The influences of specimen diameter on continuous cooling transformation curves measured with dilatation method

The continuous cooling transformation (CCT) curves of C45 steel were measured by the dilatation method with different diameter specimens in a Gleeble 1500D. The microstructures were analyzed by an optical microscope OLYMPUS-PMG3. The experimental results show that: the effects of the specimen diameter on the CCT curves are significant. With increasing the specimen diameter, the temperature in the specimen core increases and the supercooled austenite transformation temperature measured decreases, which makes the CCT curves moving down. However, the specimen diameter has no significant influence on the microstructures of the sample. In order to obtain precise CCT curves measured in the Gleeble 1500D, the specimen diameter should be machined into the small size, such as Ф6 mm or less in diameter