The 16MND5 ferritic steel specimens were strained in uniaxial tension at -196 to 25C. Transmission electron microscopic observations made after the tests revealed that strain localization took place at the scale of lath blocks, where the individual laths underwent bending straining. Noticeably, the lath boundary dislocations represent an important fraction of the initial sources. Within the deformed laths, dislocations were homogeneously distributed at low plastic strain and gradually condense into high density structures, with increasing deformation. Dislocation condensation takes place in the form of cell walls or tilt boundary structures at T ≥ 0C; in the form of sub-lath size clusters at T ≤ -90C. Unlike in pure Fe, screw dislocation motion in 16MND5 steel was characterized by very active cross-slip and subsequent formation of cross-kinks. It was believed that this self-locking effect contributes to strain hardening, in addition to dislocation accumulation at the lath boundaries.

Dislocation Structures in 16MND5 Pressure Vessel Steel Strained in Uniaxial Tension at Different Temperatures from -196C up to 25C. C.F.Robertson, K.Obrtlik, B.Marini: Journal of Nuclear Materials, 2007, 366[1-2], 58-69