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 $\mathrm{P}=150 \mathrm{W}$, laser scanning speed of v = 1200 mm/s, and layer thickness of $\mathrm{t}=40 \mathsf{\mu }\mathrm{m}$. 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 $({1200}^{\circ }$, $4 \mathrm{h})$, solution treatment (${1060}^{\circ }$, $1 \mathrm{h})$, cooling (${-70 }^{\circ }\mathrm{C},2 \mathrm{h}$), and ageing (${482}^{\circ }$, $4 \mathrm{h}$) led to yield limit, tensile strength, and Vickers hardness values of $\mathrm{Y}\mathrm{L}=1071 \mathrm{M}\mathrm{P}\mathrm{a}$, $\mathrm{T}\mathrm{S}=1410 \mathrm{M}\mathrm{P}\mathrm{a}$, and $523 \mathrm{H}\mathrm{V},$ 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 ${563 \mathrm{H}\mathrm{V}}_{0.05}$ and the maximum values of the compressive axial and hoop RSs of $-1426.3 \mathrm{M}\mathrm{P}\mathrm{a}$ and $-1095.9 \mathrm{M}\mathrm{P}\mathrm{a}$, respectively, were measured.