高温におけるソルバイト炭素鋼の超塑性変形能

概要

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Elevated temperature tensile tests have been conducted for several steels with different carbon content over the temperature range (700℃～800℃) including A_1 and A_3 transformation points. The effects of temperature, strain rate and microstructure on the superplastic formabilities have been studied and the results obtained are as follows ; (1) In Sorbite material of the higher carbon steel, the more remarkable drop of the strength and the greater elongation are observed at the temperature just above A_1 point. This is considered to be superplastic phenomena due to (α+γ) microduplex structure producted by the precipitation of many fine γ particles on the eutectoid transformation. (2) The superplastic deformation is by no means uniform, but a large fraction of the total elongation is contributed by the elongation due to necking. The sustained stress at the bottom of the neck is constant during tensile test and so the creep process may take part in the deformation. (3) The Sorbite materials of each steels have larger strain rate sensitivity index of flow stress than the as-received materials and is considerably superior to the superplastic formability.
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