Cooling of hypoeutectoid steels in done is furnace by decreasing

cooling-of-hypoeutectoid-steels-in-done-is-furnace-by-decreasing

Cooling of hypoeutectoid steels in done is furnace by decreasing the temperature to at least ________ below the A1 line.

A. 4^oC

B. 10^oC

C. 16^oC

D. 30^oC

I have been asked this question by my school principal while I was bunking the class.

Origin of the question is Annealing topic in portion Heat Treatment of Engineering Material & Metallurgy

The correct choice is D. 30^oC

For explanation I would say: For full annealing of this steel, it is heated 30-60^oC above the A3 line. Then it is cooled within the furnace by decreasing the temperature 10-30^oC per hour, to at least 30^oC below A1 line.