The Development of Ferrous Metal Matrix Composites for Use in the Mining and Mineral Processing Industry

Abstract

The mining and mineral processing industries feature very harsh service environments that often severely limit the service life of components and equipment used. High Cr white cast irons are usually the material of choice for many high wear applications that also require some amount of corrosion resistance. The excellent wear performance of these alloys is attributed to both a volume fraction of hard Cr carbides (a ceramic phase) and a hard, corrosion resistant ferrous matrix. These alloys present, however, poor fracture toughness. This thesis proposes that stainless steel matrix composites reinforced with ceramic particles that are harder than Cr carbides could potentially be viable alternatives to conventional high Cr white cast irons by being able to achieve greater wear performance with little detriment to corrosion resistance and toughness. As the eventual goal is for the manufacturing of large-scale mining components through direct melting and casting, the density of the ceramic particles used should be similar to that of molten steel to prevent the particles from sinking or floating. For this reason, Nb-based carbides are proposed as the reinforcements. Additionally, depending on the type of stainless steel matrix used, a wide range of mechanical and chemical properties are achievable, allowing these composites to be used in environments that are deemed unsuitable for high Cr white cast irons. This thesis shows that different stainless steel grades can be effectively reinforced with Nb-based carbides, with martensitic stainless steel composites easily surpassing the wear performance of high Cr white cast irons without compromising corrosion resistance despite having a lower volume fraction of ceramic reinforcement phases. The latter also implies a better toughness for the metal matrix composite.