Theoretical and experimental study on laser surface hardening by repetitive laser pulses

An analytical solution for the temperature variation in a semi-infinite workpiece heated by repetitive laser pulses has been derived and the effects of various process parameters, viz. laser power, beam diameter, scan speed, pulse duration, repetition frequency and duty cycle on the surface transformation hardening have been investigated. The study shows that the soaking time of the top surface layer at a temperature above the phase transformation temperature, on which the homogeneity of microstructure and the depth of hardening depend, can be increased by repetitive laser pulse heating in comparison to continuous wave laser heating. The depth of hardness increases with the number of incident laser pulses at low frequencies in the range of Hz. This has been demonstrated by comparing the surface hardness characteristics of AISI 1055 steel specimens resulted by the continuous wave and repetitive laser pulse hardening processes.