Development of MnS and IGF Control in Microalloyed Steels in Baosteel Special Steel Branch

摘要

The development of MnS and intragranular ferrite (IGF) control in ferrite-pearlite type microalloyed steels since 1987 in Baosteel Special Steel Branch is reviewed in this paper. MnS inclusion as the nucleus of ferrite transformation, its quantity, size and shape have the big changes in the different development stages. Decreasing of Mn content in the steels raised gamma->alpha transformation temperature and increased driving force for transformation, so the nucleation probability of IGF on MnS inclusions was improved, which compensated the insufficient nucleation positions of ferrite in the bigger ingot. The average aspect ratio (length-width) and the length of MnS reduced more than 10 times fore and after, furthermore, the most of ferrite which precipitated formerly along grain boundary transformed mainly at intergranular locations at present stage. With developing of MnS and IGF control, the microalloyed steel production has combined toughness with machinability better.