Study on Welding Technology and Weld Joint Micro-structural Properties of 2205/X65 Clad Pipe

Obvious differences exist between the 2205 duplex stainless steel and the X65 linepipe steel in terms of chemical composition, physical properties and micro-structural properties, resulting in reduction of the mechanical properties and the corrosion resistance of the welded joint of the clad pipe.Accordingly,research on the automatic welding technology for the 2205/X65 clad pipe is conducted.As a result,it is determined to employ the multi-layer welding technology,i.e.,using the TIG (tungsten inert gas) welding process for both the clad metal and the transition metal,and the MIG (metal inert gas) process for the base metal.Examination of the metallographic structure of welded joint illustrates that the micro structure of weld transition metal is mainly composed of austenite and fishbone and vermicular-shaped ferrites,while the micro structure of weld clad metal is composed of ferrite and acicular and blocky austenite.The contents of the ferrite are controlled within the range of 40%~55% in the base metal,weld and the HAZ,and a transition section wide as about 20μm is formed at interface between the base metal and weld metal.As a result it is ensured that the welded joint has excellent mechanical properties like tensile property and impact property,while its intergranular corrosion-resistance is also up to applicable specification as well relevant requirements by related projects.