Development of high modulus steels based on the Fe - Cr - B system

We present a novel alloy design strategy for cost-efficient high modulus steels with an increased stiffness / mass density ratio. The concept is based on the liquid metallurgy synthesis of Fe - Cr - B based alloys, straightforward processability, and well tuneable mechanical properties via plain heat treatments. The base alloy Fe - 18 Cr - 1.6 B (wt%) contained 14-17 vol% of (Cr,Fe)2B particles of ellipsoidal morphology in a ferritic matrix. Hot rolled materials revealed a specific modulus of 32.8 GPa g−1 cm3, exceeding that of conventional Fe-Cr steels by almost 30%. Mechanical properties obtained are comparable to TiB2 based high modulus steels. Addition of 1 wt% Cu to the base alloy did not interact with the formation, fraction, size and morphology of (Cr,Fe)2B particles, and allowed to mildly increase the strength values by ageing treatments, however at the price of a reduction of the specific modulus. C additions of 0.2 wt% did not affect the (Cr,Fe)2B particle microstructure greatly, but free C dissolved in the matrix enables for the first time to utilize the wide range of microstructures and mechanical properties of established C-containing high strength steels also in high modulus steels.