Abstract
Stainless steels are being evaluated for use in industrial gas turbine exhaust components experiencing temperatures as high as 650°C. This study focuses on fatigue crack
growth, creep fatigue crack growth, and creep crack growth behavior of two austenitic
stainless steels, 321SS and 253MA. Tests were performed on compact tension specimens at
550°C and 650°C. Fatigue crack growth testing was performed in accordance with ASTM
E647 at a frequency of 5Hz, creep fatigue crack growth testing was performed in accordance
with ASTM E2760 with hold times of 60 s and 600 s, and creep crack growth testing was
performed in accordance with ASTM E1457. The study showed that under fatigue crack
growth testing, both materials exhibited a similar behavior with transgranular crack growth.
For creep fatigue crack growth, 253MA exhibited higher crack growth rates than 321SS for a
similar stress intensity factor range, ∆K, and for a similar average contour integral value,
(Ct)avg. 253MA was less creep resistant and crack growth was dominated by creep while
321SS had a higher creep resistance with crack growth being driven by fatigue. SEM
imaging confirmed this crack growth behavior (CFCG) showing intergranular crack growth
in 253MA and transgranular crack growth in 321SS. In creep crack growth testing 253MA
again showed less creep resistance than 321SS at both test temperatures. Both materials
exhibited intergranular crack growth under these conditions. Creep crack growth showed that
the contour integral C* was a better correlating parameter for crack growth rates than the
stress intensity factor K.