Solidified microstructures and elastic modulus of hypo-eutectic and hyper-eutectic TiB2-reinforced high-modulus steel

Abstract

The solidified microstructures and elastic modulus of both hypo-eutectic and hyper-eutectic TiB2-reinforced high-modulus steels (HMS) with different TiB2 fractions were investigated. The solidification sequence for hyper-eutectic liquid HMS was as follows: (i) primary Ti(CN) particles, (ii) primary TiB2 particles and iron halos, (iii) first eutectic TiB2 particles having a radial pattern or screw shape and fine TiC particles, (iv) second eutectic TiB2 particles having a lamellar morphology, and (v) Fe3C particles that precipitated in the solid. The screw-shaped and fiber-like TiB2 particles corresponded to two different sectional views of the hexagonal TiB2 tube. Both density and Young's modulus were measured from the hot-rolled HMS having different fractions of TiB2. It was found that density decreased but elastic modulus remained almost constant when the TiB2 fraction increased from 12.1% to 33.3%. The latter is because coarse primary TiB2 particles were formed at the middle of specimen and their aggregates at the top due to the floating up of such a high fraction of TiB2 particles in the experimental condition. Local plastic deformation might be generated near them, leading to the decreased elastic modulus measured for the entire specimen.