Research on the evolution of corrosion products of 17-4 PH martensitic stainless steel in the tropical marine environment

Abstract

Deterioration of stainless steel is significantly influenced by the characteristics of corrosion products. Evolution of corrosion products of 17-4 PH martensitic stainless steel (17-4 PH MSS) in the tropical marine environment was systematically studied by field-exposure, combined with morphological observation, compositional characterization and electrochemical testing in this work. The corrosion process of 17-4 PH MSS was divided into three stages: stage I–rapid formation and shedding of corrosion products, stage II–adhesion and transformation of corrosion products and stage Ⅲ–remarkable increase in the protective properties of corrosion products. Corrosion rate of 17-4 PH MSS was maximum in the first stage and then decreased continuously in the second and third stages, which is closely related to the morphology, distribution and composition of the corrosion products. In terms of morphological evolution, corrosion products of 17-4 PH MSS showed the dynamic cycle characteristic of ''nucleation-growth-cracking-shedding''. In view of compositional transformation, the high content of Cr, Ni, and Cu in stainless steel is involved in the formation of corrosion products, and the production of Cr2O3, Cr(OH)3, FeCr2O4, NiFe2O4, and CuFeO2 after 6 months of exposure was an important shift. Argument from protective properties, increase in coverage percentage and the generation of Cr-containing products are responsible for the enhancement of protective properties of the corrosion products. This work prepares the way for further research on the generation and growth mechanism of pitting under corrosion products and provides technical support for the design, selection, and protection of stainless steel in tropical marine environments.

Keywords

• 17-4 PH
• Stainless steel
• Corrosion product
• Tropical marine environment
• Field exposure