Pitting corrosion behavior of cerium treated HSLA steel induced by sulfide inclusions in 3.5 wt% NaCl solution

Effect of Cerium on Inclusion Evolution and Pitting Corrosion of Nb-Microalloyed Steel

Nb-microalloyed steels are widely used in construction engineering fields due to their excellent mechanical properties, but they face serious corrosion problems in service environments. Pitting corrosion is the severest form of corrosion, and the types of inclusions are the leading cause to induce pitting corrosion. A new strategy is proposed to enhance the corrosion resistance of steels by achieving a beneficial transformation of inclusions with Ce treatment. In this paper, two types of Nb-microalloyed steels (0% Ce and 0.0058% Ce steel) were prepared to study the modification effect on inclusions in industrial production. The spherical CaS•C12A7 inclusions were modified to smaller ellipsoidal Ce2O2S inclusions, and the proportion of inclusions (0-2 μm) increased significantly from 27 to 66%, while large inclusions (>6 μm) disappeared. A kinetic model of inclusion evolution was established. The results of electrochemical tests indicated that the corrosion potential was positively shifted, and the corrosion current was reduced after Ce treatment. Additionally, the number of defects in the passivation film was decreased, and the corrosion resistance of the steel was significantly improved. The addition of Ce changed the types of inclusions and reduced the number of pitting nucleation points, which led to a remarkable reduction in the number and size of pitting pits. The mechanism of pitting corrosion induced by different types of inclusions was further investigated, and a pitting corrosion model was modeled based on the immersion experiments. Research results provide theoretical support for enhancing the corrosion resistance of steel.

Local Corrosion Behaviors in the Coarse-Grained Heat-Affected Zone in a Newly Developed Zr-Ti-Al-RE Deoxidized High-Strength Low-Alloy Steel

Oxide metallurgy technology can improve the microstructure of a coarse-grained heat-affected zone (CGHAZ) but introduces extra inclusions. Local corrosion behavior of the CGHAZ of a Zr-Ti-Al-RE deoxidized steel was investigated in this work using theoretical calculations and experimental verification. The modified inclusions have a (Zr-Mg-Al-Ca-RE)O_x core claded by a CaS and TiN shell. CaS dissolves first, followed by the oxide core, leaving TiN parts. This confirms that the addition of rare earth can reduce lattice distortion and prevent a galvanic couple between the inclusions and the matrix, while the chemical dissolution of CaS causes localized acidification, resulting in the pitting corrosion initiation.

Experimental Measurement of Deposition Chloride Ions in the Vicinity of Road Cut

Chloride ions are nowadays the main cause of the degradation of steel and reinforce concrete construction in the vicinity of the road. On the other hand, chloride ions, usually in the form of de-icing salts or brine, are very important for safe winter traffic on the roads. This creates a slightly schizophrenic situation where it is necessary to ensure safe traffic in the winter period and at the same time to affect the service life of the structure as little as possible. The effect of the roadway on chloride deposition is a long-studied, but still imprecisely understood, part of the effect of chloride ions on structures in the vicinity of the roadway. This paper discusses the experimental measurement of chloride deposition in the vicinity of the I/11 road in the Czech Republic by dry plate method, wet candle method and corrosion coupons. Statistical analysis of correlation and regression is performed on the results of measurements by wet candle and horizontal dry plate methods. The methods are interdependent. A detailed analysis of the surface and chemical properties of the corrosion products is performed on the corrosion coupons. Using the corrosion loss, the environmental category C2 is determined. Observation of the microclimate in the vicinity of the roads gives to engineers a basis for the correct design of structures around the roads. The conclusions of the experimental measurements are intended to help engineers to design a structure that is safe, serviceable and sufficiently resistant to chloride ions within its service life.