It fails all the time! The fact that 75% has failed me very close to 50% or maybe more than that. There's supposed to be 1/4 chance that it fails but that clearly seems to be wrong.
The other annoying thing is that when 75% fails and I try it again, it fails again! Same for 80%! You know how unlikely failing 75% or 80% twice in a row should be?! And no, failing twice in a row is not a one-off thing that just happened to me, it has happened to me about 4 times now; 8 attempts of forging have failed this way (that does NOT include the ones that failed on their own).
No, I do not attempt forging anything under 75% but it seems that now I'll only be doing 100% until the forge is fixed. I don't even know why they changed the heat system as it just causes hassle but I wouldn't mind if it didn't fail so much.
I never fail since I always pick 100% one.
And you can't calculate luck. I think it is safe to assume that you have a bad luck.