Fatigue behavior of a sintered high-strength steel

Stress-controlled fatigue tests were performed on a common high-strength powder metallurgy (PM) alloy steel (Fe-4 w/o Ni-1.5 w/o Cu-0.5 w/o Mo-0.6 w/o C) to provide fatigue strength data at 10 7 cycles. Four unnotched and four notched geometries were compacted, each with two different densities and sintered in 95 v/o N 2 5 v/o H 2 at 1,120°C for nominally 30 mm in the same industrial belt furnace on ceramic plates. All geometries were analyzed by finite element modeling (FEM) to determine the locations of the highest stress concentrations and the corresponding first principal stresses. For the chamfered specimens the reduction of the section modulus by the chamfers was taken into account. The nominal stress of rectangular cross sections in torsion was calculated from Szabó's exact solution. The local fatigue strengths conform well with a density-modified three-parameter Weibull distribution and, within the range investigated, do not deviate significantly from a two-parameter Weibull distribution.