In-situ Characterization of Martensitic Transformation in High Carbon Steel Under Continuous-cooling Condition

To inspect volume expansion effect on the morphological features of martensite under continuous cooling conditions in which the transformation area (i.e. austenite) steadily decreases, we observed the martensitic transformation behaviour of 0.9C steel in-situ on free surfaces. The microstructural evolution of surface martensite with an abnormal grain size and that of coarse and fine lath martensites was observed, in the stated order, under continuous cooling conditions; each martensite exhibited a different morphology. The differences in martensite morphology are discussed from elastic strain viewpoint induced by incipient-formed martensite..