Five microalloyed plate steels were evaluated for impact and fracture tough- ness. Results at room and low temperatures were compared. These... Show moreFive microalloyed plate steels were evaluated for impact and fracture tough- ness. Results at room and low temperatures were compared. These steels are com- monly ordered to meet ASTM A572/A709 Grade 50 or EN 10025-2 Grade S355 requirements in the normalized condition for wind tower and other structural ap- plications. One of the ve steels was in the normalized condition, while the rest were left as-rolled. Furthermore, the e ects of carbon content and alloy additions are investigated, with niobium and vanadium as the principal strengthening elements. Impact toughness testing using Charpy V-notch specimens was performed to deter- mine the ductile-to-brittle transition temperature (DBTT). Fracture toughness was measured using the J-integral method. The critical fracture energy Jc was converted to the critical plane strain stress intensity factor KIc if validity requirements were met. Compact tension samples of each steel were tested at room temperature and at -40oC. The results of room temperature tests are compared to those obtained in previous work. The steels with niobium demonstrate signi cantly lower DBTT than vanadium steels. At room temperature, fracture toughness performance is comparable for low carbon grades. Among medium carbon steels, the vanadium one fares slightly better than the as-rolled niobium, with the normalized niobium steel o ering the highest room temperature fracture toughness of the three. Overall, the lower carbon content is noted to provide a signi cant increase in toughness for a modest trade-o in tensile strength. M.S. in Material Science Engineering, May 2015 Show less
