Heat treatment

[fifesjeep]

If I wanted to heat treat a shaft made from 4140 with the major O.D. @ 2.5"... what would be the ideal temp/amount of time and proper quenching method be?... My gears that I tested have a Rockwell of 62 on the "C" scale... So if anything I'd like to match the hardness or be a little under that of the gear...It'll need to handle decent torque loads (I know this isn't the best material to use, but it's all I had). I know I'll have to stress relieve or temper it to bring it down etc... Any thoughts Ideas wouod be highly appreciated...
Also, how much will this material expand after the heat treatment... And how would I compensate for this?

 

[TVP]

The proper austenitizing temperature for 4140 is 845-870 C. The time at temperature should be 30 minutes. Depending on the section size, it may take 30 minutes or longer for the entire cross-section to achieve this temperature, so the total furnace time may be ~ 60 minutes. This grade should be oil quenched, which will produce a hardness of ~ 49 HRC at the surface and ~ 38 HRC in the center. It will not transform to 100% martensite in the center because it does not possess sufficient hardenability for this large of a diameter. Tempering should be performed in order to improve the toughness. This grade is usually tempered in the range of 530-600 C which will reduce the hardness to ~ 30 HRC. Ideally the hardness would be higher, say 34-38 HRC, but since the diameter is so large, it will be difficult to achieve this. Tempering at lower temperatures will not sufficiently temper the martensite and will render the shaft brittle. With regards to distortion, I would be more concerned with dimensional changes to diameters, concentricity, straightness, etc. rather than pure length change. You really should work with a good heat treater rather than try to do this yourself.

 

[swall]

Why do you want to have the shaft hardness close to the hardness of your gears? Normally, this would not be desirable nor acheivable.

 

[thundair]

Where is Nick when we need him?

I have a lot of experience with heat treating 4140
and it will not safely get over R/c 42
If you haven't made it yet I would use 4340 HT to R/c 48 and nitride to 60C
There are a lot of other options for shaft material, I wouldn't lock in on any one until you have all your engineering requirements worked out. Run the numbers it is cheaper then putting something in and seeing if it works..

Cheers

I don't know anything but the people that do.

 

[fifesjeep]

I have no 4340... I had a piece of 8620 which was already used... and 4140 was what I had left or remaining.. I guess I can go yank a pinion out of a 14 bolt rear and full-anneal it and turn the teeth off of it... and then spline it for the output shaft...
On the old shaft and and gear they both Rockwell 62 on the "C"...
So I figured if Iget it close to the original etc.. These aren't running gears.. More or less the shaft is splined and slides in the center of the gear...

Do you guys think that if I heat treat or carbon pack it and then temper, and finally Nitride the shaft that it would be sufficient to maintain for a while...
Let me make note to what this is going to be used for... so you guys can get abasic Idea of what I'm dealing with..
I'm building a Jeep basically a Crawler... Something that won't see more than 30mph.. Maybe... It won't be a daily driver for reasons listed above..
Also the larger Diameter will have the back side bored to 1.760" I.D. so the thickest part on the larger diameter will be 334". (from top of the tooth to edge of the I.D.... and from the root of the tooth to the I.D. is .254" thick).. The main shaft/shank O.D. is 1.6265"...

 

[TVP]

Only the spline section requires the elevated hardness, which could be achieved with nitriding. The rest of the shaft should be quenched and tempered to Rockwell C 30-something.

 

[swall]

Well, since you are determined to use what you have (4140) I would follow TVP's heat treat schedule and be done with it. I might be inclined to back the tempering temperature down to 800F to get a little more hardness and strength, however. Forget about nitriding.

 

[NickE]

Thundair- me Nick?

 

[fifesjeep]

Thanks TVP... I'll do as you said..
Swall... why not have the splines nitrided?... Will it make them too brittle?

 

[swall]

Yes, I would be concerned about fracturing the nitride case with the loading that a spline would see. Keep in mind that nitriding is performed at 1000F and this will further drop the hardness of the 4140. If you really must have high spline hardness, you could consider induction hardening of the splines after you perform the quench and temper of the shaft. But,by then you will have more money in this project than you probably would want. Build it, run it, break it and then come back here for advice on material and processing upgrades.

 

[thundair]

Nick:.. yes you


I use Nitride for wear factor only and because you can get a minuscule growth from it I have saved some under sized shafts. In the long run a nitride surface is the way to go and if you say there is not a lot of tooth load and you are just worried about wear, then you have options to case harden 8620 or nitride 4140..

But I will bow to the experts as all my experience is from the manufacturing side and I am not sure what the books say.

Cheers

I don't know anything but the people that do.

 

[NickE]

Hm... I guess I'm kinda flummoxed that you recommended me. TVP adn Swall are way more experienced.

 

[thundair]

OK Nick I will remember that... Just a name I remember from an earlier response on materials
I need help in that area as I am often running in the dark as I have designed a few PSRU's (power supply reduction unit) for experimental aircraft and I have a feeling that I could manage some of my harmonics inside the transmission with heat treat and variable materials.
I will get into that later I don't want to hi jack this thread....

Cheers

I don't know anything but the people that do.

 

[fifesjeep]

Thundair... Please feel free to talk about what-ever... Now I'm interested in hearing about an experimental aircraft... harmonics... heat treat and the usage of variable materials etc...

 

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Regards

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