Your leaf spring is most likely 5160 which is a great steel for making kinves. I've been using it for about 6 years now. What Frosty said about the oil. It is an oil quench steel. I used olive oil for years with good results (I was heating to about 130-140).
Prior to quench heat it to a dull red and let cool two or three times. This will help reduce the grain size (smaller grain= better performance)...
If you want a quench line, only submerge the edge to about 1/3 of the way up the blade. Keep dipping it in and bringing it up and back down in a slightly different place as the oil will form a vapor barrier which will slow the cooling if you leave it still. Go vertically not side to side as this may cause warpage. Do this till the color leaves the spine then quench the whole thing until it cools.
If you want to keep the line pretty even, you can put something in the oil that will stop the blade at the same depth every time you dip. I use a piece of sheet metal with holes drilled all over it for the oil to criculate through. It has long screws on the corners to adjust the height.
After it cools test the edge with a dull file. It should skate and not bite in. If it bites its not hard enough and you'll have to harden it again. Critical temp is when it turns non-magnetic. Usually an orange color, but the magnet is much more accurate at telling you when. Let is soak at critical for a few min to make sure its all the way through, keep it moving so you don't get hot spots.
If you did get it hard in the first quench, temper at 350 for two hours three times. If you really want flexibility (nice in a chef knife), set up a pan with water in it and prop the blade up in it with the water covering the edge. Draw the spine down to a blue color with a torch ( three times). The water will preserve the hardness of the edge and the rest will be nice and springy.
Xxxx, did I just write all of that? Sorry, I get carried away as blades are my passion. Just trying to be helpful
Ed Wilson
Happycat Cutlery
