: electron beam I w =45-55mA, working distance w=250mm, welding speed v=35-40mm / s.

[0007] Existing electron beam welding of ultra-high strength steel does not control the interlayer temperature between welds; in addition, the product needs to be annealed and heat treated within 4 hours after welding. However, this welding method cannot suppress the generation of thermal cracks in the weld during the welding process, and cannot guarantee that the product will not generate cold cracks before heat treatment, which ultimately results in the weld failing to meet the Grade I weld requirements and design requirements in GJB1718A-2005.

[0008] Electron beam welding belongs to high-energy beam welding methods. Its welding characteristics are fast welding speed. When welding ultra-high strength steels such as 30Cr3, the welding speed can reach 40mm / s. Since D506A has good hardenability, too fast cooling speed will cause hardened structure in the weld, resulting in increased hardness of the welded joint, thereby increasing the risk of cold cracks. Therefore, it is necessary to develop an electron beam welding method suitable for thin-walled ultra-high strength steel D506A to avoid cold cracks, reduce the hardness of the heat-affected zone, and improve the plasticity of the joint. Summary of the invention

[0009] The present invention provides an electron beam welding method for thin-walled ultra-high strength steel D506A. By optimizing electron beam welding parameters and controlling the interlayer temperature, the problem of easy cracking in electron beam welding of thin-walled ultra-high strength steel D506A is solved, thereby ensuring the use requirements of solid rocket engines.

[0010] A thin-walled ultra-high strength steel D506A electron beam welding method, the specific steps include parts cleaning, assembly, demagnetization, welding, post-weld treatment, inspection, wherein: the welding steps are positioning welding, preheating, deep penetration welding, first modification welding, second modification welding, all of which are completed in a vacuum electron beam welding machine.

[0011] The specific steps are:

[0012] S1. Parts cleaning: Use a scouring pad to remove the oxide scale on the part to be welded until the metallic luster is exposed. Use a white silk cloth dipped in alcohol to wipe the part to be welded to remove oil and other excess substances.

[0013] S2. Assembly: Use tooling to assemble the parts to be welded into place. After the two parts to be welded are butt-jointed, an I-type butt ring weld is formed to ensure that the misalignment is less than 0.2mm and the assembly gap is less than 0.02mm.

[0014] S3, Demagnetization: Demagnetize the assembled components to ensure that the magnetic flux density of the welded parts is less than 2×10 -4 T.

[0015] S4. Welding: Send the product into the vacuum electron beam welding machine for vacuuming, monitor the temperature of the welding area through the infrared thermal imager, control the preheating temperature and interlayer cooling time, and perform positioning welding, preheating, deep melting welding, first modification welding, and second modification welding in sequence.

[0016] S41, the positioning welding adopts 6-stage positioning welding, the positioning welding sequence is 0°, 180°, 240°, 60°, 120°, 300°, and the angle of each positioning weld is 15°; the electron beam current I w =7-10mA, focused beam current I f =560-570mA, working distance w=250mm, welding speed v=35-40mm / s.

[0017] S42, the preheating adopts electron beam welding defocusing method to locally heat the joint, thereby reducing the welding cooling rate; the preheating parameters are: electron beam current I w =7-10mA, focused beam current I f =640-650mA, working distance w=250mm, welding speed v=35-40mm / s, preheating temperature 200-230℃, preheating angle 1080°. If the preheating temperature range is not reached, the preheating angle is increased by 360° until the preheating temperature range is reached.

[0018] S43, the deep penetration welding is performed immediately after preheating is completed; the deep penetration welding parameters are: electron beam current I w =40-50mA, focused beam current I f =610-620mA, working distance w=250mm, welding speed v=20-30mm / s.

[0019] S44, the first modification welding is performed in the range of 150-200°C; the first modification welding bead deviates from the center of the deep penetration welding bead by 0.5-1mm; the specific parameters of the first modification welding are: electron beam current I w =15-25mA, focused beam current I f =640-650mA, working distance w=250mm, welding speed v=35-40mm / s.

[0020] S45, the second modification welding is performed in the range of 150-200°C; the second modification welding bead deviates from the center of the deep penetration welding bead by 0.5-1mm, and the deviation direction of the first modification welding bead is opposite; the specific parameters of the second modification welding are: electron beam current I w =15-25mA, focused beam current I f =640-650mA, working distance w=250mm, welding speed v=35-40mm / s.

[0021] The vacuum electron beam welder is a medium-voltage electron beam welder with an acceleration voltage of 60 kV. The vacuum degree in the vacuum chamber should be less than 7.0×10 -2 Pa.

[0022] After the product is sent into the vacuum electron beam welder for vacuuming, the temperature of the welding area is monitored by an infrared thermal imager. The accuracy of the infrared thermal imager is no more than ±10°C, and the feedback time is less than 250ms.

[0023] S5. Post-weld treatment: After welding, slowly cool in the vacuum chamber until the temperature of the welding area is lower than 50°C and then open the vacuum chamber.

[0024] S6. Inspection: After welding, X-rays are used to perform non-destructive inspection on electron beam welds. The weld quality meets the requirements of Grade I welds in GJB1718A-2005.

[0025] The beneficial effects of the present invention are:

[0026] (1) The present invention optimizes the electron beam welding process and controls the interlayer temperature to perform preheating treatment before welding and slow cooling in the furnace after welding, which can increase the residence time of the molten pool and reduce the cooling rate of welding to 20 mm / s, thereby reducing the risk of welding cold cracks and the embrittlement problem of the overheated zone. Slow cooling in the furnace after welding can make the workpiece cool slowly and evenly, thereby reducing welding stress and avoiding the generation of cold cracks.

[0027] (2) The preheating treatment before welding in the present invention can increase the base temperature of the substrate, thereby reducing the cooling rate of the weld. The defocused electron beam is used to preheat the weld for a certain period of time, which can not only avoid the generation of cold cracks, but also reduce the hardness of the heat-affected zone and improve the plasticity of the joint.

[0028] (3) The present invention reduces the heat input of the modification welding by reducing the electron beam current of the modification welding. However, after reducing the electron beam current, the weld width is not enough to cover the deep penetration welding bead, resulting in poor weld appearance. Therefore, two modification welds are used to cover the deep penetration welding bead to ensure the weld formation quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions disclosed in the present invention, the following briefly introduces the drawings required to be used in some embodiments disclosed in the present invention. Obviously, the drawings described below are only drawings of some embodiments disclosed in the present invention. For ordinary technicians in this field, other drawings can also be obtained based on these drawings. In addition, the drawings described below can be regarded as schematic diagrams, and are not limitations on the actual size of the products involved in the embodiments disclosed in the present invention, the actual process of the method, etc.

[0030] Figure 1 Schematic diagram of the cross-section of the vacuum electron beam weld of ultra-high strength steel D506A.

[0031] The accompanying drawings are marked as follows: 1. deep penetration welding bead; 2. first modification welding bead; 3. second modification welding bead. DETAILED DESCRIPTION

[0032] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0033] A thin-walled ultra-high strength steel D506A electron beam welding method, the specific implementation steps are as follows:

[0034] S1. Parts cleaning: Use a scouring pad to remove the oxide scale on the part to be welded until the metallic luster is exposed. Use a white silk cloth dipped in alcohol to wipe the part to be welded to remove oil and other excess substances.

[0035] S2. Assembly: Use tooling to assemble the parts to be welded into place. After the two parts to be welded are butt-jointed, an I-type butt ring weld is formed to ensure that the misalignment is less than 0.2mm and the assembly gap is less than 0.02mm.

[0036] S3, Demagnetization: Demagnetize the assembled components to ensure that the magnetic flux density of the welded parts is less than 2×10 -4 T.

[0037] S4. Welding: Schematic diagram of the cross-section of the vacuum electron beam welding weld of ultra-high strength steel D506A is as follows Figure 1 As shown, the product is placed in a vacuum electron beam welder for vacuuming, and the temperature of the welding area is monitored by an infrared thermal imager to control the preheating temperature and interlayer cooling time. The specific welding steps and process parameters are as follows:

[0038] S41, positioning welding: 6 sections of positioning welding are used, the angle of each section of positioning weld is 15°, the positioning welding sequence is 0°, 180°, 240°, 60°, 120°, 300°, and the positioning welding parameters are: electron beam current I w =7-10mA, focused beam current I f =560-570mA, working distance w=250mm, welding speed v=35-40mm / s;

[0039] S42, preheating: electron beam welding defocusing method is used to locally heat the joint, thereby reducing the welding cooling rate. The preheating parameters are: electron beam current I w =7-10mA, focused beam current I f =640-650mA, working distance w=250mm, welding speed v=35-40mm / s, preheating temperature 200-230℃, preheating angle 1080°. If the preheating temperature range is not reached, the preheating angle is increased by 360° until the preheating temperature range is reached.

[0040] S43, deep penetration welding: deep penetration welding is performed immediately after preheating. The deep penetration welding parameters are: electron beam current I w =40-50mA, focused beam current I f =610-620mA, working distance w=250mm, welding speed v=20-30mm / s;

[0041] S44, first modification welding: control the temperature of the welding area within the range of 150-200℃, implement the first modification welding, the first modification welding bead deviates from the center of the deep penetration welding bead by 0.5-1mm, the specific parameters are: electron beam current Iw =15-25mA, focused beam current I f =640-650mA, working distance w=250mm, welding speed v=35-40mm / s;

[0042] S45, second modification welding: control the temperature of the welding area within the range of 150-200℃, implement the second modification welding, the second modification welding bead deviates from the center of the deep penetration welding bead by 0.5-1mm, and the first modification welding bead deviates in the opposite direction. The specific parameters are: electron beam current I w =15-25mA, focused beam current I f =640-650mA, working distance w=250mm, welding speed v=35-40mm / s.

[0043] S5. Post-weld treatment: After welding, slowly cool in the vacuum chamber until the temperature of the welding area is lower than 50°C and then open the vacuum chamber.

[0044] S6. Inspection: After welding, X-rays are used to perform non-destructive inspection on electron beam welds. The weld quality meets the requirements of Grade I welds in GJB1718A-2005. Specific embodiments

[0046] A solid rocket engine casing is made of D506A, with a wall thickness of 1.6 mm, a diameter of 204 mm, and a type I butt girth weld. The weld quality is required to meet the requirements of level I welds in GJB1718A-2005. The specific implementation method is as follows:

[0047] S1. Parts cleaning: Use a scouring pad to remove the oxide scale on the part to be welded until the metallic luster is exposed. Use a white silk cloth dipped in alcohol to wipe the part to be welded to remove oil and other excess substances.

[0048] S2. Assembly: Use tooling to assemble the parts to be welded into place. After the two parts to be welded are butt-jointed, an I-type butt ring weld is formed. The misalignment is 0.2mm and the assembly clearance is 0.02mm.

[0049] S3, Demagnetization: Demagnetize the assembled components, and the magnetic flux density of the welded parts is 1×10 -4 T.

[0050] S4. Welding: Schematic diagram of the cross-section of the vacuum electron beam welding weld of ultra-high strength steel D506A is as follows Figure 1 As shown, the product is placed in a vacuum electron beam welder for vacuuming, and the temperature of the welding area is monitored by an infrared thermal imager to control the preheating temperature and interlayer cooling time. The specific welding steps and process parameters are as follows:

[0051] S41, positioning welding: 6 sections of positioning welding are used, the angle of each section of positioning weld is 15°, the positioning welding sequence is 0°, 180°, 240°, 60°, 120°, 300°, and the positioning welding parameters are: electron beam current I w =10mA, focused beam current I f =566mA, working distance w=250mm, welding speed v=40mm / s;

[0052] S42, preheating: electron beam welding defocusing method is used to locally heat the joint, thereby reducing the welding cooling rate. The preheating parameters are: electron beam current I w =8mA, focused beam current I f =650mA, working distance w=250mm, welding speed v=340mm / s, preheating temperature is 220℃, preheating angle is 1080°;

[0053] S43, deep penetration welding: deep penetration welding is performed immediately after preheating. The deep penetration welding parameters are: electron beam current I w =45mA, focused beam current I f =615mA, working distance w=250mm, welding speed v=25mm / s;

[0054] S44, first modification welding: the temperature of the welding area is 170°C, and the first modification welding is performed. The first modification welding bead deviates from the center of the deep penetration welding bead by 0.8 mm. The specific parameters are: electron beam current I w =20mA, focused beam current I f =650mA, working distance w=250mm, welding speed v=40mm / s;

[0055] S45, second modification welding: control the temperature of the welding area within the range of 170℃, implement the second modification welding, the second modification welding bead deviates from the center of the deep penetration welding bead by 0.8mm, and the deviation direction of the first modification welding bead is opposite. The specific parameters are: electron beam current I w =20mA, focused beam current I f =650mA, working distance w=250mm, welding speed v=40mm / s.

[0056] S5. Post-weld treatment: After welding, slowly cool the workpiece in the vacuum chamber, the temperature of the welding area is 45°C, and the workpiece is removed from the vacuum chamber.

[0057] S6. Inspection: Immediately after welding, the electron beam weld is subjected to nondestructive inspection by X-rays. The weld quality meets the requirements of Grade I welds in GJB1718A-2005. 24 hours after welding, the electron beam weld is subjected to nondestructive inspection by X-rays again. The weld quality meets the requirements of Grade I welds in GJB1718A-2005.

[0058] Although the present invention has been disclosed as above in the form of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art may make possible changes and modifications to the technical solution of the present invention using the above disclosed contents without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the contents of the technical solution of the present invention shall fall within the protection scope of the technical solution of the present invention.

Claims

1. A thin-walled ultra-high strength steel D506A electron beam welding method, the specific steps include parts cleaning, assembly, demagnetization, welding, post-weld treatment, inspection, characterized in that: The welding steps are positioning welding, preheating, deep melting welding, first finishing welding and second finishing welding, which are all completed in a vacuum electron beam welding machine.

2. The electron beam welding method for thin-walled ultra-high strength steel D506A according to claim 1, characterized in that: The positioning welding adopts 6-section positioning welding, the positioning welding sequence is 0°, 180°, 240°, 60°, 120°, 300°, and the angle of each positioning weld is 15°; Position welding parameters: electron beam current I w =7-10mA, focused beam current I f =560-570mA, working distance w=250mm, welding speed v=35-40mm / s.

3. The electron beam welding method for thin-walled ultra-high strength steel D506A according to claim 1, characterized in that: The preheating uses electron beam welding defocusing to locally heat the joint, thereby reducing the welding cooling speed; The preheating parameters are: electron beam current I w =7-10mA, focused beam current I f =640-650mA, working distance w=250mm, welding speed v=35-40mm / s, preheating temperature 200-230℃, preheating angle 1080°. If the preheating temperature range is not reached, the preheating angle is increased by 360° until the preheating temperature range is reached.

4. The electron beam welding method for thin-walled ultra-high strength steel D506A according to claim 1, characterized in that: The deep penetration welding is performed immediately after preheating is completed; The deep penetration welding parameters are: electron beam current I w =40-50mA, focused beam current I f =610-620mA, working distance w=250mm, welding speed v=20-30mm / s.

5. The electron beam welding method for thin-walled ultra-high strength steel D506A according to claim 1, characterized in that: The first modification welding is performed at a temperature within a range of 150-200° C.; the modification welding bead deviates from the center of the deep penetration welding bead by 0.5-1 mm; The specific parameters of the first modification welding are: electron beam current I w =15-25mA, focused beam current I f =640-650mA, working distance w=250mm, welding speed v=35-40mm / s.

6. The electron beam welding method for thin-walled ultra-high strength steel D506A according to claim 1, characterized in that: The second modification welding is performed at a temperature of 150-200° C. The second modification welding bead deviates from the center of the deep penetration welding bead by 0.5-1 mm, in the opposite direction to the deviation of the first modification welding bead; The specific parameters of the second modification welding are: electron beam current I w =15-25mA, focused beam current I f =640-650mA, working distance w=250mm, welding speed v=35-40mm / s.

7. The electron beam welding method for thin-walled ultra-high strength steel D506A according to claim 1, characterized in that: The vacuum electron beam welder is a medium-voltage electron beam welder with an acceleration voltage of 60 kV. The vacuum degree in the vacuum chamber should be less than 7.0×10 -2 Pa.

8. The electron beam welding method for thin-walled ultra-high strength steel D506A according to claim 1, characterized in that: After the product is sent into the vacuum electron beam welder for vacuuming, the temperature of the welding area is monitored by an infrared thermal imager. The accuracy of the infrared thermal imager is no more than ±10°C, and the feedback time is less than 250ms.

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