Stress Corrosion Cracking Susceptibility Of Stainless Steels and Nickel-Base Alloys In Polythionic Acids and Acid Copper Sulfate Solution

Abstract

Abstract Intergranular cracking tendencies of fourteen stainless steels and two high-nickel alloys have been evaluated by exposing numerous specimens to polythionic acid and standard acid copper sulfate solutions. The sensitization curves for solution-annealed wrought stainless steels, which had been held for varying times at temperatures from 800 to 1700 F (427 to 927 C), had the same lower temperature limit for both solutions. The higher temperature limit for acid copper sulfate was significantly higher than for polythionic acid so the more standard acid copper sulfate test can be used for control. Decreasing the carbon content shifted the sensitization curve to longer times. Times in excess of 1000 to 4000 hours were required to sensitize steels stabilized with columbium or titanium. Molybdenum additions decrease the sensitization range, but the higher-carbon molybdenum-bearing stainless steels had an unexplained sensitization zone from 900 to 1000 F (482 to 538 C) for holding times exceeding 200 hours. The 25 percent Cr-Ni materials became sensitized over a narrower range of temperature than the plain 18 percent Cr-Ni alloys and, for a given carbon content, were more stable. If 1200 F (649 C) sensitizing followed thermal stabilization, the low-carbon Type 310 and Types 347 and 321 steels were sensitized the least. Two high-nickel alloys and a cast stainless steel failed when sensitized for 4 hours at 1200 F.