Influence of heat input on the Charpy ductile fracture behavior of reheated HAZ in GMAW multilayer welded joints on HSLA steel using digital fractographic analysis

Abstract

The effect of the heat input on the fracture behavior of reheated heat affected zone in multi-layered welded joints of ASTM A633 steel was evaluated using the impact test, fractography, scanning electron microscopy and digital images processing. The impact results indicated a reduction in the Charpy energy as a function of the wire feed rate, which was confirmed by fractographs after digital images processing that showed a decrease in volumetric fractions of micro-dimples in ductile failures accompanying the increase in feed rate, favoring brittle fractures in transgranular cleavage facets containing river marks. The minimum fractions in micro-voids and the largest size of facets showing a higher number of river patterns were found at maximum feed rate of 200 mm·s-1. Heterogeneous microstructure of heat affected zone formed by fine acicular ferrite network surrounded by allotriomorphic ferrite showed that an increase in the feed rate induced a grain refinement by the formation of acicular ferrite, which was linked to the deterioration of absorbed energy and brittle failures.