钒：改造未来

The Role of Nitrogen in Microalloyed Steels

Abstract:

he key microstructural features of microalloyed steels, i.e. grain refinement and precipitation strengthening, are achieved by the precipitation of microalloy-species in austenite and during or after the transformation to ferrite. The effectiveness of any precipitation reaction depends on the degree of dispersion and particle size. Since nitrides of the microalloying elements are more stable and show less tendency to coalesce than carbides, an enhanced nitrogen content will maximise the ratio between particle volume fraction and particle size and hence maximise grain refinement and precipitation strengthening. 
This review considers some of the more important effects of the interaction of nitrogen with microalloying elements in microalloyed steels. The importance of nitrogen for precipitation phenomena, grain size control, transformations, precipitation strengthening and weldability are discussed in relation to various steel chemistry and processing technologies which have been developed within the past twenty years. To provide a basis for improved understanding of the interaction of nitrogen with other alloying elements in HSLA steels a new thermodynamic database for precipitation of carbonitrides in multicomponent systems has recently been developed for use with "Thermo-Cale" software. 
The value of nitrogen is particularly recognised in steels microalloyed with vanadium and titanium and it is demonstrated that nitrogen should be considered as an essential and inexpensive alloying element giving several beneficial effects. Nitrogen may be very effectively utilised in microalloyed steels with the aid of knowledge concerning its physical and chemical interactions.