Research On Welding Technology And Mechanism For 2205 Duplex Stainless Steels

Use of duplex stainless steels is on the increase because of their combination of excellent comprehensive mechanical properties and corrosion resistant properties, especially in fields of petrochemical industry,offshore engineering and food engineering, and so on. 2205 is one of the most important duplex stainless steels. It is difficult to control phase ratio for the effect of welding thermal cycle, mechanical and corrosion resistance properties will decline. The welded joints should meet the requirements of mechanical properties and corrosion resistance to ensure using security after welding. In this paper, on the basis of the optimum phase ratio (the volume of austenite in heat~affected zone is about 50%), two groups welding procedures were chosen, which were carried out through alter the volume of nitrogen gas in protective gas or welding heat input. Shielded metal arc welding (SMAW) and tungsten arc welding (GTAW) were used. Through analyzing the experiment result, the optimal welding parameters and welding mechanism were discovered.Through the mechanical properties and corrosion tests of the welded joints made by all kinds of welding procedure, the resuts show that the welded joints can meet the need of engineering by GTAW. The specific elongation of welded joints is enhanced greatly by increasing nitrogen content, but the tensile strength and microhardness are decreased little. The same results can be gained by increasing weld heat input, but the effect is smaller than the enhancing nitrogen.The volume of austenite and it's microstructure in the welded joints are all affected by the content of nitrogen gas or welding heat input, the better microstructure will be obtained by selecting the first. When the phase ratio of welded joints was analyzed in the microstructure, relation of the austenite content in the welded joints and nitrogen gas content in protective gas was deducted. But the results analysis show that the phase ratio is not the only aim to evaluate the comprehensive properties of duplex stainless steels, the crystalline form of austenite should be regarded, which is proved by corrosion resistance properties tests. The volume of austenite is increased by altering welding heat input, but microstructure of austenite phase is changed. At the same time, the harmful phase may appear, such as sigma phase,χphase and carbonization, et al, these will deteriorate corrosion resistance properties.