  The galling behaviour of 316L stainless steel was investigated in both the
unoxidised and oxidised states, after exposure in simulated PWR water for 850
hours. Galling testing was performed according to ASTM G196 in ambient
conditions. 316L was found to gall by the wedge growth and flow mechanism in
both conditions. This resulted in folds ahead of the prow and adhesive
junction, forming a heavily sheared multilayered prow. The galling trough was
seen to have failed through successive shear failure during wedge flow.
Immediately beneath the surface a highly sheared nanocrystalline layer was
seen, termed the tribologically affected zone (TAZ). It was observed that
strain-induced martensite formed within the TAZ. Galling damage was quantified
using Rt (maximum height - maximum depth) and galling area (the proportion of
the sample which is considered galled), and it was shown that both damage
measures decreased significantly on the oxidised samples. At an applied normal
stress of 4.2 MPa the galled area was 14 % vs. 1.2 % and the Rt was 780 um vs.
26 um for the unoxidised and oxidised sample respectively. This trend was
present at higher applied normal stresses, although less prominent. This
difference in galling behaviour is likely to be a result of a reduction in
adhesion in the case of the oxidised surface.
