Transmission Electron Microscopy Studies of Structural Changes in 13Ni-15Co-10Mo Maraging Steel as a Result of Aging

Abstract

Transmission electron microscopy studies were carried out in order to reveal the structural changes in maraging steel as a result of aging. Two kinds of intermetallic compounds of Ni3Mo and Fe2Mo are found to precipitate in the martensite. The precipitation takes place in two stages. Ni3Mo precipitates first and in the latter stage both Ni3Mo and Fe2Mo are found to precipitate in the martensite. The average size of precipitates is about 5 nm in the maximum hardeness state. Relation between the distribution of precipitates and the properties of maraging steel such as strength, temperature dependence of hardening characteristics, and brittleness in early stage of aging is examined. These properties are influenced by the size of precipitates. Specimens containing precipitates smaller than 4 nm have different properties from those with precipitates larger than 4 nm.