• Ilie, Sergiu
• Harrer, Bernhard
• Großeiber, Simon
• Degischer, Hans Peter
• Poletti, Maria Cecilia

Abstract

The hot ductility and malleability of a vanadium-microalloyed steel is investigated by means of tensile and compression tests at temperatures ranging from 700 to 850°C and strain rates of 3 × 10−4 to 0.3 s−1. The deformation tests are performed after austenitization and cooling to test temperature. The so-called second ductility minimum is located around 750°C for all strain rates except for the highest one, where no ductility trough is observed. Ductility steadily increases with strain rate at a given temperature, and the fracture mode progressively changes from intergranular to transgranular. In the region of minimum ductility, intergranular cracking occurs at low strain rates by void nucleation, growth and coalescence within thin layers of deformation induced ferrite covering the austenite grain boundaries. Cracking is favoured by V(C,N) precipitation associated with the γ/α phase transformation. Ductility remains low above the temperature of minimum ductility, where no apparent ferrite formation is observed (790 °C). Void formation takes place as a result of grain boundary sliding in combination with matrix and grain boundary precipitation. These voids are able to grow and link up forming intergranular cracks. Ductility increases with strain rate mainly due to the short time available for precipitation as well as for intergranular void growth and coalescence

Topics

• impedance spectroscopy
• grain
• phase
• grain boundary
• crack
• steel
• compression test
• precipitation
• forming
• void
• ductility
• vanadium