Hi Gordon,
Thanks for your kind reply
Quote:I think you are referring to the copper sulphate test (copper sulphate solution acidified with sulphuric acid, various concentrations and exposure times).
I think you are right. In fact, I have used these solutions in the past but didn't know for sure how they where formulated.
Quote:The primary use is for testing stainless steels ability to resist corrosion or to identify stainless steel from carbon steel. The idea being that carbon steel is readily attack by copper sulphate solutions forming a copper deposit, while a good passivated austenitic stainless steel should not.
The presents of a nitrided surface should reduce the degree of attack from copper sulphate and the presence of a white layer probably further.
My experience tells that Cu++ solutions do not work for treatments producing rather thin (if any) white layer. I remember arguing with a supplier of low pressure gas nitriding service who asked me to try the dies they treated in the press even when they had failed to pass the CuSO4 test. In the end, he was right. Low pressure gas nitrided tools outperformed salt bath nitrided ones which had passed the test (the solution kept its blue-green color when poured on die surfaces).
Trying to think chemically I do not found any reason for Cu++ not reacting with iron except when a continuous compound layer (white layer) is present.
As you surely know, extruders actually try to keep white layer's thickness as low as possible since they are fragile and tend to spall.
All in all, my concern is that the test is probably telling that I have what I don't want to. Is this correct?
Quote:I can only see this being useful to determine whether a steel surface is nitrided or not. To be honest I think testing with a hard file to assess the hardness or grit/shot blasting to highlight soft areas would be far more informative, plus a lot less messy and hazardous to health. I assume you are wanting to test worn dies with this test.
Actually, I would like to develop a test for nitriding treatment quality
Quote:Testing nitrided cases after heat treatment really should involve hardness testing and metallographic evaluation.
I know this but our testing facilities and equipment for metallographic analysis are rather poor.
Thank you very much replying to my inquiry,
Sandero
Note: edited quotes to make reading easier