Microstructures and Fatigue Behavior of Additively Manufactured Maraging Steel Deposited on Conventionally Manufactured Base Plate

Maraging steel powder was additively deposited on the conventionally manufactured (CMed) maraging steel base plate by powder bed fusion type selective laser melting. Residual tensile stress was introduced into the additively manufactured (AMed) part due to the re-solidification of melted powder on the base plate. Tensile fatigue tests were conducted using the specimens having hybrid structure of AMed and CMed parts. The fatigue strengths of the specimens with hybrid structure were lower than those of the CMed specimens because fatigue cracks predominantly initiated at the defects in the AMed part. Two kinds of post-aging treatments could increase the hardness of the AMed and CMed parts, while had little effect on the fatigue strengths. The maximum size of the defects in the AMed part of the specimen was estimated based on the statistics of extremes. The fatigue limits of the as-built and post-aged samples were estimated by the linear elastic fracture mechanics approach. However, the predicted values were slightly higher than the experimental values.