Ultra-high-cycle fatigue properties and fracture mechanism of modified 2.25Cr–1Mo steel at elevated temperatures

This paper shows the fatigue properties and fracture mechanism of modified 2.25Cr–1Mo steel. In refineries or chemical plants, modified 2.25Cr–1Mo steel is used in hot and high-pressure environments. Recently, a new fatigue problem concerning these facilities has become important, because number of cycles to failure that should be taken into consideration for maintenance has increased to over 107 cycles. For ultra-high-cycle fatigue, interior inclusions in the material are the dominant factor in a fatigue life, but the fracture mechanism for this has not been clearly elucidated. The results of ultra-high-cycle fatigue properties at elevated temperatures are presented. Interior fracture takes place at an ultra-high-cycle region, although many cases show no inclusions in the origins of an interior fracture. Crack growth life is predicted using fracture mechanics, so that life prediction for modified 2.25Cr–1Mo steel is possible.