The critical point of hypereutectoid steel (its composition is 1.18% C, 0.23% Si, 0.28% Mn, 0.017% P, 0.023% S) was measured by the Sato's self-recording dilatometer when it was quenched in oil, after being coiled slowly (lamellar pearlite specimen), annealed (globular pearlite specimen), quenched in oil (martensite specimen) or cooled in air (sorbit specimen) from 950°. The Ar''-points do not appear on the latter two while they appear on the former two when they are quenched in oil from 780°. The more the quenched temperature rises, the more the Ar''-point decreases on the martensite specimen. This chance is due to the numbar of cementite nucleus in austenite by the quenching temperature.
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