what is the different between tempering& Tuffening

As already explained by Mr. Kailash, tempering is carried out immediately after Quench hardening. It is a process of controlled heating till 300 deg. C., to reduce brittle nature of steel, by stress relieving in structure and improve structure and toughness.

Tuffening, I think is  process carried out on Glass, to increase tuffness.

Tempering is done on steel,when the steel is cooled from the hardened state it becomes too brittle   The purpose of tempering is to reduce the brittleness imparted by hardening and to produce definite physical properties within the steel. Tempering always follows, never precedes, the hardening operation. Besides reduc­ing brittleness, tempering softens the steel. That is un­avoidable, and the amount of hardness that is lost depends on the temperature that the steel is heated to during the tempering process. That is true of all steels except high-speed steel. Tempering increases the hard­ness of high-speed steel.

And tuffening is more about glass thing where glass has been given certain properties for strength and  resistant.