Fatigue Design Curves for Laser-Metal-Deposited Type 420 Stainless Steel and Effect of an Interval during Deposition Process

Abstract Fully-reversed axial loading fatigue tests were conducted using type 420J1 martensitic stainless steel. The specimens were additively manufactured by a laser metal deposition (LMD) process. The results were compared with conventionally-manufactured (CMed) type 420J2 stainless steel. According to the axial loading fatigue test results, the fatigue strengths of the laser-metal-deposited (LMDed) specimens were nearly comparable to those of the CMed specimens. Fractographic analyses revealed that process-induced defects were hardly seen at the fatigue crack initiation sites of the LMDed specimens. It indicates that defect-free deposition was possible by the LMD process. On the other hand, when the LMD specimens experienced intervals during deposition processes, local softening occurred due to the tempering of the building plate. Fatigue tests revealed that the interval during LMD process had detrimental effect on the fatigue strengths due to the local softening. The upper and lower bounds of S-N curves were proposed as fatigue design curves for the samples with and without the interval during LMD process.