Kazuki Inujima, Kazutoshi Ichikawa
Abstract: The use of "recycled steel" to reduce environmental impacts is being considered by various organisations because such steel can contribute to a reduction in CO2 emissions compared with steel made of iron ores. In the case of "recycled steel", however, the concentration of impurities may increase if the steel is made of low-quality recycled materials; especially, it is difficult to remove some elements such as Cu and Sn from steels. These elements are called as “tramp elements”, and the concentrations of these elements in scrap have been found to increase recently. "Recycled steel" steels are often used as structural steels (i.e., for construction purposes). Thus, recycled steel should exhibit good strength, toughness and weldability. Sn is particularly well known as a detrimental element for structural steels. Therefore, it is important to identify the influence of Sn on mechanical properties of structural steels. Mechanical properties, such as strength, ductility and Charpy toughness, were then examined in the directions of length and width for all the plates with different Sn concentrations, which were subjected to laboratory-casting. Furthermore, characteristics of thickness direction were also investigated to evaluate the lamellar tear susceptibility, which is a weld flaw. Microstructures and ferrite matrix hardness were measured and investigated to discuss the influence and mechanisms of Sn on the mechanical properties of steels. As a result, the yield, tensile strength, and absorbed energy at 20°C were decreased, and the fracture appearance ductile to brittle transformation temperature (FATT) was increased with increasing Sn content. Toughness (FATT and absorbed energy) in the thickness direction was particularly deteriorated by Sn. It can be assumed that according to the tensile and hardness test results, strengthening and deterioration in toughness by Sn are due to solid-solution strengthening.
Keywords: Recycled steel, mechanical properties, thickness direction, tin, environmental impacts
Date Published: March 25, 2020 DOI: 10.11159.ijmmme.2020.003View Article