In this paper, quenching and tempering effects on the machining conditions of
medium carbon steel were investigated. The samples were quenched in a saltwater and
polymer solution after heated to austenitizing temperature at 870°C, then, the tempering
process of the samples were conducted to reduce internal stresses and hardness. In the
tempering process the samples were heated again to 400°C with a soaking time was one hour,
so cooled in still air. So the samples were machined by lathe machine with selected cutting
conditions. The results appeared the effect of heat treatments on hardness, surface finishing,
cutting force and microstructure that were evaluated before and after heat treatment with
various cutting conditions.

CONCLUSIONS
From the previous results can be concluded the following;
1- The improvement of machinability was obtained with heat-treated samples more than the untreated
samples at all cutting conditions.
2-There are effects of heat treatment on roughness for all processes, the best results with tempering
after quenching by polymer with less feed and DOC.
3- The highest value of hardness and brittleness was with quenching by water, but the machinability
was poor.
4-The cutting force increases gradually at the increasing of feed and depth of cut with the cutting
speed is fixed for all processes.
5- The microstructure after improvement by tempering was achieved best results of cutting force and
roughness.