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Item Aqueous corrosion behaviour of ductile iron and ductile iron containing 1 wt. pct. chromium(1997) Surendranathan A.O.; Hebbar, K.R.; Sudhaker Nayak, H.V.Ductile irons with graphite in spheroidal form enjoy the processing characteristics of grey iron and mechanical properties of steel. This paper describes the corrosion behaviour of ductile iron containing 1 wt. % chromium in sea water, dilute sulphuric acid and dilute sodium hydroxide solutions and compares with that of unalloyed ductile iron. Study is made in as-cast, annealed and cold worked (upto 28% reduction in thickness) conditions at three different temperatures. Since the alloying addition brings changes in the proportion of phases, the corrosion behaviour of the two materials studied were different, though alloying addition is small, indicating corrosion behaviour to be structure sensitive.Item Study of corrosion behaviour of ductile iron by electrochemical polarisation techniques(1998) Surendranathan, A.O.; Hebbar, K.R.; Sudhaker, Nayak, H.V.The use of electrochemical methods to characterize materials for their corrosion behaviour is well known. Both linear polarisation and Tafel extrapolation techniques are made use of to study the corrosion behaviour of ductile iron (DI) in natural sea water, 5 v/o H2SO4 and 5 w/o NaOH. Samples were tested in the as cast, annealed and cold worked conditions at 300 K, 325 K and 340 K. It was found that annealed material had the least corrosion rate. This is explained on the basis of the proportion of phases in the microstructure, the DI has on annealing. On annealing as cast DI, certain amount of cementite in the pearlite is converted into ferrite. Since a single phase material is always more corrosion resistant than a multiphase one, ferrite phase increases corrosion resistance. High degree of cold working is detrimental with respect to corrosion resistance as it increases the stored energy and dislocation density in the material thereby enhancing the kinetics of corrosion reactions. The activation energy for DI was found to be lowest in sulphuric acid medium and highest in sodium hydroxide medium. The corrosion rates for DI in H2SO4 medium were the highest while in NaOH they were the lowest irrespective of material condition and technique of rate measurement.Item Stress corrosion failure of Zircaloy?2 sheets in methanolic HCl solution: Role of crystallographic texture(1982) Hebbar, K.R.; Sudhaker, Nayak, H.V.; Ramchandran, T.The stress corrosion cracking (SCC) characteristics of Zircaloy?2 sheets in methanol?0.4 vol. pct. hydrochloric acid have been studied in the annealed and cold?rolled conditions using longitudinal and transverse specimens. The times to failure for annealed longitudinal specimens were longer than those for similarly tested transverse specimens at stress levels below ?45% UTS. The cold?rolled specimens developed resistance to SCC, but failed totally by cleavage when notched, unlike annealed specimens which failed by intergranular initiation followed by cleavage. The crystallographic texture developed by cold rolling is such that the crack initiation is difficult because of quicker passivation characteristics of the crack initiating plane. The texture also gives unfavourable orientation of slip and twinning planes with respect to tensile axis. The crack initiating planes are identified with the help of X?ray pole figures. The apparent activation energy is found to be texture dependent at a given stress level. On the basis of apparent activation energy measurements, dynamic tests at constant cross?head speeds and electrochemical measurements, the mechanism of SCC is identified to be the one involving stress?aided anodic dissolution. Copyright 1982 Verlag GmbH & Co. KGaA, Weinheim