Analysis of white spot defect of large forging

Core tip: The white spots and hydrogen embrittlement defects of large forgings are very harmful, so the heat treatment of white spots and hydrogen embrittlement should be prevented after forging of large forgings. At the same time, the forging stress should be removed, the hardness should be reduced, and the grain should be refined

The white spots and hydrogen embrittlement defects of large forgings are very harmful, so the heat treatment of white spots and hydrogen embrittlement should be prevented after forging of large forgings. At the same time, the forging stress should be removed, the hardness should be reduced and the grain should be refined. The forging factory will give you a detailed and comprehensive answer.

White spots are an internal crack caused by hydrogen in steel. When the hydrogen content in solid steel is too high, the steel becomes significantly brittle. In essence, white spots are also brittle damage. The existence of white spots greatly reduces the mechanical properties of steel, especially the transverse plasticity and toughness, and becomes the most dangerous fracture source, which seriously affects the service performance and life of parts. Therefore, once a white spot is found in the forging, the forging must be scrapped.

The appearance of white spots on the longitudinal fracture surface of forging presents as round or oval silver-white spots with clear edges. In the transverse low - power test piece is hair-like small crack, the length of a few millimeters, dozens of millimeters.

Conditions and forming temperature of white spots After forging, hydrogen in steel and stress (deformation stress, thermal stress, microstructure stress, especially in the microstructure stress) under the combined action. The white spot formation temperature is the forging blank cooled to a relatively low temperature of about 250℃ to room temperature this range.

Hydrogen and stress in the formation of white point of the relationship between the literature [2: according to the authors of "steel contains a sufficient number of hydrogen is the necessary conditions of forming white point, the existence of internal stress has a role for promoting the white dots, so the hydrogen content of supersaturated" culprit "is the white dots, and the internal stress is" accomplice ". "a very thorough out the relationship between the white dots.

Three characteristics of white spots

1. White spots never form on the surface of the forging. According to the relevant information shows that its formation is always inside the forging, the area containing white spots from the forging surface always has a considerable distance, about 5O mm parts;

2. White spots are formed after forging, when the forging is cooled to a relatively low temperature of 250℃ to room temperature;

3. White spots are not formed instantaneously, but gradually. From the cessation of exercise to the appearance of white spots, need to go through a period of time, this period of time is called the incubation period or incubation period of white spot formation. The incubation period depends on the hydrogen content of the steel and also on the thickness of the forgings.

this is open die forgings produced by tongxin forging: