TY - CHAP
T1 - Influence of material, environment and strain rate on environmentally assisted cracking of austenitic nuclear materials (DEFSPEED). Strain localisation in sensitised Type 304 stainless steel in simulated BWR-environment
AU - Ehrnsten, Ulla
AU - Saukkonen, Tapio
AU - Hänninen, Hannu
PY - 2009
Y1 - 2009
N2 - Intergranular, environmentally assisted cracking (EAC)
has been observed, not only in sensitised austenitic
stainless steels in oxidising BWR conditions, but also in
non-sensitised, cold deformed stainless steels. Further,
EAC has recently been reported also in PWR plants, in
connection to local non-specified water chemistry
conditions. Environmentally assisted cracking in
nickel-based weld metals is considered to be one of the
most challenging issues for operating power plants today.
Mechanistic understanding of the effects of main factors
affecting environmentally assisted cracking of austenitic
materials is important, especially as the trend in the
NDE inspection strategy is moving towards risk-informed
inspection.
In the SAFIR 2010 DEFSPEED project (Influence of
material, environment and strain rate on environmentally
assisted cracking of austenitic nuclear materials),
investigations are performed using super slow strain rate
tests (SSSRT) in LWR environments and the deformation is
characterised using versatile methods such as FE-SEM EBSD
and TEM. The investigations aim to increase the
mechanistic understanding of precursors to crack
initiation as well as factors affecting crack growth in
austenitic nuclear materials. The results achieved from
the SSSRT's on deformed and sensitised austenitic
stainless steel of Type 304 and from EBSD
characterisation of a Type 304 nuclear pipe weld show
non-uniform distribution of micro-strains in the
material, being higher in the vicinity of grain
boundaries than inside the grains. The results indicate
that several phenomena can occur during extremely slow
deformation, such as heterogeneous creep, dynamic
recovery and relaxation leading to grain boundary
sliding, dynamic strain ageing and short range ordering.
The results also show that non-homogeneous
microstructures, e.g. local changes in the grain size,
affect strain localisation.
AB - Intergranular, environmentally assisted cracking (EAC)
has been observed, not only in sensitised austenitic
stainless steels in oxidising BWR conditions, but also in
non-sensitised, cold deformed stainless steels. Further,
EAC has recently been reported also in PWR plants, in
connection to local non-specified water chemistry
conditions. Environmentally assisted cracking in
nickel-based weld metals is considered to be one of the
most challenging issues for operating power plants today.
Mechanistic understanding of the effects of main factors
affecting environmentally assisted cracking of austenitic
materials is important, especially as the trend in the
NDE inspection strategy is moving towards risk-informed
inspection.
In the SAFIR 2010 DEFSPEED project (Influence of
material, environment and strain rate on environmentally
assisted cracking of austenitic nuclear materials),
investigations are performed using super slow strain rate
tests (SSSRT) in LWR environments and the deformation is
characterised using versatile methods such as FE-SEM EBSD
and TEM. The investigations aim to increase the
mechanistic understanding of precursors to crack
initiation as well as factors affecting crack growth in
austenitic nuclear materials. The results achieved from
the SSSRT's on deformed and sensitised austenitic
stainless steel of Type 304 and from EBSD
characterisation of a Type 304 nuclear pipe weld show
non-uniform distribution of micro-strains in the
material, being higher in the vicinity of grain
boundaries than inside the grains. The results indicate
that several phenomena can occur during extremely slow
deformation, such as heterogeneous creep, dynamic
recovery and relaxation leading to grain boundary
sliding, dynamic strain ageing and short range ordering.
The results also show that non-homogeneous
microstructures, e.g. local changes in the grain size,
affect strain localisation.
M3 - Chapter or book article
SN - 978-951-38-7266-3
T3 - VTT Tiedotteita - Meddelanden - Research Notes
SP - 418
EP - 429
BT - SAFIR2010. The Finnish Research Programme on Nuclear Power Plant Safety 2007-2010
PB - VTT Technical Research Centre of Finland
CY - Espoo
ER -