Yes, re flatten. A higher carbon steel will be harder even when in an unhardened state due to the carbon, depending on the actual steel. But if I were wanting a hard face, I would get a 2 inch thick 4140 plate, bevel the bottom for welding, harden the face under flowing water (water hose running full open in circular motion), then weld it with an arc welder trying to keep the top 1/2 inch cooled for the most part. I think a sprayer on a water hose would serve to keep it cooled. Wear gloves an watch out for the steam.