Heat treating large/broad items like a hatchet.

[Langadune]

I'm looking at eventually getting my own heat treat set up (will continue to outsource in the mean time). My blades will typically range from 3 to 12 inches... usually 1095. I want to eventually make some full tang hatchets with handles up to 18 inches long. I guess my question is more about hatchets. Will I need to be able to heat treat the entire piece or would he axe be particularly vulnerable to breaking if there is a differential temper between the head and the tang?

 

[Storm Crow]

I heat treat the full length of my full tang 'hawks, the reason being that I want the tang not to bend under stress. I'm using 4140, and the same heat treatment that makes the tang tough also makes for a good wood-chopping edge.