You can enter your own Ultimate Tensile Strength.
(Safe stress can be taken as 1/3 of the ultimate strength.)
See the following websites for ultimate strength values:
matmatch.com
matweb.com
*Special Considerations need to be taken if the Pitch Line VELOCITY exceeds: 1200 FPM for Metallic Spur Gears Or 2400 FPM for Helical Gears or Nonmetallic Spur gears