Influence of titanium and niobium on the strength – ductility – hole expansion ratio balance of hot-rolled low-carbon high-strength steel sheets

It has been demonstrated that the demand for high strength sheet steels with excellent balances of strength, ductility and hole expansion ratio could be met by steels with a ferrite or bainitic-ferrite matrix strengthened by a large amount of finely dispersed precipitates. In this study, the influence of the precipitation forming elements, Ti and Nb on the balance of strength, ductility and hole expansion ratio has been investigated. Individually, neither Ti nor Nb produces optimum performance but it has been proposed that a carefully selected balance of added Ti and Nb can succeed in meeting the desired combination of properties. The reasons why the individual elements, when used alone, produce inferior performance is explored and the role of sulphides and the formation of textural colonies are both highlighted as playing important roles. Titanium alone can go part way towards satisfying the property demands whilst this has been shown to be more difficult with niobium as a single alloying addition. These observations are thoroughly discussed and explained. (AU) Copyright © 2014 Companhia Brasileira de Metalurgia e Mineração (CBMM) All rights reserved.