Embrittlement of Hot-dip Galvanized Steel and How to Avoid It
ASTM A143 Standard Practice for Safeguarding Against Embrittlemnet of Hot-Dip Galvanized Structural Steel Products defines the practice of procedures that can be followed to safeguard against the possible embrittlement of steel hot-dip galvanized after fabrication, and outlines test procedures for detecting embrittlement. Cold-working of steel prior to galvanizing is the key factor for strain-age embrittlement to develop and the heat in the galvanizing process simply accelerates the recognition of embrittlement. Thermal treatment and increasing bend radii effectively minimize the potential for strain-age embrittlement. A second type of embrittlement, hydrogen embrittlement, is recognized when stresses are applied to the steel in use. Both areas severely cold-worked steel and steel with ultimate tensile strength greater than 150 ksi may exhibit hydrogen embrittlement due to a tight grain structure trapping hydrogen molecules readily available from the pickling acid used in the galvanizing process. Heating the steel to 300 F after pickling or blast cleaning in lieu of pickling is an effective means of guarding against hydrogen embrittlement.
A 143 also describes how to test for embrittlement, essentially by comparing the bending properties of ungalvanized steel to galvanized. A specific lot size of samples must be tested.