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

• Panoramic microstructure of the duplex–austenitic weldment was visualised.
• Micro-hardness distribution at the duplex–austenitic weldment was determined.
• Statistical analysis of cryogenic effect on impact toughness of the weldment revealed.

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 Widmanstätten 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 °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 °C and −176 °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.

Panoramic microstructure of an austenitic–duplex stainless steel weldment. (Transverse side view).Figure optionsDownload as PowerPoint slide