Jj. Horn et al., INFLUENCE OF DENSITY AND SINTERING TEMPERATURE ON FATIGUE-CRACK GROWTH AND FRACTURE-TOUGHNESS OF FL4405 HIGH-STRENGTH PM STEEL, Powder Metallurgy, 41(3), 1998, pp. 205-210
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.