Structures And Properties Of Ultra Super Critical Generator Heat-resistant Steel

ZG1Cr10MoWVNbN heat-resistant steel is usually used to fabricate the key parts such as high pressure cylinder, intermediate cylinder and main air valve. The research and development of ZG1Cr10MoWVNbN steel are very important to develop ultra super critical generator because of the energy shortage. Orthogonal test method was used to study the heat treatment process of heat-resistant steel ZG1Cr10MoWVNbN for ultra supercritical steam turbine. The influences of three factors, i.e. normalizing temperature, tempering temperature and holding times, on structures and properties of heat-resistant steel were analyzed. The optimal heat treatment process was found by orthogonal test in least experimental times. The results show that the best properties of steels are obtained which normalized at 1000℃for 5 hours, tempered at 670℃for 5 hours and then cooled in furnace.TEM, SEM and OM were used to oberve and analyze the fracture and micro-structure. The results show that the structure of the heat-resistant steel mainly consists of lath martensite and carbide precipitation phases. The substructures of martensites are high density dislocations and the precipitated phases are mainly consisted by MC, M₂₃C₆. The second phases in the grain boundary and lath of martensite hinder the movement of dislocations. Dispersed compound MX (M is metal element, such as V,Nb. X is C, N, ect) in the grain precipitate strengthened ZG1Cr10MoWVNbN. Because of the strength of second phase and the solid solution harden, the heat-resistant steel have good toughness and high creep strength. On the base of macro and micro observation of impact fracture, the morphology of the fracture is dimple and quasi-cleavage appearance and the fracture mechanism are confirmed to be quasi-cleavage fracture.