T91管外径蠕变对组织与力学性能影响

Effect of creep strain on microstructure and mechanical properties of T91 steel tube

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。

Effect of creep strain on microstructure and mechanical properties of T91 steel tube was investigated using specimens taken from superheater wall in a power plant. Microstructure of T91 steel tube with different diameter creep strains was observed by means of optical microscopy( OM) and scanning electron microscopy( SEM). The amount of precipitated phase in the microstructure of the T91 steel tube was determined and its mechanical properties were measured. Results show that microstructure of the T91 steel tubes is evolved with the increasing of their diameter creep strain. The lath characteristics of martensite gradually disappear and precipitation phase such as M23C6 carbide is aggregated and coarsened for the T91 steel during long-term service. Some precipitation phases are gradually precipitated along the prior austenite grain boundaries and martensite substructure,and aggregated and coarsened,consequently the original austenite grain boundaries and martensite substructure boundaries are gradually widened and conspicuous. With the increasing of tubes diameter creep strain,the room temperature yield strength and tensile strength of the T91 steel decrease,while the percentage elongation after fracture first increases and then decreases. M23C6 carbide coarsening and lath substructure degradation and grain boundary widening lead to the significant decrease of yield strength and tensile yield strength,which is the main cause for the tube bursting.