Checking Hardness of Nitrided 4140/4340 Parts
Checking Hardness of Nitrided 4140/4340 Parts
(OP)
Can anyone recommend a testing method for nitrided parts? The tester our QC is using is a Hartip 3000, and we seem to always get lower values than expected. It is possible to 'break through' the case and read a lower value than actually present? The case depth is supposed to be >.015". Also, generally how hard a case can you expect with these matrials?





RE: Checking Hardness of Nitrided 4140/4340 Parts
RE: Checking Hardness of Nitrided 4140/4340 Parts
As you note - on thin cases it is very easy to affect the apparent surface hardness if you try to test directly on the part and start to deform the substrate material.
RE: Checking Hardness of Nitrided 4140/4340 Parts
RE: Checking Hardness of Nitrided 4140/4340 Parts
With regards to nitriding, a microhardness traverse is definitely the way to go. You want to measure both hardness and depth. Knoop or Vickers with an indentation load of 0.025-0.050 kgf is best, with the indentations at least 3 diagonals apart. As swall mentioned, the hardness will likely be 62 HRC maximum (~ 750 HV or ~ 775 HK).
Nitrex has a nice description of this type of testing in Issue 25 (September 2003, page 3) of their newsletter called Nitrex Communicator. Use the following link to obtain more information:
http://www.nitrex.com/library_archives.ch2
RE: Checking Hardness of Nitrided 4140/4340 Parts
http://www.nitrex.com/iactivefiles/Nwsl026.pdf
http://www.nitrex.com/iactivefiles/Nwsl025.pdf
RE: Checking Hardness of Nitrided 4140/4340 Parts
Regards,
Cory
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Checking Hardness of Nitrided 4140/4340 Parts
RE: Checking Hardness of Nitrided 4140/4340 Parts
RE: Checking Hardness of Nitrided 4140/4340 Parts
You gave up an old trade secret of the metallurgical technician. I was shown this trick by my boss in about my third week on the job in 1952. I could even do the math. Used it many, many times.
Another one you can do if the part will allow it is to zig-zag, offset each reading.