Temperature colours

[Bill DawesParticipant @billdawes]

[Bill DawesParticipant @billdawes]

Hi all, does anyone know if the type of metal affects temperature colours.

In my 50 pus years in engineering I cannot recall researching this, maybe because I have not generally been much involved in the non ferrous side.

Asking the question because my 'googles' for temperature charts don't seem to differentiate.

Bill D.

[Michael GilliganParticipant @michaelgilligan61133]

Bill,

The emitted colour when hot [as opposed to any cold coloration] is "black body radiation" and a such will, to all practical "engineering" purposes, be the same for every material.

MichaelG.

[Les Jones 1Participant @lesjones1]

Hi Bill,
If you are talking about the colours for tempering (Eg straw, blue etc.) I think it depends very much on the metal as the colours are due to the oxide formed on the surface. If you are talking about red heat then I would think it would not depend on the metal as the colour is a function of the wavelength of the radiation at a particular temperature. This is just my feeling on the subject. I have not verified that my understanding is correct.

Les.

[Bill DawesParticipant @billdawes]

Thank's guys, that is the conclusion I came to having looked at various sources, but without finding anything definitive or conclusive.

Take your point about tempering colours though Les.

My question came about by recent annealing of copper by heating to red heat, it set off a train of thought as sometimes happens.

Bill D.

[JonParticipant @jon]

Bill with steels I haven't in 23 years noticed any difference be it weldable quality ms of varying specs, 01, silver steel, CR4, EN8, 9, 32, Vanadis, various spring steels new and old, cfs or dom to name a few. Normally 230 degrees to 280/285.

Stainless steels G303, 304, 316S11 do require a lot more heat to cherry red to achieve similar colouration when cooled. Bit hit and miss.

[Neil WyattModerator @neilwyatt]

The colour is caused by light interference effects that depend on the thickness of the very thin oxide film (same effect as a soap bubble or some beetle's shells). This just involves the iron and oxygen so is pretty much constant for all steels, but it gets thicker with time as well.

This is also why you don't get a proper colour inside the flame, as there isn't normally enough oxygen for the film to form properly

Neil

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