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Bearing steel macroscopic defects - bearing knowledge

by:Waxing     2020-05-30
(1), shrinkage cavity, liquid steel in the process of condensation after pouring, due to the volume shrinkage in the center of ingot form holes, called shrinkage cavity. In order to reduce the harm of pipe steel, so the liquid steel casting, to adopt reasonable in the process of crystallization process, the volume shrinkage and the formation of the hole to move to the head of the ingot, the ingot after the breakdown, the shrinkage cavity part cut off, but, because of the improper casting, cooling technology, such as unreasonable set, ingot head insulation, sufficiently ingot head after excision quantity is little, etc, make the residual shrinkage cavity in steel, macroscopic examination, will be displayed. (2), white spots: after pickling of steel sample cross section near the center or its present short, discontinuous, show the distribution of the radiation condition commonly hairline open seam, or on the longitudinal fracture of steel surface is smooth, approximate circular or oval shape of silvery white spots, known as the white dots. The causes of the formation of white, one is the presence of hydrogen in steel, 2 it is steel forging in 600 ~ 300 ℃ after slow cooling, hydrogen is not fully spread, produce organizational stress and cracking. White steel or parts, the longitudinal and transverse mechanical properties have dropped significantly, in white is a steel or parts no use value. (3), burnt: ingot or billet in forging heating, the temperature is too high, the surface oxygen invasion and the oxide along the grain boundary. At the grain boundary and some branches between the major axis of low melting point compound melting occurs, so that after the condensation to form cracks or holes. This phenomenon is called burnt. When steel after burn, forging again will cause cracking, even if not cracking, fill in the day bath in strength and impact toughness are greatly reduced, it cannot be used. (4), bubble: the ability of steel gases dissolved in the liquid state than solid is big, the liquid steel in the cooling process, the escape of gas from the liquid steel, such as too late, the formation of porosity. In addition, the ingot mould bake bad, will exist in the steel surface, water or gas and within the ingot mould surface coating, forming a large number of gas, the liquid or gas to discharge the liquid steel, subcutaneous bubble is formed. The existence of the bubble is greatly reduced the strength of the steel. (5), segregation: in the steel surface in the process of coagulation, due to various kinds of chemical composition of carbon in steel, chromium, tungsten, phosphorus and other elements of crystallization, diffusion velocity and formation of the chemical composition of different uneven phenomenon known as segregation. The existence of the segregation will cause deformation after machining difficulty, analysis of sulfur are prone to heat brittle, the segregation of phosphorus are prone to cold short. The existence of segregation easy cause metal fatigue fracture. 6, osteoporosis: liquid steel in the cooling process, due to the volume shrinkage of small pore called osteoporosis. Scattered distribution of small pore called osteoporosis in general. Tiny pore distribution in the center of the steel parts referred to as the center of osteoporosis. Osteoporosis reduces the density of steel, make a significant reduction in the mechanical properties, reduce the service life of bearing.
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