Alloy design in the system Fe-C-B

Abstract

In this study, the Fe-C-B system is used as a basis for alloy development of tool steels. Thereby,
boron is used as hard phase forming element. The effect of chromium on the phase stability,
microstructure and hard phase properties of Fe-C-B-Cr alloys is investigated. In this manner,
thermodynamic equilibrium calculations are performed and experimentally validated. Laboratory
alloys were casted and investigated using scanning electron microscopy (SEM), energy dispersive
spectroscopy (EDS) and electron backscatter diffraction (EBSD). Nanoindentation was performed
to investigate the effect of Cr on the micromechanical properties of the particular hard phases
(elastic modulus and indentation hardness). It is shown, that Cr stabilizes the orthorhombic, Cr-rich
M₂B type boride with a hardness of 22.8 GPa. In addition Cr stabilizes the Cr-rich M₂₃(C,B)₆
carboboride, which possess a lower hardness (14 GPa). In a next step, the findings are
implemented in an alloy development and alloying additions of chromium, silicon and manganese
are used to specifically stabilize the M₂B type boride with high Cr content to adjust a high hardness
of the M₂B phase. Subsequently, a scratch test is performed to investigate the governing wear
mechanisms in the developed alloy.