一种硅增强型9Cr铁素体/马氏体钢持久性能的研究

Stress Rupture Properties of a Silicon-Enhanced 9Cr Ferritic/Martensitic Steel

摘要:

利用SEM、TEM、EBSD、维氏硬度计等表征手段对一种硅增强型9Cr铁素体/马氏体钢（记为H-Si钢）在550 ℃条件下的持久性能以及持久断后样品夹持段和平行段的组织和硬度差异进行研究，深入分析了H-Si钢在温度和应力耦合作用下的组织演变规律及其对持久性能的影响。结果表明：H-Si钢具有良好的持久性能，在550 ℃、167 MPa条件下，持久断裂时间为2252 h，且本实验应力条件下样品的断裂模式均为韧性断裂。不同应力下，H-Si钢断后夹持段的基体组织均相对稳定，板条宽度在380?440 nm之间，硬度基本不变，保持在230 HV左右。相比而言，H-Si钢断后平行段在应力作用下的微观组织发生明显退化，位错密度快速降低，板条发生显著宽化，位错强化和晶界强化作用均显著减弱，导致硬度明显下降，持久断裂时间最长的167 MPa@2252 h试样平行段硬度下降至193 HV，导致其高温持久性能低于9Cr-1Mo-V-Nb马氏体耐热钢（P91）。

Abstract:

The stress rupture properties at 550 ℃ and the microstructure and hardness of the grip and gauge sections from ruptured specimens of a silicon-enhanced 9Cr ferritic/martensitic steel (denoted as H-Si steel) were investigated by SEM, TEM, EBSD and Vickers hardness tester. A comprehensive investigation was conducted, which included the microstructure evolution of H-Si steel under the coupling effect of temperature and stress and its influence on the creep behavior. The results show that H-Si steel exhibits good stress rupture properties and the stress rupture life is 2252 h under the conditions of 550 ℃ and 167 MPa. The fracture modes under experimental stress conditions are all ductile fracture. The grip section of H-Si steel exhibits relatively stable microstructure under different stresses, with a lath width ranging from 380 nm to 440 nm and the hardness being approximately 230 HV. However, the microstructure of the gauge section undergoes obvious degradation due to the stress, with the rapid decrease in dislocation density and the significant widening of laths. Correspondingly, the hardness drops obviously due to significantly decreasing dislocation strengthening and interface strengthening. The hardness of the 167 MPa@2252 h specimen decreases to 193 HV, which induces a lower high-temperature stress rupture property compared to 9Cr-1Mo-V-Nb martensitic steel (P91).