If you allow the heat to migrate back into the hardened edge it will start to temper the edge. If allowed to continue it will continue to temper the edge back to it's original soft state. If you want the edge to remain as hardened, as quenched, continue to keep the edge cooled until the heat drops in the remainder of the blade to under 400 deg. The slower cooling of the spine will keep it in the tougher/softer state you desire. You can also quickly abrade the edge to reveal clean shiny steel and allow the heat to temper the edge, observing the color changes and re-quenching when the edge tempers to the desired light to straw color that yields a hard yet tough edge on the blade. Treating in an acid etch after cleaning may etch the different temper zones differentially and give you a visual indication of a hamon. Just my two cents.
Terry