Testing Hardness

I have a part that gets induction heat treated in one small area to Rc 53-59. Material is 4340. The length of the area to be heat treated is specified on the print. The print also specifies a depth. My question is this, is there any non-destuctive method to test the hardness of this area to the specified depth. The area is approx 2.000 wide by .500 long by .200 deep. Right now I test the hardeness at the surface, and I have sectioned a few samples to test the hardness at the specified depth. I need a method to test every part without cutting it open. Any suggestions? Thanks in advance!

Only thing I can suggest is to get a set-up established, prove it out by destructive testing, & once you are satisfied that results are OK, go into production. Decide on how many parts you want to harden between tests. As long as spot samples are OK, production ones should be good, too, provided the heating/quenching process is closely repeated..... Just My Opinion...

Years ago I heard about a process for alloy identity testing using an eddy current tester. At the time it also said that eddy current testing could also identify hardness variations for a consistent material. If you could find an eddy crrent tester, it might be worthwhile to find out if it would distinguish between a properly hardened part and an improperly hardened one.

Obviously, destructive testing of every production part is out. I don't know of any testing process to determine deep hardness in locally hardened parts. Few non-destructively accessible deep physical properties of steels change through heat treatment except magnetic properties.

Magnetic properties of hardened steel differs from that of unhardened steel. It's quite possible that eddy current as Jpfalt mentioned or some other magnetic property test can give you a value for acceptable production parts that corresponds with a proven part.

In the oldy days they used to make test coupons of production material (bar ends are convenient) to be included with every batch of high confidence, high consequence parts like aviation crankshafts, ship's propulsion shafting, surgical appliances, armor plating, and the like. One coupon is used to prove the starting process parameters, two or more to run at random in process, and a final coupon to demonstrate consistancy over the full run. These need not be machined except in the hardened area or be of full part size and configuration except where it counts.

Running the coupons cannot interfer with or require any changes in the hardening set-up if it is to reflect production parts. Consult with your heat treater for suggestions he can live with.

The people to get in touch with is Krautkramer-Branson. They do both ultrasonic and eddy current. GE recently purchased them from Emerson. Without seeing your part, I can't say for sure that you can test that way. Have them look at it.

http://www.geinspectiontechnologies.com/
JR

Thanks for the responses. Eddy current testing might be the way to go, I'll have to do some research. I already proposed the idea of coupon samples to be processed with each lot of parts. However, this part is for the government and they are insisting on a certification for each and every part.

Thanks for the useless post, spammer.

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