Si-Mn鋼のギガサイクル疲労特性に及ぼす改良オースフォームの影響
2003 年 89 巻 10 号 p. 1082-1089
詳細
2003 年 89 巻 10 号 p. 1082-1089
This report reveals gigacycle fatigue properties for a modified-ausformed Si-Mn steel (SMn443) with the chemical composition of 0.42C-0.2Si-1.52Mn in mass%. The Si-Mn steel has an advantage in recycling since the steel does not contain Cr and Mo which are difficult to be removed in re-melting. On the other hand, disadvantages of the Si-Mn steel are low tempering resistance and low hardenablility.
Modified-ausformed, oil-quenched and water-quenched steels were prepared for fatigue tests, followed by tempering at 473K and 673K to prepare two different strength specimens. The tensile strengths of steels tempered at 473K and 673K were nearly 1400 MPa and 2000 MPa, respectively. The problem of hardenablility was solved by modified-ausforming, while the tempering resistance was not improved. The low-strength modified-ausformed steel (AF1400) was free from fish-eye fracture with a fatigue limit of 770 MPa at 109 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 1010 cycles was 830 MPa that was higher than 710 MPa of the water-quenched steel (QT2000W) tempered at 473K. The fatigue limit at 109 or 1010 cycles for both oil-quenched steels (QT1400 and QT2000) could not be determined because of temperature increase of specimens in 20 kHz tests. The fracture surfaces revealed optically dark areas (ODA) even in modified-ausformed steel since the modified-ausforming was not perfect in this research.
