New insight into the hardenability of high strength low alloy steel from the perspective of crystallography

Abstract A Jominy specimen of low carbon low alloy steel was investigated to elucidate the relationship between crystallographic features and hardness. As the Jominy distance increased from 2 to 20 mm and then to 50 mm, the morphological structure changed from lath martensite to lath bainite and then to granular bainite. The cooling rate was lowered with increasing Jominy distance, and the density of high angle grain boundaries (HAGBs) and the hardness were decreased, showing a near-linear relationship between the HAGBs density and hardness. The high cooling rate led to a large driving force and a low transformation temperature, which contributed to producing high density of HAGBs and hardness.