When austenitic stainless steels are heated or cooled through the temperature
 range 800-1650F, chromium tends to combine with carbon to form chromium
 carbides.  The carbides precipitate preferentially at grain boundaries
 depleting chromium from the adjacent areas.  This reduces the corrosion
 resistance of the chromium depleted areas, sensitizing the alloy to
 Intergranular Corrosion Cracking (IGC).

Sensitization may result from slow cooling from solution annealing
 temperatures, or stress relieving - after welding - in the 800F to 1650F
 temperature range.  In welded fabrications, sensitization and IGC may occur
 in aggressive environments in a rather narrow band on either side of or on
 the side opposite the weld, known as the heat affected zone (HAZ).


          Methods of Minimizing Intergranular Corrosion - IGC.

     1) Solution anneal above 1900F followed by a rapid quench.

     2) Use type 347, a Cb stabilized grade, or 321, a Ti stabilized grade.

     3) Use a low carbon, 0.03% max. carbon grade such as 304L, 316L, 317L
          and 904L.

 In today's technology with AOD melting furnaces, carbon is easily and
  routinely reduced to very low residuals.  AOD melting is making the low
  carbon grades the standard for welded fabrication.

 ASTM A262 practice A to E are standard tests to determine susceptibility to
  IGC.  Practice E, the Huey test, is widely used.