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Why does brass crack after blasting?

Brass parts that are cold formed after Anneal show no cracks. After blasting with glass bead the cracks are present after cold form. Why?

Don J. Huffman
- Torrance, California
2002

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2002

The blasting deforms the surface layer, work-hardening it. The strength of the surface layer is increased and its ductility is reduced. When you then coldform, as far as the surface of the material is concerned you are coldforming a low-ductility material, which cracks rather than deform further.

You could anneal after blasting, which would restore ductility, but I guess the reason you're blasting is to clean up the surface after annealing, so that could lead to a perpetual circle of activity! Using a softer blasting medium could help - enough to clean off the annealing scale but not enough to deform the metal itself.

Bill Reynolds [deceased]
consultant metallurgist - Ballarat, Victoria, Australia
We sadly relate the news that Bill passed away on Jan. 29, 2010.

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I assume your parts are very thin. Blasting will work harden the surface of any material, but thin materials less than .020+ can crack.

AF Kenton
retired business owner - Hatboro, Pennsylvania
2002