Formation of Widmanstatten Austenite in Strip Cast Grain-Oriented Silicon Steel

The formation of Widmanstatten austenite was studied in strip cast grain-oriented silicon steel. The microstructure was investigated by optical microscopy and scanning electron microscopy. The orientations of the ferrite, Widmanstatten austenite, and martensite were determined using electron backscatter diffraction. The Widmanstatten austenite exhibits a lath-like shape and nucleates directly on the ferrite grain boundaries. This differs significantly from earlier work on duplex stainless steels. The orientation relationship between the Widmanstatten austenite and the parent ferrite is closer to Kurdjumov-Sachs than to Nishiyama-Wassermann. The ferrite boundaries migrate so as to accommodate the habit planes of the laths, leading to the presence of zigzag boundaries in the as-cast strip. Carbon partitioning into the Widmanstatten austenite and silicon partitioning into the parent ferrite were observed.