Electrochemical assessment of the self-healing properties of cerium doped sol-gel coatings on 304L stainless steel substrates

The present work aims at assessing the corrosion behavior of 304L stainless steel substrates pre-treated with 3-glicidoxypropyltrimethoxy silane (GPTMS) solutions modified with cerium nitrate or cerium oxide nanoparticles. Furthermore, the work aims at evaluating the self-healing properties of the dopant in intact and artificially scratched silane films via natural salt spray tests, electrochemical impedance spectroscopy (EIS) and d.c. potentiodynamic polarization. The morphological features of the coated substrates were evaluated by atomic force microscopy (AFM) and optical microscopy. The results confirmed the formation of transparent cerium modified sol-gel films without any defect and cracks and revealed the formation of a comparatively smooth nanostructure surface with a small heterogeneity in coating thickness in the sol-gel coatings modified with Ce(NO3)3.6H2O. Corrosion tests indicated that the CeO2 nanoparticles have good corrosion inhibition properties on scratched surfaces due to their ability to complex other species, therefore contributing for the stabilization of the passive film. In this way, these particles display an anodic inhibition mechanism. It was found that the positive impact, both in the barrier properties and corrosion inhibition, was significantly improved by modifying the silane solution with cerium nitrate. Presence of cerium nitrate, reinforces the barrier properties of the silane films, reducing the corrosion activity and self-healing the corroded areas

The impact of hydrogen on the ductility loss of bainitic Fe–C alloys

The influence of hydrogen on the mechanical properties of generic lab-cast Fe-C bainitic alloys is studied by tensile tests on notched samples. The bainitic microstructure is induced in a 0.2% C and 0.4% C Fe-C alloy by an appropriate heat treatment. The hydrogen embrittlement susceptibility is evaluated by mechanical tests on both in situ hydrogen pre-charged and uncharged specimens. The observed ductility loss of the materials is correlated with the present amount of hydrogen and the hydrogen diffusion coefficient. In addition to the correlation between the amount of hydrogen and the hydrogen-induced ductility loss, the hydrogen diffusion during the tensile test, quantified by the hydrogen diffusion distance during the test, appears to be of major importance as well

Electrochemical hydrogen charging of duplex stainless steel

This study evaluates the electrochemical hydrogen charging behavior and interaction between hydrogen and the microstructure of a duplex stainless steel. A saturation level of approximately 650 wppm is reached after 10 d of charging. The data are compared with a model resulting in a diffusion coefficient of 2.1 x 10(-14) m(2)/s. A two-step increase of the concentration is observed and ascribed to saturation of ferrite followed by charging of austenite grains. Microstructural changes are observed during charging, i.e., formation and interaction of dislocations, as a result of the high residual stresses inherent to the production process of duplex stainless steels

FeS corrosion products formation and hydrogen uptake in a sour environment for quenched & tempered steel

Surface corrosion product formation is one of the important factors affecting the corrosion rate and hydrogen uptake in a H2S environment. However, it is still unclear how the base material composition will affect the corrosion products that are generated, and consequently their impact on the corrosion rate. In this paper, corrosion product formation and the impact of the Mo content of the base material on the composition of the corrosion products and hydrogen absorption in a sour environment was investigated. The corrosion layer was composed of a double layered mackinawite (FeS1−x) structure, which was enriched with molybdenum and chromium. The layers were formed via two different mechanisms, i.e., the inner layer was created via a general oxide film formation corrosion mechanism, whereas the upper layer was formed by a precipitation mechanism. The presence of this double corrosion layer had a large influence on the amount of diffusible hydrogen in the materials. This amount decreased as a function of contact time with the H2S saturated solution, while the corrosion rate of the materials shows no significant reduction. Therefore, the corrosion products are assumed to act as a physical barrier against hydrogen uptake. Mo addition caused a decrease in the maximal amount of diffusible hydrogen

Control of the Austenite recrystallization in Niobium Microalloyed steels

The use of heavy gauge steel sheets for structural applications very often requires a combination of high yield strength and adequate toughness. The most cost effective way to realize a high yield strength and a high ductility in a low alloyed steel is grain refinement. In industrial practice, this refinement is realized by controlled processing. This process consists of controlling the slab reheating temperature, applying a large amount of hot deformation below the nonrecrystallization temperature (T-nr) and accelerated cooling. A better knowledge of T-nr could optimize the process and the best mechanical properties could be reached against the lowest cost. T-nr can be raised by the addition of microalloying elements such as Nb. Nb can retard the static recrystallization of austenite at low temperatures either by solute drag or by precipitation pinning. In this study, the recrystallization behavior of five Nb-microalloyed model alloys with various Nb contents, was evaluated by double hit compression tests. Further, the precipitation state of the materials was investigated experimentally by Inductively Couples Mass Spectroscopy and X-ray Diffraction. The construction of recrystallization-time-temperature diagrams and precipitation-time-temperature diagrams showed that both mechanisms, i.e. recrystallization and precipitation, strongly influence each other

Interactive industrial application to represent isothermal sections of multi component phase diagram

“Make the slag and the steel will make itself” is an old phrase in steelmaking. The converter or basic oxygen furnace (BOF) process is a necessary step in the steel production during which carbon, phosphorus and other impurities present in the hot metal, coming from the blast furnace, are removed and steel is produced. This steel is tapped from the converter and further refined, next cast, rolled and finished. The BOF process is complex due to many reasons: high temperatures, multiple phases present, interactions of kinetics and thermodynamics, etc. Emphasis in this work is put upon the BOF steelmaking slag. Yet, even though this has been topic of many research projects no full understanding of all the slag related phenomena has been far from achieved. One of the difficulties is the multi-component nature of the slag. In its most simplified form, the slag is a three component system consisting of CaO, SiO2 and FeOn. However, in practical applications this slag contains more than three components, making graphical representations of equilibria complex and difficult. This work shows the potential to apply CALPHAD based data for industrial applications via an interactive visual tool. Isothermal sections of multi-components phase diagrams were constructed with Factsage 7.1 software. Addition of extra components to the calculated isothermal sections, gives a graphical representation which can be used to gain insight in certain observed phenomena in the BOF process. To illustrate that the interactive visualisation yields an interesting tool to integrate CALPHAD based calculations in industry two case studies from steelmaking are discussed: the effect of MgO upon the refractory wear and the effect of MgO upon dephosphorization