Effect of Tempering on Cyclic Loading of Medium Carbon Steel

Abstract

The utility of Medium Carbon steel is well known now days. It has got such a variety of uses in distinctive commercial ventures because of its moderately low cost and great mechanical properties. The failure due to cyclic loading or dynamic loading is a crucial topic in the field of mechanical behaviour of materials since cyclic loading counts about ninety percent of the failures resulted from mechanical causes. In this work the cyclic loading behaviour of Medium Carbon Steel has been studied. The properties of steel are greatly influenced by various heat treatment techniques and tempering is the most common and important heat treatment technique. In the present work the effect of tempering on microstructure, tensile properties, hardness and most importantly on cyclic loading behaviour has been studied. The emphasis is given to the endurance limit. Attempts have been made to find out the best set of tempering conditions. The Medium Carbon Steel specimens were first austenitized at 850oC, hold for 1hr for soaking and then quenched in water bath maintained at room temperature. The quenched specimens were then tempered at three different temperatures 200oC, 400oC and 600oC the duration of tempering treatment was 60min., 90min., and 120min. for all of the above temperatures. Attempts have been made to correlate the microstructure with the mechanical properties of Medium Carbon Steel. The cyclic loading test was carried out in R.R. Moore Rotating Beam Testing Machine with a completely reversed stress pattern. Here the maximum stress and minimum stress are equal in magnitude but opposite in sense so the stress ratio i.e. the ratio of maximum stress to minimum stress becomes R= -1, the mean stress becomes zero. From this work, it may be concluded that tempering significantly improves the mechanical properties as well as the fatigue life of the material, and the best results have been seen for low temperature tempering at 200oC, for 60 min.