Microstructural changes due to laser ablation of oxidized surfaces on an AISI M2 tool steel

Surface modifications due to high intensity laser interaction on oxidized M2 steels were studied by optical and electron microscopy, and X-ray diffraction. First, it was shown that surface ablation of the oxide layer was possible when the laser fluency was above 0.4 J cm−2. Above this threshold, the surface presented craters due to the spread of the liquid metal. Second, it was demonstrated that the region near to the surface was partly transformed. The prior carbides were dissolved in the liquid metal and the martensite was decomposed during heating. During the rapid cooling, part of the austenite was retained and the remelted zone showed lower hardness than the matrix. A chemical homogeneous layer at surface balanced this hardness decrease.