4130 Oven Heat Treat

[gbumstead]

I started with a piece of 7/8 O.D 4130 chromoly tube. Had them bent to make a pair of bicycle handle bars aprox 30" width and 4" rise. The bars bent the first day about 7 degrees at the first bend. My thoughts are to heat treat again after the bending process. Things Ive read and heard from fellow small time manufacturers, heat up the furnace, home oven in my case, to about 450-500 degrees F. let bake for 20minutes and then dip in motor oil to seal the heat process. This is a final touch to the handlebars before production levels. I need to know if this process can harden the chromoly just enough to hopefully prevent bending again.

thanks,

G

[EricJergensen]

It won't harden anything, but you wouldn't want handlebars fully hardened. That would make them brittle (subject to cracking and spectacular failure).

 

Most of that process sounds like post-welding heat treating. (Without that dip in oil bit.) It would relieve some of the stress left in the metal by welding (if allowed to cool slowly -- no oil dip). Doesn't sound like that is pertinent here. And, 4130 is pretty forgiving on welding. In most cases it will perform admirably without it.

 

The dip into oil sounds like hardening, but it would only be effective at a much higher temperature. If you heated the metal to its critical temperature (which I think would be about 1480° F) and did an oil quench you'd harden it. Then, if you tempered it by heating it to about 650° F you'd have something useful for suspension springs.

 

4130 is popular for bicycle frames (and aircraft frames) primarily because it doesn't demand heat treating post-welding. You can also get work hardening stress from bending. This 450-500° heating would relieve some of the bending stress but I'd guess a 7° bend introduced next to no stress. (Again, no fast cooling by dipping in oil. Turn off the oven and leave it in to cool slowly.)

 

I'm not an expert in this. My knowledge only comes from basic blacksmith metalworking and some very basic welding.

[Steve Sells]

I explained in the chat today that  tempering does not do anything unless you harden it first, I never saw any home oven  get to 1500F.

what is this about oil sealing heat process? your "process" will not harden anything.  I explained it, and told you where to read for more information, as I refuse to retype all that again, when its just the same effort to you to read the links I gave you, If you wanted to know.  it seems you may do better to hire this out

[Frosty]

4130 chromoly only has 30 points of carbon so it's not going to harden appreciably no matter what you do. 4130 is used in airframes because it doesn't bend easily or work harden. You don't want your Piper's wings to work harden while they flex and light plane wings flex, heck they flap sometimes. 4130 is most commonly used in aircraft frames.

 

Under some conditions of manufacture you MAY want to "normalize" or anneal 4130 but that'd be after some serious movement. Bending a set of handlebars does NOT fall under the same ball park, not even the same town. Sounds to me like this heat treatment is something someone figured out who didn't know diddly in the first place.

 

If you have the bender, make the bends and use it as is. If you have to know specifically call the local A&P mechanic and ask, they have to complete school, pass tests and maintain current certifications. A&P = Airframe and Powerplant.

 

Frosty The Lucky.

[Rich Hale]

If you do make the call Frosty suggested tell them abouit the wall thickness of the material you used and see it that would be wot they suggest.

[doc]

I am an A&P and all though it's been years since I've worked as one (full time smith for years) I'll tell you that the only heat treat ever done to 4130 or 4140 for aircraft was normalizing after welding. Airframes made of these materials were always o/a welded. When the repair or fabrication was completed the entire weld area was brought to a visible dull red heat in normal ambient light with the torch. The torch was then withdrawn from the material slowly until color was no longer visible and allowed to cool to room temp.

 

The heat treat you describe is no heat treat at all and will probably have little or no effect on the material. I personally would wonder if your handle bar was made from 4130 in the first place. Or if your original measurements and post measurements for comparison were accurate. And yes as Rich suggests too thin a wall thickness could be a problem. You can't expect structural strength from the equivalent of tissue paper.   

[gbumstead]

There are no welds on this type of handle bar. No cross bar which can contribute to the bending factor. I had the shop that is bending the bars, over bend the first set of bars 6 degrees and then bend them back to original geometry. I think this will ellinimate most of the problem. I am not trying to get any major structural change from the final baking process, more of a sealant. I read your article and appreciate the insight Steve. Although the Oil dip sounds more fun I can understand the letting cool at room temp if i want the heat process to even remotely affect the material. I trust the company i purchased the raw materials from originally that it is 4130 chromoly and heat treated. I have worked in the bicycle industry for some time and have seen raw chromoly, although steel is very similar. I plan on baking this weekend ill report back with results.

[kerrystagmer]

4130 will harden to 48 Rc when quenched from critical temperature (around 1500f , right when it becomes non-magnetic)

 

It will harden considerably.  More importantly it will change in toughness and the ability to hold form/shape. 

 

Normally 4130 aircraft materials are fully annealed at 32 Rc when purchaced with somewhere around 35,000 psi Yield.  Heat treated they should show around 180,000 PSI Yield.

 

Stress relieveing is more important then tempering as there is no real need to get below 48 Rc for most applications.  400 deg F for 2 hours post heat treating should be fine. 

 

We process around 10,000 lbs of 4130 AV grade stock each year in thicknesses from 20 ga to 1/4 inch.

 

Many people will tell you it is case harden only and cannot be through hardened and they are half right.  It will only harden about 1/8" on each side of the material thickness, so stock up to 1/4 inch will fully harden.

 

You must get it up to a non magnetic state to harden it. 

[thingmaker3]

The notion of steels with less than 0.6% carbon "not getting hard" is one of the won't-die blacksmith myths. Kerry gets it. Read his post carefully. He knows what he's talking about. Don't forget to agitate your oil.

 

Oh, and for "sealing" try an epoxy based enamel. "Sealing" is for keeping out rust! "Heat treating" is for altering material properties. :)