Quenching defects on the appearance of: cracks, cracking, deformation (including bending, size expansion or shrinkage tolerance), surface corrosion and other microstructure defects are: excessive hardness (high or insufficient hardness and uneven hardness), thick tissue , Oxidation (including surface oxidation and intergranular oxidation), deprivation of carbon, and abnormal tissue. 1: quench distortion and quenching cracks: Quenching distortion is an unavoidable phenomenon. It only constitutes waste when it exceeds specified tolerances or can't be corrected. By properly selecting materials, improving the design of sufficient knots, reasonable selection of quenching, tempering methods, and specifications can effectively reduce and control quenching. Distortion can be corrected by using hot and cold effects, hot spot straightening, and heating and tempering. Cracks are irreversible quenching defects. Only active preventive measures are taken, such as reducing and controlling the stress direction distribution of quenching, and controlling raw material quality and correct structural design. 2: Oxidation decarburization overheating Overheating of burned parts, if surface protection is not performed, defects such as oxidative decarburization will occur. The consequence is that the surface hardenability is reduced, the technical requirements are not met, or mesh cracks are formed on the surface of parts. And seriously reduce the appearance of parts quality, increase the roughness of the parts, and even out of tolerance, so quenching heating of finished parts need to be carried out in a protective atmosphere or salt bath furnace, small quantities can be protected by oxidation-resistant surface coating. Overheating leads to the formation of coarse martensite after quenching, which will lead to the formation of quench cracks or severely reduce the impact toughness of the quenched parts. It is prone to short cracks along the crystal. The quenching heating temperature should be selected correctly, the holding time should be appropriately shortened, and the furnace must be strictly controlled. To prevent the overheating, the overheated tissue that emerges can be re-annealed if there is enough margin for processing, and the refined grains are quenched and repaired again. Overburning often occurs in quenched high-speed steels, which are characterized by the formation of fishbone eutectic beryllite. After overheating, the quenched steel is severely brittle and forms waste products. 3: insufficient hardness Hardening after quenching and tempering is generally due to insufficient heating of quenching, surface decarburization, excessive residual austenite quenching in high carbon alloy steel, or insufficient tempering, when quenching with CR bearing steel oil It is also often found that the hardness after surface quenching is lower than that of the inner layer, which is a phenomenon of reverse quenching, mainly due to the fact that if the part is quenched into a vapor film with a long vapor phase and the characteristic temperature is low, the surface is protected by the vapor film. The period of pregnancy is longer than that of the center, and it is more likely to cause reverse quenching than the heart. 4: soft spot quenching parts appear uneven hardness called soft spots, and the main difference between the hardness of the lack of hardness in the surface of the parts have obvious flicker phenomenon, this defect is due to the original tissue is too coarse and uneven, (such as Severe tissue segregation, large chunks of carbides, or large free ferrites. Contaminated quench media. Oxide scales on the surface of the parts or parts do not move properly in the quenching solution, resulting in the formation of vapor films in local areas. Cooling and other factors, through the crystal phase analysis and study of process performance, can further determine what is causing the waste. 5: Other organizational defects Qualified parts for the quenching process require not only meeting the hardness requirements after quenching, but also often requiring the quenched structure to conform to specified levels, such as quenched martensite structure, residual austenite amount, and the amount of undissolved ferrite, The distribution and morphology of the carbides, etc., have been specified. When these specifications are exceeded, despite the passing of the hardness test, the tissue inspection is still qualified. The common structural defects are coarse quenched martensite (overheated) carburized steel and tool steel quenched. After the mesh carbides, and large carbides, quenched and tempered steel in the large free ferrite, (organized hereditary coarse martensite) and tool steel quenched after excessive austenite and so on. Information Sources.
