Brittle crack propagation resistance inside grain and at high angle grain boundary in 3% Si-Fe alloy

Abstract Brittle fracture in carbon steel has a strong impact on the safety of the structures. Especially, the arresting technology of the running crack is the measure of last resort for ensuring structural integrity. Due to such high importance, many experimental and theoretical studies of brittle crack propagation have been conducted from both mechanical and microstructural viewpoints. It is thought that the elementary step of the brittle fracture of polycrystalline steel is the cleavage in each crystal grain and their connection process. However, the detailed mechanisms of brittle fracture have not been fully understood; for example, it is still unclear why the propagation rate under a large driving force is not increased up to the Rayleigh wave speed. Several difficulties hinder the achievement of a detailed understanding so far: 1) crack propagation is quite rapid, 2) the crystal grain is usually too small (10–100 μm) to collect sufficient information, 3) the microstructure is very complicated in most case, i.e., containing different phases, microstructures, precipitates and inclusions. In this study, to eliminate such difficulties, 3% silicon steel in which microstructure is the ferrite single phase and the grain size is increased to 4–5 mm is used. This steel can be fractured in a brittle manner, even under ambient temperature. For this steel, by using a high speed camera and strain gauge data with a high sampling rate, the elementary process of brittle crack propagation is elucidated. As a result, it is revealed that the brittle crack propagation rate even in a single-crystal grain is much slower than the Rayleigh wave speed. This seems to be due to the presence of twin deformations and twin boundary cracks in crystal grain as observed on the fracture surface. Using the analysis of electron back scatter diffraction (EBSD) data, the mechanism of twin deformation and twin boundary crack is revealed. Additionally, it is shown that the brittle crack propagation rate where the path includes crystal grain boundaries is much slower. This delay seems to be related to the misorientation angle at the GB. By applying our simplified model, the delay effect at the grain boundary can be successfully explained.

[1]  Yu Qiao,et al.  Cleavage crack-growth-resistance of grain boundaries in polycrystalline Fe–2%Si alloy: experiments and modeling , 2003 .

[2]  Yoshiya Yamaguchi,et al.  Long Crack Arrestability Of Heavy-Thick Shipbuilding Steels , 2006 .

[3]  Hiroshi Tada,et al.  The stress analysis of cracks handbook , 2000 .

[4]  M. Matsuo.  Textures in Steel Products , 1981 .

[5]  L. B. Freund,et al.  Crack propagation in an elastic solid subjected to general loading—I. Constant rate of extension , 1972 .

[6]  J. Gilman.  Propagation of Cleavage Cracks in Crystals , 1956 .

[7]  Zhe-feng Zhang,et al.  Wavy cleavage fracture of bulk metallic glass , 2006 .

[8]  Y. Qiao,et al.  Propagation of a cleavage crack front across a field of persistent grain boundaries , 2012 .

[9]  K. Ravi-Chandar,et al.  An experimental investigation into dynamic fracture: II. Microstructural aspects , 1984 .

[10]  Susumu Machida,et al.  Some Basic Considerations on Crack Arresters for Welded Steel Structures (The 7th Report) : with special reference to arrest of a extremely long crack and the design of crack arresters , 1972 .

[11]  T. Anderson,et al.  Fracture mechanics - Fundamentals and applications , 2017 .

[12]  P. Kotula,et al.  Focused ion beam and scanning electron microscopy for 3D materials characterization , 2014 .

[13]  S. Aihara,et al.  Effect of stress field around running crack tip on fracture surface energy during brittle crack propagation - Proposal of a numerical model of brittle crack propagation (report2) - , 2015 .

[14]  S. Aihara,et al.  A simulation model for cleavage crack propagation in bcc polycrystalline solids , 2011 .

[15]  Gross,et al.  Energy dissipation in dynamic fracture. , 1996, Physical review letters.

[16]  K. Ravi-Chandar,et al.  An experimental investigation into dynamic fracture: I. Crack initiation and arrest , 1984 .

[17]  K. Ravi-Chandar,et al.  An experimental investigation into dynamic fracture: III. On steady-state crack propagation and crack branching , 1984 .

[18]  P. Flewitt,et al.  The role of deformation twins in brittle crack propagation in iron–silicon steel , 2009 .

[19]  K. Broberg.  Cracks and Fracture , 1999 .

[20]  J. Achenbach,et al.  Crack-tip fields for fast fracture of an elastic-plastic material , 1981 .

[21]  A. Argon,et al.  Cleavage cracking resistance of high angle grain boundaries in Fe–3%Si alloy , 2003 .