Influence of production methods on creep deformation of cold rolled 329LA lean duplex stainless steel in continuous annealing condition

• Published in: Journal of materials processing technology 2015-11, Vol.225, p.9-18
• Main Authors: Saenarjhan, N., Lee, Soo Chan, Kim, Sung-Joon
• Format: Article
• Language: English
• Subjects: 329LA; Cold reduction; Cold rolling; Continuous annealing; Continuous casting; Creep deformation; Creep strength; Deformation; Duplex stainless steel; Duplex stainless steels; Phase boundaries; Strip; Strip casting; Texture
• ISSN: 0924-0136
• DOI: 10.1016/j.jmatprotec.2015.05.001

The effects of processing methods, line tension, cold reduction and temperature on creep deformation of 329LA lean duplex stainless steel under continuous annealing condition are investigated. Two different processes, conventional continuous casting followed by hot rolling process and strip casting process, were used to make steel plates. Creep tests were carried out at 1010°C up to 1100°C using cold rolled specimens with various cold reductions for both kinds of specimen. It was found that continuous cast specimens show higher strain rate than strip cast specimens when tested with the same cold reduction and stress condition at all temperatures. Creep strain rate increases with the increase of line tension, temperature and the amount of cold reduction. The measured strain rate sensitivity values (m), around 0.5, show the superplastic behavior of both continuous and strip cast specimens at all test conditions, while the stress exponents (n), around 2, are consistent with the model of grain/phase boundary sliding as the rate controlling mechanism. The strip cast specimen has a very inhomogeneous microstructure which leads to larger average grain size, while the continuous cast specimen shows a uniform distribution of ferrite (δ) and austenite (γ). Electron back scattered diffraction (EBSD) results show that cold rolled texture is destroyed during heating to deformation temperature and δ/γ interface becomes high angle boundary which slides easily. Lastly, phase boundary sliding during creep deformation was confirmed by scanning transmission electron microscopy (STEM) in both specimens.