This study aims to establish fundamental knowledge for online non-destructive inspection in the laser quenching process utilizing acous-tic emission. Acoustic emission is the transient
elastic wave phenomenon due to release of strain energy in a solid material. And it is well known that the martensitic transformation can induce the acoustic emission. In this study, the acoustic
emission monitoring of martensitic transformation during laser quenching experiment was conducted with the chromium molybdenum carbon steel ÿSCM440 in Japanese Indus-trial Standardsÿ
as the specimen. The experiment was carried out with seven kinds of laser irradiation power for different volume generation of heat-affected zone. After experiment, the martensite structure was
conrmed at the heat-affected zone and the volume of the martensite structure within the zone was estimated. Only the specimen irradiated by the lowest laser power had no martensite structure.
The acoustic emission waves were analyzed using parameters that showed the generation time duration and scale of source phenomenon. As a result, the relationship between the volume of
martensite structure and information of acoustic emission was positive. It was suggested that the acoustic emission monitoring have application for the online non-destructive inspection for the
laser quenching process.