Warren A D, Griffiths I J, Flewitt P E J
1Interface Analysis Centre, HH Wills Laboratory, University of Bristol, Bristol, BS8 1FD UK.
2School of Physics, HH Wills Laboratory, University of Bristol, Bristol, BS8 1FD UK.
J Mater Sci. 2018;53(8):6183-6197. doi: 10.1007/s10853-017-1748-4. Epub 2018 Jan 9.
A Type 316H austenitic stainless steel component containing Cr and impurity element-rich localised regions arising from component fabrication was aged for a prolonged period during service at a temperature of approximately 550 °C. These regions make up approximately 5% of the total volume of the microstructure. Previous work has shown that these regions contain ferrite and carbide precipitates and a finer austenite grain size than the adjacent matrix. The present study has used high-resolution transmission electron microscopy combined with compositional microanalysis to show that these regions have a highly complex microstructure containing G phase, chi phase and intragranular γ' precipitates within the austenite grains. There is phosphorus migration to the chi austenite phase boundary, and the basis for this equilibrium impurity segregation is discussed. A Cr-depleted region was observed surrounding the chi phase precipitates, and the impact of this on the other precipitates is considered. The diversity of precipitates in these Cr-rich regions means that they behave significantly differently to the bulk material under long-term creep conditions leading to preferred nucleation and growth of creep cavities and the formation of localised creep cracks during service.
一个含有因部件制造产生的富铬和杂质元素局部区域的316H型奥氏体不锈钢部件，在大约550°C的服役温度下经过了长时间时效处理。这些区域约占微观结构总体积的5%。先前的研究表明，这些区域含有铁素体和碳化物析出物，且奥氏体晶粒尺寸比相邻基体更细小。本研究使用高分辨率透射电子显微镜结合成分微分析表明，这些区域具有高度复杂的微观结构，在奥氏体晶粒内含有G相、χ相和晶内γ'析出物。观察到磷向χ奥氏体相界迁移，并讨论了这种平衡杂质偏析的基础。在χ相析出物周围观察到一个贫铬区域，并考虑了其对其他析出物的影响。这些富铬区域析出物的多样性意味着它们在长期蠕变条件下与块状材料的行为有显著不同，导致蠕变空洞优先形核和生长，并在服役期间形成局部蠕变裂纹。
