TBW technique by varying weld polarities in SMAW as an alternative to PWHT

This paper proposes the temper bead welding (TBW) technique as an alternative to post-weld heat treatment (PWHT) by varying the polarity between the deposited layers while other welding variables remain the same. The work was conducted to study the effect of changing welding polarities using the shielded metal arc welding (SMAW) process on microstructure, microhardness, grain size, weld bead geometry and distortion of low carbon steel AISI 1020. The results show that higher heat input, larger heat affected zone (HAZ) and higher distortion was noticed when applying DC- polarity. It was also found that welding using the DC + polarity produced higher concentration of pearlite structure in all regions of the weld when compared with DC- polarity. The amount of pearlite structure decreased with increasing the heat input when using DC- polarity. In addition, high heat input and slow cooling rate would lead to a greater tendency for formation of ferrite structure from the grain boundaries than pearlite. Analysis of the test results showed that there is a marked decrease in hardness in the HAZ and weld zone regions in both DL cases as some of the weld passes would have been partially tempered by subsequent passes. Samples welded using the DC + polarity showed an overall higher hardness value, smaller grain size and preferable weld bead geometry in comparison with the DC- polarity. It can be concluded that for efficient tempering, the additional layers should be welded using DC- polarity since the heat distribution is larger and thus can temper the underneath layers adequately.