Factors affecting eutectic solidification of Cr–Ni (–Si–Mn) white cast irons

Abstract

The crystal structure and morphology of eutectic carbides are known to strongly determine the mechanical and tribological properties of Cr–Ni white cast irons. In an effort to improve these properties, investigators at the US Bureau of Mines have studied the effects of alloying additions of 0·0–1·8%Si, 0·0–6·7%Ni, and 0·0–3·2%Mn (all wt-%) and solidification rates of from 1·0 to ∼500 K min⁻¹ on hypoeutectic irons containing ∼3%C and ∼8%Cr. The structure and morphology of the eutectic carbides formed were identified using electron microprobe analysis, X-ray diffraction, and scanning electron and optical microscopy. Differential thermal analysis was used to study the effects of alloying additions on the solidification reactions. The results show that these irons can have carbide structures consisting of (Fe, Cr)₃C or (Fe, Cr)₇C₃ or both. These observations are explained in terms of the effects of Si, Ni, and Mn on the liquidus surface of the metastable Fe–Cr–C phase diagram.

MST/1288