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Modeling phase transformation behavior during thermal cycling in the heat-affected zone of stainless steel welds

Description: An implicit finite-difference analysis was used to model the diffusion-controlled transformation behavior in a ternary system. The present analysis extends earlier work by examining the transformation behavior under the influence of multiple thermal cycles. The analysis was applied to the Fe-Cr-Ni ternary system to simulate the microstructural development in austenitic stainless steel welds. The ferrite-to-austenite transformation was studied in an effort to model the response of the heat-affected zone to multiple thermal cycles experienced during multipass welding. Results show that under some conditions, a transformation ``inertia`` exists that delays the system`s response when changing from cooling to heating. Conditions under which this ``inertia`` is most influential were examined. It was also found that under some conditions, the transformation behavior does not follow the equilibrium behavior as a function of temperature. Results also provide some insight into effect of composition distribution on transformation behavior.
Date: December 31, 1995
Creator: Vitek, J.M.; Iskander, Y.S. & David, S.A.
Partner: UNT Libraries Government Documents Department

Development of the Cylindrical Wire Electrical Discharge Machining Process.

Description: Results of applying the wire Electrical Discharge Machining (EDM) process to generate precise cylindrical forms on hard, difficult-to-machine materials are presented. A precise, flexible, and corrosion-resistant underwater rotary spindle was designed and added to a conventional two-axis wire EDM machine to enable the generation of free-form cylindrical geometries. A detailed spindle error analysis identifies the major source of error at different frequency. The mathematical model for the material removal of cylindrical wire EDM process is derived. Experiments were conducted to explore the maximum material removal rate for cylindrical and 2D wire EDM of carbide and brass work-materials. Compared to the 2D wire EDM, higher maximum material removal rates may be achieved in the cylindrical wire EDM. This study also investigates the surface integrity and roundness of parts created by the cylindrical wire EDM process. For carbide parts, an arithmetic average surface roughness and roundness as low as 0.68 and 1.7 {micro}m, respectively, can be achieved. Surfaces of the cylindrical EDM parts were examined using Scanning Electron Microscopy (SEM) to identify the craters, sub-surface recast layers and heat-affected zones under various process parameters. This study has demonstrated that the cylindrical wire EDM process parameters can be adjusted to achieve either high material removal rate or good surface integrity.
Date: January 22, 2002
Creator: McSpadden, SB
Partner: UNT Libraries Government Documents Department

Glass particles produced by laser ablation for ICP-MSmeasurements

Description: Pulsed laser ablation (266nm) was used to generate glass particles from two sets of standard reference materials using femtosecond (150fs) and nanosecond (4ns) laser pulses with identical fluences of 50 J cm{sup -2}. Scanning electron microscopy (SEM) images of the collected particles revealed that there are more and larger agglomerations of particles produced by nanosecond laser ablation. In contrast to the earlier findings for metal alloy samples, no correlation between the concentration of major elements and the median particle size was found. When the current data on glass were compared with the metal alloy data, there were clear differences in terms of particle size, crater depth, heat affected zone, and ICP-MS response. For example, glass particles were larger than metal alloy particles, the craters in glass were less deep than craters in metal alloys, and damage to the sample was less pronounced in glass compared to metal alloys samples. The femtosecond laser generated more intense ICP-MS signals compared to nanosecond laser ablation for both types of samples, although glass sample behavior was more similar between ns and fs-laser ablation than for metals alloys.
Date: June 1, 2007
Creator: Gonzalez, J.; Liu, C.; Wen, S.; Mao, X. & Russo, R.E.
Partner: UNT Libraries Government Documents Department

Stressed Heat Affected Zone Simulations of AerMet 100 Alloy

Description: AerMet 100 is a high strength, high fracture toughness alloy designed for use in aerospace applications. In previous work the welding behavior of this alloy has been evaluated, and it has been shown that a softened region in the heat-affected zone (HAZ) is a principal feature of the weld zone. A model for this softening, based on classical theories of precipitate coarsening and isothermal softening data, was developed and found to provide a reasonable description for weld thermal cycle simulation (Gleeble) experiments. Recent work has shown, however, that softening in real welds is not always well predicted by this model, so that additional effects, which are not captured in conventional Gleeble thermal cycle simulations must be addressed. In particular, the stresses associated with real weld HAZ's may modify the softening kinetics. In the current work, Gleeble simulations in both stress-free and stressed conditions have been conducted and the kinetics compared. The accuracy of the thermal model predictions have also been considered regarding their impact on estimated hardness values.
Date: August 3, 1999
Creator: Puskar, Joseph D. & Smith, Mark F.
Partner: UNT Libraries Government Documents Department

Integrated thermal-microstructure model to predict the property gradients in resistance spot steel welds

Description: An integrated model approach was proposed for relating resistance welding parameters to weldment properties. An existing microstructure model was used to determine the microstructural and property gradients in resistance spot welds of plain carbon steel. The effect of these gradients on the weld integrity was evaluated with finite element analysis. Further modifications to this integrated thermal-microstructure model are discussed.
Date: November 1, 1998
Creator: Babu, S.S.; Riemer, B.W.; Santella, M.L. & Feng, Z.
Partner: UNT Libraries Government Documents Department

Neutron diffraction studies of welds of aerospace aluminum alloys

Description: Neutron diffraction and electron microscopy were done on residual stress in various regions comprising variable polarity plasma arc welds of alloys 2219 (Al-6.3Cu) and 2195 (Al-4.0Cu-1.0Li-0.5Mg-0.5Ag). Results indicate that lattice parameter changes in the various weld regions may be attributed to residual stresses generated during welding, as well as local changes in microstructure. Distribution of longitudinal and transverse stress of welded panels shows peaks of tension and compression, respectively, within the HAZ and corroborate earlier theoretical results. Position of these peaks are related to position of minimum strength within the HAZ, and the magnitude of these peaks are a fraction of the local yield strength in this region. Weldments of alloy 2195-T8 exhibited higher peak residual stress than alloy 2219-T87. Comparison of neutron diffraction and microstructural analysis indicate decreased lattice parameters associated with the solid solution of the near HAZ; this results in decreased apparent tensile residual stress within this region and may significantly alter interpretation of residual stress measurements of these alloys. Considerable relaxation of residual stress occurs during removal of specimens from welded panels and was used to aid in differentiating changes in lattice parameters attributed to residual stress from welding and modifications in microstructure.
Date: October 1, 1996
Creator: Martukanitz, R.P.; Howell, P.R.; Payzant, E.A.; Spooner, S. & Hubbard, C.R.
Partner: UNT Libraries Government Documents Department

Optical and analytical electron microscopy of ductility-dip cracking in Ni-base filler metal 52 -- Initial studies

Description: Microcharacterization studies were performed on weld-metal microstructures of a Ni-base filler metal. Specimens were taken from the fusion zone and the weld-metal heat-affected zone of transverse- and spot-Varestraint welds. The filler metal was first deposited onto a steel substrate by hot-wire, gas tungsten arc welding before specimen removal. Optical microscopy indicates the crack morphology is intergranular and is along high-angle, migrated grain boundaries. At low magnifications, scanning electron microscopy reveals a relatively smooth fracture surface. However, at higher magnifications the grain faces exhibit microductility. Analytical electron microscopy reveals high-angle, migrated grain boundaries decorated with MC (Ti, Cr) and M{sub 23}C{sub 6} (Cr, Ni, Fe) precipitates ranging from 10 to 200 n. Auger electron spectroscopy of pre-strained Gleeble specimens fractured in situ revealed internal ductility-dip cracks decorated with magnesium aluminate (MgAl{sub 2}O{sub 4}) spinel particles (1,000 nm).
Date: January 1, 1998
Creator: Cola, M.J. & Teter, D.F.
Partner: UNT Libraries Government Documents Department

Modeling of residual stresses by HY-100 weldments

Description: Residual stress distribution in a HY-100 steel disk, induced by GTA spot welding, was analyzed by finite element (FE) formulations and measured by neutron diffraction (ND). Computations used temperature- dependent thermophysical and mechanical properties. FE model predictions are in good agreement with ND data in far heat affected zone (HAZ) and in base metal. Predicted residual stresses in fusion zone and near HAZ were higher than those measured by ND. This discrepancy was attributed to microstructural changes and associated material properties in the HAZ and fusion zone due to phase transformations during the weld thermal cycle.
Date: February 1, 1997
Creator: Zacharia, T.; Taljat, B. & Radhakrishnan, B.
Partner: UNT Libraries Government Documents Department

Direct Observation of Phase Transformations in Austenitic Stainless Steel Welds Using In-situ Spatially Resolved and Time-resolved X-ray Diffraction

Description: Spatially resolved x-ray diffraction (SRXRD) and time resolved x-ray diffraction (TRXRD) were used to investigate real time solid state phase transformations and solidification in AISI type 304 stainless steel gas tungsten arc (GTA) welds. These experiments were conducted at Stanford Synchrotron Radiation Laboratory (SSRL) using a high flux beam line. Spatially resolved observations of {gamma} {leftrightarrow} {delta} solid state phase transformations were performed in the heat affected zone (HAZ) of moving welds and time-resolved observations of the solidification sequence were performed in the fusion zone (FZ) of stationary welds after the arc had been terminated. Results of the moving weld experiments showed that the kinetics of the {gamma}{yields}{delta} phase transformation on heating in the HAZ were sufficiently rapid to transform a narrow region surrounding the liquid weld pool to the {delta} ferrite phase. Results of the stationary weld experiments showed, for the first time, that solidification can occur directly to the {delta} ferrite phase, which persisted as a single phase for 0.5s. Upon solidification to {delta}, the {delta} {yields} {gamma} phase transformation followed and completed in 0.2s as the weld cooled further to room temperature.
Date: September 23, 1999
Creator: Elmer, J.; Wong, J. & Ressler, T.
Partner: UNT Libraries Government Documents Department

Towards a reliable laser spray powder deposition system through process characterization

Description: A series of experiments have been performed to characterize the laser spray powder deposition tea-one (HAZ) in the process. Goal of these experiments was to minimize the heat affected base substrate while obtaining a maximum build-up rate of the deposited material. Response surface models have been developed to achieve this goal. These models indicate that laser irradiance and component travel speed are both important factors to be considered in optimization of this process. These models suggest that a minimum HAZ can be obtained with a maximum material build-up height by maintaining with a slow travel speed. Although these models are useful in identifying significant factor and process trends, further refinement is required for practical use in industrial applications. Weighting of the response variables used in generating the models is being considered to improve the model robustness. High speed imaging of the deposition process suggests that the powder particle size and/or size distribution affects the stability of this process.
Date: July 1, 1995
Creator: Keicher, D.M.; Jellison, J.L.; Schanwald, L.P.; Romero, J.A. & Abbott, D.H.
Partner: UNT Libraries Government Documents Department

Aging and phase stability of waste package outer barrier

Description: After aging for 16,000 hr at 593 C, P phase was found at Alloy 22 grain boundaries. At higher temperatures (as much as 760 C for the same aging time), both {mu} and P phase formed on grain boundaries and within the grains. Grain boundary carbides also form at 593 C and higher, but the amount of carbide is small compared to the p and P phases. A small amount of sigma phase forms in Alloy 22 after 16,000 hr at 704 and 760 C. LRO was seen after aging for 16,000 hr at 593 C and for 40,000 hr at 427 C, but ordering most likely begins at shorter times. More work must be done in phase identification. Samples aged at times less than 16,000 hr must be examined so that the phase evolution during aging can be determined. A procedure being developed for phase extraction and x-ray diffraction should make phase identification and quantification of the relative amounts of each phase easier. The times at which various stages of intermetallic precipitation occur in Alloy 22 base metal displayed an exponential (Arrhenius-type) temperature dependence. The activation energy was determined to be 290 kJ/mol. A more quantitative model based on precipitate volume fraction measurements that can be integrated over a variable temperature profile must be developed before a reasonable prediction of the phase stability of Alloy 22 base metal under repository conditions can be made. In addition, the effect of intermetallic and carbide precipitation on Alloy 22 properties must be determined. Precipitation kinetics in weld heat-affected zones, as well as in the base metal, must be studied because the thermal pulse given the HAZ during the welding process may alter nucleation of intermetallics and therefore the precipitation kinetics. Intermetallic and carbide precipitates form in Alloy 22 welds during the welding ...
Date: July 14, 1999
Creator: Summers, T & Turchi, P
Partner: UNT Libraries Government Documents Department

INVESTIGATION IN HARDSURFACING A NICKEL-COPPER ALLOY (MONEL400).

Description: Brookhaven National Laboratory (BNL) investigated the causes of weldability problems and materials failures encountered with the application of Monel (Ni-Cu) 400 as a base material and Stellite 6 (Co-Cr) as the hard-surfacing material when using the oxyacetylene welding process. This work was performed under a cooperative research and development agreement (CRADA) with the Target Rock Division of the Curtiss-Wright Flow Control Corporation. BNL evaluated two heats of Monel 400 material. One of the heats had performed well during manufacturing, producing an acceptable number of ''good'' parts. The second heat had produced some good parts but also exhibited a peculiar type of hardsurfacing/base metal collapse during the welding process. A review of the chemistry on the two heats of material indicated that they both met the chemical requirements for Monel400. During examination of the failed component, linear indications (cracks) were evident on the valve body, both on the circumferential area (top of valve body) and below the hard surfaced weld deposit. independent measurements also indicated that the two heats met the specification requirement for the material. The heat affected zone (HAZ) also contained linear discontinuities. The valve body was welded using the oxyacetylene welding process, a qualified and skilled welder, and had been given a pre-heat of between 1400-1600 F (760-871 C), which is the Target Rock qualified procedure requirement. Both original suppliers performed mechanical testing on their material that indicated the two heats also met the mechanical property requirements of the specification. The BNL investigation into the cause of the differences between these heats of material utilized the following techniques: (1) Heat Treatment of both heats of material; (2) Hardness testing; (3) Optical microscopy; (4) Scanning electron microscope (SEM)/Fractography; and (5) Energy dispersive spectroscopy (EDS). The report concludes that the cause of the failure of the valve body during welding ...
Date: December 1, 2001
Creator: CZAJKOWSKI,C. & BUTTERS,M.
Partner: UNT Libraries Government Documents Department

The Stress-Relief Cracking Susceptibility of a New Ferritic Steel - Part I: Single-Pass Heat-Affected Zone Simulations

Description: The stress-relief cracking susceptibility of single-pass welds in a new ferritic steel, HCM2S, has been evaluated and compared to 2.25Cr-1Mo steel using Gleeble techniques. Simulated coarse-grained heat-affected zones (CGHAZ) were produced under a range of energy inputs and tested at various post-weld heat treatment (PWHT) temperatures. Both alloys were tested at a stress of 325 MPa. The 2.25 Cr-1Mo steel was also tested at 270 MPa to normalize for the difference in yield strength between the two materials. Light optical and scanning electron microscopy were used to characterize the CGHAZ microstructure. The ''as-welded'' CGHAZ of each alloy consisted of lath martensite or bainite and had approximately equal prior austenite grain sizes. The as-welded hardness of the 2.25Cr-1Mo steel CGHAZ was significantly higher than that of the HCM2S alloy. Over the range studied energy input had no effect on the as-welded microstructure or hardness of either alloy. The energy input also had no effect on the stress-relief cracking susceptibility of either material. Both alloys failed intergranularly along prior austenite grain boundaries under all test conditions. The 2.25Cr-1Mo steel samples experienced significant macroductility and some microductility when tested at 325 MPa. The ductility decreased significantly when tested at 270 MPa but was still higher that than of HCM2S at each test condition. The time to failure decreased with increasing PWHT Temperature for each material. There was no significant difference in the times to failure between the two materials. Varying energy input and stress had no effect on the time-to failure. The ductility, as measured by reduction in are% increased with increasing PWHT temperature for 2.25 Cr-1Mo steel tested at both stresses. However, PWHT temperature had no effect on the ductility of HCM2S. The hardness of the CGHAZ for 2.25Cr-1Mo steel decreased significantly after PWHT, but remained constant for HCM2S. The differences in ...
Date: December 15, 1999
Creator: NAWROCKI,J.G.; DUPONT,J.N.; ROBINO,CHARLES V. & MARDER,A.R.
Partner: UNT Libraries Government Documents Department

Stress corrosion cracking of austenitic stainless steel core internal welds.

Description: Microstructural analyses by several advanced metallographic techniques were conducted on austenitic stainless steel mockup and core shroud welds that had cracked in boiling water reactors. Contrary to previous beliefs, heat-affected zones of the cracked Type 304L, as well as 304 SS core shroud welds and mockup shielded-metal-arc welds, were free of grain-boundary carbides, which shows that core shroud failure cannot be explained by classical intergranular stress corrosion cracking. Neither martensite nor delta-ferrite films were present on the grain boundaries. However, as a result of exposure to welding fumes, the heat-affected zones of the core shroud welds were significantly contaminated by oxygen and fluorine, which migrate to grain boundaries. Significant oxygen contamination seems to promote fluorine contamination and suppress thermal sensitization. Results of slow-strain-rate tensile tests also indicate that fluorine exacerbates the susceptibility of irradiated steels to intergranular stress corrosion cracking. These observations, combined with previous reports on the strong influence of weld flux, indicate that oxygen and fluorine contamination and fluorine-catalyzed stress corrosion play a major role in cracking of core shroud welds.
Date: April 14, 1999
Creator: Chung, H. M.; Park, J.-H.; Ruther, W. E.; Sanecki, J. E.; Strain, R. V. & Zaluzec, N. J.
Partner: UNT Libraries Government Documents Department

Role of beam absorption in plasma during laser welding

Description: The relationship between beam focus position and penetration depth in CW laser welding was studied numerically and experimentally for different welding conditions. Calculations were performed using a transient hydrodynamic model that incorporates the effect of evaporation recoil pressure and the associated melt expulsion. The simulation results are compared with measurements made on a series of test welds obtained using a 1650 W CO{sub 2} laser. The simulations predict, and the experiments confirm, that maximum penetration occurs with a specific location of the beam focus, with respect to the original sample surface, and that this relationship depends on the processing conditions. In particular, beam absorption in the plasma has a significant effect on the relationship between penetration and focus position. When the process parameters result in strong beam absorption in the keyhole plasma, the maximum penetration will occur when the laser focus is at or above the sample surface. In a case of weak absorption however, the penetration depth reaches its maximum value when the beam focus is located below the sample surface. In all cases, the numerical results are in good agreement with the experimental measurements.
Date: May 15, 2000
Creator: SEMAK,V.V.; STEELE,R.J.; FUERSCHBACH,PHILLIP W. & DAMKROGER,BRIAN K.
Partner: UNT Libraries Government Documents Department

Transverse texture and microstructure gradients in friction-stir welded 2519 aluminum.

Description: Friction-stir welding produces severe thermomechanical transients that generate crystallographic texture evolution throughout the weld-affected microstructure . In this study, a friction stir weld in a coarse-grained 2519 aluminum plate was investigated in order to resolve the influence of these thermal and deformation effects on texture and microstructure development . Automated electron backscatter diffraction (EBSD) was applied to spatially resolve orientations in the base metal, weld nugget, and thermomechanical and heat-affected zones. Results show a gradient demarcated by an alteration in boundary character, texture, and precipitate distribution between the thermomechanical affected zone and the recrystallized weld nugget . EBSD scans and microstructural characterizations reveal substructure evolution from the base plate to the nugget indicative of dynamic recovery and recrystallization processes . Experimental results of texture evolution, however, did not directly follow from considerations of simplified deformation gradients and resultant simple shear textures resulting from restricted glide .
Date: January 1, 2003
Creator: Bingert, J. F. (John F.) & Fonda, R. W. (Richard W.)
Partner: UNT Libraries Government Documents Department

STRESS CORROSION CRACKING IN TEAR DROP SPECIMENS

Description: Laboratory tests were conducted to investigate the stress corrosion cracking (SCC) of 304L stainless steel used to construct the containment vessels for the storage of plutonium-bearing materials. The tear drop corrosion specimens each with an autogenous weld in the center were placed in contact with moist plutonium oxide and chloride salt mixtures. Cracking was found in two of the specimens in the heat affected zone (HAZ) at the apex area. Finite element analysis was performed to simulate the specimen fabrication for determining the internal stress which caused SCC to occur. It was found that the tensile stress at the crack initiation site was about 30% lower than the highest stress which had been shifted to the shoulders of the specimen due to the specimen fabrication process. This finding appears to indicate that the SCC initiation took place in favor of the possibly weaker weld/base metal interface at a sufficiently high level of background stress. The base material, even subject to a higher tensile stress, was not cracked. The relieving of tensile stress due to SCC initiation and growth in the HAZ and the weld might have foreclosed the potential for cracking at the specimen shoulders where higher stress was found.
Date: May 1, 2009
Creator: Lam, P; Philip Zapp, P; Jonathan Duffey, J & Kerry Dunn, K
Partner: UNT Libraries Government Documents Department

Phase stability in austenitic stainless steels -- New approaches, results, and their relation to properties

Description: In recent years, the phase stability of austenitic stainless steels, and its effect on the mechanical properties of stainless steels, have been the subject of much interest. With the availability of new experimental techniques, new theoretical methods, and new computational procedures, significant advances have been made in understanding, and being able to predict, phase stability and mechanical properties of stainless steel welds. This paper reviews some of these developments, with an emphasis on recent work that has been done at Oak Ridge National Laboratory.
Date: December 31, 1995
Creator: Vitek, J.M. & David, S.A.
Partner: UNT Libraries Government Documents Department

Simulation of the weld heat affected zone of a 0.5Cr-Mo-V steel

Description: By using a Monte Carlo grain growth algorithm and a methodology for obtaining a one-to-one correlation between Monte Carlo and real parameters of grain size and time, the grain structure in the weld heat affected zone of a 0.5 Mo-Cr-V steel has been simulated. The simulations clearly show that the kinetics of grain growth can be retarded by the presence of steep temperature gradients in the weld heat affected zone. Additional pinning, due to the formation of grain boundary liquid near the solidus temperature, has also been simulated. It is shown that in order to accurately predict the observed grain size in the weld heat affected zone of the 0.5Cr-Mo-V steel, the retardation in growth kinetics due to temperature gradients as well as liquid pinning should be considered.
Date: December 1, 1995
Creator: Radhakrishnan, B. & Zacharia, T.
Partner: UNT Libraries Government Documents Department

Modeling the ferrite-to-austenite transformation in the heat-affected zone of stainless steel multi-pass welds

Description: The ferrite/austenite transformation in austenitic stainless steel welds was modeled by considering the transformation as a diffusion-controlled process. A finite-difference method was used to solve the diffusion equations. The transformation behavior was evaluated for both isothermal aging and linear cooling over a range of cooling rates. The analysis provides information on the change in ferrite content as a function of heat treatment as well as the rate of the formation (or dissolution) of ferrite. The compositions of the ferrite and austenite are also obtained in the analysis. the results show that the approach to equilibrium can often be indirect and sometimes counter to intuition. The analysis is useful in providing information on the microstructural stability in austenitic stainless steel welds that cannot be obtained experimentally.
Date: December 31, 1995
Creator: Vitek, J.M.; Vitek, S.A. & David, S.A.
Partner: UNT Libraries Government Documents Department

Modeling of residual stresses in core shroud structures

Description: A BWR core shroud is a cylindrical shell that surrounds the reactor core. Feedwater for the reactor is introduced into the annulus between the reactor vessel wall and the shroud. The shroud separates the feedwater from the cooling water flowing up through the reactor core. The shroud also supports the top guide which provides lateral support to the fuel assemblies and maintains core geometry during operational transients and postulated accidents to permit control rod insertion and provides the refloodable volume needed to ensure safe shutdown and cooling of the core during postulated accident conditions. Core shrouds were fabricated from welded Type 304 or 304L stainless steel plates and are supported at the top and bottom by forged ring support structures. In 1990, cracking was reported in the core shroud of a non-U.S. BWR. The cracks were located in the heat-affected zone (HAZ) of a circumferential core shroud weld. Subsequent inspections in U.S. BWRs have revealed the presence of numerous flaw indications in some BWR core shrouds, primarily in weld HAZs. In several instances, this cracking was quite extensive, with the cracks extending 75% or more around the circumference of some welds. However, because the applied stresses on the shroud are low during operation and postulated accidents and because of the high fracture toughness of stainless steel, adequate structural margins can be preserved even in the presence of extensive cracking. Although assessments by the USNRC staff of the potential significance of this cracking have shown that core shroud cracking does not pose a high degree of risk in the short term, the staff concluded that the cracking was a safety concern for the long term because of the uncertainties associated with the behavior of core shrouds with complete 360{degrees} through-wall cracks under accident conditions and because it could eliminate a layer ...
Date: October 1997
Creator: Zhang, J.; Dong, P.; Brust, F. W.; Mayfield, M.; McNeil, M. & Shack, W. J.
Partner: UNT Libraries Government Documents Department

Effect of CTE on Fatigue Cracking of Stainless Steel Vessels

Description: Visual examination of lithium hydride reactor vessels revealed cracks that were adjacent to welds. Most cracks were parallel to the weld in the bottom portion of the vessel. Sections were cut out of the vessel containing these cracks and examined using the metallograph, scanning electron microscope, and microprobe to determine the cause of cracking. most of the cracks originated on the outer surface just outside the weld fusion line in the heat affected zone and propagated along grain boundaries. Crack depth of those sections examined ranged from about 300 to 500 {micro}m. Other cracks were reported to have reached a maximum depth of 0.32-cm (0.125-inch). The primary cause of cracking was the creation of high tensile stresses associated with the CTE differences between the filler metal and the base metal during operation of the vessel in a thermally cyclic environment. This failure mechanism could be described as creep-type fatigue whereby crack propagation might have been aided by the presence of brittle chromium carbides along the grain boundaries, which is indicative of a slightly sensitized microstructure.
Date: January 31, 2002
Creator: Bird, E. L. & Mustaleski, T. M.
Partner: UNT Libraries Government Documents Department

Heavy-section steel technology program. Semiannual progress report, April--September 1995 Vol. 12, No. 2

Description: The Heavy-Section Steel Technology (HSST) Program is conducted for the Nuclear Regulatory Commission by Oak Ridge National Laboratory (ORNL). The program focus is on the development and validation of technology for the assessment of fracture-prevention margins in commercial nuclear reactor pressure vessels. The HSST Program is organized in seven tasks: (1) program management, (2) constraint effects analytical development and validation, (3) evaluation of cladding effects, (4) ductile-to-cleavage fracture-mode conversion, (5) fracture analysis methods development and applications, (6) material property data and test methods, and (7) integration of results. The program tasks have been structured to place emphasis on the resolution of fracture issues with near-term licensing significance. Resources to execute the research tasks are drawn from ORNL with subcontract support from universities and other research laboratories. Close contact is maintained with the sister Heavy-Section Steel Irradiation Program at ORNL and with related research programs both in the United States and abroad. This report provides an overview of principal developments in each of the seven program tasks from April 1995 to September 1995.
Date: January 1, 1997
Creator: Pennell, W.E.
Partner: UNT Libraries Government Documents Department

Crack growth rates and fracture toughness of irradiated austenitic stainless steels in BWR environments.

Description: In light water reactors, austenitic stainless steels (SSs) are used extensively as structural alloys in reactor core internal components because of their high strength, ductility, and fracture toughness. However, exposure to high levels of neutron irradiation for extended periods degrades the fracture properties of these steels by changing the material microstructure (e.g., radiation hardening) and microchemistry (e.g., radiation-induced segregation). Experimental data are presented on the fracture toughness and crack growth rates (CGRs) of wrought and cast austenitic SSs, including weld heat-affected-zone materials, that were irradiated to fluence levels as high as {approx} 2x 10{sup 21} n/cm{sup 2} (E > 1 MeV) ({approx} 3 dpa) in a light water reactor at 288-300 C. The results are compared with the data available in the literature. The effects of material composition, irradiation dose, and water chemistry on CGRs under cyclic and stress corrosion cracking conditions were determined. A superposition model was used to represent the cyclic CGRs of austenitic SSs. The effects of neutron irradiation on the fracture toughness of these steels, as well as the effects of material and irradiation conditions and test temperature, have been evaluated. A fracture toughness trend curve that bounds the existing data has been defined. The synergistic effects of thermal and radiation embrittlement of cast austenitic SS internal components have also been evaluated.
Date: January 21, 2008
Creator: Chopra, O. K. & Shack, W. J.
Partner: UNT Libraries Government Documents Department