Cite this document

Usually bainitic microstructures exhibit good toughness and austempering is typically the preferred heat treatment when toughness is the primary requirement of the component. Several reports have shown such characteristics when compared to tempered martensite. High-carbon steel may exhibit brittle characteristics but it is a good steel with respect to mechanical properties and wear resistance. The objective of this study was to compare the impact properties of AISI O1, a high-carbon tool steel, designated VND in Brazil. This was done by comparing Charpy impact strength under different heat-treatment cycles. Steel test specimens were quenched from 820°C and tempered at 450°C to obtain tempered martensite, then austenitized, cooled, and held at 350°C to obtain bainite by holding at temperature for 20, 40, and 60 min. Because hardness influences impact behavior, comparative studies were performed at the same surface hardness level. The austempered samples with bainite microstructures obtained at a constant temperature and, by varying holding times, exhibited lower impact properties as compared to the quenched and tempered condition.