Research On Weldability Of SAF2205 Duplex Stainless Steel And Dissimilar Metals

Duplex stainless steels present an attractive combination of good mechanical properties and localized corrosion resistance, and they are successfully used in the many vital departments of national economy,such as petrochemical industries and offshore engineering. Under the circumstance, the welding of dissimilar metals between duplex stainless steels and carbon steels, austenitic stainless steels is usually inevitable in the engineering structure. However, the joining of dissimilar metals is generally more challenging than that of similar metals, which is due to several factors such as the differences in chemical compositions, physical and chemical properties, and it results in different residual stresses situation across the different regions of weldments as well as the migration of carbon element during welding. If the welding process is not well controlled, some weld defects such as dilutions and cracks will generate in the weld metal and lead to great decrease of the properties of welded joint. Consequently, the welding technology and weldability between 2205 DSS and 304 austenitic stainless steel, Q235A carbon steel are investigated respectively in the current work.According to the weldability characteristic between 2205 DSS and dissimilar metals, the dissimilar metals welding are performed respectively by tungsten inert gas arc welding (GTAW) and shielded metal arc welding (SMAW) with welding wire ER2209, welding wire ER309 and welding electrode E2209 which contain high contents of Cr and Ni elements. On the basis of the appropriate biphase ratio (the ferrite content about 50%) and the test results of properties, thus the optimized welding procedures and parameters are determined from a variety of attempt welding.The analyses of microstructure characterizations, chemical compositions and phase constitution of the dissimilar joints are conducted by means of optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), together with X-ray diffraction (XRD) respectively. Results show that in the 304-WM (weld metal) interface, there is a transition area with much fine and acicular semicontinuous ferrite distributed in the matrix of austenite. And no elements segregation and deteriorative phases appeared in the interface. However, in the Q235A-WM interface, a decarburized layer close to the fusion line at the side of Q235A is formed as a result of the migration of carbon element. And the variations of Cr, Ni contents present the obvious characteristic of gradient distribution, but no deteriorative phases such as chromium carbide or martensite, etc are produced in that region. The biphase microstructure of weld metals and HAZ are tested by using point counting method, which are controlled in the requirement range of microstructure of welded joint. Mechanical properties tests of welded joints indicate that the dissimilar joints have over-matching mechanical properties, which can satisfy the engineering application. Chemical immersion method and electrochemical test are used respectively to evaluate the pitting corrosion resistance of dissimilar joints of 2205 DSS and 304 austenitic stainless steel. Results show that the joint performed by GTAW with ER2209 welding wire has the better capability of pitting corrosion resistance under the experiment condition.In a word, the dissimilar joints between 2205 DSS and austenitic stainless steel, carbon steel can be successfully welded under such experiment conditions.