CHQ steel can be formed into rivets but coating may need special care

CHQ steel can be formed into rivets, but coating may need special care.

Cold-Heading Part Splitting

On 1020 steel, surface cracking on zinc-plated annealed parts Check for seams Lower annealing temp

Q: We use 1020 steel wire to produce a cold-headed rivet that is annealed after production. After heating, the parts test OK, but after zinc plating we experience splitting on 2-3% of the parts. Is there a better approach?  The splitting occurs immediately after plating. The plating is an electro-galvanized process based on alkaline chemicals. We supply the parts very clean and we have per formed tests in which we did not do any pickling or cleaning before the plating, with the same result. I’ll appreciate your insights.

A: You have an interesting problem. Are you sure that the headed rivets are not already defective with light seams? This can be the cause of some splitting that occurs after plating, which tends to concentrate hydrogen at stress points and, thus, some brittleness.

Baking the parts at a relatively low temperature after plating would minimize cracking from this source, if it were confirmed as the cause. If there are no tiny seams on the starting wire, I do not have a reasonable explanation without the benefit of actual samples and or metallographic photographs.

For more than 40 years H. James Henning held key technical positions in the forging industry, including as director of technology for the Forging Industry Association, and as president of Henning Education Services, a Columbus, OH, firm specializing in customized education and training in forging technologies.

Guidelines and recommendations offered in this column are based on information believed to be reliable and are supplied in good faith but without guarantee. Operational conditions that exist in individual plants and facilities vary widely. Users of this information should adapt it, and always exercise independent discretion in establishing plant or facility operating practice.

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