一种硅增强型9Cr铁素体/马氏体钢持久性能的研究

Study on the stress rupture properties of a silicon enhanced 9Cr ferritic / martensitic steel

摘要:

本工作利用SEM、TEM、EBSD、维氏硬度计等手段研究了一种硅增强型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，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的断裂模式均为韧性断裂。不同应力下，H-Si钢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，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，因位错强化和界面强化均显著减弱，导致硬度明显下降，如时间最长的167MPa@2252h试样平行段硬度下降到193 HV，导致其高温持久性能不如P91。

Abstract:

In this work, the stress rupture properties of a silicon-enhanced 9Cr ferritic/martensitic steel (denoted as H-Si steel) at 550℃, the microstructure and hardness of the grip and gauge sections from ruptured specimens were investigated by SEM, TEM, EBSD and Vickers hardness tester. A comprehensive investigation was conducted into the microstructure evolution of H-Si steel under the coupling effect of temperature and stress and its influence on the creep behavior. The results indicate that H-Si steel exhibits good stress rupture property 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 fractures. The grip section of H-Si steel exhibits relatively stable microstructure under different stresses, with a lath width ranging from 380 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 rapid decrease in dislocation density and significant widening lath. Correspondingly, the hardness drops obviously due to significantly decreasing dislocation strengthening and grain boundary strengthening. For instance, the hardness of the 167MPa@2252h sample decreased to 193 HV, which induces a lower high-temperature stress rupture property compared to P91 steel.