Electron Microscope Study of the Microstructure of BIS 812 EMA Submarine Steel.

摘要

The hull steel for Australia's Collins class submarine, BIS 812 EMA, is somewhat unusual in that it contains significant additions of boron and the substitutional hardenability elements nickel, chromium and molybdenum, and is also microalloyed with titanium, niobium and vanadium. It is used in the quenched and tempered condition, rather than being control-rolled, and therefore the role and benefit conferred by the microalloying additions are not clear. The electron microscope study reported here is concerned with characterizing the microstructure of the steel and determining the distribution of the titanium, niobium and vanadium. The steel consists of tempered lath martensite typical of quenched and tempered steels of similar carbon content. The titanium occurs as cuboidal particles, ten to one hundred nanometers in size (probably TiN), formed after solidification or during the soak, and largely unaffected by subsequent processing. The niobium and vanadium appear to be mostly taken into solution during the austenitizing treatment and precipitate as a fine carbide dispersion during tempering, although some niobium is incorporated in the TiN cuboids.... Carbo-nitride inclusions, Austenite, Quenching, Inclusions, Tempering.