焼結Si-Ni鋼の熱処理組織と引張り特性

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Sintered low alloy steels with the composition of 2%Si-3%Ni-O0.6%C were austempered or quenched in water and tempered after (α+γ) solution treatment, then, the effect of their structures on the tensile nronerties was studied. The results are summarized as follows:<BR>Ferrite played an important role in improving the ductility of the specimens with mixed structure of ferrite (α), upper bainite (B), and retained austenite (γR).<BR>Both in sintered (α+β+γR) tri-phase steels and (α+tempered martensite) dual-phase steels, the elongation increased and the strength decreased with increasing the volume fraction of a-phase. In connection with this behavior, as the ratio of hardness of harder phase to that of a-phase increased, the relation between tensile properties and the volume fraction deviated from a linear relationship.<BR>A model for the tensile fracture process of the specimen with (50 vol%α+β+γR) mixed structure was proposed. The growth and the coalescence of secondary voids in the a-phase or at the α/(β+γR) interface resulted in the propagation of ductile cracks.
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