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Towards predicting weld metal microstructure from fundamentals of transport phenomena

Description: Heat transfer and fluid flow during manual metal arc welding Of low alloy steels were investigated by solving the equations of conservation of mass, momentum and energy in three dimensions. Calculated cooling rates were coupled with an existing phase transformation model to predict the microstructure in low alloy steel welds. The computed results were found to be in good agreement with experimentally observed microstructures. The agreement indicates significant promise for predicting spatial distribution of weld metal microstructure from the fundamentals of transport phenomena.
Date: June 1, 1995
Creator: Mundra, K.; DebRoy, T.; Babu, S. S.; David, S. A. & Paul, A. J.
Partner: UNT Libraries Government Documents Department

Influence of orientation pinning on the Goss-texture in Fe-3%Si electrical steel

Description: Despite a large number of investigations on the formation of the Goss-texture in Fe-3%Si electrical steels, the exact mechanisms leading to the preference of this particular orientation are not completely understood so far. As an alternative to the standard explanation of a favored growth of Goss-oriented grains during secondary recrystallization, recently the concept of orientation pinning has been proposed, which considers that the growth of grains with special orientation relationships corresponding to low-angle and twin grain boundaries is disfavored. The present paper present preliminary EBSD-results on the growth of Goss-grains during secondary recrystallization in high-permeability (HiB) transformer steel sheets. A semi-quantitative model to simulate the effect of orientation pinning on the evolution of the Goss-texture is introduced.
Date: December 1, 1998
Creator: Engler, O. & Friedel, F.
Partner: UNT Libraries Government Documents Department

The effect of potential upon the high-temperature fatigue crack growth response of low-alloy steels. Part 1: Crack growth results

Description: Corrosion-fatigue crack propagation experiments were conducted on several low-alloy steels in elevated temperature aqueous environments, and experimental parameters included temperature, sulfur content of the steel, applied potential level, and dissolved hydrogen (and in one case, dissolved oxygen) concentration in the water. Specimen potentials were controlled potentiostatically, and the observation (or non-observation) of accelerated fatigue crack growth rates was a complex function of the above parameters. Electrochemical results and the postulated explanation for the complex behavior are given in Part II.
Date: April 1, 1997
Creator: James, L.A. & Moshier, W.C.
Partner: UNT Libraries Government Documents Department

The effect of potential on the high-temperature fatigue crack growth response of low alloy steels: Part II, electrochemical results

Description: Environmentally assisted cracking (EAC) in low alloy steels was found to be dependent on externally applied potential in low sulfur steels in high temperature water. EAC could be turned on when the specimen was polarized anodically above a critical potential. However, hydrogen (H) additions inhibited the ability of potential to affect EAC. The behavior was related to formation of H ions during H oxidation at the crack mouth. A mechanism based on formation of H sulfide at the crack tip and H ions at the crack mouth is presented to describe the process by which sulfides and H ions affect the critical sulfide concentration at the crack tip.
Date: April 1, 1997
Creator: Moshier, W.C. & James, L.A.
Partner: UNT Libraries Government Documents Department

Cessation of environmentally-assisted cracking in a low-alloy steel: Experimental results

Description: The presence of dissolved metallurgical sulfides in pressure vessel and piping steels has been linked to Environmentally-Assisted Cracking (EAC), a phenomenon observed in laboratory tests that results in fatigue crack growth rates as high as 100 times that in air. Previous experimental and analytical work based on diffusion as the mass transport process has shown that surface cracks that are initially clean of sulfides will not initiate EAC in most applications. This is because the average crack tip velocity would not be sufficiently high to expose enough metallurgical sulfides per unit time and produce the sulfide concentration required for EAC. However, there is a potential concern for the case of a relatively large embedded crack breaking through to the wetted surface. Such a crack would not be initially clean of sulfides, and EAC could initiate. This paper presents the results of a series of experiments conducted on two heats of an EAC susceptible, high-sulfur, low-alloy steel in 243{degrees}C low-oxygen water to further study the phenomenon of EAC persistence at low crack tip velocities. A load cycle profile that incorporated a significant load dwell period at minimum load was used. In one experiment, the fatigue cycling history was such that relatively high crack tip velocities at the start of the experiment produced a persistent case of EAC even when crack tip velocities were later reduced to levels below the EAC initiation velocity. The other series of experiments used initial crack tip velocities that were much lower and probably more realistic. Air precracking of the compact tension specimens produced an initial inventory of undissolved sulfides on the crack flanks that directly simulates the array of sulfides expected from the breakthrough of an embedded crack. In all cases, results showed EAC ceased after several hundred hours of cycling.
Date: January 1, 1997
Creator: Li, Y.Y.
Partner: UNT Libraries Government Documents Department

Cessation of environmentally-assisted cracking in a low-alloy steel: Theoretical analysis

Description: Environmentally Assisted Cracking (EAC) can cause increases in fatigue crack growth rates of 40 to 100 times the rate in air for low alloy steels. The increased rates can lead to very large predicted crack growth. EAC is activated by a critical level of dissolved sulfides at the crack tip. Sulfide inclusions (MnS) in the steel produce corrosive sulfides in solution following exposure by a growing crack. In stagnant, low oxygen water conditions considered here, diffusion is the dominant mass transport mechanism acting to change the sulfide concentration within the crack. The average crack tip velocity is below the level required to produce the critical crack tip sulfide ion concentration required for EAC. Crack extension analyses also consider the breakthrough of large, hypothetical embedded defects with the attendant large freshly exposed sulfide inventory. Combrade et al. noted that a large inventory of undissolved metallurgical sulfides on crack flanks could trigger EAC, but did not quantify the effects. Diffusion analysis is extended herein to cover breakthrough of embedded defects with large sulfide inventories. The mass transport via diffusion is limited by the sulfide solubility. As a result, deep cracks in high sulfur steels are predicted to retain undissolved sulfides for extended but finite periods of time t{sub diss} which increase with the crack length and the metallurgical sulfide content in the steel. The analysis shows that the duration of EAC is limited to t{sub diss} providing V{sub eac}, the crack tip velocity associated with EAC is less than V{sub In}, the crack tip velocity below which EAC will not occur in an initially sulfide free crack. This condition on V{sub eac} need only be met for a short time following crack cleanup to turn off EAC. The predicted crack extension due to limited duration of EAC is a small fraction of ...
Date: February 1, 1997
Creator: Wire, G.L.
Partner: UNT Libraries Government Documents Department

Thermo-Chemical-Mechanical Effects on Microstructure Development in Low-Alloy Steel Welds

Description: Effect of aluminum on the decomposition of 5 ferrite to austenite was investigated in a low-alloy steel weld. In addition, the effect of inclusion composition on the transition from bainite to acicular ferrite during austenite decomposition was analyzed. Stress relaxation during decomposition of austenite to allotriomorphic and acicular ferrite was also characterized. Results from the above experiments illustrate the importance of thermomechanical effects on weld microstructure evolution.
Date: May 24, 1999
Creator: Babu, S.S.; David, S.A. & Vitek, J.M.
Partner: UNT Libraries Government Documents Department

Microstructure evaluation in low alloy steel weld metal from convective heat transfer calculations in three dimensions

Description: Heat transfer and fluid flow during manual metal arc welding of low alloy steels were investigated by solving the equations of conservation of mass, momentum, and energy in three dimensions. Cooling rates were calculated at various locations in the weldment. Calculated cooling rates were coupled with an existing phase transformation model to predict percentages of acicular, allotriomorphic, and Widmanstaetten ferrites in various low alloy steel welds containing different concentration of V and Mn. Computed microstructures were in good agreement with experiment, indicating promise for predicting weld metal microstructure from the fundamentals of transport phenomena.
Date: December 31, 1995
Creator: Mundra, K.; DebRoy, T.; Babu, S.S. & David, S.A.
Partner: UNT Libraries Government Documents Department

Residual stress and microstructural characterization using Rietveld refinement of a carburized layer in a 5120 steel

Description: Rietveld refinement of X-ray diffraction patterns has been used to provide microstructural information complementary to conventional X-ray residual stress measurements through a carburized layer containing a maximum vol. 25 % of retained austenite. Layers in a simple specimen were removed incrementally by electropolishing and, at each depth in addition to conventional residual stress measurements in both the martensite and retained austenite, data were collected at {Psi} = 0 for Rietveld refinement. The refinements provide accurate values for the lattice parameters in the respective phases that can be related to carbon content and microstructure. Besides to providing qualitative information concerning the microstructure and possible surface decarburization, the c/a ratio of the martensite potentially offers an independent technique for determining carbon content profiles.
Date: September 1, 1995
Creator: Rangaswamy, P.; Bourke, M.A.M.; Lawson, A.C.; O`Rourke, J. & Goldstone, J.A.
Partner: UNT Libraries Government Documents Department

Temperature and environmentally assisted cracking in low alloy steel

Description: Environmental assisted cracking (EAC) can be defined as the propagation of fatigue cracks in water at rates from 3 to over 40 times the growth rates in air. For low alloy steels with sulfur contents > 0.0125% by weight, EAC is normal behavior in the 240 to 290C range. However, literature yields mixed results for low alloy steels with compositions just below this sulfur level; some reports indicate EAC while others do not. Also, several authors have reported an increased tendency toward EAC when the water temperatures were lowered. In the present work, five ASTM A 508 Class 2 forgings with ladle and check analyses that ranged from 0.010 to 0.019 wt% S were tested in high purity deaerated water in the temperature range of 93 to 260C. At 260C these forgings did not exhibit EAC, reinforcing earlier results for two similar forgings. This broad sampling indicates strong resistance to EAC for this class of forging at 260C. On the other hand, EAC occurred consistently in the three of these forgings that were tested below 204C, provided the test conditions (loading frequency, {Delta}K, and R) were high enough to produce a high baseline fatigue crack growth rate (FCGR), where the baseline FCGR is that expected in air. At 149C, EAC occurred at test conditions that combined to yield a baseline FCGR greater than {approx}2E-6 mm/s. At 204, 121, and 93C, this critical crack growth rate appeared to shift to lower baseline values. The EAC that occurred at lower temperatures was a factor of 3 to 12 times higher than baseline air rates, which was not as strong as the effect for higher sulfur steels at 240 to 290C. Also, no plateau in the growth rates occurred as it does with the higher sulfur steels. In another approach, EAC was induced ...
Date: April 1, 1995
Creator: Auten, T.A. & Monter, J.V.
Partner: UNT Libraries Government Documents Department

Effect of Fluid Flow on Inclusion Coarsening in Low-Alloy Steel Welds

Description: Oxide inclusions form in welds because of deoxidation reactions in the weld pool. These inclusions control the weld microstructure development. Thermodynamic and kinetic calculation of oxidation reaction can describe inclusion characteristics such as number density, size, and composition. Experimental work has shown that fluid-flow velocity gradients in the weld pool can accelerate inclusion growth by collision and coalescence. Moreover, fluid flow in welds can transport inclusions to different temperature regions that may lead to repeated dissolution and growth of inclusions. These phenomena are being studied with the help of computational coupled heat transfer, fluid-flow, thermodynamic, and kinetic models. The results show that the inclusion formation in steel welds can be described as a function of the welding processes, process parameters, and steel composition.
Date: February 28, 1998
Creator: Babu, S.S.; David, S.A.; DebRoy, T. & Hong, T.
Partner: UNT Libraries Government Documents Department

Inclusion formation in low-alloy steel welds

Description: This paper summarizes four models for describing inclusion formation in steel welds. These methods include simple fixed oxidation sequence model, thermodynamic model, thermodynamic-kinetic model, and thermodynamic-kinetic-fluid flow model. Complexities of these models increase with a need to describe details of the inclusion formation. The applicability of the models was illustrated with two examples. In one of the examples, thermodynamic calculations of phase stability between liquid steel, AlN and Al{sub 2}O{sub 3} explained the inclusion formation in self-shielded flux cored arc weld. In the second example, thermodynamic-kinetic calculations illustrated the competing effects of weld metal composition and cooling rate effects on the inclusion formation in electron beam and laser beam welds. Limitations of the current inclusion models and recommendations for future work on the inclusion formation were highlighted.
Date: November 1, 1998
Creator: Babu, S.S.; David, S.A. & DebRoy, T.
Partner: UNT Libraries Government Documents Department

Temperature measurements on a HSLA-100 steel confinement vessel

Description: Temperature measurements have been made on HSLA-100 steel confinement vessel number 6-2-3-1. These measurements are intended to give a view of the vessel temperature response under conditions similar to operational conditions, starting from worst case. The vessel`s temperature must be above the minimum operating temperature when used to contain an explosive event to ensure that the vessel material has the desired crack arrest properties. Several series of temperature measurements have been conducted over 24 and 48 hour periods during February 1998. These tests were intended to demonstrate that after running the heaters in the environmental shelter for some time, (1) the vessel warms up to temperatures well above the minimum operating temperature, (2) that through-thickness temperature gradients are negligible, and (3) that the temperature differences from one part of the vessel to another are small.
Date: May 7, 1998
Creator: Lohsen, R.A.
Partner: UNT Libraries Government Documents Department

Comparision of Limit Load Solutions with Results of a Collapse Tests of Perforated Plates with a Triangular Penetration Pattern

Description: Limit load solutions obtained by elastic-perfectly plastic finite element analysis (EPP-FEA) are compared to results of tests of low-alloy steel perforated plate geometries loaded to full plastic collapse. Results are given for two plastic-collapse tests of flat circular disks with circular penetrations arranged in a triangular pattern and drilled normal to the surface of the plate. The ligament efficiency (minimum distance between holes divided by the distance between the centers of the holes) of the pattern is 0.32 and the plate thickness is 2.39 inches (60.7 mm). The tests were designed so that a transverse load generated plastic collapse in the outer row of penetrations due to a combination of transverse shear and in-plane bending. Limit-load solutions were obtained using EPP-FEA with small-strain, small-defection linear geometry assumptions. Two FEA models are used: one where the perforated region is modeled using an equivent solid plate (EQS) representation and another where each hole is explicitly modeled by FEA. The results presented in this paper demonstrate that the deformation patterns produced by the EPP-FEA solutions match exactly with the deformation patterns produced by the test. The EQS-EPP FEA solution is about 15% lower than the explicit-hole EPP-FEA solution. Using one-third the actual ultimate strength of the material as the strength parameter in the limit load calculation produces a calculated limit load that is greater than a factor of three less than the mean measured plastic-collapse load obtained in the tests. This paper adds to the qualification of the use of limit-load solutions obtained using small-strain, small deflection EPP-FEA programs for the calculation of the limit load for perforated plates.
Date: December 13, 2001
Creator: Jones, D.P. & Gordon, J.L.
Partner: UNT Libraries Government Documents Department

Effects of Inclusions in HSLA Carbon Steel on Pitting Corrosion in CaCl2

Description: Susceptibility of high strength low alloy steel to localized corrosion was studied in 6.7 M CaCl{sub 2} for oil and natural gas drilling applications. Results of the immersion and electrochemical experiments showed that the steel is susceptible to pitting corrosion. Optical microscopy investigations of the polished samples revealed that 10% of the surface area was occupied by defects in the form of pits. The energy dispersive X-ray (EDX) and wavelength dispersive X-ray (WDX) chemical analyses revealed higher concentrations of Mn and S compared to the metal matrix in defected areas. These areas served as the sites for development of corrosion pits during both immersion and electrochemical experiments. The fatigue results of the corroded samples indicate that if the pit was the most significant defect, the fatigue crack initiated and propagated at this site.
Date: December 5, 2011
Creator: Ziomek-Moroz, M.; Bullard, S.; Rozman, K. & Kruzic, J.J.
Partner: UNT Libraries Government Documents Department


Description: This report is a compendium of sets of mechanical properties of carbon and low alloy steels following the short-term effects of hydrogen exposure. The property sets include the following: Yield Strength; Ultimate Tensile Strength; Uniform Elongation; Reduction of Area; Threshold Cracking, K{sub H} or K{sub th}; Fracture Toughness (K{sub IC}, J{sub IC}, and/or J-R Curve); and Fatigue Crack Growth (da/dN). These properties are drawn from literature sources under a variety of test methods and conditions. However, the collection of literature data is by no means complete, but the diversity of data and dependency of results in test method is sufficient to warrant a design and implementation of a thorough test program. The program would be needed to enable a defensible demonstration of structural integrity of a pressurized hydrogen system. It is essential that the environmental variables be well-defined (e.g., the applicable hydrogen gas pressure range and the test strain rate) and the specimen preparation be realistically consistent (such as the techniques to charge hydrogen and to maintain the hydrogen concentration in the specimens).
Date: June 8, 2006
Creator: Lam, P
Partner: UNT Libraries Government Documents Department

Quantitative Microanalysis with high Spatial Resolution: Application of FEG-DTEM XEDS Microanalysis to the Characterization of Complex Microstructures in Irradiated Low Alloy Steet

Description: To assist in the characterization of microstructural changes associated with irradiation damage in low alloy steels, the technique of quantitative x-ray mapping using a field emission gun scanning transmission electron microscope (FEG-STEM) equipped with an x-ray energy Dispersive spectrometer (XEDS) has been employed. Quantitative XEDS microanalyses of the matrix and grain boundaries of irradiated specimens have been compared with previous quantitative analyses obtained using 3D-Atom Probe Field-Ion Microscopy (3D-APFIM). In addition, the FEG-STEM XEDS maps obtained from the irradiated steel have revealed the presence of 2 to 3 nm Ni-enriched 'precipitates' in the matrix, which had previously been detected using 3D-APFIM. These quantitative FEG-STEM XEDS results represent the first direct and independent microchemical corroboration of the 3D-APFIM results showing ultra-fine irradiation-induced hardening features in low alloy steel.
Date: November 14, 2001
Creator: Williams, D.B., Watanabe, M. and Burke, M.G.
Partner: UNT Libraries Government Documents Department

Evaluation of Irradiation Embrittlement of A508 Gr 4N and Comparison to Other Low-Alloy Steels

Description: A508 Gr 4N has improved fracture toughness because of the addition of 3% nickel, compared to typical low alloy steels which have less than 1% nickel. However, there is an expectation in much of the recent literature, based mostly on low-alloy steels with nickel below 1%, that irradiation embrittlement will increase with increasing nickel (Ni) content. In contrast, the raw irradiation test data show that ASTM A508 Grade 4N containing up to 3.7% nickel, 0.1% Cu and 0.01% P does not show enhanced irradiation embrittlement. A simple statistical fit to irradiation dose and irradiation temperature was developed to make direct comparisons to other low-alloy steels. Since the A508 Gr 4N data showed little discernible effect of Cu in the raw data, the damage may be classified as 'matrix' damage. The peak irradiation embrittlement of A508 Gr 4N is no greater than that of A508 Gr 2, a 0.7% Ni forging material tested under similar conditions with similar limits on Cu and P. At high dose (80 mdpa) the average embrittlement of A508 Gr 4N is slightly higher (33%) than the lower nickel materials. This trend also occurs for low copper A533B and A302B plate material. The irradiation temperature dependence of embrittlement in A508 Gr 4N is nearly the same as other low copper low-alloy steels tested over a wide range of temperatures. The increase in Charpy transition temperature in A508 Gr 4N is due to radiation hardening, and the ratio of TTS to yield strength increase in 3 Ni steels is nearly identical to that observed for conventional low-alloy steels with lower nickel. A very detailed statistical fit was made to the overall data on A508 Gr 4N to evaluate the sensitivity of embrittlement to minor elements and to compare to results from the US surveillance test data, which is ...
Date: June 17, 2002
Creator: G.L. Wire, W. J. Beggs and T.R. Leax
Partner: UNT Libraries Government Documents Department

Computational Modeling and Assessment Of Nanocoatings for Ultra Supercritical Boilers

Description: Forced outages and boiler unavailability in conventional coal-fired fossil power plants is most often caused by fireside corrosion of boiler waterwalls. Industry-wide, the rate of wall thickness corrosion wastage of fireside waterwalls in fossil-fired boilers has been of concern for many years. It is significant that the introduction of nitrogen oxide (NOx) emission controls with staged burners systems has increased reported waterwall wastage rates to as much as 120 mils (3 mm) per year. Moreover, the reducing environment produced by the low-NOx combustion process is the primary cause of accelerated corrosion rates of waterwall tubes made of carbon and low alloy steels. Improved coatings, such as the MCrAl nanocoatings evaluated here (where M is Fe, Ni, and Co), are needed to reduce/eliminate waterwall damage in subcritical, supercritical, and ultra-supercritical (USC) boilers. The first two tasks of this six-task project-jointly sponsored by EPRI and the U.S. Department of Energy (DE-FC26-07NT43096)-have focused on computational modeling of an advanced MCrAl nanocoating system and evaluation of two nanocrystalline (iron and nickel base) coatings, which will significantly improve the corrosion and erosion performance of tubing used in USC boilers. The computational model results showed that about 40 wt.% is required in Fe based nanocrystalline coatings for long-term durability, leading to a coating composition of Fe-25Cr-40Ni-10 wt.% Al. In addition, the long term thermal exposure test results further showed accelerated inward diffusion of Al from the nanocrystalline coatings into the substrate. In order to enhance the durability of these coatings, it is necessary to develop a diffusion barrier interlayer coating such TiN and/or AlN. The third task 'Process Advanced MCrAl Nanocoating Systems' of the six-task project jointly sponsored by the Electric Power Research Institute, EPRI and the U.S. Department of Energy (DE-FC26-07NT43096)- has focused on processing of advanced nanocrystalline coating systems and development of diffusion barrier ...
Date: April 11, 2011
Creator: Gandy, David W. & Shingledecker, John P.
Partner: UNT Libraries Government Documents Department

Mechanical Properties of Irradiated Plain Carbon and Alloy Steels. A Compilation of the Data in the Literature

Description: Changes in the mechanical properties of plain carbon and alloy steels that are caused by fast neutron irradiation are presented in graphic form. These data were abstracted from classified and unclassified reports published since 1948 by USAEC, AECL, and AERE. Data are included for the following steels: A- 105-55T, A-106, A-200-55T-T22 (Croloy), A-201, A-242, A-301-B, A-302-B, AlSI-C- 1013, AISI-C-1065, SA-70, SA-193,4, SA-212, SA-285, SA-336, SAE-1018, SAE-1020, SAE-1042, SAE-1045, SAE-1095, SAE-1113, SAE-1141, SAE-4130, and SAE-4340. The mechanical properties for which data are reported include hardness, yield strength, tensile strength, total and uniform elongation, reduction of area, fatigue strength, notch factor, creep, impact energy, and transition temperature. (auth)
Date: October 1, 1961
Creator: Schreiber, R. E.
Partner: UNT Libraries Government Documents Department

Pressure reversal study through tensile tests

Description: This paper is a summary of the results from a study of the variables related to pressure reversal and was sponsored by the US Department of Transportation, Office of Pipeline Safety. The circumferential pipe stress, which is the most significant variable in pressure reversal, was examined by using tensile specimens and then relating the results to pressurized pipe. A model is proposed that gives some insight into how pressure reversal can be minimized when a section of pipe is being hydrotested. Twenty tensile specimens from X-42 electric resistance welded (ERW) pipe and twenty specimens from X-52 ERW pipe were tested. Each specimen had a machined flaw. The flaw regions were monitored using strain gages and photoelasticity. These tensile tests represent the first phase of a research effort to examine and understand the variables related to pressure reversal. The second phase of this effort will be with pipe specimens and presently is in progress.
Date: December 31, 1997
Creator: Swinson, W. F.; Battiste, R. L.; Wright, A. L.; Yahr, G. T. & Robertson, J. P.
Partner: UNT Libraries Government Documents Department

Microstructure modeling in weld metal

Description: Since microstructure development in the weld metal region is controlled by various physical processes, there is a need for integrated predictive models based on fundamental principles to describe and predict the effect of these physical processes. These integrated models should be based on various tools available for modeling microstructure development in a wide variety of alloy systems and welding processes. In this paper, the principles, methodology, and future directions of modeling thermochemical reactions in liquid, solidification, and solid state transformations are discussed with some examples for low-alloy steel, stainless steel, and Ni-base superalloy. Thermochemical deoxidation reactions in liquid low-alloy steel lead to oxide inclusion formation. This inclusion formation has been modeled by combining principles of ladle metallurgy and overall transformation kinetics. The model`s comparison with the experimental data and the ongoing work on coupling this inclusion model with the numerical models of heat transfer and fluid flow are discussed. Also, recent advances in theoretical and physical modeling of the solidification process are reviewed with regard to predicting the solidification modes, grain structure development, segregation effects, and nonequilibrium solidification in welds. The effects of solid state phase transformations on microstructure development and various methods of modeling these transformations are reviewed. Successful models, based on diffusion-controlled growth and plate growth theories, on microstructure development in low-alloy steel and stainless steel weld metals are outlined. This paper also addresses the importance of advanced analytical techniques to understand the solid state transformation mechanisms in welds.
Date: December 1995
Creator: David, S. A. & Babu, S. S.
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 microstructure development in weld materials

Description: Microstructure development in the weld metal region is controlled by various physical processes such as thermochemical reactions in liquid, solidification, and solid state transformations. There is a need for fundamental and generalized models that can predict the effect of these physical processes on microstructure development in a wide variety of alloy systems during welding processes. This paper describes certain advances made in the area of modeling the microstructure development in low-alloy steel, stainless steel, and Ni-base superalloy. In addition, this paper describes the importance of advanced analytical techniques for fundamental understanding of phase transformation mechanisms in welds.
Date: September 1, 1996
Creator: David, S.A. & Babu, S.S.
Partner: UNT Libraries Government Documents Department