Morphology, substructure and crystallography of lath martensite in Fe-C alloys

Morphology, crystallography and dislocation density of lath martensite were examined in Fe-C alloys with various carbon contents ($0.0026{\sim}0.78$ wt%C). It was found that, in low carbon alloys ($\leqq$0.18%C), a martensite block observed in optical microscopic scale consists of two groups of laths misoriented each other by about 10 degrees on analysis of microtexture. This result is largely different from the current view on the crystallography of martensite block, in which laths in a block is of the same variant. In contrast, a block contains laths of a single variant in high carbon alloys ($\geqq$0.61%C). As carbon content increases, block and packet sizes are refined whereas size of lath does not change significantly. Dislocation density largely increases with carbon content