What is indicated by a Rust Grade A classification?

A Rust Grade A classification indicates the presence of 100% adherent mill scale. Mill scale is a tough and adherent oxide layer that forms on steel during the manufacturing process, particularly during hot rolling. This classification signifies that the surface is in a relatively good condition, lacking significant rust or corrosion, and that the mill scale is firmly attached, providing a suitable substrate for coatings.

Maintaining this adherent mill scale is crucial, as it can enhance the adhesion of protective coatings. In contrast, the other classifications indicate various degrees of rust or corrosion that would typically require surface preparation before painting or coating to ensure long-term effectiveness and protection of the underlying metal.