Is the heat treatment process of large forgings complicated?

Is the heat treatment process of large forgings complicated? Jiangyin Puyang Heavy Industry Co., Ltd. pointed out that the heat treatment of large forgings is usually combined with the cooling of forgings, because of the large section size of large forgings and the complex production process. In the process of heat treatment, the structure and properties of forgings are not uniform, so some forgings are easy to produce white spot defects. Therefore, large forgings heat treatment in addition to eliminate stress, reduce hardness, the main purpose of the first is to prevent the appearance of white spots forgings, improve the uniformity of chemical components of forgings, adjust and refine the organization of forgings.

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White spot in large forgings White spot is a very fine brittle crack inside the forgings, round or oval silver white spots, diameter size from a few millimeters to dozens of millimeters. According to the microscopic observation, no trace of plastic deformation was found in the adjacent area of the white spot, so the white spot belongs to the brittle fracture.

The existence of white spots in forgings not only leads to a sharp decline in mechanical properties, because the white spots bring high stress concentration, heat treatment and quenching will make the parts crack, or parts in use suddenly fracture, resulting in machine damage accidents.

Therefore, white spot is a defect of forgings, large forgings technical conditions clearly stipulate that once found white spot must be scrapped. There are many theories about the formation of white spot. At present, the consensus is that white spot is caused by the combined action of hydrogen in steel and internal stress (mainly structural stress). White spots cannot form without a certain amount of hydrogen and large internal stresses.

Cooling after forging in which, with the temperature decrease due to austenite transformation, in addition to produce internal stress within forgings (mainly organizational stress), at the same time, the solubility of hydrogen in steel decreases, and at this point, the internal stress dislocation in the grain boundary and the microscopic fissure assembling, when hydrogen atoms precipitated from the solid solution precipitation into the microscopic fissure, Hydrogen atoms combine in the crack to form hydrogen molecules and create a lot of pressure. Therefore, in the local brittle place with high hydrogen content in steel, under the action of tissue stress and hydrogen precipitation stress, the submicroscopic crack continues to expand and rupture, resulting in extremely fine internal cracks, thus forming white spots.Is the heat treatment process of large forgings complicated? The above is the relevant introduction in this respect, I hope to be helpful to you.


Post time: Jun-10-2021