Abstract
The interaction of microstructural evolution, precipitation and mechanical properties of cold rolled 27Cr–4Mo–2Ni steels stabilised by Nb/Ti during annealing are investigated. Prior deformations provide an acceleration effect on bulk sigma precipitation and increase the starting precipitation temperature to ~1000 °C, which can induce a brittle fracture mode for annealed specimens. The precipitation temperature of Fe2Nb-type Laves phase is observed to be as high as 1050 °C, and these nanoscale Laves phases are intertwined with Nb2C particles, which are located at sub-grain boundaries. The abnormal relationship between the grain size and the annealing temperature, which is also related to the formation of Nb-containing particles, is determined. The transformation from Nb2C to Laves phase below 1050 °C release C atoms into the matrix around the Nb2C particles. This further leads to Lüders deformation during tensile test because of Cottrell atmosphere formation. The γ-fibre texture development during the annealing process is explained based on orientated nucleation and orientation growth theory. Super ferritic stainless steels exhibit a good combination of strength and ductility via Laves phase precipitation control during annealing at approximately 1050 °C for 5–60 min; these properties are advantageous for their application with strong γ-fibre texture.
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