Thermodynamic Calculation for Precipitated Phases in 3325YC1 Steel Used for High Temperature Blade of Steam Turbine and Composition Optimizing for the Steel

The contents of precipitated phases M23C6 and M2B in 3325YC1 steel at different temperature were obtained by Thermo-Calc software, as well as the effects of Cr, W and Mo contents on precipitation temperature and content of the precipitated phases. Based on the above, the chemical composition of the steel was adjusted by decreasing the contents of Cr, W and B elements, and the comparative high temperature properties like tensile, fatigue and rupture tests for 3325YC1 steel with/without adjusting were carried out. The results show that Cr is the main element to form M23C6 and Cr2B, but adding Cr content has no effects on precipitation contents of the two precipitated phases. W is the main element to form M2B, with the increase of W content, the precipitation content raised, but the precipitation temperature is not affected. B can not change the precipitation temperature of Cr2B and M2B, but can obviously increase their precipitation contents. The high temperature tensile and fatigue properties of 3325YC1 steel with adjusting has not affected basically, and 100 000 hour creep rupture stress at 620 ℃ is still higher than 100 MPa predicted by Larson-Miller parameter method.