The temperature point at which the change starts on heating the steel is called

Explanation

Explanation:- Lower critical temperature (point) A 1is the temperature of the austenite-to-pearlite eutectoid transformation. Below this temperature austenite does not exist. Critical temperatures Upper critical temperature (point)A 3 is the temperature, below which ferrite starts to form as a result of ejection from austenite in the hypoeutectoid alloys. Upper critical temperature (point)A CM is the temperature, below which cementite starts to form as a result of ejection from austenite in the hypereutectoid alloys. Magnetic transformation temperature A 2 is the temperature below which α- ferrite is ferromagnetic . Phase compositions of the iron-carbon alloys at room temperature Hypoeutectoid steels (carbon content from 0 to 0.83%) consist of primary (pro eutectoid) ferrite (according to the curve A3) and pearlite. Eutectoid steel (carbon content 0.83%) entirely consists of pearlite. Hypereutectoid steels (carbon content from 0.83 to 2.06%) consist of primary (pro eutectoid)cementite (according to the curve A CM ) and pearlite. Cast irons (carbon content from 2.06% to 4.3%) consist of pro eutectoid cementite C 2 ejected from austenite according to the curve A CM , pearlite, and transformed ledeburite (ledeburite in which austenite transformed to pearlite). The point of decalescence occurs at the temp where the pearlite changes to austenite as the steel is heated. The point of decalescenes occurs as the temperature is rising The point of recalescence occurs as the steel is cooled slowly the autunite returns to pearlite. The point of recalescences occurs as the temperature is falling.