These alloys have superior carburisation and oxidation resistance to alloys based on25%Cr-35%Ni but with some reduction in creep strength. In the as-welded condition the multi-pass weld metal microstructure consists of austenite with primary eutectic and secondary precipitated carbides. For the thicker section materials a preheat may prove beneficial owing to the low ductility of the material. There would not normally be any requirement for PWHT. Typical applications include tubes for steam cracking pyrolysis transfer lines, pyrolysis furnace outlet lines and steam reformer headers in the petrochemical industry.