A deformation mechanism map plots normalized stress against homologous temperature $T/T_m$, and splits that plane into zones, each one owned by a different way a material deforms plastically: dislocation glide at high stress, power law creep at intermediate stress and high temperature, and diffusion controlled creep (Nabarro-Herring, Coble) at low stress and high temperature. Let's look at what property this map is built to give us.
Fatigue strength: this number comes out of cyclic stress versus number-of-cycles-to-failure (S-N) testing, a completely separate experiment from the static stress-temperature mechanism map. Not what the map gives.
Creep rate: the map carries contour lines of constant strain rate $\dot{\varepsilon}$ drawn across the mechanism fields. Once the operating stress and temperature of a part are located on the map, both the active mechanism and the corresponding steady state strain rate, that is, the creep rate, can be read off directly. This is the entire purpose the map was built for.
Tensile strength: this is obtained from a stress-strain curve in a standard tensile test performed at one fixed strain rate and temperature, not from a stress-temperature mechanism field.
Impact toughness: this comes from notched impact tests like the Charpy test, which measure energy absorbed under sudden dynamic loading. It has nothing to do with the steady deformation mechanisms plotted on this map.
The property this map is built to give directly is the creep rate, read off the strain-rate contour lines at the operating stress and temperature.
Let's summarize:
The two axes of the map are normalized stress and homologous temperature.
Contour lines on the map are lines of constant strain rate, which give the creep rate.
Fatigue strength, tensile strength and impact toughness all come from separate, dedicated mechanical tests, not from this map.
So the deformation mechanism map is used to determine the creep rate.
