STRUCTURAL EVOLUTION OF PULSED ND-YAG LASER WELDS OF AISI 1006-STEEL

Although correlations of welding parameters with the metallurgical fea tures of conventional fusion welds in low carbon steels are well estab lished information on process-structure-property relationships associa ted with pulsed laser welds is more limited. This paper presents resul ts on the characterisation of weld metal and heat affected zone (HAZ) microstructures observed in laser welded AISI 1006 steel. Pulsed Nd-YA G laser welds in the bend on plate configuration were used for this pu l pose, both in overlapping and non-overlapping bead configurations, A s very rapid heating and cooling cycles occur during laser welding, th e microstructures observed in the weld metal are the result of rapid s olidification producing thin columnar austenite grains extending from the fusion boundary, which transform ro martensite and bainite during fast cooling to ambient temperature. The HAZ structure in the base pla te can also be rationalised in terms of the rapid thermal cycling expe rienced. The HAZ is narrow with the intercritical reheated subzone bei ng dominant. As microstructural development has a critical effect on t he mechanical properties of welds, microstructural characterisation pl ays an integral role not only in the understanding of pulsed laser wel ding, but also in the selection of optimum welding conditions for the material of interest.