An analysis of the influence of heat treatments and surface finishing conditions on the high cycle fatigue behaviour of W360 hot work tool steel produced by Powder Bed Fusion – Laser Beam

High-cycle fatigue behaviour of W360 steel produced by Powder Bed Fusion – Laser Beam (PBF-LB) is explored by comparing post-processing of industrial interest, involving both heat treatments (conventional quenching and multiple tempering (CHT), or innovative high-pressure heat treatment (HPHT)) and surface finishing (sandblasting, machining, shot peening). The combination of HPHT and machining returns the highest fatigue strength (767 ± 10 MPa) by reason of: i) reduced number and size of process-related defects compared to CHT and machining (457 ± 19 MPa); ii) reduced surface roughness compared to HPHT and sandblasting (243 ± 23 MPa) and HPHT and shot-peening (403 ± 19 MPa). The latter combination, however, shows an improved fatigue strength than the sandblasted one, thanks to compressive residual stress in the superficial region. The correlation between killer defect and fatigue performance is also discussed based on the Kitagawa-Takahashi diagram and the El-Haddad model, and compared to the conventionally manufactured steel. • High-pressure heat treatment (HPHT) on PBF-LB W360 steel reduces defect content and size. • HPHT leads to higher fatigue strength then quenching and multiple tempering. • Machining post-HPHT represents the best surface finishing solution to improve fatigue. • Shot peening improves fatigue strength over sandblasting by compressive residual stress. • A unique curve can represent the relationship between defect size and fatigue strength.