Method of ultrasonic nano-crystal surface modification for improvement of surface characteristics of AISI D2 heat-treated with different tempering conditions

AISI D2, an alloy tool steel, has been widely used as a cold-work die steel because of its excellent wear resistance, toughness, and machinability. However, when it is mold or under high load, hardness resistance are required to improve service life. This study aimed apply ultrasonic nanocrystal surface modification (UNSM), local hardening technology, the D2 steel. To maximize improvement effect achievable through UNSM, important select optimal process conditions according characteristics base metal. Therefore, effects UNSM were compared for different initial values in this study. end, metal was subjected heat treatment exhibit (approximately 40, 45, 50, 55 HRc). Changes observed three main parameters process: inter-pass interval, feed rate. No significant changes roughness caused by As interval decreased static load increased, increased. specimen with low (D2-H40), On other hand, increased regardless It also found that highest (D2-H55) exhibited greatest rate 9% smallest hardened layer thickness 220 μm. In addition, largest compressive residual stress (− 1,130.6 MPa) formed on D2-H55 after which occurred had limited plastic flow due fine grains ductility, causing thus energy repeatedly delivered be concentrated area. Consequently, reducing effective improving material hardness. must applied at appropriate level, depending heat-treated product requirements, will consider based derived