Influence of Austenitizing Temperature on the Microstructure and Corrosion Resistance of 55Cr18Mo1VN High-Nitrogen Plastic Mould Steel

Abstract

The influence of austenitizing temperature on the microstructure and corrosion resistance of 55Cr18Mo1VN high-nitrogen plastic mould steel was investigated. The microstructure, elemental distribution and Cr-depleted zone of different heat-treated samples were investigated by X-ray diffraction, electron probe microanalyzer analysis, and transmission electron microscopy. The corrosion resistance was evaluated using electrochemical measurements, and the analysis of passive film was carried out by X-ray photoelectron spectroscopy. The results indicated that the volume fraction of precipitates decreased, and the homogeneity of elements was improved with increasing austenitizing temperature. The degree of Cr-depleted zone around coarse M 23C6 was severer than that around M 2N, and pitting corrosion initiated preferentially around M 23C6. The corrosion resistance of the samples increased with the austenitizing temperature. With the increase in austenitizing temperature, the passive film was thickened and \( {\text{Cr}}\left( {\text{III}} \right)_{{{\text{Cr}}_{2} {\text{O}}_{3} }} \) in the inner layer of passive film was enriched, which enhanced the corrosion resistance of the steel. The higher content of nitrogen in solid solution at higher austenitizing temperature contributed to the increased intensity of CrN and NH3, leading to the increase in pH value in the pit, and promoting the repassivation of 55Cr18Mo1VN steel.