You're action would have been carburized and quenched. The issue isn't "softness", it is embrittlement.
This is common to all carburized materials - especially when we realize that temperature was determined by colour changes sensed by human eyes. Often varied by several hundred degrees depending on ambient light and other factors.
Embrittlement of steels
http://faculty.up.edu/lulay/failure/Lesson3.pdf
Not "softer", brittleness is the real concern.