From your opinion, is it a closed pore or a hole made by corrotion?

[Okaman]

This is my first case. I found this in the small size bearing on the face, on outer diameter of the bearing. The material is JIS based standard SUJ2 with 1,3-1,6 percent chrome. It is restricted from the company for publishin any other materials than this, so i want to know any other opinions about this defect. I hope this will continue into a good discussion. Thanks.

 

[redpicker]

From those two options, I'd have to pick "a hole made by corrosion", particularly since steel does not have pores, open or closed.

rp

 

[TVP]

Can you section through the black spots? This would provide more information on the nature of the defect.

 

[Okaman]

@rp
what if the pores were made from the making of the steel from the foundry? Like the pores made from the bubbles of CO2? If the pores is deep in the steel, it need to be grinded to peel and reveal it, is it possible?

@TVP
it is the highest magnification in my lab, is it not good enough to interpret?

 

[TVP]

It would be helpful to look at the cross section instead of the surface. The magnification is ok.

 

[redpicker]

Holes left by gas bubbles during steelmaking are typically referred to as voids. Bearing steels are generally produced using processes that eliminate voids. Yes, it is possible to have voids in steel, but in a bearing steel? Not likely.

Have you tried to remvoe it with a fine abrasive such as scotchbrite or steel wool?

rp

 

[tomwalz]

It is awfully round to be corrosion in my experience.

Is it a hole? Could the hole represent part of a sphere?

I'd second the Scotchbrite suggestion.

Any chance it is a production or post production handling issue? Any information on the rate of occurrence? I have a pretty good list of things that occurred once over the years. Monday morning problems. Problems after a 3 day weekend. A sticky torch valve and so on.

In thirty years of consulting and teaching I have learned to recognize various facial expressions among my audience. One occurs when I explain why you shouldn’t do something. I sometimes see a facial expression that very clearly says (Oh Sh--, I better quit doing that.)


Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

Good engineering starts with a Grainger Catalog.

 

[Ron]

Have you tried cleaning your lens?

 

[Okaman]

@all
the defect is found on in-house production, which means it never leave the company. The production line consist of lathing process from bar and tube material, heat treatment to make the double-temper martensitic structure, grinding + super finish, and assembly.

@TVP
Oh, okay, i`ll try to take picture on the cross section, i will post it on Monday.

@rp
when the defect occurs, it is founded in all production line in the my company. My mentor said those defect caused by the supplier of bar and tube steel, because they target a higher sell so they turn down the quality by speeding the process. I suspect rather void or the hole left by intemetallic compound. But i'm not sure...

The bearing is cleaned, not using scotchbrite, but using another brands, hehe....
but is it important? we didn't see any spalling after the cleaning...

@tomwalz
By my experience when training, it is hard to make an those kind of indentation with the machine. And the defect is not reciprocal, so i think it is not because the machine. Plus the black mark on the spot, i don`t think any machine in my company leave that trail...
i'll find any new information regarding this. Thanks mister. Wow, you have been teaching for 30 years? where have you been teaching?

@ron
yup, the lenses is clean =D

 

[Okaman]

I have attached other files from my case. I follow the advice from rp about scotchbrite, and that is the result. My prediction so far, it is because some void made from the casting process. But I am not sure. The defect is found on after-grinding process, in high ammount. There are no reports on lathing process that they found this kind of defect.

I want to ask your opinion, is it any possibilities of void from the casting process? if that so, how the void created? Is there any parameter that i have to consider about the steel-maker and supplier?

Thank you =D

 

[EdStainless]

Could they be causing these in the heat treat process?
Since these are all on the outside (I take it that you don't find them on the bearing surface) I doubt that it is the steel.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[stanweld]

Okaman,
What is the base material form (tube or bar) exhibiting the pore-like surface?

 

[TemperedMartensite]

I think Ed may be onto something. Were these parts heat treated in a salt bath? An incorrect wash and then a temper would give you something similar to that.

Also, is this a as-cast part, forged, or cast and HIP? That surface looks either forged or at least peened.

 

[metengr]

Not enough information to determine a cause. Have a proper metallurgical analysis performed.

 

[Okaman]

@EdStainless and @TemperedMartensite so far i did not check the heat treatment process. But for further description, this is the process flow of heat treatment on the company : After finish lathing, the next process is precleaning, using Teclean (the liquid is vapourized and the vapour is used to clean the material from oil, dust, etc, leaving the material clean and shiny, no moisture detected), then to austenizing temperature on vaccum chamber, and then go to quenching using special oil (cooling stop at ~95 celcius), after that, cleaning using Teclean with same method, and then material go to sub-zero process to reduce the retained-austenite, then post cleaning (same method), then tempering (for normal process the temperature are 170 celcius for two hours, and another elevataed temperature for another process).

If there is something wrong, in what process it will be?

@stanweld the material shape is bar for inner ring, and tube for outer ring, with SUJ2 (JIS standard), same with AISI 52100.

@metengr i have asked the lab to add adequate instrument for metallography, but no respond, sigh... =(

 

[metengr]

okaman;
Why don't you send the piece out for proper analysis to another metallurgical lab? If this is important enough, it should be done.