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Problems that need to be paid attention to when welding stainless steel pipes and copper pipes

by:HHGG     2021-04-22
Issues that need attention when welding stainless steel pipes and copper pipes 2020-12-16    As a stainless steel pipe manufacturer, stainless steel accepts customers' various processing and customization of pipes. Recently, a batch of condenser tubes welded by stainless steel tubes and copper tubes has attracted the attention of the editor. For this reason, the editor specially compiled some matters needing attention when welding stainless steel tubes and copper tubes for everyone. It's helpful to everyone. Welding analysis of red copper and austenitic stainless steel The welding of red copper and austenitic stainless steel belongs to dissimilar metal welding. The physical properties of the two are very different, and the difference in melting point is more than 400 ℃, which makes the welding more difficult, and whether satisfactory welding can be obtained The joint depends on the physical properties, chemical composition of the metal to be welded and the welding method and process used.  Physical performance difference analysis  The physical properties of steel and copper are very different. The thermal conductivity of copper is 2316 times that of steel. During welding, heat will quickly conduct outward from the heating zone, and the fusion zone is difficult to reach the melting temperature, which makes the filler metal and the base metal unable to fuse well, resulting in impermeability. The coefficient of linear expansion of copper is slightly larger than that of steel, and the shrinkage rate is 2135 times that of steel, and the thermal conductivity of copper is strong, and the amount of deformation during cooling and solidification is large, and the rigidity of the welded joint is large, and the welding deformation will be greatly hindered. The welding stress becomes the mechanical cause of welding cracks. Analysis of the difference in chemical compositionAccording to the principle of metal science, the compatibility of elements plays a decisive role in the weldability of dissimilar metals. The mutual solubility of chemical elements depends on the type of crystal lattice, atomic size, and lattice constant between the solute elements. The difference. At high temperature (912~1390℃), the crystal structure of Fe and Cu are both face-centered cubic (fcc), the atomic radius size is similar, and the lattice constant is close, so the weldability of steel and copper is better [1]. However, when copper and steel are welded, it is easy to form (Cu+Cu2O), (Fe+Fe3S2), (Ni+Ni3S2) and other low-melting eutectics between the weld metal grains. In the later stage of the solidification and crystallization of the weld metal, these The low melting point eutectic is continuously distributed in the grain boundary of solid a copper in the form of 'liquid filmAt this time, due to the significant difference in physical properties between steel and copper, the tensile stress generated more or less may cause hot cracks in the vulnerable parts of the welded joint.  According to the analysis of the weldability of copper and steel, choosing the correct welding method and suitable filling materials, and formulating a reasonable welding process are the keys to obtaining a good welded joint.  Welding method selection  Red copper and stainless steel can be welded by gas welding, argon arc welding and other welding methods. The temperature of the welding pool of gas welding is easy to control, and it is easy to realize single-sided welding and double-sided forming. It is also convenient to preheat and post-heat the weldment. However, due to the low temperature of the oxyacetylene flame and the dispersion of heat, it is difficult to overcome the defect of impermeability caused by the rapid heat dissipation of copper, and it is difficult to obtain good welding quality. Manual argon arc welding (TIG) argon protection is reliable, the molten pool metal is not easy to oxidize; the welding temperature is high, the energy is concentrated, the arc and the molten pool are visible, the operation is convenient, and it is easy to control the shape of the molten pool and the shape of the weld; there is no slag , There is no need to clean the slag after welding, and the appearance of the welded joint is of good quality, so the welding method of TIG welding is determined. The choice of welding material is to choose the red copper wire HS201 as the filler material. Preheating before welding. Because of the high thermal conductivity of copper and rapid heat dissipation, it is necessary to preheat one side of the copper tube with a neutral flame before welding (temperature 400~450℃), welding During the process, the temperature between the weld layers should be kept not lower than the preheating temperature. When welding the main points, short arc welding is used, and the center of the arc should be biased to the side of the copper tube by about 2 to 4 mm. On the one hand, the heat loss on the side of the copper tube is reduced to avoid defects such as incomplete penetration and infusion; on the other hand, it can also prevent stainless steel. Excessive heating of one side of the tube causes burn-through and undercut. The continuous wire feeding method is adopted, and the method of directly fusing the two kinds of base materials without adding welding wire can not be used.   Minimize the number of arc extinguishing during welding. In order to prevent arc crater and premature loss of protection before arc extinguishing, more filler metal should be added before arc extinguishing, and then arc extinguishing should be filled to stop sending argon gas.  Post-weld heat preservation  After welding, cover the weld joint with composite silicate felt for heat preservation and slow cooling to weaken the welding stress and prevent cracks.   The above is the stainless steel pipe manufacturer's editor for everyone to pay attention to the problems that need to be paid attention to when welding stainless steel pipes and copper pipes. I hope to help you.  
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