Induction tempering and furnace tempering of induction hardened 4140 steel – microstructural profile analysis and residual stress

Furnace tempering is experimentally compared to induction tempering on induction tempered steel rods in terms of residual stress and microstructural development. In this investigation round 38-centimeter diameter 4140 steel rods were furnace hardened and tempered to Rc 32. These rods were subsequentially induction hardened followed by induction tempering or furnace tempering to Rc = 56. These heat-treated rods were characterized for residual stress with x-ray diffraction and microhardness and microstructure profiles with optical and scanning electron microscopy. The results will be discussed in terms the thermal profiles in the rods as a function of time. Four point bending fatigue tests are planned to determine the effects on fatigue life.