Just realized I've been forging my leaf springs wrong for years

I was working on a set of kitchen knives from a Ford truck spring, the usual 5160 stuff, and the edge kept chipping after the quench. I'd been heating it to a bright orange, like I do with mild steel, and quenching in warm canola oil. A guy at the Blacksmiths Guild meet in Boise last month saw me doing it and just said, 'You're cooking the carbon out.' He explained that 5160 needs a much lower heat, more of a dull cherry red, to keep the carbon in solution for the quench. I tried it on my next piece, kept it way cooler, and the difference was night and day. The blade came out tough and held an edge like a dream. I feel like an idiot for all the springs I've ruined. How do you all judge the right heat for different high-carbon steels when you're working with scrap?