Fracture Behavior of Medium Carbon Micro Alloyed Steel for Automotive Components

The micro alloyed steels(MAsteels) developed to reduce the manufacturing cost of automotive parts, have reasonable mechanical properties, but their lower toughness compared to conventional quenched and tempered steels(QT steels) has limited their application to the automotive components. To understand the fracture behavior of MA steel, the simple mechanical properties were investigated and three kinds of fracture related tests; three point bend test, compact specimen fracture toughness test and fatigue test were performed. From the results of three point bend tests, absorbed energy for both materials, except for V-notched specimen of MA steels, was independent of strain rate with each notch geometry. And, MA steels were more sensitive to notch geometry than QT steels. Therefore, in practical application, components need to be designed to have low restrained notch geometry. The results of compact tension specimen fracture toughness tests showed that, from linear elastic fracture mechanics, MA steels have a reasonable fracture toughness value. So, it is believed that MA steel can be successfully substituted for conventional QT steels. Fatigue tests showed that fatigue strength of MA steel is similar to that of QT steel in both smoothed and notched specimen.