I know its not the ideal steel for hot chisels but i have a piece of 4140 that is the perfect size for a slitter..Anyone tried it? How would you temper the 4140 for a chisel?

4140 will make a bad hot slitting chisel because it is not very hard when its hot and it would lose its temper way too easily on a thin chisel it will work but poorly and it may need to be re hardened and re edged constantly to keep it from curling up inside the piece you are slitting and sticking on you

If you read Mark Aspery books thats about all he uses ...

Brian Brazeal uses it also :

I have made several, the one thing you want to keep in mind, is after about 3 seconds of hot metal contact, you want to cool it, as long as you do that, the tool will stay relatively undamaged, that is if it was properly heat treated in the first place. After a lot of reading and taking Mark Aspery's class, I have learned to triple draw to straw, and that seems to work very well.