dc.description.abstract | The aim of this study is to investigate the influence of environmental
factors, including pH value, temperature, chloride, and pitting inhibitor, on the
corrosion fatigue properties of AISI 347 stainless steel. In particular, the
high-cycle fatigue (HCF) and fatigue crack growth (FCG) behavior in air and
five aqueous environments were made a comparison. The effect of
environmentally assisted cracking mechanisms on the degradation of fatigue
resistance was characterized. The electrochemical properties in five aqueous
environments were also made a comparison. Fractography and
microstructural analyses with optical microscopy (OM) and scanning electron
microscopy (SEM) were conducted to determine the corrosion fatigue crack
initiation and propagation modes.
Results showed that the fatigue strength of AISI 347 in H2SO4 and 3.5%
NaCl solutions was lower than that in air, water, 80oC water, and 3.5% NaCl
with inhibitor; especially fatigue strength in H2SO4 was the lowest.
However, the FCG rates in all environments were almost the same. These
results indicated that the initial fatigue cracking stage controlled the HCF life
of AISI 347.
The H2SO4 and 3.5% NaCl solutions had more detrimental effects on the
HCF of AISI 347 in crack initiation and stage I cracking stages as compared
with other aqueous environments. The fatigue-strength reduction in 3.5%
NaCl solution resulted from the formation of corrosion pits as the stress
concentrations for premature fatigue crack initiation. The lower pH value in
H2SO4 would dissolve the protective passive surface film and enhance the
synergism between corrosive environment and cyclic stresses leading to the
shoter fatigue life by reducing the periods of stage I cracking and transition
from stage I to stage II cracking. Adding pitting inhibitor in 3.5% NaCl
solution can prevent formation of corrosion pits on specimen surface and
extend HCF life. This is due to the fact that the inhibitor added in 3.5%
NaCl solution can prevent pitting formation by reacting with the metal ions to
form a protective film on specimen surface. | en_US |