Determination of Cone Bore Growth Due to Microstructural Changes

Abstract

A finite element analysis is used to model cone bore growth in a railroad bearing. Factors which influence the growth and profile of the cone include (a) the initial interference fit between the cone and axle journal, (b) the axial restraint from the torqued cap screws, and (c) a microstructural change in the cone. The primary microstructural change is a transformation of retained austenite to martensite, resulting in a volume expansion. In the model transformation of retained austenite occurred under the raceway of the cone where high contact stresses are located. The analysis shows that the bore profile becomes concave, which in turn does not allow for uniform interface forces between the cone and axle journal. It is shown that with sufficient microstructural change, the initial interference fit is overcome along part of the cone/journal contact, producing a gap between the cone and axle journal. Increasing the initial interference fit reduces the possibility of this gap from developing.