Microstructure and flow behavior of cast 2304 duplex stainless steel at elevated temperatures
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A. Momeni Department of Materials Science and Engineering, Hamedan University of Technology, Hamedan 6516913733, Iran (Received 13 July 2016; accepted 18 November 2016)
Hot deformation characteristics of 2304 duplex stainless steel were analyzed by hot compression tests at temperature range of 850–1150 °C and strain rates of 0.001–1 s1. The flow curves at low temperatures and high strain rates were suggesting sluggish dynamic recovery (DRV) in ferrite and partial dynamic recrystallization (DRX) in austenite. However, at high temperatures and low strain rates, the flow curves showed implied the domination of DRV in ferrite. The hyperbolic sine equation with activation energy of 508 kJ/mol could relate the processing parameters. Microstructural observations showed that DRV in ferrite is the controlling mechanism at all deformation conditions. However, at high temperatures and strain rates partial DRX could also occur in austenite. Based on the law of mixture and Baragar’s equations a modified model was proposed to consider work hardening and dynamic softening in the constituents. The model could satisfactorily predict the flow curves at different deformation regimes.
I. INTRODUCTION
Duplex stainless steels (DSSs) are a class of stainless steels with wide applications in different industries. DSSs are comprised of d-ferrite and austenite with comparable volume fractions. Since d-ferrite is more stable at higher temperatures, its content increases with increasing temperature and microstructure becomes fully ferritic at temperatures over 1200 °C.1–3 Hence, in the hot working temperature range of 900–1200 °C, most of DSSs have a duplex microstructure. The coexistence of austenite and ferrite with different deformation and restoration mechanisms makes it difficult to easily interpret the flow behavior of DSSs through hot or cold working. This complexity has been the motive force for a number of investigations in the past decades.4–7 The major source of complexity in the hot deformation behavior of DSSs is that ferrite and austenite have different specific strengths and are softened by different mechanisms. While ferrite undergoes dynamic recovery (DRV),8–10 austenite tends to soften by dynamic recrystallization (DRX).11–14 The major difference in the softening behaviors of ferrite and austenite makes it difficult to find a simple model for the flow curves. In other words, the phenomenological and physical-based models, which have been so far developed for single-phase ferritic Contributing Editor: Jürgen Eckert a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2016.457
or austenitic steels, cannot be used to predict the flow behavior of DSSs. In the past decades, some researchers have tried old constitutive equations such as the hyperbolic sine function for modeling the flow curves of DSSs.15–17 Other researchers tried to develop new constitutive equations based on the law of mixture rule and the individual behaviors of ferrite and austenite.18,19 Given the efforts devoted to the issue, t
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