Effects of the microstructure and retained/reversed austenite on the corrosion behavior of NiCrMoV/Nb high-strength steel

A comparison of microstructure and corrosion performance has been made between NiCrMoV/Nb steel under different heat treatments in artificial seawater. The microstructures as well as the volume fraction of austenite strongly affect corrosion resistance. Atomic force microscopy (AFM) results reveal that both retained/reversed austenite and the grain boundary have a higher Volta potential than the matrix. The morphology of pits and the nature of retained/reversed austenite were investigated by field emission scanning electron microscopy (FESEM). Results can be discussed in terms of a model that describes the microgalvanic effect and the change of morphology and content of retained/reversed austenite resulting from a heat treatment process. The role of the microstructure and retained austenite on corrosion resistance evolution in the corrosion process is discussed. The X-ray diffraction (XRD) results reveal that the corrosion products formed on distinct microstructures primarily contain lepidocrocite (gamma-FeOOH), goethite (alpha-FeOOH) with little difference after long time immersion.