Abstract
This report reveals gigacycle fatigue properties for a modified-ausformed SMn443 steel. The steel has an advantage in recycling since the steel dose not contain Cr and Mo which are difficult to be removed in re-melting. Modified-ausformed, oil-quenched and water-quenched steels were prepared for fatigue test, preparing two different tensile strength specimens of 1400 and 2000MPa. The low-strength modified-ausformed steel (AF1400) was free from fish-eye fracture with a fatigue limit of 770MPa at (10)^9 cycles, while the low strength oil-quenched steel (QT1400) caused fish-eye fracture. Although the high-strength modified-ausformed steel (AF2000) was suffered from fish-eye fracture, the fatigue limit at (10)^<10> cycles was 830MPa that was higher than 710MPa of the water-quenched steel (QT2000W) tempered at 473K. The fatigue limit at (10)^9 or (10)^<10> cycles for both oil-quenched steels (QT1400 and QT2000) could not be determined because of temperature increase of specimens in 20kHz tests. The fracture surfaces revealed optically dark areas (ODA) even in modified-ausformed steel since the modified-ausforming was not perfect in this research.
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