INFLUENCE OF DENSITY AND SINTERING TEMPERATURE ON FATIGUE-CRACK GROWTH AND FRACTURE-TOUGHNESS OF FL4405 HIGH-STRENGTH PM STEEL

Density and sintering temperature effects were investigated with FL440 5 low alloy PM high strength steel. Room temperature, plane strain fra cture toughness K-Ic, and constant amplitude fatigue crack growth with (min/max) load ratios of 0.05 and 0.5 and macro- and microfractograph y were evaluated. Two density levels, 7.0 and 7.4 g cm(-3), and two si ntering temperatures, 1120 and 1315 degrees C, were investigated. Incr easing the density and sintering temperature had no influence on stres s intensity threshold and near threshold fatigue crack growth resistan ce where transcrystalline/transparticle cleavage existed. At higher fa tigue crack growth rates, where ductile dimples existed, both higher d ensity and higher sintering temperature enhanced fatigue crack growth resistance. The K-Ic and K-max values at fatigue crack growth fracture increased at the higher density and increased further at the higher s intering temperature. All final fracture regions were brittle at the m acroscale while containing ductile dimples at the microscale. No crack closure was found in fatigue crack growth tests and no load ratio eff ects were present at low fatigue crack growth rates. Significant load ratio effects were present at high fatigue crack growth rates.