Tried quenching a leaf spring in old motor oil and it came out way too soft

I had a piece of 5160 from a truck spring and wanted to harden it for a knife. My normal quench oil was low, so I used some old 10W-30 I had in the garage. Heated it to a bright orange and dunked it. The file just skated right off like it was still annealed. I guess the additives in the used oil messed with the cooling speed. What's a good cheap quenchant you guys keep on hand for stuff like this?

3 comments

3 Comments

oscarm2411d ago

The canola oil trick works but you gotta preheat it to around 120-130F for it to work right on leaf springs. Room temp canola is actually a little slower than warm motor oil and might not harden 5160 all the way through. I keep a cheap deep fry thermometer in my oil bucket for that reason.

angela_wilson782mo ago

Yeah, the "additives in the used oil" thing is exactly it. I used to think any oil was fine in a pinch, but man, that stuff is too slow. I burned up a good piece of steel the same way. Now I just keep a big jug of canola oil from the grocery store. It's cheap, it works way better for simple steels, and it doesn't stink up the whole shop like motor oil does.

noahw532mo ago

Used to grab whatever oil was in the garage for quenching. Your point about the additives slowing things down makes total sense now. I never connected the slow quench to burning the steel. The canola oil idea is smart, definitely switching to that.