Diode laser welding of stainless steel 304L

The feasibility to achieve deep penetration welding of stainless steel utilising a 15 kW laserline® diode laser has been studied. This was approached by first characterising the properties of melt run welds on stainless steel 304L plates and then transferring the gained knowledge to perform the butt welds.

The results from the melt run analysis indicated that there was an increase in penetration and weld width with heat input, i. e. with either increasing the laser power (9–15 kW) or decreasing the welding velocity (3 m/min–1 m/min). Melt run penetrations up to 12 mm were achieved. The increased welding velocity was shown to reduce the solidification grain and subgrain size. Cracks along the weld centreline were observed at the higher heat inputs and sinking at the crowns at the lower. Good melt run welds were obtained at laser powers of 9–13 kW and a welding velocity of 1.5 m/min.

Butt welding of 10 mm thick plates was successfully achieved with full penetration along the length of the weld at a laser power of 12 kW and a welding velocity of 1.5 m/min. The weld properties were comparable to the corresponding melt run welds using a similar parameter set of laser power and welding velocity. No detrimental subsurface defects were recorded with only the presence of a negligible amount of porosity. Oxidisation on the surface of the cap and sinking towards the end of the weld run was observed.

It was demonstrated that high powered diode lasers are capable of deep penetration welding. Keyhole mode welding was achieved and the weld properties are comparable to that of other high energy density welding processes. For welding of plates in the 10 mm thickness range, the results suggested that the more economic high power diode lasers may become a competitor to different laser beam systems which may be more expensive in both procurement and operation.