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Advances in Materials Science and Engineering
Volume 2018, Article ID 4780638, 9 pages
https://doi.org/10.1155/2018/4780638
Research Article

Microstructure Evolution and Surface Cracking Behavior of Superheavy Forgings during Hot Forging

1School of Mechanical Engineering, Yanshan University, Qinhuangdao 066004, China
2State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, China
3Hebei Iron & Steel Technology Research Institute, Shijiazhuang 050023, China
4China First Heavy Industries, Qiqihar 161042, China

Correspondence should be addressed to Zhenhua Wang; nc.ude.usy@auhnehzgnaw

Received 1 August 2017; Revised 30 November 2017; Accepted 4 December 2017; Published 30 January 2018

Academic Editor: Francesco Ruffino

Copyright © 2018 Zhenhua Wang et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

In recent years, superheavy forgings that are manufactured from 600 t grade ingots have been applied in the latest generation of nuclear power plants to provide good safety. However, component production is pushing the limits of the current free-forging industry. Large initial grain sizes and a low strain rate are the main factors that contribute to the deformation of superheavy forgings during forging. In this study, 18Mn18Cr0.6N steel with a coarse grain structure was selected as a model material. Hot compression and hot tension tests were conducted at a strain rate of 10−4·s−1. The essential nucleation mechanism of the dynamic recrystallization involved low-angle grain boundary formation and subgrain rotation, which was independent of the original high-angle grain boundary bulging and the 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.