Imported bearing parts are often seen after heat treatment quality defects are: heat quenching microstructure overheating, owe, hardness, quenching crack don't apply, decarburization heat treatment deformation, appearance, soft point etc.
1. The overheating
Can see from the coarse mouth imported bearing parts to the microstructure after quenching overheat, but we need to distinguish the level of its overheating must examine the microstructure. If present in the gcr15 steel quenching organization coarse acicular martensite, organization for quenching overheating. A reason is able to quenching heating temperature through high or heat preservation time is too long to form the specific overheating; Can also be due to the original organization banded carbide is serious, the low carbon zone between two belts part needlelike coarse martensite, of the eve of the formed part is overheating. Overheating in the organization retained austenite increase, size invariability. Overheating due to quenching organization, steel coarse crystal eve will cause parts of toughness, impact resistant function is reduced, the service life of bearing is also reduced. Serious overheating even quenching cracks.
2. Less hot
Quenching temperature is low or poor cooling will occur in the microstructure beyond the standard rules of austenite organization, called owe hot organization, it decreased the hardness, wear resistance reduced sharply, affect the bearing life.
3. The quenching crack
Imported bearing parts in the process of hardening cooling by internal stress of crack quenching cracks. Form the crack reason has: because weather is high or cooling quenching heating temperature, the thermal stress and quality of metal stress steel of the eve of the volume change of the organization of the fracture strength; Task appearance of the original defects (such as appearance fine cracks or scratches) or steel internal defects such as slag, serious non-metallic dopant, white spots, shrinkage cavity, etc.) remaining to form stress concentration when quenching; The appearance of serious decarburization and carbide segregation; Parts hardening after tempering lack or real-time temper; Process form of cold stress in front of the Chinese New Year eve, forging folding, deep turning tool and the oil groove sharp edges and corners, etc. In conclusion, the cause of the formation of quenching cracks can be elements of one or more of the above, the existence of internal stress is constitutes the primary reason of quenching crack. Quenching crack deep and tall, fracture straight, broken section without oxidation color. It is often a longitudinal straight on bearing ring crack or annular crack; On the bearing steel ball shape with s-shaped, t or ring. The characteristics of the quenching crack is crack on both sides without decarburization, distinct differences and forging cracks and crack.
4. Heat treatment deformation
Imported bearing parts in heat treatment, there is the thermal stress and organization stress, the internal stress can offset each other or local, is complex and changeable, because it can follow the heating temperature, heating rate, cooling methods and cooling speed, parts appearance changes and intrusive, so the heat treatment deformation is unavoidable. Views and grasp its transformation rules can make deformation of bearing parts (such as elliptic, size up, etc.) of the eve of the ring in the limitation of the controllable, beneficial to produce. , of course, in the process of heat treatment of mechanical collision can also make components deformation, but the deformation can be cut by a modified operation and prevent.
5. Appearance decarburization SKF 6203 Bearing http://www.bearing-sa.com/product/SKF-6203-Bearing-149605.html .
Imported bearing parts in the process of heat treatment, if be in oxidizing medium heat, oxidation effect appearance will attack to make carbon mass fraction cut parts appearance, decarburization form appearance. Appearance of the decarburization layer depth beyond the final machining allowance will make the parts scrap. Surface decarburization layer depth measurement in the metallographic examination of metallography and microhardness method available. Outside surface microhardness distribution curve measurement method, can be used as criterion of arbitration.
6. The soft point
Because of the lack of heating, cooling, inappropriate quenching operation reasons such as partial form of bearing parts appearance known as quenching soft point hardness does not apply. It can form looks like appearance decarburization of abrasion resistance and falters, strength of serious decline.