I figured old mower blades would be good steel, so I threw one in the forge, got it up to a good quenching temperature, and dunked it in oil.
Nope. Not hard at all.
I tried again, this time using water.
Nope. Not hard at all.
I took it to a higher temperature, getting it almost white hot.
Not hard in oil, not hard in water.
I took it to white hot. All I did was ruin the steel.
I tried taking it to a lower quenching temperature.
Not hard in oil, not hard in water.
Unless you know something I don't, the average mower blade is low carbon steel, and you can't make a decent knife out of it, unless your idea of a decent knife is something that dulls as soon at it cuts a few sheets of paper.