Tensile behaviour of duplex stainless steel at low temperatures

The tensile behaviour of the fertile and austenite phases of Fe-22Cr-5Ni (w t-%) duplex stainless steel containing a maximum of 17.2% austenite was inv estigated in the temperature range 65-298 K. The results indicate that mech anical twinning occurred in the testing temperature range, and that austeni te impeded the growth of twinning. Mechanical twinning in ferrite was well decorated with a 'dislocation shelf: and the density of dislocations at the coherent twin boundary and within a twin was much higher than in the matri x above the ductile-brittle transition temperature (DBTT). This supported t he occurrence of slip localisation next to coherent twin boundaries. Disloc ations in the material with no austenite tested below the DBTT were charact erised by coplanar slip dislocation on the {110} plane, and both coplanar s lip on {110} and cross-slip dislocations were observed above the DBTT Dislo cation in ferrite was negligibly affected by the presence of austenitic par ticles. Strain induced martensite transformation occurred in austenitic par ticles at or below 220 K, and the characteristics of the transformation wer e essentially similar to those in type 304 stainless steel. The DBTT of the material was lowered from similar to 140 to 110 K in the presence of auste nite, independent of the volume fraction of austenite. This suggests that t he decrease in the DBTT of the material was mainly due to austenite scaveng ing carbon and other interstitial elements from the ferritic matrix. The fr acture of the material at low temperatures was primarily controlled by the fracture of twin boundaries inferrite. MST/4193.