Processing conditions of an ultra low carbon/Ti stabilised steel developed for automotive applications

Abstract

The current research investigated the microstructure and tensile properties of as-cast low carbon steels manipulated by TiC-TiB2 nanoparticles. It was found that the microstructure mainly contained blocky ferrite and pearlite. Widmanstatten structure consisting of acicular ferrite was also obtained in the matrix of unmodified low carbon steels. After introducing 0.01 wt% and 0.02 wt% TiC-TiB2 nanoparticles, the formation of widmanstatten structure was inhibited. The pearlite content increased from 26.3% to 36% and 36.7% respectively. The grain size reduced from 58.3 μm to 43.3 μm and 42.8 μm. For tensile properties, the yield strength, tensile strength and elongation of low carbon steels increased by 9.8%, 7.6%, 20.4% and 14.0%, 11.0% and 8.2%. The as-cast microstructure was refined since the nanoparticles act as heterogenous cores to promote the nucleation rate and hinder the growth of grains. The improved strength could be associated with the fine-grain, thermal-mismatch and dispersion strengthening mechanisms, and the improved ductility could be associated with the fine microstructure and scattering effects of nanoparticles.