Delamination toughening in a low carbon microalloyed steel plate rolled in the dual-phase region

Abstract

It is still a big challenge to obtain excellent low-temperature toughness for bulk steel materials. Delamination is an effective method to improve low-temperature toughness. In the present study, delamination toughening in a low carbon microalloyed steel plate with elongated and ultrafine-grained microstructure rolled in the dual-phase region has been investigated in detail. When toughness was measured along normal direction, the steel plate had a high upper shelf energy and no delamination occurred in the upper shelf region. A large delaminated crack parallel to rolling plane started to appear and changed the propagation path of main crack when testing temperature was lower than −60°C. We find this kind of delamination induces a second upper shelf in the Charpy transition-temperature curve. The second upper shelf, reaching up to 300 J in the temperature range of −60°C to −140°C, results in excellent low-temperature toughness for the steel plate, and the ductile-brittle transition temperature is lowered to −157°C. The developed steel plate also has high low-temperature toughness measured along transverse direction due to delamination. The effect factors on upper shelf energy, delamination mechanism and delamination toughening are discussed.

The Role of Splitting Phenomenon under Fracture of Low-Carbon Microalloyed X80 Pipeline Steels during Multiple Charpy Impact Tests

“…We observed the split formation only during ductile fracture (Figures 3-5). According to the literature data, there is a temperature below which splits are not formed [16]. In our experiments, we revealed that splits' maximum number and size are observed at −100 • C test temperature.…”

“…However, studies of the splitting phenomenon have led to very contradictory conclusions. According to some studies, the occurrence of splits reduces impact toughness [8][9][10][11], but others have come to the opposite conclusions [12][13][14][15][16]. These contradictions are a reflection of the complexity of the very splitting phenomenon in different materials.…”

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

“…The existence of weak laminated interfaces is the cause of delamination. [ 9,12,13,21 ] Shen et al's [ 8 ] previous research found that the generated microvoids arranged linearly at the laminated interface during the impact process of laminated and ultrafine‐grained steel. Then, the microvoids grow and propagate along the laminated interface, thus delaminated crack forms.…”

“…The tensile strength was 1,850 MPa, and the Charpy V-notch impact toughness (CVN) was up to 290 J at À60 °C. [1] Song et al, [4,5] Zou et al, [6] Shen et al, [7,8] and others [9][10][11][12][13] have performed some work on the delamination toughening of steel plates. Zou et al [6] obtained a low-carbon medium manganese steel with a laminated microstructure containing retained austenite generated by intercritical rolling (IR).…”