TWI Industrial Member Report Summary 176/1982
By M N Watson
There is a dearth of published information relating to the fracture toughness of laser welds. But laser welds in quenched and tempered shipbuilding steels and in pipeline steels are reported to have good fracture toughness properties. However, there is some doubt about the validity of results in which the fracture path deviates from the fusion zone into the heat-affected zone or parent plate.
Laser welds were made at powers in the range 6.25-6.5kW and at travel speeds 0.24-0.5m/min, in a 12.5mm thick C-Mn-Si-Nb-A1 steel (BS 4360 grade 50D). Porosity was encountered in some of the welds and appeared to be related to the oxygen content of the base material. Charpy V-notch impact testing showed that the toughness properties were poor, both as-welded and when heat treated at 600°C; the best 27J temperature achieved being -15°C. Comparison with electron beam welds and attempts to modify the laser weld microstructure have indicated possible techniques for improving the toughness properties.