Knife-Line Attack. Stabilized austenitic stainless
steels may become susceptible to a localized
form of intergranular corrosion known as knifeline
attack or knife-line corrosion. During welding,
the base metal immediately adjacent to the
fusion line is heated to temperatures high enough
to dissolve the stabilizing carbides, but the cooling
rate is rapid enough to prevent carbide precipitation.
If weldments in stabilized grades are then
heated into the sensitizing temperature range of
425 to 815 C (800 to 1500 F), for example, during
stress-relieving treatments, high-temperature
service, or subsequent weld passes, chromium
carbide can precipitate. The precipitation of chromium
carbide leaves the narrow band adjacent
to the fusion line susceptible to intergranular
corrosion.
Knife-line attack can be avoided by the proper
choice of welding variables and by the use of stabilizing
heat treatments.