The compound formation mechanism of butterfly martensite

The butterfly martensites formed in Fe-1.20% C, CrMn, GCr18Mo, and 25Cr2Ni4WA steels have been investigated by optical and transmission electron microscopy. It has been found that the mid-rib of a butterfly martensite is a thin-plate martensite and that the formation of butterfly martensite is a multi-stage process. In the initial stage, crossed or kinked thin-plate martensites are formed. Subsequently, these become mid-ribs, grow more, then create butterfly martensite in various forms. Crossed thin-plate martensite thickens into butterfly martensite with tails, while the kinked form transforms to tailless butterfly martensite by thickening on only one side of the wings. The formation of butterfly martensite may not be a single continuous process, but rather a compound one comprised of separate stages.