Science question about heating metal

[veryredbike]

Ok, so a bit back I failed in making a fork with some stainless dropouts (pricey ones!) was told not to heat them off and use them on the next one "just in case" even though it never made it past dull red as it's a fork and failures are costly. I have a mild steel crown (the henry james ) that went on a bit crooked (just visible enough to make me crazy) that I'm assuming I shouldn't re-use for the same reason. I also know folks do repairs and keep some of the original lugs, but don't have a good idea of where the line is on that.

This stuff got me thinking... there seem to be engineers and people with materials science backgrounds floating around here every now and again... anyone want to do a brief explanation of what's happening to the steel at different heats? I'm also curious about framebuilder's feelings on the risk of re-use of steel parts.

Icebreaker:

Metal color	mild steel	stainless	heat treated	risks
Just shy of red
Red
Orange
Yellow

Edit: this isn't a "tell me these things are OK to work with, I'll keep asking until you do" thread. I'm resigned to calling them good practice. I'm just curious about how to find the line and what's going on with those crazy steel molecules.

[Mark Kelly]

Ordinary metals approximate a black body under low light conditions, see Wikipedia on Black Body Radiation for a colour chart.

As a rough guide, dull red is just above the Draper point (a little over 500C) becoming brighter red beyond about 600C, increasingly orange from about 800C and yellow is too bloody hot (1500C or so).*

The rest of your chart is too general to be useful; as an example the heat responses of the three most common "stainless" steels used in bikes (cast austenitic steel as used in lugs, 17-4 precipitation hardening as used in machined fittings and martensitic as used in tubing) are quite different from one another.

*I got very familiar with this colour range working on thermionic emitters in valves (= 'tubes' for Septics).

[Clockwork]

What type of light were you brazing in? I always braze in the dark which helps me read the metal color.

-Joel

[steve garro]

IMG_1737.JPGIMG_1522.jpgIMG_4854.JPGIMG_4480.JPGI pay zero attention to the metal color = I read the flux........
- Garro.

[gearheadgary]

I pay zero attention to the metal color = I read the flux........
- Garro.

Can you elaborate? I've just done some frame mods and I had a devil of a time seeing what I was doing.

Is it just when it goes liquid?

[EricKeller]

Can you elaborate? I've just done some frame mods and I had a devil of a time seeing what I was doing.

are you using #5 shade welding glasses? I think my #3 green Ace glasses cost me $75 and are much better to see with.

[Mike Mcdermid]

What are you asking here

rule of thumb by the time metal is red its usually become annealed, ie you have removed its temper and treatment a quick google of annealing will explain ,the temperature at which this happens and also the type and size of the fabrication will affect how this occurs for bikes you shouldn't worry (broad sweeping statement but thats a lot more info) on bigger fabrications for example mixing castings forgings thick parts you need to be more careful this will involve preheat etc

Stainless Steel - Heat Treatment but honestly to fill out any of the boxes in your list is


what lighting do you have in your workshop is a good point lighting can distort your colour perception well its not actually that (ask a surgeon )or look at colour temperature I actually use a gold coated shade 9 tig lense so i can see colour as opposed to green

what steves saying is he doesnt depend on colour as its not as important when he sees the flux do its thing he knows its at the right temperature as above on bigger fabrications which use different techniques again they use a temperature stick like a crayon that melts when its time to do the buisness on aluminium we used to use soap it goes black

Its a big big topic metallurgy of metals and heat more than you could fit in your table

I would reccommend making everything out of inconel

[veryredbike]

Interesting info, thanks guys!

[shirk]

Might be a side topic, but is anyone colour blind? How do you deal with reading colour temp of the metal?

[Mark Kelly]

I can kind of answer that since I'm the only male in my family with normal vision and one of my brothers is so severely affected that he has to remember to stop for the top traffic light.

He's missing one of the three sets of cones the rest of us have, in his case the red ones. He wouldn't be able to see what we call dull red and by the time we said it was bright red he'd see it as a dull greenish clolour. He knows his vision is impaired.

One of my other brothers has all three sets of cones but his green cones respond better to red than they should (and less well to green). He'd be able to see all the red heats but not be able to tell the difference between them - as far as he's concerned he has good vision, the rest of us have too many names for colours and an excessive fondness for stupid dot patterns. This is the most common kind of colour blindness.

Neither of them brazes.

[Andrew R Stewart]

15 years ago i moved to a house that required me to have an outside brazing shop. I got an event tent to protect me from rain and lessen the wind. The white walls and very bright setting really played with my perception of brazing temps. I posted on the, then available, lists for advice and the response was the same as what Steve G said, watch the flux.

So I went back to my basics. When i started out my mentor said the same. Many years of brazing in poorly lit basements limited my learning to but one setting. I refocused my attention and relearned my flux's changes as I heated the joints. For brass with classic blue/white flux this is: The flux first drips off, then starts to harden/dry out, then seems to melt down a bit, then flows out and turns clear. This is the right temp. If it goes dark it's too hot.

Do test brazings helps to calibrate your flux's look. I braze so little these days that I practice/test a few times before committing to the actual piece. Andy

[Imperial Bikes]

We had this poster in the shop for years... Id just walk past it but, little by little I started checking it out and looking up what everything was. Then I bought the book Metallurgy for the non-metallurgist. I learned the basic understanding of whats going on... and that I have so much more to go.

I hope this helps.

http://www.tempil.com/wp-content/plu...rrous_2010.pdf

[Andrew R Stewart]

We had this poster in the shop for years... Id just walk past it but, little by little I started checking it out and looking up what everything was. Then I bought the book Metallurgy for the non-metallurgist. I learned the basic understanding of whats going on... and that I have so much more to go.

I hope this helps.

http://www.tempil.com/wp-content/plu...rrous_2010.pdf

Great chart! added it to my favorites list, thanks. Andy.

[steve garro]

what steves saying is he doesnt depend on colour as its not as important when he sees the flux do its thing he knows its at the right temperature as

Yep - not everything is the same thickness (BB shell, ST, stays or HT/TT/DT so one's red is another's burnt. Get the flux all liquid evenly on all surfaces.
Check my pics for what clear flux looks like, the triple tube one is still molten....
- Garro.

[shirk]

Time to change my learning technique. Watching the flux specifically should be better for me as I am Red-Green colour blind.

[afwalker]

Nice first post Imperial Bikes:)
Great chart
thanks
andy walker