"The persistence of an electric motor's torque is why our rail system uses diesel over electric. The diesel engine cannot stall like electric."
Perhaps you mistyped. Diesel is not the motive power. It only turns the generator that powers the electric motor.
Google: "Diesel Locomotives use electricity to drive forward motion despite the name 'diesel'. A large diesel engine turns a shaft that drives a generator which makes electricity. This electrical energy powers large electric motors at the wheels called 'traction motors'."
"Does tempering increase strength?
The reduction in hardness is usually accompanied by an increase in ductility, thereby decreasing the brittleness of the metal. ... Higher tempering temperatures tend to produce a greater reduction in the hardness, sacrificing some yield strength...