Mathematical Relationship between Ferritic, Pearlitic and Average Grain Size of Steel

Shamail Ahmad and Iftikhar Ahmed Channa

It is an established fact that the grain size of the steel has a marked impact on its mechanical properties. Steel with large grain size has lower yield strength, tensile strength, impact toughness, fatigue life and susceptibility to brittle fracture while has better creep resistance. Besides this it also affects the corrosion resistance and other properties of the steel. The purpose of this paper is to establish a definite mathematical relationship between the ferritic, pearlitic and average grain size for the steel having ferritic-pearlitic structure. For this reason a hot rolled AISI 1060 sample is selected and are cut into three pieces. Out of these three samples, one sample is normalized from 815 C and one from 845 C. Then all the samples are subjected to volume fraction, ferritic, pearlitic and average grain size measurements. Ferritic and pearlitic grain sizes are measured by Intercept Method for Two-Constituents and average grain size is measured by Heyn/Hilliard/Abrams Intercept Method. The results have shown that the experimentally measured average grain size of steel is equal to the sum of the products of ferritic and pearlitic grain sizes with their relative volume fractions that is it satisfies the rule of mixtures.