Identification of surface precipitates found on the surface of steel annealed for tinplating

Tin plate products are widely used in the packaging industry. The quality of the surface tin coating is paramount as it protects the material from corrosion. Grain boundary precipitates may form on the surface of low carbon steels during annealing prior to tin plating. These precipitates affect the quality of the tin coating when they are greater than 250nm in diameter as they act to de-wett the coating disrupting the tin coating process not only leaving the coating uneven which appears as a region of low reflectivity in affected areas but can also reduce the corrosion resistance of the tin plate product in the affected areas.