Correlation between structural aspects and mechanical properties of an Interstitial Free steel for automotive application

Abstract

The application of IF steels in the automotive industry has increased significantly due to their excellent deep drawability. The chemical composition, the microstructure, the precipitation phenomena and texture of the material determine the mechanical properties. This paper proposes, a more profound study of some aspects related to the application of high plastic deformation, as well as its relation with the formation of fine grain structures, texture, precipitates and grain boundaries interaction. The structure of an IF steel plate with ultra-low carbon was characterized using optical microscopy and scanning electron microscopy (SEM). A ferritic structure with very fine and recrystallized grains containing high number of triple point was observed. The precipitation kinetic of the steel was simulated applying Fact Sage 7.1. The main precipitates predicted are: TiN and TiS, these types of second phases improve the drawability behaviour. The formability aptitude of the sheet was evaluated by different mechanical tests: Hole Expansion, Erichsen and n-r determination. Finally, yield strength, tensile strength, percentage elongation and average r-value results, are correlated with the structural information. A strong (111) <110> recrystallization texture confirms the high formability of the IF steel sheet.