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1.
M. J. Perricone J. N. Dupont T. D. Anderson C. V. Robino J. R. Michael 《Metallurgical and Materials Transactions A》2011,42(3):700-716
A series of 31 Mo-bearing stainless steel compositions with Mo contents ranging from 0 to 10 wt pct and exhibiting primary
δ-ferrite solidification were analyzed over a range of laser welding conditions to evaluate the effect of composition and cooling
rate on the solid-state transformation to γ-austenite. Alloys exhibiting this microstructural development sequence are of particular interest to the welding community
because of their reduced susceptibility to solidification cracking and the potential reduction of microsegregation (which
can affect corrosion resistance), all while harnessing the high toughness of γ-austenite. Alloys were created using the arc button melting process, and laser welds were prepared on each alloy at constant
power and travel speeds ranging from 4.2 to 42 mm/s. The cooling rates of these processes were estimated to range from 10 K
(°C)/s for arc buttons to 105 K (°C)/s for the fastest laser welds. No shift in solidification mode from primary δ-ferrite to primary γ-austenite was observed in the range of compositions or welding conditions studied. Metastable microstructural features were
observed in many laser weld fusion zones, as well as a massive transformation from δ-ferrite to γ-austenite. Evidence of epitaxial massive growth without nucleation was also found when intercellular γ-austenite was already present from a solidification reaction. The resulting single-phase γ-austenite in both cases exhibited a homogenous distribution of Mo, Cr, Ni, and Fe at nominal levels. 相似文献
2.
In situ dynamic observation of the progress of a peritectic reaction and transformation of Fe-(0.14 pct C)- and Fe-(0.42 pct C)-peritectic
Fe-C alloys has been successfully made with a combination of a confocal scanning laser microscope and an infrared image furnace.
The peritectic reaction is characterized by the formation of the γ-austenite phase at the junction of the liquid and the grain boundary of δ-ferrite crystals and subsequent propagation of the three-phase point, liquid/γ/δ, along the liquid/δ boundary, whereas the peritectic transformation occurs by the thickening of the intervening γ toward both the liquid side and the δ side. The rates of the peritectic reaction for the two peritectic alloys are found to be much faster than the rate that would
be controlled by carbon diffusion, suggesting that either massive transformation to γ or solidification as γ controls the rate. This is also the case for the Fe-0.14%C transformation in the hypoperitectic alloy. However, the rate
of the peritectic transformation in the Fe-0.42%C alloy is determined by carbon diffusion.
This article is based on a presentation made in the “Geoffrey Belton Memorial Symposium,” held in January 2000, in Sydney,
Australia, under the joint sponsorship of ISS and TMS. 相似文献
3.
Macro-microscopic models have been developed to describe the macrosegregation behavior associated with the peritectic reaction
of low carbon steel. The macrosegregation model has been established on the basis of previously published work and experimental
data. A microscopic model of a three-phase reaction L+δ→γ has been modeled by using Fredriksson’s approach. Four horizontal and unidirectional solidified experimental groups simulating
continuous casting have been performed with a low carbon steel containing 0.13 wt pct carbon. The extent of macrosegregation
of carbon was determined by wet chemical analysis of millings. It is confirmed, by comparing calculated results with experimental
results, that this model successfully predicts the occurrence of macrosegregation. The results indicate that a peritectic
reaction which is associated with a high cooling rate generates high thermal contraction and a high tensile strain rate at
the peritectic temperature. Therefore, the macrosegregation, particularly at the ingot surface, is very sensitive to the cooling
rate, where extremely high positive segregation was observed in the case of a high cooling rate. However, in the case of slow
cooling rate, negative segregation was noted. The mechanism of macrosegregation with peritectic reaction is discussed in detail. 相似文献
4.
T.D. ANDERSON J.N. DuPONT M.J. PERRICONE A.R. MARDER 《Metallurgical and Materials Transactions A》2007,38(1):86-99
The good corrosion resistance of superaustenitic stainless steel (SASS) alloys has been shown to be a direct consequence of
high concentrations of Mo, which can have a significant effect on the microstructural development of welds in these alloys.
In this research, the microstructural development of welds in the Fe-Ni-Cr-Mo system was analyzed over a wide variety of Cr/Ni
ratios and Mo contents. The system was first simulated by construction of multicomponent phase diagrams using the CALPHAD
technique. Data from vertical sections of these diagrams are presented over a wide compositional range to produce diagrams
that can be used as a guide to understand the influence of composition on microstructural development. A large number of experimental
alloys were then prepared via arc-button melting for comparison with the diagrams. Each alloy was characterized using various microscopy techniques. The
expected δ-ferrite and γ-austenite phases were accompanied by martensite at low Cr/Ni ratios and by σ phase at high Mo contents. A total of 20 possible
phase transformation sequences are proposed, resulting in various amounts and morphologies of the γ, δ, σ, and martensite phases. The results were used to construct a map of expected phase transformation sequence and resultant
microstructure as a function of composition. The results of this work provide a working guideline for future base metal and
filler metal development of this class of materials.
An erratum to this article can be found at 相似文献
5.
Steel solidifies either by a primary precipitation of δ-Fe or by a primary precipitation of γ-Fe. In the former case the steel
can either go through a peritectic reaction or a solid state transformation to form y-Fe during cooling. The influence of
the rate of solidification and/or the transformation sequence on the sulfide precipitation in steels was studied in unidirectionally
solidified Fe-Ni-S and Fe-Ni-Mn-S alloys. Nickel was used to govern the solidification sequence. It was shown that the solid
state transformation could give rise to iron sulfide films according to a metatectic reaction. It was also shown that the
peritectic reaction favored the formation of iron sulfide films. These films solidified at a very low temperature. During
cooling the films contracted and small sulfide particles were formed. If the alloy contained manganese the composition of
the films was changed during cooling from nearly pure iron sulfide to nearly pure manganese sulfide due to diffusion of manganese
from the matrix. 相似文献
6.
John W. Elmer Joe Wong Thorsten Ressler 《Metallurgical and Materials Transactions A》2001,32(5):1175-1187
Phase transformations that occur in the heat-affected zone (HAZ) of gas tungsten arc welds in AISI 1005 carbon-manganese steel
were investigated using spatially resolved X-ray diffraction (SRXRD) at the Stanford Synchrotron Radiation Laboratory. In situ SRXRD experiments were performed to probe the phases present in the HAZ during welding of cylindrical steel bars. These real-time
observations of the phases present in the HAZ were used to construct a phase transformation map that identifies five principal
phase regions between the liquid weld pool and the unaffected base metal: (1) α-ferrite that is undergoing annealing, recrystallization, and/or grain growth at subcritical temperatures, (2) partially transformed
α-ferrite co-existing with γ-austenite at intercritical temperatures, (3) single-phase γ-austenite at austenitizing temperatures, (4) δ-ferrite at temperatures near the liquidus temperature, and (5) back transformed α-ferrite co-existing with residual austenite at subcritical temperatures behind the weld. The SRXRD experimental results were
combined with a heat flow model of the weld to investigate transformation kinetics under both positive and negative temperature
gradients in the HAZ. Results show that the transformation from ferrite to austenite on heating requires 3 seconds and 158°C
of superheat to attain completion under a heating rate of 102°C/s. The reverse transformation from austenite to ferrite on
cooling was shown to require 3.3 seconds at a cooling rate of 45 °C/s to transform the majority of the austenite back to ferrite;
however, some residual austenite was observed in the microstructure as far as 17 mm behind the weld. 相似文献
7.
8.
A. Kumar S. Mishra T. Debroy J. W. Elmer 《Metallurgical and Materials Transactions A》2005,36(1):15-22
A nonisothermal Johnson-Mehl-Avarami (JMA) equation with optimized JMA parameters is proposed to represent the kinetics of
transformation of α-ferrite to γ-austenite during heating of 1005 steel. The procedure used to estimate the JMA parameters involved a combination of numerical
heat-transfer and fluid-flow calculations, the JMA equation for nucleation and growth for nonisothermal systems, and a genetic
algorithm (GA) based optimization tool that used a limited volume of experimental kinetic data. The experimental data used
in the calculations consisted of phase fraction of γ-austenite measured at several different monitoring locations in the heat-affected zone (HAZ) of a gas tungsten arc (GTA)
weld in 1005 steel. These data were obtained by an in-situ spatially resolved X-ray diffraction (SRXRD) technique using synchrotron radiation during welding. The thermal cycles necessary
for the calculations were determined for each monitoring location from a well-tested three-dimensional heat-transfer and fluid-flow
model. A parent centric recombination (PCX) based generalized generation gap (G3) GA was used to obtain the optimized values
of the JMA parameters, i.e., the activation energy, pre-exponential factor, and exponent in the nonisothermal JMA equation. The GA based determination
of all three JMA equation parameters resulted in better agreement between the calculated and the experimentally determined
austenite phase fractions than was previously achieved. 相似文献
9.
10.
Xiaolei Xu Liang Wang Zhiwei Yu Jianbing Qiang Zukun Hei 《Metallurgical and Materials Transactions A》2000,31(4):1193-1199
The microstructure of the low-temperature plasma-nitrided layer on AISI 304 austenitic stainless steel was studied by transmission
electron microscopy (TEM). The results show that the surface of the layer consists of a supersaturated solid solution (γ′N) based on the γ′-Fe4N phase whose electron diffraction pattern (EDP) has a strong diffuse scattering effect resulting from supersaturating nitrogen
(above 20 at. pct) and 〈110〉 streaks arising from matrix elastic strain due to the formation of paired or clustered Cr-N.
The latter is due to the N above the 20 at. pct γ′-Fe4N-phase value and leads to a lattice parameter that is greater than that of the γ′-Fe4N phase. The subsurface of the layer is composed of a supersaturated solid solution based on γ-austenite, which is an expanded austenite, γ
N. Its morphology shows the basketweave or “tweedlike” contrast consisting of so-called stacking fault precipitates having
twin relationships with the matrix whose EDP shows diffuse scattering streaks with certain directions. The ε martensite transformation was observed in the subsurface of the layer. The increase in stacking faults compared with the
original stainless steel and formation of ε martensite in the subsurface of the layer indicate that nitrogen lowers the stacking fault energy of austenite. 相似文献
11.
Dominic Phelan Mark Reid Rian Dippenaar 《Metallurgical and Materials Transactions A》2006,37(12):985-994
An experimental study has been conducted into the role of cooling rate on the kinetics of the peritectic phase transformation
in a Fe−C alloy. The interfacial growth velocities of the peritectic phase transformation were measured in situ for cooling rates of 100, 50, and 10 K/min. In-situ observations were obtained using high-temperature laser scanning confocal microscopy (HTLSCM) in a concentric solidification
configuration. The experimentally measured interface velocities of the liquid/austenite (L/γ) and austenite/delta-ferrite
(γ/δ) interphase boundaries were observed to increase with higher cooling rates. A unique finding of this study was that as
the cooling rate increased there was a transition point where the L/γ interface propagated at a higher velocity than the γ/δ
interface, contrary to the findings of previous researchers. Phase field modeling was conducted using a commercial multicomponent,
multiphase package. Good correlation was obtained between model predictions and experimental observations in absolute values
of interface velocities and the effect of cooling rate. Analysis of the simulated microsegregation in front of the L/γ and
γ/δ interfaces as a function of cooling rate revealed the importance of solute pileup. This microsegregation plays a pivotal
role in the propagation of interfaces; thus, earlier modeling work in which complete diffusion in the liquid phase was assumed
cannot fully describe the rate of propagation of the L/γ and δ/γ interfaces during the course of the peritectic transformation. 相似文献
12.
Kinetics of the peritectic phase transformation: In-situ measurements and phase field modeling 总被引:1,自引:0,他引:1
Dominic Phelan Mark Reid Rian Dippenaar 《Metallurgical and Materials Transactions A》2006,37(3):985-994
An experimental study has been conducted into the role of cooling rate on the kinetics of the peritectic phase transformation
in a Fe-C alloy. The interfacial growth velocities of the peritectic phase transformation were measured in situ for cooling rates of 100, 50, and 10 K/min. In-situ observations were obtained using high-temperature laser scanning confocal microscopy (HTLSCM) in a concentric solidification
configuration. The experimentally measured interface velocities of the liquid/austenite (L/γ) and austenite/delta-ferrite
(γ/δ) interphase boundaries were observed to increase with higher cooling rates. A unique finding of this study was that as
the cooling rate increased, there was a transition point where the L/γ interface propagated at a higher velocity than the
γ/δ interface, contrary to the findings of previous researchers. Phase field modeling was conducted using a commercial multicomponent,
multiphase package. Good correlation was obtained between model predictions and experimental observations in absolute values
of interface velocities and the effect of cooling rate. Analysis of the simulated microsegregation in front of the L/γ and
γ/δ interfaces as a function of cooling rate revealed the importance of solute pileup. This microsegregation plays a pivotal
role in the propagation of interfaces; thus, earlier modeling work in which complete diffusion in the liquid phase was assumed
cannot fully describe the rate of propagation of the L/γ and δ/γ interfaces during the course of the peritectic transformation. 相似文献
13.
Dominic Phelan Mark Reid Rian Dippenaar 《Metallurgical and Materials Transactions A》2006,37(13):985-994
An experimental study has been conducted into the role of cooling rate on the kinetics of the peritectic phase transformation
in a Fe−C alloy. The interfacial growth velocities of the peritectic phase transformation were measuredin situ for cooling rates of 100, 50, and 10 K/min.In-situ observations were obtained using high-temperature laser scanning confocal microscopy (HTLSCM) in a concentric solidification
configuration. The experimentally measured interface velocities of the liquid/austenite (L/γ) and austenite/delta-ferrite
(γ/δ) interphase boundaries were observed to increase with higher cooling rates. A unique finding of this study was that as
the cooling rate increased there was a transition point where the L/γ interface propagated at a higher velocity than the γ/δ
interface, contrary to the findings of previous researchers. Phase field modeling was conducted using a commercial multicomponent,
multiphase package. Good correlation was obtained between model predictions and experimental observations in absolute values
of interface velocities and the effect of cooling rate. Analysis of the simulated microsegregation in front of the L/γ and
γ/δ interfaces as a function of cooling rate revealed the importance of solute pileup. This microsegregation plays a pivotal
role in the propagation of interfaces; thus, earlier modeling work in which complete diffusion in the liquid phase was assumed
cannot fully describe the rate of propagation of the L/γ and δ/γ interfaces during the course of the peritectic transformation. 相似文献
14.
Room temperature tension-tension fatigue tests were performed on two lamellar γ/γ′-δ alloys, one with 0 pct Cr and one with
6 pct Cr. The 6 pct Cr alloy was solidified at 3 cmJh while the 0 pct Cr alloy was solidified at 3 cm/h and 5.7 cm/h. Fatigue
testing was done on both alloys in the as-directionally solidified condition and on the 0 pct Cr alloy after heat treatment.
Increasing the growth speed of the 0 pct Cr alloy increased the fatigue life of the material at stresses above the 107 cycle fatigue limit. Partial solution treating and aging of the 0 pct Cr alloy,R = 3 cm/h, increased the fatigue life relative to the as-directionally solidified material at high stresses, to the same extent
as increasing the growth speed. Full solution treatment and aging of the 0 pct Cr alloy,R = 5.7 cm/ h, caused a reduction in the fatigue life relative to the as-directionally solidified material. Fatigue cracking
tended to be faceted in the 6 pct Cr alloy as opposed to the more ductile failure of the 0 pct Cr alloy. Microstructural perfection,
grain size and shape, interlamellar spacing, longitudinal cracking, and longitudinal and transverse ductility all are believed
to have influenced the fatigue resistance of the alloys. 相似文献
15.
Solidification of an alloy 625 weld overlay 总被引:1,自引:0,他引:1
J. N. DuPont 《Metallurgical and Materials Transactions A》1996,27(11):3612-3620
The solidification behavior (microsegregation, secondary phase formation, and solidification temperature range) of an Alloy
625 weld overlay deposited on 2.25Cr - 1Mo steel by gas metal arc welding was investigated by light and electron optical microscopy,
electron microprobe, and differential thermal analysis techniques. The overlay deposit was found to terminate solidification
at ≈ 1216 °C by aγ/Laves eutectic-type reaction. The Laves phase was highly enriched in Nb, Mo, and Si. The solidification reaction and microsegregation
potential of major alloying elements in the overlay deposit are compared to other Nb-bearing Ni base alloys and found to be
very similar to those for Alloy 718. Solidification cracks observed in the overlay were attributed to the wide solidification
temperature range (≈170 °C) and formation of interdendritic (γ+Laves) constituent. Reasonable agreement is obtained between the calculated and measured volume percent (γ+Laves) constituent with the Scheil equation by treating the overlay system as a simpleγ-Nb “binary” and using an experimentally determinedk
Nb value from electron microprobe data. 相似文献
16.
Kinetics of austenite-ferrite and austenite-pearlite transformations in a 1025 carbon steel 总被引:4,自引:0,他引:4
E. B. Hawbolt B. Chau J. K. Brimacombe 《Metallurgical and Materials Transactions A》1985,16(4):565-578
Isothermal and continuous-cooling transformation kinetics have been measured dilatometrically for the γ → α+ γ′ and γ′→ P reactions in a 1025 steel. The isothermal transformation of austenite for each reaction was found to fit the Avrami equation
after the fraction transformed was normalized to unity at the completion of the reaction and a transformation-start time was
determined. The transformation kinetics under isothermal conditions therefore were characterized in terms of then andb parameters from the Avrami equation together with the transformation-start times. The parametern was found to be independent of temperature over the range studied (645 to 760 ‡C) and to have values of 0.99 and 1.33 for
the ferrite and pearlite reactions, respectively. This indicates that the nucleation condition is essentially constant and
site saturation occurs early in the transformation process. The continuous-cooling experiments were conducted at cooling rates
of 2 to 150 ‡C per second to determine the transformation-start times for the ferrite and pearlite reactions and the completion
time for transformation to pearlite under CCT conditions. Both reactions were found to obey the Additivity Principle for continuous
cooling provided that the incubation (pre-transformation) period was not included in the transformation time. The isothermal
transformation data and CCT transformation-start times have been incorporated in a mathematical model to predict continuous-cooling
transformation kinetics that agree closely with measurements made at three cooling rates. 相似文献
17.
Wei-di Cao R. L. Kennedy A. Choudhury 《Metallurgical and Materials Transactions A》1993,24(9):1897-1907
Increased interest has been paid to grain boundary segregation in alloy K-500 due to severe intergranular cracking recently
observed in forged bars. However, little systematic study of this segregation has been performed so far. A detailed auger
electron spectroscopy (AES) study of grain boundary segregation in alloy K-500 has been carried out as a function of alloy
chemistry. To determine C segregation, the C and O contamination rates in a vacuum chamber were measured and the necessary
condition for C grain boundary segregation determination was established. It has been found that severe C, Al, and Cu segregation
to grain boundaries occurred and depended on alloy chemistry. High bulk Ni and low bulk Al promoted C and Al grain boundary
segregation, and low bulk Ni and high bulk Al significantly enhanced Cu segregation to grain boundaries. The depth profiles
of intergranularly segregated elements also showed different features for high and low Ni content alloys. In high Ni alloys,
C and Al levels dropped continuously as a function of distance from the grain boundaries but the Cu level dropped only slightly.
In low Ni alloys, the Al and C levels rose from relatively low grain boundary levels to a peak at a certain distance from
the grain boundary where the high grain boundary Cu level dramatically dropped. Transmission electron microscope (TEM) observation
revealed a grain boundaryγ′-depleted zone followed by a region with coarser and denserγ′ particles in low Ni and high Al alloys but quite uniformly distributedγ′ particles with no depleted zone in high Ni and low Al alloys. These can be explained by the observed segregation behavior.
The occurrence of Cu segregation is explained according to available theories about surface segregation in binary Ni-Cu alloys,
and the segregation of C and Al to grain boundaries is suggested to be probably due to their interaction with Ni and Cu. 相似文献
18.
The phase relationships between the liquid phase and the primary solid phases were investigated in the iron-rich corner of
the Fe-Cr-Ni system as part of a larger study of the Fe-Cr-Ni-C system. The investigation consisted of measurements and modeling
of tie-lines and the liquidus surfaces of the liquid-delta (bcc) and liquid-gamma (fcc) equilibria and the peritectic surface
involving all three phases in the iron-rich corner of the Gibbs triangle bounded by 0 to 25 wt pct Cr and 0 to 25 wt pct Ni
(bal Fe). The temperature ranged from the melting point of iron (1811 K) to about 1750 K. Compositions for tie-lines were
obtained from liquid-solid equilibrium couples and temperatures for the surfaces were obtained by differential thermal analysis.
Parameters for modeling the system were then selected in the subregular solution model to minimize the square of the difference
between experimental and calculated tie-lines. With one ternary parameter employed for each phase, calculations by the model
are in excellent agreement with the tie-line and liquidus measurements and in fair agreement with the temperatures for the
peritectic surfaceL + δ/L + δ + γ. The usefulness of the model is demonstrated by calculation of the solidification paths of selected alloys in the
composition field investigated for the limiting cases of (a) complete equilibrium followed by the alloy system, and (b) no
solid diffusion (i.e., segregation) with equilibrium maintained at the solidifying front and complete mixing in the liquid
phase. 相似文献
19.
A model has been developed to describe the microscopic behavior of phase transformation of carbon steels in the range of cooling
rate occurring in continuous casting. In the liquid-to solidphase transformation, this model simulates the phenomena of dendrite
nucleation and growth during solidification. Both δ- and γ-dendrites are involved. The nucleation and growth model has been established on the basis of published experimental
data and previous work. Also, a model of the peritectic transformation of carbon steels has been included. In the solid-to
solidphase transformation, the model considers the δ→ γ, γ→ α, and γ→ α + Fe3C phase transformations. The δ→ γ and γ→ α phase transformations have been modeled by using the Johnson-Mehl equation, also known as the Avrami equation. For the
pearlite transformation, a nucleation law, as well as the growth kinetics, has been established. Good agreement has been found
between the prediction of the model and the experimental data. 相似文献
20.
Solidification of M2 high speed steel 总被引:5,自引:0,他引:5
R. H. Barkalow R. W. Kraft J. I. Goldstein 《Metallurgical and Materials Transactions B》1972,3(4):919-926
The freezing process in AISI type M2 high speed tool steel (6 pct W, 5 pct Mo, 4 pct Cr, 2 pct V, 0.8 pct C) was studied by
metallographic and thermal analysis techniques. Unidirectional solidification of small laboratory melts in a modified crystal
growing apparatus was employed to provide metallographic sections of known macroscopic growth direction. Also cooling curves
were obtained on 40 g specimens solidified in thimble crucibles. X-ray microradiography, electron probe scanning techniques,
and quantitative microanalysis of dendrites and interdendritic carbides were extensively used to supplement conventional metallography.
Carbon and vanadium contents of M2 were varied in order to observe the effect of an austenite and ferrite stabilizer on the
thermal analysis curves and microstructure. The nonequilibrium freezing process in M2 includes three major liquid-solid reactions:
1) Liquid → Ferrite, 1435°C; 2) Liquid + Ferrite → Austenite, 1330°C; 3) Liquid → Austenite + M6C + MC, 1240°C. These reactions account for the as-cast structure of the commercial alloy. The addition of carbon depresses
the liquidus (1) and solidus temperatures (3) and narrows the gap between the liquidus (1) and peritectic transformation (2).
This gap is eliminated at > 1.39 wt pct C, where the initial freezing reaction is the crystallization of austenite. The accompanying
microstructural change is the elimination of σ eutectoid dendrite cores. The addition of vanadium promotes ferrite formation
by strongly depressing the peritectic reaction and thus widening the gap between the liquidus and the peritectic. 相似文献