Tetsu-to-Hagane
Online ISSN : 1883-2954
Print ISSN : 0021-1575
ISSN-L : 0021-1575
Superplasticity of δ-ferrite/austenite Duplex Stainless Steels
Yasuhiro MAEHARA
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1984 Volume 70 Issue 15 Pages 2168-2175

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Abstract

Superplastic behavior of δ-ferrite/austenite duplex stainless steels has been studied by means of isothermal hot tensile test at temperatures (T) from 700 to 1 100°C at initial strain rates (ε) from 10-4 to 10-1s-1 with particular emphasis on microstructural aspect prior to and during deformation. Large elongations are observed in the wide renges of T and ε. The maximum value, above 2 500%, is obtained under the condition that σ phase precipitation occurs. The elongation depends on the precipitation rate of σ phase especially in the lower temperature deformation as well as on the prior microstructure. The most suitable prior microstructure can be obtained by refining δ-ferrite matrix as well as fine dispersion of γ particles. In the deformation of the specimens with such optimum conditions, even if ε_??_10-1s-1, large elongations above 200 % can be observed at T≅1 000°C. During superplastic flow, the microstructure largely changes, i.e, at above 1 000°C γ phase is separated and refined into spheroidized particles within the δ-ferrite matrix and at below 1 000°C γ/σ mixed structure is formed by the eutectoid decomposition from δ-ferrite, resulting finally in the stable equiaxied micro-duplex structures with δ/γ and γ/σ, respectively. Such microstructural changes can play an important role for the superplastic behavior in addition to the effect of m-value.

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© The Iron and Steel Institute of Japan
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