共查询到20条相似文献,搜索用时 31 毫秒
1.
R. K. Singh Raman 《Metallurgical and Materials Transactions A》1999,30(8):2103-2113
This study is an attempt to understand the combined role of variations in oxidizing environment and secondary precipitation,
in the microstructurally different regions of a standard Cr-Mo steel weldment, on the intensity of internal oxidation during
high-temperature oxidation in air and steam environments. Samples of the weld-metal, heat-affected zone (HAZ), and base-metal
regions were separated from the weldment of 2.25Cr-1 Mo steel and oxidized in the environments of air and steam at 873 K.
The oxide scales and underlying subscales were characterized using scanning electron microscopy (SEM), energy-dispersive X-ray
(EDX) analysis, and electron probe microanalysis (EPMA). Extensive internal oxidation and oxidation-induced void formation
in the subscale zone and grain-boundary cavitation in the neighboring region were found to occur during oxidation in the steam
environment. However, the internal oxidation and void formation were much more extensive in the subscale regions of the HAZ
than in the subscales of the weld-metal and base-metal regions. As a result, the alloy matrix in the area neighboring the
subscale region of the HAZ specimen suffered extensive grain-boundary cavitation. This behavior has been attributed to a rather
specific combination and complex interplay of the environment, alloy microstructure, oxidizing temperature, and nature of
the resulting external scale in causing and sustaining internal oxidation. The article also discusses the role of internal
oxidation-assisted microstructural degradation in deteriorating the service life of components of 2.25Cr-1Mo steel. 相似文献
2.
R. K. Singh Raman 《Metallurgical and Materials Transactions A》1998,29(2):577-586
Microstructural degradations in the base metal adjacent to the weld pool, i.e., the heat-affected zone (HAZ), caused during welding of 2.25Cr-1Mo steel, were characterized by electron and optical microscopy
of different regions of the weldments. In order to study the influence of the microstructural degradations on scaling kinetics
in steam and the resulting subscale features, samples of the base metal, the HAZ, and weld metal specimens were extracted
from the weldment and oxidized in an environment of 35 pct steam+nitrogen at 873 K for 10 hours. Oxide scales formed in the
three regions and the underlying subscales were characterized using scanning electron microscopy (SEM) and electron probe
microanalysis (EPMA). Influence of the “free” chromium content in the three weldment regions on protective scale formation
and on the subscale features has been investigated. As the principal achievement, this study has clearly shown the occurrence
of oxidation-induced void formation in the subscale zone and grain boundary cavitation in the neighboring area during steam
oxidation of the HAZ. This article also discusses the possible role of oxidation-induced void formation and grain boundary
cavitation in the inferior service life of welds in 2.25Cr-1Mo steel components. 相似文献
3.
Sarvesh Pal R. K. Singh Raman R. Rihan 《Metallurgical and Materials Transactions A》2012,43(9):3202-3214
Determination of the threshold stress intensity for stress corrosion cracking (K Iscc) of narrow areas such as weld and heat-affected zone (HAZ) of a weldment is a nontrivial task because of the requirements of large specimens in testing by the traditional techniques and the difficulty of restricting crack propagation to narrow regions in such specimens. This article describes a successful application of the circumferential notch tensile (CNT) technique to determine the K Iscc of narrow regions of the weld and HAZ. Also, the microstructure of the HAZ of the manual metal arc-welded steel was simulated over a relatively small length of specimens and its K Iscc in a hot caustic solution was determined successfully. Intergranular stress corrosion cracking was confirmed with a scanning electron microscope. 相似文献
4.
Liangyun Lan Xiangwei Kong Zhiyuan Chang Chunlin Qiu Dewen Zhao 《Metallurgical and Materials Transactions A》2017,48(9):4140-4153
This paper analyzed the evolution of microstructure, composition, and impact toughness across the fusion line of high-strength bainitic steel weldments with different heat inputs. The main purpose was to develop a convenient method to evaluate the HAZ toughness quickly. The compositions of HAZ were insensitive to higher contents of alloy elements (e.g., Ni, Mo) in the weld metal because their diffusion distance is very short into the HAZ. The weld metal contained predominantly acicular ferrite at any a heat input, whereas the main microstructures in the HAZ changed from lath martensite/bainite to upper bainite with the increasing heat input. The evolution of HAZ toughness in relation to microstructural changes can be revealed clearly combined with the impact load curve and fracture morphology, although the results of impact tests do not show an obvious change with heat input because the position of Charpy V notch contains the weld metal, HAZ as well as a part of base metal. As a result, based on the bead-on-plate welding tests, the welding parameter affecting the HAZ toughness can be evaluated rapidly. 相似文献
5.
X. Xu G. D. West J. A. Siefert J. D. Parker R. C. Thomson 《Metallurgical and Materials Transactions A》2018,49(4):1211-1230
The microstructure in the heat-affected zone (HAZ) of multipass welds typical of those used in power plants and made from 9 wt pct chromium martensitic Grade 92 steel is complex. Therefore, there is a need for systematic microstructural investigations to define the different regions of the microstructure across the HAZ of Grade 92 steel welds manufactured using the traditional arc welding processes in order to understand possible failure mechanisms after long-term service. In this study, the microstructure in the HAZ of an as-fabricated two-pass bead-on-plate weld on a parent metal of Grade 92 steel has been systematically investigated and compared to a complex, multipass thick section weldment using an extensive range of electron and ion-microscopy-based techniques. A dilatometer has been used to apply controlled thermal cycles to simulate the microstructures in distinctly different regions in a multipass HAZ using sequential thermal cycles. A wide range of microstructural properties in the simulated materials were characterized and compared with the experimental observations from the weld HAZ. It has been found that the microstructure in the HAZ can be categorized by a combination of sequential thermal cycles experienced by the different zones within the complex weld metal, using the terminology developed for these regions based on a simpler, single-pass bead-on-plate weld, categorized as complete transformation, partial transformation, and overtempered. 相似文献
6.
Ferritic steels are often used in thick-plate form. The feasibility of electron-beam welding such thick plates and the mechanical
properties of these welds were examined in a recent study. In this investigation, the microstructures of these thick-plate,
electron-beam welds were evaluated. The study was carried out on a 3Cr-1.5Mo-0.1V steel. Weld simulations were used to aid
in the study of the heat-affected zone (HAZ) microstructure. Such simulations allowed for a more reliable and detailed evaluation
of the variation in microstructure with distance from the fusion line. The structures were related to microhardness measurements
made across the width of the weld and the HAZ. The fusion zone and the immediately adjacent HAZ consisted of bainite platelets
with narrow films of retained austenite at many of the bainite platelet boundaries. Farther away from the fusion zone, the
structure was a two-phase mixture of bainitic platelets and ferrite produced by heating base metal between theAc
1 and theAc
3 temperatures. Still farther from the weld, the structure consisted of tempered bainite, with the degree of tempering decreasing
with distance from the fusion line. The bainite plus ferrite region and the tempered bainite section are associated with a
soft zone in the hardness profile across the weld. A postweld heat treatment (PWHT) was found to reduce the hardnesses of
the fusion zone, HAZ, and base material to relatively uniform levels. The structure across the weld and HAZ after a PWHT is
tempered bainite except in one section of the HAZ in which tempered bainite and ferrite coexist. 相似文献
7.
C. R. Das S. K. Albert J. Swaminathan S. Raju A. K. Bhaduri B. S. Murty 《Metallurgical and Materials Transactions A》2012,43(10):3724-3741
The roles of boron and heat-treatment temperature in improving the type IV cracking resistance of modified 9Cr-1Mo steel weldment were studied. Two different heats of P91 steel, one without boron, designated as P91 and the other with controlled addition of boron with very low nitrogen, designated as P91B, were melted for the current study. The addition of Boron to modified 9Cr-1Mo steel has increased the resistance against softening in fine-grained heat-affected zones (FGHAZ) and intercritical heat-affected zones (ICHAZ) of the weldment. Creep rupture life of boron containing modified 9Cr-1Mo steel weldment, prepared from 1423?K (1150?°C) normalized base metal, was found to be much higher than that prepared from 1323?K (1050?°C) normalized base metal because of the stabilization of lath martensite by fine M23C6 precipitates. This finding is in contrast to the reduction in creep rupture life of P91 weldment prepared from 1423?K (1150?°C) normalized base metal compared with that of the weldment prepared from 1323?K (1050?°C) normalized base metal. The trace of failure path from the weld metal to ICHAZ in P91B weldment was indicative of type II failure in contrast to type IV failure outside the HAZ and base metal junction in P91 weldment, which suggested that boron strengthened the microstructure of the HAZ, whereby the utilization of boron at a higher normalizing temperature seemed to be significantly greater than that at the lower normalizing temperature. 相似文献
8.
P. Deb K. D. Challenger A. E. Therrien 《Metallurgical and Materials Transactions A》1987,18(13):987-999
Structure-property relationships of two HY-100 steel weldments prepared by submerged arc (SAW) and gas metal arc (GMAW) welding processes using identical heat input (2.2 kJ mm-1) have been studied. It has been found that submerged arc welded (SAW) HY-100 steel weldments have a lower weld toughness than welds produced by the gas metal arc welding (GMAW) process. Optical, scanning, and transmission electron microscopy were used in conjunction with microhardness traverses to characterize and compare the various microconstituents that are present in the last weld pass of both weldments. TEM examination revealed the presence of coarse upper bainite, B-II bainite, and carbides in a highly dislocated ferrite matrix as well as in ferrite laths in the SAW weldment, while the GMAW weldment exhibited a typical fine low carbon lath martensite, autotempered martensite, and mixed B-II and B-III bainites which occasionally contained small regions of twinned martensite. The measured cooling rate in the SAW was found to be about 40 pct slower than that in GMAW. It was also found in the SAW that the weld metal inclusion number density was about 25 pct greater than that in GMAW. Micro-hardness traverses exhibited significantly lower hardness (about 50 HV) in the SAW weldment compared with GMAW, but the tempered weld metal microhardness in both the weldments was measured about the same, at 250 HV. The ductile-to-brittle transition temperature (DBTT) of both weldments was determined by Charpy impact test. Based on an average energy criterion, the DBTT of the SAW weldment was 323 K (50 °C) higher than that of the GMAW weldment. This difference in fracture resistance is due to the different weld metal microstructures. The different microstructures most probably result from differences in cooling rate subsequent to welding; however, the SAW weld also has a higher inclusion number density which could promote a higher transformation temperature for the austenite. 相似文献
9.
M. Arivarasu P. Roshith R. Padmanaban S. Thirumalini K. V. Phani Prabhakar G. Padmanabham 《Canadian Metallurgical Quarterly》2017,56(2):232-244
In the research work, an attempt is made to join nickel-based alloy 825 by employing CO2 laser beam welding. Successful full penetration weld joint of a 5?mm thick plate is achieved with a very low heat input of 120?J-mm?1. Narrow weld bead width of 0.6?mm at the root and 1.6?mm at the cap is observed fusion zone; the interface and base metal microstructures have been examined using both optical and scanning electron microscopic techniques to understand the microstructural changes which have occurred due to laser welding. A range of tests of Vickers micro hardness, tensile and impact tests had been performed on the weldment to ascertain the mechanical properties of the joint. Tensile failure at the base metal and a 180° root bend test conducted on the weldment ascertain the soundness of the weld joint produced. An attempt is made to correlate the microstructure and mechanical properties of the weldment. Intermetallics TiN and Al4C3 observed in the SEM\EDS analysis at the fusion zone are found to have improved the weld metal strength and hardness. 相似文献
10.
P. Deb K. D. Challenger A. E. Therrien 《Metallurgical and Materials Transactions A》1991,22(1):987-999
Structure-property relationships of two HY-100 steel weldments prepared by submerged arc (SAW) and gas metal arc (GMAW) welding
processes using identical heat input (2.2 kJ mm-1) have been studied. It has been found that submerged arc welded (SAW) HY-100 steel weldments have a lower weld toughness
than welds produced by the gas metal arc welding (GMAW) process. Optical, scanning, and transmission electron microscopy were
used in conjunction with microhardness traverses to characterize and compare the various microconstituents that are present
in the last weld pass of both weldments. TEM examination revealed the presence of coarse upper bainite, B-II bainite, and
carbides in a highly dislocated ferrite matrix as well as in ferrite laths in the SAW weldment, while the GMAW weldment exhibited
a typical fine low carbon lath martensite, autotempered martensite, and mixed B-II and B-III bainites which occasionally contained
small regions of twinned martensite. The measured cooling rate in the SAW was found to be about 40 pct slower than that in
GMAW. It was also found in the SAW that the weld metal inclusion number density was about 25 pct greater than that in GMAW.
Micro-hardness traverses exhibited significantly lower hardness (about 50 HV) in the SAW weldment compared with GMAW, but
the tempered weld metal microhardness in both the weldments was measured about the same, at 250 HV. The ductile-to-brittle
transition temperature (DBTT) of both weldments was determined by Charpy impact test. Based on an average energy criterion,
the DBTT of the SAW weldment was 323 K (50 °C) higher than that of the GMAW weldment. This difference in fracture resistance
is due to the different weld metal microstructures. The different microstructures most probably result from differences in
cooling rate subsequent to welding; however, the SAW weld also has a higher inclusion number density which could promote a
higher transformation temperature for the austenite.
Formerly Adjunct Research Professor with the Materials Engineering Group, Naval Postgraduate School
Formerly Graduate Student at NPS 相似文献
11.
R. K. Singh Raman 《Metallurgical and Materials Transactions A》2000,31(12):3101-3108
Measurement of the thickness of oxide scales that develop over high-temperature components has found an innovative application
in life assessment of steam generation and handling systems. The present study is an investigation of the high-temperature
corrosion and scale thickness across the weldments of a “chromium-molybdenum” steel, and reviews its possible relevance to
the life assessment of the welded high-temperature components by scale thickness measurement. Results are presented of the
recent investigations on the combined roles of the oxidizing environment and secondary carbide precipitation on the extent
of void formation in the microstructurally different regions of weldments of the chromium-molybdenum steel. Specimens of the
weld metal, heat-affected zone (HAZ), and base metal of a 2.25Cr-1Mo steel weldment were oxidized in steam. Extensive internal
oxidation and oxidation-induced void formation (with a much greater intensity in the case of the HAZ) is discussed. The greater
intensity of oxidation-induced void formation in the HAZ may facilitate preferential cracking in this region of the weldments
and, hence, is proposed to be an important parameter in the context of the recently developed codes for life assessment of
aging high-temperature components. 相似文献
12.
Christian B. Fuller Murray W. Mahoney 《Metallurgical and Materials Transactions A》2006,37(12):3605-3615
Friction stir processing (FSP) is used locally to modify the microstructure and thus mechanical properties of 5083-H321/5356
aluminum gas metal arc welds (GMAWs). Four specimen approaches were examined: as-arc welded, weld toe FSP (with arc weld on
either the advancing or the retreating side of tool), and weld crown FSP. Microstructures within the fine-grained FSP region
contained smaller constituent particles. Mg2Si and Al6(Fe,Mn), than those particles found in the arc weld nugget, heat-affected zone (HAZ), and base-metal (BM) locations. The FSP
improved the monotonic tensile strength, yield strength, and elongation of 5083-H321/5356 Al arc welds by 6 to 9 pct, 7 to
13 pct, and 46 to 80 pct, respectively. The addition of FSP produced a 30 pct increase in the load necessary to reach 107 cycles during four-point bending fatigue. An analysis of strengthening mechanisms determined that solid-solution, grain-size,
and precipitation strengthening made contributions to the calculated yield strength of the BM, are weld nugget, and FSP regions.
In addition, the strength mechanism analysis demonstrated that FSP increased the amount of grain-size strengthening and precipitate
strengthening by nearly 110 MPa, when compared to the arc weld nugget. 相似文献
13.
K. Laha K. S. Chandravathi K. Bhanu Sankara Rao S. L. Mannan D. H. Sastry 《Metallurgical and Materials Transactions A》2001,32(1):115-124
The evaluation of the creep deformation and fracture behavior of a 2.25Cr-1Mo steel base metal, a 2.25Cr-1Mo/2.25Cr-1Mo similar
weld joint, and a 2.25Cr-1Mo/Alloy 800 dissimilar weld joint at 823 K over a stress range of 90 to 250 MPa has been carried
out. The specimens for creep testing were taken from single-V weld pads fabricated by a shielded metal arc-welding process
using 2.25Cr-1Mo steel (for similar-joint) and INCONEL 182 (for dissimilar-joint) electrodes. The weld pads were subsequently
given a postweld heat treatment (PWHT) of 973 K for 1 hour. The microstructure and microhardness of the weld joints were evaluated
in the as-welded, postweld heat-treated, and creep-tested conditions. The heat-affected zone (HAZ) of similar weld joint consisted
of bainite in the coarse-prior-austenitic-grain (CPAG) region near the fusion line, followed by bainite in the fine-prior-austenitic-grain
(FPAG) and intercritical regions merging with the unaffected base metal. In addition to the HAZ structures in the 2.25Cr-1Mo
steel, the dissimilar weld joint displayed a definite INCONEL/2.25Cr-1Mo weld interface structure present either as a sharp
line or as a diffuse region. A hardness trough was observed in the intercritical region of the HAZ in both weld joints, while
a maxima in hardness was seen at the weld interface of the dissimilar weld joint. Both weld joints exhibited significantly
lower rupture lives compared to the 2.25Cr-1Mo base metal. The dissimilar weld joint exhibited poor rupture life compared
to the similar weld joint, at applied stresses lower than 130 MPa. In both weld joints, the strain distribution across the
specimen gage length during creep testing varied significantly. During creep testing, localization of deformation occurred
in the intercritical HAZ. In the similar weld joint, at all stress levels investigated, and in the dissimilar weld joint,
at stresses ≥150 MPa, the creep failure occurred in the intercritical HAZ. The fracture occurred by transgranular mode with
a large number of dimples. At stresses below 150 MPa, the failure in the dissimilar weld joint occurred in the CPAG HAZ near
to the weld interface. The failure occurred by extensive intergranular creep cavity formation. 相似文献
14.
Yongjoon Kang Gitae Park Seonghoon Jeong Changhee Lee 《Metallurgical and Materials Transactions A》2018,49(1):177-186
A large fraction of reheated weld metal is formed during multi-pass welding, which significantly affects the mechanical properties (especially toughness) of welded structures. In this study, the low-temperature toughness of the simulated reheated zone in multi-pass weld metal was evaluated and compared to that of the as-deposited zone using microstructural analyses. Two kinds of high-strength steel welds with different hardenabilities were produced by single-pass, bead-in-groove welding, and both welds were thermally cycled to peak temperatures above Ac3 using a Gleeble simulator. When the weld metals were reheated, their toughness deteriorated in response to the increase in the fraction of detrimental microstructural components, i.e., grain boundary ferrite and coalesced bainite in the weld metals with low and high hardenabilities, respectively. In addition, toughness deterioration occurred in conjunction with an increase in the effective grain size, which was attributed to the decrease in nucleation probability of acicular ferrite; the main cause for this decrease changed depending on the hardenability of the weld metal. 相似文献
15.
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
16.
D. J. Chastell P. Doig P. E. J. Flewitt P. J. Norman 《Metallurgical and Materials Transactions A》1988,19(6):1445-1460
The environmental cracking of Type 316 austenitic stainless steel manual metal arc (MMA) weldments in high temperature CO2 has been investigated. The welding thermal transient has been analyzed and used to predict the sensitization of the parent
material and resulting residual stresses. Sensitization is considered to result from the local depletion of chromium about
grain boundaries and this has been considered theoretically and measured using STEM combined with energy dispersive X-ray
analysis. Residual stresses have been measured using the X-ray diffraction method. Flux residues over the HAZ of the weldment
have been identified using X-ray diffraction analysis. Chemical changes in these residues which resulted in cracking of test
samples exposed to high temperature (673 to 823 K) CO2 gas have been analyzed by X-ray diffraction. The susceptibility of the weldments to cracking was found to be influenced by
the carbon content and hardness of the material. In materials of high carbon content and high hardness, the necessary cracking
parameters are satisfied by the combined contribution of the microstructural sensitization, tensile residual stresses, and
the chemical interaction of weld flux residue with the CO2 gas which provides a molten salt environment capable of allowing rapid transport of aggressive species to active crack sites. 相似文献
17.
Divya Jain David N. Seidman Erin J. Barrick John N. DuPont 《Metallurgical and Materials Transactions A》2018,49(4):1031-1043
Newly developed low-carbon 10 wt pct Ni-Mo-Cr-V martensitic steels rely on the Ni-enriched, thermally stable austenite [formed via multistep intercritical Quench-Lamellarization-Tempering (QLT)-treatment] for their superior mechanical properties, specifically ballistic resistance. Critical to the thermal stability of austenite is its composition, which can be severely affected in the weld heat-affected zones (HAZs) and thus needs investigations. This article represents the first study of the nanoscale redistributions of C, Ni, and Mn in single-pass HAZ microstructures of QLT-treated 10 wt pct Ni steels. Local compositions of Ni-rich regions (representative of austenite compositions) in the HAZs are determined using site-specific 3-D atom-probe tomography (APT). Martensite-start temperatures are then calculated for these compositions, employing the Ghosh-Olson thermodynamic and kinetics approach. These calculations predict that austenite (present at high temperatures) in the HAZs is susceptible to a martensitic transformation upon cooling to room temperature, unlike the austenite in the QLT-treated base-metal. While C in the QLT-treated base-metal is consumed primarily in MC and M2C-type carbide precipitates (M is Mo, Cr, V), its higher concentration in the Ni-rich regions in the HAZs indicates the dissolution of carbide precipitates, particularly M2C carbide precipitates. The role of M2C carbide precipitates and austenite stability is discussed in relation to the increase in microhardness values observed in the HAZs, relative to the QLT-treated base-metal. Insights gained from this research on austenite stability and carbide precipitation in the single-pass HAZ microstructures will assist in designing multiple weld cycles for these novel 10 wt pct Ni steels. 相似文献
18.
Manidipto Mukherjee Tapan Kumar Pal 《Metallurgical and Materials Transactions A》2012,43(6):1791-1808
This article describes in detail the effect of the modes of metal transfer on the microstructure and mechanical properties
of gas metal arc-welded modified ferritic stainless steel (SSP 409M) sheets (as received) of 4 mm thickness. The welded joints
were prepared under three modes of metal transfer, i.e., short-circuit (SC), spray (S), transfer, and mix (M) mode transfer using two different austenitic filler wires (308L and
316L) and shielding gas composition of Ar + 5 pct CO2. The welded joints were evaluated by means of microstructural, hardness, notched tensile strength, Charpy impact toughness,
and high cycle fatigue. The dependence of weld metal microstructure on modes of metal transfer and filler wires has been determined
by dilution calculation, WRC-1992 diagram, Creq/Nieq ratio, stacking fault energy (SFE), optical microscopy (OM), and transmission electron microscopy (TEM). It was observed
that the microstructure as well as the tensile, Charpy impact, and high cycle fatigue of weld metal is significantly affected
by the mode of metal transfer and filler wire used. However, the heat-affected zone (HAZ) is affected only by the modes of
metal transfer. The results have been correlated with the microstructures of weld and HAZ developed under different modes
of metal transfer. 相似文献
19.
K. LAHA K.S. CHANDRAVATHI P. PARAMESWARAN K. BHANU SANKARA RAO S.L. MANNAN 《Metallurgical and Materials Transactions A》2007,38(1):58-68
In the postweld heat-treated (PWHT) fusion welded modified 9Cr-1Mo steel joint, a soft zone was identified at the outer edge
of the heat-affected zone (HAZ) of the base metal adjacent to the deposited weld metal. Hardness and tensile tests were performed
on the base metal subjected to soaking for 5 minutes at temperatures below Ac1 to above Ac3 and tempering at the PWHT condition. These tests indicated that the soft zone in the weld joint corresponds to the intercritical
region of HAZ. Creep tests were conducted on the base metal and cross weld joint. At relatively lower stresses and higher
test temperatures, the weld joint possessed lower creep rupture life than the base metal, and the difference in creep rupture
life increased with the decrease in stress and increase in temperature. Preferential accumulation of creep deformation coupled
with extensive creep cavitation in the intercritical region of HAZ led to the premature failure of the weld joint in the intercritical
region of the HAZ, commonly known as type IV cracking. The microstructures across the HAZ of the weld joint have been characterized
to understand the role of microstructure in promoting type IV cracking. Strength reduction in the intercritical HAZ of the
joint resulted from the combined effects of coarsening of dislocation substructures and precipitates. Constrained deformation
of the soft intercritical HAZ sandwich between relatively stronger constitutes of the joint induced creep cavitation in the
soft zone resulting in premature failure. 相似文献
20.
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