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The IF steels are free of interstitial elements in the ferritic matrix. These elements are controlled in the refining process in the steel plant through the application of vacuum degassing techniques and the addition of stabilizing elements. During the manufacture and in some specific applications of the IF steels, as for example in welding where the phase transformation ã ? á and the effect of the alloying elements on their kinetics have strong influence on the final microstructure. In this context, this work characterized microstructurally and compared the phase transformation kinetics of two types of IF steels with different chemical compositions, one being stabilized to Ti (IF-Ti) and the other stabilized to Ti and Nb (IF-TiNb) with addition of Mn. It was concluded that the IF-TiNb steel in the delivery state has a more refined microstructure due to the presence of Nb and its role as a grain refiner in the controlled rolling of the steel. It was found that the critical temperatures Ar3 and Ar1 of the IF-TiNb steel are lower than the measured temperatures for the IF-Ti steel. This effect is attributed to the difference in Mn content between the studied steels, which seems to potentiate the grain refining in the final stage of cooling of the rolled steel sheet. [ABSTRACT FROM AUTHOR]

This work describes the development and use of a hot-rolled low carbon steel, semi stabilized with boron-titanium to reduce interstitial nitrogen and to act as inclusion morphology agent. The RH vacuum degassing process was used to refine the content range of carbon and manganese, as well to limit the content of residual elements and to optimize the use of this equipment. As performance, criteria was evaluated the mechanical properties, mainly the drawnability, estimated by a semi-quantitative equation. The drawing final performance at customers was monitored. [ABSTRACT FROM AUTHOR]