A common factor of bearing outer ring of the magnetic mark defect

Metal hot working process is relatively easy to defects, such as forging processing, forging overheating of empty, micro cracks are likely to be bearing fatigue source of contact fatigue failure. China bearing network (for short ） For a railway under a certain bearing outer ring cross section of the magnetic mark example, hope everyone drops of bearing forging processing common problems will understand it. 1, the condition of bearing outer ring section of the magnetic mark 1) Appearance inspection bearing outer ring magnetic marks on the condition of the railway section a bearing outer ring magnetic marks on the ring width, a short line or dot distribution in the direction along the circumference, about 1/3 circular distribution, shape as shown in figure 1. 2) Microscopic observation of bearing outer ring section of the magnetic mark in metallographic specimen preparing bearing outer ring end face of the magnetic mark, will be observed under a magnifying glass sample after mild abrasive, visible on the bearing outer ring end face a large number of small hole shape defect density distribution, shape as shown in figure 2. The flaw in light shine, is due to the bottom or side wall reflections. By the figure 2 shows, the pit defect sizes, but can be roughly see its shape distribution direction along the circumferential direction. Microscope, visible tiny flaws in the hole, the hole in the bar, internal inclusion has not been found, the length is about 0. 3 mm, have a certain depth, shape as shown in figure 3. 2, the bearing surface of some common defects in the process of bearing production, similar pit type bearing surface defects, there are several possible: mechanical injury, corrosion pit, forging burnt hole outcrop and raw material defects, etc. Among them, mechanical injury is due to hit or knock against the surface of the parts, corrosion pit is caused by the surface in contact with the corrosive medium surface pit corrosion marks, these two kinds of defects from mechanism determines its internal will not appear in parts. Defects and raw materials for the metallurgy defects, the distribution of the final part is irregular; Forging burnt holes for hot working defects, and its distribution in segregation serious position within the organization. These two kinds of defects not only distributed in the surface of parts. 3, bearing processing is well known, in the manufacturing process of bearing, bearing steel only experienced three high temperature ( More than 800 ℃) Process: hot rolling forming, forging and heat treatment were bainite hardening process. In general, in three heating process, the heat treatment quenching heating temperature is lower than forging and rolling forming temperature. And organizes the rating qualified magnetic marks of bearing ring, prove that there is no overheating in the process of heat treatment conditions, so the production of bearing ring inside the hole should be not produced in the process of heat treatment. Forging burnt can lead to bearing steel grain growth, cracking, serious when not only the surface of metal grain boundary oxidation and metal composition segregation more serious area, grain boundary also began to melt, forming Angle shaped holes. If the bearing steel forging burnt product ring holes within the organization, also can be divided into two kinds of circumstances: 1) Temperature range in the process regulation, ring on local tissue serious segregation leads to local burnt; 2) Forging temperature lead to the entire ring grain growth, grain boundary melting, holes in the organization. Above two situations, the hole location of the grain growth is inevitable, so the forging burnt fracture observation of the region generally presents the glittering grain surface edges, said stone fracture. The smashing of the magnetic mark ring fracture observation, fracture of fine porcelain shape on the whole, metal grain grew up and had no obvious phenomenon; Holes through the scanning, fracture surface defects. The status with forging burnt typical fracture status differences, and metallographic inspection found holes are mostly distributed in carbide, which makes the ring holes in the organization is in the case of forging process. 4, the causes of the bearing outer ring section of the magnetic mark after analysis, that the bearing ring holes has been in the bar, the steel supply factory analysis, rolling temperatures cause steel ingot sufficiently low melting point material segregation places to melt, producing local burn, is a fundamental cause of the microscopic pore. Due to the tiny holes in carbide gather location, carbide with low melting point material first melt and gaps, holes. Based on the analysis of above, the ring width of magnetic marks related to raw material microscopic pore. 5, the bearing outer ring section of the defective magnetic common factor 1) Bearing outer ring end face magnetic marks one of the common factor is due to raw material microscopic pore and carbide distribution is banded together. 2) Bearing outer ring end face magnetic marks the second common common factors cause of microscopic holes and bearing steel rolling process.