Inhibitory Effect of Commercial Inhibitor VCI 379/611 on the Corrosion Behaviour of HTCS-130 Tool Steel for Hot Work

Abstract

This paper presents the results of a study of the influence of water and the commercial inhibitor VCI 379/611 on the corrosion behaviour of HTCS-130 hot work tool steel. Using the thermodynamic program Thermo-Calc, phase equilibria were determined according to the choice of calculation conditions and the known chemical composition of tool steels. From the obtained projections, it is possible to observe the secretion of individual phases at certain temperatures. To obtain insight into the corrosion resistance of steel, the following electrochemical methods were used: open circuit potential measurement; electrochemical impedance spectroscopy; and Tafel extrapolation. Metallographic tests were performed on a sample previously etched in nital to identify the microstructure of the steel. Using an optical microscope, the sample surface was analysed after each measurement. Images of the sample surface subjected to water without inhibitors indicate the occurrence of pitting corrosion. The presence of tungsten and molybdenum carbides was identified by scanning electron microscopy and energy dispersion spectroscopy. It was found that the corrosion process is more pronounced in the area of the metal base while in the areas of excreted carbides, weaker corrosion activity was observed.