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.
A143 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.
See the Embrittlement category within the Dr. Galv section of the website for more information regarding embrittlement.