Intergranular Corrosion Resistance of Carpenter 20Cb-3

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.