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Stress Crack on C1045 6" diameter 24' long 2

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ranparn

ranparn

Agricultural
Aug 18, 2011
5
I have a 6" diameter chrome plated bar C1045 steel that is induction hardened to 60 HRc on the surface with a case depth of around .050". My customer found the bar in the condition as shown in the attached picture. The bar didn't look like this before we shipped it. Not sure if this is a quench crack or a stress induced brittle fracture. One thing that confused me is, there is an area on the bar that shows a drop in hardness to 30 HRc right where I believe the crack initiated. The hardness is 62 HRc about an inch before the start and about an inch into the cracked area. What are some suggestions on how to re-create this type of fracture?
 
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This looks like delayed cracking from hydrogen embrittlement. Was the shaft baked (heated to 450-500 deg F) after chrome plating?
 
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I tend to agree with metengr, assuming that the part was electroplated. Have you confirmed the crack depth as being essentially limited to the hardened case depth?
 
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The depth of the crack goes well beyond the case depth. The shaft was not baked after chrome plating. The bar was ground prior to plating to establish a good surface finish. The only thing done with the bar after plating was a couple of saw cuts. I sent the sample where I believe the crack initiated to a Metallurgical lab for failure analysis.
 
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The crack could well extend into the bar depending on the original heat treated condition prior to induction hardening.

 
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Induction hardening of a shaft normally puts the surface stresses into a state of compression. As you grind the surface, you are removing some of the favorable residual compressive stresses, particularily with the subject part, which has a shallow case relative to the bar diameter. The residual stresses could have been tensile after grinding and led to crack initiation from hydrogen embrittlement from the plating.
 
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