440 C SS corrosion
440 C SS corrosion
(OP)
This part has been passivated per AMS-QQ-P-35, TYPE II.
It is a shaft .025" OD. Hardness: 580 to 820 HV under 500g load.
It appears it has some surface corrosion. Microscope observation shows small pits. Corrosion product is black.
This shaft works together with a bearing, which is made of brass, CDA 36000, half hard.
What can be done to eliminate/decrease this corrosion, please?
It is a shaft .025" OD. Hardness: 580 to 820 HV under 500g load.
It appears it has some surface corrosion. Microscope observation shows small pits. Corrosion product is black.
This shaft works together with a bearing, which is made of brass, CDA 36000, half hard.
What can be done to eliminate/decrease this corrosion, please?





RE: 440 C SS corrosion
RE: 440 C SS corrosion
The distance between the bearing and the shaft is .001" each side. However, the load is very low.
Temperature: mostly room but can be from -65C to +125C.
See the picture attached.
RE: 440 C SS corrosion
8-12 Micron thick which is a dry lubricant. If you can not use a coating from some reason I would make a pin from Custom 455/465 H1000 or H950. 580HV is 53.7 RC so the Custom will do. 820HV is 63.3RC which makes the pin too brittle.
The range of temperatures you mention indicate, Military, Aerospace or Space use.
RE: 440 C SS corrosion
This material will rust in a humid environment.
You might even get the strength that you need from 17-4PH, but custom 455 would also be a viable option.
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P.E. Metallurgy, Plymouth Tube
RE: 440 C SS corrosion
The reason I offered Custom 455/465 is to get the minimum hardness hardness and toughness together with corrosion resistance. I am not sure you can have both hardness and toughness with 17-4PH. The selection of 440C at 63 RC is too brittle to have toughness.
RE: 440 C SS corrosion
I cant see any reason to mate it something harder than about RC40.
455/465 don't really have great corrosion resistance, hence my preference for 17-4PH H1025.
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P.E. Metallurgy, Plymouth Tube
RE: 440 C SS corrosion
I have no data for 440 C, or alloys you recommended.
Are they comparable in regards of BH curve? Or comparable in regards of Coercivity and Residual flux density?
RE: 440 C SS corrosion
I understand HT is heat treatment, correct?
If this material is tempered above 370C, Chromium carbide will precipitate, and it is not Stainless any more.
Is that what you mean?
RE: 440 C SS corrosion
How magnetic do you need it? AC or DC? What saturation level? All of these alloys will have fairly high coercivity, after all Cr steels similar to 440 used to be used for permanent magnets.
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P.E. Metallurgy, Plymouth Tube
RE: 440 C SS corrosion
It is a DC application. No, it will be not saturated. It is a part of the coil core.
There is another part of the coil core, which plays a major role. Shaft plays a minor role in the magnetic circuit.
Sorry, I have NO data on 440C magnetism.
If two materials you suggested are somewhat close to 440C in regards of coercivity and residual flux density, then I will try them.
Otherwise I will use dry lubricant, suggested by israelkk.
RE: 440 C SS corrosion
The magnetic issue complicates things. In one hand you use the 440c as bearing shaft which needs high hardness 53-63RC. On the other hand, stainless steels for magnetic use are martensitic stainless steels from the 400 series. Therefore, are not really good for corrosion as austenitic stainless steels that are non-magnetic. It seems the designer wanted two properties that doesn't go together for a robust design.
RE: 440 C SS corrosion
Yes, I have the same understanding of this situation.
I am reading the MIL spec you recommended for the lubricant.
RE: 440 C SS corrosion
RE: 440 C SS corrosion
It looks like Br for both would be roughly 5-7kGauss.
Hc is another matter, I find values for similar alloys ranging from a low of 20 Oe up to 100 Oe.
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P.E. Metallurgy, Plymouth Tube
RE: 440 C SS corrosion
You are right about Military, Aerospace application.
MIL-PRF-46010G, p.6.9 reads:
6.9 Aerospace Components – Types I and II lubricants previously found under MIL-L-0046010E are now under SAE Aerospace Standard AS5272. The SAE document still allows and use lead material to meet aerospace application requirements. For other than aerospace applications products under MIL-PRF-46010 shall be used. (Use of MIL-PRF-46010 in aerospace applications must first be validated.)
It looks like this dry lubricant is NOT for Aerospace application.
RE: 440 C SS corrosion
RE: 440 C SS corrosion
Do I start with MoS2 application? Any documents/MIL standards on that, please?
RE: 440 C SS corrosion
http://www.globalspec.com/search/products?page=mi#...
You can call them.
RE: 440 C SS corrosion
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P.E. Metallurgy, Plymouth Tube
RE: 440 C SS corrosion
They list Boeing and Pratt & Whitney and Airbus approved dry lubes.
RE: 440 C SS corrosion
Should work.
RE: 440 C SS corrosion
Very important, as I have a distance of 0.001" between the shaft and the bearing.
RE: 440 C SS corrosion
1. For Boeing, Everlube 9002 (MIL-L-46010- Type. III) is covered by Boeing spec. BAC 5811 Rev. P thru U- Type VI- Cl. 4
2. For Lockheed Martin, Everlube 9002 (MIL-L-46010- Type III) (Old Formulation) is covered by Lockheed Martin spec. FMS-3101B Class III.
Therefore, you should be familiar with these specs and to decide if they meet your design.
You should make sure that you can actually purchase it.
As to your dimension problem this is a delicate design issue requires the knowledge of the spec. itself how it is done, preparations, what is the recommended coating thickness for your application and how accurate a coat can be and controlled. This is beyond the scope of the posting. I suggest either you study the matter carefully or rely on an expert that can specify it and make sure you get it. It will be a shame to find that the bearing will not be able to install over the shaft. For that, you need to know the exact shaft dimensions spec. including outside dia. tolerances, the bearing inside hole dimensions and tolerances and specify the MoS2 minimum and maximum thickness coatings in the shaft drawing to insure correct fitting.
RE: 440 C SS corrosion
They specify Everlube 620 for aerospace too.
RE: 440 C SS corrosion
RE: 440 C SS corrosion
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RE: 440 C SS corrosion
RE: 440 C SS corrosion
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P.E. Metallurgy, Plymouth Tube