Nitriding crankshafts and bending

[tomeQ]

Hello. A few hours ago i had interesting conversation about nitriding crankshafts for cars.Then I heard that always after this proces cranakshaft had to be straighten by using burner and press, hmm. Is that so usual in this method because i've never met with this and think that's rather fault of bad prepare and course of process. What experience do You have?

 

[swall]

You would run the risk of cracking the nitriding. Not only would you lose the favorable compressive stresses nitriding imposes, but the resulting micro cracks would act as stress raisers for fatigue crack initiation.

 

[tomeQ]

Ok, I think similar, but my main question is, is it normal repercussion of nitriding or is it caused by low quality of workshop ?

 

[swall]

Any residual stresses in the crank will cause the crank to distort during the 1000F nitriding process, which will act as a stress relief. Proper sequencing in the machine shop would be to rough machine, stress relieve 100F above the nitriding temperature and final machine prior to nitriding.