Reasons for common cracks in NSK imported bearings and countermeasures
2023-05-11 06:09:41
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Reasons for common cracks in NSK imported bearings and countermeasures
Source: China Bearing Network Time: 2013-05-12
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Modern technologies such as nuclear power systems, jet engines, and gas turbines often operate at temperatures of hundreds of degrees and thousands of degrees. Significantly general NSK bearing steels cannot be used. It is necessary to use high-temperature NSK bearing steel or other high-temperature materials. Exceeding the temperature condition of 120 °C; it is considered to be a high temperature operation condition; at this moment, NSK bearing steel will have a change in the arrangement of the attack and a decrease in the yield strength; the accuracy will gradually decrease, and when the operating temperature of the NSK bearing exceeds the tempering temperature of the NSK bearing data; The hardness is drastically reduced when the operating temperature exceeds 180 °C; the early fatigue and wear are quickly presented. The central link to ensure the accuracy and service life of the NSK bearing at high temperatures is to ensure that the NSK bearing has a hardness and scale at high temperatures. The degree of stability of the shape; thus Professor pointed out that the demand for high temperature NSK bearing steel is as follows:
1) The hardness at high temperature is not lower than HRC50～56, and the metallographic arrangement is stable.
2) Excellent stability at high temperature scale; temperature expansion coefficient. Swinging é‚¢ æ·–æ©¹æµ è±¢ æ·–æ©¹æµ è±¢ 浔湫 浔湫 浔湫 茫徊 茫徊 茫徊 嘤 嘤 Ï€ α ..
3) Good oxidation resistance; the formed oxide film is strong with the matrix; and the wear resistance and fatigue strength are good; the thermal shock resistance is good; the temperature change can be satisfactorily tested; the thermal conductivity is better,
4) Other data characteristics that should be available as NSK bearing steel.
1. Longitudinal crack crack characteristics and composition conditions: often occur in hardened parts, carbide strips in the original data and arrangement of severe segregation or longitudinal extension of non-inclusions; cracked inward from the outside; cracks are deep and long.
Treatment and preventive measures: Eliminate the carbide banding and segregation arrangement in the original data; prohibit the impurity overrun, reasonably formulate the heat treatment process parameters, and try to remove the artificial operation elements.
2. Characteristics and composition conditions of quenching cracks of special-shaped cracks: often occur in unhardened parts or carburized parts; cracks are located at sharp corners of parts and thicknesses.
Treatment and preventive measures: Guan I is a reasonable preparation of heat treatment process parameters, improve the operator's operating technology; try to remove artificial operating elements, design as much as possible with arc transition; prevent sharp corners.
3, mesh cracks (also known as cracks) quenching crack characteristics and composition conditions: the surface is easy to attack such cracks. High hardness parts, chemical heat treatment parts, high frequency quenching parts are also often cracked; cracks in parts Appearance; depth is about 0. 005 ~ 0. 02mm.
Treatment and preventive measures: The tempering after heat treatment should be sufficient, and the amount of cutting should be increased during grinding.
4, peeling crack crack characteristics and composition conditions: often presented in the external quenching parts or chemical heat treatment parts. The peeling layer is the transition zone.
Treatment and preventive measures: Immediate tempering after quenching, reasonable selection of quenching heating parameters and cooling medium.
5, microscopic cracks The cause of such cracks is more complicated.
5.1 Crack characteristics and composition conditions: often presented in the shortcomings of high carbon steel needle martensite, austenite grain boundary and crystal memory.
Treatment and preventive measures: to ensure that the chemical composition and arrangement of raw materials are in normal condition, the heat treatment process parameters should be strictly controlled, the operator should continuously improve the technology; compensate some unforeseen elements; prevent the occurrence of cracks
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