服役条件下马氏体耐热钢中碳化物演变与寿命相关性

Carbides evolution in 12Cr martensitic heat resistant steel with life depletion in service condition

12Cr马氏体耐热钢是发电及其它行业高温高压部件的关键用材。在高温高压环境下长期服役会导致材料的性能下降和组织结构退化。评价服役材料的可靠性一直是高度关注的实际问题。本文通过对发电锅炉X20再热器炉管在不同服役时期的性能和组织结构比较研究,材料硬度随寿命减损而下降,尤其是晶界硬度低于基体硬度。相应的微观结构出现碳化物粗化和蠕变损伤现象。定量分析显示,主要碳化物M23C6成分显示出明显的合金元素富集,粗化的M23C6碳化物中Cr/Fe原子比随服役时间的变化规律存在明确的动力学规律。

12% Cr martensitic heat-resistant steels are favored for high temperature applications in power plants and other industries.The severe service conditions of elevated temperature and high pressure for long-term lead to degradation in the microstructure and properties,so new theories or models are expected to give much a reliable life assessment under real service condition.A series of superheater tube samples for various service periods had been carefully investigated.The value of hardness decreases obviously with life depletion,and corresponding microstructure show carbide coarsening,microstructure recovery,and other damage characteristics.The morphology and distribution and composition of main precipitates M23C6 varied distinctly.The study of carbide composition evolution shows the most regular trend is the Cr enrichment in M23C6.The Cr/Fe ratio in coarsening particles shows a clear dynamical growth law,a power correlation with service time.