MINIMUM CARBON % TO GUARANTEE SCUFFING RESISTANCE

[ibf]

Does anybody know what could be the minimum C % on a HSLA steel used for through hardening gears (8 in. thick rim)in order to guarantee not only hardness range (310-350 BHN through hardened) but also to be scuffing resistant ? I know that I can easily achieve that range of hardness, as well as improve hardenability and weldability by increasing other alloy elements and by reducing carbon. However, that`s my metallurgist state of mind. The gear designer , on the other hand, does not want to give up carbon because of its "self-lubricating" properties when gear teeth go through mesh with pinion. Today, we fabricate those gears out of 4340 Q & T plates with 0.30% C min. Also, I would appreciate if you could suggest a literature that reffers to C% as an anti-scuffing recommended element (I did not find it on AGMA standards).

Thank you.

 

[Carburize]

Ivo

I don't think there is any relationship between carbon content and scuffing resistance in alloy steels. If you change to a cast nodular iron gear then perhaps some benefit may be observed due to the lubricating effect of the free graphite???

 

[diamondjim]

If your metallurgist meant
nickel or lead might have some
anti scuffing qualities, I would
agree. Have never seen any reference
to carbon having anti galling or
anti scuffing qualities.
I think I have seen some references
to boron having anti scuffing qualities.
Can you have the gear designer site
his references?

 

[NickE]

Both the above posts are correct. AFAIK (as far as I know) 4340 is not anHSLA steel. 4340 is a low alloy deep hardening steel commonly used in the application you describe. In these steels with carbon <1% there is definately not any free carbon available for lubrication, It is all tied up in the carbides.

The HSLA steels I've seen have relatively low strengths compared to the 4xxx alloys. In fact generally the ones I've seen are sheet material for stamping, have yeilds no higher than 80ksi and tensiles up to 20ksi> the yeild. Carbon content is generally restricted (in the drawing steels) to less than .13% and wont through harden at all....

IF you were to go to a hypo-eutectic casting , (as carburize noted), then there would be free graphite available for lubrication.

nick

 

[Metalguy]

Any reasons why you don't use a case-hardened gear?

 

[metengr]

ibf;
This article may be of interest to you related to reducing gear scuffing

http://www.geartechnology.com/mag/archive/rev1102.pdf

 

[ibf]

diamondjim; The only reference found to substantiate that statement is : "Modern Gear Production" by H. J Watson - PAGE 60 item 4.2.1 (Pergamon Press - 1970).

Carburize: I am in fully agreement with you and f.y.i, we also design gears made out of ductile iron when possible (it depends on service factor , rpm , H.P of the equipment, .... and so on ).

Nicke: Our Pinions are usually carburized in order to take the advantages you have mentioned. Our gears, on the other hand, are fabricated in segments (2 or 4) due to their size (38 to 40 feet in diameter).

 

[NickE]

Oh my those ARE really big gears.... Ahh I see mining after your name. What school did you go to? What mining company/ore are you after....

(just chatting now, I really have no other help for you.)
nick

 

[ibf]

Nicke: give me a call when you have time - 610-264 6046

Metengr : Thank you.

 

[diamondjim]

ibf,
Have you looked into long and short
addendum gears to reduce the scuffing?
Also called semi-recess action gearing.

 

[ibf]

diamondjim: Sorry for the delay in answering your question. Yes we did.

 

[unclesyd]

ibf,
I don’t think that you can get a definitive answer to your question concerning carbon vs scuffing except for specific steel. You might be an work up a relationship up to 0.65% C, but then the whole thing will probably get murky even in alloy steels, unless you are talking carburized case. I think the best correlation would be by looking a machineability and possible surface finish on a particular steels. They are just too many variables in the equation concerning wear on gears.

We used Austenitic Ductile Iron with great success running against flame hardened CI and carburized case steel straight cut spur gears. The results were varied with DP's below 4.5 (4'' OD), but above 4.5 the biggest factor we found influencing scuffing was the lubrication. If we didn’t have the proper lubrication package we essentially got scuffing, then wear no matter what the combination of materials. The secret was that the lubrication had to be heavy on the EP additive plus a dry film package. Tackiness was also an attribute, but was frowned on by operations due to the lubricant finding the leaking seals and gaskets.

 

[ibf]

Thanks unclesyd. Please see above the sizes of my gears : 38 to 40 ft. in diameter. That kind of eliminates A.D.I & case hardening. I just want to know if there is any info other than the one I gave to diamondjim in April 22(see it above) , as far as carbon % vs. scuffing is concerned ? If I could use less carbon (less than 0.30%), weldability during fabrication would improve but scuffing resistance would be impaired as per mentioned literature. It is not an easy task to modify something of that order of magnitude ! That`s the dilema. NOTE: We are aware of the important observations you`ve brought up on lubrication.

Thank you.

 

[unclesyd]

OOOP'S,
Have you looked at Astralloy-V material? If not, you might give them a call as they were quite familiar with large segmented gears. As I've mentioned in previous posts we have used this material for both it's toughness and wear resistance.

As NickE stated the 43XX alloys above 4330 and below 4345 can give good wear resistance for gears. The application of this family of alloys for gears is supposedly optimum at 4337.

 

[ibf]

Yes, actually ASTRALLOY represents our French supplier in the USA.

Thank you anyway.