Alloy and process design of novel high strength formable multiphase packaging steel

This study presents the development and characterisation of a novel multiphase steel designed for food packaging applications, combining high strength and excellent formability while adhering to stringent chemical composition limits defined by the ASTM A623-22 standard for food-contact materials. The alloy design was carefully engineered to limit elements such as Mn, Cr and Si which are commonly used in automotive steels but pose potential risks in food related applications. Thermodynamic simulations and dilatometric analyses were employed to determine the critical transformation temperatures and guide the annealing strategy. Controlled intercritical annealing at 780°C and 820°C, followed by cooling at rates ranging from 30 to 150°C/s, enabled the formation of tailored microstructures with varying martensite fractions. Microstructural examinations revealed that lower annealing temperatures combined with higher cooling rates significantly enhanced martensitic transformation, resulting in improved tensile strength without compromising ductility. The optimum mechanical performance-tensile strength exceeding 580 MPa and elongation above 19% was achieved at 780°C with a cooling rate of 150°C/s. These results demonstrate that it is feasible to produce multiphase packaging steels with advanced mechanical properties through precise thermal cycle control and alloy design while maintaining full compliance with food safety regulations.