Effect of Coiling Temperature on the Microstructure and Strength Contribution in One Novel Fe-1.5Al-2Mn-0.18C Automobile Steel

Abstract

An automobile steel with density of 7.55 g/cm3 and composition consisting of Fe-1.5Al-2Mn-0.18C was successfully produced, exhibiting remarkable tensile strength of 897.7 MPa and ductility of 19.3%. This steel’s microstructural transformations and their contributions to strength were analyzed after undergoing coiling treatments at temperatures of 400°C, 500°C, and 600°C. Our findings reveal an inverse relationship between the coiling temperature and both the steel’s strength and the product of strength and elongation (PSE), whereas ductility shows a positive correlation with rising coiling temperatures. The primary factors accounting for these variations in strength across different coiling temperatures are phase transformation strengthening, grain refinement strengthening, dislocation strengthening, and precipitation strengthening, with phase transformation and dislocation strengthening being the most influential. Furthermore, the reduction in size and volume fraction of (Ti, V)C particles observed at lower coiling temperatures is attributed to differences in carbide ripening and nucleation processes. In conclusion, this optimized low Mn-Al alloy chemistry combined with a hot rolling process provided a novel method to produce the automobile with low density and acceptable mechanical properties.