<...FACTORS RESPONSIBLE FOR HARDENING OF STEELS ...>

The inappropriate use of Caps Lock, for starters.

Heat treating steel is a complex business and it depends on the steel and it's intended usage.
There is no rule of thumb that I'm aware of...except maybe..if you want it hard as hell but brittle get it red hot and quench it.
Del

1. The hardening of steel (or the hardness after hardening) is mainly dependant upon the microstructure that is achieved after the Heat Treatment process is over. This is dependent upon the carbon(mainly) and the alloys like Ni etc.

http://www.vacaero.com/News-Info-From-Industrial-Heating-Magazine/News-Info-From-Industrial-Heating-Magazine/Hardness-Hardenability-Part-2-A-Discussion-on-Hardenability-and-Hardenability-Testing.html

2. There is no rule of thumb for heat treatment (if you mean hardening or tempering) or even others. Each of the steel has some specific curves and these decide the rate of cooling to achieve the desired microstructure and hence the properties.