The morphology and crystallography of lath martensite via high pressure martensitic transformation in Fe-0.45 wt.% C steel

The morphological and crystallographic characteristics of lath martensite induced in one thermal cycle treatment (heating to 950 °C and holding for 30 min, followed by cooling to room temperature using circulating water) under hydrostatic pressure of 1∼6 GPa were studied. The key findings are as follows: (1) As pressure increases, three pairs of Bain variants with low misorientation are gradually replaced by three pairs of twinned variants (martensitic variant pairs exhibiting twin misorientation) within a packet and twinned lath martensite (three pairs of twinned variants in each packet) is formed in 6 GPa. This evolution is accompanied changes in the morphology of lath martensite, such as grain size of prior austenite, macroscopic features and straightness of variant boundaries. The above changes can be reasonably attributed to the self-accommodation mechanism of martensitic laths, which is driven by the yield strength of austenite at the martensite start temperature ( M _s) and the low energy boundaries of the twinned variants. (2) Twinned variants consist of {110}-type and {112}-type twins, following the Kurdjumov–Sachs (K-S) orientation relationship (OR) with the parent austenite. This work further supplements the understanding of the morphological and crystallographic characteristics of lath martensite. It offers a theoretical basis for more comprehensive performance regulation of Fe-C alloys, particularly by utilizing twinned lath martensite composed by as a fundamental microstructure.