Experimental rolling trials were performed at different temperatures on EN 1.4462 duplexsteel imposing also different reduction ratios and a possible solution quenching. A clearand significant relation between the applied thermo-mechanical process and themicrostructural evolution was shown, and it is useful for designing the steelmicrostructure. The mechanical properties, the micro-structural features and the texturecharacteristics were defined for each condition in order to point out the operativeparameters (i.e. thermal level, imposed strains and application of solution quenching)that permit to maximize the formability of the final hot-rolled products.

The Hollomon-Jaffe parameter is commonly used to characterize thermal cycles and definetime-temperature equivalences during tempering, but it can only be computed for simplethermal cycles defined by a couple of values [temperature; time]. Its use is not adaptedfor complex thermal cycles. Three tempering parameters which integrate the full thermalcycles were investigated: the Hollomon-Jaffe derivative parameter, and the Tsuchiyama andArrhenius laws. Simple and complex thermal cycles were performed on a water-quenchedcarbon steel (i.e. different heating and cooling rates or two-step cycles, withtemperature varying between 450 °C and 750 °C and times from 30 s to 3 days). All threetempering parameters show good correlation with the tensile properties of the material,even when complex cycles were performed, provided that the material constant is optimized.The sensitivity to the determination of this constant is low for the Tsuchiyama andArrhenius laws: they can be considered as robust and reliable. On the contrary, theHollomon-Jaffe derivative parameter proved unstable.

The Ternium Siderar steel plant in San Nicolas, Argentina, experienced a period of singleblast furnace operation in 2006, first due to one furnace’s unavailability, and later dueto the other’s relining. In order to exploit the excess steelmaking capacity, processeswere adjusted to reduce the amount of hot metal needed for the production of a ton ofsteel. The principal changes in the process are described in this paper: an increase inthe manganese content of hot metal to avoid manganese addition in the converter; heatingof scrap; coke additions; increase in pig iron; use of large quantities of SiC or FeSiduring the blow; temperature decrease at the end of the blow. All of this permitted anincrease in slab production compared with the standard process.

Ternium Siderar has recently installed a commercial sensor that measures the soundoriginated during blowing. A proper analysis of this signal may give valuable informationabout the slopping tendency of the heat. Data from more than 4000 heats were collected andthoroughly analyzed. The influences of the materials charged and of their compositions onthe slag slopping tendency were investigated. Based on these results, an application toevaluate the risk of slopping for given process conditions was developed.

The recent decrease in Blast Furnace production as well as changes in raw materials andprocess conditions has produced an increase in the silicon and phosphorus contents in hotmetal. This situation increases the probability of slopping and fume emissions duringconverter blowing because of the large volume of highly viscous slag. To carry out thesilicon oxidation and dephosphorization steps, a double slag practice has to be used. Thefirst slag is rich in silicon and phosphorus and has a low basicity. The first slag isremoved. Then the second slag is formed; this low-viscosity slag is subject to the strongagitation created by a high decarburization rate. The second slag is characterized byhigher CaO and phosphorus contents. These conditions yield a better dephosphorization atthe end of the blow. In order to implement the double slag practice, the converter controlsystem was modified. The changes included the design of the lance blowing pattern, theflux additions, the static control, and the logic of the gas collection and cleaningsystem. For a silicon content larger than 0.60% in the hot metal, the results show asignificant reduction in the fume emissions and in slopping, a lower flux consumption, andopen up the possibility of working with iron ore with higher phosphorus content.

L’évolution des teneurs en CO et CO2 dans les gaz à la sortie d’unconvertisseur industriel présente un comportement reproductible, qui reflète ladécarburation du bain métallique. Malgré les limitations présentes dans les équipements demesure installés au convertisseur de Siderar – analyse des gaz seulement et pas de mesurede débit des gaz produits – il a été possible de mettre en place une méthode permettantd’estimer la teneur en carbone de l’acier à la fin du soufflage d’oxygène. Il a étédéterminé que le temps écoulé entre le moment où le maximum de la courbe de teneur enCO2 apparaît, quelques minutes avant la fin du soufflage, et le moment del’arrêt du soufflage est la variable qui permet d’estimer au mieux la teneur en carbone del’acier. La méthode développée permet d’améliorer de façon significative la précisiond’obtention de la teneur en carbone d’arrêt par rapport aux pratiques conventionnelles.Les analyses réalisées ont montré que parmi les variables évaluées, celle-ci est la plusrobuste car elle est peu sensible à l’influence des paramètres qui affectent les entréesd’air dans le système et qui ont une influence directe sur les analyses du gaz. Afin demettre en œuvre cette méthode en tant qu’outil de contrôle de process en temps réel, il aété développé un système expert qui analyse point par point l’évolution de l’analyse desgaz du convertisseur, détecte le maximum de CO2 et envoie un signal au PLC pourremonter la lance de soufflage d’oxygène au moment voulu pour obtenir la teneur en carbonevisée.