Hardening would be a bad idea. One maker does put something like drill
tek or borium on the flat side of the edge.(cub cadet)
If you want the blade to last longer file or grind a 30 degree bevel
and then flatten the very edge to be about 1/32"


EW wrote:
I'm assuming that new lawn mower blades are sharpened, then hardened
before
sold. Question: after sharpening the blades on a bench grinder
(after much
use) is it necessary to harden them for longer life, and if so, how?
Thanks.

EW