Welding and Joining Brochure

Welding and Joining Brochure
Welding and Joining Guidelines
The HASTELLOY® and HAYNES® alloys are known for their good weldability, which is
defined as the ability of a material to be welded and to perform satisfactorily in the imposed
service environment. The service performance of the welded component should be given
the utmost importance when determining a suitable weld process or procedure. If proper
welding techniques and procedures are followed, high-quality welds can be produced with
conventional arc welding processes. However, please be aware of the proper techniques
for welding these types of alloys and the differences compared to the more common
carbon and stainless steels. The following information should provide a basis for properly
welding the HASTELLOY® and HAYNES® alloys. For further information, please consult
the references listed throughout each section. It is also important to review any alloyspecific welding considerations prior to determining a suitable welding procedure.
The most common welding processes used to weld the HASTELLOY® and HAYNES®
alloys are the gas tungsten arc welding (GTAW / “TIG”), gas metal arc welding (GMAW
/ “MIG”), and shielded metal arc welding (SMAW / “Stick”) processes. In addition to
these common arc welding processes, other welding processes such plasma arc welding
(PAW), resistance spot welding (RSW), laser beam welding (LBW), and electron beam
welding (EBW) are used. Submerged arc welding (SAW) is generally discouraged as this
process is characterized by high heat input to the base metal, which promotes distortion,
hot cracking, and precipitation of secondary phases that can be detrimental to material
properties and performance. The introduction of flux elements to the weld also makes it
difficult to achieve a proper chemical composition in the weld deposit.
While the welding characteristics of Ni-/Co-base alloys are similar in many ways to those
of carbon and stainless steel, there are some important differences that necessitate the
use of different welding techniques. Ni-/Co-base molten weld metal is comparatively
“sluggish”, meaning it is not as fluid compared to carbon or stainless steel. In addition
to the sluggish nature of the weld pool, Ni- and Co-base alloys exhibit shallow weld
penetration characteristics. Therefore, weld joint design must be carefully considered, and
proper welding techniques are needed to ensure that there is adequate fusion. Since the
oxides that form on the surface of the metal typically melt at much higher temperatures
than the Ni-/Co-base alloys being welded, it is especially important that they be removed
prior to welding and between passes in multi-pass welds. These important considerations
will be discussed in more detail in later sections.
Generally, it is suggested that welding heat input be controlled in the low-to-moderate
range. In arc welding, heat input is directly correlated with welding current and arc voltage,
and is inversely correlated to travel speed. To achieve successful welding results, it
is suggested that relatively low welding currents and slow travel speeds be employed.
Stringer bead welding techniques, with some electrode/torch manipulation, are preferred;
wide weave beads are not recommended. Preferably, weld beads should be slightly
convex, and flat or concave beads that may be acceptable with carbon and stainless
steel should be avoided. Both Ni- and Co-base alloys have a tendency to crater crack, so
grinding of starts and stops is recommended.
Welding and Joining Guidelines
© Haynes International Inc., 2017
Welding and Joining Guidelines Continued
It is suggested that welding be performed on base materials that are in the annealed
condition. Materials with greater than 7% cold work should be solution annealed before
welding. The welding of materials with large amounts of residual cold work can lead to
cracking in the weld metal and/or the weld heat-affected zone.
Chemical treatments, such as passivation, are normally not required to achieve corrosion
resistance in Ni-/Co-base weldments. The solid-solution strengthened alloys can typically
be put into service in the as-welded condition. In certain instances, a postweld stress
relief may be desirable prior to exposure to certain service environments. Precipitationstrengthened alloys must be heat treated after welding to achieve their full properties.
As a way of achieving quality production welds, development and qualification of welding
procedure specifications is suggested. Such welding procedures are usually required
for code fabrication, and should take into account parameters such as base and filler
metals, weld joint design/geometry, preheat/interpass temperature control, and postweld
heat treatment (PWHT) requirements. Haynes International does not develop or provide
specific welding procedures. The general welding guidelines and any alloy-specific
welding considerations should be used to develop a specific welding procedure.
Weld Joint Design
Selection of a correct weld joint design is critical to the successful fabrication of
HASTELLOY® and HAYNES® alloys. Poor joint design can negate even the most optimum
welding conditions. The main consideration in weld joint design of Ni-/Co-base alloys is to
provide sufficient accessibility and space for movement of the welding electrode or filler
metal. Slightly different weld joint geometries are required compared to those for carbon
or stainless steel; in particular, a larger included weld angle, wider root opening (gap), and
reduced land (root face) thickness are typically required.
The most important characteristic that must be understood when considering weld joint
design is that Ni- and Co-base molten weld metal is relatively “sluggish”, meaning that it
does not flow or spread out as readily to "wet" the sidewalls of the weld joint. Therefore,
care must be taken to ensure that the joint opening is wide enough to allow proper
electrode manipulation and placement of the weld bead to achieve proper weld bead tiein and fusion. The welding arc and filler metal must be manipulated in order to place the
molten metal where it is needed. The joint design should allow for the first weld bead to be
deposited with a convex surface. An included weld angle or root opening that is too narrow
promotes the formation of a concave weld bead that places the weld surface in tension and
promotes solidification cracking in the weld metal.
Additionally, weld penetration is significantly less than that of a typical carbon or stainless
steel. This characteristic requires the use of reduced land thickness at the root of the joint
compared to carbon and stainless steel. Since this is an inherent property of Ni-/Co-base
alloys, increasing weld current will not significantly improve their shallow weld penetration
characteristics.
Haynes International - Welding and Joining Guidelines
Weld Joint Design Continued
Typical butt joint designs that are used with the gas tungsten arc welding (GTAW), gas
metal arc welding (GMAW), and shielded metal arc welding (SMAW) processes are:
(i) Square-Groove, (ii) Single-V-Groove, and (iii) Double-V-Groove, as shown in Figure
1. Gas tungsten arc welding is often the preferred method for depositing the root pass
for square-groove or single-V-groove joints, where there is access to only one side of
the joint. The remainder of the joint can then be filled using other welding processes as
appropriate. For groove welds on heavy section plates greater than 3/4 inch (19 mm) thick,
a J-groove is permissible. Such a joint reduces the amount of filler metal and time required
to complete the weld. Other weld joint designs for specific situations are shown in Figure 2.
Various welding documents are available to assist in the design of welded joints. Two
documents that provide detailed guidance are:
Welding Handbook, Ninth Edition, Volume 1, Welding Science and Technology, Chapter 5,
Design for Welding, pg. 157-238, American Welding Society, 2001.
ASM Handbook, Volume 6, Welding, Brazing and Soldering, Welding of Nickel Alloys, pg.
740-751, ASM International, 1993.
In addition, fabrication codes such as the ASME Pressure Vessel and Piping Code may
impose design requirements.
The actual number of passes required to fill the weld joint depends upon a number of
factors that include the filler metal size (electrode or wire diameter), the amperage, and
the travel speed. The estimated weight of weld metal required per unit length of welding is
provided in Figure 1.
Figure 1: Typical Butt Joints for Manual Welding
Haynes International - Welding and Joining Guidelines
Weld Joint Design Continued
Material
Preferred
Root
Land
Thickness (t) Joint Design
Opening (A)
Thickness (B)
in
mm
in
mm
in
mm
1/16
1.6
I
0-1/16
0-1.6
N/A
3/32
2.4
I
0-3/32
0-2.4
N/A
1/8
3.2
I
0-1/8
0-3.2
N/A
1/4
6.3
II
1/16-1/8 1.6-3.2
3/8
9.5
II
1/2
12.7
II
1/2
12.7
III
1/32-3/32
1/32-5/32
(0.8-2.4)
5/8
15.9
II
(0.8-4.0)
5/8
15.9
III
3/4
19.1
II
3/4
19.1
III
Included
Weld
Angle (C)
degrees
None
None
None
60-75
60-75
60-75
60-75
60-75
60-75
60-75
60-75
Approx. Weight
of Weld Metal
Required
lbs/ft
kg/m
0.02
0.03
0.04
0.06
0.06
0.09
0.3
0.45
0.6
0.89
0.95
1.41
0.6
0.89
1.4
2.08
0.82
1.22
1.9
2.83
1.2
1.79
Figure 2: Other Weld Joint Designs for Specific Situations
Haynes International - Welding and Joining Guidelines
Weld Joint Preparation
Proper preparation of the weld joint is considered a very important part of welding HASTELLOY®
and HAYNES® alloys. A variety of mechanical and thermal cutting methods are available for
initial weld joint preparation. The plasma arc cutting process is commonly used to cut alloy
plate into desired shapes and prepare weld angles. Waterjet cutting and laser beam cutting are
also permissible. Edge preparation can be performed using machining and grinding techniques
applicable to Ni- and Co-base alloys. Air carbon-arc cutting and gouging are permissible, but
generally not suggested due to the very likely possibility of carbon pick-up from the carbon
electrode. Not completely removing carbon contamination from the surface could lead to
metallurgical issues during subsequent welding or processing. Additionally, high heat input
during arc gouging could promote excessive grain growth and reduce material ductility. Thus,
plasma arc cutting is generally a better alternative to air carbon-arc cutting and gouging because
it does not introduce carbon contamination in the re-solidified layer and requires minimal postcutting conditioning. The use of oxyacetylene welding and cutting is not recommended because
of carbon pick-up from the flame.
It is necessary to condition all cut edges to bright, shiny metal prior to welding. In addition to the
weld angle, generally a 1 inch (25 mm) wide band on the top and bottom (face and root) surface
of the weld zone should be conditioned to bright metal with an 80 grit flapper wheel or disk. It
is especially important that surface oxides be removed prior to welding and between passes in
multi-pass welds. Since the melting temperatures of the surface oxides are much higher than
the base metals being welded, they are more likely to stay solid during welding and become
trapped in the weld pool to form inclusions and incomplete fusion defects.
Cleanliness is considered an extremely important aspect of Ni-/Co-base weld joint preparation.
Prior to any welding operation, the welding surface and adjacent regions should be thoroughly
cleaned with an appropriate solvent, such as acetone, or an appropriate alkaline cleaner. All
greases, cutting oils, crayon marks, machining solutions, corrosion products, paints, scale, dye
penetrant solutions, and other foreign matter should be completely removed. Any cleaning
residue should also be removed prior to welding. Contamination of the weld region by lead,
sulfur, phosphorus, and other low-melting point elements can lead to severe embrittlement or
cracking. For Co- and Fe-base alloys, surface contact with copper or copper-bearing materials
in the weld region should be avoided. Even trace amounts of copper on the surface can result
in copper contamination cracking, a form of liquid metal embrittlement, in the heat-affected zone
of the weld.
Surface iron contamination resulting from contact with carbon steel can result in rust staining,
but it is not considered a serious problem and, therefore, it is generally not necessary to remove
such rust stains prior to service. In addition, melting of small amounts of such surface iron
contamination into the weld pool is not expected to significantly affect weld-metal corrosionresistance. While such contamination is not considered a serious problem, if reasonable care is
exercised to avoid the problem, no particular corrective measures should be necessary prior to
service.
Stainless steel wire brushing is normally sufficient for interpass cleaning of weldments. The wire
brushes that are used during welding should be reserved for use on Ni- and Co-base alloys only,
and should not be used for carbon steel. The grinding of starts and stops is recommended for
all arc welding processes. If oxygen- or carbon dioxide-bearing shielding gases are used, light
grinding is necessary between passes prior to wire brushing. Slag removal during SMAW will
require chipping and grinding followed by wire brushing.
Haynes International - Welding and Joining Guidelines
Temperature Control and Heat-treatment of Weldments
Preheating of HASTELLOY® and HAYNES® alloys is generally not required. Ambient or
room temperature is generally considered a sufficient preheat temperature. However,
the alloy base material may require warming to raise the temperature above freezing or
to prevent condensation of moisture. For example, condensation may occur if the alloy
is brought into a warm shop from cold outdoor storage. In this case, any metal near the
weld should be warmed slightly above room temperature to prevent the formation of
condensate, which could cause weld metal porosity. Warming should be accomplished by
indirect heating if possible, e.g. infrared heaters or natural warming to room temperature.
If oxyacetylene warming is used, the heat should be applied evenly over the base metal
rather than in the weld zone. The torch should be adjusted so that the flame is not
carburizing. A "rosebud" tip, which distributes the flame evenly, is suggested. Care should
be taken to avoid local or incipient melting as a result of the warming process.
Interpass temperature refers to the temperature of the weldment just prior to the deposition
of an additional weld pass. It is suggested that the maximum interpass temperature
be 200°F (93°C). Auxiliary cooling methods may be used to control the interpass
temperature; water quenching and rapid air cooling are acceptable. Care must be taken to
ensure that the weld zone is not contaminated with traces of oil from air lines, grease/dirt,
or mineral deposits from hard water used to cool the weld joint. When attaching hardware
to the outside of a thin-walled vessel, it is good practice to provide auxiliary cooling to the
inside (process side) of the vessel to minimize the extent of the heat-affected zone.
Under the vast majority of service environments, corrosion-resistant alloys and solidsolution-strengthened high-temperature alloys are used in the as-welded condition, and
post-weld heat-treatment (PWHT) of these alloys is generally not required to assure
good weldability. Post-weld heat-treatment may be required, or advantageous in certain
situations, such as to relieve weld residual stresses. However, stress relief heattreatments at temperatures commonly used for carbon steels are normally ineffective for
these alloys. If PWHT is conducted at these intermediate temperatures, it may result in
the precipitation of secondary phases in the microstructure which can have a detrimental
effect on material properties, such as corrosion resistance. For most alloys, PWHT in the
1000 to 1500ºF (538 to 816ºC) temperature range should be avoided. If stress relief heat
treatment of attendant carbon steel components is required, contact Haynes International
for guidance. In general, the only acceptable PWHT for solid-solution strengthened alloys
is a full solution-anneal. The heat-treatment guidelines should be consulted to determine
the appropriate solution-annealing temperature for an alloy. Annealing time is normally
commensurate with weld joint thickness.
For precipitation-strengthened alloys, PWHT is normally required in order to develop
appropriate material/weldment properties. In almost all cases, this involves a full solutionanneal followed by an age hardening heat treatment. Consult the heat-treatment
guidelines to determine the appropriate annealing and age-hardening heat-treatment
schedule for an alloy.
Haynes International - Welding and Joining Guidelines
Welding Defects
A weld discontinuity is defined by the American Welding Society as “an interruption
of the typical structure of a material, such as a lack of homogeneity in its mechanical,
metallurgical, or physical characteristics.” Welding defects are a type of discontinuity that
compromises the usefulness of a weldment, which could render it unable meet minimum
applicable acceptance standards/specifications. Welding defects can be welding process-/
procedure-related, or related to the chemical composition or metallurgy of the alloy(s)
being welded.
Weld metal porosity is a cavity-type of welding defect formed by gas entrapment during
solidification as a result of contamination by certain gases, such as hydrogen, oxygen, or
nitrogen. Porosity caused by hydrogen pickup can be minimized by keeping the weld joint
area and filler metal free of hydrocarbon contaminants and moisture. To avoid porosity
caused by oxygen and nitrogen, it is important that the weld pool is properly shielded
through the use of high purity shielding gases, and sufficient shielding gas flow rates are
being utilized. Although porosity can occur in HASTELLOY® and HAYNES® weldments,
they are not particularly susceptible to porosity since most alloys contain a significant
amount of Cr, which has a natural affinity for the gases that are formed during welding.
Weld metal inclusions can form as a result of oxides that become trapped in the weld pool.
This can occur from the tenacious oxide film that forms on the surface of most alloys.
Since the melting temperatures of surface oxides are usually much higher than the base
metal, they are more likely to stay solid during welding and become trapped in the weld
pool. Thus, it is especially important that surface oxides be removed prior to welding and
between passes in multi-pass welds. During GTAW, if the tungsten electrode accidentally
contacts the molten weld pool or if there is excessive weld current, tungsten inclusions
can be produced in the weld metal. Elements with a strong affinity for oxygen, such
as aluminum or magnesium, can combine with oxygen to form oxide inclusions in the
weld metal. Slag inclusions are associated with flux-based processes such as SMAW,
SAW, and FCAW. These inclusions form in the weld metal when residual slag becomes
entrapped in cavities or pockets that form due to inadequate weld bead overlap, excessive
undercut at the weld toe, or an uneven surface profile of the preceding weld bead. Thus,
an important consideration in flux-based processes is the ease with which the slag can
be removed between weld passes. Inclusions must be ground out from the weld or they
will act to initiate fracture prematurely, which can have a detrimental effect on mechanical
properties and service performance.
Other common process-related defects that are encountered are undercut, incomplete
fusion/penetration, and distortion. These defects are generally attributed to improper
welding technique and/or welding parameters. Undercut is a groove that is melted into
the base metal, usually at the root or toes of the weld, and can occur due to excessive
welding current. This discontinuity creates a notch at the periphery of the weld and can
significantly weaken the strength of the weldment. Incomplete fusion defects are promoted
by the “sluggish” nature of Ni-/Co-base molten weld metal and their poor weld penetration
characteristics.
Haynes International - Welding and Joining Guidelines
Welding Defects Continued
Distortion characteristics of the HASTELLOY® and HAYNES® alloys are similar to those of
carbon steel, with less tendency to distort than austenitic stainless steel weldments due
to their lower coefficient of thermal expansion. Jigs, fixturing, cross supports, bracing,
and weld bead placement and sequence will help to hold distortion to a minimum. Where
possible, balanced welding about the neutral axis will assist in keeping distortion to a
minimum. Proper fixturing and clamping of the assembly makes the welding operation
easier and minimizes buckling and warping of thin sections. It is suggested that, where
possible, extra stock be allowed to the overall width and length. Excess material can then
be removed in order to achieve final dimensions. Weld distortion for different joint designs
are shown in Figure 3.
During normal fabrication of HASTELLOY® and HAYNES® alloys, weld-cracking is rare
and one should expect to fabricate large, complex components with few instances of
cracking. The most common type of weld-cracking encountered is hot-cracking, which is
associated with the presence of liquid in the microstructure. Hot-cracking can occur in the
weld metal and heat-affected zone of a weld, and usually results from liquid films along
grain boundaries. These strain-intolerant microstructures temporarily occur at elevated
temperatures within the melting and solidification range of all alloys. Due to their nominal
chemical composition, certain alloys are more susceptible to hot-cracking than other alloys.
In general, hot-cracking is a more common occurrence with high-temperature alloys due
to their higher alloy content. Impurity elements, such as sulfur and phosphorus, and minor
alloying additions, such as boron and zirconium, can have a strong influence on cracking
susceptibility even though they are present in very low concentrations.
In addition to a susceptible microstructure, the level of tensile stress on the weld is a critical
factor for hot-cracking. The development of stress is inevitable during welding because
of the complex thermal stresses that are created when metal solidifies and cools. This is
in part related to the inherent restraint placed on the weldment due to weld-joint geometry
and thickness. In general, weldments with increased joint thickness are more susceptible
to hot-cracking. Additionally, a “teardrop-shaped” weld pool created due to fast travel
speed tends to increase cracking susceptibility since it produces a distinct weld centerline
where elemental segregation is enhanced and transverse stresses can be high. Large
concave weld beads that place the weld surface in tension tend to promote solidification
cracking and should be avoided. Further information about weld-cracking mechanisms
and welding metallurgy of Ni-base alloys can be found in the following textbook:
J.N. DuPont, J.C. Lippold, and S.D. Kiser, Welding Metallurgy and Weldability of NickelBase Alloys, John Wiley & Sons, Inc., 2009.
Haynes International - Welding and Joining Guidelines
Welding Defects Continued
Figure 3: Weld Distortion for Different Joint Designs
Post-weld Inspection and Repair
In order to determine the suitability of the weldment for its intended purpose, some degree
of nondestructive examination/testing (NDE/NDT) should be conducted as part of sound
fabrication practice and quality assurance. For non-code fabrication, NDE may be as simple as visual or liquid/dye penetrant inspection. For code fabrication, certain mandatory inspections may be required. These NDE methods should be considered for both intermediate inspections during multi-pass welding, as well as for final acceptance of the weldment.
NDE methods are similar to those used for carbon and stainless steels. Liquid/dye penetrant inspection is commonly used to reveal surface defects, such as hot-cracking. Radiographic and ultrasonic testing can be used to detect for subsurface defects and thoroughly
check the soundness of the weldment; however, the results can be difficult to interpret and
these methods are generally not well suited for inspection of fillet welds. Magnetic particle
inspection is not an effective NDE method for Ni-/Co-base alloys since they are non-magnetic. If further information is required, it is suggested that the fabricator consult with an
outside laboratory that is experienced with NDE of Ni-/Co-base alloy welds.
Welding defects that are believed to affect quality or mechanical integrity should be removed and repaired. Removal techniques include grinding, plasma arc gouging, and air
carbon-arc gouging. As explained previously in the weld joint preparation section, extreme
care must be exercised during air carbon-arc gouging to insure that carbon contamination of the weld joint area does not occur. It is suggested that the prepared cavity is liquid/
dye penetrant inspected to insure that all objectionable defects have been removed. The
repair cavity should then be thoroughly cleaned prior to any welding repair. Since Ni-/Cobase alloys have low weld penetration characteristics, the ground cavity must be broad
enough and have sufficient sidewall clearance in the weld groove to allow for weld electrode/bead manipulation. The technique of "healing” or "washing out" cracks and defects
by autogenously re-melting weld beads, or by depositing additional filler metal over the
defect, is not recommended.
Haynes International - Welding and Joining Guidelines
Gas Tungsten Arc Welding (GTAW / “TIG”)
The gas tungsten arc welding (GTAW) process is a very versatile, all-position welding process that is widely used to join Ni-/Co-base alloys. In GTAW, the heat for welding is generated from an electric arc established between a non-consumable tungsten electrode and
the workpiece. GTAW can be performed manually or adapted to automatic equipment, and
can be used in production as well as repair welding situations. It is a process that offers
precise control of welding heat, and is therefore routinely used for welding thin base metal
and depositing root passes of thicker section welds. The major drawback of the GTAW
process is productivity, as weld metal deposition rates during manual welding are low.
Two percent thoriated tungsten electrodes (AWS A5.12 EWTh-2) have been traditionally
used for GTAW of Ni‑/Co-base alloys, but now other compositions are becoming more
common due to possible health concerns associated with EWTh-2 and other thoriated
tungsten electrodes. The thorium oxide contained in the EWTh-2 electrode is a low-level
radioactive material that presents a small external radiation hazard and an internal hazard
from ingestion or inhalation. The greatest risk for a welder is associated with the inhalation
of radioactive dust while grinding the tungsten electrode tip to maintain the desired conical
shape. Consequently, it is necessary to use local exhaust ventilation to control the dust at
the source, complemented if necessary by respiratory protective equipment, and precautions must be taken in order to control any risks of exposure during the disposal of dust
from grinding devices. As a result of these health concerns, thoriated tungsten electrodes
are being phased out by certain governing bodies and organizations. Fortunately, there
are alternatives that provide comparable performance to EWTh-2, including two percent
ceriated (AWS A5.12 EWCe-2) and lanthanated (AWS A5.12 EWLa-2) electrodes. For
further information on the different types of tungsten electrodes, the reader is referred to:
AWS A5.12/A5.12M, Specification for Tungsten and Oxide Dispersed Tungsten Electrodes
for Arc Welding and Cutting, American Welding Society.
The diameter of the tungsten electrode should be selected according to weld joint thickness and filler wire diameter. It is suggested that the electrode be ground to a cone shape
(included angle of 30 to 60 degrees) with a small flat of 0.040 to 0.060 in (1.0 to 1.5 mm)
ground at the point. See Figure 4 for the suggested tungsten electrode geometry.
Welding-grade argon shielding gas with a 99.996% minimum purity is suggested for most
welding situations. Helium, or mixtures of argon/helium or argon/hydrogen may be advantageous in certain situations, such as high travel speed, highly mechanized welding operations, in order to increase weld penetration. Shielding gas flow rates are critical; too low
of a rate will not provide adequate protection of the weld pool, while too high of a rate can
increase turbulence and aspirate air. Typically, flow rates for 100%Ar shielding gas are
in the 20 to 30 cubic feet per hour (CFH) (9 to 14 L/min) range. Generally, the shielding
gas cup should be as large as practical so that the shielding gas can be delivered at lower
velocity. It is also recommended that the welding torch be equipped with a gas lens in order to stabilize the gas flow and provide optimum shielding gas coverage. While weldinggrade shielding gases are of a very high purity, even a small amount of air can compromise
the protective shielding and cause weld metal oxidation/discoloration and porosity. This
can be caused by air movement from fans, cooling systems, drafts, etc., or from leakage
of air into the shielding due to a loose gas cup or other welding torch components. When
proper shielding is achieved, the as-deposited weld metal should typically have a brightshiny appearance and require only minor wire brushing between passes.
Haynes International - Welding and Joining Guidelines
Gas Tungsten Arc Welding (GTAW / “TIG”) Continued
In addition to welding torch shielding gas, a back-purge at the root side of the weld joint
with welding-grade argon is suggested. The flow rates are normally in the range of 5 to
10 CFH (2 to 5 L/min). Copper backing bars are often used to assist in weld bead shape
on the root side of the weld. Backing gas is often introduced though small holes along the
length of the backing bar. There are situations where backing bars cannot be used. Under
these conditions, open-butt welding is often performed. Such welding conditions are often
encountered during pipe or tube circumferential butt welding. Under these conditions
where access to the root side of the joint is not possible, special gas flow conditions have
been established. Under these open-butt welding conditions, the torch flow rates are
reduced to approximately 10 CFH (5 L/min) and the back purge flow rates are increased
to about 40 CFH (19 L/min). Detailed information concerning back-purging during pipe
welding is available from Haynes International upon request.
It is recommended that the welding torch be held essentially perpendicular to the workpiece, with the work angle at 90° from the horizontal and only a slight travel angle of
0° to 5°. If a large drag angle is utilized, air may be drawn into the shielding gas and
contaminate the weld. The arc length should be maintained as short as possible,
especially during autogenous welding. Stringer bead techniques, or narrow weave
techniques, using only enough current to melt the base material and allow proper fusion of
the filler, are recommended. Filler metal should be added carefully at the leading edge of
the weld pool to avoid contact with the tungsten electrode. During welding, the tip of the
welding filler metal should always be held under the shielding gas to prevent oxidation.
Pausing or “puddling” the weld pool adds to the weld heat input and is not recommended.
Electrical polarity for the GTAW process should be direct current electrode negative
(DCEN / “straight polarity”). Typical manual GTAW parameters for welding HASTELLOY®
and HAYNES® alloys are provided in Table 1. The parameters should be viewed as
approximate values that are ultimately dependent on many other factors, including the
particular welding power source, weld joint geometry, and welder skill level. Thus, it is
suggested that the parameters be used as a guideline for developing a specific welding
procedure. Smaller diameter filler wire is suggested for depositing root passes. A power
source equipped with high-frequency start, pre-purge/post-purge and up-slope/down-slope
(or foot peddle) controls is highly recommended. Weld travel speed has a significant
influence on the quality of Ni-/Co-base welds, and is typically lower than for carbon and
stainless steel. The suggested travel speed for manual GTAW is 4 to 6 inches per minute
(ipm) / 100 to 150 mm/min.
Haynes International - Welding and Joining Guidelines
Gas Tungsten Arc Welding (GTAW / “TIG”) Continued
Figure 4: Tungsten Electrode Geometry
Table 1: Typical Manual Gas Tungsten Arc Welding Parameters (Flat Position)
Joint
Thickness
in
mm
0.030-0.062 0.8-1.6
0.062-0.125 1.6-3.2
0.125-0.250 3.2-6.4
> 0.250
>6.4
Tungsten
Electrode Diameter
in
mm
0.062
1.6
0.062/0.093 1.6/2.4
0.093/0.125 2.4/3.2
0.093/0.125 2.4/3.2
Filler
Wire Diameter
in
mm
0.062
1.6
0.062/0.093 1.6/2.4
0.093/0.125 2.4/3.2
0.093/0.125 2.4/3.2
Welding Arc
Current Voltage
Amps
Volts
15-75
9-15
50-125
9-15
100-175
12-18
125-200
12-18
Gas Metal Arc Welding (GMAW / “MIG”)
The gas metal arc welding (GMAW / “MIG”) process utilizes an electric arc established
between a consumable wire electrode and the workpiece. GMAW can be implemented as
a manual, semi-automatic, or automatic process, and the flexibility offered by the various
process variations is advantageous in many applications. GMAW provides a considerable
increase in weld metal deposition rates compared to GTAW or SMAW, and when
implemented as a semi-automatic process, less welder skill is typically required. However,
GMAW equipment is more complex, less portable, and generally requires more routine
maintenance than for the GTAW and SMAW processes. GMAW is the most common
process for welding corrosion-resistant alloys and for performing thick-section welds.
In GMAW, the mechanism by which the molten metal at the end of the wire electrode is
transferred to the workpiece has a significant effect on the weld characteristics. Three
modes of metal transfer are possible with GMAW: short-circuiting transfer, globular
transfer, and spray transfer. In addition, there is a variation of the spray transfer mode
called pulsed spray.
Electrical polarity for GMAW of HASTELLOY® and HAYNES® alloys should be direct
current electrode positive (DCEP / “reverse polarity”). Typical parameters for different
GMAW transfer modes are provided in Table 2 for flat position welding. Since different
GMAW power sources vary greatly in design, operation, and control systems, the
parameters should be viewed as an estimated range for achieving proper welding
characteristics with specific welding equipment. GMAW travel speeds are typically 6 to 10
inches per minute (ipm) / 150 to 250 mm/min.
Haynes International - Welding and Joining Guidelines
Gas Metal Arc Welding (GMAW / “MIG”) Continued
Short-circuiting transfer occurs at the lowest current and voltage ranges, which results in
low weld heat input. It is typically used with smaller diameter filler wire, and produces a
relatively small and easily controlled weld pool that is well-suited for out-of-position welding
and joining thin sections. However, the low heat input makes short-circuiting transfer
susceptible to incomplete fusion (cold lap) defects, especially when welding thick sections
or during multipass welds.
Globular transfer occurs at higher current and voltage levels than short-circuiting, and is
characterized by large, irregular drops of molten metal. The globular transfer mode can
theoretically be used to weld Ni-/Co-base alloys, but is seldom used because it creates
inconsistent penetration and uneven weld bead contour that promotes the formation of
defects. Since the force of gravity is critical for drop detachment and transfer, globular
transfer is generally limited to flat position welding.
Spray transfer occurs at the highest current and voltage levels, and is characterized by a
highly directed stream of small metal droplets. It is a high heat input process with relatively
high deposition rates that is most effective for welding thick sections of material. However,
it is mainly useful only in the flat position, and its high heat input promotes weld hotcracking and the formation of secondary phases in the microstructure that can compromise
service performance.
Pulsed spray transfer is a highly controlled variant of spray transfer, in which the welding
current alternates between a high peak current, where spray transfer occurs, and a
lower background current. This results in a stable, low-spatter process at an average
welding current significantly below that for spray transfer. Pulsed spray offers lower
heat input compared to spray transfer, but is less susceptible to the incomplete fusion
defects that are common to short-circuiting transfer. It is useful in all welding positions
and for a wide range of material thickness. In most situations, Haynes International highly
encourages the use of pulsed spray transfer for GMAW of HASTELLOY® and HAYNES®
alloys. The use of a modern power source with synergic control and the provision for
waveform adjustment (“adaptive pulse”) is highly beneficial for pulsed spray transfer.
These advanced technologies have facilitated the use of pulsed spray transfer, in which
pulse parameters such as pulse current, pulse duration, background current, and pulse
frequency are included in the control system and linked to the wire feed speed.
Haynes International - Welding and Joining Guidelines
Gas Metal Arc Welding (GMAW / “MIG”) Continued
Shielding gas selection is critical to GMAW procedure development. For Ni-/Co-base
alloys, the protective shielding gas atmosphere is usually provided by argon or argon
mixed with helium. The relatively low ionization energy of argon facilitates better arc
starting/stability and its low thermal conductivity provides a deeper finger-like penetration
profile. If used alone, helium creates an unsteady arc, excessive spatter, and a weld
pool that can become excessively fluid, but when added to argon, it provides a more fluid
weld pool that enhances wetting and produces a flatter weld bead. Additions of oxygen
or carbon dioxide, while commonly used with other metals, is to be avoided when welding
Ni-/Co-base alloys. These additions produce a highly oxidized surface and promote weld
metal porosity, irregular bead surfaces, and incomplete fusion defects. The optimum
shielding gas mixture is dependent on many factors, including weld joint design/geometry,
welding position, and desired penetration profile. In most instances, a mixture of 75% Ar
and 25% He is suggested; good results have been obtained with helium contents of 15 to
30%. During short-circuiting transfer, the addition of helium to argon helps to avoid overly
convex weld beads that can lead to incomplete fusion defects. For spray transfer, good
results can be obtained with pure argon or argon-helium mixtures. The addition of helium
is generally required for pulsed spray transfer as it greatly enhances wetting.
Since argon and helium are inert gases, the as-deposited weld surface is expected to be
bright and shiny with minimal oxidation. In this case, it is not mandatory to grind between
passes during multipass welding. However, some oxidation or "soot" may be noted on the
weld surface. If so, heavy wire brushing and/or light grinding/conditioning (80 grit) between
weld passes is suggested in order to remove the oxidized surface and ensure the sound
deposit of subsequent weld beads. Shielding gas flow rates should generally be in the 25
to 45 CFH (12 to 21 L/min) range. A flow rate that is too low does not provide adequate
shielding of the weld, while excessively high flow rates can interfere with the stability of the
arc. As with GTAW, back-purge shielding is recommended to ensure the root side of the
weld joint does not become heavily oxidized. If back-purge shielding is not possible, the
root side of the weld joint should be ground after welding to remove all oxidized weld metal
and any welding defects. The weld joint can then be filled from both sides as needed.
During GMAW, the welding gun should be held perpendicular to the work-piece at both a
work angle and travel angle of approximately 0°. A very slight deviation from perpendicular
may be necessary for visibility. If the gun is positioned too far from perpendicular, oxygen
from the atmosphere may be drawn into the weld zone and contaminate the molten weld
pool. A water-cooled welding gun is always recommended for spray transfer welding and
anytime higher welding currents are being utilized.
It should be recognized that some parts of the GMAW equipment, such as the contact tip
and filler wire conduit/liner, experience high wear and should be replaced periodically. A
worn or dirty liner can cause erratic wire feed that will result in arc instability, or cause
the filler wire to become jammed, a situation known as a “bird nest”. It is recommended
that sharp bends in the gun cable be minimized. If possible, the wire feeder should be
positioned so that the gun cable is nearly straight during welding.
Haynes International - Welding and Joining Guidelines
Gas Metal Arc Welding (GMAW / “MIG”) Continued
Table 2: Typical Gas Metal Arc Welding Parameters (Flat Position)
Wire
Diameter
in
mm
Wire
Welding
Average
Feed Speed
Current
Arc Voltage
ipm
mm/s
Amps
Volts
Short-Circuiting Transfer Mode
0.035
0.9
150-200
63-85
70-90
18-20
0.045
1.1
175-225
74-95
100-160
19-22
Spray Transfer Mode
0.045
1.1
250-350 106-148
190-250
28-32
0.062
1.6
150-250 63-106
250-350
29-33
Pulsed Spray Transfer Mode*
0.035
0.9
300-450 127-190 75-150 Avg.
30-34
0.045
1.1
200-350 85-148 100-175 Avg.
32-36
*Detailed pulsed spray parameters are available upon request
Shielding
Gas
-
75Ar-25He
75Ar-25He
100Ar
100Ar
75Ar-25He
75Ar-25He
Shielded Metal Arc Welding (SMAW / “Stick”)
The shielded metal arc welding (SMAW / “Stick”) process generates an arc between a fluxcoated consumable electrode and the work-piece. SMAW is well known for its versatility
because it can be used in all welding positions, and in both production and repair welding
situations. It is one of the simplest welding processes in terms of equipment requirements
and can be easily operated in remote locations. However, it is strictly a manual welding
process that generally requires a high welder skill level. In addition, it is typically restricted
to material thickness greater than approximately 0.062 in (1.6 mm).
HASTELLOY® and HAYNES® coated electrodes for SMAW undergo a number of
qualification tests to determine the usability of the electrode, the chemical composition of
the weld deposit, and the soundness and mechanical properties of the weld metal. Coated
electrodes are generally formulated to produce a weld deposit with a chemical composition
that corresponds to that of the matching base metal. The coating formulations are
generally classified as slightly basic to slightly acidic depending on the particular alloy. For
further information on the requirements for the classification of Ni-base coated electrodes,
the reader is referred to: AWS A5.11/A5.11M, Specification for Nickel and Nickel-Alloy
Welding Electrodes for Shielded Metal Arc Welding, American Welding Society.
Prior to their use, coated electrodes should remain sealed in a moisture-proof canister.
After the canister has been opened, all coated electrodes should be stored in an electrode
storage oven. It is recommended that the electrode storage oven be maintained at 250 to
400ºF (121 to 204ºC). If coated electrodes are exposed to an uncontrolled atmosphere,
they can be reconditioned by heating in a furnace at 600 to 700ºF (316 to 371ºC) for 2 to 3
hours.
Haynes International - Welding and Joining Guidelines
Shielded Metal Arc Welding (SMAW / “Stick”) Continued
Typical SMAW parameters are presented in Table 3 for flat position welding. While the
coated electrodes are classified as AC/DC, in almost all situations electrical polarity should
be direct current electrode positive (DCEP / “reverse polarity”). For maximum arc stability
and control of the molten pool, it is important to maintain a short arc length. The electrode
is generally directed back toward the molten pool (backhand welding) with about a 20° to
40° drag angle. Even though stringer bead welding techniques are generally preferred,
some electrode manipulation and weaving may be required to place the molten weld metal
where it is needed. The amount of weave is dependent on weld joint geometry, welding
position, and type of coated electrode. A rule of thumb is that the maximum weave width
should be about three times the electrode core wire diameter. Once deposited, weld beads
should preferably exhibit a slightly convex surface contour. Appropriate welding current
is based on the diameter of the coated electrode. When operated within the suggested
current ranges, the electrodes should exhibit good arcing characteristics with minimum
spatter. The use of excessive current can lead to overheating of the electrode, reduced
arc stability, spalling of the electrode coating, and weld metal porosity. Excessive spatter is
an indication that arc length is too long, welding current is too high, polarity is not reversed,
or there has been absorption of moisture by the electrode coating. The suggested travel
speed for SMAW is 3 to 6 inches per minute (ipm) / 75 to 150 mm/min.
Out-of-position welding is recommended only with 0.093 in (2.4 mm) and 0.125 in (3.2 mm)
diameter electrodes. During out-of-position welding, the amperage should be reduced to
the low end of the suggested range in Table 3. In order to keep the bead profile relatively
flat during vertical welding, a weave bead technique is necessary. Using 0.093 in (2.4
mm) electrodes will reduce the weave width that is required and produce flatter beads.
In vertical welding, a range of electrode positions is possible from forehand (up to 20°
push angle) to backhand welding (up to 20° drag angle). In overhead welding, backhand
welding (drag angle of 0°to 20°) is required.
Starting porosity may occur because the electrode requires a short time to begin
generating a protective atmosphere. This is a particular problem with certain alloys, such
as HASTELLOY® B-3® alloy. The problem can be minimized by using a starting tab of the
same alloy as the work-piece or by grinding each start to sound weld metal. Small crater
cracks may also occur at the weld stops. These can be minimized by using a slight backstepping motion to fill the crater just prior to breaking the arc. It is recommended that all
weld starts and stops be ground to sound weld metal.
The slag formed on the weld surface should be completely removed. This can be
accomplished by first chipping with a welding/chipping hammer, then brushing the
surface with a stainless steel wire brush. In multi-pass welds, it is essential that all slag is
removed from the last deposited weld bead before the subsequent bead is deposited. Any
remaining weld slag can compromise the corrosion resistance of the weldment.
Haynes International - Welding and Joining Guidelines
Shielded Metal Arc Welding (SMAW / “Stick”) Continued
Table 3: Typical Shielded Metal Arc Welding Parameters (Flat Position)
in
0.093
0.125
0.156
0.187
Electrode
Diameter
mm
2.4
3.2
4
4.7
Arc
Voltage
Volts
22-25
22-25
23-26
24-27
Welding
Current
Amps
45-75
75-110
110-150
150-180
When using this data, please refer to our disclaimer located at www.haynesintl.com
Plasma Arc Welding (PAW)
The plasma arc welding (PAW) process is a gas-shielded process that utilizes a constricted
arc between a non-consumable tungsten electrode and the workpiece. The transferred
arc possesses high energy density and plasma jet velocity. Two distinct operating modes
are possible, referred to as melt-in-mode and keyhole mode. The melt-in-mode utilizes
lower welding current and generates a weld pool similar to that formed in GTAW, whereby
a portion of the workpiece material under the arc is melted. In the keyhole mode, higher
welding current is utilized so that the arc fully penetrates the workpiece material to form a
concentric hole through the joint thickness. The molten weld metal solidifies behind the
keyhole as the torch traverses the workpiece. Shielding of the weld pool is provided by
the ionized plasma gas that is issued from the torch orifice, which is supplemented by an
auxiliary source of shielding gas. The PAW process can be utilized with or without a filler
metal addition.
Since the constricted arc of PAW allows for greater depth of fusion compared to GTAW,
PAW is potentially advantageous for autogenous welding (i.e. without the use of filler
metal) of Ni-/Co-base material in the thickness range of approximately 0.125 to 0.3 in (3.2
to 7.6 mm). In comparison, filler metal is typically required for GTAW of material greater
than about 0.125 in (3.2 mm) thickness. Square-groove weld joints can be utilized up to
about 0.3 in (7.6 mm) thickness. While it is possible to weld a wide range of thicknesses
with PAW, better results can usually be achieved with other welding processes for
thicknesses outside of the 0.125 to 0.3 in (3.2 to 7.6 mm) range. For joint thicknesses
greater than 0.3 in (7.6 mm), autogenous keyhole welding can be utilized for the first pass,
followed by non-keyhole (melt-in) PAW with filler metal. Another welding process, such as
GTAW, could also be utilized for the second and succeeding passes.
Haynes International - Welding and Joining Guidelines
Plasma Arc Welding (PAW) Continued
Electrical polarity for the PAW process should be direct current electrode negative (DCEN /
“straight polarity”). A proper balance must be achieved between welding current, gas flow,
and travel speed to provide consistent keyhole welding. An unstable keyhole can result
in turbulence in the weld pool. Argon or argon-hydrogen mixtures are normally utilized for
the orifice gas and shielding gas. The orifice gas has a strong effect on the penetration
depth and profile. Small amounts of hydrogen (~5%) are typically sufficient to increase
the arc energy for autogenous keyhole welding, and higher amounts can lead to porosity
in the weld metal. For greater joint thicknesses, increased orifice gas flow and upslope of
the welding current may be required to initiate the keyhole. To fill the keyhole cavity at the
end of the weld, decreased orifice gas flow and downslope of the welding current may be
required. Higher travel speeds require higher welding currents to obtain keyhole welding.
Excessive travel speeds can produce undercut, which is a groove melted into the base
metal adjacent to the weld toe or weld root and left unfilled by weld metal. The welding
torch should be held essentially perpendicular to the work piece in both the longitudinal
and transverse directions, and maintained on the centerline of the weld joint. Even a slight
deviation from this condition can cause incomplete fusion defects in the weld metal.
Electron Beam Welding (EBW) and Laser
Beam Welding (LBW)
The electron beam welding (EBW) and laser beam welding (LBW) processes are highenergy density welding processes that offer several possible advantages, including low
welding heat input, high weld depth-to-width ratio, narrow heat-affected zone (HAZ), and
reduced distortion. To impinge on the weld joint and produce coalescence, EBW utilizes a
moving concentrated beam of high-velocity electrons, while LBW utilizes the heat from a
high-density coherent laser beam.
Most Ni-/Co-base alloys that can be joined with conventional arc welding processes can
also be successfully joined via EBW and LBW. These beam welding processes are even
considered more suitable for alloys that are difficult to arc weld and can provide better
overall weld properties compared to arc welding. The low welding heat input results in a
shorter time spent in the solidification temperature range and relatively fast cooling rates,
which suppresses precipitation of secondary phases during weld solidification.
Haynes International - Welding and Joining Guidelines
Electron Beam Welding (EBW) and Laser
Beam Welding (LBW) Continued
Weld joint preparation and fit-up are especially important for the EBW and LBW processes.
In most cases, a square butt joint design is utilized. Although filler metal is not normally
added to the weld pool, it can be added via bare wire. EBW generally needs to be
performed in a vacuum environment without the use of shielding gas, which provides
excellent protection against atmospheric contamination. LBW is normally performed with
argon or helium shielding gases to prevent oxidation of the molten weld pool. Porosity can
be a weldability issue due to the rapid solidification rates and deep weld pools that do not
readily allow for dissolved gases to escape; this effect is exacerbated by high weld travel
speeds. Oscillation or agitation of the weld pool by weaving the beam may provide the
time necessary to help gases escape the weld pool and reduce porosity. Susceptibility to
liquation cracking in the ‘nail-head’ region of the HAZ is promoted by the stress/strain state
in this region. Slower weld travel speeds produce a shallower temperature gradient in the
HAZ and are beneficial towards reducing liquation cracking susceptibility.
For detailed information on EBW, please refer to: AWS C7.1M/C7.1, Recommended
Practices for Electron Beam Welding and Allied Processes.
For detailed information on LBW, please refer to: AWS C7.2M, Recommended Practices
for Laser Beam Welding, Cutting, and Allied Processes.
Brazing and Soldering
Brazing
Brazing refers to a group of joining processes that produces the coalescence of materials
by heating them to the brazing temperature in the presence of a brazing filler metal having
a liquidus above 840°F (450°C) and below the solidus of the base metal, i.e. without
melting of the base metal. The liquidus, or melting point, is the lowest temperature at
which a metal or an alloy is completely liquid, and the solidus is the highest temperature at
which a metal or an alloy is completely solid. Brazing is characterized by the distribution
of a brazing filler metal between the closely fitted faying surfaces of the joint. With the
application of heat, the brazing filler metal flows by capillary action, and is melted and resolidified to form a metallurgical bond between the surfaces at the joint. Furnace brazing is
the usual method of brazing Ni-/Co-base alloys, especially when high-temperature brazing
filler metals are employed, and the information that follows will focus on furnace brazing.
The keys to successful brazing of Ni-/Co-base alloys are:
• Thorough cleaning and preparation of base metal surfaces
• Proper filler metal selection for the intended application
• Proper fit-up and freedom from restraint during brazing
• Proper atmospheric protection during brazing
• Minimal thermal exposure to avoid secondary precipitation in the base metal
Haynes International - Welding and Joining Guidelines
Brazing and Soldering Continued
Base Metal Surface Preparation
All forms of contamination such as dust, paint, ink, chemical residues, oxides, and scale
must be removed from part surfaces prior to brazing. Otherwise, the molten brazing
material will have difficulty "wetting" and flowing along the surface of the base metal.
Surfaces must be cleaned by solvent scrubbing or degreasing and then by mechanical
cleaning or pickling. Tenacious surface oxides and scales may require grinding. Once
cleaned, the parts should be assembled as soon as possible using clean gloves to prevent
subsequent contamination. It is important to note that proper cleaning techniques should
be used on the entire component assembly prior to brazing, not just the surfaces being
brazed.
Some high-temperature alloys may benefit from the application of a thin nickel flashing
layer before brazing, particularly those alloys containing higher aluminum and titanium
contents. This layer is normally applied by electroplating; electroless nickel deposits using
nickel-phosphorus alloys are not recommended. Flashing layer thicknesses of up to about
0.001 in (0.025 mm) maximum are normally employed, depending upon the specific base
metal alloy and the specific joint geometry.
Brazing Filler Metal Selection
Proper selection of a brazing filler metal for the intended application depends upon
a number of factors, including component design, base metal alloy(s), and service
environment. Brazing filler metals are typically classified according to chemical
composition. HASTELLOY® and HAYNES® alloys may be successfully brazed using
a variety of nickel-, cobalt-, silver-, copper-, and gold-based filler metals; some of the
possible brazing filler metals are listed in Table 4. The exact alloying content of the brazing
filler metal determines the temperature range between the liquidus and solidus, i.e. the
melting temperature range. The magnitude of the melting temperature range indicates the
potential filling capability, and a brazing filler metal with a larger melting range is generally
more capable of filling a larger joint clearance. If the brazing filler metal melts at a specific
temperature, it is referred to as a eutectic filler metal. As a result, eutectic filler metals
have less filling capability and require tight joint clearances. Examples of eutectic filler
metals are the AWS A5.8 BAg-8, BAu-4, and BCu-1 classifications.
Filler metals are commonly applied as a powder mixed with a liquid binder. The brazing
filler metal powder can also be mixed with a water-based gel suspension agent to produce
a paste. Filler metals are also available as foil and tape. Every effort should be made
to confine the brazing filler metal to the joint area as any spatter upon non-joint surfaces
could severely degrade the environmental resistance at that location, particularly if it is
exposed to service temperatures above the melting point of the brazing filler metal. Since
most brazing filler metals do not possess the same level of corrosion resistance as Ni-base
corrosion-resistant alloys, it is preferable that brazing is used for joining only when the
brazed joint will be isolated from the corrosive environment.
Haynes International - Welding and Joining Guidelines
Brazing and Soldering Continued
Brazing Filler Metal Selection Continued
Nickel-based brazing filler metals can be utilized for high-temperature service applications
up to 2000°F (1093°C). They generally have additions of boron, silicon, and manganese to
depress the melting range and accommodate brazing at various temperatures. The boroncontaining brazing filler metals are used for aerospace and other applications subject to
high temperature and stress conditions. However, they are susceptible to the formation of
brittle borides. These brazing filler metals may also contain chromium to provide for more
oxidation-resistant joints.
Cobalt-based brazing filler metals are typically useful for achieving compatibility with Cobase alloys, and obtaining good high-temperature strength and oxidation resistance.
Silver-based brazing filler metals have been successfully used for brazing Ni-base
corrosion-resistant alloys intended for service applications below approximately 400ºF
(204ºC). They are known for excellent flow characteristics and ease of usage. Filler
metals containing low-temperature constituents, such as zinc and tin, are difficult for
furnace brazing since they will evaporate prior to reaching the brazing temperature.
Most furnace brazing with silver-based filler metals should be conducted in an argon
atmosphere. It should be cautioned that most Ni-base alloys are subject to stresscorrosion cracking when exposed to molten silver-rich compositions, so it is imperative
that the base metal be stress-free during brazing when utilizing silver-based filler metals.
This liquid metal embrittlement form of cracking occurs catastrophically at the brazing
temperature.
Copper-based brazing filler metals tend to alloy rapidly with Ni-base alloys, raising the
liquidus and reducing fluidity. Therefore, they should be placed as close to the joint as
possible, and the assembly should be heated rapidly to the brazing temperature. Copperbased brazing filler metals are only suggested for joining components to be used at service
temperatures below 950°F (510°C). Copper-based brazing filler metals that contain
significant amounts of phosphorus should be used with caution since they tend to form
nickel phosphides at the bond line that promote brittle fracture. Copper-based filler metals
should not be used for brazing Co-base alloys.
Gold-based brazing filler metals are mostly used when joining thin base metals due to their
low interaction with the base metal. They are also useful when good joint ductility and/or
resistance to oxidation and corrosion are primary concerns.
For more detailed information on different brazing filler metal classifications, please
refer to: AWS A5.8M/A5.8, Specification for Filler Metals for Brazing and Braze Welding,
American Welding Society. There are also numerous proprietary brazing filler metals and
alloy compositions that are commercially available. It is suggested that brazing filler metal
manufacturers be consulted when selecting a filler metal for a specific base metal alloy or
application.
Haynes International - Welding and Joining Guidelines
Brazing and Soldering Continued
Fit-Up and Fixturing
Since most brazing alloys flow under the force of capillary action, proper fit-up of the parts
being brazed is crucially important. To facilitate uniform flow of the molten brazing filler
metal through the joint area, joint gap clearances on the order of 0.001 to 0.005 in (0.025
to 0.125 mm) must be maintained at the brazing temperature. Excessive external stresses
or strains imposed on the brazed joint during brazing may cause cracking, especially when
brazing fluxes are involved. If possible, components should be brazed in the annealed
condition (i.e., not cold worked).
Making use of appropriate joint fixturing is also helpful. Fixtures used in furnace brazing
must have good dimensional stability and generally low thermal mass to facilitate rapid
cooling. Metallic fixtures are limited in their ability to maintain close tolerances through
repeated thermal cycles, and are relatively high in thermal mass. Accordingly, graphite
and ceramic fixtures are normally better suited for use in high-temperature furnace brazing
applications. Graphite has been widely used in vacuum and inert gas furnace brazing, and
provides excellent results. However, graphite should not be used for fixturing in hydrogen
furnace brazing without a suitable protective coating, as it will react with the hydrogen and
possibly produce carburization of the parts being brazed. Ceramics are also used, but
typically for smaller fixtures.
Haynes International - Welding and Joining Guidelines
Brazing and Soldering Continued
Protective Atmospheres and Fluxes
In addition to proper cleaning procedures prior to brazing, control of furnace environment
and purity of the brazing atmosphere is vitally important to ensure proper flow
characteristics of the brazing filler metal. Since most Ni-/Co-base alloys are designed to
form tenacious oxide films, these same oxide films will cause problems during brazing if
atmospheres are not rigorously controlled. Exclusion of oxygen, oxidizing gas species,
and reducible oxide compounds from the furnace environment is required as oxygen
derived from any source within the furnace can produce surface contamination in the joint
area. Ni-based brazing filler metals, for instance, are commonly used in conjunction with
vacuum, high purity argon, or hydrogen (reducing) furnace atmospheres. The interior of the
furnace and fixtures should be kept clean and free of any type of reducible oxide deposits,
and outside atmospheric leak rates should be kept as low as possible. A high atmospheric
leak rate through a vacuum furnace could easily cause a thin oxide film to form on the
base metal surfaces being brazed. The presence of a surface oxide film impedes the flow
of the brazing filler metal, and often results in a poor brazed joint. Flux-based brazing
operations can be carried out by using an induction coil heating source, or in a furnace with
a reducing atmosphere.
Brazing fluxes are utilized to protect and assist in wetting of base metal surfaces. Fluxes
are usually mixtures of fluorides and borates that melt below the melting temperature of
the brazing filler metal. Standard brazing fluxes can be used with most Ni-/Co-base alloys.
Specialized formulations may be necessary for use with certain brazing filler metals or
for base metal alloys containing aluminum and titanium. There are many variables that
influence the choice of the most appropriate flux, including base metal, filler metal, brazing
time, and joint design. To be effective, a brazing flux must remain active throughout the
brazing temperature range. Recommendations from a brazing flux supplier should be
sought when considering the use of a specific flux for the first time. Flux removal after
brazing is necessary, and particularly important on brazed components that will experience
corrosive or high-temperature environments. Grinding or abrasive blasting may be
required to remove any tenacious flux residue.
Haynes International - Welding and Joining Guidelines
Brazing and Soldering Continued
Effect of Brazing Thermal Cycles
The thermal cycles associated with brazing can have deleterious effects upon the
microstructure and properties of HAYNES® and HASTELLOY® alloys. Thermal cycle
exposure during brazing includes both the time at the selected brazing temperature,
and the time taken to heat and cool from elevated temperature. Care should be taken
to ensure that the respective brazing thermal cycle does not produce deleterious
precipitation of secondary phases in the component. Thus, thermal cycles associated
with the brazing operation should be controlled to minimize exposure to temperatures in
the approximate range of 1000 to 1800ºF (538 to 982ºC) where most Ni-/Co-base alloys
tend to precipitate secondary phases. For corrosion-resistant alloys, such secondary
precipitation could strongly influence their corrosion resistance in service. Normal cooling
rates from the brazing temperature, particularly in vacuum furnace brazing, are usually
too slow to prevent carbide precipitation in most Ni-/Co-base alloys. Cooling rates in a
vacuum environment can be increased by backfilling the furnace with argon or helium.
Where brazing is performed in the solution annealing temperature range of the base metal
alloy, there is the possibility for both normal and abnormal grain growth, which could be
deleterious to service performance.
Table 4: Some Possible Brazing Filler Metals for HASTELLOY® and HAYNES® Alloys
Designation/Specification
AWS A5.8 ISO 17672
AMS
Nominal Composition
(wt.%)
Liquidus - Solidus
Brazing Temperature
Range
45Ag-15Cu-16Zn-24Cd
1125-1145°F (607-618°C)
1145-1400°F (620-760°C)
BAg-1
Ag 345
4769
BAg-2
Ag 335
4768
35Ag-26Cu-21Zn-18Cd
1125-1295°F (607-702°C)
1295-1550°F (700-840°C)
1170-1270°F (632-688°C)
1270-1500°F (690-815°C)
BAg-3
Ag 351
4771
50Ag-15.5Cu-15.5Zn-16Cd3Ni
BAg-4
Ag 440
----
40Ag-30Cu-28Zn-2Ni
1240-1435°F (671-779°C)
1435-1650°F (780-900°C)
BAg-8
Ag 272
----
72Ag-28Cu
1435°F (779°C)
1435-1650°F (780-900°C)
BAu-4
Au 827
4787
Au-18Ni
1740°F (949°C)
1740-1840°F (950-1005°C)
BAu-5
Au 300
4785
Au-36Ni-34Pd
2075-2130°F (1135-1166°C) 2130-2250°F (1165-1230°C)
BAu-6
Au 700
4786
Au-22Ni-8Pd
1845-1915°F (1007-1046°C) 1915-2050°F (1045-1120°C)
BCu-1
Cu 141
----
Cu-0.075P-0.02Pb
1981°F (1083°C)
2000-2100°F (1095-1150°C)
BNi-1
Ni 600
4775
Ni-14Cr-3.1B-4.5Si-4.5Fe0.75C
1790-1900°F (977-1038°C)
1950-2200°F (10651205°C)
BNi-1a
Ni 610
4776
Ni-14Cr-3.1B-4.5Si-4.5Fe0.06C
1790-1970°F (977-1077°C)
1970-2200°F (10801205°C)
BNi-2
Ni 620
4777
Ni-7Cr-3.1B-4.5Si-3Fe0.06C
1780-1830°F (971-999°C)
1850-2150°F (1010-1180°C)
BNi-3
Ni 630
4778
Ni-3.1B-4.5Si-0.5Fe-0.06C
1800-1900°F (982-1038°C)
1850-2150°F (1010-1180°C)
BNi-4
Ni 631
4779
Ni-1.9B-3.5Si-1.5Fe-0.06C
1800-1950°F (982-1066°C)
1850-2150°F (1010-1180°C)
BNi-5
Ni 650
4782
BNi-6
Ni 700
----
Ni-11P-0.06C
1610°F (877°C)
1700-2000°F (930-1095°C)
1630°F (888°C)
1700-2000°F (930-1095°C)
Ni-19Cr-0.03B-10.1Si-0.06C 1975-2075°F (1079-1135°C) 2100-2200°F (1150-1205°C)
BNi-7
Ni 710
----
Ni-14Cr-0.02B-0.1Si-0.2Fe0.06C-10P
BCo-1
Co 1
4783
Co-19Cr-17Ni-0.8B-8Si1Fe-4W-0.4C
2050-2100°F (1120-1149°C) 2100-2250°F (1150-1230°C)
Haynes International - Welding and Joining Guidelines
Brazing and Soldering Continued
Soldering
Soldering refers to a group of joining processes that produces the coalescence of materials
by heating them to the soldering temperature in the presence of a soldering filler metal
having a liquidus below 840°F (450°C) and below the solidus of the base metal, i.e. without
melting of the base metal. Ni/Co-base alloys can be successfully soldered, although alloys
containing higher levels of chromium, aluminum, and titanium can be more difficult to
solder. Many of the considerations for soldering are similar to those previously outlined for
brazing of HASTELLOY® and HAYNES® alloys.
Common soldering filler metals are composed of mixtures of lead and tin. Most of the
common types of filler metals can be used to solder Ni-/Co-base alloys. Soldering filler
metals with a relatively high tin content provide the best wettability, such as the 60 wt.
% tin-40% wt. % lead or 50 wt. % tin-50 wt. % lead compositions. If color matching is a
priority, certain filler metals, such as the 95 wt. % tin-5 wt. % antimony composition, may be
best. However, the soldered joint may eventually oxidize and become noticeable if there is
exposure to elevated temperatures.
The soldering filler metal can be used to seal the joint, but should not be expected to
provide a mechanically strong joint or carry the structural load. Mechanical strength needs
to be provided for by another means of reinforcement, such as lock seaming, riveting,
spot welding, or bolting. For precipitation-strengthened alloys, soldering should be
performed after the alloy has gone through its age hardening heat treatment. The relatively
low temperatures involved in soldering should not soften or weaken the precipitationstrengthened alloy. Any welding, brazing, or other heating treating operations should
also take place before soldering. Ni-/Co-base alloys are susceptible to liquid metal
embrittlement when in contact with lead and other metals with low melting points. While
this will not occur at normal soldering temperatures, overheating of the soldered joint should
be avoided.
Fluxes containing hydrochloric acid are typically required for soldering most Ni/Co-base
alloys that contain chromium. Rosin-base fluxes are generally ineffective. Since most flux
residues absorb moisture and can become highly corrosive, they should be thoroughly
removed from the workpiece after soldering. Rinsing in water or aqueous alkaline solutions
should be effective for removing most residues; however, in the presence of oil or grease,
the material must be degreased before rinsing.
Joint designs that will be inaccessible for cleaning after soldering, such as long lap joints,
should be coated with soldering filler metal prior to assembly. This is generally performed
with the same filler metal alloy to be used for soldering. The workpieces may be immersed
in a molten bath of the soldering filler metal or the surfaces may be coated with flux
and heated to allow the soldering filler metal to coat the joint. Pre-coating may also be
accomplished by tin plating.
Visual inspection is usually sufficient for evaluating the quality of a soldered joint. The
soldered metal should be smooth and continuous; lumps or other visual discontinuities
are indicative of insufficient heat. Holes are most likely caused by contamination or
overheating, and can result in leaks. Soldered joints with leak-tight requirements should be
pressure tested.
Haynes International - Welding and Joining Guidelines
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