Wear-and corrosion-resistant steels containing niobium carbide

Niobium, like titanium and vanadium, forms super-hard mono-carbides (MC) which remain relatively pure in Fe-base alloys on account of their low solubility for other metallic alloying elements. Because the super-hard mono-carbides have a higher hardness than the precipitated chromium carbides commonly used in wear-resistant alloys, they are suitable as alternative hard phases. This paper deals with new wear- and corrosion-resistant steels containing niobium carbide that were produced by ingot and powder metallurgy (PM) for use as plastic mould and bearing steels. Based on equilibrium calculations by CALPHAD (CALculation of PHAse Diagrams) methods, the microstructures developed during the production of these steels were analysed, and the results are discussed with respect to important properties such as abrasive wear and corrosion resistance. Alloys can be produced by precipitation of primary niobium carbides of the MC type, which are embedded in a martensitic metal matrix that can be subjected to secondary hardening. Because of the high affinity of niobium for carbon, the formation of chromium carbides can be suppressed even in high-chromium alloys, thus leaving chromium contents of more than 12 wt.% in the metal matrix as are required to impart corrosion resistance. This allows the production of stainless, wear-resistant cold-work tool steels for the food processing and pharmaceu ical industries, as well as corrosion-resistant bearing steels. (AU) Copyright © 2018 Companhia Brasileira de Metalurgia e Mineração (CBMM)All rights reserved