Explore the vast range of titles available.

Thermal excursions during post-weld heat treatment (PWHT) and on-site fabrication frequently compromise the integrity of Grade 92 steel. While hardness fluctuations are documented, the correlation between initial properties and long-term creep stability remains controversial. This study aims to evaluate the relationship between thermal history and subsequent creep performance. Heat treatments of T92 steel across a wide temperature range (760–1000 °C) were performed, followed by creep tests at 600 °C/130 MPa and microstructural characterization. Results reveal a non-monotonic evolution of hardness and strength, reaching a minimum at 850 °C due to martensitic lath recovery into ferrite, but nearly doubling the as-received (AR) values above 900 °C due to fresh martensite formation. Creep life drops to a minimum at 850 °C and recovers to the AR level at 950 °C. A significant “decoupling” occurs at 1000 °C, where the sample possesses the highest hardness but only exhibits one-fourth the life of the 950 °C sample. Superior performance stems from the retained M23C6 and its dynamic precipitation, which pins dislocations to form micro-lath structures. Conversely, 1000 °C facilitates full carbide dissolution, accelerating dislocation recovery. These findings emphasize precise PWHT control and demonstrate that a 950 °C rejuvenation treatment can restore over-tempered or damaged components.

The purpose of this article is to explore the remaining service life of the main steam pipeline in power plants that have been in operation for an extended period. The main steam pipeline, which operates in a high-temperature and high-pressure environment for a long time, experiences a series of microstructural transformations in its materials (such as 10CrMo910 steel), including pearlite spheroidization and carbide precipitation, leading to a significant decline in the mechanical properties of the pipeline, thereby affecting the safe and stable operation of the power plant. This study conducts an in-depth investigation into the microstructure, mechanical properties, and their relationship with the remaining service life of the main steam pipeline through methods such as metallographic examination, mechanical performance analysis, and high-temperature creep life assessment. Based on the data from high-temperature sustained strength performance tests, a life assessment model was established by using the L-M parameter equation to estimate the remaining service life of the high-temperature steam pipeline. The results indicate that after long-term service, there is a noticeable occurrence of pearlite spheroidization and carbide precipitation in the pipeline’s microstructure, and the remaining service life of the pipeline meets the requirements for subsequent operation. This research provides a theoretical basis and technical support for the safe operation of high-temperature steam pipelines in power plants, aiding in the formulation of scientific and reasonable maintenance strategies and replacement plans to ensure the safe and efficient operation of the power plant. In the future, further exploration of more precise life prediction methods and the application of new materials will continue to enhance the durability and safety of high-temperature steam pipelines in power plants.

Thermal and nuclear power systems require materials capable of sustaining high mechanical and thermal loads over prolonged service durations. Among these, 9Cr heat-resistant steels are particularly attractive due to their superior mechanical strength and extended creep rupture life, making them suitable for extreme environments. In this study, multiple machine learning models were explored to predict the creep rupture life of 9Cr heat-resistant steels. A comprehensive dataset of 913 samples, compiled from experimental results and literature, included eight input variables—covering chemical composition, stress, and temperature—and one output variable, the creep rupture life. The optimized artificial neural network (ANN) model achieved the highest predictive accuracy with a regularization coefficient of 0.01, 10,000 training iterations, and five hidden layers with 30 neurons per layer, attaining an R2 of 0.9718 for the test dataset. Beyond accurate prediction, single- and two-variable sensitivity analyses were used to elucidate statistically meaningful trends and interactions among the input parameters governing creep rupture life. The analyses indicated that among all variables, test conditions—particularly the test temperature—exert a pronounced negative effect on creep life, significantly reducing durability at elevated temperatures. Additionally, an optimization module enables identification of input conditions to achieve desired creep life, while the Index of Relative Importance (IRI) and quantitative effect analysis enhance interpretability. This framework represents a robust and reliable tool for long-term creep life assessment and the design of 9Cr steels for high-temperature applications.

This study proposes a coupled constitutive model that captures the anisotropic failure characteristics and damage evolution of nickel-based single-crystal (SX) superalloys under various temperature conditions. The model accounts for both creep rate and material damage evolution, enabling accurate prediction of the typical three-stage creep curves, macroscopic fracture morphologies, and microstructural features under uniaxial tensile creep for specimens with different crystallographic orientations. Creep behavior of SX superalloys was simulated under multiple orientations and various temperature-stress conditions using the proposed model. The resulting creep curves aligned well with experimental observations, thereby validating the model’s feasibility and accuracy. Furthermore, a finite element model of cylindrical specimens was established, and simulations of the macroscopic fracture morphology were performed using a user-defined material subroutine. By integrating the rafting theory governed by interfacial energy density, the model successfully predicts the rafting morphology of the microstructure at the fracture surface for different crystallographic orientations. The proposed model maintains low programming complexity and computational cost while effectively predicting the creep life and deformation behavior of anisotropic materials. The model accurately captures the three-stage creep deformation behavior of SX specimens and provides reliable predictions of stress fields and microstructural changes at critical cross-sections. The model demonstrates high accuracy in life prediction, with all predicted results falling within a ±1.5× error band and an average error of 14.6%.

Creep is defined as the permanent deformation of materials under the effect of sustained stress and elevated temperature for long periods of time, which can essentially lead to fracture. Due to very time-consuming and expensive testing requirements, existing experimental creep data are often analyzed using derived engineering parameters and models to predict and find the correlations between creep life (time to rupture), temperature and stress. The objective of this study was to analyze and compare different numerical algorithms by using the Larson–Miller parameter (LMP) extrapolation model. Calculations were performed using the classical LMP equation where different values of parameter C were selected, as well as using a modified LMP equation in which parameter C was stress dependent C(σ). The impact of two different approaches of extrapolation and correlation functions (linear and polynomial) applied to fit the LMP model was also investigated. A detailed analysis was performed to choose the best extrapolation fit function and error tolerance. The numerical algorithm implemented was validated through creep rupture testing performed on 10CrMo9–10 steel at 600 °C (873 K) and 80 MPa. Creep model behavior analysis proved that different values of C can significantly change the estimated time to rupture. An excellent response of the LMP model was obtained by considering polynomial dependency when parameter C was assumed to be 18, especially for the temperature range from 773 to 873 K. Promising results were also achieved when parameter C was taken as stress-dependent, but only for linear fitting, which requires further analysis. However, at validation stage it turned out that only the linear extrapolation function and C taken as a constant value provided adequate time-to-rupture prediction. In the case of C = 18, estimated time was slightly overestimated (~8%) and for C = 20 it was underestimated by 27%. In all other cases error largely exceeded 50%.

This study evaluates the use of quantitative analytical electron microscopy for microstructure-based creep life assessment of service-exposed 1CrMoV steel turbine rotors. Changes in the microstructure (bainitic laths, carbide phases) were related to creep life exhaustion estimations done using conventional methods based on cavities and hardness. The volume-weighted average size and surface density of bainitic laths correlate with cavity-based estimated creep life exhaustion. However, the heterogeneity of grain structure limits the use of bainitic lath parameters for assessing creep life based on microstructure. The phase proportions of M 3 C, M 2 C, and M 7 C 3 carbides, as determined by TKD-EDS mapping, show a strong correlation ( R 2 : 0.64, 0.61, and 0.86) with creep life exhaustion estimations and could potentially be used as an additional indicator of the material state of the critical failure region in 1CrMoV turbine rotors.

To investigate the mechanical properties and microstructure evolution of P92 steel during long-term service, the operated P92 main steam pipes from the first ultra-supercritical units in China were sectioned into samples representing various service durations and stresses (0# (as-received state, 1# (82,000 h, 67.3 MPa), 2# (85,000 h, 78.0 MPa), and 3# (100,000 h, 80.3 MPa)). Thereafter, a comprehensive assessment of their mechanical properties, including tensile strength, impact, hardness, and creep resistance, as well as a detailed microstructure analysis, was carried out. The effect of stress on the aging of material properties during operation is discussed. The results show that the circumferential stress caused by the increase in the internal steam pressure can significantly promote the creep life consumption of P92 steel, resulting in the degradation of mechanical properties and the expedited aging of the microstructure. The Rp0.2 and Rm of the P92 main steam pipe at room temperature and 605 °C decreased with the service time increase, reflecting the influence of stress in operation, which is expected to be used for the residual life evaluation of P92 steel. The relationship between the impact absorption energy (FATT50), Brinell hardness, and the operating time of P92 operating pipes is non-monotonic, indicating that these parameters are not sensitive indicators of material aging due to stress. The evaluation of performance degradation in P92 operating pipes due to stress-induced aging is not reliably discernible through optical metallography alone. To achieve a thorough assessment, the use of transmission electron microscopy (TEM) is essential.

The available datasets provided by our previous works on creep life for nickel-based single crystal superalloys were analyzed through supervised machine learning to rank features in terms of their importance for determining creep life. We employed six models, namely Back Propagation Neural Network (BPNN), Gradient Boosting Decision Tree (GBDT), Random Forest (RF), Gaussian Process Regression (GPR), XGBoost, and CatBoost, to predict the creep life. Our investigation showed that the BPNN model with a network structure of “24-7(20)-1” (which consists of 24 input layers, 7 hidden layers, 20 neurons, and 1 output layer) performed better than the other algorithms. Its accuracy is 1.82% higher than that of the second-best CatBoost regression model, with a mean absolute error reduction of 93.07% and a root mean square error reduction of 88.12%.

Life consumption is one of the serious concerns for turbine disk performance and maintenance cost. The low cycle fatigue of turbine disk coming from the creep and their interaction has a direct influence on life and reliability of an aero engine. So, in this paper, the finite element analysis fatigue creep on Nickel base super alloy GH4133 turbine disk at 650 °C is computed based on the material properties, load and performance parameter of the low cycle fatigue as a random factor. The LCF Manson coffin model for cycles to failure ( N f ) and Larson Miller ( N c ) are calculated. Damage fraction summation is used to calculate the low cycle fatigue creep life and fitted by two parameter Weibull distribution. Therefore, Monte Carlo simulation is used in random sampling from two parameter Weibull distribution to estimate the reliability assessment of turbine disk.

The creep rupture life of weld joints decreases to values from half to one-tenth of that of the base metal in Cr–Mo heat-resistant steels. It is industrially very important to understand the creep performance of weld joints and to minimize the reduction in the creep performance of weld joints relative to the base metal. In this study, a consistent prediction computational workflow was developed for practical three-layer cladding welds that connect two modules. These are the weld heat transfer analysis module, which predicts the heat-affected zone (HAZ) shape from welding conditions, and the creep damage analysis module, which calculates the creep rupture life from the predicted shape of the HAZ. Using this workflow, we examined the effects of welding conditions on creep rupture life of 2.25Cr-1Mo steel. Welding conditions were selected on the basis of the design of experiment method, and the correlation between each factor and creep rupture life was evaluated by factorial effect analysis. The results clarify that the creep rupture life changed significantly depending on the control of welding heat input under conditions that simulate practical welding. This suggests that there is an appropriate welding heat input to bring the creep rupture life of weld joints close to that of the base metal. Although previous studies of creep rupture life with relatively simple HAZ geometries have indicated the correlation with the width and angle of HAZ, it was newly discovered that these indices cannot simply explain the creep rupture life of the weld joints with complex HAZ geometries that appear in practical welding. The effect of HAZ shape on creep rupture life is more complicated than previously reported, suggesting that more appropriate HAZ shape factors should be considered.