Duplex surface treatment of chromium pack diffusion and plasma nitriding of mild steel

Abstract

The use of mild steels has usually been restricted to low-cost applications of a structural nature, because of their poor physical chemical properties. Recently, new duplex surface treatments involving the use of packing diffusion, electroplating and plasma nitriding have led to the possibility of using this material for applications usually typical for tool steels. In this work, we present results concerning the duplex treatment of chromium pack diffusion and plasma nitriding of AISI 1020 mild steel. The samples were chromized in a vacuum furnace at temperatures varying from 1073 up to 1573 K for 5 h. After chromizing, the samples were plasma-nitrided for 1 h at 723 K. The samples were characterized using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and microhardness testing. Chromium-diffused layers of up to 150 μm were obtained. The subsequent plasma nitriding increased the surface hardness to 1400 HV0.1 due to the formation of CrN and Cr2N. The corrosion resistance of the chromized and duplex-treated specimens was also studied. The improvements in hardness and corrosion resistance are discussed considering microstructural modifications in the treated samples.