Improvement of impact toughness of simulated heat affected zone by addition of aluminium

The effect of aluminium content (0.023, 0.038 and 0.070 wt-%) on microstructure and impact toughness of simulated coarse grained heat affected zone (CGHAZ) of high strength low alloy steels with different heat inputs (20, 100 and 200 kJ cm(-1)) was investigated. The microstructure of simulated CGHAZ consisted of predominantly granular bainite. The martensite-austenite constituents became finer and its volume fraction decreased with increasing aluminium content, irrespective of heat input level. The impact toughness of the simulated CGHAZ improved remarkably with increasing aluminium content even at high heat input of 200 kJ cm(-1). It was attributed to the reduction in volume fraction of martensite-austenite constituents and the refined martensite-austenite constituents by addition of appropriate aluminium.