The influence of gas on the Duplex Stainless Steel

According to data analysis, nitrogen has an important role in welding material and protective gas. However, it will lead to weld metal hole if the nitrogen content is too high. Compared with Austenitic stainless steel, Duplex stainless steel has lower nitrogen solubility when it is solid. As a result, a certain risk occurs when it is curdled from liquid, depending on welding parameters and alloy composition. When using azo electrode manual welding Cr22 and Cr25 type duplex stainless steel, differently from TIG welding, nitrogen is not loss in the process. Although limited, there is a tendency to increase nitrogen. In addition, weld metal hole can be prevent by controling the weld nitrogen content and improving the protection ability of electrode covering on weld liquid metal as well as improving the slag air permeability.

Argon also has great effect on stainless steel welding. It should be point out that when welding with tungsten argon arc welding, hydrogen induced crack will occur in weld metal if protective gas contains 2% - 10% H'. However, after a certain induction period, the delay cold crack tend to appear in high constraint weld, with high ferritic content which is more than 50% - 60%. In fact, the crack can be avoided if it is 200 ℃ preheated before welding and the status should be remained for 100h, or taking immediate heat treatment after welding.

When multi-pass welding with electrode, subsequent weld bead has heat treatment effect on the former bead. As a result, the ferritic in the weld metal will further change to Austenite, leading to a two phase organization with austenitic dominant. Besides, the austenite phase in the adjacet welding HAZ tissue will increase as well, which significantly improves the welding joint microstructure and the properties. At the end of welding, a layer of process weld shold be added on to the weld surface, so that the suface weld and nearby welding HAZ can be heat treated, for improving the organization and performance.

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