Correlating thermal history with characteristics of Laser Welded 15-5 PH Stainless Steel

Laser Beam Welding (LBW) has been carried out on precipitation-hardened 15-5 PH stainless steel. Different scanning speeds ranging from 2.4 m/min to 4.0 m/min with an interval of 0.4 m/min have been used for LBW at a laser power of around 2 kW to study the effect of weld-speed on melt-pool thermal properties, weld-microstructure, microhardness, and joint strength. A non-contact type infrared pyrometer was used to monitor the weld pool thermal cycles. The time required for solidification and the lifetime of the melt pool were found to decrease with welding speed while a corresponding significant increase in solidification rate was observed. FZ geometry changed from an hourglass to a key-hole shape with increasing welding speed along with decreasing overall FZ dimensions. A significant increase in FZ microhardness took place with the increase in welding speed as the result of finer grain structure evolution. A similar trend was not distinct in HAZ which has been reasoned to be due to low precipitation of Cu particles as a result of low heat input. Yield tensile strength increased by around 12% while ultimate strength improved by 7% when the laser beam scan speed was changed to 4.0 m/min from 2.4 m/min.