Study on the Microstructure and Properties of 1Cr10NiMoW2VNbN Steel Used for Ultra-Supercritical Gas Turbine
|School||Shanghai Jiaotong University|
|Keywords||Ferritic heat-resistant steel Heat treatment Creep Stress relaxation Activation energy Subgrain|
1Cr10NiMoW2VNbN (10705AJ) is a modified 12% Cr ferritic / martensitic steel, mainly used in the manufacture conditions below 600 ℃ ultra (ultra) supercritical steam turbine blades and bolts. To accelerate the steel using ultra-supercritical generating units, the urgent requirements of their own grasp of the steel microstructure evolution and performance data for a more safe to use. In this paper, optical microscopy (OM) and transmission electron microscopy (TEM) were used to study the heat treatment of steel structure for the short-long-term creep and stress relaxation tests, analysis of its high-temperature mechanical behavior and optical metallography and Atomic force microscopy study of short-term creep sample topography image. Using electron backscatter diffraction pattern (EBSD) studied the long-time creep tissue microstructure, and with the sub-structure in the TEM study of microstructure evolution during creep. The following conclusions: 10705AJ steel 1100oC ~ 1140 ℃ temperature range to form a high density of dislocations quenched lath martensite, at 600 ℃ ~ 700 ℃ temperature range tempering, tempering troostite between organizations and Sorbite between. Its performance can meet the standard requirements. 660 ~ 680 ℃ peak exists between the carbide precipitation. Mainly M23C6 carbide precipitation types, as well as a small amount of M6X and NbN type. The steel at 1100 ℃ ~ 1140 ℃ quenching, 660 ℃ ~ 680 ℃ tempering is ideal. 10705AJ creep compliance is the first stage of a power transient creep rate description, and its index ranged between 0.385 ~ 0.614, and the creep stress and monotonous relationship does not exist. The first phase of the activation energy of creep and stress related, 150 MPa under 161.3 kJ / mol, other stress conditions is 88.0 ~ 98.9 kJ / mol, were lower than the Fe self-diffusion activation energy. 10705AJ steel relaxation curve there are two phases, the first stress relaxation much faster than the second phase; temperature is the most important factor in the behavior of the stress relaxation, the higher the temperature, the greater the stress relaxation rate; the same temperature, to improve early Stress will increase the rate of stress relaxation, and regardless of the size of initial stress in the relaxation process in both stress relaxation at the same tendency. Use double logarithmic trinomial model and gold - Wei model achieved 25,000 hours of residual stress data extrapolation. Both showed a lower fitting error, extrapolation similar results; former is slightly conservative extrapolation of results; latter extrapolation results slightly optimistic. With creep prolonged tissue increases the degree of recrystallization, carbide aggregation occurred during creep grew up within the grain boundary carbides gathered from the grain; high temperature and low stress exacerbated carbide precipitation grew more uneven sex. OIM and TEM analyzes show that the creep process of sub-grain (boundary) generation, in addition to the original large-angle grain boundaries exist continuous destruction, but also the existence of sub-grain boundaries and high angle grain boundaries dynamically generated phenomenon. 10705AJ the creep exists generation and sub-sub-grain boundaries to the large-angle grain boundaries in continuous evolution; abundant presence of dislocation substructure description 10705AJ is dislocation creep. Particles on the motion of dislocations play a strong barrier effect.