Effects of Heat Treatment Procedures and Diamond Burnishing on Tensile Properties and Surface Integrity of Additively Manufactured 17-4PH Steel Cylindrical Parts

This article presents a new combined post-processing concept to improve the quality of laser powder bed fusion (LPBF) of 17-4PH stainless steel (SS) cylindrical parts fabricated from N2-atomised LaserForm 17-4PH (B) powder. The concept is based on consecutive heat treatment procedures and diamond burnishing (DB) processes. A two-stage study was conducted. The first stage was an LPBF process experiment. The following combination of LPBF parameter values was selected after optimisation: a laser power of P=150 W, laser scanning speed of v = 1200 mm/s, and layer thickness of t=40 μm. In the second stage, this combination was used to evaluate the effects of two heat treatment procedures (HT1 and HT2) and two DB processes (using burnishing forces of 100 N and 300 N) on the tensile properties and surface integrity of LPBF 17-4PH SS cylindrical samples. The HT2 procedure, including annealing (1200∘, 4 h), solution treatment (1060∘, 1 h), cooling (−70 ∘C,2 h), and ageing (482∘, 4 h) led to yield limit, tensile strength, and Vickers hardness values of YL=1071 MPa, TS=1410 MPa, and 523 HV, respectively. The concept presented takes advantage of the combination of the transformation, precipitation and strain-hardening effects. The combined effect was most pronounced in the samples subjected to the HT2 procedure and subsequent DB (300 N), for which a retained austenite fraction of 6.93%, surface microhardness of 563 HV0.05 and the maximum values of the compressive axial and hoop RSs of −1426.3 MPa and −1095.9 MPa, respectively, were measured.