Dear Rajeshkumar, I guess it should depend on the material properties on the initiation sites. In most occasions, fatigue initiation takes place in the material surface, so it would may have sense to consider the case properties. As a rule of thumb, the FITNET FFS Procedure suggests that the fatigue limit in case hardining steels is 40% of the material ultimate tensile strength, but it does not specify which ultimate tensile strength is referring to. Being conservative you could take the lowest one until you find more info.

Finally, there are other factors affecting fatigue life, such as surface roughness, size effect, stress gradient (notch effect) and mean stress.

Dear Sergio,

Thank you for your concern. AS you said it does not specify which UTS is referring to ., that is what my question

Dear Rajeshkumar,

just in case it is helpful for you: the original reference for the FITNET FFS Procedure (second) fatigue route is:

Nieman G., et al. Maschinenelemente, Band 1: Konstruction und Berechnung von Verbindungen, Lagern, Wellen, 4, Springer Verlag, Berlin Heidelberg, 2005, ISBN 3-540-21125-1.

I don´t have it, but you may try to find it!