Experimental rolling trials were performed at different temperatures on EN 1.4462 duplex steel imposing also different reduction ratios and a possible solution quenching. A clear and significant relation between the applied thermo-mechanical process and the microstructural evolution was shown, and it is useful for designing the steel microstructure. The mechanical properties, the micro-structural features and the texture characteristics were defined for each condition in order to point out the operative parameters (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 define time-temperature equivalences during tempering, but it can only be computed for simple thermal cycles defined by a couple of values [temperature; time]. Its use is not adapted for complex thermal cycles. Three tempering parameters which integrate the full thermal cycles were investigated: the Hollomon-Jaffe derivative parameter, and the Tsuchiyama and Arrhenius laws. Simple and complex thermal cycles were performed on a water-quenched carbon steel (i.e. different heating and cooling rates or two-step cycles, with temperature varying between 450 °C and 750 °C and times from 30 s to 3 days). All three tempering 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 and Arrhenius laws: they can be considered as robust and reliable. On the contrary, the Hollomon-Jaffe derivative parameter proved unstable.

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

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

The recent decrease in Blast Furnace production as well as changes in raw materials and process conditions has produced an increase in the silicon and phosphorus contents in hot metal. This situation increases the probability of slopping and fume emissions during converter blowing because of the large volume of highly viscous slag. To carry out the silicon oxidation and dephosphorization steps, a double slag practice has to be used. The first slag is rich in silicon and phosphorus and has a low basicity. The first slag is removed. Then the second slag is formed; this low-viscosity slag is subject to the strong agitation created by a high decarburization rate. The second slag is characterized by higher CaO and phosphorus contents. These conditions yield a better dephosphorization at the end of the blow. In order to implement the double slag practice, the converter control system was modified. The changes included the design of the lance blowing pattern, the flux additions, the static control, and the logic of the gas collection and cleaning system. For a silicon content larger than 0.60% in the hot metal, the results show a significant reduction in the fume emissions and in slopping, a lower flux consumption, and open 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’un convertisseur industriel présente un comportement reproductible, qui reflète la décarburation du bain métallique. Malgré les limitations présentes dans les équipements de mesure installés au convertisseur de Siderar – analyse des gaz seulement et pas de mesure de débit des gaz produits – il a été possible de mettre en place une méthode permettant d’estimer la teneur en carbone de l’acier à la fin du soufflage d’oxygène. Il a été déterminé que le temps écoulé entre le moment où le maximum de la courbe de teneur en CO2 apparaît, quelques minutes avant la fin du soufflage, et le moment de l’arrêt du soufflage est la variable qui permet d’estimer au mieux la teneur en carbone de l’acier. La méthode développée permet d’améliorer de façon significative la précision d’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 plus robuste car elle est peu sensible à l’influence des paramètres qui affectent les entrées d’air dans le système et qui ont une influence directe sur les analyses du gaz. Afin de mettre en œuvre cette méthode en tant qu’outil de contrôle de process en temps réel, il a été développé un système expert qui analyse point par point l’évolution de l’analyse des gaz du convertisseur, détecte le maximum de CO2 et envoie un signal au PLC pour remonter la lance de soufflage d’oxygène au moment voulu pour obtenir la teneur en carbone visée.