Welding is the common cause of the sensitization
of stainless steels to intergranular corrosion.
Although the cooling rates in the weld itself and
the base metal immediately adjacent to it are sufficiently
high to avoid carbide precipitation, the
weld thermal cycle brings part of the heataffected
zone (HAZ) into the precipitation temperature
range. Carbides can precipitate, and a
zone somewhat removed from the weld becomes
susceptible to intergranular corrosion (Fig. 2).
Welding does not always sensitize austenitic
stainless steels. In thin sections, the thermal
cycle may be such that no part of the HAZ is at
sensitizing temperatures long enough to cause
carbide precipitation. Once the precipitation has
occurred, it can be removed by reheating the
alloy to above 1035 C (1895 F) and cooling it
rapidly. This thermal treatment dissolves the
chromium carbide precipitates and restores the
chromium-depleted zone. This practice is commonly
termed solution anneal