Cracks formation and residual stress in chromium carbide overlays

A chromium carbide overlay is often welded on the surfaces that are subject to severe wear attack, of mining equipment in order to prolong its service time. The welding causes unequal and unsynchronized thermal expansion/shrinkage between the overlay and its substrate, leading to a significant level of thermal strain/stress in the overlay. When the stress level at any location becomes higher than material strength, at that location a crack will start to form and propagate, resulting in partial release of stress. The residual stress varying by location can lead to delamination and spalling of chunks of the overlay. This paper tries to give better understanding of cracks-formation and residual stress, covering the driving force for cracks formation and residual stress, the locations where cracks initiate, the directions towards to which the cracks propagate, the resulting patterns of the cracks and the residual stress at the interfaces between the overlay and its substrate. The approach to realize this is through mechanics modeling and simulation plus experimental observations. The practical significance of this work lies in its values to improvement of welding processes and the basis for evaluating overlay quality.