620℃高效超超临界机组用FB2钢高温持久过程组织演变分析

Microstructure Evolution Analysis of FB2 Steel Used for High-efficiency Ultra Supercritical Unit During 620℃High Temperature Creep-Rupture Tests

为研究长期服役过程中FB2钢组织的变化规律,在620℃下对FB2钢进行高温持久试验,并对持久试样进行微观组织观察,分析其组织及析出相的演变规律。结果表明:在高温持久过程中,FB2钢的组织仍为回火马氏体;随着持久时间的增加,马氏体组织发生回复,板条略微变宽,位错密度略减小;M_(23)C_(6)碳化物尺寸未发生明显粗化,持久时间达到9577 h后平均尺寸仍在250 nm左右,对马氏体板条边界具有良好的钉扎作用;FB2钢在高温持久过程中新析出Laves相,该相以单独形核和依附M_(23)C_(6)碳化物形核2种方式析出且快速生长,并吞咽M_(23)C_(6)碳化物颗粒;持久时间达到9577 h后,Laves相的最大尺寸可达1μm,仍未达到热力学平衡状态。

In order to study the microstructure change of FB2 steel during long-term service,high temperature creep-rupture tests were carried out at 620℃,and microstructure of the creep-rupture sample was observed,so as to analyze evolution law of its microstructure and precipitates.Results show that the microstructure of FB2 steel is still tempered martensite during high temperature creep-rupture tests.With the rise of creep-rupture time,the martensite structure recovers with its lath becomes wider,and dislocation density decreases slightly.The size of M_(23)C_(6)carbide is not obviously coarsened,its average size is still about 250 nm after creep-rupture time reaches 9577 h,which shows good pinning effect on martensite lath boundary.During high temperature creep-rupture tests,new Laves phase precipitates in FB2 steel by single nucleation and attaching M_(23)C_(6)to nucleation,which grows rapidly and would engulfs M_(23)C_(6)carbide particles.After 9577 h,the maximum size of Laves phase reaches 1μm,while the thermodynamic equilibrium state is not yet reached.