Microstructural Characterization and Failure Analysis of a Wear-Resistant, High Molybdenum and Chromium White Iron Used for Metal-to-Metal Wear Systems

An Fe-15Mo-18Cr-3.3C-1.65V white iron has been widely used in industries for many years due to its excellent wear performance, but never been reported to academic circle. This paper studied its phase constituents in as-cast condition and its wear performance for metal-to-metal contact wear applications. Microstructural analyses were performed using optical microscopy and scanning electron microscopy with phase identification performed using a transmission Kikuchi diffraction (TKD) technique. A solidification sequence was proposed by correlating thermodynamic equilibrium calculations with the distribution and size of the phase constituents. Field-returned components were analyzed after approximately 10,000 service hours. Micro-galling defects exhibited regions of material flow, white layer formation, subsurface cracking, and material loss. For the first time, white layer was found in a highly alloyed white iron, which was determined to be nanocrystalline with an average grain size less than 15 nm and a phase constitution similar to the base metal. Material loss contributed to abrasive wear scars and eventual leakage of the lubricant protecting the wear components.