Comparative Analysis of Corrosion Behavior of Martensitic and Annealed Stainless Steel in H2SO4 and NaOH
Abstract
Using weight lose techniques (WLT), the comparative analysis of the corrosion characterization behavior of cast stainless steel (70.90% Fe, 19% Cr 10%Ni, 0.0% C) alloys in ( 0.25M- 0.5M) H2SO4 and NaOH has been evaluated. The cast stainless steel specimen was sectioned into three sets labeled M, A, U and machined to the same cross sectional area. M and A is subjected to a temperature of 900oC (1173K or 1652oF) where the grains forms austenitic phase which was further heat- treated to form martensitic stainless steel (M) and annealed stainless steel (A) test coupon respectively. Then, (U) is left untreated as a control test coupon sample. These preweighed test coupon samples were immersed in 0.25M and 0.5M simulated tetraoxosulphate (vi) acid (H2SO4) and sodium hydroxide (NaOH) respectively. The experimental process is allowed for a total of 168hr with each set withdrawn 24hr interval for weight lose analysis. The findings showed that of a passivating metals with initial steady rise in corrosion penetration rate (CPR) followed by gradual decrease in CPR which increases as molar concentration increase for the annealed specimen(A) in H2S04 while the martensitic test specimen(M) is severely attacked in NaOH. The annealed specimen exhibit high passivity in H2S04 with lowest CPR of 0.0071mm/yr. The severe attack of the annealed specimen is due to increase in ionization which results in redistribution of grain boundary structure.
Key words: Passivation, Corrosion kinetics, Basic Environment, Acidic Environment, Martensitic, Annealing, Weight Lose Techniques, Austenitic phase.
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ISSN (Paper)2224-3224 ISSN (Online)2225-0956
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