this one would not oil harden. made from nondescript leaf spring, probably china. water hardened. went ping in 5 minutes. 3 times. next photo, same leaf spring, other side of centre hole. warm oil quench, hardened beautifully, torch tempered. excellent edge.

same bunch of springs, different leaf. cold oil quench didn't harden, so used water. got this lesson twice, except this one split along the spine of the blade and perpendicular to the edge. 

lesson: warm oil for free springs that are of origins unknown for me

hmm if you  read the HT  posts I made,  in there I explained the need to always warm the oil. Hopefully lesson learned young grasshopper :)

these made and broke as i self taught. about 3 month before joining IFI. i keep them around as reminders and i may actually shadowbox them as they were a lot of work. but yes, i have a lot to learn and more to read. heat treating mystery metals is a somewhat fun if not exact science. always test. lesson learned.

Yep, been there, and occasionally still am. Stuff.. happens. Hopefully you'll be able to diagnose the problem, and read Steve's suggestions.

John

there are four other knives that made it thru to finishing, and another broken, so i guess i have about a 75%ish success rate. but it always seems to be the ugly that survive.

eggwelder - that last line of yours applies to more than just knife making!