共查询到20条相似文献,搜索用时 15 毫秒
1.
H. T. Lin M. L. Grossbeck B. A. Chin 《Metallurgical and Materials Transactions A》1990,21(9):2585-2596
Helium was implanted in type 316 stainless steel, through tritium decay, to levels of 0. 18, 2. 5, 27, 105, and 256 atomic
parts per million (appm). Bead-on-sheet welds were then made using the gas tungsten arc (GTA) process. Intergranular cracking
occurred in the heat-affected zones (HAZs) of specimens with helium concentrations equal to or greater than 2.5 appm. No such
cracking was observed in helium-free control specimens or in specimens containing the lowest helium concentration. In addition
to the HAZ cracking, brittle, centerline cracking occurred in the fusion zone of specimens containing 105 and 256 appm helium.
Transmission and scanning electron microscopy results indicated that both the HAZ cracking and centerline cracking in the
fusion zone resulted from the stress-induced growth and coalescence of cavities initiated at helium bubbles on interfaces.
For the HAZ case, the cavity growth rate is modeled and shown to predict the experimentally measured 1-second time lag between
peak weld temperature and the onset of cracking. 相似文献
2.
Improvement in Laser Weldability of INCONEL 738 Superalloy through Microstructural Modification 总被引:1,自引:0,他引:1
A.T. Egbewande H.R. Zhang R.K. Sidhu O.A. Ojo 《Metallurgical and Materials Transactions A》2009,40(11):2694-2704
Microstructural study of laser-beam-welded IN 738 superalloy was carefully performed to better understand the causes of heat-affected
zone (HAZ) cracking and to determine an improved approach of alleviating the weldability problem. The HAZ cracks in the alloy
were intergranular liquation cracks that resulted from the liquation reaction of both secondary solidification products (MC
carbides and γ-γ′ eutectic) and solid-state reaction products (γ′ particles) present in the preweld material. In contrast to the expectation based on Chadwick’s equation, a reduction of
grain boundary liquid film thickness did not produce a decrease in HAZ cracking owing to increased base alloy hardness that
accompanied a preweld heat treatment designed to reduce the intergranular liquation. Moreover, a major factor limiting the
effectiveness of an existing preweld heat treatment with low base alloy hardness in reducing HAZ cracking was found to be
the formation of intergranular M5B3 boride particles during the heat treatment. These borides can widen the HAZ brittle temperature range (BTR) during weld cooling
and increase the propensity for cracking. Based on the results, a new preweld heat treatment that induces a moderate hardness
and precludes grain boundary boride formation was found and was shown to produce a significant reduction in HAZ cracking in
the welded alloy compared to the most effective pre-existing preweld heat treatment. 相似文献
3.
M. J. Cieslak J. J. Stephens M. J. Carr 《Metallurgical and Materials Transactions A》1988,19(3):657-667
The weldability and weld metal microstructure of Cabot Alloy 214 have been investigated with a variety of experimental and
analytical techniques. These include Varestraint hot crack testing, hot ductility testing, pulsed Nd:YAG laser welding, scanning
and analytical electron microscopy, electron microprobe analysis, and X-ray diffraction. A heat of Alloy 214 containing intentionally
alloyed B (0.003 wt pct) and Zr (0.07 wt pct) was much more sensitive to both fusion zone hot cracking as quantified by the
Varestraint test and to simulated heat-affected-zone (HAZ) cracking as quantified by hot ductility testing than a heat of
Alloy 214 containing no intentionally added B (0.0002 wt pct) or Zr (0.02 wt pct). Scanning electron microscopy of the high
B and Zr alloy showed the presence of dendritically-shaped, Zr-rich constituents in interdendritic regions in the gas-tungsten-arc
(GTA) welds. Electron microprobe analysis of these welds revealed a segregation pattern of Cr, Al, Mn, and Zr enrichment in
interdendritic regions and Ni and Fe enrichment in dendrite core regions. Analytical electron microscopy revealed the presence
of ZrX (X = B, C, N, O), M23C6, andγ′ in the fusion zone of GTA weld specimens,γ′ was also found in the as-received base metal and in the GTA weld HAZ. X-ray diffraction analysis of extractions from the
high B and Zr GTA weld metal also indicated the presence of a ZrX-type constituent. The results of this study are in qualitative
agreement with earlier work performed on alloys such as NIMONIC 90 and INCONEL 718∗ relative to the detrimental effect of B and Zr additions on fusion zone and HAZ hot cracking susceptibility.
Formerly with Sandia National Laboratories, Albuquerque, NM 相似文献
4.
Charles G. Schmidt Robert D. Caligiuri Lawrence E. Eiselstein Sharon S. Wing Daniel Cubicciotti 《Metallurgical and Materials Transactions A》1987,18(8):1483-1493
Large-diameter Type 304 stainless steel pipe weld heat-affected zone (HAZ) was investigated to determine the rate at which
low temperature sensitization (LTS) can occur in weld HAZ at nuclear reactor operating temperatures and to determine the effects
of LTS on the initiation and propagation of intergranular stress corrosion cracks (IGSCC). The level of sensitization was
determined with the electrochemical potentiokinetic reactivation (EPR) test, and IGSCC susceptibility was determined with
constant extension rate tests (CERT) and actively loaded compact tension (CT) tests. Substructural changes and carbide compositions
were analyzed by electron microscopy. Weld HAZ was found to be susceptible to IGSCC in the as-welded condition for tests conducted
in 8-ppm-oxygen, high-purity water at 288 °C. For low oxygen environments (i.e., 288 °C/0.2 ppm O2 or 180 °C/1.0 ppm O2), IGSCC susceptibility was detected only in weld HAZ that had been sensitized at temperatures from 385 °C to 500 °C. Lower
temperature heat treatments did not produce IGSCC. The microscopy studies indicate that the lack of IGSCC susceptibility from
LTS heat treatments below 385 °C is a result of the low chromium-to-iron ratio in the carbide particles formed at grain boundaries.
Without chromium enrichment of carbides, no chromium depleted zone is produced to enhance IGSCC susceptibility. 相似文献
5.
A. Foroughi M. Shamanian M. Kasiri-Asgarani J. Kangazian 《Transactions of the Indian Institute of Metals》2018,71(3):533-544
In the present research, microstructure and mechanical properties of 2205 duplex stainless steel/A517 quench and tempered low alloy steel dissimilar joint were investigated. For this purpose, gas tungsten arc welding was used with ER2209 filler metal. Characterizations were conducted by optical microscopy, scanning electron microscopy equipped with an energy dispersive spectroscopy and X-ray diffraction. Mechanical properties were evaluated in micro-hardness, tensile and impact tests. Microstructure in the weld zone included an austenitic continuous network in the matrix of primary ferrite. No brittle phases were formed in the weld metal and stainless steel heat affected zone (HAZ). The weld metal/A517 interface showed higher hardness than other regions. Tensile tests indicated that the values of the yield and tensile strength were 663 and 796 MPa, respectively. Impact tests indicated that the weld zone had almost the same impact energy as base metals. The minimum impact energy of 12 J was related to A517 HAZ. The results of scanning electron microscopy for fracture surfaces indicated that weld zone, 2205 HAZ and A517 HAZ had ductile, ductile–brittle and brittle fracture mode, respectively. 相似文献
6.
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
7.
Sunil Goyal K. Laha K. S. Chandravathi K. Bhanu Sankara Rao 《Transactions of the Indian Institute of Metals》2010,63(2-3):461-466
Creep tests were carried out on 2.25Cr-1Mo ferritic steel base metal and its fusion welded joint at 823 K over a stress range of 100–240 MPa. The weld joint possessed lower creep rupture strength than the base metal and the reduction was more at lower applied stresses. The failure occurred in the intercritical region of heat-affected zone (HAZ) of the joint, commonly known as Type IV cracking. Type IV cracking in the joint was manifested as pronounced localization of creep deformation in the soft intercritical region of HAZ coupled with preferential creep cavitation. The creep cavitation in intercritical HAZ was found to initiate at the central region of the creep specimen and propagate outwards to the surface. To explain the above observations, the stress and strain distributions across the weld joint during creep exposure were estimated by using finite element analysis. For this purpose creep tests were also carried out on the deposited weld metal and simulated HAZ structures (viz. coarse-grain structure, fine-grain structure, and intercritically annealed structure) of the joint. Creep rupture strength of different constituents of joint were in the increasing order of intercritical HAZ, fine-grain HAZ, base metal, weld metal and coarse-grain HAZ. Localized preferential creep straining in the intercritical HAZ of weld joint as observed experimentally was supported by the finite element analysis. Estimated higher principal stress at the interior regions of intercritical HAZ explained the pronounced creep cavitation at these regions leading to Type IV failure of the joint. 相似文献
8.
基于块体离散单元数值模拟方法(UDEC-GBM),以钾长石矿物颗粒为例,详细研究了矿物晶粒解理倾角、解理倾角围压效应及解理间距对硬质岩石力学性质、微观开裂过程及机理的影响,并探讨了解理特征在工程实际中可能带来的影响。数值研究结果表明:(1)晶粒解理具有明显倾角效应,当解理倾角由0°增加到90°时,岩石的弹性模量、单轴压缩强度及峰后脆延特征都会发生变化,穿晶总裂纹数受影响明显,主要体现在钾长石张拉穿晶裂纹显著增加,钾长石剪切裂纹数量在60°增加到最大值后减少,石英穿晶张拉裂纹数量也有明显变化,总体而言不断增加,而沿晶裂纹数量呈减少趋势,整个开裂过程仍以张拉沿晶主导;(2)晶粒解理倾角效应受围压影响,围压会导致沿晶裂纹和穿晶裂纹数量和二者比值发生变化,但不同倾角下围压对沿晶裂纹和穿晶裂纹数量和比值变化影响不一样;(3)当解理间距由2 mm增加到4 mm时,穿晶裂纹数量有增加趋势,而沿晶裂纹数量减少,总剪切和张拉裂纹数量比值不变,对岩石微观张拉、剪切破坏机制无明显影响。此外,具有解理结构的矿物晶粒含量较高且矿物晶粒本身性质对岩石性质及响应影响显著时,解理特征对板裂、岩爆等破坏的影响应给予重视。 相似文献
9.
O. A. Ojo N. L. Richards M. C. Chaturvedi 《Metallurgical and Materials Transactions A》2006,37(2):421-433
The fusion zone and heat-affected zone (HAZ) microstructures obtained during tungsten inert gas (TIG) welding of a commercial
superalloy IN 738LC were examined. The microsegregation observed during solidification in the fusion zone indicated that while
Co, Cr, and W segregated to the γ dendrites, Nb, Ti, Ta, Mo, Al, and Zr were rejected into the interdendritic liquid. Electron
diffraction and energy-dispersive X-ray microanalyses using a transmission electron microscope (TEM) of secondary phases,
extracted from the fusion zone on carbon replicas, and of those in thin foils prepared from the fusion zone showed that the
major secondary solidification constituents, formed from the interdendritic liquid, were cubic MC-type carbides and γ-γ’ eutectic.
The terminal solidification reaction product was found to consist of M3B2 and Ni7Zr2 formed in front of the interdendritic γ-γ’ eutectic. Based on the knowledge of the Ni-Ti-C ternary system, a pseudoternary
solidification diagram was adapted for IN 738 superalloy, which adequately explained the as-solidified microstructure. The
HAZ microfissuring was observed in regions surrounding the fusion zone. Closer and careful microstructural examination by
analytical scanning electron microscopy revealed formation of re-solidified constituents along the microfissured HAZ grain
boundaries, which suggest that HAZ cracking in this alloy involves liquation cracking. Liquation of various phases present
in preweld alloy as well as characteristics of the intergranular liquid film contributing to the alloy’s low resistance to
HAZ cracking were identified and are discussed. 相似文献
10.
Raghuvir Singh Mukesh Kumar Mainak Ghosh Gautam Das P. K. Singh I. Chattoraj 《Metallurgical and Materials Transactions A》2013,44(1):173-187
Low temperature sensitization of 304LN stainless steel from the two pipes, differing slightly in chemical composition, has been investigated; specimens were aged at 623 K (350 °C) for 20,000 hours and evaluated for intergranular corrosion and degree of sensitization. The base and heat-affected zone (HAZ) of the 304LN-1 appear resistant to sensitization, while 304LN-2 revealed a “dual” type microstructure at the transverse section and HAZ. The microstructure at 5.0-mm distance from the fusion line indicates qualitatively less sensitization as compared to that at 2.0 mm. The 304LN-2 base alloy shows overall lower degree of sensitization values as compared to the 304LN-1. A similar trend of degree of sensitization was observed in the HAZ where it was higher in the 304LN-1 as compared to the 304LN-2. The weld zone of both the stainless steels suffered from cracking during ASTM A262 practice E, while the parent metals and HAZs did not show such fissures. A mottled image within the ferrite lamella showed spinodal decomposition. The practice E test and transmission electron microscopy results indicate that the interdendritic regions may suffer from failure due to carbide precipitation and due to the evolution of brittle phase from spinodal decomposition. 相似文献
11.
The kinetics of hydrogen attack (HA) has been studied in the heat affected zone (HAZ) in a 2.25Cr-1Mo steel weld to determine
the relative rates of attack and bubble nucleation in the HAZ, base metal, and weld metal. The HAZ was found to suffer hydrogen
attack at nearly twice the rate of the base metal, but not as rapidly as the weld metal. Nucleation of bubbles does not occur
during HA of the HAZ of a 2.25Cr-1Mo steel, on exposure to hydrogen pressure of 20.5 MPa or less, but does occur at higher
pressures up to 31.5 MPa (4500 psi) at 550 °C, or up to 27.5 MPa (4000 psi) at 580 °C. Such nucleation results in enhancement
of the HA rate by a factor of six. The weak dependence of nucleation effects on hydrogen pressure and the saturation of the
nucleation effects in a short time suggest some thermally activated nucleation of fresh bubbles.
Formerly with The Ohio State University. 相似文献
12.
J. A. Donovan R. J. Burger R. J. Arsenault 《Metallurgical and Materials Transactions A》1981,12(11):1917-1922
The effect of helium, from tritium decay, on the mechanical properties of single crystal noibium were determined. The yield
stress in compression of helium charged niobium increased at all test temperatures. Annealing decreased the yield stress.
Transmission electron microscopy was used to examine the as charged samples and to analyze the effects of annealing on nucleation
and growth of helium bubbles. The results support the following conclusions: 1) Helium exists in niobium as clusters at ambient
temperatures, 2) these clusters punch out prismatic dislocation loops, 3) the increase in strength due to the presence of
helium can be explained by a cluster and bubble shearing model. 相似文献
13.
P. K. Liaw M. G. Burke A. Saxena J. D. Landes 《Metallurgical and Materials Transactions A》1991,22(2):455-468
Elevated-temperature fracture toughness properties were developed on ex-service 2-l/4Cr-1Mo steel weldments. Fracture toughness
was measured on both base and heat-affected zone (HAZ) metals. A composite specimen consisting of base, HAZ, and weld metals
was used to develop fracture toughness properties in the HAZ area. It was observed that the J-R curve of the HAZ was significantly
lower than that of the base metal. Increasing crack extension increased the difference between theJ-R curves of the base metal and the HAZ. Dimpled fracture was the prime fracture mode in the base metal specimen, and a mixed-mode
(ductile and “granular”) fracture was found in the HAZ specimens. Scanning transmission electron microscopy (STEM) examination
revealed significant intergranular carbide precipitation and agglomeration within the HAZ. The lower fracture toughness of
the HAZ, as compared to the base metal, was attributed to the large accumulation of carbides in the grain boundaries of the
HAZ, which weakened the grain boundaries and caused “granular” fracture. 相似文献
14.
The aluminum alloy 6013 was friction-stir welded in the T4 and the T6 temper, and the microstructure and mechanical properties
were studied after welding and after applying a postweld heat treatment (PWHT) to the T4 condition. Optical microscopy (OM),
transmission electron microscopy (TEM), and texture measurements revealed that the elongated pancake microstructure of the
base material (BM) was transformed into a dynamically recrystallized microstructure of considerably smaller grain size in
the weld nugget. Strengthening precipitates, present before welding in the T6 state, were dissolved during welding in the
nugget, while an overaged state with much larger precipitate size was established in the heat-affected zone (HAZ). Microhardness
measurements and tensile tests showed that the HAZ is the weakest region of the weld. The welded sheet exhibited reduced strength
and ductility as compared to the BM. A PWHT restored some of the strength to the as-welded condition. 相似文献
15.
K. Laha K. S. Chandravathi P. Parameswaran Sunil Goyal M. D. Mathew 《Metallurgical and Materials Transactions A》2012,43(4):1174-1186
Evaluations of creep rupture properties of dissimilar weld joints of 2.25Cr-1Mo, 9Cr-1Mo, and 9Cr-1MoVNb steels with Alloy
800 at 823 K were carried out. The joints were fabricated by a fusion welding process employing an INCONEL 182 weld electrode.
All the joints displayed lower creep rupture strength than their respective ferritic steel base metals, and the strength reduction
was greater in the 2.25Cr-1Mo steel joint and less in the 9Cr-1Mo steel joint. Failure location in the joints was found to
shift from the ferritic steel base metal to the intercritical region of the heat-affected zone (HAZ) of the ferritic steel
(type IV cracking) with the decrease in stress. At still lower stresses, the failure in the joints occurred at the ferritic/austenitic
weld interface. The stress-life variation of the joints showed two-slope behavior and the slope change coincided with the
occurrence of ferritic/austenitic weld interface cracking. Preferential creep cavitation in the soft intercritical HAZ induced
type IV failure, whereas creep cavitation at the interfacial particles induced ferritic/austenitic weld interface cracking.
Micromechanisms of the type IV failure and the ferritic/austenitic interface cracking in the dissimilar weld joint of the
ferritic steels and relative cracking susceptibility of the joints are discussed based on microstructural investigation, mechanical
testing, and finite element analysis (FEA) of the stress state across the joint. 相似文献
16.
《Acta Metallurgica Materialia》1990,38(12):2383-2392
Neutron small angle scattering (SANS) combined with transmission electron microscopy (TEM) has been applied to obtain detailed information on the bubble structure in Ni, implanted with 1200 appm helium at room temperature and annealed at temperatures up to 1173 K. Besides conventional information such as size distributions of “small” bubbles in the bulk and “large” bubbles near grain boundaries, the density of helium in the bubbles could directly be determined by a contrast variation method of SANS. The most important result is the finding that even after the highest annealing temperature of 1173 K (≈ 70% of the melting temperature), the bubbles contain an overpressure which lies about 3 GPa above the value for thermodynamic equilibrium. 相似文献
17.
This article deals with the study of the influence of thermomechanical heat treatments, aging conditions (temperature and
time), and helium concentration on helium bubble precipitation in a 316L austenitic steel. Helium was generated by the radioactive
decay of tritium (tritium trick). Helium bubbles impede the grain growth in 316L steel aged at 1373 K and also the recrystal-lization
reaction at this temperature if cold working is performed prior to aging. Transmission electron microscopy (TEM) observations
indicated a weak helium precipitation at 1073 and 1223 K, presumably due to the presence of trapping sites for tritium, and
no bubble growth after aging up to 100 hours. Precipitation sites are mainly dislocations in the matrix at 1073 K and grain
boundaries and individual dislocations in the matrix at 1223 K. The large bubble size (50 nm) observed at 1373 K, even for
short aging times (0.083 hour), can partly be attributed to bubble dragging by dislocations toward the grain boundaries. Cold
deformation prior to aging leads to a larger bubble size due to growth enhancement during recrystallization. Decreasing the
helium content leads to a smaller helium bubble size and density. Tritium trapping at helium bubbles may favor helium 3 accumulation
on defects such as grain boundaries, as observed by tritium autoradiography.
Formerly with CNRS, is Postdoctor, Department PuA, CEA-DAM, Bruyères Le Chatel, France. 相似文献
18.
R. G. Thompson D. E. Mayo B. Radhakrishnan 《Metallurgical and Materials Transactions A》1991,22(2):557-567
The ability of NbC and Laves phases to promote intergranular liquation cracking in the weld heat-affected zone (HAZ) of cast
alloy 718 is examined in this paper. The term liquation cracking as used in this paper is synonymous with the terms microfissuring
and hot cracking as used by the authors in previous papers. Many alloys are susceptible to intergranular liquation cracking
due to the formation of incipient intergranular liquid films which can open into intergranular cracks. Previous studies on
alloy 718 showed that both NbC and Laves phases produce intergranular liquid films when subjected to the rapid thermal cycles
of the HAZ. When seeking a correlation between microstructure and liquation cracking, it is thus necessary to account for
changes in the volume fractions and distributions of both NbC and Laves phases. The volume fractions and distributions of
NbC and Laves phases were varied by heat treatment and also by using two bulk carbon concentrations. Increasing the bulk carbon
from 0.02 to 0.06 wt pct caused a 70 pct increase in the volume fraction of NbC but no significant change in the amount of
Laves phase. This increase in NbC was accompanied by an 18 pct increase in liquation cracking in the as-cast metal as measured
using the spot varestraint test. When the volume fraction of NbC and Laves phases were varied using heat treatment, a very
different behavior was observed. One hour heat treatments at 1200°F (649°C) and 1700°F (927 °C) reduced the amount of NbC
by 40 pct, and the 1200°F (649°C) treatment also reduced the volume of Laves phase. Surprisingly, although the 1200°F (649°C)
treatment reduced the amounts of both Laves phase and NbC, it produced a 23 pct increase in liquation cracking, while the
1700°F (927°C) treatment produced an opposite 22 pct decrease in liquation cracking. The effect of carbon content on the as-cast
liquation cracking susceptibility is discussed in terms of its effect on the volume fraction of liquid produced during the
welding thermal cycle and the subsequent resolidification kinetics of the liquid during cooling. The effects of different
heat treatments are discussed in terms of their ability to redistribute solute, impurities, and precipitates within the matrix
and to grain boundaries in deleterious or beneficial ways.
Formerly Graduate Student, University of Alabama 相似文献
19.
20.
Improved Resistance to Laser Weld Heat-Affected Zone Microfissuring in a Newly Developed Superalloy HAYNES 282 总被引:1,自引:0,他引:1
Gleeble thermomechanical simulation and microstrucutural analyses of laser beam weldability of a newly developed precipitation-hardened nickel-base HAYNES alloy 282 were performed to better understand the fundamental cause of heat-affected zone (HAZ) cracking and how to prevent the cracking problem in the material. Submicron size intergranular M5B3 particles are identified for the first time in the present work by transmission electron microscopy, and were found to be the primary cause of HAZ grain boundary liquation cracking in the alloy. Complete dissolution of the liquating M5B3 particles by preweld heat treatment exacerbated rather than reduced susceptibility to cracking, which could be attributed to nonequilibrium intergranular segregation of boron atoms, liberated by the complete dissolution of the boride particles, during cooling from heat treatment temperature. Consequently, to reduce the HAZ cracking, a preweld heat treatment that reduces the volume fraction of the M5B3 particles while minimizing nonequilibrium grain boundary boron segregation is necessary, and this is possible by heat treating the alloy at 1353?K to 1373 K (1080?°C to 1100 °C). Further improvement in cracking resistance to produce crack-free welds is achieved by subjecting the alloy to thermomechanically induced grain refinement coupled with the preweld heat treatment at 1353 K (1080 °C). A Gleeble hot ductility test showed that formation of the crack-free welds is unexplainable by mere reduction in grain size without considering the effect of grain refinement on intergranular liquid produced by subsolidus liquation of the M5B3 borides. 相似文献