Heat Treat Colors of Steel Chart

Ah, I see my problem now...

Or rather I don't see it...

If you have red/green colour deficiency (very common in males) the bottom two just look black

Del

'...The lower critical temperature is the temperature of the austenite-to-pearlite eutectoid transformation in steels- below this temperature austenite does not exist. ...'

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The latter part of the preceding deserves some qualification or modification. Would it be more accurate to say 'austenite does not form below this temp' or 'austenite is not stable in bulk form (i.e. without stabilizing elements alloyed)'?

[My 2-cents] Re: "Would it be more accurate to say..."

From my own (*very*) limited expertise in metallurgy, I would interject here that much depends on context. And, in asking your question, you removed the parentheses from around the statement, and pulled it out from the context in which it resided ("Temper colors of 0.95% carbon steel"... somewhat above eutectoid).

"Would it be more accurate to say 'austenite does not form below this temp'?" Depends on a number of factors, not the least of which is, at what percentage (retained austenite) would you consider it to be nonexistant (or, not formed)?

Read under "Properties", at Martensite.
[...subscribing simply/primarily to see Milo's response...]

I had one of those deja-vu moments, checking (your) link in: "Our Temper Colors for Steel Chart Post".

For a brief moment (until reading to the bottom), I felt that something was missing.

(The chart is also provided as a "glossy-insert" in Anderson's "Inspection of Metals: Visual Examination, Volume I", which I have had for many years.)

Was glad to see the "credit" (at bottom of the post) to Bethlehem Steel.

Back in one of my past lives (ref'd in THIS post), I had occasion to drive into the heart of their facility to pick-up a unit needing repair. Even then (already in its downturn), it was one impressive giant...(!)

It literally blew-me-away, when I learned some years after-the-fact, what had become of this veritable icon of American History!

Except for the casino (Sands Bethlehem) and the Arts (SteelStacks), it may as well be Detroit.