Wear and corrosion properties of low-temperature nitrocarburized 17-4PH SLM components

Abstract

3D printing has demonstrated manufacturing and economic advantages in terms of customization, flexibility and rapid prototyping of precision complex geometric components. The 17-4PH precipitate hardening steel is notable for its excellent corrosion resistance. This study aims on enhancing the wear resistance of SLM-printed 17-4PH components through interstitial surface hardening. To eliminate microstructural defects introduced by the SLM process, the components were first subjected to solution heat treatment. Following this, a low-temperature nitrocarburizing (LTNC) process was applied at temperatures below 400 °C, resulting in the formation of an interstitial surface layer with an average thickness of approximately 17 μm. Optical microscopy and XRD analyses confirmed the presence of a dual-phase structure composed of expanded BCC and FCC phases within the hardened layer, with no detectable nitride/carbide precipitates. Quantitatively, the LTNC process significantly enhanced the surface microhardness of the components, increasing it to a minimum of 1000 HV0.2. The bulk microhardness also increased from 360 HV0.2 to 480 HV0.2, indicating an aging effect during the diffusion treatment. In terms of performance, LTNC substantially improved the wear resistance of the components. However, a slight reduction in corrosion resistance was observed, attributed to increased surface roughness and the presence of the dual-phase expanded structure.