日本金属学会誌

J. Japan Inst. Metals, Vol. 41, No. 9 (1977),
pp. 851-855

On the TTA (Time-Temperature-Austenitization) Diagram in the Carbon Steels

Yoshiyuki Miwa1 and Hidetaka Ono2

1School of Science and Engineering, Waseda University, Tokyo
2Graduate School, Waseda University, Tokyo

Abstract:

The TTA (Time-Temperature-Austenitization) diagram was determined for a commercial pure iron, an eutectoid steel and various hypo-eutectoid steels (0.1, 0.4 and 0.6% carbon), using a newly designed experimental apparatus previously reported.
It has been observed that in the TTA diagram the starting time of the transformation shifts to the left side with the increased over-heating and finally reaches 0 sec at 950°C in the commercial pure iron, and at 840°C in the hypo-eutectoid and eutectoid steels. Therefore there exists an upper limiting temperature at the zero-time axis that coincides with the upper limit of the transformation start on super-rapid heating.
The transformation finish line with the degree of over-heating in the hypo-eutectoid steel shifts to the left side above Ae_3, but it does not show the same behaviour below Ae_3; in other words, there is a refraction point at the Ae_3 point. It follows that the shape of the finish line in hypo-eutectoid steel is different from those in pure iron and eutectoid steel.


(Received 1976/9/6)

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