Voids

If the application demands a sizable void in the part such as in a cylindrical part with a center axial hole, the magnetic properties will not be developed. CMI delivers the metal in a pre-stressed state so that the energy us available to promote the grain growth of ferrite. If the center is drilled out, as the temperature of the anneal rises, the OD increases and decreases with cooling because the “hoop” stress is removed. To retain the excellent magnetic properties, machine the cylinder, anneal, drill the center hole per matching instructions and reanneal the part to remove the machining cold work stress. If the slight deterioration of magnetics can be tolerated, don’t second anneal.