From a ferrite/martensite cold-rolled microstructure, the interaction between ferriterecrystallization and austenite formation is investigated. It is observed that a slowheating rate promotes the ferrite recrystallization and a homogeneous microstructure,whereas a fast heating rate delays the recrystallization and leads to heterogeneouslydistributed austenite islands.

The nature of the intermetallic layer which forms on the steel surface during immersionin typical galvanizing baths for galvannealed (GA) sheets production has been investigatedon two commercial Titanium-stabilized Interstitial-Free (Ti-IF) steel substratesgalvanized in baths with different Al contents. Results from this study show that in bothcases the inhibition layer is biphasic and composed of a very thin Al-rich phase layer,identified as Fe2Al5Znx, and a thicker Zn-rich phase layeron top of it, identified as δ. Experimental results also show that theFe2Al5Znx phase layer becomes discontinuouswhen decreasing the bath Al content. Discussions about the mechanisms of formation and thefinal microstructure of this inhibiting layer are also tackled in this paper by means ofthe Al-Fe-Zn ternary phase diagram at 460 °C and assumptions to justify any deviation fromthermodynamic equilibrium are as well proposed.

The influence of variable Manganese content (2.4−4.6 wt%), while keeping constant Silicon(1.5 wt%) and Chromium (0.3 wt%) levels, and variable oxidation potential of the annealingatmosphere on hot dip galvanizability was investigated. Surface oxides prior to hot dipgalvanizing were analyzed and coating quality assessed. The increasing oxidation potentialof the annealing atmosphere led to a transition from external to internal selectiveoxidation of Mn, Si and Cr; their enrichment at the surface could be reduced and themetallic iron at the surface was increased. Hot dip galvanizability could thus be obtainedup to 2.9%Mn. With increasing Mn content, the surface was covered by a rising amount ofMn-oxides. By exceeding a critical amount of Manganese, reactivity in the Zinc bath wasdeteriorated. This amount was found to be between 2.9 and 3.8 wt% for Si content of 1.5wt%.

In this work, direct potential measurements during cold rolling of zinc and X20Cr13stainless steel were carried out in the rolling slit to follow the tribologic and galvanicmechanisms of hydrogen formation and absorption on the surface of the working rolls madeof DHQ1 grade steel. An Ag/AgCl in 3.5 M KCl reference microelectrode was used to recordthe open circuit potential of the electrochemical system roller-product immersed intocommercially relevant electrolyte (rolling emulsion) with a pH value of 4.5 and anelectric conductivity 46 mS cm-1. The potential shift into either negative or positivedirection of the rolls-product system gives information on the processes taking place atthe surface in the course of the friction. A detailed discussion of the in-situpotentiometry experiments reveals a stationary situation established between thedestruction and repassivation of the surface structures during continuous cold rollingaccompanied with intensive hydrogen evolution. Galvanic coupling of the working rolls withthe product significantly intensifies the hydrogen embrittlement related problems of therolls. Atomic hydrogen is adsorbed on the surface and exhibits a pressure supportedabsorption into the rolls during their whole lifetime.

In order to obtain the dynamic variation rule of the sulfur content of liquid steel inthe LF refining process, a complete mathematical model including a desulfurization kineticmodel and temperature model in the deep desulfurization process is presented, based on thepractical production and reaction mechanism of ultra-low-sulfur steel in a LF. The resultsshow that the calculated values of the sulfur content in liquid steel using the model fitthe experimental values well, and the relative error is less than 8%. The effects ofrefining slag on the desulfurization process are analyzed in this paper, which shows thatslag basicity is most important at the early and middle stages of the process, while slagweight is most important at the middle and late stages. The effect of the above factors onthe final sulfur content of liquid steel is further analyzed quantitatively. The simulatedresults provide a theoretical basis to segment control the refining process in order toachieve the maximum effect, improving efficiency, saving energy and reducingconsumption.

The paper reports the results of studies on the validation of a numerical model of theflow of liquid steel through the tundish used for continuous casting of steel. Thefacility under investigation is a single-nozzle tundish designed for casting concastslabs. For the description of the turbulence of steel flow through the tundish, thek-ε, RNG k-ε and Realizable k-ε turbulence model wereadopted. Computer simulations of liquid steel flow were performed using the commercialprogram Ansys-Fluent®.For the validation of the numerical model and verification of the hydrodynamic conditionsoccurring in the examined tundish furniture variants, obtained from the computersimulations, a physical model of the tundish was employed. During laboratory testssimulating the process of steel flowing through the tundish, E and F-type RTD (ResidenceTime Distribution) curves were recorded, which were then juxtaposed with results obtainedfrom computer simulations. In order to obtain a complete hydrodynamic picture in thetundish furniture variants tested, the computer simulations were performed for bothisothermal and non-isothermal conditions.

Low temperature degradation (LTD) of iron oxides was investigated with the aim ofunderstanding how natural iron ores degrade under different conditions. Minimisation ofthis degradation would increase the acceptance level of natural iron ores as feedmaterials without prior beneficiation. In addition to temperature and reduction gascomposition, sample positioning in the reduction furnace and sample’s original weight werealso found to influence LTD. Samples placed in the top reaction zone of the furnace, whichhave the first contact with the reducing gas, were found to degrade 1.5 times more thanthose in the middle and bottom reaction zones. In addition, they presented a wide range ofsize in the disintegrated particles than those in the middle and bottom reaction zones.Furthermore, the samples with an original weight equal to or greater than 5 g, had adisintegration extent of less than 10%. Therefore, if the reduction gas comes into contactwith a certain material first, before contacting the iron oxide, it may serve to reduce onLTD during reduction. Furthermore, in laboratory conditions, the occurrence of lowtemperature breakdown of the natural iron oxides can be minimised by using samples with anoriginal weight equal to or greater than 5 g.