High-temperature Laves precipitation and its effects on recrystallisation behaviour and Lüders deformation in super ferritic stainless steels

• Main Authors: Hui-Hu Lu, Hong-Kui Guo, Wei Liang, Jian-Chun Li, Gang-Wang Zhang, Tao-Tao Li
• Format: Article
• Language: English
• Published: Elsevier 2020-03-01
• Series: Materials & Design
• Online Access: http://www.sciencedirect.com/science/article/pii/S0264127520300101

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. Keywords: Super ferritic stainless steel, Lüders deformation, Annealing, Recrystallization texture, Laves phase, Embrittlement