Technology, properties and applications of niobium carbide reinforced steel and iron alloys

The large cost and considerable downtime caused by replacing worn parts in earth moving and mining equipment, as well as in the materials processing industry, represents a continuous challenge to material development. Components designed for sacrificial wear must in the first place possess adequate abrasion resistance. Frequently, however, they must also have the ability to withstand impact and to resist chemical attack. The requirement of good abrasion resistance in combination with good toughness is generally in contradiction. Typically, hard iron-based materials such as martensite or ledeburite are highly resistant to abrasion, yet very brittle and difficult to machine. An innovative approach is to compose a more ductile iron-based matrix, embedding a much harder wear resistant phase. Amongst those extremely hard phases are carbides of the transition metals titanium, niobium, and tungsten with hardness of over 2000 HV. Particularly, NbC is a very interesting hard phase since its hardness is one of the highest among the transition metals carbides and its density is very similar to that of molten iron, so that gravity segregation effects in the liquid phase are small. Volume fractions up to 35% of NbC can be formed in-situ as primary carbide in the liquid phase or added externally using a FeNbC master alloy. The latter approach is particularly applicable when higher amounts of NbC need to be added. Molybdenum additions are important to adjust the properties of the matrix towards high toughness and good ductility. This paper elucidates the strategies and possible technologies of achieving such composite materials and demonstrates several examples of applications along with the achieved sustainability benefits. In particular, fundamental and tribological properties of NbC are presented. (AU) © 2015 Companhia Brasileira de Metalurgia e Mineração (CBMM)