Abstract
The relation between the fine spherical cementite precipitated in the proeutectoid ferrite of a plain carbon steel by quick thermal cycling, and the maximum heating temperature and constrained stresses of the thermal cycle was investigated mainly by the point counting method. The specimens, solid bars 6 mm in diameter, were subjected to a repetition of rapid heating and cooling in air under no load and constrained condition by electric resistance heating and jeted water cooling. The maximum heating temperature of the thermal cycle was 690°∼200°C and the minimum temperature was 20°C. The results of obtained are summarized as follows:
(1) The number of fine spherical cementite was increased by increasing the maximum heating temperature.
(2) The constrained stress of the specimens during thermal cycling promoted the nucleation and growth of the fine spherical cementite.
(3) The fine spherical cementite precipitated in the proeutectoid ferrite of low carbon steel. The number of the fine spherical cementite was increased by increasing the size of ferrite.
(4) The fine spherical cementite precipitated in the ferrite of commercial grade pure iron (0.03%C). Many sub-grains appeared in the ferrite after thermal cycling.
