What happens to steel (and ti) if you heat it to ~800 degrees C for 2 minutes or so?

Preliminary research suggests the heat treatment of steel would go, which presumably means its strength would go down to basic 4130…correct?

Depends on the steel Al, which alloy?

I think Ti spontaneously combusts somewhere around that temperature… (seriously!)

Bike frame steel!

Based on your previous metallurgic experiments you’d burn your mouth trying to eat the soup.

Bike frame steel is rarely heat treated.
Exceptions are bmx frames (not uncommon) and 853.

Regular 4130 frames aren’t Heat treated usually.

What does strength mean? tensie strength, compression strength, fatigue strength, flexural strength, resistance to chemical attack, hardness….

brant – Member
Bike frame steel is rarely heat treated.
Exceptions are bmx frames (not uncommon) and 853.
Regular 4130 frames aren’t Heat treated usually.

Hmmm…what about mention of “heat affected zones” in TIG welding and brazing, and use of low-temperature process like silver brazing on braze ons?

Is it all a pile of crock?

edward2000 – Member
What does strength mean? tensie strength, compression strength, fatigue strength, flexural strength, resistance to chemical attack, hardness….

Resistance to breaking I guess.

Interesting, from Curtis’s website:

Chromoly tubing also requires heat treating after any welding or brazing

Mind you they say this also so they must have been smoking crack:

all imported steel frames are made from American or Taiwanese 4130 Chromoly.

Hmmm…what about mention of “heat affected zones” in TIG welding and brazing, and use of low-temperature process like silver brazing on braze ons?

Is it all a pile of crock?

Certainly welding affects frames. Welding is hot. Steel gets melty. Those zones are affected by heat. And those areas are weaker. It’s not really because of the annealing of the parts, it’s because it’s just utterly messed up the steel.

George describes (and understands) it better than I do here – http://www.gsportbmx.com/2004/12/living-in-a-material-world/

Silver solder is used when adding braze on parts to very thin areas of steel like the centres of tubes where wall thicknesses are 0.6 or 0.5mm thick (thin).

Chromoly tubing also requires heat treating after any welding or brazing

BMX frames are routinely heat treated. They are small and fit in the ovens easily. I don’t know of any steel mountainbikes that are heat treated POST WELD.

What happens to steel (and ti) if you heat it to ~800 degrees C for 2 minutes or so?

Bike frame steel!

4130, and the like??

Depends on how fast it cools down: 800 C is probably hot enough to allow the formation of martensite if you cool it quick enough (thin sections, no pre-heat, etc..)

Martensite is really, really strong in terms of tensile strength(really) and as hard as hell. Trouble is, it’s also as brittle as glass and has hopeless fatigue strength.

would it not also cause an issue with corrosion around the weld?

I should really know this, but first thoughts are not a lot.

Not hot enough for recrystallisation, so not “resetting” the structure as it were, too short of a time to really instigate any phase changes or leeching of any impurities or introducing any others.

Again, I should really know this, but can’t remember. Might pop back in my head in a bit.

Don’t know much about ti though.

Great link Brant

Cheers. George is as smart as I wish I was.

A good basic book on this subject is Hardening, Tempering and Heat Treatment (Workshop Practice)

http://www.amazon.co.uk/Hardening-Tempering-Treatment-Workshop-Practice/dp/0852428375

Give a good non technical introduction to the subject but enough no know about the different structure, how rate of heating and cooling effects a material e.t.c.

Dare we ask why 800C and what you are planning to do with the two materials?…..

Some typical melting points from my old Reynolds catalogue:-

Silver solder for Reynolds 753 (which I think was heat treated 531 but could be very wrong) – solder melting point between 600C and 675C with the aim to keep the whole joint below 700C.

Brazing rods for 653, 531, 525 melt range from 850C to 950C.

Brazing rods for induction / furnace brazing of 501 and 500 melt range up to 1100C (but cooler better).

The book is too old to mention TIG welding which will be even hotter (but more localised).

“Joining operations should be carried out in still air, without making any attempt to slow down or increase the natural rate of air cooling. This ensures that the alloying constituents in the steel can do the job they were put there for, giving the optimum grain structure and physical properties after joining”

Also, on hot bending:-

“Setting operations must be done cold. Hot setting can lead to dire metallurgical problems”

The metallurgist at work explained why 531 (and maybe also T45 which I vaguely remember might also be similar Mang Moly alloy) is better brazed than welded (the amount of Manganese acts like having a lot of carbon and is borderline acceptable for welding according to the British Standard).

As I understand it we don’t see 531 much as 4130 (520) has roughly the same properties but is much better for welding

A bit of googling has come up with this sheet

http://www.azom.com/article.aspx?ArticleID=6742

Lots of the heat treatments are described at or around 800oc, suggesting that 2 minutes at 800oc will effect it properties.

From memory (very rusty) you don’t have recrystallise a metal to change its properties. Its things coming in and out of solution in the metal that changes things. For high carbon steel heating followed by rapid cooling gives a very brittle material as the carbon dissolves in the metal at high temperature and then is locked in by the rapid cooling. Slow cooling (annealing?) allows the carbon to come out of solution resulting in a less brittle metal that has a lower yield stress

This has some nice graphs here (but don’t look at the phase diagrams)

http://www.uvm.edu/~dhitt/me124/TensileTestNotes-II.pdf

What happens if you heat 4130 for 2 minutes to 800 degrees

I don’t know but know one will know until we know what happens next. The rate of cooling will effect the answer

PS my 531 road bike was made be sustained heating of the lugs and tubes in hearth and then the braze being applied after the joint was removed from the hearth. I can still see the ends of the nails round inside the bottom bracket shell that held it together during this process

DMR used to do this –

This DMR 898 frame uses our premium Cro.Mo tubing and it is tig welded to our normal high standard, it’s also Heat Treated… but with a difference.
Most good dirt-jump frames are heat treated, but BEFORE welding. This means that the welding process sets up all sorts of stress and strain in the frame that can weaken it and destroy the ride quality.
The 898 is heat treated AFTER welding. It goes through a DMR devised process of heating and cooling, this helps it relax and soothes away all it’s angst.
The result is a lighter, tougher, more dependable, longer lasting and friendlier frame.
‘POST WELD HEAT TREATMENT’ costs more, but I’m pretty sure that you will agree that it’s worth it.
898? 898oC is the temp that helps the frame to relax at the start of it’s therapy. It’s the key to the whole process, then it’s hardened and toughened [we’ll keep those temps secret] making it one of the lightest, strongest and smoothest riding frames that you will ever own.

Not sure if that helps,but it was expensive and they don’t do it now.

mick_r – Member
Dare we ask why 800C and what you are planning to do with the two materials?…..

You may, but I will not answer 8)

The Q should have been “what happens to a bike frame when put in an oven at 800°C for 2 minutes, then being cooled in air at room temperature.

If non heat treated tubes at ok at high temps then then why use silver soder on the thin parts?…is one of many questions I need to answer.

If non heat treated tubes at ok at high temps then then why use silver soder on the thin parts?…is one of many questions I need to answer.

because the metal is so thin, there’s a risk of burning through the tube with a torch at hotter temperatures, so you merely waft it somewhere near and things work a lot better.

Ta Brant, sounds like I’m ok then on that score.

Don’t forget that some of the point of the fancy pre-heat treated ultra high yield strength tubing isn’t related to the hot bit around the joints – it is so you can run thinner sections and / or bigger diameters elsewhere without the tubes breaking, denting or buckling.

Those bits don’t tend to be heated so maintain full strength (or if they are heated it is very localised silver solder temperatures). You are talking about heating everywhere :-)…….

I get that mick r, tho the effect of my process on heat treated steel is yet to be established!

I tend to consider bike tubes to be thicker at the ends, rather than thinner in the middle.
I assume you are doing some sort of cool coating?

“Process” makes it sound very controlled and technical – I’m impressed!

You do know that home made Celotex ovens start smouldering around 140C? 🙂

can’t wait for this – when do we get pictures?

The Q should have been “what happens to a bike frame when put in an oven at 800°C for 2 minutes, then being cooled in air at room temperature.

If you mean the oven is at 800 C and the bike frame is at ambient temperature prior to entering the oven and is then left in the oven for 2 mins one can’t answer the question. The important variable is the steel temperature which may not be 800 C after 2 minutes.

bullroar – Member
If you mean the oven is at 800 C and the bike frame is at ambient temperature prior to entering the oven and is then left in the oven for 2 mins one can’t answer the question. The important variable is the steel temperature which may not be 800 C after 2 minutes.

Well the cool coating would need to get to 800* to adhere, so we can assume the steel will get there too

*ish – need to check details.

The cool coating may need to be at 800 and may achieve that temperature more rapidly than the steel.

If the coating is already on the steel before it goes in the oven it may insulate the steel thus increasing the time for the steel to reach 800.

Does the steel surface also have to be at 800 for the coating to adhere? If so how do you know the steel surface reaches that temperature in 2 minutes? Making that assumption without good supporting data may is potentially risky for both the coating and the steel.

What are you going to make Al?

Top secret bear!

bullroar – Member
Does the steel surface also have to be at 800 for the coating to adhere? If so how do you know the steel surface reaches that temperature in 2 minutes? Making that assumption without good supporting data may is potentially risky for both the coating and the steel.

Hmmm…well you stick the coated steel (or other metal) in an oven at 800 and after a couple of minutes it goes off.