Influence of ageing on kinetics and strain-hardening behaviour of duplex stainless steels Available to Purchase

In this work, the effect of long-term isothermal heat treatment on the kinetics of sigma-phase precipitation of super duplex steels was qualitatively and quantitatively examined in detail. Microstructural examination showed that the sigma phase was only an intermetallic phase even after ageing for a longer holding time (4500 min). As the ageing time increased, the amount of sigma-phase precipitation also increased. In order to assess the transformation characteristics, the experimental results were fitted with the Johnson–Mehl–Avrami equation. The results showed that the kinetics of sigma precipitation was very sensitive to the holding time at 900°C. Also, in this investigation, the strain-hardening behaviour was evaluated by using Holloman’s model. As the ageing time increased, the tensile strength of the samples also increased because of the sigma-phase precipitation in both the ferritic phase and ferrite/austenite interface. The embrittled ferrite phase was found to be harder than the austenitic phase, and the strain-hardening behaviour of both the austenitic and ferritic phases was found to be monotonic in nature.