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EUROMAT 2005 Prague,
5-9 September 2005
Abstract
A
Steady-State Creep Model for the AISI 316 L(N) in the Technically Relevant Stress
Range
M. Rieth
Forschungszentrum Karlsruhe,
Institut für Materialforschung I, P.O. Box 3640, 76021 Karlsruhe
Among many other
applications the austenitic 17/12/2–CrNiMo steel
316 L(N) (DIN 1.4909) is used or envisaged for both conventional and nuclear
power plant construction as well as for ITER within the International Nuclear
Fusion Project. Worldwide a huge number of experimental investigations have
already been carried out to determine the material properties (including creep
behavior) of this steel type in the conventional stress and temperature range.
In the design relevant low-stress range at 550 °C and 600 °C, however, creep
data allowing statements to be made about the stress dependence of the minimum
creep rate or about the technically relevant creep strain limits are almost
unavailable. This is not only due to reasons of time, but to technical reasons,
too. In this stress-temperature range, the expected creep or strain rates are
so small that they can hardly be measured by conventional creep tests.
Therefore, we have started a special long-term creep testing program at 550 °C
and 600 °C, respectively, in 1991. After an experimental period of about 10
years the creep tests have been either finished or aborted, and evaluated. Now,
this low-stress creep data not only allow for a much better long-term prediction
of the reliability of 316 L(N) applications but also enable deformation modeling
for a broader stress range. The present work focuses mainly on the set-up of a
steady-state creep model for the 316 L(N) steel which explains the
accelerated creep velocity observed at the low stress range. Due to the small
number of adjustable parameters it may also be easily adapted to other
materials. Since austenitic stainless steels are well known for their
problematic aging behaviour at elevated temperatures, microstructure and
precipitation formation as well as their impact on creep are outlined above
all.
290 words