Long-Period Stacking Structure within Martensite in Melt-Quenched δ⁄γ Duplex Phase Stainless Steel

The stacking structure of close-packed planes within the martensite from δ-ferrite in a melt-quenched δ⁄γ duplex stainless steel ribbon has been investigated by means of high resolution transmission electron microscopy. The observed structure images show that the martensite consists of stackings of close-packed planes with shuffling and lots of stacking faults. The existence probability of the extended shuffling including stacking faults is about 0.35, and more than 80% of the extended shuffling occurs as the two-layer shuffling expressed as ABC-B-ABC. Although the arrangement of the two-layer shuffling was rather in disorder, there exist the areas with the (3\={2})3, (4\={2})3 or (5\={2})1, type stackings of close-packed planes in the Zhdanov’s notation. The existence probability of the (4\={2})3 type stackings is the largest, being 0.27 to 0.43. This martensitic transformation is considered to be that from the δ-ferrite to the (4\={2})3 type long period stacking structure which contains stacking faults with a probability of about 0.16 as the lattice invariant strain.