Micro-residual stresses caused by deformation, heat, or their combination during friction welding

The influences of mechanical and thermal treatments on the macro- and microstresses in two-phase materials were investigated. On samples of an austenitic–ferritic duplex steel the alterations of micro-residual stresses caused by different parameters of material treatments, e.g. deformation rate, deformation temperature, tempering, cooling rates were studied. The friction welding procedure is an example of the combination of all these mechanical and thermal parameters. Its effects on macro- and microstresses were investigated on friction welded joints of a quenched and tempered low alloyed steel, of a duplex steel and on joints between both steels. The distributions of macro- and micro-residual stresses were determined versus the distance from the welding zone and from the surface using X-ray and neutron diffraction. Strain measurements on the compact specimens and on thin plates as well as measurements on both phases allow to separate between macro- and microstresses. Both kinds show up with pronounced profiles. The results reveal that microstresses should not be neglected in the assessments of X-ray results.