Investigation on the microstructure and toughness properties of austenitic and duplex stainless steels weldments under cryogenic conditions

This study presents deep-resolved metallurgy and fractography of the weldments beyond the routine examination of the welded constructions working under cryogenic conditions. Duplex-austenitic and austenitic-austenitic stainless steel plates were welded by means of a shielded metal arc welding. The impact toughness of the weldments was assessed at both subzero and ambient temperatures. The weld microstructure was composed of Widmanstatten austenite and a ferrite matrix at the duplex-austenitic weldment. The microhardness values varied from a maximum of 330 HV0.1 at the duplex parent metal to 200 HV0.1 at the austenitic parent metal due to the phase transitions from an f.c.c. plus b.c.c. to a fully f.c.c. crystalline structure. Under cryogenic conditions, greater impact toughness for the weld metal was determined at the duplex-austenitic weldment relative to the austenitic-austenitic weldment. The weldments exhibited ductile fracture failures down to -80 degrees C. In accordance with the decrease in the sub-zero test temperatures, the standard deviation in the impact energy values decreased, and the fracture was still ductile and stable for the weldments. At -80 degrees C and -176 degrees C, cleavage surfaces were observed in the duplex-austenitic welded impact bar samples and cleavage fracture data were more reproducible with respect to ductile fracture data. (C) 2015 Elsevier Ltd. All rights reserved.