Count Alois von Beckh Widmanstätten is the man for whom these structures are named, but it was a curious scientist by the name of Thompson who, in the process of cleaning rust from a meteorite, first observed and recorded a strange new structure now most commonly known as a Widmanstätten pattern (Fig. 1).
Formally, a Widmanstätten structure is a microstructure resulting when steel is cooled (e.g., after welding) from extremely high temperatures faster than a certain critical rate. The structure is characterized by a geometric pattern resulting from the formation of a new phase along certain crystallographic planes in the parent phase. In general, it consists of ferrite and sometimes pearlite (Fig. 2) in what is often described as a cross-hatched pattern.