Structure formation mechanisms and properties of powdered carbon steels during laser thermal modification. II. Properties of modified steels

Abstract

When low and medium carbon steel surfaces are thermally modified with a CO 2 laser [i], the fusion zone is typified by a low-carbon martensitic structure, the hardness of which increases as the tetragonality level increases. Ferrite and martensite are present in the original ferritic and ferriticpearlitic structure in the laser-affected zone; the former are developed at the original pearlitic colony site and retaintheir identity. Pearlitic colonies present in the laser-affected zone are typically nonuniform in composition. Apparently, this structure is formed when the steel is quenched from the two-phase (~ + ~)region. It may also be a condition of its formation that there is inadequate austenite homogenization of the carbon content due to the rapid heating rate above the point at which the phase-transformations begin.