NSK bearings parts by heat treatment of common quality defects: microstructure of quenched quenching crack, overheating, lack of heat, hardness, deformation of heat treatment, surface removal, soft enough.
　　1. overheating
　　Bearing rough opening can be observed after quenching microstructure of overheating. But to exactly determine the degree of overheating must be observed microstructure. If it occurs in the quenched steel GCr15 needle-like martensite, hardening heat organization. Causes may be hardening heating temperature is too high or full overheating caused by heating holding time is too long; or it may be due to serious original Ribbon carbide, formed in the low carbon zone between two large local Markov and body acupuncture, causing local overheating. Overheating increased residual austenite in the Organization, dimensional stability decline. Overheated due to quenched steel large crystals, will result in lower part of toughness, impact resistance performance, NSK bearing life is reduced. Overheating caused by serious or even quenching crack.
　　2. less heat
　　Poor low temperature of quench or cool in microstructure generated exceeded the standard requirements of supporting tissue, known as the due to the heat organization, bringing down the hardness, abrasion resistance sharply reduced, affecting the life of NSK bearing.
　　3. quenching crack
　　NSK bearing on internal stress in quenching process due to the formation of crack quench cracks. Caused this crack of causes has: due to quenching heating temperature high or cooling too rush, hot stress and metal quality volume changes Shi of organization stress is greater than steel of anti-break strength; work surface of original defects (as surface micro-crack or classified marks) or steel internal defects (as clip slag, and serious of non-metallic clip debris, and white, and shrinkage residual,) in quenching Shi formed stress concentrated; serious of surface off carbon and carbide partial analysis of; parts quenching Hou tempered insufficient or is not timely tempered; front processes caused of cold rushed stress had large, and Forged folding knife sharp edges, oil ditch, deep turning and so on. In short, resulting in quenching cracks could be due to one or more of the above factors, the main cause of stress is the formation of quenching crack. Quenching crack deep, slender, fracture, straight and cutting plane no oxidation. It is often straight vertical crack on the bearing ring or annular cracks; on steel ball bearings, in the shape of s-shaped, t-shaped or annular. Characteristics of quenching crack is cracked on both sides without removal, significant differences and forging crack crack and material.
　　4. heat treatment distortion
　　In heat treatment of bearing parts, heat stress and organizational stress, this stress can overlap each other or partially offset is complex because it can speed, cooling, heating and cooling heating temperature, speed changes, changes in the shape and size of the part, so heat treatment deformation is unavoidable. Understand and master it can make the change of NSK bearing variants (such as the oval ring, size up, and so on) at the range of controlled, productive. Of course in the heat treatment process of mechanical collision also cause a deformation of parts, but this variant is could be reduced by improving operations and avoid.
　　5. surface decarburization
　　In heat treatment of bearing parts, if it is heating in oxidizing medium, surface oxidation make parts of the surface carbon concentration reduction caused by surface decarburization. Surface decarbonization layer depth over the last scrap of machining allowance for the parts. Determination of surface decarbonization layer depth available in the metallographic examination of metallographic method and micro-hardness method. The surface microhardness distribution curve measurement shall prevail, can do arbitration criterion.
　　6. soft point
　　Due to insufficient heating, poor cooling, quenching caused improper operation of NSK bearing phenomenon called quenching soft enough surface hardness. Like surface decarburization can cause surface wear resistance and fatigue strength of serious decline.