The document discusses various challenges and considerations for welding dissimilar metals. It notes that dissimilar metals often have different physical, chemical, and metallurgical properties, requiring compromise when welding. Key factors discussed include weld metal composition and properties, dilution rates, differences in melting temperatures, thermal expansion, and heat treatments between base metals. The document provides examples of dissimilar metal welds that failed, including a superheater tube weld that cracked due to carbon migration and increased hardness. It emphasizes the importance of selecting suitable welding processes, filler metals, joint designs, preheat/post-weld heat treatments to successfully join dissimilar metals.

1. By:-
Mr. K M Varun
6/1/2018 1

2. A A A B
A B
A+B
B A
A+B
A+B+C
C(1)
(3)
(2)
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3.  Demand for materials to fit in heterogeneous working condition
 Dissimilar weld
 Weldability difference- Different physical, chemical, mechanical properties and
metallurgical characteristics
 Compromise often required
Welding 2 different alloy system
Chemically different Metallurgically different
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4.  Integration of efficient quality weld technology – key to successful dissimilar weld
.
Processes to join DM
Fusion weld- SMAW, GTAW, GMAW, FCAW,
SAW
Low-dilution- Electron beam, laser etc.
Non fusion weld- Solid state, brazing and soldering
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5. a • Weld Metal
b • Dilution and alloying
c • Melting temperature ranges
d • Coefficient of thermal expansion
e • Thermal conductivity
f • Heat treatments
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6.  Weld metal composition & its properties
 WM composition – BM & FM composition and relative dilutions
 Composition gradient exists
 Solidification characteristics- Example high δ ferrite content in SS
 Phase diagram investigation necessary
 Study of intermetallic compounds – crack sensitivity, ductility, susceptibility to
corrosion etc..
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7. Welding of similar metals/alloys Welding of dissimilar metals/alloys
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8.  Weld metal- single or mixture of 2 or more phases
 WM – stronger than weakest BM
 WM – sufficient Tensile strength and ductility – withstand failure
 Weld bead composition differ in multipass welding
 Ductile matrix phase with good toughness
 Dilution = Wt. of BM melted/Total wt. of WM
 Calculation of avg. comp. of whole WM:-
(a) Ratio of vol. of BM melted.
(b) Comp. of BM & FM.
[Xw = DaXa + DbXb + Xf(1-Dt)]
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9. SNO. METHODS ADVANTAGES LIMITATIONS
1 Chemical Analysis of the weld Most accurate determination Time consuming,
expensive
2 Approximation of base metal dilution
by weld cross section and
composition calculated
Less expensive and less time
consuming than chemical
analysis
Estimating the % often
difficult in weld
particularly multipass
weld
3 Approximate dilution for common
welding processes and composition
calculated
Very fast way of estimating
“rough” composition, no
laboratory work involved
Welding technique can
have a strong influence
of dilution in some
processes like GMAW,
GTAW.
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[Ref- Guidelines for welding dissimilar
metals, NiDi, Richard E. Avery]

10.  Fusion welding involves melting of metals
 Relationship of Physical Properties of Various Base Metals to Those of Carbon Steel
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[Ref- AWS handbook vol4]

11.  Wide difference in melting temperature range- fusion welding difficult
 Result- liquation cracking of the metal with lower melting temp.
 Example
 Solidification and contraction induces stresses.
 Remedy :- Buttering by filler metal with intermediate melting temp. – reduce
melting temp. differential.
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12.  Heat flow = f (Temp., K)
 Significant difference in K- rapid heat conduction
 Affect the energy input required to locally melt the base metal
 Remedy:- (a) Directing heat source to BM with higher K
(b) Preheating BM with Higher K
 Example- Welding pure Cu with steel or stainless steel
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13.  Differences in α generates stresses during changes in temp.
 BM subjected to Tensile stress – Hot crack or cold crack.
 Example- Joining Austenitic SS to Cr Mo LAS pipe butt joints
 Remedy- Ideally the α of WM should be of intermediate value b/w BMs.
 Dilution can alter expansion coefficient
 Linear CTE defined as [α = Δε/ ΔT], Stress in HAZ of one of the metal [σ = EΔ α ΔT]
 Solid state welding best for high CTE differential
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14. Mean Coefficients of Thermal Expansion as a function of Temperature for Alloys Used in
Transition Joints
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[Ref- ASM handbook vol6, fig43, Pg no.825]

15.  Heat treatment for one metal may be detrimental to another
 May affect the service condition
 Example- Welding of age hardenable nickel chromium alloy to nonstabalized
austenitic SS
 Solution- (a) Use a stabalized ASS – but high fabrication cost
(b) Buttering Ni-Cr alloy with non age hardenable similar alloy
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16. 6/1/2018 16
[Ref- Edison welding institute website]

17.  Parameters required to be taken care of :-
(a) Welding Process
(b) Selection of suitable FM
(c) Joint Design
(d) Buttering
(e) Preheat & PWHT.
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18.  Fusion weld, low dilution and non fusion weld process available
 Depth of fusion, resulting dilution rates vary for different processes
 Dilution % for Arc welding process- SMAW – 10 to 25%, GMAW – 10 to 50%,
GTAW – 10 to 40%, SAW – 20 to 50%
 Electrode manipulation controls dilution rate
 For low dilution and non fusion weld process- filler metal as an interlayer of
appropriate thickness can be used
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19.  Necessary criteria to be met:-
(a) Compatible with both BMs
(b) Sound weld within a range of acceptable dilution rates
(c) Meet four requirements – metallurgical compatibility, mechanical, physical and
corrosion properties
 Use of overalloyed filler metal
 Production of transition joints
 Constitution diagram – FM selection (SS)
Like Schaeffler diagram, WRC-1992 etc..
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20.  ASME Section IX, QW/QB492 : The addition of material, by welding, on one or
both faces of a joint, prior to the preparation of the joint for final welding.
 Advantages of buttering:-
(a) Reduce differential material properties
(b) Barrier layer – slow migration of undesirable elements from BM to WM.
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21.  Melting characteristics of base and filler metal is affected
 Wide groove angle- less dilution, better control of viscous weld metal, better arc
manipulation
 Back gouging for double sided weld- better dilution control
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22. Wide Final Layer in a Joint Design
for Dissimilar Metals
Relative Life of Weld Joints Between Ferritic Steels and
Austenitic Stainless Steels Made with Various Filler Metals
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[Ref- AWS handbook vol4, Pg no.358]

23. Magnetic Effects
 Interact with DC arc or electron beam- deflection
 Arc blow, beam deflection, metal transfer affected, excessive dilution at
ferromagnetic base metal side
 Remedy- AC arc, short circuit mode of GMAW
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24. Service
life
Mechanical &
Physical Properties
Corrosion &
oxidation resistance
Microstructure
stability
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25.  Weld metal and 2 HAZs
 DMW intended for elevated temperature
 Design component- DMW is located in areas of known low service stress-
because of addition of thermal stress
 Select filler metal like Ni alloy- are notch tough and resistance to thermal fatigue
 Coarse dendritic cast weld structure- less thermal fatigue than wrought base metal
of same composition
 Remedy- Filler metal overmatching the base metal
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26.  Composition gradient- Weld metal and HAZ’s
 Microstructural changes- interdiffusion at elevated temperature b/w base and weld
metal
 Reduces the service life of DMW
 Example- C migration (diffusion phenomenon) form LAS to ASS during heat
treatment or elevated service temp.- weakens HAZ of LAS and increases hardness
of weld metal
 Remedy- Use of Ni alloy as filler wire, buttering
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27.  Galvanic cells formation – Corrosion of anodic metal
 Several microstructural phases – galvanic corrosion
 Compositional variation at interfaces – selective oxidation at high temp – notches
 Corrosion types- galvanic, pitting
 Remedies:-
(a) Join materials with similar corrosion potential
(b) Cathodic protection providing electrode
(c) Coating
(d) Reduce residual stress- to avoid SCC
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28. 6/1/2018 28
[Ref- AWS handbook vol4, Pg no.347]

29. Joining
techniques
for
Dissimilar
Joints
Formation of
brittle
intermetallic
phases
Differences in
M.P., K, α, σ
Formation of
oxide layer
Poor solubility in
each other
Hybrid structure
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Proper Welding
Procedure

30. 6/1/2018 30

31.  Application- DMW joint b/w SA213 (T12) and SA213 (TP 347H) for superheater
tubes in steam generation boiler plant
 Process- Machine GTAW, Joint- V groove
 Filler metal used TGS-70NCb ( Equivalent to AWS A5.14 ERNiCr-3)
 Preheat temp.- 121°C, PWHT- 540°C
 Service temperature- above 540°C
 Failure- After 8 years circumferential cracking at HAZ of LAS side with no plastic
deformation
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32. 6/1/2018 32

33. Microstructure of
SS sample
(a) Near the weld
junction
(b) Away from the
weld junction
Microstructure of
AS side
(c) HAZ 1
(d) HAZ 2
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34.  SEM result- micro cracks along grain boundaries in weld area. Possible reason
◦ Residual internal stresses due to improper PWHT
◦ High hardness due to formation of carbides combined with thermal fatigue
Hardness measurements of AS and SS super heater tube parts.
AS superheater tube part SS superheater tube part
HRB Equivalent BHN Location HRB Equivalent BHN Location
75.4 138.2 Away from weld 83.8 161.9 Away from weld
80.1 150 Near the HAZ 85.6 167 Near the HAZ
92 195 At the welding 90.3 186.3 At the welding
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35.  Possible causes of failure:-
◦ Expansion differences b/w the 2 steels
◦ Carbon migration
◦ Formation of oxide wedge on OD of LAS tube due to corrosion resistance
differences to flue gases
◦ Bending stresses- Horizontal positioning of the tubes
 Based on microstructure- Carbon migrated from LAS to SS
 Precipitation of carbides- increased hardness
 Decrease in creep strength of AS at weld interface
 Thermal fatigue mechanism can be excluded
[Ref:- Premature failure of dissimilar metal weld joint at intermediate temperature superheater tube. By-
Mohammed Al Hajri, Anees U. Malik & Abdelkader Meroufel. April 2015]
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36.  Material used- 1060 Al alloy+C10100 pure Cu
 Application- Chemical, aerospace, transportation & electronics industry
 Fusion welding, brazing techniques difficult
 Experimental setup:-
(a) Plates dimension- 300x100x3mm
(b) Tool rpm- 1050, Welding speed- 30mm/min
(c) Stir pin dia.- 4.5mm, Length- 2.8mm
(d) Soaked in 3.5% NaCl for 24hr- Corrosion test
 Tool offsetting, tool rpm and traverse speed influence
weld properties
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H13
steel

37.  Microstructure
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Cross section morphology
(macrostructure)
WN Microstructure (Magnified image of A, B, C & D)

38. 6/1/2018 38
Microstructure of interface
Corrosion morphology of the interface
TEM micrographs of nugget zone

39.  Results & Discussion
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Transverse cross section hardness
Surface Morphology of Al-Cu FSW joint
[Ref- “Microstructure & Mechanical properties of Al-Cu
joints by FSW” by Qiu-zheng, Wen-biao Gong, Wei Liu,
Nov 2014]
Surface Morphology of Al-Cu FSW joint

40. Check the results
Optimize welding procedure
Select proper welding process
Study the compatibility
Material selection based on application
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41.  “Guidelines for welding dissimilar metals” By Richard E. Avery, Nickel
Development Institute
 “Premature failure of dissimilar metal weld joint at intermediate temperature
superheater tube”. By- Mohammed Al Hajri, Anees U. Malik & Abdelkader
Meroufel. April 2015
 “Microstructure & Mechanical properties of Al-Cu joints by FSW” by Qiu-zheng,
Wen-biao Gong, Wei Liu, Nov 2014
 Friction Welding to join dissimilar metals by Shubhavardhan RN & Surendran S,
Dept. of ocean engg. & IIT Madras
 “Creep behavior of dissimilar metal weld joints between P91 and AISI 304”by
Javed Akrama, Prasad Rao Kalvalaa, Mano Misraa & Indrajit Charit Dept. of
Metallurgical Engineering, University of Utah, USA
 AWS welding handbook Vol 4 “Materials and Applications”, Part 2
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42. Thank You !
Any Questions ?
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