45# steel H10 grade M30 nut, after quenching and tempering, it is found that the hexagonal cross section has visible arc and radial cracks in the circumferential direction, and the bearing surface also has a circular crack visible to the naked eye. This is a common heat treatment crack, the surface of the fracture is mostly dull, the part has been blackened, a small part is shiny and has a tear-like strip (caused when the fracture is broken), and no other defects are seen.
The metallographic examination showed no decarburization layer on both sides of the crack, and most of the fracture surface of the open crack was oxidized and blackened, and a small portion of the fracture after the break had metallic luster, indicating that the surface oxidation blackening was caused by oxidation at high temperature tempering. The crack is cracked along the crystal, the tail is sharper, and the straightness is straight and strong. There are two possible causes for decarburization on both sides of the crack. One is that there is no crack before quenching, and cracking occurs during quenching and cooling. No oxidative decarburization is observed on both sides of the crack. Second, the crack is serious due to cracking of the nut. The sample is an extended crack when the crack propagates after heat treatment. The author believes that the crack is the quenching crack, the thermal stress and the superposition of the microstructure stress cause the quenching stress to increase significantly and cause the nut to crack.
It is recommended that the original quenching process be 830 ° C, there is local overheated structure in the microstructure, now changed to 800 ~ 810 ° C, the use of aqueous solution quenching cooling to fast quenching oil. The cooling ability of the oil quenching medium is lower than that of water, especially in the range of 300 to 200 ° C, and the cooling rate is much lower than that of water. Therefore, the quenching with the rapid quenching oil can alleviate the quenching purpose, and the deformation of the internal thread of the nut can be reduced. 
Editor in charge: Hu Na
By using the mechanical and thermal properties of glass ceramics such as high temperature resistance, thermal shock resistance, thermal expansion and other mechanical properties, it is possible to manufacture a variety of materials that meet the mechanical requirements. Using mica's machinability and orientation, it is possible to produce high-strength and machinable glass ceramics. As a mechanical mechanics material, glass ceramics can be widely used in pistons, rotating blades and cookware, and can also be used as structural materials for aircraft, rockets, and artificial satellites.
Machinable Glass Ceramic Plunger,Glass Prefilled Syringe Using,Stainless Steel Plunger,Glass Coffee Plunger
Dongguan Haikun New Material Co., Ltd. , https://www.nitrideceramic.com