Anisotropie embrittlement in high-hardness ESR 4340 steel forgings

Olson, Gregory B.; Anctil, Albert A; DeSisto, Thomas S.; Kula, Eric B.

doi:10.1007/bf02654394

Cited by 5 publications

(3 citation statements)

References 11 publications

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“…• Structural heterogeneities such as "ghost lines" in wrought steels of grade 16 MND 5, whose shapes are parallelepipedic platelets of thickness of the order of 1 mm, width 10 mm, and length 25 mm, "segregated bandings" (14) in wrought steels, or "local brittle zones" in the heat affected zones of structural steels C-Mn (15), whose shapes are truncated pyramids with parallelepipedic bases of side of order of Il1I1l, can constitute a transgranular site of easy crack nucleation, leading to final transgranular fracture. The condition for fracture can also be fonnulated with a Griffith equation.…”

Section: Grain Boundary Crossingmentioning

confidence: 99%

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Microscopic aspect of fracture: Cleavage and ductile rupture

Miannay

1998

Mechanical Engineering Series

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In Chapter I, the theoretical cohesive stress of the material on the scale of the crystalline lattice, i.e., on the scale of nm, has been estimated from the theoretical surface energy. This energy for some metals is given in Table 5.1. The value is ofthe order of 10-5 da J . cm-2 . In Chapters 2 and 3, it was emphasised that the fracture theories based only on this theoretical stress and on purely elastic behaviour were insufficient and in fault, because for microcracks and cracks, a plastic deformation that appears around the crack normally for physical reasons is to be taken into account. This plastic behaviour will have to particularly explain why energies of the order of G tC = O.5daJ . cm-2 (with Ktc = 100M Pa.,;m for a steel) are associated with fracture.In fact, as it is experimentally observed, plasticity is necessary to trigger a fracture nucleation, which will lead to the whole fracture of the cracked or uncracked body. This aspect is illustrated in Figure 5.1, first with a tensile test of a plain specimen, i.e., without flaw, with a dimension of the order of cm, of an ideal totally homogeneous material, which breaks in an ideal manner after a total plastic deformation when the stress reduced to the current section and the area of this section go simultaneously to zero. But more in agreement with experience, some inhomogeneity appears during the plastic deformation and at the scale ofthe specimen, fracture occurs at various levels of deformation, (Fig. 5.1): for low values of deformation, fracture is said to be brittle; it requires low strain deformation energy and the preceding deformation does not allow the detection of its occurrence. For high values of deformation and generally beyond the necking, fracture is said to be ductile: it needs high energy and its occurrence can be predicted a long time before. As for necking, this corresponds to a geometrical instability and not to a fracture mechanism. (Exercise 5.1).When the preceding fractures are observed and analysed on their fracture surfaces and on axial metallographic sections, at a midway scale between the inter-atomic spacing, the nm, and the dimension of the specimen, the cm, i.e., at the scale of the inclusion, the /J-m, or at the scale of the grain, 10 /J-m, these fractures can be classified in a decreasing order of brittleness ( Figures 5.2 and 5.3) as • brittle or semi-brittle intergranular fracture, D. P. Miannay, Fracture Mechanics

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Section: Grain Boundary Crossingmentioning

confidence: 99%

“…14. Variation ofductility at fracture with stress triaxiality for the two orientations L-T and S-T ofquenched and tempered HY 130 steel (afterHancock and Mackenzie, 1977).…”

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confidence: 99%

Microscopic aspect of fracture: Cleavage and ductile rupture

Miannay

1998

Mechanical Engineering Series

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“…There have been many studies showing that such nonuniform solute distribution exist within RHA. The work of Olson et al (1983) showed that these composition striations can lead to an anisotropic embrittlement process wherein failure occurs in the elongated regions of high solute content. This is consistent with the fibering studies of Shockey and Erlich (1980) and the observation that the solidification processing technique (ESR versus VIM) can have a major impact on the penetration resistance of the steel.…”

Section: Formation Of Shear Bandsmentioning

confidence: 99%