13th International Conference on Fracture June 16–21, 2013, Beijing, China -4- Figure. 3 Discontinuous martensite in center of steel wire 3.2. Plane shaped fracture There was almost no necking or significant surface defects of plane shaped fracture, whose fracture surface was likely a plane shown in Fig. 4, so called as plane shaped fracture. Generally, the cause of plane shaped fracture was abnormal microstructure or larger grain which increased brittleness of wire [6]. Cleavage character and its microstructure of a plane shaped fracture were shown in Fig. 5. Bad welding zone could lead to plane shaped fracture as well [7], and the unusual color of blue or white could be the proof of joint. There were cleavage character, inclusion and dimples of different region of fracture, and longitudinal metallographic examination could show variation tendency of grain size which were shown in Fig. 6. Therefore microscopic analysis and metallographic examination procedure of plane shaped fracture should be: (1) wire surface should be inspected whether had defects or unusual color. (2) SEM was used to observe cleavage character, dimple, inclusion or other microstructural feature. (3) Transversal metallurgical examination should be adopted if cleavage character was found. Longitudinal metallurgical examination should be adopted if there were more than one microstructural character or unusual color of wire surface. Figure. 4 Morphology of plane shaped fracture (a) Cleavage Character (b) Metallurgical analysis Figure. 5 Cleavage character and Metallurgical analysis of plane shaped fracture
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