Long-term creep characterization of Gr. 91 steel by modified creep constitutive equations

Abstract

This paper focuses on the long-term creep characterization of Gr. 91 steel using creep constitutive equations. The models of three such equations, a combination of power-law form and omega model (CPO), a combination of exponential form and omega model (CEO), and a combination of logarithmic form and omega model (CLO), which are described as sum decaying primary creep and accelerating tertiary creep, are proposed. A series of creep rupture data was obtained through creep tests with various applied loads at 600°C. On the basis of the creep data, a nonlinear least-square fitting (NLSF) analysis was carried out to provide the best fit with the experimental data in optimizing the parameter constants of an individual equation. The results of the NLSF analysis showed that in the lower stress regions of 160 MPa (σ/σys< 0.65), the CEO model showed a match with the experimental creep data comparable to those of the CPO and CLO models; however, in the higher stress regions of 160 MPa (σ/σy > 0.65), the CPO model showed better agreement than the other two models. It was found that the CEO model was superior to the CPO and CLO models in the modeling of long-term creep curves. Using the CEO model, the long-term creep curves of Gr. 91 steel were numerically characterized, and its creep life was predicted accurately.

Application of a Composite Model in the Analysis of Creep Deformation at Low and Intermediate Temperatures

“…A similar analysis is also completed here, which indicates that a similar linear relationship can also be found between the composite model parameters and applied stress as follows: With the increase of stress, the log(A), log(θ3), log(θ4) increase and the log(B) decreases. Thus, the four parameters under low temperature can be determined and the creep curve can be extrapolated to any temperature and stress [20].…”

The interpretation of experimental observation date for the development of mechanisms based creep damage constitutive equations for high chromium steel

“…In order to design the safe components for power generation industry, particularly in fossil fuel plants and nuclear reactors, it is necessary to estimate their long-term creep behaviour such as creep deformation, rupture time by experimental or calculations. On the other hand, obtaining long term creep data is time consuming and cost expensive, thus the long term creep data is limited, and the extrapolation using the conventional empirical methods may not be reliable [3]. With more accurately predicting the life, components could work for longer time and in a more operationally flexible manner before being retired or fracture [4].…”

“…The BSE micrographs of creep specimen which creep at 700 for 8232h in the necked section shows cavities nucleation at the interface of the large Laves phases, and M 23 C 6 carbide and Laves phases provide potential sites for creep cavities nucleation [26]. performed a creep test of 9.5% Cr chromium steel without addition of C and N at 650 under different stresses, in order to avoid the influence of other phase precipitations such as M 23 C 6 and MX, and summarized and reported three points [27]: (1) The precipitation of Laves phase mainly on the grain boundary during creep in the alloy studies; (2) There is no influence for the rate of Laves phase precipitation or the rate of growth and coarsening of Laves phase precipitation; (3) Suggest that increasing cavity nucleation triggered by the coarsening of Laves phase is the reason for the more rapid drop in creep rupture strength at lower stresses testing.…”

Tensile Creep Characterization and Prediction of Zr-Based Metallic Glass at High Temperatures

“…It also allows the short-term data derived from tests lasting less than three months to predict the full creep strain and creep lifetime characteristics of complex alloys for 10 years or more. Up until now, the θ projection method has been proven to accurately predict the creep curves of Al alloy, steel, and Ti alloy [19][20][21][22][23].…”