On the effect of carbon content and tempering on mechanical properties and stiffness of martensitic Fe–18.8Cr–1.8B–xC high modulus steels

We studied the effects of C concentration (0.1, 0.3 and 0.5 wt%) and tempering temperature (100–700 °C) on the dynamic Young's modulus, mass density, hardness and impact toughness of quenched and tempered martensitic Fe–18.8Cr–1.8B (wt.%) based high modulus steels. Increasing C concentration lead to consistent hardness levels above 600 HV5 for tempering temperatures below 500 °C. While the tensile strength could be adjusted tailored from about 1000 MPa to more than 2000 MPa depending on the tempering temperature and respective C concentration, dynamic Young's modulus and mass density were left virtually unaffected. The E/ρ ratio shows little variability between approximately 31.2–33 GPa g⁻¹ cm³, which is superior to conventional high strength steels and comparable to ferritic Fe–Cr–B steels without carbon additions. Particles identified within the martensitic matrices are mainly (Fe,Cr)₂B type borides stemming from solidification, as well as an increasing fraction of (Fe,Cr)₂₃(C,B)₆ carbo-borides with increasing C content and tempering temperatures.