Untitled

Delaminating Crack Paths in Ultrafine, Elongated Ferritic Steel

“…This has been confirmed in the conventional alloys by the previous research. 21) After initiation, the crack propagates in all directions. A part of the crack propagates towards to the notch root, and finally connects with it, forming a macrocrack.…”

Effect of Bainitic Packet Size Distribution on Impact Toughness and its Scattering in the Ductile-Brittle Transition Temperature Region of Q&T Mn-Ni-Mo Bainitic Steels

“…If the principal tensile stress exceeds the cleavage fracture strength, which depends on the size of the microcracks, the microcrack then propagates in an unstable manner, i.e., brittle cleavage fracture occurs. [27] Chen et al [21] defined this unstable propagation of the critically sized microcrack as the "critical event" for the cleavage fracture, which is the most decisive step in the whole fracture process and, in turn, determines the impact toughness. Therefore, the critical size of the microcracks is suggested as an important microstructure parameter for the cleavage fracture.…”

“…[23] Moreover, ref. [21] revealed that when the stable propagation of microcrack occurs, the critical event of cleavage fracture for ferrite steel is the propagation of grain-sized microcrack across the grain boundary into adjacent grains for notched specimens, where the "grain" is the ferrite grain. Similarly, Figure 5 shows the typical fracture surface of the IFG sample fractured at -60 8C.…”

“…In the fibrous and cleavage zones, dimples and cleavage facets can be clearly seen under high magnification, respectively. Therefore, according to ref., [21] the microstructure feature corresponding to the critical event is a "grain-sized" microstructure. Combining these observations, the microstructure feature that confines the critical microcrack prior to the unstable propagation is the bainitic packets, and the critical event of cleavage fracture for the Q&T bainitic steel under impact testing conditions is the propagation of packet-sized microcracks across the packet boundary into the neighboring packets.…”

“…[12][13][14][15]19,20] It is believed that brittle fracture occurs when a microcrack with a certain size propagates into the adjacent grains under a normal stress around the notch root or pre-crack which exceeds the critical local fracture stress s f . [20] Chen et al [21] defined this process as the "critical event" of cleavage fracture and suggested that it is the most difficult step in the whole fracture process. As such, it determines the toughness of the material.…”