Heat Treatment Effect on the Microstructure and Tribological Behaviour of a High Chromium Cast Iron with 0.5% of Niobium

A high chromium cast iron (HCCI) with 0.5%Nb was subjected to destabilization heat treatments (950°C, 1000°C, and 1050°C) for 2 hours. Specimens were characterized by optical and scanning electron microscope (SEM). It was found coarser secondary carbides as the temperature treatment increased. Niobium carbides were found agglomerated in petal-like and blade-like forms. Abrasion tests using a Dry Rubber Wheel Abrasion Tester (DRWAT) were carried out. Results indicated that the wear resistance was proportional to the matrix microhardness, the 1000°C and 1050°C temperatures presented the best wear resistance. SEM images have shown wear by plastic deformation preferentially on the matrix. The worn surfaces were scanned by a contact profilometer. Specimens which had more removed material presented a higher average roughness (Sa). Also, the average roughness (Sa), maximum values of peaks (Sp) and pits (Sv) tended to be lower as the temperature of the heat treatment increased. This can be related to the plastic deformation caused by the wear. The presence of pits was predominant on the worn surfaces.