Investigation of Special Misorientations in Lath Martensite of Low-Carbon Steel Using the Method of Orientation Microscopy

Abstract

Special misorientations between the laths of martensite packets in a low-carbon structural steel have been investigated by the method of EBSD-based orientation microscopy. It has been established that, in the process of the γ → α transformation, as a consequence of Kurdjumov—Sachs orientation relationships (ORs), special misorientations of the Σ3, Σ11, Σ33c, and Σ99a types are formed between the laths of a packet. The Σ3 misorientation is exact, and the remaining misorientations close to the special ones are formed with identical angular deviations as a result of the need to match the misorientations of laths in triple junctions (Σ3 + Σ11 → Σ33c, Σ3 + + Σ33c → Σ99a). Triple junctions of laths also appear in the packet that include a low-angle boundary (LAB) (between two laths of one orientation) and two boundaries of the Σ33c type, which can lead to the appearance of a boundary of the Σ41c type (Σ33c + LAB → Σ41c). The misorientation that corresponds to the Σ25b boundary discovered in the structure probably appears between the laths as a consequence of the fulfillment of the Nishiyama ORs.