Effects of hydrogen pressure, test frequency and test temperature on fatigue crack growth properties of low-carbon steel in gaseous hydrogen
Effects of hydrogen pressure, test frequency and test temperature on fatigue crack growth properties of low-carbon steel in gaseous hydrogen
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DOI：
10.1016/j.prostr.2016.06.068
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发表时间：
2016
期刊：
影响因子：
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通讯作者：
J. Yamabe;M. Yoshikawa;H. Matsunaga;S. Matsuoka
中科院分区：
文献类型：
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作者：
J. Yamabe;M. Yoshikawa;H. Matsunaga;S. Matsuoka
在氢压为0.1 ~ 90 MPa，试验频率为0.001 ~ 10 Hz，试验温度为室温（RT）、363 K和423 K的不同组合下，对退火低碳钢JIS-SM 490 B紧凑拉伸（CT）试样进行了疲劳裂纹扩展（FCG）试验。在室温氢压为0.1、0.7和10 MPa时，FCG速率随试验频率的降低而增加，然后达到峰值。在较低的试验频率范围内，FCG率下降，并变得几乎等于在空气中的FCG率。此外，在RT下45 MPa的氢压力下，氢辅助FCG加速在0.01至0.001 Hz的测试频率附近显示出上限。另一方面，在RT下90 MPa的氢压力下，FCG率随着试验频率的降低而单调增加，最终在0.001 Hz的试验频率下不能确认FCG加速度的上限。在氢压为0.7 MPa、试验频率为1 Hz、温度为363 K和423 K的条件下，随着试验温度的升高，FCG加速开始的应力强度因子范围ΔK向更高的Δ K移动。对试样表面的激光显微镜观察表明，氢助FCG加速总是伴随着裂纹尖端附近的塑性变形局部化。这些结果表明，氢辅助FCG加速的主要影响因素不是材料中氢的存在与否，而是氢如何在裂纹尖端附近局部化。即氢浓度梯度的增大会导致裂纹尖端的滑移局部化，从而增强了作者提出的氢增强连续疲劳裂纹扩展（HESFCG）。提出了用一个新的表征裂纹尖端氢浓度梯度的参数来统一裂纹疲劳裂纹扩展速率对氢压、试验频率和试验温度的依赖关系。
Fatigue crack growth (FCG) tests for compact tension (CT) specimens of an annealed, low-carbon steel, JIS-SM490B were performed under various combinations of hydrogen pressures ranging from 0.1 to 90 MPa, test frequencies from 0.001 to 10 Hz and test temperatures of room temperature (RT), 363 K and 423 K. In the hydrogen pressures of 0.1, 0.7 and 10 MPa at RT, the FCG rate increased with a decrease in the test frequency; then, peaked out. In the lower test frequency regime, the FCG rate decreased and became nearly equivalent to the FCG rate in air. Also, in hydrogen pressure of 45 MPa at RT, the hydrogen-assisted FCG acceleration showed an upper limit around the test frequencies of 0.01 to 0.001 Hz. On the other hand, in the hydrogen pressure of 90 MPa at RT, the FCG rate monotonically increased with a decrease in the test frequency, and eventually the upper limit of FCG acceleration was not confirmed down to the test frequency of 0.001 Hz. In the hydrogen pressure of 0.7 MPa at the test frequency of 1 Hz and temperatures of 363 K and 423 K, the stress intensity factor range, ΔK, for the onset of the FCG acceleration in hydrogen gas was shifted to a higher ΔKwith an increase in the test temperature. The laser-microscope observation at specimen surface revealed that the hydrogen-assisted FCG acceleration always accompanied a localization of plastic deformation near crack tip. These results infer that the influencing factor dominating the hydrogen-assisted FCG acceleration is not the presence or absence of hydrogen in material but is how hydrogen localizes near the crack tip. Namely, a steep gradient of hydrogen concentration can result in the slip localization at crack tip, which enhances the Hydrogen Enhanced Successive Fatigue Crack Growth (HESFCG) proposed by the authors. It is proposed that such a peculiar dependence of FCG rate on hydrogen pressure, test frequency and test temperature can be unified by using a novel parameter representing the gradient of hydrogen concentration near crack tip.