TWI Industrial Member Report Summary 243/1984
By M N Watson
An investigation is reported of the laser welding of six 12.5mm thick C-Mn-Si-Al-Nb structural steels to BS 4360 Grade 50D. Carbon contents were in the range 0.15 to 0.19% which is representative of a wide range of engineering steels, although not as low as those in modern 50D compositions. Laser powers in the range 5.2 to 9.1 kW were used. Weldability lobes are presented which show that welds free from porosity cannot be made at powers less than 7kW for this material and thickness. Mechanisms for the formation of porosity are proposed. Charpy and CTOD properties were determined and it is shown that good weld metal impact toughness results, which are associated with a martensite microstructure, are obtained at welding speeds of 0.9m/min and above.