Material Substitution 9310 steel 4

[mewhg]

We have legacy part traditionally made from 9310 AQ steel, vacuum carburized and shotpeened. It is highly loaded in a semi-shock mode and under low cycle fatigue (75k cycle expected lifespan). Failure (cracking) of the component has always been a problem way before 75 k is reached. Changing geometry of the part is not an option.

Can anyone suggest a different steel that might be a better candidate for the high load/low cycle fatigue situation? I am thinking that 9310 is more suited for lower loading and high cycle fatigue applications.

TIA

 

[tbuelna]

mewhg,

At 10^4 cycles, carburized 9310 should be good for at least 120 ksi with unidirectional loading. I don't know of any carburizing grade alloy that would do much better.

You might try a VIM-VAR grade of 9310 such as AMS 6265.

Good luck.
Terry

 

[mewhg]

Thanks for the suggestion Terry. The problem with this part is that it is overloaded and needs a redesign. But because of how long this part has been in the field (mid 1960s) the geometry can't be changed because it has to still fit with the rest of the machines still in use.

It's a bit of a mess actually. I am hoping to come up with a material/heat treat solution to the problem.

I'll look and see if your suggestion of the AMS spec is covered in the AQ grade we are going to use. Going to an aircraft quality 9310 steel was the next step I was going to take. I would like to try some other alloys in parallel with the 9310 AQ.

 

[unclesyd]

i would look at nitriding/nitrocarburizing your part in lieu of carburizing to gain a little in fatigue strength. The gain will not be in orders of magnitude but probably enough to get the required component lifespan.

Assuming you are carburizing for wear resistance and are getting fatigue initiation from some type of impact loading you may need to go to an impact resistance steel and give up a little in wear resistance , though some impact resistant steels are very wear resistant.

Here are two sources of nitriding and carbonitriding that I would contact with your problem.

http://www.nitrex.com/english/technologies_modern.htm

http://www.nitromet.com/

 

[metengr]

You also might want to evaluate 4320 AQ steel for carburizing. Excellent hardenability, increased resistance to shock loading and increased fatigue strength.

 

[TVP]

I think you would obtain better results with diffferent processing than with a change in alloy. I agree that using a vacuum processed version of 9310 (VIM-VAR) would be the first upgrade. Second, have you investigated the details of the shot peening process? Perhaps a larger intensity could be obtained by using cemented carbide shot, or dual peening, maybe with microfine shot as the second media. Definitely talk with Metal Improvement about options. Last, have you investigated isotropic superfinishing from REM Chemical or CASE from Metal Improvement? Both can substantially improve fatigue performance of gears, even highly stressed aerospace apps.

 

[RPstress]

QuesTek make some claims for their Ferrium C61 over 9310. Latrobe's data sheet for C61 has some fatigue data:

http://www.latrobesteel.com/assets/documents/datasheets/Ferrium_c61.pdf

. R=~0 unnotched fatigue runout claimed to be about 150 ksi as opposed to 110 ksi for 9310.

 

[gearHTr]

I agree with moving to VIM/VAR grade.
As for vacuum carburized - is it getting gas quenched? Or getting oil quench, followed by deep freeze and temper?(preferred)

Pyrowear53 is carburizing grade steel that will have better toughness and may be suitable alternate.

 

[metman]

mewhg,

Is the carburized case for wear resistance or is it for tensile/bending stress fatigue resitance?

If the case is not needed for wear resistance, you should check fatigue propeties of maraging steel which is excellent. There is a grade 300M maraging steel(not to be confused with M300 (Modified 4340 which is also high in fatigue resistance)with YS of 300ksi. Shot peening can also be applied to the maraging steel. Although I have not heard of carburizing or nitriding maraging steel, maybe an option. Comments?

 

[tbuelna]

mewhg,

If you can provide some additional detail of how your part is configured, how it is loaded, and precisely how and where it is failing, then it would be easier to make some effective recommendations.

Double vacuum melt steels, changes in your shot peening procedure, using a double quench and temper with sub-zero stabilization, or using a different type of case hardening process and alloy, all might be effective but each may only be suitable in certain situations.

Good luck.
Terry

 

[QTAPP]

Hi mewhg,

While there is no strain controlled fatigue data currently available for Ferrium C61, the alloy has been used in the SCORE OFF-ROAD 1/2-1600 Series as a replacement for 9310 VW 091 ring and pinion sets in the gear box. In this severe loading application, C61 has shown an increase in component life of ~3x compared to 9310.

-Chris

 

[mfgenggear]

word of caution to mewhg

changing material may not be the solution, be very carefull
about what material change there is.

In addition to the other good sugestions I would recomend
using AMS6265 (9310 steel). I do not recomned MAR Aging 300
it is a royal pain in the arse to mfg.

there is not sufficient data given for a better solution.
what heat treat is currently used. if case harden what depth & hardness. is the case depth controlled? what is the stock removal? what is the basic fit, form & function.

what are the other processes specified on the engineering drawing?

changing material is very risky for flight articles that have been in service.

 

[metman]

I do not recomned MAR Aging 300
it is a royal pain in the arse to mfg.

Yes it is tough to machine but if its performance solves the problem, maybe that is the bullet they need to bite. This is why it has such excellent fatigue properties because it is just plain TOUGH. We used it in a similar situation where we could not change the geometry until years later and needed an interim material solution. It was not a final solution for every customer but provide 3X life for users who had the most severe service applications.

...risky for flight articles...

Maybe I missed something but I did not see anything about flight articles from the OP.

Yes inadequate info given!

QTAPP, What is Ferrium C61? This sounds interesting. Can you provide a link?

 

[unclesyd]

I'll answer for QTAPP, look at the post by RP Stress(1/10/10) as I was about to ask had he used the Ferrium C89. This material is listed specifically for rolling contact fatigue.
The post by RPstress list Latrobe Steel as a source and here is the manufacturer

http://www.questek.com/producthead.shtml

PS: Their knife material is very good.

 

[RPstress]

Unclesyd: no! Sorry. Ferrium S53 is on our list for secondary structure hinge pins as it will give a smaller diameter than Custom 465, but we haven't had a chance to specify it yet. However, Ferrium C69 isn't of that much interest to us in airframe. (I'm assuming C89 was a typo.) I only mentioned C61 because its manufacturers specifically compared it favorably to 9310 in fatigue. (QTAPP's actual example indicates that just maybe they're right to do so.)

 

[mewhg]

Thanks for all the replies........

The part is partially splined and about 3/4" diameter. The splines transmit some rotary motion but sometimes they are loaded longitudinally. Its the longitudional loading that is causing problems as the splines are not very long and they are fairly tall.

Currently the part is vacuum carburized with surface hardness of R15N 89.5 (RC50 of .015"), cryo treated, double tempered and the spline area shotpeened.

I looked into Ferrium at one time but the heat treatment was over $2,000 per lot and I had to send it to an approved heat treater.

The part does need 'some' wear resistance and a surface hardness of 57-60 HRC should work even if the steel is not particulary wear resistant.

The AQ grade of steel is a VAR steel. The part is not for an aircraft.

The 300 Maraging steel sounds interesting. Is there a specification or trade name?

thanks again

 

[TVP]

The only specifications for maraging steels are aerospace (SAE AMS, etc.). Allvac, Cartech, and Latrobe all produce maraging steels. You can obtain datasheets using the following links:

VascoMax® C-300 and C-350

http://www.alleghenytechnologies.com/allvac/pages/PDF/tech/VascoMaxC.pdf

NiMark® Alloy 300

http://www.cartech.com/techcenter.aspx?id=1698

Marvac 300

http://www.latrobesteel.com/assets/documents/datasheets/Marvac_300.pdf

 

[unclesyd]

RPstress,

Yes, C89 is a typo, it should be C69. Too high of a screen resolution on a small monitor for these old eyes.

Appreciate the heads up on the Questek alloys.

 

[mfgenggear]

mewhg

verify existing parts

I would recommend a deeper case, .020-.025 effective case depth.

test the case hardness on an actual part, and see if it really is 60 min HRc at the surface.
core should be 33-43 HRc

check for any de-carburize or oxidation

my forte is manufacturing, however I know what to look for.
premature failure could be attributed to manufacturing
practices.

How ever if it's a bad design not much will help.

9310 steel is use with good success.

problems with steels such as mar aging 300 is only a very shallow nitride case depth can be achieved. .005-.007
on the aging it contracts I believe it was .0015 in/in
the stuff is hard to gear hob or shape because it's so tough. cost will be through the roof.
if it is not simple geometry the stuff has to be turned, milled & gear cut before aging & nitriding.
if you grind any gears, diameters after nitride the case may be removed or be to shallow.

any other material chosen cost & reliability must really be considered. my above is actual experience.

most materials chosen for gears that I have worked with work very well, 9310, 4340M, 17-4ph, 15-5ph, aermet 100 was
very good but very expensive material, aging 300 is also very good but material cost was high difficult to work with.

 

[metman]

Changing geometry of the part is not an option.

To reiterate. We had the same situation and yes the cost for Vascomax C-300 (thanks TVP) was sky high at $750 per part twenty years ago but this was a 4 inch diameter splined shaft X 2 feet long whereas you have only 3/4 inch diameter. Therefore your material cost is comparativley minimal and hobbing of splines will not be prohibitive with so very little material to remove.

We did not surface harden the C-300 but you might be able to get away with nitride and no grind if you really need the wear restistance as it seems like you are faced with some axial sliding of the teeth.

TVP -- Without adobe/acrobat I cannot download the links you provided and I have forgotten. What is the hardness of the aged steel? Maybe enough for mewhg's application? It seems like the Hertzian stresses would not be a problem with so many teeth on splines sharing the load thereby reducing contact stress. The material we were replacing with with C-300 was AQ VAR 4340 polished radii, shot peened, deep carburized case, Q&T more for max strength and fatigue resistance rather than wear resistance because we were driving thru a CV joint which added bending stress along the axis added to bending stress at spline roots plus torsional shear stress. This complex stress pattern resulted in fatigued shafts looking like an exploded cigar trashing $40,000 gear cases.

Its the longitudional loading that is causing problems as the splines are not very long and they are fairly tall.

This difficult to visualize. Can you explain further or sketch laoding?