钒：改造未来

The Role of Nitrogen in Microalloyed Forging Steels

Abstract:

This paper reviews some beneficial effects of nitrogen in microalloyed forging steels. Because of high solubility in medium-carbon steels, vanadium is the most suitable microalloying additive in microalloyed forging steels. Vanadium added into steel plays two essential effects -- grain refinement and precipitation strengthening by the precipitation of fine carbo-nitrides. Since higher affinity of vanadium to nitrogen than to carbon, and nitrides are more stable than carbides, therefore nitrogen plays a key role on controlling precipitation of vanadium carbo-nitrides in microalloyed steels. Experimental results show that an enhanced nitrogen content promote the precipitation of V(C,N) and decrease the particle size of V(C,N) precipitates, hence increase precipitation strengthening effect of vanadium. Nitrogen refines the ferrite grain by promoting the intragranular ferrite nucle;ition and retarding the ferrite grain-boundaries motion due to the precipitation of V(C,N) in the interior of austenite and on the austenite-ferrite boundary. In the steels utilizing the technology of TiN dispersion, enhanced nitrogen makes TiN particles more stable and efficient in pinning the austenite grain boundaries. For a given strength level, the vanadium content can be reduced by 20-40% by making fully use of the cheap nitrogen. So, nitrogen is a very cost-effective alloy element to microalloyed forging steels. 

Keywords:

V-N Microalloying, Precipitation Strengthening, Microalloyed Forging Steels