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To learn more about our privacy policy Click hereMetallurgical defects in steel, cracks or white spots formed by press working, coarse grains left by finishing, sharp corners and tool marks, excessive heat treatment temperatures, and improper cooling can cause quench cracks. The quenching crack is characterized by coarse cracks and is cracked in the shape of the project. Generally, the middle is hypertrophy, and the ends are sharp and finely curved. There is no oxidation color around the crack and there is no decarburization. The quenching crack is generally deep, the magnetic powder accumulation is very sharp, and the magnetic powder accumulation is very thick. During the quenching process, the surface of the part is subjected to tensile stress and the center is subjected to compressive stress. In another case, internal cracks are likely to occur at the large tensile stress portion and develop toward the center portion. If the surface tension of the part during the quenching process is too large, the medium core is not subjected to force, and a mesh or ladder crack is formed at this time, and the crack propagation direction is perpendicular to the moving direction of the induction ring.
When the shape of the part is complicated, the quenching crack often occurs when the cross section changes abruptly, such as the intersection of a thin wall and a thick wall or a hole, a groove, or a groove. In summary, it is necessary to analyze the heat treatment stress distribution of the parts and the shape, size and distribution of the cracks found, and then compare them to make conclusions. White spots are a drawback of hot rolled and wrought alloy steels. The white spot is formed during the cooling process after the steel is subjected to hot pressing treatment and belongs to the internal cracking of the steel.
Most of the white spots are distributed near large rolling or forging centers or at a distance from the surface. They are round or elliptical silver spots in the longitudinal section of the steel, with a diameter of about 5 mm to 10 mm. White spots often appear in groups. The white point found in magnetic particle inspection is a cross section, that is, a small crack with a jagged edge. The white point distribution is mostly parallel to the fiber direction of the steel, and sometimes it is radial, and the larger the forging, the more likely it is to produce white spots. White spots have a great influence on the mechanical properties of steel and are an unacceptable defect. The white point magnetic powder pattern is larval-like or broken, and the middle of the crack is thick and the ends are thin. The white spot is characterized in that the formation of the base material of the part is cracked, so that the accumulation of the magnetic powder is thick and dense. The measure to prevent white spots is to reduce the hydrogen content in the steel, that is, to reduce the hydrogen content in the steel to a low level, which can be achieved by selecting a dry pure charge. Where possible, the X-ray Orientation Analyzer can use vacuum smelting and molten steel vacuum treatment or dehydrogenation annealing to reduce the hydrogen content in the ingot.