Tem study of the microstructure of HSLA100 steel

In this study, investigations of microstructures of as-quenched and aged HSLA100 steel by using transmission electron microscopy showed that as-quenched HSLA100 has a mixed microstructure of 50% lath martensite + 40% acicular ferrite + 9% retained austenite + 1% twinned martensite. During aging, HSLA100 undergoes the following microstructural changes: (1) tempering of lath martensite and twinned martensite, (2) recovery of acicular ferrite, and (3) precipitation of a second phase during aging. Retained austenite is very stable and remains undecomposed even after aging at 650 °C for 1 12 h. The precipitates observed in this study include ϵ-Cu, Mo2C, M23C6,TiN, and Nb(C,N). The contribution of precipitation strengthening for HSLA100 steel after 1 12 h of aging at 650 °C is about 140MPa.