高温服役50 000 h脆化HR3C钢的持久寿命分析

通过室温拉伸试验、高温短时拉伸试验、高温冲击试验、高温持久性能试验、显微组织观察和能谱分析研究了服役50 000 h的HR3C钢的组织和性能。结果表明:服役50 000 h的HR3C钢在室温下明显脆化,塑性大幅下降,但强度和硬度仍符合标准要求;665 ℃高温下的韧性和塑性较室温时有显著提升,高温强度也满足标准要求;晶界和晶内析出大量第二相,晶界处聚集分布的块状M₂₃C₆相是导致HR3C钢脆化的主要因素,晶内析出的NbCrN相则可以产生弥散强化效应;665 ℃高温下持久强度仅比标准推荐值降低10%,以末级过热器管为例,估算脆化HR3C钢的剩余寿命仍超过100 000 h。

Creep rupture life of embrittled HR3C steel after service for 50 000 h

Microstructure and properties of the HR3C steel after service for 50 000 h were studied by means of room temperature and high temperature mechanical properties test, high temperature impact test, stress rupture test, metallographic structure, scanning electron microscopy (SEM) and energy dispersive spectrum (EDS) analysis. The results show that after service for 50 000 h, the HR3C steel has obvious brittleness, the plasticity decreases greatly, while the room temperature strength and hardness are satisfied with the standard specification. Compared to room temperature, the toughness and plasticity of the embrittled HR3C steel at 665 ℃ are significantly resumed, and the high temperature strength also meets the standard requirements. A large number of second phases precipitate in the crystal or grain boundary, bulk M₂₃C₆ phase accumulated at the austenite grain boundary is the main cause of embrittlement, while the NbCrN phase in the crystal produces dispersion strengthening effect. The creep rupture strength of the HR3C steel at 665 ℃ is only 10% lower than the standard recommended value, and taking final-stage superheater tube as an example, the residual life of the steel is estimated to be still more than 100 000 h.