You say the material is being hardened during the cutting. This suggests you start with annealed material, or at least not fully hard, and the rapid extreme heat of the chop saw cut is being 'quenched' by the bulk of material on either side of the cut acting as a big heat sink.
One possible way to prevent this is to preheat the bar before cutting. Nowhere near hot enough to be near heat treating temperatures, more like up to the lower range of tempering temperatures. With this the bulk of material adjacent to the cut does not act as such a good heat sink so the extreme heat right at the cut is not quenched. It may still finish up a bit harder than it started but certainly not fully hard.
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