Influence of Density and Sintering Temperature on Smooth, Notched, and Cracked Variable Amplitude Fatigue Behaviour of FL4405 High Strength PM Steel

Abstract

Density and sintering temperature effects were investigated with FL4405 low alloy PM high strength steel. Room temperature variable amplitude loading was applied to smooth axial specimens, keyhole notch specimens, and compact disc precracked specimens. Each block of the variable amplitude load spectrum contained 20 127 reversals involving both tensile and compressive mean loads. Two density levels, 7·0 and 7·4 g cm⁻³, and two sintering temperatures, 1120 and 1315°C, were investigated. Increasing the density decreased pore size and volume while increasing the sintering temperature increased pore roundness. All final fracture regions were brittle at the macroscale and contained ductile dimples at the microscale. Fatigue regions contained principally cleavage, principally ductile dimples, or mixtures of cleavage and ductile dimples. Keyhole notch specimens with K _t = 3·5 were fully notch sensitive for all material conditions. Increasing the density resulted in a significant increase in fatigue resistance, while increasing the sintering temperature showed only a small additional increase. PM/0771