Chemical modification and the attending surface hardness of low alloy steel through medium energy nitrogen ion implantation

A surface hardenable low alloy carbon steel was implanted with medium energy (20-50 KeV) N2+ ions to produce a modified hardened surface. The implantation conditions were varied and are given in several doses. The surface hardness of the treated and untreated steels was studied using depth sensing ultra microindentation system (UMIS). It is shown that the hardness of nitrogen ion implanted steel samples varied from 35 to 50 GPa depending on the implantation conditions and the doses of the N2+ implantation. These hardness values were higher than those previously published for ion implanted tool steels. The surfaces of the treated samples were examined by X-ray photoelectron spectroscopy (XPS). It was found that the high hardness on the implanted surfaces was as a result of formation of non-equilibrium nitrides. High-resolution XPS studies indicated that the nitride formers were essentially C and Si on the surface of the steel. These results suggest that the ion implantation provided the conditions for a preferential formation of C and Si nitrides. The combination of evidences from nano-indentation and XPS, points towards possible formation of silicon carbo-nitride in a suspected (C,Si)xNy stoichiometry. This finding is consistent with recent reports for the preparation of ultra hard silicon carbo-nitride. The present results sets up case for investigating and exploring silico-carbo-nitrided surfaces in order to develop improved wear resistance low alloy steels for use in high contact applications.