Old Elsmar Cove guy here. Glad I found this forum! What am I missing? I am unable to do a controlled study at this moment because of lack of parts but I have a mystery that I can't explain. Three different times we sent 4140 material forgings to be heat treated to 18-24 Rc and they were certed to that spec. receiving inspection verified it all three times. The parts were then shot blasted to clean them and then Magnetic Particle Inspected to test for cracks. The customer then finds 100+ pcs. testing from 10-15 Rc. They sent a sample, I test it to be 10-15 Rc depending where I test it. First thought...customer had a process that changed it before they tested it. Fourth lot of parts sent to HT, certs say they are in spec., I verify correct hardness at receiving, parts are shot blasted & Mag Inspected, I retest 5-6 pieces and every one is 10-16 Rc. Is either of our process capable of softening the parts like that? Any ideas would be appreciated!