Abstract: The characteristic and regularity of γ≒α+ Fe3C transformational superplasticity of carbon steels have been studied. An interesting phenomenon was found that an unusual peak appeared in the elongation curve of lower carbon steel during the tension stress increased. The author deduced that the directional diffusion of matrix atoms was maior mechanism of the phenomenon.

Key words: 超塑性, 化学势, 扩散, 相变