MICROSTRUCTURE AND MECHANICAL PROPERTIES OF MICROALLOYED PM STEELS

Microalloying is used in wrought steels to refine grain size during thermo-mechanical controlled processing (TMCP), with an attendant improvement in mechanical properties. With the exception of powder forging (PF), powder metallurgy (PM) does not utilize TMCP. In previous work by the authors, however, it has been shown that in PM steels microalloying elements such as niobium and vanadium can limit austenite grain growth prior to oil quenching and tempering. By limiting grain growth, the precipitates that form cause a significant improvement in strength and ductility. In addition, the precipitates that form during microalloying can also improve the strength of the pearlite that forms in the sintered condition. The objective of this study was to explore the use and potential benefits of microalloying with vanadium and niobium in iron-carbon and iron-molybdenum-carbon PM steels. The resulting mechanical properties and accompanying microstructures of these microalloyed PM steels are evaluated and rationalized.