Machining method for large-scale welding, milling and welding impeller

Abstract

The invention provides a machining method for a large-scale welded and milled impeller. The machining method comprises the following steps: welding a cover disc and a blade or welding a shaft disc and the blade, and then carrying out heat treatment; milling the blade and the welding seam; correspondingly, after the shaft disc and the blade are welded or the cover disc and the blade are welded, stress relief treatment, semi-finish machining, performance heat treatment and finish machining are sequentially conducted, wherein heat treatment sequentially comprises stress relief treatment, shot blasting treatment, high-temperature aging treatment and low-temperature aging treatment. According to the machining method for the large-scale welding, milling and welding impeller, through postweld heat treatment including stress relief treatment, shot blasting treatment, high-temperature aging treatment and low-temperature aging treatment in sequence, the machining efficiency of the large-scale welding, milling and welding impeller can be greatly improved.

Description

Technical Field

[0001] The invention relates to the technical field of impeller processing, and in particular to a processing method for a large-scale welding and milling impeller. Background Art

[0002] The compressor industry is currently developing rapidly, and large-scale impellers are constantly emerging. Therefore, the processing and manufacturing of large-scale impellers has become the focus of research today.

[0003] The conventional manufacturing methods for large impellers include integral processing methods, such as Figure 1 As shown. The overall processing of the impeller is of high quality and the cost of raw materials is relatively low, but the manufacturing cycle is long and the manufacturing cost is high. There is also a two-piece welding method, that is, the cover plate and the blades are first processed as a whole and then welded to the shaft plate, or the shaft plate and the blades are first processed as a whole and then welded to the cover plate. Figure 2 As shown. The two-piece welded impeller has a high material cost compared to the integrally processed impeller, but the manufacturing cycle and manufacturing cost are relatively low. Therefore, combining the above two conventional manufacturing methods, a new impeller manufacturing method has been developed, which is to manufacture the impeller by welding and milling. That is, the impeller includes a cover plate, a shaft plate and blades. The welding and milling impeller processing method first completes the welding of the cover plate (or shaft plate) and the blades, and then performs stress relief treatment on the welding part to avoid cracking caused by excessive welding stress. The welding part is then milled. After meeting the requirements, the shaft plate (or cover plate) is welded to the other end of the blade, and then stress relief treatment is performed again, followed by semi-finishing, performance heat treatment, and finally finishing to obtain a welded and milled impeller, as shown in FIG. Figure 3 This welding and milling impeller processing method can not only reduce material costs, but also reduce manufacturing cycles and manufacturing costs. However, the hardness of the weld position after blade welding is relatively high, generally with a hardness of Hv5 ≥ 330, which is not conducive to milling processing, thus affecting the processing efficiency of large welding and milling impellers.

[0004] Therefore, there is an urgent need for a processing method for large-scale welding and milling impellers that can improve processing efficiency. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a processing method for a large-scale welding and milling impeller with high processing efficiency.

[0006] In order to solve the above technical problems, the present invention provides a processing method for a large welding milling impeller, comprising the following steps:

[0007] Heat treatment is performed after welding the cover plate and the blades;

[0008] Milling of blades and welds;

[0009] After welding the shaft disc and the blades, stress relief treatment, semi-finishing, performance heat treatment and finishing are carried out in sequence; or,

[0010] Heat treatment is performed after welding the shaft disc and the blades;

[0011] Milling of blades and welds;

[0012] After the cover plate and the blade are welded, stress relief treatment, semi-finishing, performance heat treatment and finishing are carried out in sequence;

[0013] The heat treatment includes stress relief treatment, shot peening treatment, high temperature aging treatment and low temperature aging treatment in sequence.

[0014] Furthermore, the stress relief treatment is to heat the welded impeller to 620-660°C at a heating rate of ≤50°C / h, keep the temperature for 4-8h, and then take it out of the furnace and air cool it to room temperature.

[0015] Furthermore, the high temperature aging treatment is to heat the shot peened impeller to 730-860°C at a heating rate of ≤70°C / h, keep it at that temperature for 4-8h, then cool it to below 300°C at a cooling rate of 20-50°C / h, and then air cool it to room temperature.

[0016] Furthermore, the low-temperature aging treatment is to heat the impeller after the high-temperature aging treatment to 630-640°C at a heating rate of ≤50°C / h, keep it warm for 7-12h, and then cool it to below 300°C at a cooling rate of 20-50°C / h, take it out of the furnace and air-cool it to room temperature.

[0017] Furthermore, the cooling to below 300°C at a cooling rate of 20-50°C / h and air cooling to room temperature can be directly air-cooled, oil-cooled or water-cooled to room temperature after heat preservation. Furthermore, the performance heat treatment includes solution treatment and aging treatment, wherein:

[0018] Solution treatment: keep at 1030-1060℃ for 4-8h and then cool to room temperature;

[0019] Aging treatment: Keep at 470-635℃ for 7-12h and then cool to room temperature.

[0020] Furthermore, the performance heat treatment includes solution treatment, high temperature aging treatment and low temperature aging treatment, wherein:

[0021] Solution treatment: keep at 1030-1060℃ for 4-8h and then cool to room temperature;

[0022] High temperature aging treatment: keep at 740-880℃ for 4-8h and then cool to room temperature;

[0023] Low temperature aging treatment: keep at 470-635℃ for 7-12h and then cool to room temperature.

[0024] Furthermore, the performance heat treatment includes high temperature aging treatment and low temperature aging treatment, wherein

[0025] High temperature aging treatment: keep at 740-880℃ for 4-8h and then cool to room temperature;

[0026] Low temperature aging treatment: keep at 470-635℃ for 7-12h and then cool to room temperature.

[0027] Furthermore, the cooling is air cooling, oil cooling, water cooling or water-based medium cooling.

[0028] Furthermore, the large welding, milling and welding impeller is an ASTM A705-630 steel, 17-4PH steel or 15-5PH steel impeller.

[0029] The present invention provides a processing method for a large-scale welding and milling impeller. During the heat treatment process after the cover plate or the shaft plate is welded to the blades, the internal stress in the impeller welding process is first eliminated by means of stress relief treatment, and then the internal stress in the welding process is further eliminated by shot peening after the stress relief. The shot peening can also convert the internal stress on the welding surface into compressive stress, thereby preventing cracking caused by excessive welding stress during the later heat treatment process. Finally, high-temperature aging treatment and low-temperature aging treatment are used to improve the hardness of the weld position, so that the hardness is controlled at Hv5≤280, which can effectively improve the processing efficiency of the subsequent milling processing of the impeller.

[0030] Moreover, the processing method of a large welding milling impeller provided by the present invention and the post-welding heat treatment method thereof can not only be well applied in the manufacturing process of the welding milling impeller, but also can be used in the post-welding manufacturing process of other materials such as ASTM A705-630 steel, 17-4PH steel or 15-5PH steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a structural schematic diagram of a large impeller obtained by an integral processing method in a conventional manufacturing method of a large impeller in the prior art;

[0032] Figure 2 It is a schematic diagram of the structure of a large impeller obtained by welding two pieces in the conventional manufacturing method of large impellers in the prior art;

[0033] Figure 3 It is a schematic diagram of the structure of a large welding and milling impeller obtained by the welding and milling manufacturing method in the prior art;

[0034] Figure 4 A flow chart of a processing method for a large welding and milling impeller provided by an embodiment of the present invention;

[0035] Figure 5A metallographic microstructure diagram obtained by heat treatment of an impeller after welding in a method for processing a large-scale welding and milling impeller provided in Example 1 of the present invention;

[0036] Figure 6 A metallographic microstructure diagram obtained by heat treatment of an impeller after welding in a method for processing a large-scale welding and milling impeller provided in Example 2 of the present invention;

[0037] Figure 7 The metallographic microstructure diagram obtained by heat treatment of the impeller after welding in a processing method of a large-scale welding and milling impeller provided as a comparative example of the present invention. DETAILED DESCRIPTION

[0038] See also Figure 4 The present invention provides a large-scale welding milling impeller processing method, which is applicable to large-scale welding milling impellers made of ASTM A705-630 steel, 17-4PH steel or 15-5PH steel, and the method comprises the following steps:

[0039] Step 1) Weld the cover disc to the blades, or weld the shaft disc to the blades.

[0040] Step 2) heat treating the welded parts after welding.

[0041] The heat treatment includes stress relief treatment, shot peening treatment, high temperature aging treatment and low temperature aging treatment in sequence.

[0042] Among them, the stress relief treatment is to heat the impeller to 620-660℃ at a heating rate of ≤50℃ / h, keep it at this temperature for 4-8h, and then take it out of the furnace and air cool it to room temperature. Through the stress relief treatment, the internal stress in the impeller welding process can be eliminated.

[0043] By shot peening the impeller after stress relief treatment, the internal stress of welding can be further eliminated. In addition, shot peening can also transform the internal stress of the welding surface into compressive stress, preventing cracking caused by excessive welding stress during the later heat treatment process.

[0044] Among them, the high temperature aging treatment is to heat the impeller after shot peening to 730-860°C at a heating rate of ≤70°C / h, keep it warm for 4-8h, and then cool it to below 300°C at a cooling rate of 20-50°C / h and air-cool it to room temperature.

[0045] Among them, the low-temperature aging treatment is to heat the impeller after high-temperature aging treatment to 630-640°C at a heating rate of ≤50°C / h, keep it warm for 7-12h, and then cool it to below 300°C at a cooling rate of 20-50°C / h and air-cool it to room temperature.

[0046] Among them, during the high-temperature aging treatment and the low-temperature aging treatment, the cooling method of cooling to below 300°C at a cooling rate of 20 to 50°C / h and air cooling to room temperature can also be adopted. The cooling method of directly cooling to room temperature by air, oil or water can be adopted after heat preservation.

[0047] The hardness of the weld can be improved through high-temperature aging treatment and low-temperature aging treatment, and its hardness can be controlled at Hv5≤280, which can effectively improve the processing efficiency of the subsequent milling of the impeller.

[0048] Because within the high-temperature aging treatment temperature range, the increase in temperature enhances the atomic diffusion ability, making it easier for NbC to precipitate and grow, thereby inhibiting the precipitation of Cr carbides at the grain boundaries. When the strengthening phase particles are relatively large and sparsely distributed, dislocations are allowed to bypass these strengthening phase particles according to the Owrrone mechanism, dislocation lines no longer accumulate, and the hardness of the material decreases. When the high-temperature aging treatment is followed by the low-temperature aging treatment, the martensitic structure "inherits" the miniaturization characteristics of the high-temperature aging treatment state, and the grain boundaries are interconnected into a network, encapsulating the grains mainly composed of martensite and retained austenite. This organizational morphology is related to the production of more reversed austenite in the steel, thereby further reducing the hardness.

[0049] Step 3) Milling the welded parts to form blades and welds.

[0050] Step 4) If the cover plate and the blades were welded before, the shaft plate and the blades are welded to obtain a welding, milling and welding impeller. If the shaft plate and the blades were welded before, the cover plate and the blades are welded to obtain a welding, milling and welding impeller.

[0051] Step 5) welding to obtain the stress relief treatment of the welded and milled impeller.

[0052] Step 6) semi-finishing the welded and milled impeller after stress relief treatment.

[0053] Step 7) performing a performance heat treatment on the semi-finished welded and milled impeller.

[0054] As a specific embodiment of the present invention, the performance heat treatment of the welding and milling impeller includes solution treatment and aging treatment, wherein:

[0055] Solution treatment: keep at 1030-1060℃ for 4-8h and then cool to room temperature;

[0056] Aging treatment: Keep at 470-635℃ for 7-12h and then cool to room temperature.

[0057] As another specific embodiment of the present invention, the performance heat treatment of the welding milling impeller includes solid solution treatment, high temperature aging treatment and low temperature aging treatment, wherein:

[0058] Solution treatment: keep at 1030-1060℃ for 4-8h and then cool to room temperature;

[0059] High temperature aging treatment: keep at 740-880℃ for 4-8h and then cool to room temperature;

[0060] Low temperature aging treatment: keep at 470-635℃ for 7-12h and then cool to room temperature.

[0061] As another specific embodiment of the present invention, the performance heat treatment of the welding milling impeller includes high temperature aging treatment and low temperature aging treatment, wherein

[0062] High temperature aging treatment: keep at 740-880℃ for 4-8h and then cool to room temperature;

[0063] Low temperature aging treatment: keep at 470-635℃ for 7-12h and then cool to room temperature.

[0064] The cooling method during the heat treatment process of the welding and milling impeller can be air cooling, oil cooling, water cooling or water-based medium cooling.

[0065] Step 8) finishing the welded and milled impeller after performance heat treatment.

[0066] Among them, the large welding milling impeller is an impeller made of ASTM A705-630 steel, 17-4PH steel or 15-5PH steel.

[0067] The present invention provides a processing method for a large welding and milling impeller, which specifically includes welding of a cover plate (or a shaft plate) and blades, post-weld heat treatment, milling of blades and welds, welding of a shaft plate (or a cover plate) and blades, stress relief, semi-finishing, performance heat treatment and finishing. The processing method for a large welding and milling impeller provided by the present invention is specifically described below with respect to the post-weld heat treatment process through embodiments and comparative examples.

[0068] Example 1

[0069] This embodiment provides a processing method for a large welding and milling impeller, wherein the post-welding heat treatment includes several processing processes, including stress relief treatment, shot peening treatment, high temperature aging treatment and low temperature aging treatment. The details are as follows:

[0070] After the impeller is welded, the temperature is raised to 635°C at a heating rate of 20°C / h, kept at this temperature for 4 hours, and then taken out of the furnace and air-cooled to room temperature.

[0071] The impeller is then shot peened.

[0072] The shot peened impeller was heated to 740°C at a heating rate of 40°C / h, kept at this temperature for 4h, then cooled to below 260°C at a cooling rate of 30°C / h, and air-cooled to room temperature.

[0073] After high temperature aging treatment, the impeller was heated to 635°C at a heating rate of 40°C / h, kept at this temperature for 7h, then cooled to 200°C at a cooling rate of 40°C / h, and air-cooled to room temperature.

[0074] The hardness after heat treatment is Hv5=273, and its metallographic microstructure is as follows Figure 5 shown.

[0075] Example 2

[0076] This embodiment provides a processing method for a large welding and milling impeller, wherein the post-welding heat treatment includes several processing processes, including stress relief treatment, shot peening treatment, high temperature aging treatment and low temperature aging treatment. The details are as follows:

[0077] After the impeller is welded, the temperature is raised to 640°C at a heating rate of 30°C / h, kept at this temperature for 8 hours, then cooled to 140°C at a cooling rate of 30°C / h, and air-cooled to room temperature.

[0078] The impeller is then shot peened.

[0079] The shot peened impeller was heated to 760°C at a heating rate of 20°C / h, kept at this temperature for 8h, and then taken out of the furnace and air-cooled to room temperature.

[0080] After high temperature aging treatment, the impeller was heated to 630°C at a heating rate of 25°C / h, kept at this temperature for 10h, and then taken out of the furnace and air-cooled to room temperature.

[0081] The hardness after heat treatment is Hv5=268, and the metallographic microstructure is as follows Figure 6 shown.

[0082] Comparative Example 1

[0083] Different from the post-weld heat treatment of Examples 1 and 2 of the present invention, which includes several treatment processes including stress relief treatment, shot peening treatment, high temperature aging treatment and low temperature aging treatment, the post-weld heat treatment of this comparative example only performs stress relief treatment on the impeller after welding, which is specifically as follows:

[0084] After the impeller is welded, the temperature is raised to 640°C at a heating rate of 45°C / h, kept at this temperature for 8h, and then taken out of the furnace and air-cooled to room temperature.

[0085] The hardness after heat treatment is Hv5=343, and the metallographic microstructure is as follows Figure 7 shown.

[0086] From the comparison of hardness after post-weld heat treatment of the embodiment of the present invention and the comparative example, it can be seen that after the embodiment of the present invention adopts post-weld heat treatment including stress relief treatment, shot peening treatment, high temperature aging treatment and low temperature aging treatment, the hardness of the impeller after welding is Hv5≤280, and its hardness is significantly reduced, which is conducive to milling processing, thereby effectively improving the processing efficiency of subsequent milling processing of the impeller, thereby improving the processing efficiency of the entire large-scale welding and milling impeller.

[0087] From the comparison of the metallographic microstructures after post-weld heat treatment of the embodiment of the present invention and the comparative example, it can be seen that the martensitic structure of the embodiment of the present invention that is aged after high-temperature aging treatment "inherits" the miniaturization characteristics of the high-temperature aging treatment state, and the grain boundaries are interconnected into a network, which encloses the grains mainly composed of martensite and residual austenite. This organizational morphology is related to the production of more reversed austenite in the steel, resulting in further reduction in hardness; after the diameter is stress-relieved after welding, the martensitic laths are coarse, the elements do not diffuse significantly, the carbides precipitated at the original austenite grain boundaries are less, and the relative hardness is higher.

[0088] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A method for processing a large welding and milling impeller, comprising the following steps: Heat treatment is performed after welding the cover plate and the blades; Milling of blades and welds; After welding the shaft disc and the blades, stress relief treatment, semi-finishing, performance heat treatment and finishing are carried out in sequence; or, Heat treatment is performed after welding the shaft disc and the blades; Milling of blades and welds; After the cover plate and the blade are welded, stress relief treatment, semi-finishing, performance heat treatment and finishing are carried out in sequence; It is characterized in that The heat treatment includes stress relief treatment, shot peening treatment, high temperature aging treatment and low temperature aging treatment in sequence.

2. The processing method of a large welding and milling impeller according to claim 1 is characterized in that: The stress relief treatment is to heat the welded impeller to 620-660°C at a heating rate of ≤50°C / h, keep the temperature for 4-8h, and then take it out of the furnace and air cool it to room temperature.

3. The processing method of a large welding and milling impeller according to claim 1 is characterized in that: The high temperature aging treatment is to heat the impeller after shot peening to 730-860°C at a heating rate of ≤70°C / h, keep it at that temperature for 4-8h, then cool it to below 300°C at a cooling rate of 20-50°C / h, and then take it out of the furnace and air cool it to room temperature.

4. The processing method of a large welding and milling impeller according to claim 1 is characterized in that: The low-temperature aging treatment is to heat the impeller after high-temperature aging treatment to 630-640°C at a heating rate of ≤50°C / h, keep it warm for 7-12h, and then cool it to below 300°C at a cooling rate of 20-50°C / h, take it out of the furnace and air cool it to room temperature.

5. The processing method of a large welding and milling impeller according to claim 3 or 4, characterized in that: The cooling to below 300° C. at a cooling rate of 20-50° C. / h and air cooling to room temperature can be performed by directly cooling to room temperature by air, oil or water after heat preservation.

6. The processing method of a large welding and milling impeller according to claim 1 is characterized in that: The performance heat treatment includes solution treatment and aging treatment, wherein: Solution treatment: keep at 1030-1060℃ for 4-8h and then cool to room temperature; Aging treatment: Keep at 470-635℃ for 7-12h and then cool to room temperature.

7. The processing method of a large welding and milling impeller according to claim 1 is characterized in that: The performance heat treatment includes solution treatment, high temperature aging treatment and low temperature aging treatment, wherein: Solution treatment: keep at 1030-1060℃ for 4-8h and then cool to room temperature; High temperature aging treatment: keep at 740-880℃ for 4-8h and then cool to room temperature; Low temperature aging treatment: keep at 470-635℃ for 7-12h and then cool to room temperature.

8. The processing method of a large welding and milling impeller according to claim 1 is characterized in that: The performance heat treatment includes high temperature aging treatment and low temperature aging treatment, wherein High temperature aging treatment: keep at 740-880℃ for 4-8h and then cool to room temperature; Low temperature aging treatment: keep at 470-635℃ for 7-12h and then cool to room temperature.

9. The processing method of a large welding and milling impeller according to any one of claims 6 to 8, characterized in that: The cooling is air cooling, oil cooling, water cooling or water-based medium cooling.

10. The processing method of a large welding and milling impeller according to claim 1, characterized in that: The large welding milling impeller is made of ASTM A705-630 steel, 17-4PH steel or 15-5PH steel impeller.

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