2015 年 33 巻 2 号 p. 125s-129s
Effect of cold rolling before austenitization on mechanical properties in bainitic steels has been investigated. Cold rolling of ferrite (α) and isothermal holding above A1 before austenitization were done to harden ferrite and to form thin layer of austenite (γ) at/around both α grain boundaries and annealing twin-boundaries. Both coherency stress around (γ/α)-interface and transformation stress might introduce dislocations into γ. The dislocations within γ might react with each other, resulting in formation of dislocation network, whose constituent dislocations have different Burgers vectors with each other. In the high temperature region of γ, the climbing of constituent dislocations in dislocation network might occur through absorption of vacancies with an individual rate, resulting in bowing of each constituent dislocation out (increasing in dislocation energy). Therefore, the absorption of vacancies with the constituent dislocations in dislocation network would be suppressed, resulting in the dislocation network being stable. Nucleation of bainite laths might be enhanced to relax the strain field around dislocation network, resulting in refining bainite lath. The refining of bainite lath would improve both strength and ductility in bainitic steel.
