Mechanical Properties Enhancement of Conventional Mild Steel For Fastener Application

摘要

Due to the rampant brittle fracture of most mild steel fasteners, an innovative hardening process of microstructure modificaton is employed on conventional mild steel to enhance its mechanical properties. The steel specimens were subjected to inter-critical austenitising heat treatment in the temperature range of 8000-9500C and soaked for 30 minutes, quenched in water at ambient temperature and tempered at varying temperatures of 2500, 3500, 4500 and 5500C. Results of mechanical characterisation of the test specimens demonstrate improvement in ultimate tensile strength and impact energy by 58.3 and 53.8 percent respectively coupled with a modest increase in hardness from 25.7HRB to 37.5HRB. Contribution to improved mechanical properties stem from the inducement of fine needle-like lower bainite particles within the dislocation-rich ferrite matrix at 4500C and 5500C tempering temperature regime.