[Communications in Computer and Information Science] Intelligent Computing and Internet of Things Volume 924 (First International Conference on Intelligent Manufacturing and Internet of Things and 5th International Conference on Computing for Sustainable Energy and Environment, IMIOT and ICSEE 2018, Chongqing, China, September 21-23, 2018, Proceedings, Part II) || Research on Nondestructive Testing for the Depth of Hardening Zone