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Austenite Formation Kinetics During Rapid Heating in a Microalloyed Steel

Description: The model parameters for the normalized 1054V1 material were compared to parameters previously generated for 1026 steel, and the transformation behavior was relatively consistent. Validation of the model predictions by heating into the austenite plus undissolved ferrite phase field and rapidly quenching resulted in reasonable predictions when compared to the measured volume fractions from optical metallography. The hot rolled 1054V1 material, which had a much coarser grain size and a non-equilibrium volume fraction of pearlite, had significantly different model parameters and the on heating transformation behavior of this material was less predictable with the established model. The differences in behavior is consistent with conventional wisdom that normalized micro-structure produce a more consistent response to processing, and it reinforces the need for additional work in this area.
Date: September 7, 1999
Creator: Burnett, M. E.; Dykhuzien, Ronald C.; Kelley, J. Bruce; Puskar, Joseph D. & Robino, Charles V.
Partner: UNT Libraries Government Documents Department

Influence of carbon partitioning kinetics on final Austenite fraction during quenching and partitioning

Description: The quenching and partitioning (Q&P) process is a two-stage heat-treatment procedure proposed for producing steel microstructures that contain carbon-enriched retained austenite. In Q&P processing, austenite stabilization is accomplished by carbon partitioning from supersaturated martensite. A quench temperature selection methodology was developed to predict an optimum process quench temperature; extension of this methodology to include carbon partitioning kinetics is developed here. Final austenite fraction is less sensitive to quench temperature than previously predicted, in agreement with experimental results.
Date: January 1, 2009
Creator: Clarke, Amy J; Speer, John G; Matlock, David K; Rizzo, F C; Edmonds, David V & Santofimia, Maria J
Partner: UNT Libraries Government Documents Department

3D analysis of bainite morphologies and kinetics in alloy steels

Description: Serial sectioning and 3D reconstruction of austenite decomposition products were undertaken in bay-forming ternary steels to better understand their true morphologies in the bay region of their TTT diagrams. Jagged growth interfaces are revealed in allotriomorphic bainite formed at the bay in Fe-0.24C-4M0, contrasting with the idealized geometries often assumed when formulating growth models. This also has implications for experimental thickening kinetics measurments. Examination of the so-called 'degenerate' ferrite formed below the bay in Fe-Ox-6.3 W reveals that it is not degenerate at all, but rather has a Widmanstatten rod morphology which gives the appearance of degeneracy due to the multiplicity of ways that they can intersect a randomly-oriented plane of polish. Furthermore, these rods are grouped in packets posessing a common elongation direction, highlighting the crystallographic nature of their formation. The impact of these findings on the understanding of austenite decomposition in bayforming steels will be discussed.
Date: January 1, 2002
Creator: Hackenberg, R. E. (Robert E.); Nordstrom, D. P. (Dale P.) & Shiflet, G. J. (Gary J.)
Partner: UNT Libraries Government Documents Department

M-25, Butt Welds in Process Piping

Description: Metal-arc and inert-gas shielded tungsten-arc processes were compared for circumferential butt welding of austenitic stainless steel process pipe. Inert-gas tungsten-arc welding was superior to other techniques. (C.J.G.)
Date: July 10, 1958
Creator: Litman, A. P.
Partner: UNT Libraries Government Documents Department

Reducing the Variability of HSLA Sheet Steels (TRP 9807)

Description: The sensitivity of the yield strength of a 70 ksi HSLA steel to changes in processing variables was investigated using a laboratory hot-rolling mill. Along with a detailed examination of the hot-rolled microstructures, auxiliary experiments were conducted to determine how the decomposition of the austenite phase and the occurrence of ultra-fine precipitate formation could account for the yield strength variability. A set of guidelines was recommended for the reduction of the yield strength variability.
Date: March 12, 2004
Creator: DeArdo, Anthony J.
Partner: UNT Libraries Government Documents Department

Reports of the measurement of elastic properties of 51XX series steels for the heat treatment distortion project

Description: We have measured the temperature dependence of the elastic constants of the 51XX series steels [gear steels] for a range of phases. At RT the normalized steel (pearlite) has the highest value of the moduli, the bainite phase the next highest, and martensite the lowest. Extrapolation of the austenite suggests that at RT austenite has lower moduli than martensite. For all the grades and phases of steels examined, the behavior of the elastic constants is similar: a curve could be drawn for each of the moduli from all the phases and all the grades would not deviate by more than {+-}4%. The normalized phase (100% pearlite in 5180) is stable up to 900 C. Bainite is stable up to 500 C. Martensite starts to change above 150 C as it tempers or strain relieves; once this is complete, the martensite moduli increase to similar values to bainite. Extrapolations are discussed. Behavior in lower carbon steels (5140, 5120) should conform to above; there is no explanation for the anomalous behavior of the quenched 5120 steel.
Date: September 1, 1997
Creator: Darling, T.; Migliori, A.; Armstrong, P.E.; Vaidya, R.; Scherer, C. & Lowe, T.
Partner: UNT Libraries Government Documents Department

Transformation kinetics in controlled-power and controlled-temperature cycle testing

Description: On-heating transformation kinetics were investigated for several steels by using a Gleeble capable of programmable power input as well as programmable temperature cycling. Transformation kinetics determined in both modes are reported. The temperature cycles are significantly different between the two modes due to the latent heat associated with the phase transformations. Both diffusion rates and transformation driving force increase with temperature above the eutectoid temperature, therefore the latent heat can potentially have a significant impact on the transformation kinetics. Experiments with plain carbon steels illustrate that the latent heat of austenite formation causes an appreciable temperature arrest during transformation, and the dilatation response is similarly altered. A kinetic transformation model, based on the decomposition of pearlite and the diffusional growth of austenite, reproduced the transient dilatation data obtained from both control modes reasonably well using the same kinetic parameter values.
Date: June 1, 1998
Creator: Robino, C.V.; Knorovsky, G.; Dykhuizen, R.C.; MacCallum, D.O. & Damkroger, B.K.
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

A model of shape memory materials with hierarchical twinning: Statics and dynamics

Description: We consider a model of shape memory material in which hierarchical twinning near the habit plane (austenite-martensite interface) is a new and crucial ingredient. The model includes (1) a triple-well potential ({phi} model) in local shear strain, (2) strain gradient terms up to second order in strain and fourth order in gradient, and (3) all symmetry allowed compositional fluctuation induced strain gradient terms. The last term favors hierarchy which enables communication between macroscopic (cm) and microscopic ({Angstrom}) regions essential for shape memory. Hierarchy also stabilizes between formation (critical pattern of twins). External stress or pressure (pattern) modulates the spacing of domain walls. Therefore the ``pattern`` is encoded in the modulated hierarchical variation of the depth and width of the twins. This hierarchy of length scales provides a hierarchy of time scales and thus the possibility of non-exponential decay. The four processes of the complete shape memory cycle -- write, record, erase and recall -- are explained within this model. Preliminary results based on 2D Langevin dynamics are shown for tweed and hierarchy formation.
Date: July 1, 1995
Creator: Saxena, A.; Bishop, A.R.; Shenoy, S.R.; Wu, Y. & Lookman, T.
Partner: UNT Libraries Government Documents Department

Texture evolution in thin-sheets on AISI 301 metastable stainless steel under dynamic loading

Description: The evolution of texture in thin sheets of metastable austenitic stainless steel AISI 301 is affected by external conditions such as loading rate and temperature, by inhomogeneous deformation phenomena such as twinning and shear band formation, and by the concurent strain induced phase transformation of the retained austenitc ({gamma}) into martensite ({alpha}). The present paper describes texture measurements on different gauges of AISI 301 prior and after uniaxial stretching under different conditions.
Date: May 8, 1995
Creator: Kim, K.Y.; Kozaczek, K.; Kulkarni, S.M.; Bastias, P.C. & Hahn, G.T.
Partner: UNT Libraries Government Documents Department

ON THE EFFECT OF PRIOR AUSTENITE GRAIN SIZE ON NEAR-THRESHOLD FATIGUE CRACK GROWTH

Description: It is generally accepted that the fatigue or endurance strength of planar slip materials, such as steel and brass, is increased by refining the grain size, whereas in wavy slip materials, such as pure copper and pure aluminum, the fatigue strength is unaffected. However, there is little similar evidence of an effect of grain size on fatigue crack propagation. In both wavy and planar slip metals, growth rates appear independent of grain size. For example, variations in grain size from 10 to 200{micro}m in 70/30 brass (6), and from 45 to 480{micro}m in austenitic stainless steel produce no measurable change in fatigue crack propagation rates over a range of growth rates from 10{sup -5} to 10{sup -2} mm/cycle. Recently, however, there have been indications in the literature that grain size may indeed influence crack propagation behavior at growth rates less than 10{sup -5} to 10{sup -6} mm/cycle approaching the threshold for crack propagation, {Delta}K{sub 0}. Robinson and Beevers report an order of magnitude decrease in near-threshold growth rates in {alpha}-titanium after coarsening the grain size from 20 to 200{micro}m. Similar effects have been seen in Ti-6Al-4V. Furthermore, Masounave and BaIlon have observed a marked increase in threshold {Delta}K{sub 0} values in a range of low strength steels by increasing ferrite grain size. In all the above studies however, no attempt was made to control strength; and the effect of coarsening the grain size may well have been caused by a concurrent decrease in material strength, particularly since it is known that, in steels at least, near-threshold fatigue crack growth is markedly decreased by reducing the yield strength. A comparison at constant yield strength between coarse and fine-grained materials has been made in ultra-high strength steel (300-M) where it was found that, on enlarging the (prior austenite) grain size from 20 ...
Date: January 1, 1977
Creator: Carlson, M.F. & Ritchie, R.O.
Partner: UNT Libraries Government Documents Department

HYDROGEN EFFECTS ON STRAIN-INDUCED MARTENSITE FORMATION IN TYPE 304L STAINLESS STEEL

Description: Unstable austenitic stainless steels undergo a strain-induced martensite transformation. The effect of hydrogen on this transformation is not well understood. Some researchers believe that hydrogen makes the transformation to martensite more difficult because hydrogen is an austenite stabilizer. Others believe that hydrogen has little or no effect at all on the transformation and claim that the transformation is simply a function of strain and temperature. Still other researchers believe that hydrogen should increase the ability of the metal to transform due to hydrogen-enhanced dislocation mobility and slip planarity. While the role of hydrogen on the martensite transformation is still debated, it has been experimentally verified that this transformation does occur in hydrogen-charged materials. What is the effect of strain-induced martensite on hydrogen embrittlement? Martensite near crack-tips or other highly strained regions could provide much higher hydrogen diffusivity and allow for quicker hydrogen concentration. Martensite may be more intrinsically brittle than austenite and has been shown to be severely embrittled by hydrogen. However, it does not appear to be a necessary condition for embrittlement since Type 21-6-9 stainless steel is more stable than Type 304L stainless steel but susceptible to hydrogen embrittlement. In this study, the effect of hydrogen on strain-induced martensite formation in Type 304L stainless steel was investigated by monitoring the formation of martensite during tensile tests of as-received and hydrogen-charged samples and metallographically examining specimens from interrupted tensile tests after increasing levels of strain. The effect of hydrogen on the fracture mechanisms was also studied by examining the fracture features of as-received and hydrogen-charged specimens and relating them to the stress-strain behavior.
Date: December 11, 2008
Creator: Morgan, M & Ps Lam, P
Partner: UNT Libraries Government Documents Department

Advanced Integration in Multi-Scale Mechanics and Welding Process Simulation in Weld Integrity Assessment

Description: In this project, mathematical models that predict the microstructure in pipeline steel welds were to be developed. These models were to be integrated with thermal models that describe the time-temperature history in the weld as a function of location in order to derive the spatial variation of microstructure in the weld. The microstructure predictions were also to be combined with microstructure-hardness relations, based on the additivity principle, to determine the spatial variation of hardness in the weld. EMC2 also developed microstructural models based on empirical relationships. ORNL was to pursue the development of more fundamental, theoretically based models. ORNL applied a previously developed model for inclusion formation to predict the extent and nature of inclusions that form during weld cooling from the liquid. This inclusion model was directly integrated with computational thermodynamics capability. A convenient user interface was developed for both the inclusion model and the thermodynamic phase-stability calculations. The microstructure model was based on the simultaneous transformation theory analysis as applied to the transformation of austenite to various ferrite constituents during weld cooling. The model available on the Materials Algorithm Project web site was used. Extensive modification of this model was required to correct problems with compilation and calculations as a function of the computational platform (Unix, Linux, Windows, etc.) that was used. The user interface for the inclusion model and thermodynamic phase-stability calculations was delivered to EMC2 along with the modified and correct microstructure model. Evaluation of the theoretically based model will be carried out and the predictions will be compared with experimental results as well as predictions based on the empirical models developed by EMC2.
Date: January 30, 2008
Creator: Vitek, J.M.; Wilkowski, G.M.; Brust, F.W. & Babu, S.
Partner: UNT Libraries Government Documents Department

Direct Observations of Sigma Phase Growth and Dissolution in 2205 Duplex Stainless Steel

Description: The formation and growth of sigma ({sigma}) phase in a 2205 duplex stainless steel is monitored during an 850 C isothermal heat treatment using an in situ synchrotron x-ray diffraction technique. At this temperature, {sigma} phase is first observed within approximately 40 seconds of the start of the isothermal heat treatment and grows rapidly over the course of the 3600 second heat treatment to a volume fraction of approximately 13%. A simultaneous increase in the austenite ({gamma}) volume fraction and a decrease in the ferrite ({delta}) volume fraction are observed. The {sigma} phase formed at this temperature is rapidly dissolved within approximately 200 seconds when the temperature is increased to 1000 C. Accompanying this rapid dissolution of the {sigma} phase, the {delta} and {gamma} volume fractions both approach the balanced (50/50) level observed in the as-received material.
Date: June 14, 2005
Creator: Palmer, T; Elmer, J; Babu, S & Specht, E
Partner: UNT Libraries Government Documents Department

The Zirflex Process

Description: tive dissolution of zirconium or Zircaloy fuel cladding. The process involves the dissolution of the cladding material in solutions of ammonium fluoride alone or in mixture with amonium nitrate. Mixtures of amonium fluoride and amonium nitrate are preferred since they result in very little evolution of hydrogen during the is that these solutions attack austenitic stainless steels only slowly, in sharp contrast to the media (e.g., hydrofluoric acid or hydrofluoric-nitric acid mixtures) generng 6 M NH/sub 4/F, the rate of pentration of Zircaloy-2 is nearly 100 mils/hr, while that of typical austentic stainless steels is only about 0.5 mil/month. (auth)
Date: October 31, 1958
Creator: Swanson, J. L.
Partner: UNT Libraries Government Documents Department

Investigation of Thermal-Stress-Fatigue Behavior of Stainless Steels. Quarterly Progress Report No. 8

Description: Thermal-stress-fatigue (TSF) testing of 304 and 304-L austenitic stainiess steels was completed. The testing of ferritic steel (ASTM Type A302, Grade B) and of martensitic stainless steel (Type 403) was 50% completed. TSF and conventional strain-cycling fatigue (SCF) were performed on A302B and 403 steels. A new graphical technique was developed which simplifies the work required to obtain plastic strain range, the variable found to be entirely independent in TSF. The method allows greater accuracy in obtaining this parameter. (auth)
Date: January 1, 1963
Creator: Horton, K.E .
Partner: UNT Libraries Government Documents Department

Solidification Diagnostics for Joining and Microstructural Simulations

Description: Solidification is an important aspect of welding, brazing, soldering, LENS fabrication, and casting. The current trend toward utilizing large-scale process simulations and materials response models for simulation-based engineering is driving the development of new modeling techniques. However, the effective utilization of these models is, in many cases, limited by a lack of fundamental understanding of the physical processes and interactions involved. In addition, experimental validation of model predictions is required. We have developed new and expanded experimental techniques, particularly those needed for in-situ measurement of the morphological and kinetic features of the solidification process. The new high-speed, high-resolution video techniques and data extraction methods developed in this work have been used to identify several unexpected features of the solidification process, including the observation that the solidification front is often far more dynamic than previously thought. In order to demonstrate the utility of the video techniques, correlations have been made between the in-situ observations and the final solidification microstructure. Experimental methods for determination of the solidification velocity in highly dynamic pulsed laser welds have been developed, implemented, and used to validate and refine laser welding models. Using post solidification metallographic techniques, we have discovered a previously unreported orientation relationship between ferrite and austenite in the Fe-Cr-Ni alloy system, and have characterized the conditions under which this new relationship develops. Taken together, the work has expanded both our understanding of, and our ability to characterize, solidification phenomena in complex alloy systems and processes.
Date: January 1, 2003
Creator: ROBINO, CHARLES V.; HALL, AARON C.; BROOKS, JOHN ALBERT; HEADLEY, THOMAS J. & ROACH, R. ALLEN
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

Pulsed laser surface hardening of ferrous alloys.

Description: A high power pulsed Nd:YAG laser and special optics were used to produce surface hardening on 1045 steel and gray cast iron by varying the process parameters. Unlike CO{sub 2} lasers, where absorptive coatings are required, the higher absorptivity of ferrous alloys at the Nd:YAG laser wavelength eliminates the necessity of applying a coating before processing. Metallurgical analysis of the treated tracks showed that very fine and hard martensitic microstructure (1045 steel) or inhomogeneous martensite (gray cast iron) were obtained without surface melting, giving maximum hardness of HRC 61 and HRC 40 for 1045 steel and gray cast iron respectively. The corresponding maximum case depths for both alloys at the above hardness are 0.6 mm. Gray cast iron was more difficult to harden without surface melting because of its lower melting temperature and a significantly longer time-at-temperature required to diffuse carbon atoms from the graphite flakes into the austenite matrix during laser heating. The thermal distortion was characterized in term of flatness changes after surface hardening.
Date: September 30, 1999
Creator: Xu, Z.; Reed, C. B.; Leong, K. H. & Hunter, B. V.
Partner: UNT Libraries Government Documents Department

Residual stresses and retained austenite distribution and evolution in SAE 52100 steel under rolling contact loading

Description: Residual stresses are introduced and modified during manufacturing and also by normal use. In this paper the changes in magnitude and distribution of residual stresses, attending the strain induced transformation of retained austenite are examined. Tests were conducted on SAE 52100 bearing steel with different amounts of retained austenite in a 5-ball-rod rolling contact fatigue machine. The tests were accelerated by applying well-controlled micro- indentations on the wear track and using rough balls. The magnitude and distribution of residual stresses and retained austenite were measured using x-ray diffraction techniques. The contribution of the residual stresses and amount of retained austenite to the rolling contact fatigue life is analyzed.
Date: July 1, 1996
Creator: Dommarco, R.C.; Kozaczek, K.J. & Hahn, G.T.
Partner: UNT Libraries Government Documents Department