I've got a piece of ar400 steel about 1/4' by 5" was thinking about cutting it and forge welding together. Would this make a decent punch or possible drift?

How are your forge welding skills and do you know the composition of that particular brand?  I've looked at the range of composition over several manufacturers and it looks to be a bit tough to weld to itself for some of them. (Ni, Cr, Mo).

That being said it looks better for a punch or drift than for a hot cut, chisel or slitter (low C).

I would probably get a chunk of truck suspension and forge them from that and skip the forge welding---especially as impact use may cause a poor weld to fail.

My personal thought is that it seems to be a lot more work than necessary. I don't know enough about the alloy to say how possible it might be.

Steve

Not sure of the brand, and I could use the practice forge welding. I got if off a piece of plate we water jetted at work. Seems to move like butter when it's hot. 1st pic is 5 minutes after it was in the forge. 

Generally good to get good at it before trying alloys that may be challenging; but then it can be fun to weld up random stuff you run across.  I remember some of Billy Merritt's Scrapmascus that was done that way.

How does it dent when cold?

I haven't tried it yet, will let you know tomorrow. 

Two taps with the back of the crosspein got it to dent slightly. Barely scratches the surface. Pic 1 is after one heat cycle pic two is factory heat treated