Failure of a Zinc-Electroplated 1060 Steel Fastener
Fasteners, made in high-production progressive dies from 0.7 mm thick cold-rolled 1060 steel, were used to secure plastic fabric or webbing to the aluminum framework of outdoor furniture. It was found that approximately 30% of the fasteners cracked and fractured as they were compressed to clamp onto the framework prior to springback. The heat treatment cycle of the fasteners consisted of austenitizing, quenching, tempering to obtain a tempered martensite microstructure, acid cleaning, zinc electroplating, coating with a clear dichromate and thereafter baking to remove the nascent hydrogen. It was revealed that fasteners treated in this manner were brittle due to hydrogen embrittlement as the baking process was found to not be able to remove all the nascent hydrogen which had induced during acid cleaning and electroplating. The heat treatment cycle was modified to produce a bainitic structure and the method of plating the fastener with zinc was changed from electroplating to a mechanical deposition process to thus avoid hydrogen embrittlement.