Handbook of Case Histories in Failure Analysis
Failure Analysis of the 18CrNi3Mo Steel for Drilling Bit
A masonry type drill bit, designed for impact drilling in rock, fractured after a short time in service. Samples of the failed bit were analyzed using optical and scanning electron microscopy, quantitative metallography, and chemical analysis. The composition was found to be that of 18CrNi3Mo steel. Investigators also found evidence of inclusions and prior austenite grain size, although it was determined that neither played a role in the failure. Rather, according to test data, the failure occurred because of stress concentration (due to geometric discontinuities along the tooth profiles) and the cumulative effect of torque and force loading (the byproduct of continuous twisting and axial impact). Cracks readily initiate under these conditions then propagate quickly through what was found to be networks of tempered martensite, thus resulting in premature failure.
Sheng Xu, Le-yu Zhou, Yong-ming Yan, Hong-wu Zhu, Failure Analysis of the 18CrNi3Mo Steel for Drilling Bit, Handbook of Case Histories in Failure Analysis, Vol 3, Edited By Larry Berardinis, ASM International, 2019, p 247–254, https://doi.org/10.31399/asm.fach.v03.c9001787
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New Handbook: Volume 11B
Now available in the Digital Library! Volume 11B serves as a reference and guide to help engineers determine the causes of failure in plastic components and make corrective adjustments through design and manufacturing modifications.