Search Results (7)

Modeling the structure not only of whole metal products, but also of the protective coatings with which they are coated, brings a number of economic benefits through more resistant coatings and coatings that can be produced by simplifying manufacturing technology or reducing material consumption in the process. This paper presents the results of a study of dip metallization in zinc baths with Ti additions. Both steel and cast iron substrates were coated and similar results were obtained. The obtained coatings were subjected to SEM analysis with chemical composition studies, TEM characterization with selected area electron diffraction (SAED), and corrosion studies. Particle models of the elementary phases present in the zinc coating made with CaRine 3.0 software were presented and used for phase analysis. It emerged that coatings obtained in zinc baths with the addition of Ti are characterized by a more varied microstructure, the occurrence of phase separations to which Ti segregates, and higher corrosion resistance than classical zinc coatings. The higher corrosion resistance is prompted not only by the Ti content in the intermetallic phases, but also by the observed nanostructure favorably located in the alloy layer. Full article

This scientific paper aims to determine the optimal economic roughness of galvanized surfaces by studying the influence of turning surface roughness on the quality of galvanizing. The thickness of the zinc layer, its corrosion resistance, and the precision of the galvanized parts were also examined. S235J0 steel samples were processed using a turning operation to obtain different roughness values. Three galvanizing technologies, galvanic galvanizing, hot dip galvanizing, and hot dip galvanizing with centrifugation, were used in the experiments. The surface evolution from turning to zinc layer deposition was monitored, and parts were subjected to salt spray corrosion resistance testing. Statistical analysis confirmed the stability of the technologies used and the accuracy of the experimental data. Optimal roughness ranges for galvanizing were determined based on the quality of the surface before galvanizing and the galvanizing technology used. The findings show that avoiding small roughness values leads to savings in the machining phases. From the dimensional accuracy perspective, the parts have smaller dimensions after galvanizing, and the dimensional accuracy decreases. The study confirms that steel parts are protected from corrosion, and degradation of the zinc layer is more advanced in sections with less roughness. The optimal surface roughness values before galvanizing were determined to be Ra < 3.657 m in the case of HDG, Ra < 3.344 m in the case of HDG+C, and Ra > 2.928 μm in the case of ZP. The conclusions drawn from this study introduce new directions of research. Full article

In this paper, the effect of gradually increasing amounts of KMnO₄ (10⁻⁴, 10⁻³, 10⁻² mol·L⁻¹) in cement paste on the bond strength of a plain hot-dip galvanized steel bar was evaluated. The open-circuit potential of HDG samples in cement paste with various additions of MnO₄⁻ was monitored in order to follow a transfer of zinc from activity to passivity. Furthermore, the influence of the addition of these anions on the physicochemical properties of normal-strength concrete or cement paste was evaluated by means of hydration heat measurements, X-ray diffraction analysis, and compressive strength. The effective concentration of MnO₄⁻ anions prevents the corrosion of the coating with hydrogen evolution and ensures that the bond strength is not reduced by their action, which was determined to be 10⁻³ mol·L⁻¹. Lower additions of MnO₄⁻ anions (10⁻⁴ mol·L⁻¹) are ineffective in this respect. On the other hand, higher additions of MnO₄⁻ anions (10⁻² mol·L⁻¹), although they ensure the corrosion of the coating in fresh concrete without hydrogen evolution, but affect the hydration process of the cement paste that was demonstrated by slight water separation. Full article

A medium manganese steel with 7.5 wt.% Mn for automobile application was galvanized in a continuous Hot Dip Galvanizing (HDG) simulator under different galvanizing conditions. It was shown that the effects of dew point, annealing temperature and annealing atmosphere on the surface oxidation of steel could be comprehensively evaluated by the consideration of oxygen partial pressure P(O₂). Although Mn₂SiO₄ was a thermodynamic stable phase when P(O₂) varied from 10⁻²⁸ to 10⁻²¹ atm, it was difficult to form Mn–Si–O composite oxide because there was no enrichment of silicon on the steel surface. So, this oxide was generally formed in the Fe substrate and had little effect on the galvanizability. With the increase in P(O₂) above 10⁻²⁵ atm, MnO particles in the form of the thermodynamic stable phase became coarser and tended to aggregate, which hindered the formation of a continuous inhibition layer, resulting in the defects of bare spots on the galvanized surface of the steel. When the oxygen partial pressure greater than 10⁻²² atm, film-like MnO layer was formed on the surface of steel sample, which obviously deteriorated the galvanizability. The galvanizability of the steel can be improved by the regulation of oxygen partial pressure; based on this, the reasonable zinc plating process parameters can be developed. Full article

The classical thermal cycle in a Hot Dip Galvanizing (HDG) line has four steps: heating, soaking, cooling, and aging. The furnace of an ArcelorMittal HDG line was revamped to increase its heating capacity. This new configuration without the soaking step led to the redefinition of the thermal cycles for all the steel grades, especially for High Strength Low Alloyed (HSLA) steels, where it was necessary to define a new control parameter based on time and temperature. This paper presents the work done to improve the control of the mechanical properties of HSLA steels in the HDG line. Four different types of numerical models (linear and polynomial regressions, artificial neural networks, and Multivariate Adaptive Regression Splines), are applied to predict the yield strength and the tensile strength of individual coils. It is concluded that the introduction of the time–temperature parameter improves the accuracy of the predictions over 10% in most of the cases. An additional improvement is obtained with the use of the process values corresponding to the sampling area instead of the coil average ones. The use of these models makes it possible, if necessary, to adjust individually the presets of the coils before processing them in the galvanizing line and reduce the scattering of the mechanical properties. Full article

This study investigates the morphology, composition and corrosion resistance of hot dip galvanized (HDG) steel bolts in fresh water, 1% NaCl saltwater in the presence of protective compounds L-Tryptophan and three conventional corrosion inhibitors: Inhibitor 1-VCI (amine-carboxylates-based), Inhibitor 2 (based on carboxylate acid), and Inhibitor 3 (water-based, carboxylate acid). Quantitative tests performed include gravimetric analysis and electrochemical techniques, such as linear polarization, Tafel extrapolation, and Electrochemical Impedance Spectroscopy (EIS). Electrochemical measurements determined the polarization resistance R_p, corrosion rate v_corr, and corrosion potential E_corr. Furthermore, Scanning Electron Microscopy (SEM) and ATR-FTIR spectrometry were used to evaluate and characterize the formed layers on the surface of hot-dip galvanized steel samples. The results reveal that upon corrosion new compounds are formed onto the exposed areas of the treated bolts such as zinc-carbonates, zinc-hydroxides, etc. The presence of these compounds on the surface of the HDG steel bolts hinders the corrosion process by reducing the rate of the anodic and cathodic reactions. The gravimetric test showed that L-tryptophan in distilled water has mass increase, resulting from the formation of white deposits on the sample surface. In fresh water and distilled water, the best corrosion resistance was achieved with Inhibitor 1-VCI, while L-tryptophan showed best results in 1% NaCl solution. Full article

For its application development, the medium manganese lightweight steel with 3 wt.% and 10 wt.% Mn contents was galvanized in continuous hot dip galvanizing (HDG) simulator and the process parameters on the production line were adopted. Combined with the experimental analysis and thermodynamic calculation, the effect of dew point and alloy composition on the reactive wetting of the steel was investigated. It was shown that MnO existed as a stable oxide for the medium Mn steel with 5 wt.% Al as long as Mn content exceeded 5.1 wt.%. The galvanizability of the steel with 10 wt.% Mn was deteriorated resulting from the formation of a thick and continuous external MnO layer, which had adverse effects on the wettability. MnO particles in the form of unstable phase can be found at the surface of 3Mn steel galvanized at dew point +10 °C. It distributed sparsely and the reactive wettability can be obtained by “bridging connection”, which mitigated the damage of external oxidation. Moreover, the lower dew point, the less tendency to form external oxide. Although the decrease of dew point to −30 °C had a certain benefit for coating quality, the galvanizing quality of 10Mn steel could not be improved due to the formation of a thick MnO layer. Therefore, the Mn content played a stronger role than dew point on the reactive wetting of hot dip galvanized medium manganese lightweight steel. Full article