Abstract
The effect of a ferrite/mixed phase banded structure on the fatigue crack growth behavior of pipeline steel has been investigated in this work. Constant stress-controlled fatigue tests were carried out on unilateral notch specimens in the longitudinal direction (LD) and the transverse direction (TD). The strain accumulation was measured by digital image correlation (DIC) method and the fatigue fracture morphology was analyzed. The results show that the banded structure in the LD would cause a wide range of crack deflections, especially in the early stage of fatigue crack growth, which results in a lower fatigue crack growth rate compared to the TD. At the later stage, due to the increase of the plastic zone of the crack tip, more ferrite in the crack growth path of the TD specimen is also beneficial for crack tip blunting, thereby slowing down the increase of the crack growth rate.
Highlights
The fatigue failure of steel used in engineering structures can cause catastrophic losses.Investigation of the fatigue crack growth behavior in steel is of great significance for further optimizing the design of high-strength, low-alloy (HSLA) steel
According to the above-mentioned analysis, the fatigue crack growth behavior of the pipeline steel with banded structure is different in the longitudinal direction (LD) and transverse direction (TD)
The fatigue crack propagation behavior in the ferrite/mixed phase banded structure of pipeline steel was analyzed in this work
Summary
Investigation of the fatigue crack growth behavior in steel is of great significance for further optimizing the design of high-strength, low-alloy (HSLA) steel. A lot of research works have studied the mechanism of fatigue crack propagation by using the experiment and finite element method [1,2,3]. Steels with different microstructures have different fatigue crack growth characteristics. The grain type, grain size, hard phase and other factors would affect the fatigue crack growth behaviors [6,7,8]. Guan et al found that ferrite/bainite (F/B) dual-phase microstructures could inhibit the fatigue crack propagation more effectively than ferrite/pearlite (F/P) microstructures [10]. Zhao et al studied the fatigue properties of F/B duplex microstructure of X80 pipeline steel and found that film-like and rod-like martensite/austenite (M/A)
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