Furthermore the teeth of the starter ring are hardened to increase their strength and wear&tear. The normal hardness at the pitch circle diameter is 45-55 HRC (Hardness Rockwell C). Likewise the higher the number the harder the material.
The body of the ring is untreated to give ductility and this is done because to weld it to the flexplate and also for shrinking onto the flywheel.
There are multiple types of ring gears available based on the application of the vehicle. The gear ratios can be 80 Teeth, 91 Teeth, 101 Teeth etc