2003 Volume 89 Issue 3 Pages 362-368
Effect of boron on microstructure and toughness of simulated HAZ in 0.03%C-2%Mn-0.6%Cr-0.2%Mo-0.02%Nb bainitic steel was investigated. It was found that morphology of bainitic ferrite of simulated HAZ is changed from granular into lath like morphology, and that toughness is deteriorated by increasing boron. It is thought that the change in bainitic ferrite morphology deteriorates toughness, considering that facet of Charpy impact surface is coarsened with increasing boron. It has also been clarified that bainitic transformation is retarded by increasing boron. The change of bainitic ferrite morphology and the depression of bainitic transformation by increasing boron could be explained by the decrease in γ grain boundary energy due to free boron segregation to γ grain boundary.
