How to deal with the problem - bearing FAG import bearing heating knowledge

FAG bearing import parts rough on the mouth can observe the microstructure after quenching overheat. But exactly judge the degree of superheat must observe the microstructure. If appear in GCr15 steel quenching organization coarse acicular martensite, organization for quenching overheating. Reasons may be the high quenching heating temperature or heat insulation time is too long cause comprehensive overheating; Also may be due to the original organization banded carbide, low carbon zone between two belts forming local martensite acicular bulky, cause local overheating. Overheating in the organization retained austenite increase, dimension stability. Overheating due to quenching organization, steel crystal bulky, to cause a decline in parts of toughness, impact resistant performance, FAG import bearing's life also reduced. Serious overheating will cause the quenching crack quenching temperature on the low side or even bad cooling will generate more than standard stipulated in the microstructure of austenite organization, called owe hot organization, it decreased the hardness, wear resistance sharply reduce, influence FAG imported FAG bearing life bearing parts in the process of hardening cooling by internal stress formation of quenching cracks crack said. Of the cause of the crack are: due to quenching heating temperature is too high or cooling, the thermal stress and quality of metal volume change of the organization stress is greater than the fracture strength of steel; The original defects on the surface of the work ( Such as surface microcrack or scratches) Or steel internal defects ( The non-metallic inclusions such as slag, serious, white spots, shrinkage residual, etc. ) When quenching form stress concentration; Serious surface decarbonization and carbide segregation; Parts hardening after tempering lack or not timely temper; The previous process caused by salt stress, cold forging folding, deep turning tool and the oil groove sharp edges, etc. In conclusion, the causes of quenching crack could be one or more of the above factors, the existence of internal stress is the main reason for the formation of quenching cracks. Quenching crack deep and long, fracture surface is flat, the broken section without oxidation color. It is often on import FAG bearing ring longitudinal straight crack or annular crack; On imported FAG bearing steel ball shape with s-shaped, T or ring. The characteristics of the quenching crack is crack on both sides without decarburization phenomenon, with obvious difference between crack forging cracks and materials. FAG bearings imported parts in heat treatment, there is the thermal stress and organization stress, the internal stress can overlay or partially offset each other, is complex and changeable, because it can as the heating temperature, heating rate, cooling, cooling speed, parts of the change of the shape and size changes, so the heat treatment deformation is inevitable. Know and grasp its change law can make FAG bearing import parts deformation ( Such as ring elliptic, large size up, etc. ) In the scope of the controllable, be helpful for production. , of course, in the process of heat treatment, mechanical collision also can make parts deformation, but the deformation is can be used to improve operation to reduce or avoid. FAG bearing import parts in the process of heat treatment, if they are in oxidizing medium heat, surface oxidation happens to make the surface of carbon mass fraction decreases, causing surface decarburization. The depth of the surface decarburization layer over the last machining allowance can make the parts scrap. The determination of surface decarburization layer depth is available in the metallographic examination metallography and microhardness method. The surface microhardness distribution curve measurement shall prevail, to do the arbitration criterion. Due to the lack of heating, cooling, quenching causes such as improper operation FAG bearing import parts surface phenomenon known as quenching soft point of local hardness is not enough. It can cause surface to surface decarburization abrasion resistance and fatigue strength of serious decline.