Effect of tube spinning and subsequent heat treatments on strength, microstructure and residual stress state of AISI/SAE type 4140 steel

Abstract

In the present study, the effects of deformation percentage (23, 30, 50 and 66%) and subsequent stress relief and tempering heat treatments on the mechanical properties, residual stress state and microstructure of AISI/SAE type 4140 steel tubes manufactured by forward spinning were evaluated. Mechanical properties were determined by means of hardness and tensile tests. The tangential component of the surface residual stresses was determined by a slitting method. Plastic deformation of the metal during spinning refined and elongated the grains in the direction of metal flow, following a spiral path, resulting in improved mechanical properties. Tensile and yield strengths, as well as hardness, were all increased as a function of increasing percentage deformation. With stress relieving, the strength values were enhanced, whereas a slight decrease in hardness took place. Stress relieving did not change the microstructure considerably, whereas tempering resulted in a partially recrystallised microstructure, removing the effect of plastic deformation. The tangential residual stresses were tensile, and those of the as deformed tubes increased with an increasing amount of deformation up to 50%, then tended to decrease. The magnitude of the residual stresses decreased with stress relieving heat treatment, while tempering reduced the residual stresses to negligible levels.