Host: The Japan Society of Mechanical Engineers
Name : [in Japanese]
Date : November 02, 2019 - November 04, 2019
Maraging steel powder was additively deposited on the conventionally-melted (CMed) maraging steel base plate by powder bed fusion (PBF) type selective laser melting (SLM) to simulate repaired engineering dies. To ensure the reliability of repaired engineering dies, tensile fatigue tests were conducted using specimens having hybrid structure of additively-manufactured (AMed) and CMed maraging steels. It was found that tensile residual stress was induced in the AMed layer on the CMed substrate due to the deposition of melted powder on the un-melted substrate. The fatigue test results revealed that the fatigue strengths of the AMed specimens were lower than those of CMed ones. That is because fatigue cracks predominantly initiated in the AMed layer with defects, which were formed during SLM process. Tensile residual stress also played important role on fatigue crack initiation. Furthermore, the transition of fatigue crack initiation mechanism occurred depending on the applied stress levels during fatigue tests. At the highest stress level, fatigue crack initiated in the CMed layer, while fatigue cracks initiated at the defects in AMed layer at lower stress levels. It was attributed to the residual stress relaxation at the higher stress levels. On the other hand, the fatigue crack initiation transition didn’t confirmed in the aged specimens. This is because plastic deformation didn’t occur due to the higher yield stress by aging treatment.
