Relationship Between Microstructure, Delamination Behavior, and Toughness of Steel Plates Rolled in the Intercritical Region Under Variable Deformation

Abstract

Herein, the effects of microstructure on delamination behavior and toughness are discussed in detail. Steel plates have been fabricated by intercritical rolling (IR) under various strains (0.5, 0.8, and 1.1). The results show that increasing applied strain enhances the degree of laminated microstructure, and three kinds of impact fracture occur in sequence. 1) No delamination occurs in the IR0.5 steel plate with approximately equiaxed microstructure. 2) Delamination takes place in the IR0.8 steel plate with obvious laminated microstructure. But a crack parallel to the impact load direction forms beneath the delaminated crack. 3) Delamination is enhanced in the IR1.1 steel plate with enhanced laminated microstructure, and no crack forms below the delaminated crack. The delaminated crack mainly propagates along the laminated interfaces, so the laminated microstructure is the key reason for forming delamination. The more apparent laminated microstructure causes more remarkable laminated tearing at room temperature, large‐scale severe plastic deformation in the microstructure below the delaminated crack at low temperatures, and longer zigzag cracks at lower temperatures. Therefore, to improve toughness, the microstructure needs enough laminated structure to inhibit the formation of cracks parallel to the impact load direction below the delaminated crack.