The quasi-cleavage fracture is a brittle transgranular fracture, and the macroscopic fracture morphology is relatively flat, basically no macroscopic plastic deformation or minimal macroscopic plastic deformation. Most of the fractures are crystalline, and the small facets are bright but not luminous. Quasi-cleavage fractures also often show more obvious radial patterns. The origin of the fracture and the direction of propagation of the quasi-cleavage main crack can be judged according to the trend of the radial pattern, as shown in Figure 5-l.
Figure 5-1 30CrMnSi quasi-cleavage macro-fracture reflection patternSince the quasi-cleavage fracture is a kind of fracture between the cleavage fracture and the dimple fracture, the microscopic morphology of the quasi-cleavage fracture is different from the cleavage fracture and the ductile dimple fracture.
River patternQuasi-cleavage fracture river patterns usually originate from pores, non-metallic inclusions, hard spots and precipitates inside the grain. The river extends from the inside to the periphery of the facet, the river is short and discontinuous, and the confluence characteristics are not obvious. There is no continuation or surge of the river at the interface of the inclined grain boundary, the torsion grain boundary, and the large angle grain boundary. If the quasi-cleavage fracture is close to the cleavage fracture, the quasi-cleavage facets are relatively flat, the river flows in one direction and has a confluent performance. The facets are connected by tearing, and the obvious tearing ribs can be seen. This feature is obviously different from the river pattern of the cleavage fracture. If the fracture mode is close to the dimple break, it may also be seen on the fracture. The surface of the river pattern fracture is all composed of tearing ribs, see Figure 5-2.
Figure 5-2 Quasi-cleavage fracture2. tearing edge
The quasi-cleavage fracture unit is a facet, and the quasi-cleavage plane of the tempered martensite is {100}. Plastic deformation between the facets is connected in a tearing manner. When the quasi-cleavage fracture is close to the cleavage fracture mechanism, the tearing edge is small. If the fracture mechanism is close to the dimple fracture, the tearing protrusion is particularly petal-like, as shown in Figure 5-3.
Figure 5-3 45 steel impact fracture quasi-factory fracture × 5303. The quasi-cleavage facet is much larger than the tempered martensite size. It corresponds to the size of the quasi-cleavage plane of the original austenite grain before quenching, depending on the material composition, the state of the structure and the test conditions.
4. Sometimes a tongue pattern can be seen on a quasi-cleavage fracture, but it is not common.
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