A metallographic technique for detecting martensite-austenite constituents in the weld heat-affected zone of a micro-alloyed steel

The industrial demand for weldable high-strength low-alloy steel with good toughness in the weld heat-affected zone, even when high values of heat input are employed, has significantly increased in the last years. Several publications have indicated that the martensite-austenite island is the main microstructural constituent controlling this toughness, highlighting the need for a precise identification of these constituents in studies dealing with the microstructure-toughness relation. In this paper, a new metallographic technique is presented that enables a quick and accurate identification of this constituent by both light optical and scanning electron microscopy. The study was conducted in the weld simulated heat-affected zone of a micro-alloyed Nb steel with small additions of Cu and Ni; a C-Mn steel with low carbon was employed as a reference.