Microstructure and phase elemental distribution in high-boron multi-component cast irons

The novel cast irons of chemical composition (wt%) 0.7C–5W–5Mo–5V–10Cr–2.5Ti were invented with the additions of 1.6wt% B and 2.7wt% B. The aim of this work was to study the effect of boron on the structural state of the alloys and phase elemental distribution with respect to the formation of wear-resistant structural constituents. It was found that the alloy containing 1.6wt% B was composed of three eutectics: (a) “M₂(C,B)₅+ferrite” having a “Chinese Script” morphology (89.8vol%), (b) “M₇(C,B)₃+Austenite” having a “Rosette” morphology, and (c) “M₃C+Austenite” having a “Ledeburite”-shaped morphology (2.7vol%). With 2.7wt% of boron content, the bulk hardness increased from HRC 31 to HRC 38.5. The primary carboborides M₂(C,B)₅ with average microhardness of HV 2797 appeared in the structure with a volume fraction of 17.6vol%. The volume fraction of eutectics (a) and (b, c) decreased to 71.2vol% and 3.9vol%, respectively. The matrix was “ferrite/austenite” for 1.6wt% B and “ferrite/pearlite” for 2.7wt% B. Both cast irons contained compact precipitates of carbide (Ti,M)C and carboboride (Ti,M)(C,В) with a volume fraction of 7.3%–7.5%. Based on the energy-dispersive X-ray spectroscopy, the elemental phase distributions and the appropriate phase formulas are presented in this work.