Double Induction Case Hardening

[JosephGoedecke]

I saw this thread and was looking for additional detail. I am currently a studying metallurgical engineer interning at a plant where this is sometimes the common practice. They try to reach a case depth of >50Rc at .050 inches, and <40 at .100 inches. Occasionally a part will be over hardened and be around 50Rc at 0.110, for example. Can this simple be reran through? Currently when this happens it runs through and is not rechecked. But would the martensite down at .110 be tempered enough or transformed to reduce the hardness below 30Rc?

Any thoughts would be appreciated. It is ran so as to be only case hardened. Therefore the core is not heated and only the surface, which leads me to believe that it would be too hard still farther down if they merely ran it at paramaters to harden it to 0.050.

Link to a previously closed thread below.

Thanks


thread330-255489

 

[Lyrl]

I worked at a commercial heat treater that performed induction for seven years. If they overcased a part, they would anneal it (run the overcase process without a quench - which ties up the machine for a while waiting for the part to cool) before running the adjusted cycle. I've never seen a too-deep induction part just be rerun on a shorter cycle. I agree with you, that sounds like a fishy practice.

 

[dbooker630]

My thoughts on this topic remain the same as what I posted in the closed thread. The depth of hardening in your case is not as deep as the shafts referenced in the 2009 thread. But I think it would be a good practice, and perhaps a good project for yourself, to examine the 2X-induction hardened parts and compare to those which are reworked (retempering, annealing, etc) prior to the second IH. You can demonstrate your investigation skills and perhaps save the company in future warranty costs.

 

[JosephGoedecke]

Alright, that was kind of my plan. Thank you Lyrl and dbooker for the help!

I'll be sure and post any conclusions I come to here for future similar issues.