Influence of assist gas on surface quality and microstructure development of laser metal processing

Abstract

Laser engraving, which is a high-precision and non-contact processing technology, has been widely used to process the difficult-to-cut mould steel. However, the efficiency is still low and the influence of laser engraving on the microstructure and properties of engraved surface also needs further study. By varying the assist gas (Argon, Compressed air, and Oxygen) of nanosecond laser engraving of Cr12MoV mould steel, the material removal rate and surface quality were compared, and the mechanisms of elemental diffusion and microstructural evolution in surface remelting layer were investigated to understand the variation in micro-hardness values. The results showed that the exothermal chemical reactions significantly increased the efficiency of laser engraving, but the surface quality was deteriorated and the detachment of elements C and Cr in remelting layer was promoted. Thus, lower hardness was observed for the remelted layer in the presence of oxygen or compressed air compared to Argon, although the micro-hardness of remelted layers was all increased attributed to grain refinements. Results suggested that the use of oxygen gas during rough engraving increased the material removal rate and reduced the cost, and the use of Argon gas at final engraving steps improved the quality and mechanical properties of the engraved surface.