Improving the mechanical properties of medium carbon steel by heat treatment

Abstract

The effect of heat treatment on carbon steel was studied using different cooling media (water, quiet air, samples covering at different thicknesses of sand, furnace cooling) and the results were compared with a reference non heat treated sample. It was followed by a microscopic examination of the structure using an optical microscope and a study of some mechanical properties such as macro hardness (HRC), ultimate tensile strength (s_UTS), elongation (e %), yield strength (s_Y), and impact fracture toughness of the material.The microscopic examination of the samples indicated that the cover rates in the sand have an effect on changing the specifications of the studied material, which led to delaying the cooling time of the sample and thus giving it sufficient time for carbon diffusion and homogeneity in the structure. It was also observed that water-cooled samples, air-cooled samples and furnace-cooled samples had obvious differences in hardness and other properties of the material.This treatment improved machinability of this type of steel and reduced internal stresses of the material. A microscopic examination showed the formation of an bainitic structure at air-cooled condition and pearlite structure in a sandy medium, and a martensite structure due to water-cooled of sample. This effect was also observed when testing the impact fracture toughness of material.

Some important mathematical relationships between different mechanical properties and their relation to the hardness of the material have been found which are very important for industrialists to predict some characteristics of materials before casting processing.