The effect of laser transformation notching on the controlled fracture of a high carbon (C70S6 ) steel

Zhang, Deen, Harris, S. J., McCartney, D.G., Pashby, I.R., Powell, J., Shipway, P.H. and Voisey, K.T. (2008) The effect of laser transformation notching on the controlled fracture of a high carbon (C70S6 ) steel. Materials Science and Engineering: A, 489 (1-2). pp. 273-284. ISSN 0921-5093

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A high carbon (C70S6) steel has been laser surface treated using CO2 and Diode lasers in order to produce an embrittled region to act as a fracture notch. Such a process has been investigated as a precursor to the fracture splitting of automotive engine connecting rods. Microstructures of the treated regions have been examined and the fracture behaviour of notched samples has been quantified.

Depending on the laser processing parameters used, the laser transformation notch (LTN) undergoes either solid state transformations or a mixture of melting and solid state transformations. The effect of LTN depth on the peak impact force, the crack initiation energy and Charpy fracture energy was investigated on a C70S6 carbon steel using an instrumented Charpy impact facility. It was reduced to a value < 3.5 J by a LTN of ~ 0.5 mm in depth. Fracture mechanics models indicate that such a LTN can behave in a similar way to a fatigue created crack used in fracture toughness testing ie the LTN behaves as a sharp crack.

Obtaining a sharp crack effect from a LTN is attributable to a combination of: a) the presence of brittle martensite, b) intergranular cracking of favourably oriented columnar grains after melting with inclusions and defects at their boundaries, c) intergranular cracking of coarse grains produced by a high austenitising temperatures and d) minor or major cracks sometimes resulting in centre – line cracking which arises during solidification. LTN was thus shown to have the potential to lead to an effective means of obtaining consistent fracture splitting of connecting rods.

Item Type: Article
Additional Information: NOTICE: this is the author’s version of a work that was accepted for publication in Materials Science and Engineering: A. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Materials Science and Engineering: A, 489(1-2),(2008) doi: 10.1016/j.msea.2007.12.040
Keywords: fracture splitting, laser processing, laser induced phase transformation, instrumented Charpy impact testing
Schools/Departments: University of Nottingham, UK > Faculty of Engineering > Department of Mechanical, Materials and Manufacturing Engineering
Identification Number:
Depositing User: Voisey, Dr KT
Date Deposited: 28 Jan 2015 17:40
Last Modified: 04 May 2020 20:28

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