ASSESSMENT OF QT STEEL'S WELDED JOINT TOUGHNESS BASED ON REAL AND SIMULATED SPECIMENS

Conventional assessment of welded joint impact toughness, as defined in relevant standards for welding procedure qualification is based on testing of real specimens taken from base metal, weld metal, and heat affected zone. Here particularly, testing of heat affected zone may become unreliable, mainly due to the welded joint configuration and placement of initial notch. In addition, from general welding metallurgy knowledge it is well known that most weakened microstructure of welded joint, e.g. within heat affected zone is coarse-grained zone where maximum temperatures reach around 1300°C. Thus, this paper presents results and comments of one combined approach, where real specimens where taken and impact tested from gas metal arc welded X-joint configuration. Additional specimens where acquired by mean of welding thermo-cycle simulation, characterised with similar cooling condition as for real joints, but with maximum temperature of 1300°C. Base metals were quenched and tempered low-alloyed structural steels. Finally, specimens from real welds shows acceptable level of impact toughness, which may be found as favourable for welding procedure qualification, while simulated specimens shows impact toughness undermatching as prescribed for base metal. This however should not disqualify welding procedure in conventional manner, but rather should be carefully taken into consideration.