Residual Stresses in Sintered PM Steels

摘要

The effect of microstructural inhomogeneities on residual stress distributions in a prealloyed (FL4405) and two hybrid (FLC2-4405 and FLN2-4405) PM steels was evaluated. A green density of 7.4 g/cm~3 was obtained by double pressing (550/550 MPa) and double sintering. Sintering temperatures of 1120℃ and 1260℃ were utilized. A group of sintered compacts of each alloy was quenched + tempered and two groups of sintered compacts of the FLC2-4405 and FLN2-4405 alloys were sinter-hardened. The measurement of residual stresses was carried out on the shoulders of failed fatigue crack propagation specimens. A layer removal technique, combined with strain gauges, was used to monitor the stresses at various depths below the surface during electrochemical etching. Tensile residual stresses were present on the surface layers of most of the specimens. Minimum and maximum tensile stresses were 55 MPa and 585 MPa, respectively. Stress distributions in all the samples exhibited a wavy appearance. Quenched + tempered steels possessed mean tensile residual stresses in the interior; in the other conditions, the mean residual stress in the interior was essentially zero.