Influence of Density and Sintering Temperature on Fatigue Crack Growth and Fracture Toughness of FL4405 High Strength PM Steel

Abstract

Density and sintering temperature effects were investigated with FL4405 low alloy PM high strength steel. Room temperature, plane strain fracture toughness KIc, and constant amplitude fatigue crack growth with (min/max) load ratios of 0·05 and 0·5 and macroand microfractography were evaluated. Two density levels, 7·0 and 7·4 g cm−3, and two sintering temperatures, 1120 and 1315°C, were investigated. Increasing the density and sintering temperature had no influence on stress intensity threshold and near threshold fatigue crack growth resistance where transcrystalline/transparticle cleavage existed. At higher fatigue crack growth rates, where ductile dimples existed, both higher density and higher sintering temperature enhanced fatigue crack growth resistance. The KIc and Kmax values at fatigue crack growth fracture increased at the higher density and increased further at the higher sintering temperature. All final fracture regions were brittle at the macroscale while containing ductile dimples at the micro scale. No crack closure was found in fatigue crack growth tests and no load ratio effects were present at low fatigue crack growth rates. Significant load ratio effects were present at high fatigue crack growth rates. PM/0770