The process of crack initiation and effective grain size for cleavage fracture in pearlitic eutectoid steel

1979 ◽  
Vol 10 (11) ◽  
pp. 1653-1664 ◽  
Author(s):  
Y. J. Park ◽  
I. M. Bernstein
Keyword(s):  
Grain Size ◽  
Crack Initiation ◽  
Cleavage Fracture ◽  
Eutectoid Steel ◽  
Effective Grain Size ◽  
Pearlitic Eutectoid Steel

Cleavage fracture in pearlitic eutectoid steel

1989 ◽  
Vol 20 (11) ◽  
pp. 2321-2335 ◽  
Author(s):  
D. J. Alexander ◽  
I. M. Bernstein
Keyword(s):  
Cleavage Fracture ◽  
Eutectoid Steel ◽  
Pearlitic Eutectoid Steel

scholarly journals Effect of Bainitic Microstructure on Low-Temperature Toughness of High-Strength API Pipeline Steels

2020 ◽  
Vol 58 (5) ◽  
pp. 293-303
Author(s):  
Seung-Wan Lee ◽  
Sang-In Lee ◽  
Byoungchul Hwang
Keyword(s):  
Grain Size ◽  
Low Temperature ◽  
Crack Initiation ◽  
High Strength ◽  
Processing Conditions ◽  
Absorbed Energy ◽  
Pipeline Steels ◽  
Bainitic Microstructure ◽  
Effective Grain Size ◽  
Low Temperature Toughness

In this study the correlation between bainitic microstructure and the low-temperature toughness of high-strength API pipeline steels was discussed in terms of crack initiation and propagation in the microstructure. Three types of API pipeline steels with different bainitic microstructures were fabricated using varying alloying elements and thermo-mechanical processing conditions, and then their microstructure was characterized by optical and scanning electron microscopy, and electron backscatter diffraction (EBSD). In particular, the effective grain size and microstructure fraction of the steels were quantitatively measured by EBSD analysis. Although all the steels were composed of polygonal ferrite (PF), and complex bainitic microstructures such as acicular ferrite (AF), granular bainite (GB), and bainitic ferrite (BF), they had different effective grain sizes and microstructure fraction, depending on the alloying elements and thermomechanical processing conditions. Charpy impact test results showed that when the martensite-austenite constituent fraction was lowest, it resulted in higher upper-shelf energy, and absorbed energy at room temperature due to the decrease in crack initiation. In contrast, excellent low-temperature toughness, such as lower ductile-brittle transition temperature and higher absorbed energy at low temperatures, could be achieved with a bainitic microstructure with fine effective grain size and high fraction of high-angle grain boundaries, which act as obstacles to prevent cleavage crack propagation.

A Dislocation Model for Fatigue Crack Initiation

1981 ◽  
Vol 48 (1) ◽  
pp. 97-103 ◽  
Author(s):  
K. Tanaka ◽  
T. Mura
Keyword(s):  
Grain Size ◽  
Crack Initiation ◽  
Slip Band ◽  
Fatigue Crack Initiation ◽  
Strain Range ◽  
Material Surface ◽  
Dislocation Model ◽  
Plastic Strain Range ◽  
Stress Cycles ◽  
Distributed Dislocations

The slip band formed in a grain on the material surface is a preferential site for crack initiation during low strain fatigue of polycrystalline metals. The forward and reverse plastic flow within the slip band is modeled in the present study by dislocations with different signs moving on two closely located layers, and it is assumed that their movement is irreversible. Based on the model, the monotonic buildup of dislocation dipoles piled up at the grain boundary is systematically derived using the theory of continuously distributed dislocations. This buildup is associated with the progress of extrusion or intrusion. The number of stress cycles up to the initiation of a crack of the grain size order is defined as the cycle when the stored strain energy of accumulated dislocations reaches a critical value. The relation between the initiation life and the plastic strain range derived theoretically is in agreement with a Coffin-Manson type law, and that between the fatigue strength and the grain size is expressed in an equation of the Petch type.

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