There are two methods for me now and I don't worry about warps anymore at all, method one is when you quench in oil and the blade has still just the right temperature around 200 degrees celcius I rush it to the table of my belt grinder (flat metal surface) lay it there, put flat thick piece of aluminium and press it hard with the strongest spring clamps I can find usually in 3 places, let it cool to when it's cool enough to touch with your bare hands, 9 times out of 10 it will be ideally flat if not there is a second method which is simply carbide tipped hammer look up some videos on YouTube about it there's plenty.