Ordinary mild steel doesn’t have enough carbon to respond much to hardening. Case hardening could be undertaken, but it’s not really practical. After there’s the issue of tempering, if not properly tempered, hardened steel won’t have the toughness to withstand the use, instead it will tend to shatter like file steel or drill bits tend to.
A potentially much more durable steel could be gotten from automobile leaf springs. It also has good thickness, promising robust service. If a person has access to some kind of forge, a better steel could be welded into the edge of mild steel cutting blades, allowing a heavy flexible back. For that approach I would suggest welding in grade 8 straightened chain link, then forging it to a rough point before grinding, hardening and tempering. Chain link steel has outstanding toughness.
Leaf spring is likely the easiest approach, cut to size, anneal, then drill holes, maybe forge the edge, then harden, and variably temper to make a tough cutting edge, and a flexible back.
I believe the chunking application calls for toughness, more than a very sharp edge. The steel shouldn’t have flex, and the edge shouldn’t be able to dent or deform. With the right grade of steel, wear resistance and toughness can be had.
It might be practical to look into commercial chipper knives, or tool steel blanks.
Edit: different steels call for different quenching methods. Some need oil quenching, others water, some brine, some tool steels just need to be raised to a certain temperature for a specific period of time. The internet, experimentation and testing will reveal the best approach for a particular steel and application. Some steels even respond to cryogenic treatment.