Wear Mechanism of High Chromium White Cast Iron and Its Microstructural Evolutions During the Comminution Process

Abstract

The detailed deformation mechanism and its microstructural modifications of white cast iron grinding balls used in comminution have been investigated using transmission electron microscopy (TEM) and XRD. De-shaping is the primary mode of ball consumption, and fracture of balls is a relatively uncommon failure mode. Deshaping is the manifestation of abrasive wear caused during the operation, and abrasive wear is accompanied by microstructural changes. Micro-cutting is the foremost mechanism. The original microstructure of the matrix of unused grinding balls was observed to have twinned martensite with omega phase with an orientation relation of M-(1 (2) over bar1)//T-((1) over bar2 (1) over bar) and {(1) over bar(1) over bar3}M//{11 (3) over bar }T and M-(1 (2) over bar 10)//omega(0 (1) over bar 10) and {(1) over bar(1) over bar3}M// {1 (2) over bar 1 (3) over bar}omega. However, the presence of unstable omega phase, located at the twinning boundary, causes detwinning and forms lath martensite during tempering caused by localized heat during abrasion. Nano-cementite is formed at lath boundaries. Some cracking was observed, but the crack orientation is radial, indicating a response to tangential stresses associated with abrasion as opposed to dynamic stress waves from high-angle impact. Tangential tensile stresses due to surface traction during the abrasion process lead to radial cracks in brittle eutectic carbides, which join up and cause material removal.