Micrographs - hydrogen-induced fatigue failure of 304 stainless steel

The effect of 104 mass ppm of hydrogen on the evolved microstructures associated with accelerated fatigue failure in type 304 austenitic stainless steel is reported. The fracture surface morphology changed from ductile striations to mixed mode that appeared “quasi-cleavage-like” and “flat.” Detailed microstructural characterization determined these fractures were along the austenite-martensite interfaces. The morphology and orientation of the strain-induced martensite were impacted by the presence of hydrogen. Hydrogen constrained the formation of 𝛼’-martensite into linear, planar bands in the grain nearest the fracture surface, and 𝜀-martensite was formed between the 𝛼′-martensite bands. The dislocation structure generated by the cyclic loading and the restriction of the martensitic transformation to specific forms by hydrogen is explained through the hydrogen-enhanced localized plasticity mechanism and accounts for the change in fracture mode.

本研究报告了在304型奥氏体不锈钢中，104质量ppm的氢对加速疲劳失效相关微结构演变的影响。断裂表面形貌由韧性条纹转变为呈现‘准解理状’和‘平坦状’的混合模式。详细的微观结构表征确定这些断裂沿着奥氏体-马氏体界面发生。氢的存在影响了应变诱导马氏体的形态和取向。氢将𝛼′-马氏体限制在靠近断裂表面的晶粒中形成线性、平面的带状结构，并在𝛼′-马氏体带之间形成ε-马氏体。循环加载产生的位错结构以及氢对马氏体转变特定形式的限制，通过氢增强的局部塑性机制得到解释，并解释了断裂模式的改变。