Development of medium carbon microalloyed steel forgings for automotive components

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Development of medium carbon microalloyed steel forgings for automotive components

Cho, Won-Suk / Kim, Kun-Sang / Jo, Eung-Keun / Oh, Seung-Taik

Full scale developments of microalloyed steel forgings (0.4C-V modified) for connecting rods and wheel hubs are discussed in this presentation. Mechanical properties were evaluated in terms of various processing parameters and the resulted microstructures. Tensile strength obtained in MA steel by air colling was equal to or greater than that produced in the quenched and tempered steel. Generally, increasing austenitizing temperature (900-1300 deg C) and cooling rate (box cooling < air cooling < fan cooling) resulted in increased tensile strength. Impact toughness did not show the significant dependence of cooling rate, while decreasing austenitizing temperature enhanced impact toughness. The impact toughness of the microalloyed steel forgings obtained from optimum process showed poorer performance than that of quenched and tempered steel forgings but satisfied the specification made from the design view point. One of the most important efforts for microsktructural investigations is to characterize manganese sulfides. The Manganese Sulphides were revealed to act as ferrite nucleation sites and thus to improve fracture toughness. This paper also aims to evaluate and analyze the machinability of microalloyed steel in terms of cutting force, surface roughness and chip treatment, compared with the conventional quenched and tempered steel. It was found that machining performance of the microalloyed steel was dependent on cutting conditions, such as, speed, feed, and depth of cut.