This study is devoted to establish the relationship between high angle grain boundaries (HAGBs) and hardness from crystallography and provide reference for improving the hardenability of high strength ultra-heavy plate steel. The starting temperature during γ→α phase transformation was significantly decreased with the addition of boron (B). Electron backscattered diffraction and grain boundary density statistical results showed that the hardness follows a near linear relationship with the density of HAGBs. The variants of closed-packed (CP) grouping produces higher density of HAGBs and corresponding hardness than Bain grouping, such that a qualitative description that combines Jominy curves with transformation mode is proposed to evaluate hardenability.
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