Stabilized uniform deformation in a high-strength ferrite-cementite steel with multiscale lamellar structure

Abstract

In order to ameliorate the ductility and stabilize the uniform deformation of ultrafine-grained (UFG) ferrite-cementite steel while retaining its high strength, a multiscale lamellar structure was developed and compared with the UFG structure. Microstructures were characterized and tensile behaviors were analyzed in the samples with multiscale lamellar and UFG structures; the mechanisms underlying the different strain-hardening capabilities were studied. Plastic instability dominated during the tensile deformation of spheroidized UFG carbon steel, because of its low strain-hardening owing to the uniform UFG structure with high dislocation density. However, the steel with multiscale lamellar structure exhibited a marked improvement in the balance between strength and uniform deformation, ascribing to the enhanced strain-hardening capability. This result was primarily attributed to the extra strain-hardening generated by the strain gradient and stress state change caused by the multiscale lamellar structure.