I am with a cold heading company, we have been experiancing an issue where our customer cannot stake an M10 stake stud into the their exhaust flange (won't fully seat). We have been providing this stud for a number of years and just since 11/05 have had this issue. We have investigated and cannot find any process that have changed either in our process or the customers. We did have a the steel analized metalurgically and discovered a condition that we were told was called Eta phase. Our knurls are "rubbing" away during the stake operation. We have found the surface hardness to be slightly softer than the core after the studs have been precipitation hardened per ASTM A453M. We have tried different steel suppliers and different heat treat facilities, knurl diameters, but have hit a dead end every time. Any help in pointing me in a direction to finding a root cause to this would be greatly appreciated.
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