Rotating Bending Fatigue Properties of Age Hardening Treated Additive Manufactured Maraging Steel and their Improvement with Additional Treatments

Abstract

Rotating bending fatigue tests were conducted to investigate the fatigue property of age hardening treated maraging steel made by direct metal laser sintering process which was one of additive manufacturing processes. In this study, fatigue properties were evaluated firstly using the as-additive manufactured specimen with the surface shape remaining in the additive manufacturing process. After that, the effects of additional treatments such as mechanical polishing, hot isostatic press (HIP) treatment and shot peening (SP) treatment on fatigue properties were investigated. The main results obtained are as follows. The effect of surface roughness produced during manufacturing process on fatigue strength is significant, and is greater than the effect of initial defects. If HIP treatment is performed with the surface shape remaining, the fatigue life will be shortened. On the other hand, the fatigue strength of the maraging material which was made by additive manufacturing process can be dramatically improved by SP treatment and fatigue fracture from surface can be suppressed. The fatigue fracture mode shifts by SP treatment from surface origin type where fatigue cracks initiate from dents on the surface to the internal origin type where fatigue cracks initiate from cleavage crack of martensite block or initial defect. To further improve fatigue property, it is necessary to suppress the occurrence of cleavage crack.