Considering the negative effect of lead on the performance of galvanized steel sheets, the ASTM (the American Society for Testing and Materials) — which is an internationally recognized organization engaged in issuing international specifications for thousands of products — has introduced a limit of maximum 90 mg/kg of lead in zinc bath used for manufacturing of galvanized steel in accordance with ASTM A 653/A653M.
This limit was reached by consensus involving balloting among the ASTM technical committee members followed by a meeting held in May, and has resulted in the publication of newly revised ASTM A653/A653M.
The purpose of this important amendment to the ASTM Standard is to enhance the performance of galvanized steel as some galvanized steel manufacturers add excessive amounts of lead to the zinc bath used in the galvanizing process to obtain larger and brighter spangles, while disregarding its negative effects on the performance of the produced galvanized steel sheets.
Both theoretical studies and practical experiments have demonstrated that this addition of lead leads to darkening of the spangles over time, thereby impairing the aesthetics of the galvanized steel sheet.
Studies have also shown that adding lead to the zinc bath can cause a problem called "delayed adhesion failure" in hot-dip zinc coatings. Being immiscible with zinc, lead solidifies at the spangle boundaries to produce sites where corrosion cells form in humid climates. After some months this results in cracking and peeling of the coating when the product has been formed using sharp bending.
On the other hand, it is widely known that lead is a toxic substance with severe health risks for humans if it is used in quantities that exceed safe limits.
ASTM sets maximum limit of lead in zinc for making galvanized steel
