Influence of Heat-treatment on Mechanical Properties of an Fe-9Al-30Mn-1C Alloy
The purpose of this study is to examine the microstructural development of the Fe-9Al-30Mn-1C alloy through different heat-treatments by means of optical microscopy, scanning electron microscopy and transmission electron microscopy. Besides, the effects of the microstructures on the mechanical properties and fracture mechanisms were also made. In the as-quenched condition, the microstructure of the alloy was single austenite phase. Therefore, the alloy possesses good strength and toughness. When the alloy was aged at 550℃ for 6 hours, fine κ´-carbides were formed within the austenite matrix and no precipitates could be observed on the grain boundaries. It is thus that the alloy could get better strength without losing much toughness. When the alloy was aged at 650℃ for 6 hours, not only the fine κ´-carbides formed within the austenite matrix but also a few of the coarse κ-carbides started to precipitate heterogeneously on the γ/γ boundaries. This leads the alloy to get the best strength and cause the toughness down slightly. When the alloy was aged at 850℃ for 6 hours, there was deficient κ´-carbides existing within the austenite matrix but much coarse κ-carbides occurred on the grain boundaries. Obviously, the strength and the toughness of the alloy would go down greatly. In the present study, the comparison of the mechanical properties between the cast alloy and the rolled alloy was undertaken. Under the same heat-treatment condition, the cast alloy trended to be more brittle. The main fracture mechanism of the cast alloy was intergranular decohesion with a certain proportion of transgranular cleavage. The main fracture mechanism of the rolled alloy was ductile dimple fracture. With increasing the aging temperature, it would be accompanied with a certain proportion of transgranular cleavage.
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