My mentor in Boise told me to always quench a leaf spring in used motor oil

He swore it gave a better temper than new oil or water. I tried it on a knife blank last month and it came out way too soft, almost like it didn't harden at all. Had to redo the whole heat treat with canola. Anyone have a go-to quenching medium for 5160 steel?

2 comments

2 Comments

stone.simon11d ago

Listen to what @thompson.brian said, he's got it right. Used motor oil is junk for a real heat treat. It quenches too slow for 5160. What temperature was your oil when you tried it? If that used oil was cold, it would make things even worse. The canola works because it cools the steel at the right speed to get it hard. That old motor oil advice needs to stay in the past with leaf springs.

thompson.brian11d ago

My old boss at the machine shop in Toledo swore by used 10w30 for springs too. Honestly, I ruined three good blades before I gave up on that method. Tbh, for 5160 I just use warm canola oil now and it comes out perfect every time. That motor oil trick might work for some things, but it just doesn't get hard enough for a knife.