Microstructure, Micro-hardness and Impact Toughness of Welded Austenitic Stainless Steel 316L

摘要

The objective of the paper is to study the mechanical behaviour of two welded joints that differ in their filler metals in regards with the microstructure. Gas tungsten arc welding process was employed to perform the welded joints between AISI 316L as a base metal and either ER316LN or ER308LN as filler metal. For both the welded joints, the microstructure of the fusion zone was predominantly austenitic containing a small amount of residual dendritic δ-ferrite in skeletal morphology formed during solidification (FA mode) and whose transformation to austenite upon cooling was incomplete. However, XRD analysis pointed out a relatively higher amount of δ-ferrite in the fusion zone of the welded joint (316L/ER308LN) than that in the welded joint (316L/ER316LN), as it could be expected from the calculated (Cr~(eq)/Ni~(eq)) ratio of Schaeffler formula. The composite microstructure of the fusion zones exhibited higher values of micro-hardness than the heat-affected zone which contained coarse grains. Charpy impact toughness was higher for the welded joint realized using ER308LN as a filler metal but both types of welds fractured in a ductile mode.