In this work, the heat treatments were performed by three types of processes: normalizing, quenching and tempering, where the samples were heated to 900°C and held for 1 hour inside the furnace at that temperature. The first group of hot samples was cooled by air to room temperature through the normalizing process, but the second group was rapidly cooled by two types of the quenching media: (cold water at 5°C and polymer solution). The samples after quenching processes were tempered by heating to 450°C for one hour as a soaking time at this temperature. The samples were then taken out of the furnace, and cooled by air. The machinability, tensile strength, hardness, ductility and microstructure tests of carbon steel (GOST 50) have been achieved after the completion the heat treatment processes. The results appeared improvement and change in these properties after the heat treatments due to the change of the hardness, ductility and toughness of samples.

Conclusions
From the results of this study, the following points can be concluded;
? The results showed that the clear improvement of tensile strength and hardness with highest values by quenching of cold water and polymer solution, but with lowest value of ductility.
? Tempering after quenching by water and polymer achieved the highest ductility (elongation and reduction %) comparing with other processes.
? The best result of surface roughness was with quenching by polymer solution due to the toughness of the structure after quenching and the nature of the cooling rate of the polymer which prevents cracks after quenching.
? The result of surface roughness with cooling by water was good but less than polymer cooling due to rapidly cooling rate with water.
? The microstructure results showed improvement with quenching processes. The quenching behavior of polymer referred to uniformity of a needle shape due to the cooling rate which was fast at the beginning, then it was slower than the water quenching afterwards.