Ductile fracture mechanisms in shielded metal-arc and gas tungsten-arc welds of Type 347 stainless steels

The ductile fracture behavior of two different welds of Type 347 stainless steel, which are made by SMAW (shielded metal arc welding) and GTAW (gas tungsten arc welding) processes was characterized by J-integral testing and microstructural evaluation techniques. Both welds by SMAW and GTAW processes showed significantly low fracture toughness compared with that of the base metal. Metallographic and fractographic examinations revealed that different micromechanisms are operative in the fracture process of the two welds. In the SMAW weld, the fracture was dominated by void initiation and growth at the inclusions that are homogeneously distributed in the matrix. On the other hand, in the GTAW weld, a large number of Nb(CN) particles precipitated on the austenite/ferrite interface as long rod shapes and the fracture proceeded by void initiation at these particles and accompanying decohesion of the interface. It is recommended that the C and Nb contents be reduced in weld metal itself as well and that the welding atmosphere be controlled. (C) 1999 Kluwer Academic Publishers.