Brazing Technology of Ti alloy/Stainless Steel Dissimilar Metal Joint at System Integrated Modular

131 Pages·2005·2.01 MB·English

KR0100910
KAERI/AR-589/2001
Brazing Technology of Ti alloy/Stainless Steel
Dissimilar Metal Joint
at System Integrated Modular Advanced Reactor
2001. 2.
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IV
350MPa
Ti-Fe
V
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BAg-19, BVAg-30 ^ Gapasil-9^- ^-§-
^«H, Ni
40% HNOs + 2% HF + 58% H2O * °^
macroetch test
SUMMARY
I Title
Brazing Technology of Ti alloy/Stainless Steel Dissimilar Metal Joint at
System Integrated Modular Advanced Reactor
II The Development of Brazing Technology
As a joining technology, brazing has a long history since those ancient
times in about 4000 B. C, when both silver and gold brazing were carried
out at Sumer which is now Iraq. Nowadays, the technology is developed even
for the joint of metal/ceramics and applied to many industrial fields. In the
initial times, they used blowpipes and charcoal as the heat source. Now,
many kinds of heating methods including laser heating ;are being applied to
brazing. And also, a great development in technologies has been made in
filler metals, fluxes and so on. Because brazing can be applied to the joint
where cannot be welded and mass production of it is possible, it is utilized in
special fields of rockets, electronic packages and superconductor. In the
nuclear fields, the technique has been applied widely to fuel assemblies,
accelerators, laboratory equipments and measuring sensors.
III Brazing Process
Brazing processes customarily are designated according to the sources or
methods of heating like as torch brazing, furnace brazing, induction brazing,
resistance brazing, dip brazing, infrared brazing, etc.. Eacli process is selected
according to the condition of the base metal, the filler metal, the flux, the
brazing temperature and the heating rate. Whatever the process used, the
filler metal has a melting point below that of the base mtital, and should have
good wettability and spreadability. Fluxes are used to protect the surface of
the base metal and to reduce the oxides on it. Therefore, recommended fluxes
should be used in their proper temperature ranges and on the base metals for
which they are designed. When gas atmosphere or vacuum is used, fluxes
are not required. For the metal which forms oxides on the surface at the
brazing temperature, gas atmosphere or vacuum should be used. Since surface
tension forces can operate only over relatively small distances, capillary
penetration will occur only if the joint gap is below a certain maximum
value. But, too little clearance may lead in certain cases to incomplete joint
filling due to entrapment of flux or air. When electronic packages are jointed,
filler metal should be selected considering its electrical conductivity.
IV Joining of Ti alloy to Stainless Steel
It is well known that fusion welding between Ti alloy and stainless
steel is almost impossible because of brittle intermetallic compound in its
weld metal. For this reason, various methods have also been tried for joining
those dissimilar metals. Until Now, diffusion welding and friction welding
have been known as the candidate joining processes with the joint strength
of about 350 MPa. Because the joint strength doesn't reach the strength of
base metals, the designer should consider this fact and select a method to
maintain a proper joint strength. At the System Integrated Modular Advanced
Reactor Project, they applied a thread joint to get strength and solved the
problem of leakage through brazing the joint area. During brazing process,
Ti diffuses into the surface of stainless steel through the melt of filler metal
and forms brittle Ti-Fe intermetallic compounds. To reduce the formation of
intermetallic compounds, the selection of an optimal brazing condition is
required. In addition to it, the brazed joint should be resistant to corrosive
environment. Therefore, brazing technology should be developed to get both
high joint strength and sound joint.
V Brazing of Ti alloy to Stainless Steel
The joint part is assembled with male part of Ti alloy and female part
of stainless steel. A funnel is welded to the upper end of female part for
containing the filler metal. Filler metal will be selected among BAg-19,
BVAg-30 and Gapasil-9, after the comparison test of joint strength. To
increase the wettability of stainless steel, Ni or Ni-Pd will be coated by
plating or other coating methods. The filler metal and stainless steel will be
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with 40% HNO3 + 2%HF + 58% H O. Vacuum electric furnace and induction
2
furnace wil be used for heating. Brazing temperature will be about 900 °C.
Optimal brazing condition will be set up through comparison of joint strength
according to heating rate, temperature and holding time. For the evaluation of
process and performance, visual inspection, macroetch test and liquid
penetrant inpection will be carried out.
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PLEASE BE AWARE THAT
ALL OF THE MISSING PAGES IN THIS DOCUMENT
WERE ORIGINALLY BLANK
CONTENTS
Chapter 1 Introduction 1
Section 1 Definition of Brazing 1
Section 2 Development of Brazing Technology 3
1 The Ancient Orient 3
2 The Greek, Roman and Aegean Civilization 4
3 Europe, Ancient to Early Middle Age (8-11C) 5
4 Europe, Later Middle Age 5
5 The Age of Manufacture (16-17C) 5
6 Dawning of Modern Science (18C) 6
7 The Industrial Revolution (19C) 7
8 20C 8
Section 3 Procedure of Joining 10
1 Selection of Joining Method 10
2 Planning of Brazing 12
3 Preparation of Filler Metal, Flux And Others 13
4 Brazing 15
5 Test and Inspection 16
Section 4 Application of Brazing to Nuclear Industry 18
1 Fuel 19
2 Heat Exchanger 20
3 Others 21
Chapter 2 Brazing Process 21
Section 1 Brazing Methods 21
1 Torch Brazing 21
2 Furnace Brazing 21
3 Induction Brazing 22
4 Resistance Brazing 22
5 Dip Brazing 22
6 Infrared Brazing 23
7 Others 23
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Section 2 Filler Metals 23
1 Characteristics 23
2 Melting and Fluidity 24
3 Liquidation 25
4 Wetting and Bonding 25
5 Filler Metal Selection 26
6 Kinds of Filler metals 27
Section 3 Fluxes and Atmospheres 30
1 Fluxes 31
2 Atmospheres 33
Section 4 Joint Design 36
1 Types of Joints 36
2 Joint Clearance 37
3 Stress Distribution 40
4 Filler Metal Placement 40
5 Electrical Conductivity 41
6 Dissimilar Metal Combination 41
Section 5 Brazing Procedures 42
1 Precleaning and Surface Preparation 42
2 Fluxing and Stop-off 43
3 Assembly 44
4 Postbraze Treatment 45
Section 6 Inspection 45
1 Nondestructive Testing Methods 46
2 Destructive Testing Methods 48
Chapteter 3 Brazing of Ti Alloy and Stainless Steel 50
Section 1 Brazing of Ti Alloys 50
1 Chemical and Metallurgical Characteristics 50
2 Surface Preparation 50
3 Fluxes and Atmospheres 51
4 Brazing Methods 51
5 Brazing Temperature 52
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