Research On Welding Process And Structure Performance Of Inconel625Heat Exchanger Tube-Plate Welding Joint

Incone1625is a kind of solid-solution strengthening nickel-based corrosion-resistant alloy, which belongs to Ni-Cr series, it has a good cutability、excellent corrosion-resistant in majority of acid solutions、the ability to keep a good machinability and oxidation-resistance at high temperature, therefore, it can be used to manufacture in chemical producing、offshore oil and aerospace industry.In the recent years, with the rapid development in petroleum chemical industry, pressure vessel has been applied widely, the traditional stainless heat exchangers can no more satisfied the harsh operation requirements which is full of high temperature、high pressure and corrosive environment, this phenomenon impels the producing of Incone1625heat exchangers. During the production, welding is absolutely the necessary molding technology, but it is easy to initiate thermal cracks, therefore, in order to make the device run safely and reliably, it has a very important and real significance in searching the welding property of Incone1625.In this paper, we mainly study the welding procedure for Inconel625surfacing layer on Q345R by SAW and Incone1625tube-plate joint by GTAW, then using macroscopic testing、permeation testing、 microstructure analysis、welding penetration testing、HV-hardness testing and corrosion testing to test the quality of welding joint and verify the rationality of welding parameters. The results show that the surfacing layer appearance and joint appearance have no cracks、gas、 excessive oxidation and so on, good formability, permeability detection is qualified which is in AB-Grade. Through the observation and analysis of microstructure, every fusion zone is good and has no microcracks, surfacing layer is all dendritic austenite microstructures, heat exchange tube is granular austenite and some black substance residue in crystal boundary which is doubtful the over-oxidize NiO, but it won’t affect the welding joint, the joint is full of dendritic and cellular austenite, and the distribution of structure is uniform. The HV-hardness testing value shows that layer is higher than matrix, the highest value can closed to250HV, the joint seam is higher than surfacing and tube metal, the whole hardness value show a smoothing convex curve with278HV peak. Otherwise, the joint both has a good pitting corrosion resistance in10%FeCl3solution and intergranular corrosion resistance in Cu-CuSO4-16%H2SO4solution.All the testing results above show us that, when welding process parameters by SAW:welding current is850A、voltage is35-38V. welding rate is201mm/min and interlay er-temperature is no more than100℃, and when welding process parameters by GTAW:basic current is50～52A、peak current is115～120A、arc voltage is9.2～9.4V、welding rate is220mm/min、wire feeding rate is280mm/min and gas flow is10L/min, the quality of welding joint has already met the target, which validates the rationality of the welding parameters fully, therefore, it can be applied to the actual production of Incone1625heat exchanger.