TWI Industrial Member Report Summary 467/1993
By N Francis-Scrutton
Microstructures of weld beads with various Al:Ti:O ratios have been characrerised using optical microscopy. At extremely low levels of Al and Ti (<0.003 and 0.002wt%, respectively), the as-deposited microstructure contained a high (approx. 50%) proportion of fine acicular ferrite (AF). For Al:O ratios > 1 and for Ti additions equal to or greater than 0.015wt% the AF content dropped sharply and was replaced by large coarse colonies of ferrite with second phase (FS). Combined additions of Al and Ti also reduced the percentage of AF, but this was offset by an increase in the proportion of small colonies of FS. Because the FS colonies in weld metals alloyed with both Al and Ti were so small, it is likely that the welds would be significantly rougher than those alloyed individually with large Al and Ti additions.