Aluminium and Silicon additions combined with microstructural tailoring of Press Hardened Steel

Abstract

Press Hardened Steels (PHS), with tensile strength in the range 1300 and 1800 MPa, are fundamental elements in the body-in-white of automotive structures. Developed in the late 90’s, the idea of a 22MnB5 blank hardened by austenitization treatment and die quenching made its way to become a breakthrough discovery such as the development of commercial steel Usibor® 1500AS. The simplicity of its alloy design combined with a cost-efficient hot stamping process allow for achieving the technical requirements for anti-intrusion parts during crash. In this work, the chemical composition of a PHS1500 steel has been adjusted by different silicon and aluminium additions to ensure some bainite formation during press hardening process combined with isothermal transformation. This strategy is expected to lead to the formation of different combinations of tempered martensite and/or bainite with different morphologies here examined through a multi-characterization technique approach, including light optical microscopy, scanning electron microscopy, and X-ray diffraction. Silicon and aluminium additions allowed the formation of lathlike ferritic microstructures with certain amount of austenite after conventional hot stamping practices. Mechanical properties seem promising in terms of local ductility and fracture strain for automotive applications.