If the metal gets hot enough to change color, that's too hot. The crystalline structure of the metal starts changing somewhere around 600 degrees on the steel alloys I use in some of my knife making and/or gunsmithing projects. Steering and suspension parts need to be tough, not brittle, and heating to the point of changing color can seriously change those characteristics. Other important factors are how the metal is cooled- - - -oil or water quenching, air-cooling, or slow cooling buried in sand, etc.
One really fun project is making a V-shaped leaf spring for a flintlock muzzleloader hammer. A piece of annealed high-carbon steel is hacksawed and filed into the exact shape it needs to be, then it's heated cherry red and quenched in water. Then it's polished and placed in a shallow pan of non-detergent motor oil. Heat the oil with a torch until it all burns away, then cover the part with lime and let it cool for several hours. If the V can be compressed fully in a vise without breaking, you've got a spring. If it breaks, start all over!
Jerry
