Formation mechanisms of heterostructures in 304L stainless steel processed by cold rolling and annealing

This work revealed the formation mechanisms of heterostructures for a 304L stainless steel (SS) processed by cold rolling (CR) and annealing. When the 304L SS was rolled with a medium rolling reduction of ∼70%, an uneven deformation structure including lamellar nano/utrafine-grains (NG/UFGs) and residual deformation structure (RDS) was prepared. During subsequent annealing, the recrystallization nucleation preferred to occur in finer deformation NG/UFGs, and then quickly grew to equiaxed fine-grains (FGs). The recrystallized UFGs were generated in the thicker deformation NG/UFGs. In addition, the RDS exhibited a high thermal resistance. Thus, a typical heterostructure with mixed structure of FGs, UFGs, lamellar deformation structure and residual martensite was fabricated. As the 304L SS was rolled with a high rolling reduction of ∼90%, a homogeneous deformation structure with lamellar NG/UFGs was formed. Due to the lack of RDS, the final heterostructure with mixed structure of FGs, UFGs and residual martensite was prepared.