One of ways to improve properties of materials without changing the product shape to
obtain the desired engineering applications is heating and cooling under effect of controlled
sequence of heat treatment. The main aim of this study was to investigate the effect of
heating and cooling on the surface roughness, microstructure and some selected properties
such as the hardness and impact strength of Medium Carbon Steel which treated at different
types of heat treatment processes. Heat treatment achieved in this work was respectively,
heating, quenching and tempering. The specimens were heated to 850°C and left for 45
minutes inside the furnace as a holding time at that temperature, then quenching process was
performed in four types of quenching media (still air, cold water (2°C), oil and polymer
solution), respectively. Thereafter, the samples were tempered at 200°C, 400°C, and 600°C
with one hour as a soaking time for each temperature, then were all cooled by still air. When
the heat treatment process was completed, the surface roughness, hardness, impact strength
and microstructure tests were performed. The results showed a change and clear
improvement of surface roughness, mechanical properties and microstructure after
quenching was achieved, as well as the change that took place due to the increasing
toughness and ductility by reducing of brittleness of samples.

CONCLUSIONS
From the results of this investigation, it can be concluded the following points:
• Cold water was the better media of quenching due to the rapid of cooling but in this case,
the microstructure may contain cracks.
• Best results for surface roughness, microstructure, hardness and impact strength can be
obtained with cold water for quenching and tempering processes, the percentage
improvement was as follows; the hardness improvement were 2.458 %, impact strength
1.164 %, surface roughness 13.14 % with quenching process. But, the result at tempering process of impact strength was 5.52 %, at 600°C with decreasing of hardness and surface
roughness.
• Good application has been obtained when improved toughness of medium carbon steel
after the increase of tempering temperature.
•Polymer is better than oil but less than cold water for quenching and tempering process.
• By using tempering process, brittleness can be reduced by increasing the ductility.
• The surface roughness revealed more improvement after quenching by water and close
with polymer and oil but with increase of tempering temperature, the surface quality is
somewhat reduced.