High-Cycle Fatigue Properties of Modified-Ausformed SCM 440 Steels. 2nd Report. Fatigue Properties of 1600 MPa and 2000 MPa-Class Modified-Ausformed and Tempered Steels.

Abstract

Fatigue tests were carried out for 1600 MPa and 2000 MPa class modified-ausformed and tempered SCM 440 steels. The materials were called AF1600 and AF2000, respectively. The 2000 MPa class quenched and tempered steel, called QT2000, was also tested. The 1600 MPa class quenched and tempered steel, called QT1600, had been tested in the previous report. In the QT1600, fish-eye fracture had occurred from TiN inclusions and the fatigue limit at 108 cycles had been 840 MPa. AF1600 successfully achieved no fish-eye fracture and a higher fatigue limit of 920 MPa. Although fish-eye fracture occurred, AF2000 also achieved a higher fatigue limit of 1010 MPa than QT2000 of 840 MPa. The fatigue limit of QT2000 was equal to that of QT1600. The origins of fish-eye fracture for AF2000 and QT2000 were Al2O3 and TiN inclusions and matrix cracks. On the fracture surfaces of QT2000 broken at over 107 cycles, large and clear ODAs were observed whatever the origins were. On the other hand, AF2000 did not break at over 107 cycles. It suggests that AF2000 could not have ODAs on the fracture surface.