The material used by a gear manufacturer depend on the service conditions like wear and tear, noise, vibration and the like. Gear Manufacturers can use metallic and non-metallic materials.
Gear Manufacturers widely use cast iron due to its good wearing properties, machinability, and ease of production. But, gear manufacturers must rely on steel for high strength design.
In fact, a gear manufacturer could use phosphor bronze gears for worm gears to lower the wear and tear of the worms.