Butterfly martensite in industrial steels

Abstract

The morphology and the conditions of formation of butterfly martensite observed in carbon tool steels, low-alloy tool steels and bearing steels have been investigated. The results indicated that the butterfly martensite in various steels in three dimensional space can be classified into two types: i.e., the butterfly martensite with tails and the butterfly martensite without tails. But in the two dimensional metallographic morphology they may be classified as three groups: i.e., the butterfly martensite with double tails, the butterfly martensite with a single tail, and the tailless butterfly martensite. The two wings of butterfly martensite comprise a whole entity and their mid-rib planes can exhibit crossing, kinking, or branching. There are ten possible stretched angles of space between the two wings of butterfly martensite. They are: 41°, 43°, 59°, 61°, 83°, 97°, 119°, 121°, 137°, and 139°. Among them, 137°, 121°, 139° and 119° appear the most frequently. The quantity of butterfly martensite increases with the increase in carbon content and in austenitizing temperature. The morphological features and the quantity of butterfly martensite are little affected by variations in alloying elements at low concentrations.