knife hardening

[jackie]

I just have a mapgas torch.  it isn`t guite big enough to heat a 6 inch knife. could I heat half of the knife to non magnetic and quench in oil and then heat the other half of the knife and quench it. would it still make a good knife or is there something that wouldn`t be right  thank you. I usually just make 3 or 4 inch knifes and my small brick forge works very good. would like to make a  little bigger knife for a friend.  thank you

[gudspelr]

I'm assuming this is for carbon steel?  You're more than likely going to run into significant problems trying to harden portions of the blade separately.  If you were able to effectively harden part of it, then turned around and heated the remainder, the heat is going to run into that already quenched part.  While the already quenched part wouldn't reach austinizing temp, it would likely get hot enough that you'd over-shoot your tempering temperature.  After quenching the second part and trying to temper the blade, you'd probably end up with some very significant differences in hardness for your cutting edge.  That could mean too soft in one spot, while potentially still a bit too hard/chippy at another point.  That doesn't take into account that you're seriously stressing the blade during quenching.  Imagine the already quenched part having a somewhat soft spot where the 2 "halves" meet, then it all getting put in the quench again.  Might not crack or break, but could certainly warp a fair amount because of the uneven heat and quench applied.

Hope that makes some kind of sense and just my opinion.  Some of the smart guys should be along shortly   .


Jeremy

[Lin Rhea]

Everything Jeremy said. It wont work to your satisfaction. At least not in the way you are describing your possible process.

A bigger chamber would solve the problem as long as your source of heat can accommodate it.

[jackie]

thanks for the information I need a bigger torch. maybe in the future it will happen  thank you jackie