Rapid solidification of M2 high-speed steel by laser melting

The effects of laser surface melting and rapid solidification on the microstructure of M2 high-speed steel (HSS) have been investigated. A solid state pulse Nd-YAG laser of wavelength 1.06 μm, maximum power of 100 W, beam diameter ∼1 mm, and pulse duration of 0.8 and 2.5 ms. Optical, scanning electron microscopy, and X-ray diffraction techniques were used to evaluate the microstructure and identify the phases. Results show that laser surface melting has led to a complete dissolution of the carbides and re-solidification of cellular/dendritic structure of a very fine scale surrounded by a continuous interdendritic (or intercellular) network of carbides eutectic. The phases appeared were mainly δ ferrite and M6C and small amount of austenite γ. Laser surface melting leads to a refinement of the microstructure and altering the morphology and the distribution of the phases. The microhardness of this material was not increased after laser melting.