Abstract
Giga-cycle fatigue properties were investigated for an ultrafine-grained steel processed by warm tempfonning. The fatigue properties were compared with conventional tempered martensite steel. Fatigue tests were carried out at frequencies of 30Hz and 20kHz, using servo-hydraulic and ultrasonic fatigue testing machines, respectively. Both tempformed and conventional steels showed surface fracture in short life regions and fish-eye fracture in long life regions. The fatigue strength at 10^7 cycles was higher in the tempformed steel than in the conventional, while it was not in case of the 10^<10> cycles fatigue strength. The fish-eye fracture origins showed different aspects between the two types of the steel. In case of the conventional steel, Al_2O_3 inclusions caused the fish-eye fracture, while in case of the tempformed steel, Mo carbides surrounded by Mo-rich layers were observed at the origins. Sizes of the Mo carbides were smaller, while those of the Mo-rich layers were identical to the Al_2O_3 inclusions of the conventional steel. Therefore, the Mo-rich layers, as well as the carbides, would probably cause the fish-eye fracture. This means that suppression of the Mo-rich layers could lead to more improvement of the giga-cycle fatigue strength of the tempformed steel.
Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
