what's blue and brittle?

[ivymike]

actually, what's "blue brittle" testing (something to do with steel)? I'd ask my favorite metallurgist, but he's away from his desk.

 

[unclesyd]

Quoting Bethlehem Steel.

"Blue Brittleness: Brittleness occurring in steel when in the temperature range of 400F to 700F, or when cold after being worked within this temperature range."

 

[wes616]

Often you should test for blue-brittle on parts that are potentially workhardened.

Wes C.
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[ivymike]

I think I was already that far along based on the context (which I didn't provide)... but how is the test actually done?

 

[unclesyd]

Other than knowing which materials that are subject to the phenomena the only way I know is to do a metallurgical analysis. A microscopic analysis will reveal pretty severe grain distortion, greatly elongated grains. This can occur in very discrete bands.

 

[swall]

Not sure what you are looking to do, but a nital etch test is useful for identifying grinding burn, surface damage due to abusive milling, etc. And it is non-destructive.

 

[wes616]

Thanks for callin me out there Mike. I guess I should have "thought" about my previous answer (even) a little bit. Did you get your answer?

Wes C.
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[ivymike]

Wes, your answer was still helpful. It was very similar, in fact, to the answer provided by the guy who told me his parts had passed a blue-brittle test. Haven't run into anyone yet who can give me the details of the test, nor what the pass/fail criteria would be (including the guy who assured me his parts passed). Unclesyd suggests looking at the grain structure, and swall suggest nital etch... I had the impression that there was some sort of destructive test done. I guess I may have to dig deeper around here to figure out what really happened (if anything).

 

[wes616]

Mike,

I remember doing some down and dirty tests for work hardening; this is years ago though. I don't remember the specifics but the process goes something like this.

Work Hardening produces a martensitic(?) condition, and that has a specific hardness, so perform a hardness test. If the parts fail (are determined to be blue-brittle / dynamic-strain hardened / work hardened) they undergo a strain relief heat treatment (or scrapped as the case may be.

Wes C.
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