Super 304H钢在模拟烟气腐蚀环境中持久性能与组织演变研究

Influence of simulated fireside corrosion on creep rupture properties and microstructure evolution of Super 304H steel

奥氏体钢在锅炉关键部位服役过程中面临烟气/煤灰腐蚀+应力协同作用的挑战,存在一定的安全隐患。在静态空气及烟气/煤灰腐蚀环境下,通过模拟实验台对Super 304H钢进行温度为650℃、应力为200~300 MPa的持久实验,研究腐蚀环境对其持久性能及组织演变的影响。结果表明:相较于空气环境,腐蚀条件下Super 304H钢持久寿命下降幅度可达83%,且随着持久应力的降低合金寿命下降更明显;烟气/煤灰腐蚀导致合金表面连续的腐蚀产物出现开裂、剥落,基体发生内硫化,在拉应力的共同作用下试样内部出现沿晶开裂等蠕变损伤;基体表面由于合金元素的损失,在高温下发生再结晶,并在实验结束后发生马氏体转变,腐蚀-应力环境中合金表面腐蚀产物的开裂、剥落,内硫化物的形成,表层再结晶细晶区的增厚和晶界损伤的加剧共同促进了Super 304H钢的持久断裂。烟气/煤灰腐蚀环境通过影响Super 304H钢腐蚀过程,恶化合金基体组织影响其持久性能。

The synergy of fireside corrosion and stress is one of the challenges for austenitic steels used in modern fossil-fuel power plants during their service process.The creep rupture tests of Super 304H steel are carried out under static air and fireside corrosion environment at 650℃.The stress range is set at 200 to 300 MPa.The creep rupture life and microstructure evolution of different samples were studied.The results show that creep rupture life of Super 304H steel in corrosion condition decreases significantly,compared with that in static air.The rupture life decreases more seriously as the stress decreases,up to 83%at 200 MPa.The complete and continuous corrosion products scale is damaged by fireside corrosion,including the occurrence of cracks and spallation of these surface products.The formation of internal sulfide in the matrix caused by fireside corrosion leads to the deterioration of grain boundaries.Then it tends to crack along grain boundaries during creep rupture tests to accelerate the accumulation of creep damage.The surface of matrix undergoes recrystallization upon to the combination of high temperature and stress due to the loss of alloy elements caused by corrosion/oxidation.The formation of these fine recrystallized grains is unfavorable to creep properties of metals.The ferrite transformation also occurs in the same area during the cooling process after creep tests.Fireside corrosion increases the width of recrystallized grains area,thus expands its influence on the creep rupture life of the alloy.The fireside corrosion accelerates the creep rupture of Super 304H steel by promoting its corrosion process and the microstructure evolution.