Critical Evaluation Of The Effect Of Alloyed Nitrogen On The Susceptibility Of Stainless Steels To Environmentally Induced Cracking Eic Nitrogen PDF Download

Modern stainless steel melting and refining techniques now make it possible to consider nitrogen as an economic and controllable alloying addition to 18Cr-8Ni austenitic stainless steels. Studies show that nitrogen additions of up to about 0.16 percent to 18Cr-8Ni steels can result in some improved properties. Nitrogen is a strong strengthening element to 18Cr-8Ni steels and will increase yield strength by about 5.5 to 6.2 MPa (800 to 900 lb/in.2) for each 0.01 percent nitrogen. Isothermal time-temperature sensitization (TTS) diagrams developed for 18Cr-8Ni steels containing about 0.05 percent carbon and up to 0.25 percent nitrogen indicate that nitrogen at least up to 0.16 percent retards intergranular carbide precipitation. Corrosion tests on isothermally sensitized or welded specimens show reduced corrosion rates with nitrogen additions consistent with the TTS data. For low-carbon 18Cr-8Ni steels, nitrogen additions up to 0.15 percent have no apparent effect on the normally excellent sensitization resistance of these steels, at least as measured by corrosion tests on isothermally heated or welded specimens. Nitrogen additions were also found to improve pitting and crevice corrosion resistance as evaluated in anodic polarization or chloride pitting/crevice corrosion tests. Stress corrosion evaluations were conducted on solution-annealed material using constrained U-bend specimens in both severe and milder environments. The results indicated that nitrogen content up to 0.16 percent did not significantly affect stress corrosion cracking susceptibility, but 0.25 percent nitrogen appeared detrimental in some environments.