Phase Transformation and Heat Transfer during Cooling of Steel

Abstract

Studies on the cooling of a carbon-steel disk were made to discuss the heat transfer accompanied with phase transformation.
Hypereutectoid steel, eutectoid steel and hypoeutectoid steel were used as the disk. Its diameter and height are both 30 mm. The disk was cooled from the bottom by a jet of water or nitrogen gas, after it was heated inductively up to about 1 200 K. Heat-transfer coefficients which are necessary for the analysis of heat transfer in the system, were obtained by analysing the cooling curve of a copper disk, under the assumption of one dimensional heat conduction in the disk. These values of heat-transfer coefficients could be successfully used for the prediction of cooling curves of stainless steel disk.
In the case of carbon steels, the heat generation by phase transformation was accounted in the one-dimensional heat conduction equation. The fractions of various phases such as austenite, martensite, bainite, ferrite and pearlite were estimated by the use of the continuous cooling transformation diagram (CCT diagram). Calculated cooling curves in carbon steels by the present model were in good agreement with the observed ones.