Effect of Hot Working on Secondary Phase Formation in 2205 Duplex Stainless Steel

In this research, aging treatments at temperatures of 800 and 900 degrees C for different aging time of 5-60 min were conducted on solution treated as well as hot worked samples of 2205 dual phase stainless steel. The effect of aging treatment on precipitation of intermetallic phases was investigated in undeformed specimens and those subjected to hot deformation with different strain rates of 0.001-1 s(-1). It was found that sigma precipitation increased by hot working. It was also concluded that the volume fraction of phase increased with deformation temperature and decreased with strain rate. The precipitation of intermetallic phases (i.e. sigma and chi) was analyzed by an Avrami-type kinetics equation of %(sigma+chi)=A(1-exp(-kt(n))) and the values of n and In k were estimated for different thermomechanical regimes. The values of n were assessed to increase from 0.4 to 1 with strain rate in the studied range. Otherwise, It was also understood that In k decreased with strain rate. Microstructural observations by means of optical microscopy and scanning electron microscopy showed that sigma particles mostly nucleated at the ferrite-austenite interfaces. But no sign of chi-phase could be seen. This fortified the idea of certain literature that chi-phase always forms at early stages of aging and consumes through the precipitation of sigma.