I appreciate there is a ton if detail that could be added. I had hoped someone with knowledge might be able to say “well its unlikely to go over x°C so it’s OK” or “the rate of cooling will be around y so its ****ed” or similar but it seems bike-steel metallurgists don’t hang put here and I’ll need to do what maths I can and/or do a test piece, or 2, 1 to hit with a hammer, the other to ride if that doesn’t shatter.

Or speak to tubing manufacturers.

Anyway irelanst, the kiln is full of air, not purged with anything.

As per OP, it’s non heat treated steel I am asking about-will it lose its strength? (assuming that heat treated would do so).

I’m no metallurgist but mild steel at 800 deg in air is likely to oxidise significantly, I’d have thought. Also, 2 mins really isn’t very long so I’d have thought you’d have very uneven heating of the frame. Thin bits and those in contact with hot surfaces would get much hotter than thick bits.

cooling curves

Right, I’m not in the office so that’s a googled cct curve for 4130, not one from an asm handbook etc. the letters on there correspond to austenite, ferrite, pearlite, bainite and martensite, different phases with different properties, some tougher (less brittle), some stronger. The curves through the phase fields correspond to cooling rates, different rate = different final structure.

It varies a lot. 2 minutes in a kiln isn’t a lot to go on. Are you taking it straight out into a cold workshop? Cooling it in the kiln by letting colder air in? Letting the kiln cool slowly?

As for strength, you’re after tensile strength and toughness, so probably a bainite, maybe a tempered martensite.

Heat treating isn’t the only way to strengthen a steel. If the tubing is cold drawn then it’ll gain strength from work hardening, if that’s the case then h/t will soften it (which will have already happened around the welds at a slight distance, but the welds and has will actually be harder because of the rapid cool). If the tubing was hot formed or annealed then it’s already soft.

HeadingSouth, MEng, CEng MIMMM, Senior Metallugist. Btw most of the other answers are good, the question isn’t.

If I were the OP, the main thing I would get from this thread is that the lack of detail (as illustrated by the number of questions being asked) is the problem, rather than whether the frame will be ok or not. Without the specifics being asked for, the outcome is unknown. If you can find the answers to these questions and work it all out then you can make a decision based on the result. If you can’t do the working you have to assume the worst.

I would suggest that if you are able to do the calculations to a level where you would trust a loved one to ride the frame then it’s good to go. If you can’t, why take the risk yourself?

I can’t add anything to the actual question as it’s not something I would ever need to do, so I’ve never looked into it. I would take the same viewpoint as Mr Shand, I wouldn’t want to ride it without some evidence that it will be unaffected, not just ‘should be ok-ish’

If you are simply after a ceramic coated frame I would look into coatings that can be sprayed. I know Rody @ Groovy Cycleworks does quite a lot of ceramic coating and seems very methodical with his work so would trust his method (which is sprayed then a low temp bake I believe)

Matt

So I think we have a conclusion 🙂

You have probably the most experienced and educated set of respondents possible (from the ones I know you’ve got metallurgists, chartered mech engineers, structural test engineers, physics lecturers, framebuilders, engineering students plus others – including some combinations of multiple disciplines).

Your process is nothing like regular heat treatment (in terms of time, atmosphere, control etc) – so nobody is likely to have 100% direct experience of what will happen – hence all the questions required to make an educated judgement.

The temperature is well within the region that causes major changes in all types of steel – so something is very likely to happen.

Expecting somebody to say – “yeah, from my experience it’ll definitely do X” is pretty unrealistic. Sorry.

Can the supplier of whatever it is you want to do not answer these questions with more certainty than any of us?

Cheers…no one (as far as I know) has done this before, which may mean its not do-able, but not necessarily.

Headingsouth I have already said (at least once) the frame would go from room temp, into the kiln, 2mins, then out again to room temp to cool, so please don’t flame my question when you’ve not even read it properly.

I don’t doubt it would be easier for you all if I just gave up! I guess I’ll need to do the research and try and work it out, or ask tubing manufacturers.

But as described there are far too many unknowns. I suspect tubing manufacturers would be similarly vague, if not more so since they probably wouldn’t want to risk something bad happening and the finger being pointed at them for giving advice.

If you can’t define the problem more precisely then there’s probably no alternative to doing an experiment as others have suggested.

I am asking about-will it lose its strength?

See I’m not convinced that’s the right question, after all steel has plenty of ‘strength’ for you to play with. I’d be more concerned about making it brittle or some other effect.

Is the frame even going to see 800 degC? Frame goes in cold, then what happens how is the coating applied?

Surely the company doing the coating can provide some advice?

Simples – you want to be a pioneer: do it, ride it, post it

Just wondering if the coating will act as an insulator to stop the steel itself from getting as hot? And it will also presumably increase the time taken to cool down? If this is the case no-one will be able to offer too much insight as you are venturing into the unknown in terms of the actual heating and cooling curves

room temp, into the kiln, 2mins, then out again to room temp to cool

room temp of an office or a workshop where the frame’s been sat at near zero overnight and then slung straight in the kiln?

Based on steels thermal conductivity, and the relatively low mass in relation to surface area, it’s likely that the majority of the frame will reach 1100k when in the kiln.

Since it’s 853, and cooling will likely be as mentioned in my earlier post, it’s probable that you’ll maintain the Baininte crystal structure of the material.

The problem you may have is that by raising the temperature of the frame to such a high degree (beyond most heat treatment levels) and because you’re doing so in an oxygen environment, there’s a chance that you’ll force the material into the Austinitic phase. If this happens the frame will not create a self protecting oxide layer on the surface, but will form slag, effectively removing/reducing the carbon content from the material, thereby leaving you with a type of exotic iron…

If the heat treatment could be kept below 1000k, this should eliminate the problem.

I’ve said twice I think:

IT IS NOT 853

I had presumed heat treated tubes are more likely to lose strength.

I think you are getting confused and confusing others by mentioning 853 and heat treated steels, when all you have is bog standard un-treated 4130?

You are still thinking about it wrongly, strength for steel isn’t a huge issue, embrittling welds, causing sever oxidation or some other type of degradation is more a concern IMO.

So answer this:

1) What is the coating?

2) How is it applied?

3) What type of items does the company normally coat, and are they typically welded?

Just get it done, and see what happens. We are British!! This is what we’re good at

From OP:

So will non heat-treated steel be OK?

Love how so many who are flaming me for a lack of detail skim-reading themselves?

The company I’ve approached don’t do anything with load bearing structures or welded steel AFAIK.

Are you reading ANY of what I’m typing?

By heating to 1100k, you’re likely to decarbonise the frame. To what degree depends upon the carbon content of the steel, the oxygen content of the Kiln and the total surface area.

It won’t work….

carbon content for 4130 is nominally 0.30%

See link 4130 Alloy properies

At 800 degC you are sitting around the Hot work temperature of the steel.

TBH I just wouldn’t bother and send it to Argos or someone to coat normally.

Daffy, I’ve read everything, just not had time to consider/read around enought to understand.

Your post did seem the most relevant, reasoned posts and I did mean to mention that, sorry.

There endeth the thread

😀

Merry Xmas everybody!

There endeth the thread

Merry Xmas everybody!

if you wait until tomorrow there’ll be Three Wise Men along who might be able to offer advice?

I’ve been waiting a few days, 3 could come at once!