Possible Causes of Failure
Possible Causes of Failure
(OP)
Hi all,
Just wondered if anyone could point me in the right direction as to where I might find some answers on this question.
I need to suggest some possible causes for the failure of a carburized alloy steel gear, which was meant to have a surface hardness of RHC60, but, after an in-service inspection, it registered a hardness value of RHC30. I'm an electrical engineer and have absolutely no clue where to start on this.
Many thanks,
Regards,
Matt
Just wondered if anyone could point me in the right direction as to where I might find some answers on this question.
I need to suggest some possible causes for the failure of a carburized alloy steel gear, which was meant to have a surface hardness of RHC60, but, after an in-service inspection, it registered a hardness value of RHC30. I'm an electrical engineer and have absolutely no clue where to start on this.
Many thanks,
Regards,
Matt





RE: Possible Causes of Failure
What is process history of the part? What is the base chemistry? What is the failure? Is HRC30 from undamaged surface or from layer lower than carburization?
Sending the part to a metallurgical lab should help locate/solve your problem.
RE: Possible Causes of Failure
RE: Possible Causes of Failure
RE: Possible Causes of Failure
RE: Possible Causes of Failure
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RE: Possible Causes of Failure
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RE: Possible Causes of Failure
RE: Possible Causes of Failure
RE: Possible Causes of Failure
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RE: Possible Causes of Failure
The purchasing group would regularly get proposals from vendors to supply an alternative alloy that would meet the minimum hardness requirement but since it was not carburized would not have the hardened surface layer and, consequently, would be totally unsuitable for our application. Since they were significantly cheaper than the carburized parts, we would end up with a sample to test to see if they could replace this expensive part with this less expensive one.
RE: Possible Causes of Failure
If this is real world then the sky is the limit. If this is limited to the condition of hardness then you cans till get a good, long list.
In the question as presented, we don't know if there was excessive wear, pitting, chipping, cracking, deformation or anything else.
The part could have failed because it was hit with a forklift and the hardness was incidental.
In my career as a consultant there have been several times when I have told a group not to do something and seen a few faces registering surprise. You could almost hear them thinking "Shucks, I better quit doing that."
Here is my list as to why tungsten carbide might "wear out." It doesn't feel completely right to me but it is very handy. Do something like this for you project.
Theoretical considerations
1. Wear – the grains and the binder just plain wear down
2. Macrofracture – big chunks break off or the whole part breaks
3. Microfracture – edge chipping
4. Crack Initiation – How hard it is to start a crack
5. Crack propagation - how fast and how far the crack runs once started
6. Individual grains breaking
7. Individual grains pulling out.
8. Chemical leaching that will dissolve the binder and let the grains fall out.
9. Rubbing can also generate an electrical potential that will accelerate grain loss
10. Part deformation - If there is too much binder the part can deform.
11. Friction Welding between the carbide and the material being cut
12. Physical Adhesion – the grains get physically pulled out. Think of sharp edges of the grains getting pulled by wood fibers.
13. Chemical adhesion – think of the grains as getting glued to the material being cut such as MDF, fibreboard, etc.
14. Metal fatigue – The metal binder gets bent and fatigues like bending a piece of steel or other metal
15. Heat – adds to the whole thing especially as a saw goes in and out of a cut. The outside gets hotter faster than the inside. As the outside grows rapidly with the heat the inside doesn't grow as fast and this creates stress that tends to cause flaking (spalling) on the outside.
16. Compression / Tension Cycling - in interrupted cuts the carbide rapidly goes though this cycle. There is good evidence that most damage is done as the carbide tip leaves the cut and pressure is released.
17. Tribology – as the tip moves though the material it is an acid environment and the heat and friction of the cutting create a combination of forces.
Thomas J. Walz
Carbide Processors, Inc.
www.carbideprocessors.com
RE: Possible Causes of Failure
I tend to agree with Metengr...if you have no background with this one, find a metallurgical lab and pay the consultant's fee. We have metallurgists on staff but still will send stuff out for a second opinion. They'll be able to identify the material, the correct way of mounting, etc.
RE: Possible Causes of Failure
Can you post a picture or photograph of the failed gear.
Often looking at the surface where it failed can give some clue's as to failure.
In addition if you can provide any evidence of the load the gear see's might also be helpful.
regards
desertfox
RE: Possible Causes of Failure
- gears were induction heat treated;
- operator 2d shift collected his heated gears and dumped them as a grouop later;
- supervision got their a** kicked.