DEVELOPMENT OF 1200HV-CLASS GAS ATOMIZED POWDER FOR SHOT PEENING MEDIA

摘要

Shot peening is one of kinds of surface treatments by colliding metal or ceramic media at high projection speed to obtain high compressive residual stress on shot peened surface for improving the fatigue property of shot peened parts. Shot peening media with low hardness can be deformed plastically by collision to workpieces with high hardness. Thus, it cannot induce high compressive residual stress on workpieces with high hardness. Therefore, much higher hardness is required for shot peening media to obtain high compressive residual stress on workpieces with high hardness. Furthermore, high toughness is also required for shot peening media in order to show long media life. According to these backgrounds, the purpose of this work is to develop a new media with not only high hardness but also high toughness. In this study, the fundamental properties of the developed media and the effects of shot peening to the carburizing steel by using this media were investigated. The developed FeCrB media, that was manufactured by gas atomization of the alloy in hypereutectic composition region of Fe-B binary system, had a cermet-like microstructure consisting of the fine high hardness Fe2B connected by the eutectic structure containing aFe with high ductility. As a result of this microstructure, this developed media combined high hardness of 1200 HV and high toughness. The developed media had more excellent media life property than conventional steel and high speed steel media. Furthermore, the fatigue strength of the specimen shot peened by the developed media was higher than that by conventional high speed steel media.