[Closed] "Any metallurgists/framebuilders in?" II (al's not giving up)

Sounds like you are quenching it to me. High temperature and quick cooling. It's not a cycle I'd treat anything too unless I wanted it hard and brittle.

What are you trying to achieve? Stress relief?

Also what is the base material and filler wire?

Nothing like getting your own information - I'd make (at least) a couple of test samples.

2x 300mm (?) lengths of basic 28.6mm cro-mo seat tube.

2 bits of steel plate.

Tig weld each tube to a plate to give a base / something to clamp down.

Put one through your coating process, keep the other as a control sample.

Do a controlled bending load vs deflection test on each up to failure. I'd use a servo hydraulic actuator to get a consistent rate of loading but I guess that option isn't open to most people. Plot the load-deflection graphs to find the yield and ultimate loads. This would give some basic information regarding annealing, embrittlement etc.

If doing it properly (ha ha) you would really need to test a bigger batch of samples to allow statistical / weibull analysis of the results.

And maybe then some impact / fracture toughness type tests....

And then different tests with more batches of samples to investigate fatigue performance.....

redddraggon - Member

Sounds like you are quenching it to me. High temperature and quick cooling

It's the same cooling as brazing?

Al,

that frame is going to have a wall thickness of about 0.5 or 0.6 in the middle of the main triangle. You're going to be heating it up to a bright cherry red for 2 minutes. It's stupid. But I'm sure you'll keep asking the same questions until someone tells you to go ahead. Whether it's been tig welded or brazed makes no odds.

You're heating a thin walled steel component to 800c then air cooling it. Because it's so thin walled, it will cool really quickly. So yes, you are basically quenching it.

You sound like the mechanical engineers I work with. They ask me questions, and ignore me when they don't hear the answer they want to hear.

It's the same cooling as brazing?

Brazing and welding only affect a small area at the ends of the tubes, and the ends are thicker for a reason. Like Mick says, do some proper tests if you actually plan to ride this bike.

What on earth are you doing, anyhow?

You're going to be heating it up to a bright cherry red for 2 minutes

No he isn't.

I'm not sure how hot steel tubes would get in air at 800 degrees for 2 mins. But I think we can rule out 2 mins at 800 degrees

That's why the test sound like a good idea

Or even just try an infra red pyrometer on a bit as it comes out of the oven

Infrared pyrometers are a waste of time.

OK so how would you measure the temperature a piece of steel

I'd put money on it not being cherry red as it comes out of the oven

I use a thermocouple. IR pyrometers can be 100s of degrees out.

I just want to see the frame sized oven that goes up to 800c that Al's building in his spare bedroom.

But I'm sure you'll keep asking the same questions until someone tells you to go ahead.

Go Ahead - It'll be awesome and I can say so cause I'm and engineer and have built 2 frames*!!!

*out of carbon and have no metal/heat treatment experience 😉

No he isn't.

I'm not sure how hot steel tubes would get in air at 800 degrees for 2 mins. But I think we can rule out 2 mins at 800 degrees

That's why the test sound like a good idea

Or even just try an infra red pyrometer on a bit as it comes out of the oven

In a previous conversation, he told me the frame needed to be heated to 800ºC for 2 minutes. I agree putting it in an 800º oven for 2 minutes isn't the same thing. I don't know if he know this.

Assuming it's in the oven long enough to reach 800°C then what is the oxidation rate going to be? Those thin wall sections in the middle are going to be wafer thin in no time at all.

Have you bought one of these Al?

[img] [/img]

Maybe the idea is to make ceramic-coated rust?

From memory, and in an Argon heat treatment oven (to avoid Ben's critique) thin walled steel parts cooled from 1200k to 400-450k in around 20-30 seconds. The remaining 150k took a decent while longer.

It wasn't quite the same result as oil or water quenching as we still saw some bainite formation, whereas with quenching it would've been almost all martensite.

shandcycles - Member

Al,

that frame is going to have a wall thickness of about 0.5 or 0.6 in the middle of the main triangle. You're going to be heating it up to a bright cherry red for 2 minutes. It's stupid

It might be, but I want someone to explain/convince me as to how rather than just say so.. Fancy a go at that?

redddraggon - Member

You're heating a thin walled steel component to 800c then air cooling it. Because it's so thin walled, it will cool really quickly. So yes, you are basically quenching it.

You sound like the mechanical engineers I work with. They ask me questions, and ignore me when they don't hear the answer they want to hear.

See above - if all you can say is "because I say so and I'm right" I'd want a better answer.

Daffy - Member

From memory, and in an Argon heat treatment oven (to avoid Ben's critique) thin walled steel parts cooled from 1200k to 400-450k in around 20-30 seconds. The remaining 150k took a decent while longer.

It wasn't quite the same result as oil or water quenching as we still saw some bainite formation, whereas with quenching it would've been almost all martensite.

Cheers!

shandcycles - Member
In a previous conversation, he told me the frame needed to be heated to 800ºC for 2 minutes. I agree putting it in an 800º oven for 2 minutes isn't the same thing. I don't know if he know this.

I'd hoped the fact I'd posted this thread would answer your last comment quite clearly 🙄

So can anyone think outside of their box and answer/explain?

What was the final tempering temperature of the material? What are you trying to do with the 800°C???

Dunno, it's basic non-heat-treated cromoly (yeah I can/could look it up, at work just now)

Your asking the question the wrong way around IMO. You should be working out what properties you need from the material in the final condition, look at where the material is now, then design the process to take you from material now to where you want to go.

Some info below robbed from another forum, who know's if its correct:

Yes, for 4130 you heat, quench (to harden), heat, air cool (to temper) to heat treat it, and yes, this does result in a raised yield strength (the amount of force applied to a section before it gives), but no, it doesn't change it's Young's modulus (which is roughly the same for all steels), in other words, it's stiffness is he same.

If you do not heat treat the part after welding, the main sections will still have the roughly 72Ksi yield, which is really only marginally better then cold rolled mild steel at 69Ksi (and when you look at acceptable ranges you'll find that they actually overlap, so real world, the 4130 could be lower), but around the weld joints it will self quench resulting in narrow areas where it is hard/brittle and not tempered, where it will be prone to shattering into sharp pointy pieces. Attempting to normalize it in sections usually results in just moving around the hard points unless you can manage to get the whole structure over it's critical temperatures (around 1700* and then 1200*) at once.

It might be, but I want someone to explain/convince me as to how rather than just say so.. Fancy a go at that?

Sorry Al, I don't know why. What I know is that if I heat a 0.5mm downtube up to 800ºc and hold it there for a couple of minutes then I'm pretty sure that frame will break. I certainly wouldn't ride it.

I know you're looking for specifics and I'm not able to provide them for you. There is a ton of info out there for you to read but without knowing what steel alloy you have, wall thicknesses etc it might be hard to get actual data.

There's some really good (basic) info on this in the 'Machinery Handbook'. I'm sure there's better and more up to date information available too.

Would an email to Reynolds answer your questions?

Cheers Steve, I accept your position, you will no doubt that I want to find the facts tho!

dragon - Member

Your asking the question the wrong way around IMO. You should be working out what properties you need from the material in the final condition, look at where the material is now, then design the process to take you from material now to where you want to go.

Not possible unfortunately!

If you do not heat treat the part after welding, the main sections will still have the roughly 72Ksi yield,

Brant said recently that zero/few frames were heat treated post-welding.

I guess I could email Reynolds, I guessed they'd ignore me thinking me a time-waster!

Al,

I've just emailed you a tech doc from Reynolds, I'm not sure it sheds much light but it might be useful. I'm not sure if that doc is supposed to be in the public domain so I'd appreciate it if it wasn't shared.

I think (though am an Engineer not a metallurgist) that you're over thinking this massively. There's a lot of talk ^^ about normalizing, tempering, quenching etc. Most of this is more related to base materials that you use rather than welding.

I suspect what you really need to be doing is a heat treat post welding to stress relieve. The material condition post-welding is not nearly as much of a concern as the residual stresses that remain in the material after a welding operation. Stress relieving is controlled by time and temperature. As a general rule you want to stress relieve at <50°C below the final tempering temperature of the material batch supplied (you need mill certificates to work this out).....as a guide the temperature you're looking for is probably closer to 550-600°C MAX for ~4 hours (the longer the better), rather than 800°C for 2 mins. As others have stated 800°C for 2 mins is more akin to hardening (embrittling the material). 800°C for longer duration's of time could result in normalizing the steel....you would then need quench and temper to get the strength back - this is the sort of stuff that happens at mills not fabrication workshops.

Oli.

Per above....it's not the 72ksi yield you need to be concerned about - it's the 30-40 ksi residual stress around the heat affected zones (caused by welding) that results in early failure. You therefore need to stress relieve - not temper, quench, normalize or anything else that people have mentioned.

Oli.

Just to provide context. This isn't about welding, Al has an old frame that he wants to coat (ceramic? enamel?) I can't remember, and the process requires the frame being at 800ºC for 2 minutes. He wants to know if this will weaken the frame to an extent that it will effectively be unrideable.

And yes, everyone is overthinking this massively 🙂

What's the coating? 800°C for 2 mins could be an HVOF spray (probably fine), a spray then baked (maybe not fine) or a surface treatment (again probably not fine).

If it was mine.....I'd just get it powder coated for like £20 cash!

Oli.

I can see the need, I'm sick of getting baked on lasagne off my bike.

cynic-al - Member

I guess I could email Reynolds, I guessed they'd ignore me thinking me a time-waster!

Shirley not. Whyever would they think that....? 😀

I've had a few exhaust manifolds/downpipes ceramic coated (rally cars/fast road cars) to help in under bonnet/transmission tunnel heat control issues but i can't see the point in getting a bike frame done this way - it's not really the type of finish that i'd desire in a frame. I'd get a good quality powder coat done by someone who knows what they are doing (bencooper knows a good one)

Sounds like a lot of work/expertise without knowing why. Maybe you should hire a metallurgist for your boutique frame business rather than asking a forum?

Errr isn't a ceramic coat going to crack if there's any flex ?

Im sorta with soma funk on this - a quality powder coats lovely and pretty much normal...
ceramics fine if your attempting reentry.

I've got a copy of Bicycle Metallurgy for the Cyclist in the shop library - if I remember I'll bring it home this evening.

There are some people doing some kind of ceramic coating on frames - only in the States I think, and I don't think it's a baked on finish.

So can anyone think outside of their box and answer/explain?

If you want factual answers then give facts to base them on! I've read cookery books which give more information than your description of the heating process 🙂

Forget the hypothesising - Go measure on a bit of tube. Exactly how hot for how long? And what is the actual rate of cooling? Make some graphs. If you are serious it isn't that hard.

£20 buys you a 1.5m thermocouple which could be run out of the oven.
http://uk.rs-online.com/web/p/thermocouples/7877841/

£12 buys you a K type digital readout from ebay.

And when you're done you can whack it with a sledgehammer to at least see if it is still ductile and vaguely safe.

If you were armed with some facts and specific questions then I'm sure Reynolds would be approachable. Same for Columbus. Or go to Bespoked next year and talk to Engineers from them both face to face.

To be honest people have been pretty patient - the stw graphic designers get much snottier about giving work and information foc.....

It's not ceramic.

Cheers Ben.

Mick it is literally going into a kiln at 800°C for 2 minutes then coming out (that kiln being at the he other end of the country). I don't know how much more specific I can be.

What exactly do you want to know, I assume how hot will the frame get and what metallurgical effect there will be?

There are still an awful lot of unknowns for people to even attempt to give an answer, I’m not a metallurgist, but I did spend 15yrs designing furnaces so know a bit about heat transfer. So I may be able to help on that part of the problem given some more information;

What are the dimensions and construction of the kiln? What is the configuration of the heating elements? Where will the frame be positioned inside it? What will be supporting the frame? Surface area of the frame? You would need this to calculate the form factor to determine the radiant and conductive (from any supports) heat transfer.

What is the control strategy, zoned? cascade control? Both have a huge influence on how the kiln responds to a cold load being introduced.

What is the coating you’re putting on? What’s its SHC, its emissivity, its latent heat of vapourisation?

Is the kiln purged with an inert atmosphere? If so Argon or Nitrogen based? What flow rate?

What’s the frame material, you mention 853 is it all 853? What are its properties, SHC, Thermal conductivity, density?

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.

[url= ]cooling curves[/url]

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

[i]room temp, into the kiln, 2mins, then out again to room temp to cool[/i]

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 [url= http://www.suppliersonline.com/propertypages/4130.asp ]4130 Alloy properies[/url]

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!

[i]There endeth the thread

Merry Xmas everybody! [/i]

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!