Comparative Study on Stress Corrosion Behavior of High Manganese Steel and 9Ni Steel in Simulated Seawater

Abstract

In order to study the seawater stress corrosion resistance and corrosion mechanism of a new type of high manganese steel used in marine engineering，the stress corrosion cracking (SCC) sensitivity of high manganese steel and 9Ni steel in 3.5 %NaCl solution was tested by slow strain rate tension (SSRT).The microstructure，electrochemical behavior，SSRT performance，fracture morphology features and crack propagation law of the samples were compared and studied.Results showed that the elongation，reduction of fracture surface area and energy absorbed during fracture of the two steels in corrosive medium were all lower than those in air medium.The strain energy density ratio of high manganese steel deviated further from 1，and the comprehensive stress corrosion index (ISSRT) was also larger，showing higher SCC sensitivity.Moreover，the fracture morphology of all the samples in air exhibited the characteristics of dimple micropore ductile fracture.In solution，the SSRT fracture morphology of 9Ni steel presented typical ductile-brittle mixed fracture characteristics，while that of high manganese steel presented obvious transgranular quasi cleavage brittle fracture characteristics.Besides，the pretensile deformation sample of high manganese steel had higher corrosion current density and more negative corrosion potential.Mn had a strong grain boundary segregation effect，which was easy to cause transgranular SCC.In general，the SCC mechanism of high manganese steel could be attributed to the combined action of hydrogen induced cracking (HIC) and anodic dissolution (AD).

Keywords

• high manganese steel；9ni steel；slow strain rate；stress corrosion；scc sensitivity