During the past three decades the chromium-nickel stainless steels have become invaluable for handling corrosive chemicals. In numerous media, these materials provide completely satisfactory service. In certain conditions of heat treatment, when exposed to specific media, they may exhibit a type of attack known as intergranular corrosion, which can seriously affect their usefulness. Austenitic stainless steels, such as AISI Types 302, 304, 316, and 317, can become susceptible to such attack as a result of exposure in the temperature range 800-1500°F. This "sensitization" is generally attributed to the precipitation of chromium carbides at the grain boundaries, which lowers the effective chromium content and corrosion resistance near the grain boundaries. This phenomenon has long been recognized and has led to the development of extra low carbon types and columbium or titanium stabilized stainless steels which possess greatly improved resistance to carbide precipitation.

Sensitization may come about as a result of any of the following operations:

1. welding, wherein the affected zone is adjacent to the weld deposit,
2. stress relieving treatments, or
3. exposure during fabrication or in service within the sensitizing range.