Effects of ceramic particles and composition on elastic modulus of low density steels for automotive applications

Abstract

The present work deals with the effects of TiB₂ ceramic particles and selected alloying elements (Al and Mn) on the elasticmodulus of steels. Steels and its composite containing varying amounts of Al, Mn and C, and a fixed amount of TiB₂ particles (7.8 wt-% i.e. 13 vol.-%) were made using the bulk route of liquid steel metallurgy. All the materials were processed thermomechanically to sheet form following standard processing routes for automotive sheets. The steels containing only Al exhibited ferritic microstructures whereas addition of Mn and C caused the evolution of ferrite or austenite based duplex microstructures in the material depending on the Mn and C content. On the contrary, large TiB₂ particles formed mainly by eutectic reaction from the liquid state were distributed in the ferritic matrix of the composite. All the investigated materials showed a large density drop in the range of 7.4-12.7%. Al caused a drastic drop in elastic modulus of ferritic steels whereas the elastic modulus was recovered in ferrite based duplex steel by virtue of Mn.On the contrary,Mn did not improve the elastic modulus in austenite based duplex steel. TiB₂ and small amount of TiC particles in the composite were found to increase the elastic modulus by y19% in as cast condition. However, the elastic modulus of composite showed a dependence on the processing steps with decreases after subsequent hot and cold rolling steps. It was due to the delamination of particle/matrix interface, void formation and fragmentation of reinforcing particles with reduction in thickness of sheet. The elastic modulus of the composite also showed directionality due to specific alignment and various shape of ceramic particles. It was predicted that the performance and weight saving of these materials for automotive applications would be enhanced with a good combination of high strength, low density and high elastic modulus.