“Stress Generation in an Axle Shaft during Induction Hardening”

Axles are typically induction hardened to develop a hard martensitic outer surface and a ductile, tough core.  In the process of hardening the case, residual surface compressive stresses are developed, and these stresses further enhance performance by extending fatigue life.  The induction heating power, the scan speed along the axle shaft, the spray quenching intensity and the time delay between the heating and the spray all interact to affect the case depth and the residual stress state.

            Computer simulations of the magnitude and distribution of stresses during and after an induction hardening process are presented for a full-float truck axle made of 1541 steel.  Multiple simulation programs are used to address the coupling of the multiple physical phenomena involved: electromagnetic, thermal, metallurgical, stress and shape change.  The three main regions that comprise the axle are focused on: the flange and fillet area, the shaft, and the spline.

These computer based studies enhance a designer’s capabilities to predict the actual part performance from the induction hardening process.  The residual stress state and the metallurgical changes produced by the induction heat treat process are imported into an axle loading model to document the improved torsional fatigue resistance that is gained by both the surface strengthening and the surface residual compressive stress state.