Abstract

A lean alloyed steel of 0.17%C, 1.73% Mn, 1.35% Si along with 0.02% Nb, 0.04%Ti as microalloying additives was pre hardened and subjected to TRIP assisted bainitic steel heat treatment. The pre hardening treatment from 950 ℃ promotes the formation of carbide free bainite in lath form in addition to blocky form which enhance the steel properties. The steel was austenitized at 790 and 830 ℃ followed by austempering at 450 ℃. The steel developed a microstructure consisting of inter critical ferrite, bainitic ferrite, Martensite/ austenite constituents along with significant quanties (12 to 17%) of retained austenite. The microstructural phase evolution was compared with the theoretically assessed results. The mechanical properties of the steel showed that the steel developed a tensile strength in the range 766 to 968MPa with 20 to 29% elongation and yield ratio varying between 0.57 to 0.72. The tensile toughness of the steel was 17.3 to 23.7GPa %. The work hardening behavior of the steel was examined using the Hollomon equation and the modified Crussard Jaoul equations.

Keywords: Pre hardening heat treatment; TRIP assisted bainitic steel; Microstructure; Mechanical properties; Work hardening; Crussard jaoul model