Laser beam welding of austenitic/ferritic dissimilar steel joints using nickel based filler wire

Abstract

Laser beam welding of austenitic/ferritic dissimilar steel joints using a nickel based filler wire has been investigated. The feasibility of using the process to join these dissimilar steels was evaluated. Microstructural characterisation was performed using both optical and electron microscopy. The influence of the processing parameters, principally air gap width and beam alignment, on the microstructure, composition, and properties of the welds has been determined. In order to obtain a fully austenitic weld metal microstructure, an air gap 0·2 mm in width with a suitable wire feedrate is recommended, which avoids the unnecessary extra heat input and problems in controlling weld quality associated with a wider air gap. However, in some applications, the size of the air gap can be used to control the alloying effect of the filler wire and consequently to obtain the desired weld metal composition. Laser beam alignment plays an important role in processing. It can be aligned to a maximum of 0·25 mm on the stainless steel side without producing a significant change in the weld metal composition. However, beam alignment on the Cr–Mo steel side should not be used if martensite formation in the weld metals is to be avoided. Laser beam welding with nickel based filler wire shows potential for producing austenitic/ferritic dissimilar steel joints.MST/1731