Abstract:
Ferritic stainless steel is utilized to fabricate automotive exhaust systems using a ferritic weld metal.
Ductility of the weld metal is higher if its microstructure contains a significant proportion of equiaxed
grains. The formation of equiaxed (rather than columnar) grains is favoured by a higher titanium weld
metal content. In this study, the Ti content of ferritic stainless steel weld metal was changed by using Tifree
(Type 436) and Ti-containing (441) ferritic stainless steel as base metals. The metal-cored welding
consumable contained 0.4% Ti. Gas–tungsten arc welding and gas–metal arc welding processes were
compared. The weld metal Ti content ranged from zero to 0.5% Ti, as determined from scanning electron
microscopy supplemented by inductively coupled plasma optical emission spectroscopy. Cross-sections
of the weld beads were subjected to point counting (to estimate the fraction of equiaxed grains) and
image analysis (to estimate the average grain size). Point counting proved to be more reliable. The
fraction of equiaxed grains was sensitive to the Ti content, but not to the welding process. Below 0.4% Ti,
the fraction of equiaxed grains gradually increased with an increase in the weld metal Ti content; above
0.4% Ti, the fraction of equiaxed grains rapidly increased with increasing Ti content. The transition in
behaviour at 0.4% Ti corresponded to a Ti content at which Ti-rich precipitates became stable at the
estimated liquidus temperature of the weld metal.
