The magnetic powder flaw detection and common defects of bearing failure analysis

Bearing parts in the process of manufacturing, through forging, grinding, punching, cutting, grinding, heat treatment of expanding multi-channel processes, such as various kinds of defects may be present. Common defects as follows: 1, forging defects forging folding as blanking, burr, flash, such as easy to constitute a fold in appearance, its characteristic is folding is bulky, irregular appearance, easy to present the parts appearance. Stop inspection, had better use fluorescent magnetic powder flaw appeared more clear and intuitive. Forging folding magnetic mark at an Angle with looks ordinary linear, trench and scales flake, as shown in figure 1. Defect section made from metallographic specimen under the microscope view, defect tail obtuse, lubrication, on both sides have obvious oxidation phenomenon, as shown in figure 2, defects found no inclusion foreign bodies such as the information spreading. Look after cold acid etching metallographic specimen, on both sides of defective parts and have serious decarburization and oxidation; See defect layers in the appearance of morphology, the plastic deformation trace is obvious, without tearing fracture morphology. Through micro hardness testing and metallographic examine, defect layered place has different levels of carburizing and hardening phenomenon appearance. In conclusion, indicate the defect should be existed before the heat treatment quenching, and communicates with the outside world, concluded that the defects of forging folding. Figure 1 forging folding figure 2 section metallographic morphology of defects through high forging burnt forging heating temperature, holding time is too long cause overheating, serious when grain boundary oxidation and condensation. Microscopic view not only the outer surface of metal grain boundary is presented oxidative cracking Angle; And the areas with severe internal metal composition segregation, grain boundary also beginning of condensation, serious when also can constitute Angle shaped cave. Burnt the information in this state of defects to stop forging processing, came under heavy hammer forging, punching and run over expansion, would have a tear in the defect place, constitute a larger defect. Forging badly burnt outward appearance such as orange peel, it spread with tiny cracks and thick scale. Appropriate USES fluorescent magnetic powder stop inspection, make the defects appeared more clear. Pitting holes in forging defects caused by burning, as shown in figure 3. Defects along the cross section of preparing metallographic specimen under the microscope to examine, visible holes in looks and times they are scattered, partial Angle shaped, size is differ, bottomless, edge has a small crack spread, local area has grain boundary oxidation phenomenon, hole shape as shown in figure 4. Look after another along the defect hole in smashing the fracture fracture surface, visible fracture in rock fracture and its spread a large number of holes and micro crack. Figure 3 forging any temperature figure 4 hole defects in section 2, quenching crack morphology in quenching process, through the high cooling speed is too fast or when the quenching temperature, the breaking strength of the internal stress is greater than the data, will present the quenching crack. Appropriate USES fluorescent magnetic particle inspection for progress flexible and reliable. Quenching defect magnetic mark ordinary taking diagonal shape, circular arc form, dendritic or mesh, starting site wide, along with the extending direction and step by step as shown in figure 5. Fundamental direction spread along the circumference, the tail nozzle. Made for crackle look after metallographic specimen, crackle, deep root perpendicular to the surface, its not found scattered data with foreign bodies. Along the crackle on look after fracture, the fracture is brittle fracture, fracture surface has obvious heat tint, as shown in figure 6. Figure 5 quenching crack figure 6 quenching crack fracture morphology 3, grinding defects in quenching process, through high or cooling speed is too fast when the quenching temperature, the breaking strength of the internal stress is greater than the data, will present the quenching crack. Appropriate USES fluorescent magnetic particle inspection for progress flexible and reliable. Quenching defect magnetic mark ordinary taking diagonal shape, circular arc form, dendritic or mesh, starting site wide, along with the extending direction and step by step as shown in figure 7. Fundamental direction spread along the circumference, the tail nozzle. Made for crackle look after metallographic specimen, crackle, deep root perpendicular to the surface, its not found scattered data with foreign bodies. Along the crackle on look after fracture, the fracture is brittle fracture, fracture surface has obvious heat tint, as shown in figure 8. Figure 7 quenching crack figure 8 quenching crack fracture morphology of 4, the original material defect in grinding bearing parts, beating too much due to the grinding wheel feed, spindle, cutting fluid supply is abundant and grinding wheel grinding grain is blunt, grinding cracks are easy to make the parts. In addition, the heat treatment quenching temperature through high and form part of the organization is overheating, coarse grains, the residual austenite size, mesh and more massive particles. Grinding defects of the magnetic mark common net-like, radial, parallel to the line or crack, magnetic image, sharp, outline a clear, present number, usually, perpendicular to the direction of grinding as shown in figure 9. Magnetic marks spread more concentrated in the middle part, along the circumferential direction, a long linear or dendritic, part have bifurcate, magnetic marks of convergence. Look after preparing section metallographic specimen of crack, crack is fine, perpendicular to the surface, which did not see information inclusions, scale and other foreign body spread, appearance is shown in figure 10. Figure 9 original data crack figure 10 original crack morphology of inclusions