Hi Jens
i didn't find any brittleness with my crucible steel.... and in the winter, back home, it would reach -43 cel on occasion... ( fun time to be in the forest
- i do agree that "toughness" in steel goes down with temperature... but i also think that you should have a servicable blade at those temps... just not a bullet proof one..
-- lower temps may trip off some retained austenite in the blade.... and this can definitely make a blade brittle.. ( i can explain it... but it'll be a wordy post, if your patient)
-- higher alloy blades are definitely prone to retained austenite..
-- they also say sulphur in steel is problematic at low temp.. ... as some undesirable elements will sneek in when you do a crucible melt... and this could be a bad thing at cold temps....but ok at warmer climates..
-- prior stress's in the blade.... if the steel is in a stress condition ... i believe that cold will definitely act on this area and be much more brittle..
i'm sure i'll think of more
Greg