Failure Analysis of Cracking on Side Tooth Gingivae of a Percussive Drill Bit
Zhao Tianliang1, Liu Zhiyong1, 2, *, Du Cuiwei1, Dong Chaofang1, Li Xiaogang1
Identifiers and Pagination:Year: 2016
First Page: 8
Last Page: 17
Publisher Id: TOMSJ-10-8
Article History:Received Date: 15/1/2015
Revision Received Date: 26/9/2015
Acceptance Date: 29/9/2015
Electronic publication date: 30/06/2016
Collection year: 2016
open-access license: This is an open access article licensed under the terms of the Creative Commons Attribution-Non-Commercial 4.0 International Public License (CC BY-NC 4.0) (https://creativecommons.org/licenses/by-nc/4.0/legalcode), which permits unrestricted, non-commercial use, distribution and reproduction in any medium, provided the work is properly cited.
Failures of percussive drill bits have been attributed to the external mechanical force and structural design by engineers and researchers for a long time. Few attentions have been focused on the material itself. Generally, it is the unqualified material, induced by the improper metallurgy and heat treatment process, which makes the drill bits fail soon after they are put into service. Reasons of the crackings on side tooth gingivae of a drill bit, which failed prematurely at the beginning of the service, were analyzed comparatively. Scanning electron microscope, metallographic observation, mechanical performance test and chemical composition analysis were adoptedfor the failure analysis. Results show that microstructure, chemical composition and mechanic properties of the substrate were excluded from the reasons of the cracking. It is mainly the excessive inclusions and defects in the carburized layer which induced the inhomogeneity of material organization and performance. Those inclusions and defects act as stress concentrators and leading to the crack initiation. In addition, toughness of the carburized layer is also decreased due to its over-carburization. It makescracks more easily initiate from the carburized layer and then propagate into the substrate under the stress of interference fit.