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Comparison of different techniques of laser surface hardening

Grum J.

Journal of Achievements in Materials and Manufacturing Engineering

2007

Vol. 24, nr 1

17-25

Purpose: The paper gives a comparison of various techniques of laser surface hardening for various kinds of structural and tool steels, and special maraging steel and hardening of nodular graphite and gray cast irons. Design/methodology/approach: Experimental investigations of laser surface transformation hardening, laser remelting and laser shock processing were performed. Trials of laser hardening were carried out under different conditions, with different modes of laser guidance over the specimen surfaces, and with different degrees of path overlapping. Different kinds of absorbents, were tested, the depths of hardened paths or layers were measured, profiles of hardness and residual stresses were measured, the microstructures formed were analysed, and a micro-chemical analysis was made. Findings: The investigations showed that under different laser-hardening conditions quite different surface-layer properties are obtained. A very strong connection of the chosen energy input, the type of absorbent used, the degree of overlapping, and the mode of laser-beam guidance with the depth of the hardened path or layer, and the through-depth profiles of microhardness and residual stresses of the hardened path or layer was found. Research limitations/implications: The industrial requirements for the achievement of appropriate properties of surface layers, with special regard to the hardened-layer depth, and appropriate variations of microhardness and residual stresses are more and more frequent. The residual-stress profiles should have high compressive stresses at the surface and a small gradient of the residual stresses in the subsurface of the hardened layer. In this way high fatigue resistance of a material can be ensured and occurrence and propagation of cracks prevented. These findings offer engineers new concepts in the improvement of surfaces of machine and tool parts. Practical implications: With the present findings constructors and experts in laser technology can essentially improve the quality and operating life of machine parts or tools. Originality/value: The research conducted on the influences of different modes of laser-beam guidance in terms of microstructure and variations of microstructure and residual stresses in the thin surface layer are original.