Processing and Evaluation of Ferritic-Bainitic Multi-phase Steel

Abstract

Production of bainite-ferrite multi-phase steels on industrial CSP scale provides approach to improve mechanical properties along with large cost reduction opportunity. In terms of hot-rolling conditions, chemical composition, and microstructure; characterizing ferritic-bainitic steels and their difference from ferritic-pearlitic steels regarding properties and cost becomes of a great importance to understand the optimum conditions for production. This work is aiming to improve mechanical properties of steels by producing bainite-ferrite steel through industrial scale runs on the 6 stands hot strip mill (HSM) with at EZDK steel using low alloy Al-killed steel. The effect of hot rolling coiling temperature and alloy content on final properties was studied. In addition to characterizing differences between ferrite-bainite steels and conventional ferrite-pearlite steels. Ferrite-bainite steel has been successfully produced in different conditions, showing up to 27% (~100 MPa) improvement in yield strength, 8% (42 MPa) in tensile strength, 13% in total elongation, and 11% (27 J) in impact toughness. Vanadium microalloying has proven to have almost no effect on mechanical properties of ferrite-bainite steels upon its rising from 0.045% to 0.063% which is not the case in ferrite-pearlite steels. Ferrite-bainite steel offers a great margin for alloy cost saving compared to ultra-low carbon microalloyed steels (up to 56%) through replacing chemical strengthening with phase transformation strengthening. We expect this new approach to significantly reduce the cost of production without sacrificing the quality.