Hot ductility behavior of boron microalloyed steels

The current study analyses the influence of boron contents (between 29 and 105 pprn) on the hot ductility of boron microalloyed steels. For this purpose, hot tensile tests were carried out at different temperatures (700, 800, 900 and 1000 degrees C) at a constant true strain rate of 0.001 s(-1). In general, results revealed an improvement of the hot ductility of steels at increasing boron content. At 700, 900 and 1000 degrees C the ductility is higher than at 800 degrees C, where boron microalloyed steels exhibit a region of ductility loss (trough region). Likewise, dynamic recrystallization only occurred at 900 and 1000 degrees C. The fracture surfaces of the tested steels at temperatures giving the high temperature ductility regime show that the fracture mode is a result of ductile failure, whereas it is ductile-brittle failure in the trough region. Results are discussed in terms of dynamic recrystallization and boron segregation towards austenite grain boundaries, which may retard the formation of pro-eutectoid ferrite and increase grain boundary cohesion. (C) 2007 Elsevier B.V. All rights reserved.