Analysis of the toughness characteristics of cryogenic 9% nickel steels. Final report, July 1984-November 1985

A statistical analysis of the Charpy notch toughness exhibited by production heats of 9% nickel steels as affected by the year of manufacture and compositional variations was performed. Data from more than 600 heats show a notable increase in notch toughness during the past 15 years and a level of performance far superior to minimum requirements of ASTM standards. A multiple regression analysis indicated that much of the improvement was attained by lowering the sulfur and carbon contents of the steel. The unexplained variance of notch toughness may be due to effects of heat treatment, the within-heat scatter, and composition variables that lay outside the data available for analysis. Doubling the required minimum Charpy notch toughness appears feasible without hardship to steel producers but with an enhancement of the reliability of LNG storage tanks.