13th International Conference on Fracture June 16–21, 2013, Beijing, China -2- other similar fracture samples. Then, make sure whether the drawing equipment was well, such as broken of drawing die, hole eccentric of die, water shortage of die case would lead to wire fracture. Because the influence of temperature and humidity on wire drawing performance, production environment and operating person would not be ignored. 2.2. Visual Inspection and Low Magnification Test The purpose of visual inspection and low magnification test were to determine the fracture mode by the macro morphology and surface defects, and photo with relevant information should be recorded. For circle section steel wire fracture, visual inspection and low magnification test included: (1) Original surface defects, such as fold and pitting. (2) Surface defects caused by drawing, such as broken of drawing die, hole eccentric of die, water shortage of die case, etc. (3) Color of wire surface, such as corrosion and welding joints. 2.3. Microscopic Analysis and Metallographic Examination The purpose of microscopic analysis and metallographic examination was to find microstructural characteristic which caused wire fracture. Scanning electron microscope (SEM) was used to observe fracture and surface morphology. The feature of wire fracture could be divided into two categories: (1) Dimple character, which was composed of round or oval holes with different sizes, sometimes inclusions or second-phase particles could be found in dimple. (2) Cleavage character, which included river pattern, scallop pattern, grainy pattern and intergranular fracture character. Metallographic examination was used to analysis internal cracks, grain size, decarburized layer, defect microstructure, etc. And typical defect microstructure included: martensite, net carbide, widmanstatten, etc. 3. Drawing Fracture Analyses Steel wire was under drawing force, pressure and friction during the drawing that was a plastic deformation. If the drawing equipment had poor lubrication, shortage of cooling water, or die eccentric, wire drawing would be caused to fracture. Fracture and surface morphology were very important to failure analysis of wire drawing fracture. Generally, fracture modes were corresponded to macro fracture morphology and surface state of wire. Failure analysis procedure of typical macro fracture morphology was optimized, such as, pencil-point shaped, plane shaped and inclined shaped fracture. 3.1. Pencil-point Shaped Fracture One end of the pencil-point shaped facture was conical tip, and the other conical hole which was matched with each other. The conical surface was angel of 45° to drawing direction and its morphology was shown in Fig. 1. Many investigations showed that the cause of pencil-point shaped fracture was central brittle phase. During wire drawing, brittleness microstructure in center could not be well deformed with outer steel wire, cracks firstly initialized surround the brittle phase, then the cracks which extended along 45° direction to wire axis leas to fracture [4,5]. Central brittle microstructure of wire that was shown in Fig.2 consists of inclusion, net carbide, martensite, etc.
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