Correlation of Rupture Life, Creep Rate, and Microstructure for Type 304 Stainless Steel

The stress and temperature sensitivites of the rupture life and secondary creep rate were examined in detail for a single heat of type 304 stainless steel (9T2796). Assuming that the rupture life has a power law stress dependency, relatively small differences in the stress exponent were observed over a broad range of stress and temperature. In contrast, large changes were observed for equivalent parameter for secondary creep rate. As a result of these differences, the Monkman-Grant correlation was sensitive to stress and temperature below 650 C. Metallurgical studies based on light and transmission electron microscopy suggested that the temperature and stress sensitivities of secondary creep rate at temperatures below 650 C were related to features of the substructure not present at higher temperature. Specifically, the presence of a fine dislocation network stabilized by precipitates altered the stress and temperature sensitivities relative to what might be expected from high temperature studies

Correlations Between Metallurgical Characterization Studies, Exploratory Mechanical Tests, and Continuum Mechanics Approaches to Constitutive Equations

Austenitic stainless steels, such as types 316 and 304, are widely used as pressure vessel materials in the temperature range of 425 to 650 C. Stainless steel specimens were tested to rupture at two different stress levels sigma and sigma 2 sigma 1 sigma 2) to establish the normal stain-time behavior. A subsequent test was performed in which the specimen was crept at the higher stress (sigma 1) to the beginning of the secondary stage of creep, presumed to be the strain/time conditions at which a steady state microstructure is developed, and then the stress was reduced to the lower level (sigma 2). The associated microstructure, and significance of this microstructure on the creep strain-hardening model for variable uniaxial loads were assesed and found to be consistent with the use of creep-recovery models at high stresses and temperatures and strain-hardening models at low stresses and tempertures

Iterative seismic data interpolation using plane-wave shaping

textGeophysical applications often require finding an appropriate solution to an ill-posed inverse problem. An example application is interpolating irregular or sparse data to a regular grid. This data regularization problem must be addressed appropriately before many data processing techniques can begin. In this thesis, I investigate plane-wave shaping in two and three dimensions as a data regularization algorithm, which can be used for the interpolation of seismic data and images. I use plane-wave shaping to interpolate several synthetic and field datasets and test its accuracy in image reconstruction. Because plane-wave shaping adheres to the direction of the local slopes of an image, the image-guided interpolation scheme attempts to preserve information of geologic structures. I apply several alternative interpolation schemes - formulated as an inverse problem with a convolutional operator to constrain the model space - namely: plane-wave destruction, plane-wave construction, and prediction-error filters. Investigating their iterative convergence rates, I find that plane-wave shaping converges to a solution in fewer iterations than the alternative techniques. I find that the only required parameter for this method, the smoothing radius, is best chosen to be approximately the same size as the holes for missing-data problems. The optional parameter for edge padding is best selected as approximately half of the smoothing radius. Applications of this research project include potential applications in well-log interpolation, seismic tomography, and 5-D seismic data interpolation.Geological Science

Applications of elastic-viscoplastic constitutive models in dynamic analyses of crack run-arrest events

Applications of nonlinear techniques to the first series of six HSST wide-plate crack-arrest tests that were performed are described. The experiments include crack initiations at low temperatures and relatively long (20 cm) cleavage propagation phases which are terminated by arrest in high temperature regions. Crack arrest are then followed by ductile tearing events. Consequently, the crack front regions are exposed to wide ranges of strain rates and temperatures

Current activities in standardization of high-temperature, low-cycle-fatigue testing techniques in the United States

The American Society for Testing and Materials (ASTM) standard E606-80 is the most often used recommended testing practice for low-cycle-fatigue (LCF) testing in the United States. The standard was first adopted in 1977 for LCF testing at room temperature and was modified in 1980 to include high-temperature testing practices. Current activity within ASTM is aimed at extending the E606-80 recommended practices to LCF under thermomechanical conditions, LCF in high-pressure hydrogen, and LCF in metal-matrix composite materials. Interlaboratory testing programs conducted to generate a technical base for modifying E606-80 for the aforementioned LCF test types are discussed

Data requirements to model creep in 9Cr-1Mo-V steel

Models for creep behavior are helpful in predicting response of components experiencing stress redistributions due to cyclic loads, and often the analyst would like information that correlates strain rate with history assuming simple hardening rules such as those based on time or strain. On the one hand, much progress has been made in the development of unified constitutive equations that include both hardening and softening through the introduction of state variables whose evolutions are history dependent. Although it is difficult to estimate specific data requirements for general application, there are several simple measurements that can be made in the course of creep testing and results reported in data bases. The issue is whether or not such data could be helpful in developing unified equations, and, if so, how should such data be reported. Data produced on a martensitic 9Cr-1Mo-V-Nb steel were examined with these issues in mind

Assessment of Existing Alloy 617 Data for Gen IV Materials Handbook

This report talks about Assessment of Existing Alloy 617 Data for Gen IV Materials Handboo

Isochronous stress versus strain curves for normalized-and-tempered 2 {1/4}Cr-1Mo steel

Tensile and creep data were collected for normalized-and-tempered 2 {1/4}Cr - 1Mo steel and used to construct isochronous stress versus strain curves to 100,000 h for temperatures to 566{degrees}C (1050{degrees}F). A plasticity equation was selected that normalized the flow curves to the yield strength, and a creep equation was formulated that included a parabolic primary creep term and a linear term. Due to the early initiation of tertiary creep in the normalized-and-tempered steel, the isochronous curves were limited to 1% total strain

Evaluation of Stainless Steels for Primary Surface Recuperator Applications

In 1996, a Cooperative Research and Development Agreement (CRADA) was undertaken between the Oak Ridge National Laboratory (ORNL) and Solar Turbines Incorporated to develop improved stainless steels for gas turbine recuperator applications. A team was assembled that consisted of materials and fabrication specialists from ORNL, Solar Turbines, Allegheny Ludlum Research Laboratory, and the University of California-San Diego. The development strategy was to (1) identify the materials performance requirements needed for long-time operation of a recuperator with inlet gas temperatures higher than current practice, (2) select candidate commercial and near-commercial alloys with potential for meeting the performance requirements, and (3) optimize thermal-mechanical processing to meet commercial production capabilities. The performance requirements were incorporated into three categories (fabricability, corrosion resistance, and mechanical strength) and teams were assigned to address each of these issues. The composition of the steels under consideration ranged from 18 to 25% chromium and from 8 to 25% nickel. Foils of thicknesses in the range 0.08 to 0.12 mm were produced by laboratory processing and by commercial processing. Thermal-mechanical processing was varied to obtain a range of grain sizes or to vary other physical metallurgical parameters. Oxidation experiments were undertaken in laboratory air and air with controlled water vapor contents at ORNL, Allegheny-Ludlum, and the University of California San Diego. Cyclic oxidation testing was included. Testing conditions were selected to enable models to be developed that included temperature, time, water content, and foil thickness as variables. Creep testing was performed in the temperature range of 677 C to 732 C for times extending beyond 10,000 h at ORNL and Solar Turbines. Optical, scanning, and analytical electron microscopy were used to examine the evolution of microstructure during aging, corrosion, and creep exposures. Based on the experimental work, optimized compositions and thermal-mechanical processing specifications were developed

The potential of modified type 310 stainless steel for advanced fossil energy applications

An evaluation was undertaken to determine the potential of modified type 310 stainless steel for fossil energy applications. First, alloy performance criteria for components in several emerging technologies were identified. Then, a brief review of existing alloy technology was undertaken relative to performance criteria. Key issues were the tendency for type 310 stainless steel to embrittle due to the formation of intermetallic phases, the poor resistance of type 310 stainless steel to highly sulfidizing environments, the need to examine the strength and ductility of weldments, and the lack of a long-time data base and criteria for setting allowable stress at temperatures in excess of 800{degrees}C. An activity was outlined that would address several of the key issues