I wrote a little bit about making chasing tools from engine valves on August 2011
After making four larger curved chisels I decided to make a miniature set too.
I keep an assortment of partially prepared tool blanks of various tool steel origin and can quickly select a size and shape I need. In this case I chose envying valve stems. I’d already cut off the flare end with a Zip disc. I’m not sure of the alloy but think it may be EV-8 stainless steel http://www.motor.com/article.asp?article_ID=1792
http://www.enginetech.com/rebuilder-valves.php There may be a difference in alloy between intake and exhaust valves.
At a near lemon heat this steel is still difficult to forge. It seems to be air hardening and usually does not need any other heat treatment. I forged the tips in four different radius swage gutters to establish the outside radius and did the finishing with grinding tools. The cutting edge has a low angle to keep the tip strong. For the job I have in mind (carving a die face) a shallow depth cut will be fine.
It’s about an 80/20 or higher chance the edge will be hard enough without some heat treatment. If, after a quick test the edge is blunting, I polish it again and torch heat the 1/4” adjacent to the tip and oil quench. That process has a nearly 100% success rate.