Question 1, overheating. Rough opening on the part microstructure was observed after quenching overheating. But to determine the exact extent of overheating must observe the microstructure. If there is coarse acicular martensite in GCr15 steel hardened tissue, the tissue was quenched overheating. Causes may be general overheating quenching temperature is too high or too long due to heat insulation; it may be due to the original organization banded carbide serious, low carbon zone between the two with the formation of local martensite needles thick, caused by local overheating. Overheating tissue retained austenite increased size stability. Since the quenched structure overheating, coarse crystal steel, will result in decreased toughness of parts, reduce the impact resistance, the bearing life is reduced. Even cause severe overheating quenching cracks. Question 2, due to the heat. Quenching temperature is low or poor cooling will produce trust's tissue than the standard specified in the microstructure, called less heat tissue, which decrease in hardness, wear resistance drastically reduced, affecting parts of life. Question 3, quenching cracks. Parts in the quenching process due to internal stress cracks formed called quenching cracks. There are reasons for this crack: As the quenching temperature is too high or too fast cooling, thermal stress and the stress of metal mass volume change is greater than the resistance to fracture strength steel; original work surface defects (such as surface micro-cracks or draw marks) or steel internal defects (such as slag, severe heat-treated non-metallic inclusions in Ningbo, white point, residual shrinkage, etc.) are formed in the quenching stress concentration; severe surface decarburization and carbide segregation; parts after quenching back inadequate or untimely fire tempering; cold-stress caused by the previous process is too large, forging folding, turning deep marks, sharp edges and other oil groove. In short, causes the quenching cracks may be one or more of the above factors, the existence of internal stress is the main cause of quenching cracks. Quenching cracks deep and slender, straight fracture, fracture surface color without oxidation. It rings bearing on heat treatment plant in Ningbo is often straight vertical cracks or ring cracking; shape on the ball bearing has an S-shaped, T-shaped or ring. Organizational characteristics quenching cracks are cracks on both sides of decarburization phenomenon, a clear distinction with the forging cracks and the material cracks. Question 4, heat deformation. Parts during heat treatment, there is thermal stress and stress, this stress can be superimposed with each other or partially offset, is complex, because it along with the heating temperature, heating rate, cooling, cooling rate, the shape of parts and changes in the size of the change, so the heat deformation is inevitable. Understanding and mastering its variation can deform bearing parts in a controlled range, were conducive to the production. Of course, mechanical impact during the heat treatment also causes deformation of parts, but this deformation can be improved to reduce and avoid the operation. Question 5, the surface decarburization. Parts during the heat treatment, if it is heated in an oxidizing medium, so that the surface oxidation occurs part surface carbon content reduced, resulting in surface decarburization. Over the final machining allowance depth of surface decarburization layer will make parts scrapped. Determination of the depth of surface decarburization available in metallurgical metallurgical test method and microhardness method. In the surface layer microhardness distribution curve measurements prevail, do arbitration criterion. Question 6, soft spots. Due to insufficient heating, cooling parts of the surface is bad, improper operation and other causes hardening of the local phenomenon called quenching hardness enough soft spots. It is the same as the surface can cause a serious decline in decarbonization surface wear resistance and fatigue strength.

palabras clave: Bearings, heat treatment, along GF,