THE INFLUENCE OF VANADIUM IN MICROALLOYED STEELS ON THE PROPERTIES AND MICROSTRUCTURE OF THE INTERCRITICALLY REHEATED COARSE GRAINED HEAT AFFECTED ZONE

摘要

1. The addition of 0.05% V to the C-Mn boron free steel improved the Charpy and the CTOD toughness in both the GC HAZ and the IC GC HAZ compared to a carbon steel, despite an increase in hardness. 2. The effect of 0.05% V in the GC HAZ was to promote both a polygonal ferrite along austenite grain boundaries and an acicular intragranular microstructure. It is believed that these changes in microstructure were responsible for the improved toughness in the GC HAZ condition, overcoming the detrimental effects on toughness of increased hardness. 3. For the IC GC HAZ, the 0.05% V steel had a reduction in the area fraction of M-A, and a reduction in the M-A particle size, compared with the C-Mn steel. The distribution of the M-A phase along prior austenite grain boundaries was also different in the V steel, showing a lower area fraction of M-A at the grain boundaries. These changes in the distribution of the M-A phase were considered to be responsible for the improved toughness of the 0.05% V steel in the IC GC HAZ condition.