20th International Forgemasters Meeting - IFM 2017

Duplex stainless steels are in good combination with strength, ductility and corrosion resistance. For this reason, duplex stainless steels are considered as excellent choices for various industrial applications such as oil extraction, paper manufacturing and other chemical industries. From the industrial point of view, the hot deformation of these steels has drawn much attention due to cracks if hot working parameters are not adequate conditions during hot deformation. In this work, in order to manufacture bulk type hot forgings of UNS No. S32205 duplex stainless steel, the hot deformation characteristics of UNS No. S32205 duplex stainless steel were analyzed by processing map obtained from Gleeble thermal-mechanical simulator and microstructure observations. The cylindrical billets with the height of 15mm and with the diameter of 10mm were prepared. The cylindrical billets were heated to 1250oC. Then, the hot compression tests were carried out at temperature ranges of 800-1200oC, strain rates of 0.001-1.0s-1and strain of 50%. In processing map, temperature ranges from 950 to 1200oC regardless of strain rates are found to be stable hot working regimes, in which the instability parameter ξ is positive and the microstructures exhibit dynamic recovery and recrystallization without cracks. However, temperature ranges less than 950oC regardless of strain rates are unstable hot working regimes, in which the instability parameter ξ is negative and/or much closed to zero and wedge cracks are observed at austenite/ferrite grain boundaries due to sigma phase formed during hot compression tests. From the result, the obtained processing map is applied to manufacturing of hot forgings; i.e., round bars with the diameters of 260mm and 360mm respectively to prevent cracks.