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Tempering my knife blade

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Dumb newbie question, looking for confirmation

I made a 1/8" thick knife blade out of a leaf spring. After quenching in oil, I wanted a differential temper. So I heated a piece of leaf spring and put the back of the knife blade onto the hot steel.

I was looking for the change in colors across the blade, but the entire knife blade turned dark charcoal grey immediately. I didn't see any color changes develop across the blade.

Does this mean that the hot leaf spring was too hot to effect a controlled differential temper?

Does this I mean I overheated the knife blade to ~700 degrees almost immediately?

I don't want to do anything else with the knife blade until I figure out what the hell happened.

I assume that, next time, I shouldn't get the leaf spring so hot.


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Sounds like the chunk was too big for the blade, too hot, wrong position, or made too much contact. Or a combination of these.

It is better to sneak up on it. Heat a small bar, say 1/2" square, to a dull red. The smaller bar can be made to conform to the back of any blade shape. Apply it to the back of the blade, with the tang clamped in a vise, edge down, so that you can see the colors run.

Be advised that the colors will continue to run for a short while even after you pull the bar away. Have a plan to stop the heat with water or air if goes too fast. Practice on some scrap first.

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