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Microstructure evolution and surface crack behavior of heavy forgings during hot forging

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Document pages: 9 pages

Abstract: In recent years, super heavy forgings made of 600   T steel ingots have been applied to the latest generation of nuclear power plants to provide good safety. However, parts production is breaking through the limits of the current free forging industry. Larger initial grain size and lower strain rate are the main factors leading to the deformation of overweight forgings in the forging process. In this study, 18mn18cr0.6n steel with coarse grain structure was selected as the model material. The essential nucleation mechanism of dynamic recrystallization includes low angle grain boundary formation and subcrystalline rotation, which is independent of the original high angle grain boundary bulge and t-nucleatione presence of twins. Twins were formed during the growth of dynamic recrystallization grains. The grain refinement was not obvious at 1150°C. A lowering of the deformation temperature to 1050°C resulted in a fine grain structure; however, the stress increased significantly. Crack-propagation paths included high-angle grain boundaries, twin boundaries, and the insides of grains, in that order. For superheavy forging, the ingot should have a larger height and a smaller diameter.

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