Synergetic effect of niobium and molybdenum on abrasion resistance of high chromium cast irons

This research presents the systematic study of the effects of niobium and molybdenum in high chromium cast irons (HCCI). Four 18%Cr/2.7%C alloys were melted: a base alloy, an alloy containing 1% Mo (free-Nb), an alloy containing 1% Nb (free-Mo) and a fourth alloy containing 1% Nb and 1% Mo. In general, Nb and Mo additions slightly increased (~3% to 10%) the Vickers hardness and the microhardness of the matrix. Regarding niobium carbides (NbC), nanohardness was measured. The fourth alloy presented harder (~13%) NbC than the Mo-free alloy. Abrasion tests using a Dry Rubber Wheel Abrasion Tester (DRWAT) were carried out using different severity levels of wear by varying the normal load and the size of the abrasive grains. For more severe conditions all alloys presented a similar abrasive wear response while micro-cutting as the wear micromechanism dominated. On the other hand, for a less severe test condition, the fourth alloy (containing Nb and Mo) presented a higher abrasion resistance (16%) than the base alloy and the wear predominantly occurred in the matrix. Concluding that, for low severity conditions (mild wear), even rather small amounts of Nb and Mo (in combination), can lead to significant gains in abrasion resistance of HCCI; representing a significant improvement to the cost-benefit ratio for industrial applications.