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1.
Spatially resolved X-ray diffraction (SRXRD) experiments have been performed during gas tungstenarc (GTA) welding of AISI
1045 C-Mn steel at input powers ranging from 1000 to 3750 W. In-situ diffraction patterns taken at discreet locations across the width of the heat-affected zone (HAZ) near the peak of the heating
cycle in each weld show regions containing austenite (γ), ferrite and austenite (α+γ), and ferrite (α). Changes in input power have a demonstrated effect on the resulting sizes of these regions. The largest effect is on the
γ phase region, which nearly triples in width with increasing input power, while the width of the surrounding two-phase α+γ region remains relatively constant. An analysis of the diffraction patterns obtained across this range of locations allows
the formation of austenite from the base-metal microstructure to be monitored. After the completion of the α → γ transformation, a splitting of the austenite peaks is observed at temperatures between approximately 860 °C and 1290 °C.
This splitting in the austenite peaks results from the dissolution of cementite laths originally present in the base-metal
pearlite, which remain after the completion of the α → γ transformation, and represents the formation of a second more highly alloyed austenite constituent. With increasing temperatures,
carbon, originally present in the cementite laths, diffuses from the second newly formed austenite constituent to the original
austenite constituent. Eventually, a homogeneous austenitic microstructure is produced at temperatures of approximately 1300
°C and above, depending on the weld input power. 相似文献
2.
In-situ spatially resolved X-ray diffraction (SRXRD) experiments were performed during gas tung-sten arc (GTA) welding of AISI 1045
C-Mn steel. Ferrite (α) and austenite (γ) phases were identified and quantified in the weld heat-affected zone (HAZ) from
the real time SRXRD data. The results were compiled with weld temperatures calculated using a coupled thermal fluids model
to create a phase map of the HAZ. Kinetics of the α → γ transformation during weld heating and the reverse γ → α transformation
during weld cooling were extracted from the map. Superheating as high as 250 °C above the A3 temperature was observed for
the α → γ phase transformation to reach completion at locations near the fusion zone (FZ) boundary. The SRXRD experiments
revealed that the newly created γ phase exists with two distinct lattice parameters, resulting from the inhomogeneous distribution
of carbon and manganese in the starting pearlitic/ferritic microstructure. During cooling, the reverse γ → α phase transformation
was shown to depend on the HAZ location. In the fine-grained region of the HAZ, the γ → α transformation begins near the A3
temperature and ends near the A1 temperature. In this region, where the cooling rates are below 40 °C/s, the transformation
occurs by nucleation and growth of pearlite. In the coarse-grained region of the HAZ, the γ → α transformation requires 200
°C of undercooling for completion. This high degree of undercooling is caused by the large grains coupled with cooling rates
in excess of 50 °C/s that result in a bainitic transformation mechanism. 相似文献
3.
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
4.
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
5.
John W. Elmer Joe Wong Thorsten Ressler 《Metallurgical and Materials Transactions A》1998,29(11):2761-2773
Spatially resolved X-ray diffraction (SRXRD) is used to map the α → β → α phase transformation in the heat-affected zone (HAZ) of commercially pure titanium gas tungsten arc welds. In situ SRXRD experiments were conducted using a 180-μm-diameter X-ray beam at the Stanford Synchrotron Radiation Laboratory (SSRL)
(Stanford, CA) to probe the phases present in the HAZ of a 1.9 kW weld moving at 1.1 mm/s. Results of sequential linear X-ray
diffraction scans made perpendicular to the weld direction were combined to construct a phase transformation map around the
liquid weld pool. This map identifies six HAZ microstructural regions between the liquid weld pool and the base metal: (1)
α-Ti that is undergoing annealing and recrystallization; (2) completely recrystallized α-Ti; (3) partially transformed α-Ti, where α-Ti and β-Ti coexist; (4) single-phase β-Ti; (5) back-transformed α-Ti; and (6) recrystallized α-Ti plus back-transformed α-Ti. Although the microstructure consisted predominantly of α-Ti, both prior to and after the weld, the crystallographically textured starting material was altered during welding to produce
different α-Ti textures within the resulting HAZ. Based on the travel speed of the weld, the α → β transformation was measured to take 1.83 seconds during heating, while the β → α transformation was measured to take 0.91 seconds during cooling. The α → β transformation was characterized to be dominated by long-range diffusional growth on the leading (heating) side of the weld,
while the β → α transformation was characterized to be predominantly massive on the trailing (cooling) side of the weld, with a massive growth
rate on the order of 100 μm/s. 相似文献
6.
7.
Continuous cooling transformation (CCT) diagrams for HSLA-80 and HSLA-100 steels pertaining to fusion welding with heat inputs
of 10 to 40 kJ/cm, and peak temperatures of 1000 °C to 1400 °C have been developed. The corresponding nonlinear cooling profiles
and related γ → α phase transformation start and finish temperatures for various peak temperature conditions have been taken
into account. The martensite start (M
s
) temperature for each of the grades and ambient temperature microstructures were considered for mapping the CCT diagrams.
The austenite condition and cooling rate are found to influence the phase transformation temperatures, transformation kinetics,
and morphology of the transformed products. In the fine-grain heat-affected zone (FGHAZ) of HSLA-80 steel, the transformation
during cooling begins at temperatures of 550 °C to 560 °C, and in the HSLA-100 steel at 470 °C to 490 °C. In comparison, the
transformation temperature is lower by 120 °C and 30 °C in the coarse-grain heat-affected zone (CGHAZ) of HSLA-80 steel and
HSLA-100 steel, respectively. At these temperatures, acicular ferrite (AF) and lath martensite (LM) phases are formed. While
the FGHAZ contains a greater proportion of acicular ferrite, the CGHAZ has a higher volume fraction of LM. Cooling profiles
from the same peak temperature influence the transformation kinetics with slower cooling rates producing a higher volume fraction
of acicular ferrite at the expense of LM. The CCT diagrams produced can predict the microstructure of the entire HAZ and have
overcome the limitations of the conventional CCT diagrams, primarily with respect to the CGHAZ. 相似文献
8.
M. Enomoto 《Metallurgical and Materials Transactions A》2002,33(8):2309-2316
The growth of a planar ferrite (α): austenite (γ) boundary in low-carbon iron and Fe-Mn alloys continuously cooled from austenite through the (α+γ) two-phase field and the α single-phase field was simulated by incorporating carbon diffusion in austenite, intrinsic boundary mobility, and the drag
of an alloying element. At a very high cooling rate (≥ 103 °C/s), the width of the carbon diffusion spike in austenite approaches the limit at which spikes are viable, so that the
growth of ferrite in which carbon is not partitioned can occur even above the α solvus. In this context, the upper limiting temperature of partitionless growth of ferrite is the T
0 temperature. In the presence of drag of an alloying element, e.g., Mn, both carbon-partitioned and partitionless growth of ferrite begins to occur at finite undercoolings from the Ae
3, T
0, or α-solvus temperature, at which the driving force for transformation exceeds the drag force. The intrinsic mobility of the α:γ boundary may play a significant role at an extremely high cooling rate (≥105 °C/s).
This article is based on a presentation made at the symposium entitled “The Mechanisms of the Massive Transformation,” a part
of the Fall 2000 TMS Meeting held October 16–19, 2000, in St. Louis, Missouri, under the auspices of the ASM Phase Transformations
Committee. 相似文献
9.
Isothermal transformation from austenite in an Fe-9.14 pct Ni alloy has been studied by optical metallography and examination
by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In the temperature range 565 °C and 545
°C, massive ferrite (α
q
) forms first at prior austenite grain boundaries, followed by Widmanst?tten ferrite (α
W
) growing from this grain boundary ferrite. Between 495 °C and 535 °C, Widmanst?tten ferrite is thought to grow directly from
the austenite grain boundaries. Both these transformations do not go to completion and reasons for this are discussed. These
composition invariant transformations occur below T
0 in the two-phase field (α+γ). Previous work on the same alloy showed that transformation occurred to α
q
> and α
W
on furnace cooling, while analytical TEM showed an increase of Ni at the massive ferrite grain boundaries, indicating local
partitioning of Ni at the transformation interface. An Fe-3.47 pct Ni alloy transformed to equiaxed ferrite at 707 °C ±5 °C
inside the single-phase field on air cooling. This is in agreement with data from other sources, although equiaxed ferrite
in Fe-C alloys forms in the two-phase region. The application of theories of growth of two types of massive transformation
by Hillert and his colleagues are discussed.
This article is based on a presentation made at the symposium entitled “The Mechanisms of the Massive Transformation,” a part
of the Fall 2000 TMS Meeting held October 16–19, 2000, in St. Louis, Missouri, under the auspices of the ASM Phase Transformations
Committee. 相似文献
10.
E. S. Humphreys H. A. Fletcher J. D. Hutchins A. J. Garratt-Reed W. T. ReynoldsJr. H. I. Aaronson G. R. Purdy G. D. W. Smith 《Metallurgical and Materials Transactions A》2004,35(4):1223-1235
A scanning transmission electron microscope (STEM) technique was used to measure Mo concentrations at ferrite:austenite (α:γ) interfaces in an Fe-0.24 pct C-0.93 pct Mo alloy partially transformed at 650°C, 630°C, and 610°C. These concentrations
were quite small at 650°C, which is just below the bay temperature of the time-temperature-transformation (TTT) curve for
the initiation of ferrite formation. There were larger concentrations at 630°C, a temperature at which transformation stasis
(incomplete transformation) occurred. Concentrations at 610°C were intermediate between the values observed at 650°C and 630°C.
The average accumulation at the latter temperatures increased appreciably as a function of transformation time. After each
heat treatment, there was considerable variation in Mo accumulation from one α:γ interface to another and, to a lesser extent, from one region to another along the same interface. These higher Mo concentrations
were deduced to have developed largely through volume diffusion of Mo, mainly through ferrite, to interfaces whose ledgewise
growth had been interrupted by growth stasis. (Mo2C precipitation at α:γ boundaries occurred only at the end of growth stasis.) It appears that only a very small amount of Mo segregation is needed,
probably at specific interfacial sites, in order to produce growth cessation. Growth kinetics anomalies of this kind continue
to provide the best evidence available for the operation of a coupled-solute drag effect.
This article is based on a presentation given in the symposium “The Effect of Alloying Elements on the Gamma to Alpha Transformation
in Steels,” October 6, 2002, at the TMS Fall Meeting in Columbus, Ohio, under the auspices of the McMaster Centre for Steel
Research and the ASM-TMS Phase Transformations Committee. 相似文献
11.
A detailed characterization of two dissimilar high-strength steels, SCMV and Aermet 100, joined by inertia friction welding
(IFW)—a solid-state welding technique—was undertaken using high energy synchrotron X-ray diffraction and advanced electron
microscopy in order to understand the dramatic hardness variation across such a weld. It was found that the severe high-temperature
deformation in the thermomechanically affected zones (TMAZs) of the weld, stabilized ordered, and nanosized FeCo zones in
Aermet 100 and about 12 to 14 vol pct austenite in SCMV (Ni equivalent 9 wt pct). The ordered FeCo zones in Aermet 100 resulted
in exceptionally high hardness values of 700 to 725 HV. Very close to the weld line, the TMAZ of Aermet 100 also displayed
a region with about 15 vol pct austenite, while in the parent material, 8 to 9 vol pct was typically observed. No indication
of martensite was found in the weld region of Aermet 100. Ferrite texture analysis at different locations within the TMAZs
on either side of the weld showed that SCMV develops a very strong α-fiber texture near the weld line and, in addition, a γ-fiber texture toward the heat-affected zone (HAZ), suggesting the presence of ferrite during welding near the weld line and
recrystallization further away. The ferrite texture development in the TMAZ of Aermet 100 was relatively weak, suggesting
that austenite is a dominant phase in the TMAZ during IFW. 相似文献
12.
K. Banerjee N. L. Richards M. C. Chaturvedi 《Metallurgical and Materials Transactions A》2005,36(7):1881-1890
The effect of filler alloys C-263, RENé-41, IN-718, and FM-92 on heat-affected zone (HAZ) cracking susceptibility of cast
IN-738 LC, which is a high-temperature Ni-based superalloy used at temperatures up to 980 °C and is precipitation hardened
by the γ′ (Ni3Al,Ti) phase, by gas-tungsten-arc (GTA) welding was studied. In addition, autogenous welds were also made on the IN-738 parent
material. The preweld treatments consisted of the standard solution treatment at 1120 °C for 2 hours followed by air cooling,
and a new heat treatment, which was developed to improve the HAZ cracking resistance of IN-738 LC. This heat treatment consisted
of solution treating at 1120 °C followed by air cooling then aging at 1025 °C for 16 hours followed by water quenching. Welds
were observed to suffer intergranular HAZ cracking, regardless of the filler alloy; however, the autogenous welds were most
susceptible to HAZ cracking. In general, the cracking tendency for both heat treatments was maximum for C-263 and RENE-41
fillers and decreased with the use of FM-92 and IN-718 filler alloys. The HAZ cracking was associated mainly with constitutional
liquation of γ′ and MC carbides. On some cracks, liquated low melting point containing Zr-carbosulfide and Cr-Mo borides were also observed
to be present. The cooling portion of the weld thermal cycle induced precipitation hardening via γ′ phase in the γ matrix of the weld metal. The HAZ cracking increased as the weld metal lattice mismatch between γ′ precipitates and γ matrix of the weld and its hardness (Ti + Al) increased. However, the weld-metal solidus and solidification temperature range,
determined by high-temperature differential scanning calorimetry, did not correlate with the HAZ cracking susceptibility.
It is suggested that the use of filler alloys with small γ′-γ lattice mismatch and slow age-hardening response would reduce the HAZ cracking in IN-738 LC superalloy welds. 相似文献
13.
14.
The microstructure of an (α + γ) duplex Fe-10.1Al-28.6Mn-0.46C alloy has been investigated by means of optical microscopy
and transmission electron microscopy (TEM). In the as-quenched condition, extremely fine D03 particles could be observed within the ferrite phase. During the early stage of isothermal aging at 550 °C, the D03 particles grew rapidly, especially the D03 particles in the vicinity of the α/γ grain boundary. After prolonged aging at 550 °C, coarse K’-phase (Fe, Mn)3AlC precipitates began to appear at the regions contiguous to the D03 particles, and —Mn precipitates occurred on the α/γ and α/α grain boundaries. Subsequently, the grain boundary β-Mn precipitates
grew into the adjacent austenite grains accompanied by a γ→ α + β-Mn transition. When the alloy was aged at 650 °C for short
times, coarse. K-phase precipitates were formed on the α/γ grain boundary. With increasing the aging time, the α/γ grain boundary
migrated into the adjacent austenite grain, owing to the heterogeneous precipitation of the Mn-enrichedK phase on the grain boundary. However, the α/γ grain boundary migrated into the adjacent ferrite grain, even though coarse
K-phase precipitates were also formed on the α/γ grain boundary in the specimen aged at 750 °C. 相似文献
15.
M. G. Mecozzi J. Sietsma S. van der Zwaag M. Apel P. Schaffnit I. Steinbach 《Metallurgical and Materials Transactions A》2005,36(9):2327-2340
This article deals with the austenite (γ) decomposition to ferrite (α) during cooling of a 0.10 wt pct C-0.49 wt pct Mn steel. A phase-field model is used to simulate this transformation. The
model provides qualitative information on the microstructure that develops on cooling and quantitative data on both the ferrite
fraction formed and the carbon concentration profile in the remaining austenite. The initial austenitic microstructure and
the ferrite nucleation data, derived by metallographic examination and dilatometry, are set as input data of the model. The
interface mobility is used as a fitting parameter to optimize the agreement between the simulated and experimental ferrite-fraction
curve derived by dilatometry. A good agreement between the simulated α-γ microstructure and the actual α-pearlite microstructure observed after cooling is obtained. The derived carbon distribution in austenite during transformation
provides comprehension of the nature of the transformation with respect to the interface-controlled or diffusion-controlled
mode. It is found that, at the initial stage, the transformation is predominantly interface-controlled, but, gradually, a
shift toward diffusion control takes place to a degree that depends on cooling rate. 相似文献
16.
Bikas C. Maji Madangopal Krishnan V. V. Rama Rao 《Metallurgical and Materials Transactions A》2003,34(5):1029-1042
The microstructure and phase stability of the Fe-15Mn-7Si-9Cr-5Ni stainless steel shape memory alloy in the temperature range
of 600 °C to 1200 °C was investigated using optical and transmission electron microscopy, X-ray diffractometry (XRD), differential
scanning calorimetry (DSC), and chemical analysis techniques. The microstructural studies show that an austenite single-phase
field exists in the temperature range of 1000 °C to 1100 °C, above 1100 °C, there exists a three-phase field consisting of
austenite, δ-ferrite, and the (Fe,Mn)3Si intermetallic phase; within the temperature range of 700 °C to 1000 °C, a two-phase field consisting of austenite and the
Fe5Ni3Si2 type intermetallic phase exists; and below 700 °C, there exists a single austenite phase field. Apart from these equilibrium
phases, the austenite grains show the presence of athermal ɛ martensite. The athermal α′ martensite has also been observed for the first time in these stainless steel shape memory alloys and is produced through
the γ-ɛ-α′ transformation sequence. 相似文献
17.
C. Capdevila F. G. Caballero C. García de Andrés 《Metallurgical and Materials Transactions A》2001,32(3):661-669
The present article is concerned with the theoretical and experimental study of the growth kinetics of allotriomorphic ferrite
in medium carbon vanadium-titanium microalloyed steel. A theoretical model is presented in this work to calculate the evolution
of austenite-to-allotriomorphic ferrite transformation with time at a very wide temperature range. At temperatures above eutectoid
temperature, where allotriomorphic ferrite is the only austenite transformation product, the soft-impingement effect should be taken into account in the modeling. In that case, the Gilmour et al. analysis reliably predicts the progress of austenite-to-allotriomorphic ferrite transformation in this steel. By contrast,
since pearlite acts as a carbon sink, the carbon enrichment of austenite due to the previous ferrite formation is avoided,
and carbon concentration in austenite far from the α/γ interface remains the same as the overall carbon content of the steel. Hence, the soft-impingement effect should be neglected,
and allotriomorphic ferrite is considered to grow under a parabolic law. Therefore, assumption of a semi-infinite extent austenite
with constant boundary conditions is suitable for the kinetics of the isothermal decomposition of austenite. An excellent
agreement (higher than 93 pct in R
2) has been obtained between the experimental and predicted values of the volume fraction of ferrite in all of the ranges of
temperature studied. 相似文献
18.
Ferrite and bainite in alloy steels 总被引:1,自引:0,他引:1
The addition of alloying elements even in small concentrations can alter the properties and structure of ferrite and bainite.
The various morphologies of ferrite-carbide aggregates are surveyed including alloy pearlite, fibrous carbide eutectoids and
precipitation of fine alloy carbides atγ-α interfaces. Modern ideas on the morphology and growth kinetics of ferrite and upper and lower bainite are also summarized.
Using this information, an attempt is made to rationalize subcritical transformations of austenite in low alloy steels. Basic
factors influencing the strength of alloy ferrites are discussed, leading to an examination of structure-mechanical property
relationships in ferrite and bainite. Finally the exploitation of the ferrite and bainite reactions to produce useful alloy
steels by direct transformation of austenite is explored. 相似文献
19.
The influence of weld thermal simulation on the transformation kinetics and heat-affected zone (HAZ) microstructure of two
high-strength low-alloy (HSLA) steels, HSLA-80 and HSLA-100, has been investigated. Heat inputs of 10 kJ/cm (fast cooling)
and 40 kJ/cm (slow cooling) were used to generate single-pass thermal cycles with peak temperatures in the range of 750 °C
to 1400 °C. The prior-austenite grain size is found to grow rapidly beyond 1100 °C in both the steels, primarily with the
dissolution of niobium carbonitride (Nb(CN)) precipitates. Dilatation studies on HSLA-80 steel indicate transformation start
temperatures (T
s
) of 550 °C to 560 °C while cooling from a peak temperature (T
p
) of 1000 °C. Transmission electron microscopy studies show here the presence of accicular ferrite in the HAZ. The T
s
value is lowered to 470 °C and below when cooled from a peak temperature of 1200 °C and beyond, with almost complete transformation
to lath martensite. In HSLA-100 steel, the T
s
value for accicular ferrite is found to be 470 °C to 490 °C when cooled from a peak temperature of 1000 °C, but is lowered
below 450 °C when cooled from 1200 °C and beyond, with correspondingly higher austenite grain sizes. The transformation kinetics
appears to be relatively faster in the fine-grained austenite than in the coarse-grained austenite, where the niobium is in
complete solid solution. A mixed microstructure consisting of accicular ferrite and lath martensite is observed for practically
all HAZ treatments. The coarse-grained HAZ (CGHAZ) of HSLA-80 steel shows a higher volume fraction of lath martensite in the
final microstructure and is harder than the CGHAZ of HSLA-100 steel. 相似文献
20.
The influence of weld thermal simulation on the transformation kinetics and heat-affected zone (HAZ) microstructure of two
high-strength low-alloy (HSLA) steels, HSLA-80 and HSLA-100, has been investigated. Heat inputs of 10 kJ/cm (fast cooling)
and 40 kJ/cm (slow cooling) were used to generate single-pass thermal cycles with peak temperatures in the range of 750 °C
to 1400 °C. The prior-austenite grain size is found to grow rapidly beyond 1100 °C in both the steels, primarily with the
dissolution of niobium carbonitride (Nb(CN)) precipitates. Dilatation studies on HSLA-80 steel indicate transformation start
temperatures (T
s
) of 550 °C to 560 °C while cooling from a peak temperature (T
p
) of 1000 °C. Transmission electron microscopy studies show here the presence of accicular ferrite in the HAZ. The T
s
value is lowered to 470 °C and below when cooled from a peak temperature of 1200 °C and beyond, with almost complete transformation
to lath martensite. In HSLA-100 steel, the T
s
value for accicular ferrite is found to be 470 °C to 490 °C when cooled from a peak temperature of 1000 °C, but is lowered
below 450 °C when cooled from 1200 °C and beyond, with correspondingly higher austenite grain sizes. The transformation kinetics
appears to be relatively faster in the fine-grained austenite than in the coarse-grained austenite, where the niobium is in
complete solid solution. A mixed microstructure consisting of accicular ferrite and lath martensite is observed for practically
all HAZ treatments. The coarse-grained HAZ (CGHAZ) of HSLA-80 steel shows a higher volume fraction of lath martensite in the
final microstructure and is harder than the CGHAZ of HSLA-100 steel. 相似文献