| X12Cr Mo WVNb N10-1-1 rotor steel is an improved 9% Cr ferritic heat resistance steel, which named E steel in the research project COST 501. In Europe this steel was successfully developed form middle 1980 s to middle 1990 s, lasting 10 years. And it has been applied to produce ultra supercritical(USC) pressure turbine intermediate pressure and high pressure rotors in Shanghai Turbine Plant. The technology reserve of the advanced 9% Cr ferritic heat resistance steel for steam turbines is lack in our country. There is a big gap from the foreign countries. So it is urgent to study these materials, and to digest and absorb the key technologies, providing the property dates of the material for design and development.In this paper, the tensile, impact and physical properties of X12 Cr Mo WVNb N10-1-1 advanced ferritic heat resistance steel used for USC pressure turbine rotors have been studied. The long-term high temperature rupture and microstructure changes, the phase evolution rules during long time service have also been studied. Measurement of the fatigue crack propagation rate and uniaxial creep-fatigue property of the X12 Cr Mo WVNb N10-1-1 rotor steel are given in this paper.The obtained results are summarized as follows:The difference of yield strength and tensile strength at room temperature between the axial direction and tangential direction is little. The elongation percentage and contraction of area of the two directions are basically identical. The yield strength and tensile strength of the X12 Cr Mo WVNb N10-1-1 rotor steel decreased as the test temperature increased, and the descending trend became obvious when the temperature up to 400 oC. The elongation percentage and contraction of area of the X12 Cr Mo WVNb N10-1-1 rotor steel decreased slowly first, but turned to increase obviously when the temperature up to 400 oC.The axial directional fracture toughness J1 c and the fatigue crack propagation resistance of the X12 Cr Mo WVNb N10-1-1 rotor steel are bigger than these of tangential direction, indicated that the ductile fracture initiation and propagation is easier in the tangential direction.The thermodynamic calculation results of the transformation temperature indicated that the transformation temperature changed slightly, when the alloy components varied in a regulating scope. The difference of the transformation temperature can be neglected, when the heat treatment is established.The fracture strength dates were extrapolated using isothermal extrapolation method. The endurance strengths of X12 Cr Mo WVNb N10-1-1 rotor steel are 142.49 MPa and 58.21 MPa at 600 oC and 650 oC for 100000 h, respectively. These results can meet the expected target. It was found that the M23C6 carbides within the gage length of the high temperature endurance specimen coarsened and coalesced seriously with the endurance time increased, while, the M23C6 carbides within the head of the specimen did not change significantly. This fact indicates that stress accelerates the coalescence rate of M23C6 carbide. The mean grain size of the Laves phase within the head and the gage length of the high temperature endurance specimen grew with the time, or the coarsening rate of the Laves phase slowdown. It can be also found that the mean grain size of the Laves phase within the head was larger.The fatigue crack growth rate da/d N of axial and tangential specimen increased with the stress intensity factor range, â–³K. There is a good relationship between them. Both the axial and tangential crack growth rates were basically identical. The fatigue crack growth can be described using Paris formula da/d N=c( K)m. The fatigue crack growth rate of axial and tangential specimen can be fitted as da/d N = 5.716E-09( K)2.956 and da/d N = 6.614E-09( K)2.913, respectively.The non-elastic strain energy, steady-state ratcheting strain and ratcheting strain rate during secondary stage increased with the hold time, the results indicate that creep can promote ratchet effect. The creep fatigue failure life decreased, as the hold time increased. Under the case the hold time over 10 min, the failure life changed little, being basically equal. The stress ratio has little effect on the mean strain, non-elastic strain range and non-elastic strain energy. |
PDF Full Text Request