Welding Metallurgy of Austenitic-Ferritic Dissimilar Joints

Abstract

When welding stainless steel components, particularly in plant engineering applications, it may be necessary to join unalloyed or low alloyed ferritic steels to austenitic chromium-nickel-(molybdenum) stainless steels. Such dissimilar joints are also called “black-and-white joints”. With regard to corrosion resistance, there are normally no particular requirements demanded from this type of joint, because the low alloyed steel is normally not corrosion resistant. Because of the different structure between the types of steels to be joined, there may be certain difficulties experienced during welding. Low alloyed steels, for example, normally require controlled preheat and interpass temperatures during welding, slow cooling after welding and often a final tempering or stress relieving heat treatment. Austenitic steels on the other hand should be welded “cold”, the welds should cool rapidly and post weld heat treatments should be avoided wherever possible.