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Effect of Laser Quenching Overlap Rate on the Microstructure and Mechanical Properties of H13 Steel
F. P. Yao, Z. Ming, J. H. Li, Y. K. Wang and T. Y. Li

In order to obtain the best overlap rate when the surface of H13 steel is strengthened by multi-pass laser quenching with a fibre laser. Quenched layers of 20, 30, 40 and 50% overlap rates were prepared. The cross-sectional morphology and microstructure evolution mechanism of the modified layer were analysed. The mechanical properties of the modified layer were tested. The results showed that the overlap rate affects the flatness of the bottom of the section and the flatness tends to be gentle with an increase of the overlap rate. When the overlap rate is 40 and 50% the flatness of the bottom surface is the best. The lap zone is the secondary quenching zone and the microstructure characteristics are consistent with the complete phase transformation hardening zone. The martensite in the tempering softening zone decomposes to form tempered martensite and tempered sorbite, and nodular carbides are precipitated. The width of the tempering softening zone increases with the increase of overlap rate, and the lowest hardness can be reduced to about 420 HV0.3 and the optimum overlap rate is 30 and 40%. With the increase of overlap rate the wear weight loss increases, and the wear mode is mainly abrasive wear and adhesive wear. When the overlap rate is 20% the wear condition is the best. By comprehensively comparing the flatness of the bottom surface, the width of the tempering softening zone and the wear performance, it is concluded that the optimal overlap rate is 40%, the flatness of the bottom is 0.89, the width of the tempering softening zone is 0.9 mm and the wear loss is 13.57 mg.

Keywords: Fibre laser, H13 steel, laser quenching, microhardnes

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