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Micro-Forging and Peening Aging Produced by Ultra-High-Temperature and Pressure Cavitation

Toshihiko Yoshimura, Masataka Ijiri, Daichi Shimonishi and Kumiko Tanaka

From microstructural examination of specimen surfaces or sides and from the mechanical properties resulting from compressive residual stress using Cr-Mo steel (SCM435), Ni-Cr-Mo steel (SNCM630), Ti-6aAl-4V, and Inconel (UNSN06601) processed by WJC and UTPC (micro-forging), the microstructure of the WJC-processed specimen revealed that voids and cracks tended to occur in the depth region of 0.5-1 mm from the topmost surface. The microstructure of the UTPC-processed specimen showed the spheroidization of cementite observed in the depth region of 0.5-1 mm from the topmost surface. In addition, voids and cracks were not observed in the specimen bulk. The Charpy impact energy of UTPC had the highest value of 101 J because ductile layers were formed by UTPC processing. Stress relaxation behavior of various processed materials at a temperature of 500°C was investigated. Compressive residual stress of more than 100 MPa was retained after annealing both the WJC- and UTPC-processed specimens for 5 hours. After stress relaxation testing, cracks owing to thermal stress do not occur at the grain boundary in the UTPC material having a tenacious tough layer inside. Micro-forging (UTPC) is promising for high-temperature oxidation of low-alloy steel, Ti alloy, and Inconel. Moreover, low-temperature and low-pressure cavitation (LTPC) is applied to age hardening of aluminum alloy Al-Mg-Si (AC4CH).