Abstract The fatigue-crack growth rate of a ferritic-pearlitic low carbon steel was faster when the tests were conducted in high-pressure H 2 gas environments than in air. The predominant fracture feature changed from ductile fatigue striations with some “quasi-cleavage-like” regions when the test was conducted in air to mixed “quasi-cleavage” and “flat” facets when tested in a H 2 gas environment. The microstructure beneath the fracture surfaces produced in air was sub-grains, and over a distance of 15 μm from the fracture surface, the dimensions of the sub-grains increased. With hydrogen, dense dislocation bands and refined dislocation cells existed beneath the “quasi-cleavage” and “flat” fracture surfaces. The cell size increased with distance from the fracture surface. The decrease in the dimensions of the key microstructural features as the fracture surface is approached is attributed to the propagation of the crack through an already deformed matrix. The differences in evolved dislocation structure are explained in terms of the hydrogen-enhanced localized plasticity mechanism, and the hydrogen-modified dislocation structure establishes the local conditions that promote the fracture mode transition from ductile fatigue striations to a mixture of “quasi-cleavage” and “flat” features, which directly leads to enhanced fatigue-crack growth.

中文翻译：

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循环变形铁素体-珠光体低碳钢中氢改性位错结构

摘要 铁素体-珠光体低碳钢在高压H 2 气体环境中的疲劳裂纹扩展速度比在空气中快。主要的断裂特征从在空气中进行测试时具有一些“类解理”区域的延性疲劳条纹转变为在 H 2 气体环境中测试时混合的“准解理”和“平坦”面。在空气中产生的断裂面下方的微观结构是亚晶粒，在距断裂面 15 μm 的距离内，亚晶粒的尺寸增加。对于氢，在“准解理”和“平坦”断裂面下方存在密集的位错带和精细的位错单元。细胞尺寸随着距断裂面的距离而增加。随着接近断裂表面，关键微观结构特征尺寸的减小归因于裂纹通过已经变形的基体传播。位错结构演化的差异用氢增强的局部塑性机制来解释，氢改性的位错结构建立了促进断裂模式从韧性疲劳条纹过渡到“准解理”和“准解理”混合的局部条件。 “平坦”特征，这直接导致疲劳裂纹扩展的增强。