Corrosion behaviour of plastically deformed high-Mn austenitic steels

Purpose: The aim of the work was the comparison of corrosion resistance in an aqueous sulfuric acid solution of two high-manganese austenitic steels of the 0.05C-25Mn-Al-Si-Nb-Ti type in a plastically deformed state. Design/methodology/approach: Investigations were carried out on specimens obtained from a thermo-mechanically rolled sheet and then plastically deformed through bending and immersed in corrosive solutions (1N H2SO4) for 100 hours. The mass decrement was calculated by the gravimetric method, whereas the character of corrosion damages was observed in metallographic investigations using light and scanning electron microscopes both in the polished and etched states. Findings: It was found that after the thermo-mechanical processing one steel is characterized by an austenitic structure with numerous annealing twins, whereas in the second steel lamellar martensitic phases in an austenitic matrix occur. The investigations showed that the examined high-manganese steels have very low corrosion resistance in normal H2SO4. Higher impact on the corrosion resistance than the phase composition has the chemical composition. The mass decrement of the steel with martensite plates is a bit higher than that with a single-phase austenitic matrix. The specimens were intensively dissolved due to general corrosion accompanying by pitting and hydrogen cracking. Research limitations/implications: To investigate in more detail the corrosion behaviour of high-manganese austenitic steels, the polarization tests and the analysis of corrosion products should be carried out. Practical implications: The obtained results can be used for searching the appropriate way of improving the corrosion resistance of high-strength high-manganese austenitic steels. Originality/value: The corrosion resistance of two types of advanced high-manganese austenitic steels with different initial structures was compared. Hydrogen impact in austenitic steels was discussed. Keywords: Corrosion resistance; high-manganese steels; gravimetric method; pitting corrosion; general corrosion; hydrogen cracking