Effect of Inclusion on Long Life Fatigue Properties of High Strength Steel

摘要

In order to investigate the fatigue properties of high strength steels and surface hardened steels in the super-long life range (N>=1 X 10~7)), cantilever type rotating bending fatigue tests were carried out for 2 kinds of SNCM439 steel, where the cleanliness was different on these specimens. As a result of fatigue tests, the following were obtained. In the case of SNCM439 (D material), in high-stress amplitude and short lived region, the crack origin was the grinding flaw, and in low-stress amplitude and long lived region, the crack origin was the inclusion or microstructural discontinuity. But, in the case of SNCM439 (S material), the crack origin was not only the grinding flaw but also a lot of the inclusion in high-stress amplitude and short lived region, and in the low-stress amplitude and long lived region, the crack origin was the inclusion or microstructural discontinuity as well as the SNCM439 (D material). The reason is that SNCM439 (S material) is different from SNCM439 (D material) in the size and the density of inclusion, and the size and the density of SNCM439 (S material) were larger than that of SNCM439 (D material).