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 900^oC (1173K or 1652^oF) 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 The experimental process is allowed for a total of 168hr with each set withdrawn 24hr interval for weight lose analysis.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.