Microstructural changes during heating of super duplex stainless steel and its thermal deformation behavior

Microstructural changes during heating of highly alloyed Cr26Ni7 type super duplex stainless steel (SDSS2607) and its thermal deformation behavior were investigated.At different heating rates,the mechanism of phase transition from γ phase to δ phase and growth modes of δ phase differed.Variations in microstructures for ascast SDSS2607 during heat preservation at 1 220 ℃ indicated two kinds of transformations from γ phase to δ phase.In-situ observations of microstructural changes during the tensile process at 1 050 ℃ showed a mutual coordination between γ and δ phases.When the true strain increased,the mutual coordination between γ and δ phases was damaged.Subsequently,cracks nucleated at the γ/δ interface.With the increase in temperature,the strength of ascast SDSS2607 decreased while its plasticity increased.Its thermoplasticity was poor,and the reduction in area of tensile specimens was less than 80％.When the deformation strain of hot compression increased,the stable deformation zone in the heat processing maps enlarged gradually.Moreover,the unstable deformation zones were extended.