Problem with bearing structure 1

[bearingsteel]

A bearing is sold to a customer and works good for 1-2 weeks, then it breaks.
When it came back, he has a different structure than it should have. A good structure is quenched(martensite) and it came back with an annealing structure(speroidised, fine globular cementite).
I want to know what would be the different causes of this(how did it happen).

 

[mrfailure]

What makes you think it went out with a martensitic structure? The easiest explanation is it did not; that particular bearing was improperly heat treated.

Aaron Tanzer

http://www.lehightesting.com

 

[bearingsteel]

I know that theoretical it's possible if the bearing is overheated at about 900-1000 grades Celsius, it can be annealed. May this be the explanation?

 

[dbooker630]

If the bearing is made from 52100 the incoming bar stock is typically spheroidized annealed. So another question to ask is whether the bearing was heat treated at all.

 

[arunmrao]

It was never hardened to begin with. Assuming it was hardened, it is quite far fetched to suggest that over heating of the bearing caused it to spheroidize!

 

[mrfailure]

I appreciate the word "theoretical" that bearingsteel used; I think in practice the bearing would have siezed long before it could have reached those temperatures.

Aaron Tanzer

http://www.lehightesting.com

 

[Guest102023]

I concur, the bearing would have violently self-destructed before it could achieve a uniform annealed microstructure.

What kind of wear do you see?

 

[bearingsteel]

I see that it has a half speroidizing structure and a half that it is almost quenched-tempered.

 

[metengr]

I would hope you have a proper failure analysis performed and understand how the bearing performs in service instead of spoon feeding folks here information.

 

[bearingsteel]

I don't think I can do this. I would like to see how it works and then fails thou.
I work in the metallographic laboratory so I must know also how they fail and how to resolve problems that arise.
Thanks anyway for your response.

 

[Guest102023]

As metengr said, it is impossible to do a failure analysis based on fragmentary information (no pun intended).

Next bearings you supply, keep a control sample in your desk until such time as this customer returns a destroyed unit. Better yet, do some random sampling for hardness testing and metallography, a.k.a. QC.

 

[mrfailure]

Many folks in metallography labs and are highly knowledgable in their specialties, but they are not specialists in failure. They hire labs with failure analysts because they understand how things fail, and it is more important to their organizations to gain this knowledge with assurance.

 

[redpicker]

As stated above, if heated to a temperature needed to create even a partially spheroidized microstructure, at temperature the bearing would not be able to support a load high enough to create the necessary friction and would disintegrate. A one to two week lifespan for a new bearing is typical of an improperly heat treated bearing. While this does not prove the problem in this case, it does explain the responses it has received.

From your limited description of the observed microstructure, I wonder if what you are seeing is a microstructure resulting from either too low of an austenitizing temperature or excessively high tempering temperature. While a metallogropher may not be the best failure analysist, a good metallographer should be able to recognize what thermo-mechanical history is needed to produce a given microstructure, given the steel chemistry and standard processing. There is a lot you can learn from from the microstructure, you should try to find out more from the manufacturing side what could have happened during processing as well as from the customer support side as far as what the application was. Correlate these with the clues seen in the microstructre and you will have a better understanding of what has happened.

rp

 

[dbooker630]

Can you post a photomicrograph of the spheroidized structure and another of the quench-and-tempered area? Also a photograph of the bearing with arrows pointing to the noted structures would help.

 

[metman]

As stated several times, the bearing could not have reached spherodizing temperature before self destructing. Even if it were possible to reach that temperature in service, spherodizing requires extended time at temperature. It appears that heat treat was fouled to begin with. We surely would like to see the microstructure.

Design for RELIABILITY, manufacturability, and maintainability

 

[bearingsteel]

So it's an interior ring with a half annealed and a half normalized structure(not quenched as i said earlier).
The half with annealed structure has 25-30 HRC, the other half has 40-45 HRC.

Here is the etched sample.

Annealed structure

Normalized structure

 

[bearingsteel]

I'm very sorry. I did put 3 pictures in the reply but for some reason, it didn't appear. I will put them tomorrow, I have them on the computer at work.

 

[bearingsteel]

Here is the etched sample

http://img585.imageshack.us/img585/8555/dscn5273u.jpg

Annealed structure

http://img109.imageshack.us/img109/4097/dscn5277h.jpg

Normalized structure

http://img803.imageshack.us/img803/6963/dscn5280co.jpg

 

[dbooker630]

I was not able to view the web pages, they are blocked by my company server. Could you post them to Engineering.com? There should be a link on your Eng-Tips page.

 

[redpicker]

Those are interesting photos.

With the photomicrographs, it would help if you would identify the magnificaiton. I am also guessing, what you are calling "annealed structure" is taken from the right side of the "etched sample" and the "normalized structure" is from the right? The hardness of these two regions would also be enlightening.

What is the chemical composition of the steel? 52100 has been suggested, but my guess is that is only based that that is a common grade used in beraings. Do you know what the grade of steel is? Also, what is the overall size of the bearing? Is the bearing produced from bar stock? a forging? Do you know the perscribed heat treatment?

The left side of the "etched sample" appears to have multiple zones, much like what you would see with weld repair. As 52100 is not readialbe weldable, this does not make much sense, but that is the impression I get from looking at it.

We really need more information to provide much insight.

rp