What’s this term I’m looking for? Chart drastic toughness changes

[Kentucky]

This is crucibles L6 champalloy. It’s got about .30% Moly which is what differentiates it from carpenters. It’s still above 60rc at a 400 temper which I’ve found to be accurate. It’s chirpy toughness is about 43pounds at 60-62rc, drops to around 38 at around 58-60 but takes a drastic jump to around 68 pounds at 56-58 rc.. I can’t for the life of me remember what the terminology for that high-low-higher toughness is. Thanks

 

[Kentucky]

Is it temper embrittlement?

 

[Stacy E. Apelt - Bladesmith]

We should name it - Toughness Cliff? (sort of like the pearlite nose)

Tempered Martensite Embrittlement (TME) is the range between a lower rage temper and a high range temper that some steels have. The toughness drops suddenly and the steel becomes brittle. As it exits that range into the higher tempering range, the toughness rapidly increases. The embrittlement range is usually between 600°F and 1000°F, but the worst part is between 700°F and 900°F

I hear the ASPCA is going to get the Chirpy test outlawed. They are replacing it with the Charpy Impact Test

 

[Larrin]

That's tempered martensite embrittlement. It's different than temper embrittlement. Don't get mad at me I didn't name it. I wrote about it here: https://knifesteelnerds.com/2018/10/22/silicon-additions-for-improving-steel-toughness/

We have seen TME in a lot of steels tempered at 500F which is why I recommend 400F as a starting point for most steels.