Plane-strain fracture toughness of AISI 4140 steel austempered below MS

Symmetry Breakdown Related Fracture in 42CrMo4 Steel

“…The simple modelling shows that constraints induced by geometric symmetry can enhance the fracture toughness, whereas symmetry breakdown deteriorates KIC. The experimental KIC values reported in the previuos work [5] lie exactly between the threshold values predicted by Eq. ( 9) with the packet size as the selected value of ϕ.…”

“…The intensity of E is approximately half that of J. In Area II visible are the major orientations D1, E, F, J, and the transformation texture (110) [1][2][3][4][5][6][7][8][9][10]. In particular, the intensity of (110) [1][2][3][4][5][6][7][8][9][10] compares to that of J, while the intensity of D1 is approximately half that of D2 (Fig.…”

“…The chemical composition and metallurgical features of the versatile 42CrMo4 steel are represented in Table 1. The cycles of heat treatment, the preparation of circumferentially notched round bars and the performance of the notched tensile testing have been described somewhere else [5]. Cracks were introduced by the notched tensile testing interrupted right before the load reached the average notched fracture load.…”

“…3b). In plane-strain cracked Area III, the intensity of (110) [1][2][3][4][5][6][7][8][9][10] is approximately twice that of D2, E, F, and J. The {110}b fiber extends from F through J to E along the 2 direction (Fig.…”

“…The (110)[1-10] components have been emphasized in Area II and dominate in Area III, changing the symmetry of these areas significantly. As demonstrated in Table 2, the (110) [1][2][3][4][5][6][7][8][9][10] components are developed directly by the spontaneous transformation of sheared f.c.c austenite, which has been preliminarily analyzed by Wittridge and Jonas [6]. As a result, it can be concluded that the spontaneous transformation components break the symmetry and the plane-strain fracture toughness of the material deteriorates.…”