Steel Desulphurization Using Sintered Synthetic Slag

摘要

The control of residual elements has been acquiring great relevance in molten steel production, even more so in the production of special steels for various applications. According to Nadif et al.,(1) high strength steels, for automotive industry and pipes . often require low sulfur contents as to improve its ductility for cutting and bending operations, considering the harsh conditions to which steel is submitted during rolling and straining. Low sulfur content steel is obtained by means of a combination of actions, starting with hot metal desulfurization or scrap selection, involving primary refinement and culminating with secondary refining. Usually, each plant adapts its process according to the equipment and raw materials available to obtain the desired sulfur content under the best economic result. Secondary refinement desulfurization is done through slag control, where mixed, briquetted, pre-molten or sintered slags are used according to the needs of each process. These well consolidated processes have proven the economic benefits of the use of synthetic slags to guarantee deoxidation, desulfurization and the removal of bath inclusions, according to Faulring(2). Campos et al..(1) state that the desulfurization rate is dependant on the sulfide capacity of synthetic slag, on the oxygen activity as well as on the amount of slag used in the process. However, those are thermodynamic data and make no reference to either the amount of liquid or to the phases present in the slag, both features capable of bearing impact on the desulfurization rate. Computer aided thermodynamics comes in as an effective tool to assess the desulfurizing capacity of slags, for it allows calculating balance contents as well as the above mentioned properties.