THE ROLE OF “CRATERING” IN THE PROCESSING AND PROPERTIES OF GALVANNEALED STEEL SHEET

Craters in galvannealed coatings on steel sheet are depressions caused by non-uniform diffusive growth. Correlations have been sought between “crater” densities in galvannealed sheet steel and friction, powdering, and paint adherence, as relevant to the appearance, corrosion resistance and processing of auto body panels. Crater densities were established on a series of samplings from major producers, and related to frictional measurements from a binder-radius simulator, powdering levels from bend testing, and paint adherence assessments from a stone-chipping test. Results suggest that increased crater density decreases powdering, but does not aid in lubrication. In fact, decreased powdering could be correlated with increased friction levels. A strong correlation was found between increased crater density and increased paint adherence.