A lot of alloys loose hardness when taken to, or near to critical (non-magnetic). A mild steel like 1018 wouldn't suffer from the shaping within reason, but an alloy like L6 begins to loose structure at 400*. Even a mild 1018 cold rolled bar will begin to loose the rigidity of work hardening at 500*.
If you were to forge a front end out of chrome alloy, or a higher carbon steel (1045+) the uneven application of heat could render the piece weaker in areas that got hotter, or stayed hot longer. When you forge a knife the metal has to be relaxed by normalizing/annealing prior to hardening or tempering to prevent cracks in the carbon crystalline structure which weaken the blade. That doesn't even touch on the science behind quench hardening, and temp control in tempering. You'd need pretty precise equipment to get good results.
Work hardening with a hammer on steel does little more than refine surface grain, and also leaves inconsistencies in strength. Overworking certain steels outside of a narrow temperature window can cause stress fractures as well. All of which can lead to catastrophic failure under load.
Now if you are working in iron or mild steel, no big deal. Those materials bend much easier, and don't have the shape memory of spring steel, so you would need a much beefier set up with those materials than with something more rigid. Without doing any math, this could all be pointless. For all I know a 1/4" mild steel tube girder completely annealed has all the tensile strength needed to do the job, but I doubt it.
The first real blade I ever forge was a Filipino talibong out of a leaf spring (I was 13). I worked it too cold, and use a brine for my quench. The damn thing fractured and broke into 3 pieces. It all comes down to what materials you're using, the forging processes involved, and the stress to be applied to the finished product.
