Evolution of Microstructure and Mechanical Behavior of a Lean Alloyed Continuously Cooled Bainitic Steel

The effect of continuous cooling on the development of the bainite transformation process and the mechanical properties of low-carbon (0.17% C) steel alloyed with 1.73% Mn, 1.35% Si and microalloyed with Nb (0.02%) and Ti (0.04%) is studied. The microstructure and phase analysis is carried out at various continuous cooling conditions. The work hardening behavior under various conditions is examined using the Hollomon equation and modified Crussard-Jaoul work hardening model. The steel is subjected to austenitization in the intercritical range and above the A3 temperature between 790 and 900 degrees C for 5 and 30 min, followed by continuous cooling to form a dominantly bainitic microstructure, which makes it possible to achieve an ultrahigh strength (1100 MPa) at a high ductility (20%). A longer austenitization time contributes to an increase in the strength and ductility of the steel.