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通过对在役不同外径蠕变应变状态T91管取样,采用光镜、扫描电镜及力学性能试验分析T91管在长期服役中的不同外径蠕变应变状态下组织、力学性能演变规律,研究外径蠕变应变对其组织及室温力学性能影响。结果表明,随着外径蠕变应变的增加,马氏体板条特征逐渐消失,M23C6型碳化物粗化及沿晶界析出、聚集与粗化,原奥氏体晶界和亚晶界逐渐清晰、粗化;室温屈服强度、抗拉强度随外径蠕变应变增加而降低,而断后伸长率随外径蠕变应变的增加遵循先增后降的趋势。沉淀相M23C6型碳化物粗化及所导致的板条亚结构退化、碳化物沿原奥氏体晶界和亚晶界析出及所导致的晶界变宽是T91管高温运行中外径蠕变造成强度降低和最终失效的主要原因。
T91 tubes were sampled from different outer diameter creep strains in service, and the microstructure and mechanical properties of T91 tube under different OD creep strains were analyzed by light microscopy, scanning electron microscopy and mechanical tests. Effect of creep strain on the microstructure and mechanical properties at room temperature. The results show that with the increase of the creep strain of outer diameter, the martensite lath characteristics gradually disappear. The M23C6 carbides coarsen and precipitate, aggregate and coarsen along the grain boundaries. The original austenite grain boundaries and subgrain boundaries gradually Clear and coarsening. The yield strength and tensile strength at room temperature decrease with the increase of the creep strain of the outer diameter, while the elongation at break increases with the increase of the creep strain of outer diameter. The coarsening of the precipitated phase M23C6 carbide and the degeneration of the slat sub-structure, the precipitation of carbides along the original austenite grain boundaries and the subgrain boundaries and the widening of the grain boundaries are the creep of the outer diameter during high temperature operation of the T91 pipe The main reason for the reduced strength and ultimately failure.