Optimisation of Nd–YAG laser welding of superduplex stainless steel by parameter design

Abstract

Many researchers have found the welding of super duplex stainless steel UNS S32760 (Zeron 100) by high power CO₂ laser to be an unacceptable process, because the austenite/ferrite (γ/α) ratio in the laser weld bead normally deviates significantly from the optimum balance of 50 : 50. To date, the best γ/αratio in a laser weld reported in the published literature was ∼30 : 70. The high percentage of ferrite would result in lower strength and poor corrosion properties. The present investigation was aimed at achieving a near 50 : 50 γ/αratio laser weld using the Nd–YAG laser. These lasers have more process parameters that can be varied, compared to CO₂ lasers. Three different kinds of output power waveform, continuous, sine, and square waves, together with many other parameters, were investigated. The Taguchi method was used for parameter design, to reduce the number of experiments. Based on the Taguchi approach, optimum process parameters were determined and laser weld beads that consisted of 55 : 45 γ/α were achieved.