高温服役138000h后T91钢显微组织结构分析

MICROSTRUCTURE ANALYSIS OF T91 STEEL AFTER 130 000 h IN SERVICE UNDER HIGH TEMPERATURE

通过金相、碳复型萃取、TEM、EDS等方法对已运行138 000 h的T91钢的显微组织结构进行了分析,研究影响T91钢高温服役退化的因素。研究结果显示,运行138 000 h后的T91钢的组织结构发生了很大变化:(1)Laves相在晶界和板条界沉淀析出;(2)沉淀相M23C6和MX粗化;(3)Z相以消耗MX为代价在晶界和亚晶界沉淀析出并迅速长大;(4)回火马氏体发生回复,位错密度降低,亚晶块普遍粗化。Laves相的沉淀析出对T91钢长时高温运行后的性能下降作用不大,而沉淀相粗化导致强化效果下降,阻止亚晶长大的能力下降。另外,Z相的析出消耗掉大量沉淀强化相MX,导致回火马氏体发生回复,亚结构粗化,严重影响T91钢的高温蠕变断裂强度。

Through metallographic analysis, carbon replica extraction, transmission electron microscopy （TEM）, and energy dispersive spectrometer（EDS）,etc. ,the microstructure analysis of T91 steel after 130 000 h in service has been carried out, and the factors affecting deterioration of T91 steel in service under high temperature being further studied. Results of study show that the structure of T91 steel after 130 000 hin service has been largely changed： （1）the Laves-phase precipitates along grain bounderies and lath bounderies; （2）coarsening of precipitation -phases M23C6 and MX; （3）the Z- phase precipitares on grain bounderies and sub-grain bound eries, and grows rapidly there, paying cost of consuming MX; （4） the tempered martensite recovers, the dislocation density reduces, and widely coarsening the sub - grains. The precipitation of Laves - phase has little effect upon the performance of T91 steel after long - term operatin under high temperature, but the coarsening of precipitation- phase leading to decrease the strengthening effect, resisting the decrease of growing ability for sub - grains. In addition,the separation out of Z - phase consumes large amount of precipitation - strengthening phase MX, leading to recovery of tempered marttensite, and to coarsening of sub - structure, affecting seriously the creep rupture strength of T91 steel under high temperature.