Carpenter 20Cb-3 strip in the stabilized, TIG welded and solution annealed conditions has been sensitized in the range 1050 to 1625 F (566 to 885 C) prior to intergranular corrosion testing in the Huey, ferric sulfate-sulfuric acid, nitric-hydrofluoric acid and Strauss tests. In stabilized annealed material, the sensitization temperature producing maximum susceptibility is about 1450 to 1500 F (788 to 816 C). Welded plus sensitized material showed susceptibility to intergranular corrosion immediately adjacent to the weld with the most severe sensitization temperature being about 1250 F (677 C). Stress relieving stabilize annealed or welded material in the range of about 1100 to 1600 F (593 to 871 C) is not recommended unless prior testing or experience indicate satisfactory performance. Huey rates following a 1250 F (677 C) sensitization increase as the annealing temperature is increased in the range 1725 to 2250 F (941 to 1232 C). Rates following a 1400 F (760 C) sensitization increase with a 2050 F (1121 C) anneal and decrease for 2200 F (1204 C) and higher treatments. The attack in stabilize annealed material sensitized at 1450 F (788 C) is attributed primarily to M6C. M23G6 plays a role at lower temperatures particularly in the as-welded or solution annealed conditions. Sigma phase can form at the higher sensitization temperatures.

Subject
Acids, Sigma phase, Weld attack, Materials, Carbides, Corrosion rate, Acid attack, Heat, Sensitization, Carbon, Annealing, Grain boundary, Intergranular corrosion
© 1971 National Association of Corrosion Engineers
1971
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