Abstract:
300M ultra high strength steel has been widely used for over forty years
as a structural material in aerospace applications where a high strength is
required. These parts are generally protected from corrosion by
electroplated cadmium sacrificial coatings. However, there are concerns
over this coating material due to its high toxicity and alternative coatings
including Zinc-14%Nickel and SermeTel®1140/962 have been considered.
It is known that applying electrodeposited coatings causes atomic
hydrogen to be absorbed by the steel substrate producing delayed failure
by direct hydrogen embrittlement. Hydrogen is also absorbed when a
sacrificial coating undergoes corrosion in service and this process is known
as re-embrittlement. The effect of electroplated Zinc-14%Nickel and
aluminium based SermeTel®1140/962 sacrificial coatings in causing
hydrogen embrittlement and re-embrittlement of 300M steel have been
compared to that of conventional electroplated cadmium.
AerMet®100 ultra high strength steel has been also considered as
alternative replacement for the conventional 300M. Hence, the hydrogen
embrittlement and re-embrittlement susceptibilities of AerMet®100 were
studied when coated with cadmium, Zinc-14%Nickel and
SermeTel®1140/962. In addition, two alternative alloys GifloM2000 and
CSS-42LTM were also taken into consideration and only the extent of
hydrogen re-embrittlement was assessed when coated with cadmium and
SermeTel®1140/962, respectively.
Slow strain rate tests, SSRT, were carried out for plated, plated and baked
as well as plated, baked and corroded tensile specimens. The time to
failure values were compared using a Weibull distribution, statistical ttests
and embrittlement indices. Differences in hydrogen susceptibility of
the high strength steels considered might depend upon their intrinsic
hydrogen transport characteristics. These properties were studied and
compared in terms of hydrogen diffusivity and solubility.
