On the Strengthening Mechanism in Lath Martensite of As-Quenched Fe–Ni Alloys

Herein, the evolution in different strengthening contributions to yield strength of lath martensite in as-quenched Fe–Ni alloys were studied quantitatively. X-ray diffraction measurement results showed the dislocation density in lath martensite was slowly increased with increasing the Ni content. After separating different strengthening contribution to as-quenched lath martensite, it was found that with the increase in Ni content, solid solution strengthening by substitutional Ni atoms and dislocation strengthening were slightly increased and decreased, respectively. Based on the quantitative calculation results, dislocation strengthening was the largest contribution to yield strength of lath martensite in Fe–Ni alloys, accounting for at least 72% of yield strength. This work could offer deeper understanding to the strengthening mechanism of carbon-free martensite.