An Experimental Study of the Effect of Heat Treatment using Water and Air on the Hardness of Carbon Steel

Heat treatment processes are widely used in manufacturing to achieve high levels of improving the mechanical properties of metal materials, including hardening, which is multiple stages starting from high hardening of the metal until it is almost brittle and even soft, it is also used in annealing metals that industrial processes have hardened to adapt the metals to the purposes used for them in various industries. In this paper, practical experiments, such as heat treatment, are conducted on five samples of carbon steel, as it is one of the important materials in many industries. This experiment aims to demonstrate the extent of the effect of cooling media on the microstructure and the hardness that these samples reached after the operations performed on them. These samples were exposed to a temperature of 850°C in an electric furnace, then cooled in air, and also cooled in water. After cooling in water, they were exposed to different temperatures, which are 200°C, 400°C, and 600°C, then polished in several stages after that, then washed with acetone. Then they were exposed under an electron microscope to show the change that occurred in the microstructure of these samples. Then Vickers Hardness Test was conducted to show the hardness of these samples. The results showed that the samples that were immersed in water had a much higher hardness than those that were left to cool in the air, and the samples that were heated in the second stage from 200°C to 600°C had a lower hardness and increased plasticity of the metal as the temperature increased.