Controlled Phase Transformation Simulations to Design Microstructure for Tailored Mechanical Properties in Steel

Abstract

Advanced materials with light weight but having high strength and ductility are required to decrease the weight of automobiles. Hereby, advanced high-strength steels like dual-phase steels and multiphase steels are vital as they possess good strength in conjunction with good formability. Several methods have been used for the processing of multiphase steels but very limited research has been reported on their processing through controlled cooling and by using a lean composition. The present research reports on methods of production of dual-phase/ multiphase microstructures in a steel of lean chemical composition (0.11C, 1.8Mn, and 0.325Si), making the steel multifunctional. Annealing parameters were determined using Thermo-Calc and JMat-Pro software. Software predictions were validated through experiments in a muffle furnace, followed by actual annealing experiments in an annealing simulator. Multiphase microstructures were obtained from the initial ferrite-pearlite structure by inter-critical annealing involving controlled cooling in the annealing simulator. Dual-phase structures were produced by inter-critical annealing, followed by rapid cooling to room temperature, whereas multiphase microstructures were produced by holding in the bainitic and martensitic ranges, respectively. The steel exhibited good combinations of strength–ductility, with tensile strength and ductility in the range of 550–705 MPa and 11–33%, respectively.

Keywords:

• Annealing simulator
• Controlled cooling
• Dual-phase
• Inter-critical annealing
• Multiphase