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Materials at High Temperatures (2006), 23(3-4)
Creep
resistance of similar and dissimilar weld
joints
of P91 steel
Dagmar
Jandova´ , Josef Kasl and Va´ clav Kanta
Skoda
Vy´zkum s.r.o., Tylova 57, Pilsen, CZ 316 00,
E-mail:
dagmar.jandova@skodavyzkum.cz
ABSTRACT
Two
experimental weld joints, a similar weld joint of 9Cr –1Mo steel and a
dissimilar weld joint of
9Cr
– 1Mo and 2.25Cr – 1Mo steels, were fabricated by the TIGþE
method and post-weld heating
was
applied. Creep testing was carried out at temperatures ranging from 525 to 625_C
in the stress
range
40 – 240 MPa. Creep rupture strength was evaluated using the Larson–Miller
parameter.
Extended
metallography including transmission electron microscopy was performed and
critical
zones
were indicated where fractures were concentrated during the creep exposure. At
high
temperatures
rupture of the dissimilar weldment occurred in the heat affected zone (HAZ) of
the
weld
metal while rupture of the similar weldment was located in the HAZ of the
parent material. The
processes
of recovery seem to be the main causes of decrease in creep rupture strength of
both weld
joints
in comparison to the parent materials.
Keywords:
creep-resistant steels, welding, microstructure, transmission
electron microscopy
Microstructure
and mechanical properties of an
inertia
friction welded INCOLOY alloy 909 –
INCONEL
alloy 718 joint for rotating applications
O.
Rodera*, J. Albrechtb and
G. Lu¨ tjeringb
aMTU
Aero Engines GmbH, 80995
E-mail:
Olaf.Roder@muc.mtu.de
bTechnical
University Hamburg-Harburg, 21073
ABSTRACT
Inertia
welding is a common practice to join axially symmetrical parts for aero-engine
applications.
The
shaft for a new advanced high-pressure compressor will be produced by joining
the high strength
superalloys
INCOLOY_ alloy 909 (Incoloy909) and INCONEL_ alloy
718 (IN718). IN718 is the
work-horse
nickel-iron-chromium alloy for a variety of parts for aero-engine applications
due to a
good
combination of relevant mechanical properties, good corrosion resistance and
easy fabricability.
Incoloy909
is a nickel-iron-cobalt alloy used in aero-engines due to an interesting
combination of a
nearly
constant low coefficient of thermal expansion combined with a constant modulus
of elasticity
and
high strength over a wide range of temperatures. Both alloys are strengthened
by precipitationhardening
through
additions of niobium and titanium. Ring shaped specimens of fully heat-treated
Incoloy909
and IN718 are joined by inertia welding. The microstructure in the welded zone
is
investigated
by optical microscopy and transmission electron microscopy with the focus on
the
Incoloy909
side. Post-weld heat-treatments (PWHT) are evaluated by microstructural
investigations
and
by hardness measurements. The chosen PWHT is characterized by its tensile,
creep and load
controlled
fatigue properties. The results of the mechanical tests are described in terms
of the
microstructural
changes observed in the welded zone.
Characterisation
of diffusion bond TiAl –Ti 6242 joints
B.
Dogana*, X. Zhenga,b and
K.-H. Bohma
aGKSS
Research Centre, Max-Planck-Str.1, D-21502 Geesthacht,
E-mail:
bilal.dogan@gkss.de
bBeijing
ABSTRACT
The
g-TiAl based titanium aluminides are considered as candidates to
replace the current materials in
engineering
applications at high temperatures due to their light weight and high
temperature
properties.
On the other hand, Ti6242Si alloys offer tensile and long-term creep strength
which is
achieved
through microstructural tailoring of alloys with increased a stabiliser
content. The equiaxed,
duplex
and lamellar microstructures that meet the modern engine design demands qualify
these alloys
for
aero-engine applications. Both materials are well studied for processing,
characterisation and
structural
applications [1 – 3]. However, fully utilisation of these materials for
demanding engineering
applications
necessitate advanced joining technologies where homogeneous material properties
are
retained
with high deformation and crack resistant bonds.
The
present paper reports on a systematic study being carried out on the diffusion
bonding of g-
TiAl
intermetallics and equiaxed ayb Ti6242Si
alloy. Emphasis is put on the diffusion bonding
process
parameters of industrial interest, characterisation and properties of the
joints. The process
variables
including temperature, pressure and time are optimised to produce joints with
sound
microstructure,
bond quality and strength. The chemical composition and phase morphologies are
studied
using scanning electron microscopy and energy dispersive X-ray (EDX) analysis.
Mechanical
characterisation
includes the standard tensile and micro tensile tests at ambient to high
temperatures.
Deformation,
crack initiation and crack growth behaviours are studied on fracture surfaces
and side
surfaces
of the tested diffusion bond joints.
Keywords:
g (TiAl) based titanium aluminides, Ti6242Si, diffusion bonding, crack
initiation
The
creep rupture behaviour and steam oxidation
resistance
of P92 weldments
P.J.
Ennis
Institut
fu¨ r Werkstoffe und Verfahren der Energietechnik IWV-2, Forschungszentrum
Ju¨
lich GmbH, D-52425 Ju¨ lich,
E-mail:
p.j.ennis@fz-juelich.de
ABSTRACT
The
creep rupture properties of P92 autogenous welds have been investigated using
cross-weld
specimens
and weld simulation specimens. The influence of post-weld heat treatment was
also
examined.
The results have shown that the weldments in creep rupture tests failed in the
softened heat
affected
zone (Type IV failure). Transmission electron microscopy of thin foils taken
from the heat
affected
zone revealed a low dislocation density, which is associated with the low creep
rupture
strength.
The stress rupture strength reduction factor of the weldments compared with the
base
material
is, however, within acceptable limits. Steam oxidation tests were carried out
on the weld
deposit
and on cross-weld specimens and showed that the weldments exhibited lower
oxidation rates
than
the parent material, due to the higher Si and Mn contents of the filler metal.
Keywords:
creep rupture behaviour, steam oxidation resistance, P92 weldments
An
application of a phenomenological theory of creep damage
V.
Mentl
Skoda
Research Ltd., 31600
E-mail:
vaclav.mentl@skoda.cz
ABSTRACT
The
presentation summarizes a creep damage theory based on a simple
phenomenological model of
creep
and creep damage making it possible to evaluate creep stress to rupture
relationship. Four
material
constants, which can be evaluated from uniaxial creep test results, are used to
describe the
material
behaviour. The theory is validated by comparison with an Al-alloy and a steel
experimental
data,
and a temperature relationship of the material constants is presented.
Experimental creep to
rupture
data of steel tubes loaded with internal pressure are compared with the
theoretical curves
derived
from the uniaxial creep data.
Keywords:
creep, damage, parameter Larson-Miller, steel, Al-alloy
Integrity
of welded joints
R.K.
Pennya and
aR.K.
Penny & Associates,
bCape
Peninsula University of Technology,
E-mail:
kohlhoferw@cput.ac.za
ABSTRACT
The
integrity of welded joints is of prime importance from many viewpoints, not
least of which are
the
safety and economy of plant operation. A previous IMechE seminar discussing
high temperature
welds
indicated that welded joints in pressure vessels are the least tractable in terms
of design.
Progress
since then has been minimal. This is particularly true for power generating and
petrochemical
industries
in which welded vessels are subjected to aggressive environments and loading
whilst
being expected to sustain economic lifetimes beyond 30 or more years. In these
cases the
vessels
are often subjected to temperatures within the creep range causing internal
cavities to be
generated
which can be life limiting at fractions of the design lives. The welded joints
at nozzle
intersections
in these cases are clearly limiting factors in the overall success – both legal
and
economical
– of the industries concerned.
Keywords:
welded joints, safety, economy, plant operation
A
case study for reheat crack
Pedro
Veron
E-mail:
veron@ensa.es
ABSTRACT
This
paper deals with an experience of high temperature behaviour of weldments. It
relates to a case
of
reheat cracking that took place in the manufacturing of a nuclear pressure
vessel 30 years ago. At
this
time, designers did not consider the factyphenomenon
of welding postheating. Therefore, they
made
the recommendation that the manufacturers had to maintain preheating
temperature until the
weldment
entered the furnace for PWHT. In this condition, the high stresses present at
the weld toe
often
gave way to reheat cracking.
Keywords:
reheat cracking, heat affected zone, nuclear component, post weld
heat treatment, manufacturing
Small
Punch test for weld heat affected zones
Yingzhi
Lia* and Roman Sˇ turmb*
aKEMA
bUniversity
of
ABSTRACT
Small
Punch tests (SPT) have been performed on four different zones of P91 welded
joint, namely the
base
metal (BM), the weld metal (WM), the heat affected zone at base metal side
(HAZ-BM) and the
heat
affected zone at weld metal side (HAZ-WM). Besides the creep rupture times,
full creep
deflection
curves are also available from which creep properties of different HAZ zones
can be
derived.
In
this paper, an analytic approach, based on Chakrebarty’s membrane stretch model
and
Kachanov’s
creep law, is used to interpret the creep deflection curves of different zones.
First,
strains
and stresses are derived from the observed deflection curves according to the
Chakrebarty’s
membrane
stretch model, then the Kachanov’s parameters are determined by attempting to
minimize
the
sum of the squares of the residuals (difference between derived strains and
calculated strains at
each
time point). With Kachanov’s parameters known, all creep properties can be
obtained.
Keywords:
Small Punch test, weld heat affected zones
High
temperature cross-weld characterisation of
steel
weldments by microtensile testing
U.
Ceyhan*, M. Horstmann and B. Dogan
GKSS
Research Centre, Max-Planck Str.1, D-21502
E-mail:
umit.ceyhan@gkss.de
ABSTRACT
Study
of local material properties and damage mechanisms are undertaken in order to
characterise
weldments
that show significant variation of properties across weldments. One of the
methods to
characterise
the local variation of properties is microtensile (MT) testing of specimens
machined out
of
specific narrow zones of weldments. The literature data, though limited, on
microtensile specimen
testing
are reported at their low temperature behaviour. On the other hand, systematic
study of crossweld
local
material properties at high service temperatures have not yet been reported. In
the present
study,
MT tests are conducted across similar welds of P22 and P91 steels at 550 and
600_C,
respectively.
In order to study deformation mechanisms and the role of surface condition on
properties,
specimens with different surface conditions (i.e.
machined, polished and electropolished
surfaces)
are tested. Two different loading rates of 0.2mmymin
and 0.5mmymin are used to study the
effect
of loading rate on deformation and mechanical properties. Variations of
material properties
yield
strength (Rp0.2) and ultimate tensile strength (Rm),
for the weldments are presented as a function
of
surface conditions of specimens and loading speeds. Higher loading rates yield
higher values of
Rp0.2
and Rm, and specimens with
machined and polished surfaces show consistent and higher values
of
Rp0.2 and Rm compared
to specimens with an electropolished surface finish. Deformation behaviour
is
studied on the side surfaces of tested microtensile specimens using an SEM.
Deformation is
correlated
to microstructural constituent that is observed on specimen side surfaces. The
metallographic
information
is used to interpret the variation of mechanical properties determined in
tension at
high
temperatures. The MT data are compared with standard tensile data obtained on
specimens with
simulated
microstructures. The prospects of using MT tests for characterising the
material at high
temperatures
and feasibility of use of data for assessment of components under service
loading
conditions
are reported.
Keywords:
microtensile testing, high temperature deformation, high temperature
steels, SEM, microstructure
Non-destructive
characterization of thermal ageing
of
the Cu-rich WB36 steel 15 NiCuMoNb 5 (1.6368)
G.
Dobmann*,
Fraunhofer
IZFP, University Building 37, 66123 Saarbru¨ cken,
E-mail:
gerd.dobmann@izfp.fraunhofer.de
ABSTRACT
The
phenomenon of precipitation hardening in steels is usually associated with
carbon and nitrogen
additions
which precipitate out under heat treatment or specific service conditions as
carbides or
carbo-nitrides.
In some alloys, however, for instance in Western nuclear pressure vessel
steels, small
additions
of copper can be the driving force for embrittlement and hardening. In the case
of the steel
grade
WB36 (15 NiCuMoNb 5, 1.6368), which is in service in fossil power plants and
German
nuclear
power plants, the effects of copper precipitation are even larger. The progress
of precipitation
can
be characterized by Vickers hardness measurements which, however, cannot be
applied in an
area-wide
manner under practical circumstances. A demand for the development of
equivalent NDT
techniques,
therefore, arises.
To
this end, Fraunhofer IZFP has adapted and developed the so-called 3MA approach
which
combines
several micro-magnetic testing quantities for the characterization of
mechanical properties.
This
paper presents and discusses recent results obtained using the 3MA approach
applied to
characterizing
the ageing response of steel WB36.
Keywords:
precipitation, precipitates, hardening, hardness, embrittlement,
ageing, WB36, copper, 3MA, micromagnetic,
non-destructive
testing
Degradation
assessment of welded joints by X-ray
diffraction
technique
J.
Fialaa, M. Kolegaa and
V.Mentlb*
aWest-Bohemian
University,
bSkoda
Research Ltd., 31600
ABSTRACT
X-ray
diffraction technique has been recognized as a useful tool for the assessment
of material
degradation
extent after a long-time service. Framework 5 project ‘‘XPECTION’’ was dealing
with
this
task with respect to high-temperature creep degradation of boiler tube steels.
This paper
summarizes
partial results of an experimental programme concentrated on mechanical
properties
degradation
of base metals of steel and Al-alloy test specimens of welded components as a
result of
fatigue
loading.
Keywords:
damage, X-ray diffraction, fatigue, steel, Al-alloy
Determination
of residual stresses in multipass
weldments
of high strength steels with
experimental
and numerical techniques
D.
Memhard, W. Pfeiffer and D. Siegele*
Fraunhofer-Institut
fu¨ r Werkstoffmechanik,
E-mail:
dieter.siegele@iwm.fraunhofer.de
ABSTRACT
This
paper presents part of the work from the EU project ELIXIR on a series of
welded geometries.
Experimental
and numerical techniques have been applied to determine residual stresses in
buttwelded
joints
of high strength steel. Starting from simple weld geometries that served for
validation of
these
tools, residual stresses were measured and calculated for an industrial
component for offshore
application.
In spite of some simplifications in the numerical simulation of the welding
process,
satisfying
agreement with experimental data has been achieved especially if relevant
three-dimensional
effects
have been modelled. The validation of numerical techniques for residual stress
calculations
can help to enable cost effective fabrication and repair of steel components.
Keywords:
residual stresses, X-ray diffraction, hole drilling method, 2Dy3D
modelling, validation, application
Deformation
of welded assemblies modelling and
distortion
minimisation
Frederic
J. Blom
NRG
Petten, The
ABSTRACT
Welding
of assemblies is often accompanied by an undesired amount of distortion. This
results in
increased
costs for straightening or other repair activities. In order to understand and
subsequently
mitigate
the effects of weld distortion in assemblies, a technique is developed to
predict qualitative
weld
distortion by means of finite element techniques. The model is kept simple in
order to limit the
calculation
times. Therefore, shell elements are used to model the plates in the assembly.
The detailed
information
in the weld itself is therefore lost. However, the technique allows for faster
calculation
times
on larger and more complex assemblies. By means of this technique transient
deformation of
the
welding of an assembly can be visualised, which enhances insight into the
problem. The influence
of
structural details or support functions can be shown to the designer. Weld
distortion can then
subsequently
be minimised as a function of weld sequence. The model has been validated
against
various
test-cases found in the open literature. These test-cases vary from simple
T-branches to an
assembled
part of a ship hull. It has been shown that the modelling provides a good
prediction of
weld
distortion as a function of welding sequence. The model distinguishes the
distortion resulting
from
different welding sequences, thereby providing a fast simulation tool allowing
the designer to
minimise
the total deformation.
Keywords:
weld distortion, modelling, welded assemblies
Suppression
of Type IV fracture in welded joints of
advanced
ferritic power plant steels – effect of
boron
and nitrogen
F.
Abea, M. Tabuchib,
M. Kondoc and H. Okadad
aNational
Institute for Materials Science (NIMS), 1-2-1 Sengen, Tsukuba 305-0047,
E-mail:
ABE.Fujio@nims.go.jp
bNational
Institute for Materials Science (NIMS), 1-2-1 Sengen, Tsukuba 305-0047,
E-mail:
TABUCHI.Masaaki@nims.go.jp
cNational
Institute for Materials Science (NIMS), Now, Mitsubishi Heavy Industries, Ltd,
Fukahori-machi,
dNational
Institute for Materials Science (NIMS), Now, Sumitomo Metal Industries, Ltd,
ABSTRACT
The
effect of boron and nitrogen on the grain refinement in HAZ during heating and
on the Type IV
fracture
in welded joints has been investigated for P92 and 9Cr – 3W–3Co–VNb steel
containing
boron
and or nitrogen. Creep tests were carried out at 650_C
(923 K) for up to about 36104 h
for
base
metals, simulated HAZ specimens and welded joints. The addition of boron of 47
to 139 ppm to
9Cr
– 3W–3Co–VNb steel containing minimized nitrogen as low as 10 – 20 ppm
suppresses the grain
refinement
in HAZ and hence suppresses the Type IV fracture in welded joints at low
stresses. The
addition
of excess nitrogen of 0.06% causes the grain refinement during heating at
around Ac3
temperature,
in both conditions of no boron and high boron of 130 ppm. A combination of high
boron
of
130 ppm and low nitrogen of 80 ppm causes no grain refinement in HAZ during
heating at around
Ac3
temperature as well as significant improvement of creep rupture strength of
base metal by fine
MX
nitrides without any formation of boron nitrides.
Keywords:
9Cr steel, boron, nitrogen, heat affected zone, Type IV fracture,
creep strength, HAZ microstructure
New
12% Cr-steel for tubes and pipes in power
plants
with steam temperatures up to 650_C
Alfred
Dhoogea*, Staf Huysmansb,
Bruno Vandenberghec, Johan Vekemana and
Claus
Jochumd
aBelgian
Welding Institute,
and
dBo¨ hler Thyssen Welding
*E-mail:
alfred.dhooge@UGent.be
ABSTRACT
Nowadays,
intense efforts are made to increase efficiency and thereby minimize harmful
emissions of
power
plants. This can be achieved by increasing operating pressure and temperature
to ultrasupercritical
conditions.
Presently martensitic 9% Cr-steels, e.g.
P91, E911 and P92 are used for
power
plants with advanced steam parameters. Whilst these materials have the highest
creep rupture
strength
values of ferritic steels, their oxidation resistance is lower than 12%
Cr-steels, such as
X20CrMoV12-1.
With increasing steam temperature (target: 650_C)
the lifetime of components made
of
9% Cr-steel becomes limited not only by creep but also by oxidation. The
present paper reports a
new
12Cr martensitic steel developed by Vallourec & Mannesmann, which is
designed for use at
temperatures
up to 650_C. It is the outcome of a normative research
project of the Belgian Welding
Institute
in collaboration with Laborelec and with industrial partners (Carnoy Industrial
Piping,
Cockerill
Mechanical Industries, Fabricom, Stork Mec, Bo¨hler Thyssen Welding
&
Mannesmann Tubes, AIB-Vinc¸otte, VCL, Tractebel and WTCM). Base metal
properties (creep
strength,
toughness, reheat cracking susceptibility, oxidation behavior. . .), welding
and high temperature
behavior
of the new 12% Cr-steel, and welds are addressed.
Keywords:
12%Cr steel, power plant, welding, creep
Intergranular
cracking of Hastelloy C-276 in the
socket
welded assemblies
Byung-Hak
Choea*, Jin-Woo Kima,
Chong-Chun Chob, Seon-Hwa Kimc,
Ungyu Paikd,
Je
Hyun Leee and Kee-Bong Yoonf
aDepartment
of Metal and Materials Eng., Kangnung National Univ., Kangnung, 210-702, Korea
bMaterials
Evaluation Eng. Tech., #2313 AFRA Center, 66 Sangnam-dong, Changwon, 641-831,
Korea
cDepartment
of Materials Eng.,
eDept.
of Metall. & Matls. Sci.,
fSchool
of Mechanical Eng.,
*E-mail:
cbh@kangnung.ac.kr
ABSTRACT
The
cause of thermal cracking about a socket welded tube was investigated by stress
simulation and
its
comparison to hardness distribution of welding seam, HAZ and matrix of the
tube. In the condition
of
heat-input in melting range of 1349_C,
the stress was concentrated in HAZ at the opposite side of
welding
area by ANSYS program, which corresponded to the distribution of real hardness
values of
the
tube. The high stress concentration in HAZ might be induced from fine carbide
precipitation
which
formed during welding process. It could cause, therefore, tube cracking in
operating condition
simultaneously
followed by bulging inside of the welded tube. In the crack propagation through
all
the
tube originated from inside HAZ, it might be accelerated by thermal fatigue,
and propagated along
grain
boundaries accompanied by the metal dust formation.
Keywords:
intergranular cracking, Hastelloy C-276, socket welded assemblies
Effect
of water-shower cooling during welding on
tensile
residual stress improvement in multi-layer
welding
of austenitic stainless steel plates
Nobuyoshi
Yanagida a* and Hiroo Koideb
aHitachi
Research Laboratory, Hitachi, Ltd., 3-1-1, Saiwai-cho,
bHitachi
Works, Hitachi, Ltd,
ABSTRACT
A
new welding method that uses a water shower behind the welding torch has been
developed in
order
to reduce tensile residual stress in a welded region. When this method is
applied to the welding
of
austenitic stainless steel, the welding and cooling conditions mainly determine
how much the
residual
stress can be reduced. To optimize these conditions, we first used the robust
design technique
to
determine the effects of the interpass temperature, the heat input quantity and
the water-shower
area
on the residual stress distribution of bead-on-plate. We found that, to
decrease the tensile residual
stress,
the interpass temperature should be high, the heat input low, and the
water-shower area large.
Effect
of the water-shower cooling on multi-layer welding was examined analytically
and experimentally.
It
was found that the residual stresses were tensile without water-shower cooling,
but
compressive
with water-shower cooling under the optimized conditions. It can therefore be
concluded
that
the new welding method is appropriate for reducing tensile residual stress in
multi-layer welding
of
austenitic stainless steel.
Keywords:
residual stress, multi-layer welding, austenitic stainless steel,
robust design technique, FEM
Features
of thermal stress generated by welding
and
cutting of dissimilar steels
S.H.
Leea*, K.H. Changb and
G.C. Jangb
aJoining
and Welding Research Institute,
E-mail:
semtong@jwri.osaka-u.ac.jp
bDepartment
of Civil and Environmental Engineering,
Huksuk-dong,
ABSTRACT
Bridges
that are damaged by an increase of vehicle load, corrosion and earthquake need
repair or
strengthening.
Repair procedures of steel bridge generally include cutting, bolting and
welding, which
occasionally
bring in a stress concentration within limit range. Therefore, a chain of
confirmation
about
the safety of the structure is necessary. A safety evaluation method that
considers heat effect is
necessary
to repair damaged structure by welding. Generalized welding and cutting
residual stress is
employed
to estimate the safety of structure during the welding repair work. This
research investigates
the
features of thermal stress generated by welding and cutting. The pattern of
cutting residual stress