Mechanical Properties of Fe-Ni Alloys Having Microduplex Structures

Abstract

The relationship between structures and mechanical properties of seven materials having microduplex structures consisting of ferrite (α), martensite (α′) and austenite (γ) in Fe-Ni alloys has been studied by means of microscopic observation, tensile test and impact test.
The strength of the (α+γ) microduplex structures is larger than that expected by the rule of mixture due to the grain refinement. Their ductility at low temperatures is improved remarkably compared with that of α′. The shape of their grains markedly affects their mechanical properties.(α+γ) microduplex structures containing the unstable γ show the maximum strength and large elongation at a 50-50 phase ratio when they are tested at -196°C. Their low temperature toughness is lower than that containing the stable γ. The tensile properties of (α′+γ) duplex structure are almost explained by the rule of mixture. The tensile behavior of (α+γ′) microduplex structures are similar to that of α′.