Microstructural characterization of an as-quenched HSLA-100 plate steel via transmission electron microscopy

Detailed analysis of an HSLA-100 steel via transmission electron microscopy revealed a “fully” martensitic microstructure, despite a low carbon content of 0.06 mass%, a fine prior austenite grain size of about 10 μm, and a modest cooling rate of approximately 15 °C/s. Martensite laths typically contained a moderate-to-high dislocation content, and occasional regions of twinned martensite were observed. Laths were contained wholly within single grains of austenite, and about 5% austenite was present in the final as-cooled microstructure. Martensite crystals exhibited the Kurdjumov–Sachs orientation relationship with respect to the parent austenite phase, and multiple variants of this relationship were observed for adjacent packets. Autotempering of martensite resulted in a low volume fraction of cementite precipitates in the largest, first-formed laths.

► HSLA-100 steel with 0.06% C and 10 μm austenite grains transforms to martensite.
► Five pct retained austenite was documented with electron-diffraction patterns.
► Martensite contained high dislocation density and some twins.
► Kurdjumov–Sachs orientation relationships observed for martensite and austenite.