Monitoring of Laser Quenching of the Carbon Steel by Acoustic Emission

This study aims to establish fundamental knowledge for online non-destructive inspection in the laser quenching process utilizing acoustic 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 (SCM440 in Japanese Industrial Standards) 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 confirmed 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.