I have made several chisels out of mild steel with an O1 tool steel bit forge welded to it. I was wondering about tempering of the bit:

Do you see any problems with hardening the blade and not tempering it as the body of the chisel is made out of tough mild steel. reason I was thinking is that any hardness that is in the O1 after quenching will not be reduced in the tempering process.

Is this a bad idea?

thanks

Yes, that would be a bad idea. While you are correct that the mild steel body does give some shock resistance to the chisel as a whole, not tempering the high carbon edge will make it very susceptible to chipping. It will also make it much harder to sharpen.

If you do not temper the bit it will probably be too brittle and delicate. 

I would temper it by heating the struck end and watching the temper colors run down toward the bit. 

what does the mild steel shaft have to do with anything? try reading the pinned HT posts the answer is there.

ok thanks for the information. As far as tempering goes. I have seen videos and read information saying that tempering must be done over an hour or so. I have also seen videos of guys holding their work close to a orange hot piece of metal until a straw color appears and quickly pulling it away from the heat source once the desired tempering color is achieved. do you see any issues with the second method even though it is much quicker?

temper a couple of times; just like a knife blade.