Well, I think I found a datasheet for that Stepper.
Looks like it’s rated for 80 Kelvin, So as long as you don’t exceed -193.2C you should be fine.
Just kidding, Apparently “K” is winding temperature rise, that’s not confusing or conflicting with other measurement systems at all.
But again, That Stepper is also rated for 80c above AMBIENT.
Insulation class B is rated at 130c max.