Effect of Effective Grain Size on Ductile-brittle Transition Temperature in Four Different Microstructures of a Low Carbon Steel

摘要

For analyzing the good toughness of ultrafine ferrite/cementite steels, the concept of effective grain size (d_(EFF)) is applied to ductile-to-brittle transition temperature, DBTT, for ultrafine ferrite/cementite (Uf-F/C), ferrite/pearlite (F/P), quenched (Q), and quench-and-tempered (QT) microstractures in a low carbon steel. From the point of the relationship between d_(EFF) and DBTT, the Uf-F/C, Q, and QT microstructures can be placed into the same group and the F/P to a different one. Also, the Uf-F/C has the highest estimated fracture stress among the four microstractures. These might be the result of the difference in the surface energy of fracture.