Cryogenic treatment method for copper steel welded joint

Abstract

The invention belongs to the technical field of heat treatment, and provides a subzero treatment method of a copper-steel welded joint, which comprises the following steps: step 1, providing a copper-steel welded workpiece completed by adopting an argon arc welding method; secondly, the workpiece is heated to 400-500 DEG C, heat preservation is conducted for 2-3 h, and water cooling is conducted for 3-5 min after the workpiece is discharged out of the furnace; thirdly, rough machining is conducted on the welding portion of the copper steel workpiece; fourthly, the copper steel welding workpiece obtained after rough machining is quenched, heated with oil and cooled, and then subzero treatment is added; fifthly, the workpiece subjected to subzero treatment is subjected to tempering treatment; 6, item detection, wherein the hardness performance, the metallographic structure, the deformation amount and the stress of the workpiece are detected; and seventhly, the workpiece is machined to be in the finished product size, and it is guaranteed that the size and quality meet the technical requirements. According to the technical scheme, by controlling the slow cooling rate and the slow heating rate, new internal stress generated by thermal shock is avoided, and residual stress in the connector is fully released and homogenized.

Description

Technical Field

[0001] This invention belongs to the field of heat treatment technology, specifically relating to a deep cryogenic treatment method for copper-steel welded joints. Background Technology

[0002] Dissimilar metal welded structures of copper and steel have wide applications in fields such as power, refrigeration, aerospace and nuclear industries. However, due to the huge differences in physical properties (such as coefficient of thermal expansion and thermal conductivity) and chemical properties between copper and steel, their welded joints usually have the following problems: (1) large residual stress in welding, which easily leads to deformation and cracking; (2) coarse grain structure is easily formed in the weld and heat-affected zone; (3) brittle intermetallic compounds such as Fe-Cu are easily formed at the copper-steel interface, which seriously deteriorates the mechanical properties of the joint.

[0003] Cryogenic treatment, as a post-processing technique to improve the properties of metallic materials, has been applied to tool steels, aluminum alloys, and other materials to enhance their wear resistance, dimensional stability, and toughness. However, there are currently no reports on a systematic cryogenic treatment process specifically for the unique structure of copper-steel welded joints. Directly applying conventional cryogenic treatment parameters (such as cooling rate, holding temperature, and time) to copper-steel joints may lead to poor results or even negative effects due to issues such as thermal stress matching. Therefore, developing a cryogenic treatment method specifically for copper-steel welded joints is essential. Summary of the Invention

[0004] (a) Technical problems to be solved

[0005] The technical problem to be solved by the present invention is to provide a deep cryogenic treatment method for reducing residual stress in the welding of copper-steel joints.

[0006] (II) Technical Solution

[0007] To solve the above-mentioned technical problems, the present invention provides a method for cryogenic treatment of copper-steel welded joints, comprising the following steps:

[0008] Step 1: Provide copper-steel welded workpieces that have been welded using the argon arc welding method;

[0009] Step 2: Heat the workpiece to 400℃~500℃, hold for 2h-3h, and then water cool for 3min-5min after removing it from the furnace;

[0010] Step 3: Perform rough machining on the welding parts of the copper-steel workpiece;

[0011] Step 4: After rough machining, the copper-steel welded workpiece is first quenched and cooled with hot oil, and then subjected to deep cryogenic treatment.

[0012] Step 5: Temper the workpiece after cryogenic treatment;

[0013] Step Six: Project Inspection: Inspect the workpiece's hardness, metallographic structure, deformation, and stress;

[0014] Step 7: Machin the workpiece to the finished size, ensuring that the dimensions and quality meet the technical requirements.

[0015] Furthermore, the cryogenic treatment includes the following steps:

[0016] (1) Place the quenched workpiece in a cryogenic device and cool it to the target temperature T1 at a first rate V1, and keep it at that temperature for a period of time t1, wherein the temperature range of T1 is -75℃~-85℃, the time range of t1 is 0.5h~1h, and V1≤5℃ / min;

[0017] (2) Continue cooling to the target temperature T2 at the first rate V1, and keep it at that temperature for a period of time t2, where the temperature range of T2 is -120℃ to -180℃, the time range of t2 is 2h to 2.5h, and V1 ≤ 5℃ / min;

[0018] (3) After the cryogenically treated workpiece is slowly heated to room temperature at the furnace cooling rate, it is taken out of the furnace.

[0019] Furthermore, the tempering process specifically involves heating the cryogenically treated workpiece to 480℃~580℃, holding it at that temperature for 1.5h~2h, and then water-cooling it for 3min-5min after removing it from the furnace, ensuring a hardness of 32HRC-37HRC.

[0020] Furthermore, the first rate V1 = 3℃ / min.

[0021] (III) Beneficial Effects

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) Excellent stress relief effect: By controlling the slow cooling and heating rate (V1≤5℃ / min, furnace cooling), new internal stress caused by thermal shock is avoided, so that the residual stress in the joint is fully released and homogenized.

[0024] (2) Significantly improved microstructure and properties: The specific ultra-low temperature environment (below -120℃) promotes the further transformation of the residual austenite in the weld metal into martensite and refines the martensite laths; at the same time, the extremely high low temperature conditions can inhibit or reduce the precipitation and growth of brittle phases at the interface.

[0025] (3) Overall performance improvement: The tensile strength of the copper-steel welded joint treated by the method of the present invention can be increased by 15%-25% compared with the untreated joint (modified according to test data), the fatigue life is extended by more than 50% (modified according to test data), and the low temperature impact toughness is also significantly improved.

[0026] (4) Process stability and strong applicability: The method has a clear process and well-defined parameters. It can be applied to copper-steel joints formed by various high-performance beam welding methods such as argon arc welding, and has good repeatability and industrial application prospects. Attached Figure Description

[0027] Figure 1 This is a process curve diagram of the cryogenic treatment method of this invention. Detailed Implementation

[0028] To make the objectives, contents, and advantages of the present invention clearer, the specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples.

[0029] Example 1:

[0030] Workpiece preparation: Use an argon arc welding machine to surface SCu6180 aluminum bronze welding wire along the circumferential direction of the 40Cr stepped shaft with a diameter of Φ37.50 -0.16. The surfacing thickness on one side is 3mm to 5mm. Welding parameters: current intensity 100-110A, speed 2m / min, argon gas protection.

[0031] Cleaning: After welding, clean the surface of the workpiece to remove oxides and other contaminants.

[0032] Stress-relief tempering: Heat the workpiece to 400℃~500℃, hold for 2h-3h, and then water cool for 3min-5min after removing it from the furnace; eliminate welding stress and achieve uniform microstructure.

[0033] Rough machining: Rough machining of the welded parts of the workpiece after stress relief tempering to Φ430 -0.16.

[0034] Quenching: After rough machining, the workpiece is first quenched and heated to 850±10℃, held for 1h-1.5h, then oil cooled (initially oil temperature 50℃-90℃) for 20min-40min, and then deep cryogenic treatment is added.

[0035] Cryogenic treatment: (1) Place the workpiece in a cryogenic chamber and cool it from room temperature (25℃) to -80±5℃ at a rate of 3℃ / min for 30min-40min; (2) Cool it from -80℃ to -120℃ at a rate of 3℃ / min for 2h-2.5h; (3) After the cryogenic heat preservation is completed, slowly heat the workpiece to room temperature and remove it from the furnace.

[0036] Performance tempering treatment: The workpiece after cryogenic treatment is heated to 480℃~580℃ and held for 1.5h~2h. After being taken out of the furnace, it is air cooled.

[0037] Project Inspection: The tempered workpiece was tested for hardness, metallographic structure, and deformation. The inspection results show that: hardness is improved; weld microstructure is significantly refined; the copper-steel interface is dense; no continuously distributed brittle phases were observed; deformation is small; and stress is low and uniform.

[0038] The workpiece is machined to the finished size, and the dimensions and quality are checked to ensure they meet the technical requirements of the part.

[0039] Example 2:

[0040] Workpiece preparation: Use an argon arc welding machine to surface SCu6180 aluminum bronze welding wire along the circumferential direction of the 40Cr stepped shaft with a diameter of Φ37.50 -0.16. The surfacing thickness on one side is 3mm -5mm. Welding parameters: current intensity 100-110A, speed 2m / min, argon gas protection.

[0041] Cleaning: After welding, clean the surface of the workpiece to remove oxides and other contaminants.

[0042] Stress-relief tempering: Heat the workpiece to 400℃~500℃, hold for 2h-3h, and then water cool for 3min-5min after removing it from the furnace; eliminate welding stress and achieve uniform microstructure.

[0043] Rough machining: Rough machining of the welded parts of the workpiece after stress relief tempering to Φ430 -0.16.

[0044] Quenching: After rough machining, the workpiece is first quenched and heated to 850±10℃, held for 1h-1.5h, then oil cooled (initially oil temperature 50℃-90℃) for 20min-40min, and then deep cryogenic treatment is added.

[0045] Cryogenic treatment: (1) Place the workpiece in a cryogenic chamber and cool it from room temperature (25℃) to -80℃ at a rate of 3℃ / min for 30min-40min; (2) Cool it from -80℃ to -150℃ at a rate of 3℃ / min for 2h-2.5h; (3) After the cryogenic heat preservation is completed, slowly heat the workpiece to room temperature and remove it from the furnace.

[0046] Performance tempering treatment: The workpiece after cryogenic treatment is heated to 480℃~580℃ and held for 1.5h~2h. After being taken out of the furnace, it is air cooled.

[0047] Project Inspection: The hardness, metallographic structure, deformation, and stress of the tempered workpiece were tested. The results show that: hardness is improved; weld microstructure is significantly refined; the copper-steel interface is dense; no continuously distributed brittle phases were observed; deformation is small; and stress is low and uniform.

[0048] The workpiece is machined to the finished size, and the dimensions and quality are checked to ensure they meet the technical requirements of the part.

[0049] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for cryogenic treatment of copper-steel welded joints, characterized in that, Includes the following steps: Step 1: Provide copper-steel welded workpieces that have been welded using the argon arc welding method; Step 2: Heat the workpiece to 400℃~500℃, hold for 2h-3h, and then water cool for 3min-5min after removing it from the furnace; Step 3: Perform rough machining on the welding parts of the copper-steel workpiece; Step 4: After rough machining, the copper-steel welded workpiece is first quenched and cooled with hot oil, and then subjected to deep cryogenic treatment. Step 5: Temper the workpiece after cryogenic treatment; Step Six: Project Inspection: Inspect the workpiece's hardness, metallographic structure, deformation, and stress; Step 7: Machin the workpiece to the finished size, ensuring that the dimensions and quality meet the technical requirements.

2. The cryogenic treatment method for copper-steel welded joints as described in claim 1, characterized in that, The cryogenic treatment includes the following steps: (1) Place the quenched workpiece in a cryogenic device and cool it to the target temperature T1 at a first rate V1, and keep it at that temperature for a period of time t1, wherein the temperature range of T1 is -75℃~-85℃, the time range of t1 is 0.5h~1h, and V1≤5℃ / min; (2) Continue cooling to the target temperature T2 at the first rate V1, and keep it at that temperature for a period of time t2, where the temperature range of T2 is -120℃ to -180℃, the time range of t2 is 2h to 2.5h, and V1 ≤ 5℃ / min; (3) After the cryogenically treated workpiece is slowly heated to room temperature at the furnace cooling rate, it is taken out of the furnace.

3. The cryogenic treatment method for copper-steel welded joints as described in claim 1, characterized in that, The tempering process involves heating the cryogenically treated workpiece to 480℃~580℃, holding it at that temperature for 1.5h~2h, and then water-cooling it for 3min-5min after removing it from the furnace, ensuring a hardness of 32HRC-37HRC.

4. The cryogenic treatment method for copper-steel welded joints as described in claim 1, characterized in that, The first rate is V1 = 3℃ / min.

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