Abstract: In this paper, following result are found, microstructural charaterialic parameter of ductile-brittle transition in eutectoid steel of lamellar pearlite and subeutecield steels of ferrite+lamellar pearlite can be integratively expressed by compound structural charteristic parameter, D(D=dp+pp, D≈dj), by researching relationship between ductile-brittle transition temperature and microstructural characteristic parameter in steels of 10, 20, 35, 45, 55, 70 and T8A etc., and following equations are obtained: Tc=483.81-22.7dj-1/2 corr. = 0.9924 Tc=486.15-22.82D-1/2 corr. =0.9966 Therefore, compound structure size can be regarded as size of “effective grain” of cleavage fracture. The research results provide a quantitative and effective method for evaluating ductile-brittle transition temperature, Tc and diagnosing cold brittle fracture.

Key words: 钢, 韧然转移, 显微组织, 诊断