Study Of Creep Life Of Steam Turbine Rotor Steel 30Cr1Mo1V Based On Electrical Resistance Method

After a long term service at elevated temperatures and high pressure, creep damage occurs in turbine rotor, which results the degradation of properties and loss of life. Therefore, accurate and reliable prediction of damage and creep remaining life provides a basis for timely, safe, and economic replacement or repair of rotor, which helps to eliminate unnecessary replacements and reduce costly unscheduled outages caused by in-service failures.At present, the methods to study the creep life of turbine rotor can be seem as three kinds: analytic and numerical methods, destructive methods and nondestructive methods. The analytic and numerical methods need a lot of data and are very difficult to calculate, so they are not easy to be applied in engineering. The destructive methods are time-consuming and need to take samples from turbine rotor. The nondestructive methods can diagnose more parts in short time, and have the merit of simplification in calculation, so they are easy to be applied in engineering. Electrical resistance method is a novel one of the nondestructive methods. Based on the change of electrical resistance, damage and life can be valued simply and quickly. The high temperature aging damage, room temperature tensile damage and creep life expenditure of 30Cr1Mo1V rotor steel were studied with electrical resistance method and other methods in the dissertation. The main results are listed as follows:1. Aging experiments were performed at 630℃from 200h to 1200h. Electrical resistivity, Vickers hardness, fracture appearance transition temperature and microstructure of 30Cr1Mo1V rotor steel were studied with electrical resistance test, hardness test, metallic materials Charpy notch impact test and micro-structure test. The results indicate that electrical resistivity decreases with the aging time increasing and there are some linear relations between Vickers hardness and electrical resistivity, fracture appearance transition temperature and electrical resistivity. The changes of these parameters may be caused by the change of micro-structure due to the precipitation of carbide and the dissolution of solid element within matrix.2. Room temperature tensile experiments on 30Cr1Mo1V rotor steel were performed at the stress of 200MPa, 500MPa, 630MPa, 680MPa and 730MPa, and the tensile damage was studied via electrical resistance method. The results show that there is some linear relation between the resistance and tensile damage.3. Creep experiments of 30Cr1Mo1V rotor steel were carried out at 538℃and 300MPa for different time. The Vickers hardness, electrical resistance and micro-structure of creep samples were studied. The relationship between creep life and electrical resistance was described with the characteristic parameters of creep rupture and the constant of Kachanov. And the relation curve between creep life fraction and normal resistance was obtained. The study of micro-structure indicates that the crack propagation is of inter-granular and trans-granular mixture mode at 538℃and the change of electrical resistance is caused by the propagation and development of creep cavities.