What kind of heat treatment do steel frames go through?
 

I can't find this anywhere. I don't care which type of steel it is; I just need an example. I want to know what type of heat treatment is done to any particular frame and why. For example: are all frames annealed, water quenched, or maybe tempered? Any help would be appreciated :)

None at all, usually.

Steel frames are not usually heat treated after being built. The tubing can be treated during the manufacturing process to obtain certain physical properties. For example, Reynolds 531 and Reynolds 753 are the same alloy, but 753 is heat treated in order to improve ultimate tensile strength and yield strength. Overheating 753 tubes while brazing can compromise the improved strength obtained during heat treatment, so when 753 was being produced Reynolds had framebuilders "qualify" by silver brazing samples for analysis before Reynolds would "certify" them and sell them 753 tubes.

With the advent of air-hardening steels, the heat from brazing or welding the tubes actually strengthens the steel in the heat affected zone, so that kind of certification is no longer required.

So the air hardened steels are heated just from welding alone and then cooled by air temperature, making it more ductile at those points?

Mu understanding with air hardening steels is after the heat cycle of welding (and brazing might not be a hot enough cycle) is over the resulting HAZ is harder, less ductile and therefore of a higher strength. Andy.

I'm not a metallurgist, but Reynolds 853 is one example of air-hardening steels used in making steel frames. From the Reynolds website, here is the description of 853.

853 remains ductile in the weld areas with minimum elongation of 10%.

One of the main reasons frames aren't heat treated after they're brazed or welded is there is a high risk of warping. Cold setting is virtually impossible with heat treated tubes.

http://i32.photobucket.com/albums/d7...nformation.jpg

So the welding is heat treating it. What about all the other steel frames that are welded? How is this different?

If you're talking about chromium-molybdenum, normally the butts have greater wall thickness to compensate for strength lost in the HAZ due to welding heat.

I'm talking about the reynolds 853. It's made from "seamless steel". First off, why is it welded if its seamless? Also, the only heat treatment it gets is from the welding? I just don't get the difference between this and the other steel frames.

OK, 853 is seamless. It's welded when the top tube is welded to the seat tube, when the seat tube is welded to the bottom bracket shell, when the bottom bracket shell is welded to the down tube, when the down tube is welded to the head tube, when the head tube is welded to the top tube, and when the seat stays are welded to the seat cluster and the chain stays are welded to the bottom bracket shell.

And no, 853 is heat treated by Reynolds before being shipped from the factory.

Like was said, tubes are heat-treated in the factory to make them stronger. This way they can be drawn thinner & lighter (and more flexible) while maintaining sufficient strength (i.e they won't bend permanently easily). This may make them harder to cut and file.

During the brazing operation some heat-treating occurs. Here is a set of articles:http://desperadocycles.com/Lowdown_On_Tubing.html Check out part 4 by Marco Emilliani. In short, in a silver brazed joint the tube is tempered up to ~1 cm from the joint. A brassed joint retains its strength (it's normalized), but is tempered in a region ~1-3 cm from the joint. Regarding welding, you can check here: http://www.bobbrowncycles.com/eng.htm#section2 The region affected is shorter and the loss of strength is comparable to brazing.

Nice thread and links, Brian

So here comes one to help out with understanding :-)

As a general rule, steel frames undergo no heat-treatment post-manufacture as already noted by my esteemed peers, but there are always exceptions that demonstrate the rule.

Several tubesest are intentionally heat-treated before shipping though, and usually described as such. Most of these are company-specific drawn 4130 steel tubesets. Additionally, all the 'air-hardening' steels are given a proprietary heat treatment to put them in a state amenable to the transformation they are intended to undergo during welding. It's complex to explain thoroughly, but essentially it's a very special type of brochure bull****. Airhardening is a subjective term, nothing more, as both I and Warwick have discussed in previous threads. Many steels that aren't thought of as high alloy will still airharden in the section thicknesses bike frames are made in. It's entirely the wrong term, but the bike industry latched onto it and it's like a canker now. What they really mean, if anything, is secondary hardening, because that's mostly what happens in the HAZ. But anyways....

4130 itself is considered 'airhardening' in <0.8mm sections - I've made reproduction 16th century samurai armour from 4130 sheet in 1mm thicknesses and as supplied, officially 'normalised', it's well over 700 MPa UTS, which is much higher than bulk normalised 4130. Admittedly it's subsequently been hardened to about 540Hv, but that's by the by ;-)

There are steel frames that get postweld heat-treatment, the DMR 898 as an example. But they are in a very small minority. I did my DMR Trailstar II, and she's like a little tank now, and the 0.1mm wall thickness lost to scale* has made her just a little bit lighter, too :-)




*Yes, I was expecting it and prepared for it. It's actually made her ride just a little more whippy :-)




Also, 10% elongation in a precipitate rich steel at 1500MPa UTS is a huge amount.