SEGREGAÇÃO EM AÇOS ALTA-RESISTÊNCIA BAIXA LIGA (ARBL) PARA APLICAÇÕES EM SERVIÇO COM H2S- AVALIAÇÃO POR TERMODINÂMICA COMPUTACIONAL

The amount, type and distribution of non-metallic inclusions as well as the solidification segregation, which\udinfluences inclusion type and distribution, have great influence on the performance of High Strength Low Alloy (HSLA)\udsteels used in sour service in the oil industry. The effects of manganese, both on segregation and on steel cleanness have\udbeen studied through experiments and, to a lesser extent, through mathematical modeling of solidification. However, the\udeffect of some other relevant elements added to these steels, in special those effects caused by solidification segregation,\udhave not been extensively studied. In the present work, the extent of segregation and the probable effect on inclusion\uddistribution of the main elements in HSLA steels used in sour service are evaluated through different computational\udthermodynamic models. In particular, two limiting cases bound the comparison: equilibrium solidification and the Scheil\udmodel, in which no homogenization in the solid phase is assumed. Special attention is given to silicon. For relevant\udcompositions, models considering solid and liquid state diffusion are used. The results are compared with experimental\uddata available for some steel compositions and serve as basis for a first evaluation of the alloy design strategy currently\udapplied to these steels, from the point of view of segregation and internal cleanness