You can harden the washer by heating to cherry red, then quench in a brine solution.
Doing so will allow the washer to hold a good edge.
The brine solution is 2.5 gal. water, 2.5 lbs. salt, 16 oz. Dawn dish soap, 4 oz. Jet Dry ( dish washing solution)
This brine solution will give a good hard surface to mild steel.
Fred