What type of steel are gears commonly made from?

[Matt Adams]

I've been trying to hunt all over the place to find out what sort of steel that boston gear, martin, or SDP makes their gears out of. I'm trying to perform some calculations on gear teeth strength, and I'm looking to find the yield strength for the steels that are commonly used.

I've assumed thus far that 40 KSI is probably a conservative estimate, but I'm pretty sure I've heard that the yield strength on gears could be even twice or three times that. I've also heard that you don't want to assume that sort of strength with gears in calculations, and want to use half or even a third of the true yield strength?

Any thoughts? Even just dropping a few materials would be fine- I'm aware of http://www.matweb.com

Thanks!

Matt