Laser heat treatment of martensitic steel and dual-phase steel with high martensite content

Abstract

Laser heat treatment of galvanised steels with a martensite content superior to 80% were performed on a 1 cm wide area over an extensive temperature range [620 K - 1350 K]. The material softening induced is studied through uniaxial tensile testing and SEM microstructural observation. A treatment temperature close to Ac3 yields a massive increase in the ductility of the specimens while reducing the mechanical strength. This change in mechanical properties is associated with the nucleation of new austenite islands and the vanishing of the initial martensite laths. The results presented in this paper pave the way to localised variations of the strength-ductility trade-off, which could be useful for several industrial applications, particularly for enabling plastic forming or stamping of the martensitic steel sheets at low temperature.