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Microstructure of 9 Cr-1 MoVNb steel irradiated to 40 dpa at elevated temperatures in HFIR

Description: As part of an effort by the Office of Fusion Energy to evaluate the irradiation behavior of ferritic steels, a 9 Cr-1 MoVNb alloy was irradiated in HFIR to a dose of approx. 36 dpa at temperatures of 300, 400, 500, and 600/sup 0/C. In addition to the displacement damage produced during irradiation, a transmutation reaction of nickel during HFIR irradiation resulted in the simultaneous production of approx. 30 at. ppM He. Electron microscopy disks in the normalized and tempered condition were irradiated, and the microstructures were evaluated as a function of irradiation temperature. A few small cavities were observed after irradiation at 300, 500, and 600/sup 0/C. However, a pronounced cavity microstructure was found after irradiation at 400/sup 0/C. At this temperature, the cavities had a volume-averaged diameter of 15 nm and a concentration of 1.1 x 10/sup 21/ m/sup -3/, resulting in a void-swelling contribution of 0.19%. The cavities at 400/sup 0/C were homogeneously distributed throughout the tempered martensite matrix, and showed no preference for lath boundaries or precipitate interfaces. The results are compared to those recently reported on a similarly irradiated 12 Cr-1 MoVW ferritic steel.
Date: January 1, 1983
Creator: Vitek, J.M. & Klueh, R.L.
Partner: UNT Libraries Government Documents Department

Tensile behavior of three commercial ferritic steels after low-temperature irradiation

Description: The ferritic (martensitic) steels and the austenitic stainless steels are being considered for use as first wall and blanket structural components for fusion reactors. Tensile specimens of normalized-and-tempered 9 Cr-1 MoVNb and 12 Cr-1 MoVW steels, normalized-and-tempered and isothermally annealed 2-1/4 Cr-1 Mo steel, and 20%-cold-worked type 316 stainless steel were irradiated at approximately 50/sup 0/C to damage levels of up to about 9 displacements per atom (dpa) in the High Flux Isotope Reactor (HFIR). The preirradiated microstructures of the 9 Cr-1 MoVNb and 12 Cr-1 MoVW steels were a tempered martensite; the microstructure of the normalized-and-tempered 2-1/4 Cr-1 Mo steel was tempered bainite, and that of the isothermally annealed 2-1/4 Cr-1 Mo steel was primarily polygonal ferrite.
Date: January 1, 1983
Creator: Klueh, R.L. & Vitek, J.M.
Partner: UNT Libraries Government Documents Department

The aging behavior of types 308 and 308CRE stainless steels and its effect on mechanical properties

Description: Aging of 308 and 308CRE SS was studied at 475 to 850/sup 0/C for aging times up to 10,000 hours. Above 550/sup 0/C, aging of 308 steel resulted in precipitation of carbides and the transformation of ferrite to sigma phase or the formation of sigma phase in initially ferrite-free material. The elevated-temperature aging of 308CRE steel resulted in the precipitation of titanium-rich carbides, nitrides, and sulfides, and the transformation of ferrite to sigma phase. The distribution of precipitates was affected by the initial condition of the materials. The elevated-temperature creep properties, and in particular the improved properties of 308CRE, were related to the precipitate distribution. Below 550/sup 0/C, aging of welded type 308 steel, precipitation of G-phase within the ferrite was observed, as well as the decomposition of ferrite into alpha and alpha prime. With the help of a novel mechanical properties microprobe, which was capable of determining the hardness of the minor constituent ferrite phase, the hardness behavior as a function of aging could be related to the microstructures. These results are interpreted in terms of the potential susceptibility of these alloys to 475/sup 0/C embrittlement.
Date: January 1, 1987
Creator: Vitek, J.M. & David, S.A.
Partner: UNT Libraries Government Documents Department

Microstructure of HFIR-irradiated 12-Cr 1 MoVW ferritic steel

Description: As part of the fusion materials development program in the United States, a 12 Cr-1 MoVW ferritic steel was irradiated in the High Flux Isotope Reactor (HFIR) to a damage level of 36 dpa at 300, 400, 500, and 600/sup 0/C. During irradiation in HFIR, a transmutation reaction of nickel results in the production of helium, to a level of 99 at. ppM in the present experiment. The microstructures were evaluated after irradiation and the results are presented. Cavities were found at all temperatures. Small cavities (3 to 9 nm) were observed after irradiation at 300, 500 and 600/sup 0/C. At 500 and 600/sup 0/C, the cavities were found preferentially at dislocations, lath boundaries, and prior austenite grain boundaries. After irradiation at 400/sup 0/C, larger cavities (4 to 30 nm) were observed homogeneously distributed throughout the tempered martensite structure. The maximum swelling was 0.07% after irradiation at 400/sup 0/C. Comparision of the results with other studies in which helium was not present at such high levels indicated helium enhances the swelling of 12 Cr-1 MoVW.
Date: January 1, 1983
Creator: Vitek, J.M. & Klueh, R.L.
Partner: UNT Libraries Government Documents Department

Solidification behavior and microstructural analysis of austenitic stainless steel laser welds

Description: Solidification behavior of austenitic stainless steel laser welds has been investigated with a high-power laser system. The welds were made at speeds ranging from 13 to 60 mm/s. The welds sowed a wide variety of microstructural features. The ferrite content in the 13-mm/s weld varied from less than 1% at the root of the weld to about 10% at the crown. The duplex structure at the crown of the weld was much finer than the one observed in conventional weld metal. However, the welds made at 25 and 60 mm/s contained an austenitic structure with less than 1% ferrite throughout the weld. Microstructural analysis of these welds used optical microscopy, transmission electron microscopy, and analytical electron microscopy. The austenitic stainless steel welds were free of any cracking, and the results are explained in terms of the rapid solidification conditions during laser welding.
Date: January 1, 1981
Creator: David, S.A. & Vitek, J.M.
Partner: UNT Libraries Government Documents Department

Characterization of nickel-doped ferritic steels for helium production through HFIR irradiation

Description: Small heats of ferritic (martensitic) steels based on 12% Cr-1% Mo and 9% Cr-1% Mo were prepared containing about 0, 1, and 2% Ni. Additional heats were made with 2% Ni, in which the content of the ferrite-forming elements was adjusted to restore the net chromium equivalent to a value near that of the unmodified alloy. During irradiation in the High Flux Isotope Reactor (HFIR), transmutation of the /sup 58/Ni in the 2% Ni alloys will give helium concentrations approximating those produced in such steels (without nickel) in fusion reactor service. Because the addition of nickel can affect the response to heat treatment, the microstructures of the alloys are being characterized.
Date: January 1, 1980
Creator: Klueh, R.L. & Vitek, J.M.
Partner: UNT Libraries Government Documents Department

Effect of specimen size and nickel content on the impact properties of 12 Cr-1 MoVW ferritic steel

Description: The ferritic steel 12 Cr-1 MoVW is a candidate material for use in the first wall of magnetic fusion reactors. One of the primary concerns of materials in this application is service-induced embrittlement from aging and irradiation. Unirradiated Charpy impact data have been developed on three typical heats of 12 Cr-1 MoVW steel and on heats that have been modified with nickel and chromium additions for subsequent simulation of helium effects of irradiation. The ductile-to-brittle transition temperature and the upper-shelf energy were reduced by nickel additions. The addition of nickel while simultaneously maintaining a constant net chromium equivalent caused the transition temperature to increase. The use of a subsize specimen is mandated by the small volume and high gamma heating in high-flux research reactors used for very high-fluence irradiation experiments. Therefore, an understanding of the behavior of the subsize specimen is important in predicting corresponding irradiation-induced transition temperature shifts and upper-shelf drops of full-size Charpy specimens. Data are reported from subsize Charpy impact specimens, and the full- and subsize specimens are compared. The effect of specimen size on the upper-shelf energy of this material can be reduced better by volume normalization than by area normalization.
Date: January 1, 1983
Creator: Corwin, W.R.; Klueh, R.L. & Vitek, J.M.
Partner: UNT Libraries Government Documents Department

Effect of initial composition distribution on the phase transformation behavior in the Fe-Cr-Ni system

Description: A finite-difference implicit numerical model was used to study the diffusion-controlled {alpha}{minus}{gamma} (ferrite-to-austenite) solid-state phase transformation in the Fe-Cr-Ni system. The influence of a nonuniform initial composition distribution was examined in order to assess the impact that nonuniform solute profiles resulting from solidification may have on subsequent transformation behavior in weldments and castings. A significant impact on the transformation kinetics and transformation path was found in some cases. Factors that affect the degree of influence are discussed.
Date: December 31, 1995
Creator: Vitek, J.M. & David, S.A.
Partner: UNT Libraries Government Documents Department

Recent developments in the study of phase stability of austenitic stainless steels and its relation to properties

Description: Much work has been done over the years in alloy development of stainless steels and in the characterization of stainless steel microstructures and properties. However, in recent years there have been significant new advances made, and insights gained, into the physical metallurgy of these materials. In particular, advanced techniques have led to new information on the phase stability of stainless steels and the influence of the phase stability on mechanical properties. This paper will highlight some of these new advances, with an emphasis on work that has been done at ORNL on these alloys. For stainless steel alloys, the phase stability can be influenced by several factors. They include solidification behavior, the ferrite/austenite solid-state transformation, other high temperature phase transformations, and low temperature phase transformations. Recent advances in theoretical and experimental methods have led to new developments in understanding and characterizing these factors. Advanced solidification theory has been applied to understand the influence of rapid solidification on phase formation during solidification. New thermodynamic evaluation methods have shown great potential in providing details on the overall phase stability, including details on the influence of composition on phase stability. finite-difference techniques have been applied to the stainless steel alloy system to gain much insight into the ferrite/austenite transformation behavior. Finally, advanced techniques such as analytical electron microscopy, atom probe field ion microscopy, nano-indentation techniques, and specimen miniaturization techniques have provided valuable information on the response of stainless steel microstructures and properties to thermal treatment. All of these new methods and approaches are described in detail in this presentation.
Date: December 31, 1995
Creator: Vitek, J.M. & David, S.A.
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

Modeling phase transformations in ternary systems: Ferrite dissolution during continuous cooling

Description: The diffusion-controlled phase dissolution (or growth) in a ternary system of finite length has been modeled numerically using an implicit finite-difference method. The analysis has been applied to study the ferrite to austenite transformation in austenitic stainless steel weldments. The iron-chromium-nickel ternary system was taken as representative of this class of materials. The effect of system geometry was evaluated by considering planar, cylindrical, and spherical geometries. The numerical analysis was extended to the case of continuous cooling, for a range of cooling rates from 0.1 to 100 K/s. The results provide information on how quickly the system deviates from equilibrium during cooling, and what the final compositions and phase fractions are as a function of cooling rate. In most cases, the deviation from equilibrium, in terms of residual ferrite content and composition, increased as the cooling rate increased, as expected. However, under some conditions, it was found that the lowest cooling rates actually deviated further from equilibrium than intermediate cooling rates. This curious phenomenon was investigated in detail and was explained in terms of the indirect path toward final. Such indirect equilibration is often found during and typical of diffusion-controlled transformation behavior in multi-component systems.
Date: July 1, 1995
Creator: Vitek, J.M. & Vitek, S.A.
Partner: UNT Libraries Government Documents Department

Fatigue behavior of irradiated helium-containing ferritic steels for fusion reactor applications

Description: The martensitic alloys 12Cr-1MoVW and 9Cr-1MoVNb have been irradiated in the High Flux Isotope Reactor (HFIR) and subsequently tested in fatigue. In order to achieve helium levels characteristic of fusion reactors, the 12Cr-1MoVW was doped with 1 and 2% Ni, resulting in helium levels of 210 and 410 at. ppM at damage levels of 25 dpa. The 9Cr-1MoVNb was irradiated to a damage level of 3 dpa and contained <5 at. ppM He. Irradiations were carried out at 55/sup 0/C and testing at 22/sup 0/C. No significant changes were found in 9Cr-1MoVNb upon irradiation at this damage level, but effects that could possibly be attributed to helium were found in 12Cr-1MoVW. Levels of 210 and 410 at. ppM He produced cyclic strengthening of 29 and 34% over unirradiated nickel-doped materials, respectively. This cyclic hardening attributable largely to helium resulted in degradation of the cyclic life. However, the fatigue life remained comparable to or better than unirradiated 20%-cold-worked 316 stainless steel.
Date: January 1, 1986
Creator: Grossbeck, M.L.; Vitek, J.M. & Liu, K.C.
Partner: UNT Libraries Government Documents Department

Effect of preinjected helium on the response of V-20Ti pressurized tubes to neutron irradiation

Description: Vanadium-205 titanium tubes, pressurized to stresses of 34 and 39 MPa, were irradiated in the Experimental Breeder Reactor (EBR-II) at 700/sup 0/C to a displacement damage level of 22 dpa. Sections of the tubes were injected with 15 appM He prior to irradiation to determine ethe effect of helium on the microstructural and creep response of this alloy to irradiation. It was found that helium promoted cavity formation, primarily within existing precipitates, but total swelling remained low. Helium also significantly enhanced creep deformation. The results indicate that the increase in creep deformation in the presence of helium may be very sensitive to stress.
Date: January 1, 1986
Creator: Vitek, J.M.; Braski, D.N. & Horak, J.A.
Partner: UNT Libraries Government Documents Department

Helium effects on void formation in 9Cr-1MoVNb and 12Cr-1MoVW irradiated in HFIR

Description: Up to 2 wt % Ni was added to 9Cr-1MoVNb and 12Cr-1MoVW ferritic steels to increase helium production by transmutation during HFIR irradiation. The various steels were irradiated to approx.39 dpa. Voids were found in all the undoped and nickel-doped steels irradiated at 400/sup 0/C, most of them at 500/sup 0/C, but not in any of them at 300 or 600/sup 0/C. Bubble formation, however, was increased at all temperatures in the nickel-doped steels. Maximum void formation was found at 400/sup 0/C, but swelling remained less than 0.5% even with up to 440 appM He. Irradiation at 300 to 500/sup 0/C caused dissolution of as-tempered M/sub 23/C/sub 6/ precipitates and coarsening of the lath/subgrain structure in the 9-Cr steels, whereas the microstructure generally remained stable in the 12-Cr steels. Irradiation in this temperature range also causd compositional changes in the as-tempered MC phase in all the steels, and produced combinations of fine M/sub 6/C, G, and M/sub 2/X precipitates in various steels. The subgrain boundaries appear to be strong sinks that enhance resistance to void formation. Higher helium production during irradiation appears to shorten the incubation period for void formation. The effects of helium on steady state void swelling behavior, however, remain unknown.
Date: January 1, 1986
Creator: Maziasz, P.J.; Klueh, R.L. & Vitek, J.M.
Partner: UNT Libraries Government Documents Department

Postirradiation tensile behavior of nickel-doped ferritic steels

Description: Tensile specimens of normalized-and-tempered 9Cr-1MoVNb, 9Cr-1MoVNb-2Ni, 12Cr-1MoVW, 12Cr-1MoVW-1Ni, and 12Cr-1MoVW-2Ni were irradiated in the Experimental Breeder Reactor at 390, 450, 500, and 550/sup 0/C to displacement-damage levels of approximately 16 dpa. The only difference in the effect of irradiation on the tensile behavior of the nickel-doped and undoped steels was attributed to the difference in tempering treatments the two types of steels received. The nickel-doped steels were stronger prior to irradiation due to a lower tempering temperature. After irradiation, the properties of the steels with and without nickel were similar, indicating that the presence of nickel did not affect the behavior of the steels during irradiation. Nickel was added to the steels to study the effect of helium on the properties of these steels. Helium can be formed in an alloy containing nickel by irradiating in a mixed-spectrum reactor. To help determine the effect of helium on properties, these steels are also being irradiated in fast reactors, where little helium is formed. The present fast-reactor results indicate that it is feasible to use the nickel-doped ferritic steels to study helium effects.
Date: January 1, 1986
Creator: Klueh, R.L.; Maziasz, P.J. & Vitek, J.M.
Partner: UNT Libraries Government Documents Department

Neural Network Modeling of Weld Pool Shape in Pulsed-Laser Aluminum Welds

Description: A neural network model was developed to predict the weld pool shape for pulsed-laser aluminum welds. Several different network architectures were examined and the optimum architecture was identified. The neural network was then trained and, in spite of the small size of the training data set, the network accurately predicted the weld pool shape profiles. The neural network output was in the form of four weld pool shape parameters (depth, width, half-width, and area) and these were converted into predicted weld pool profiles with the use of the actual experimental poo1 profiles as templates. It was also shown that the neural network model could reliably predict the change from conduction-mode type shapes to keyhole-mode shapes.
Date: November 16, 1998
Creator: Iskander, Y.S.; Oblow, E.M. & Vitek, J.M.
Partner: UNT Libraries Government Documents Department

Effect of oxide inclusions on the solid state transformation in low-alloy steel fusion welds

Description: Non-metallic inclusions are known to influence the properties of low alloy steel weld metal by altering the microstructure development. Isothermal transformation kinetics of austenite to acicular ferrite and allotriomorphic ferrite were measured in reheated low alloy steel weld deposits with similar weld compositions and austenite grain size but different inclusion characteristics. Accelerated kinetics of the transformation to acicular ferrite were observed in the weld metal containing coarser titanium-rich inclusions. The results are also discussed in relation to the predictions of inclusion model. The kinetics of the transformation to allotriomorphic ferrite were not influenced by a change in the inclusion characteristics, but, rather, by a change in austenite grain size. A theoretical analysis of austenite grain development during weld cooling is considered in this work. The austenite grain size was found to depend on the driving force for transformation from 6 ferrite to austenite ({Delta}G{sup {sigma}->{gamma}}) calculated from ThermoCalc{trademark} software.
Date: December 31, 1995
Creator: Babu, S.S.; David, S.A. & Vitek, J.M.
Partner: UNT Libraries Government Documents Department

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

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

Weldability and microstructure development in nickel-base superalloys

Description: The integrity of nickel-base superalloy single-crystal welds depends on the weld cracking tendency, weld metal dendrite selection process, stray crystal formation, and macro- and microstructure development. These phenomena have been investigated in commercial nickel-base superalloy single crystal welds. During electron beam and laser beam welding, transverse and longitudinal weld cracking occurred. However, the weld cracking tendency was reduced with preheating. Most of the dendritic growth pattern development in these welds can be explained by a geometric model. However, the welds also contained misoriented stray crystals, which were frequently associated with weld cracks. The formation of stray crystals was related to thermal and constitutional supercooling effects. Fine-scale elemental partitioning between {gamma} and {gamma}{prime} phase was measured with atom-probe field-ion microscopy. Marked differences in partitioning characteristics in two welds were observed and are related to differences in cooling rates. In this paper, the modeling tools available to describe the above are reviewed.
Date: November 1, 1997
Creator: David, S.A.; Babu, S.S. & Vitek, J.M.
Partner: UNT Libraries Government Documents Department

Using Neural Networks to Describe Complex Phase Transformation Behavior

Description: Final microstructures can often be the end result of a complex sequence of phase transformations. Fundamental analyses may be used to model various stages of the overall behavior but they are often impractical or cumbersome when considering multicomponent systems covering a wide range of compositions. Neural network analysis may be a useful alternative method of identifying and describing phase transformation beavior. A neural network model for ferrite prediction in stainless steel welds is described. It is shown that the neural network analysis provides valuable information that accounts for alloying element interactions. It is suggested that neural network analysis may be extremely useful for analysis when more fundamental approaches are unavailable or overly burdensome.
Date: May 24, 1999
Creator: Vitek, J.M. & David, S.A.
Partner: UNT Libraries Government Documents Department

Modeling the Ferrite-Austenite Transformation in the Heat-Affected Zone of Stainless Steel Welds

Description: The diffusion-controlled ferrite-austenite transformation in stainless steel welds was modeled. An implicit finite-difference analysis that considers multi-component diffusion was used. The model was applied to the Fe-Cr-Ni system to investigate the ferrite- austenite transformation in the heat-affected zone of stainless steel weld metal. The transformation was followed as a function of time as the heat-affected zone was subjected to thermal cycles comparable to those experienced during gas-tungsten arc welding. The results showed that the transformation behavior and the final microstructural state are very sensitive to the maximum temperature that is experienced by the heat-affected zone. For high maximum exposure temperatures ({approximately} 1300{degree} C), the ferrite formation that occurs at the highest temperatures is not completely offset by the reverse ferrite dissolution at lower temperatures. As a result, for high temperature exposures there is a net increase in the amount of ferrite in the microstructure. It was also found that if compositional gradients are present in the initial ferrite and austenite phases, the extent of the transformation is impacted.
Date: December 1, 1997
Creator: Vitek, J.M. & David, S.A.
Partner: UNT Libraries Government Documents Department

Embrittlement of austenitic stainless steel welds

Description: The microstructure of type-308 austenitic stainless steel weld metal containing {gamma} and {delta} and ferrite is shown. Typical composition of the weld metal is Cr-20.2, Ni-9.4, Mn-1.7, Si-0.5, C-0.05, N-0.06 and balance Fe (in wt %). Exposure of austenitic stainless steel welds to elevated temperatures can lead to extensive changes in the microstructural features of the weld metal. On exposure to elevated temperatures over a long period of time, a continuous network of M{sub 23}C{sub 6} carbide forms at the austenite/ferrite interface. Upon aging at temperatures between 550--850 C, ferrite in the weld has been found to be unstable and transforms to sigma phase. These changes have been found to influence mechanical behavior of the weld metal, in particular the creep-rupture properties. For aging temperatures below 550 C the ferrite decomposes spinodally into {alpha} and {alpha}{prime} phases. In addition, precipitation of G-phase occurs within the decomposed ferrite. These transformations at temperatures below 550 C lead to embrittlement of the weld metal as revealed by the Charpy impact properties.
Date: December 31, 1997
Creator: David, S.A. & Vitek, J.M.
Partner: UNT Libraries Government Documents Department

Trends in microstructure modeling in weld metals

Description: Various physical processes, such as thermochemical reactions in liquid, solidification, and solid state transformations, control the microstructure development in weld metals. Some fundamental knowledge of the effects of these physical processes on weld microstructure development already exists. However, generalized and integrated models encompassing the current understanding are just evolving. Such models are needed in the design of successful welding procedures for new alloy systems and advanced materials. The principles, methodology, and future directions of modeling weld microstructure development are described in this paper, with examples in low-alloy steel, stainless steel, and Ni-base superalloys. In low alloy steels, the nucleation and growth of oxide inclusions in the melt was modeled as a function of the welding process and composition. This inclusion model has been recently coupled with solidification and numerical heat and mass transfer models. Recent advances in theoretical and physical modeling of the solidification process will be reviewed in this paper with regard to predicting the solidification modes, grain structure development, segregation effects, and nonequilibrium solidification in welds. In nickel-base superalloy welds, the effects of solidification and solid state transformations on microstructure development will be described. In these welds, the final microstructure was found to be dependent on the cooling rates and solidification modes. The weld microstructure was investigated with the help of advanced analytical techniques such as atom-probe field-ion microscopy. The result addresses the importance of advanced analytical techniques in modeling the solid state transformation.
Date: December 31, 1996
Creator: David, S.A.; Babu, S.S. & Vitek, J.M.
Partner: UNT Libraries Government Documents Department