Dissimilar Welding of Stainless

Steel to Other Metals

Prepared by: DSc Dževad Hadžihafizović (DEng)

Sarajevo 2023
 Dissimilar Welding of Stainless Steel to Other Metals

Abstract:

The main challenges of welding dissimilar relate to the range of different properties
displayed by the different materials and how these effect the finished nature of the joint itself.

There is still much to learn about welding dissimilar materials but improving the related
techniques in this complex technological subject can lead to great gains across many
industry sectors.

The need for joining dissimilar metals has existed for a long time and has generally been
considered to be beyond state of the art. Dissimilar metals have different chemistries, so
they have different properties, such as melting temperatures. Many of these metals are
alloys or a mixture of several elements, all of which melt at different temperatures.
Therefore, when accomplishing a weld, it is virtually impossible to prevent a chemical
change at the moment a melt of the parent metals occurs.

Welding the common austenitic stainless steels such as 304 and 316 to each other or
themselves is routine and the easiest of fusion welding. Nevertheless, there are many
situations where it is necessary to weld stainless steel to carbon steel or other even more
unusual combinations.

Two common examples are balustrade posts attached to structural steel or doubler plates
connecting supports to stainless steel vessels. There are differences in physical properties
such as thermal conductivity and expansion, magnetic properties, metallurgical structure and
corrosion resistance, which all require attention. This article outlines the necessary
procedures for satisfactory welding, including reference to standards, and explains the
necessary precautions. Appendix H of AS/NZS 1554.6:2012 has a more detailed technical
discussion including advice on welding carbon steel to ferritic, duplex and martensitic
stainless steels.

Dissimilar material welding is more complex than similar weld due to the necessity of the
process being applied in zones where a requirement is to improve some properties. The
main purpose of the paper B. I. Mendoza et al. is to know the mechanical behavior of a
dissimilar weld between HSLA Steel and Super-duplex Stainless Steel (SDSS) to establish if
the joint is feasible or not. The alloys were welded using the GTAW process using a 60-deg
and 90-deg single -V groove test specimens in order to observe the effect of the weld pass.
The filler metal was chosen with the aid of Schaeffler diagram. Schaeffler diagram with
different base materials link:

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https://migal.co/en/service/welding-calculators/schaeffler-diagram-with-different-base-
materials

It was found that the ER 25.10.4L filler metal provided the best equilibrium between ferrite
and austenite phase in the Super-duplex Stainless Steel final microstructure and a band of
martensite in the HSLA steel final microstructure. The dissimilar joint presented acceptable
mechanical properties which are superior to the HSLA in the as-received condition, but lower
than the SDSS in the as-received condition, proving that the filler metal was the adequate.

In Figure 1 it is possible to observe the difference on the microstructures in function of the

Figure 1: DMW with different number of welding passes.

Dissimilar metal welding (DMW) of the bio-compatible materials stainless steel (SS) and the
shape memory alloy Nickel-Titanium (NiTi) is of particular interest within the bio-medical
industry due to the exceptional mechanical properties of NiTi and the low cost of stainless
steel 316. This particular material pair, however, suffers from significant intermetallic
formation after mixing which results in brittle joints which are unable to withstand handling
and use. A number of intermetallic phases exist even in the simplified binary Fe-Ti system.

The addition of alloying elements such as Cr and Ni found in SS and NiTi introduces further
complexities in microstructure and phase formation. The dissimilar material pair between
stainless steel and titanium alleviates some of these complexities by reducing the nickel
composition from roughly 50 at% in the NiTi to only ~10 at% in the SS while still enabling the
formation of Ti-Fe-based intermetallics.

Traditional joining methods such as arc welding when applied to dissimilar material pairs
have been found to introduce excessive amounts of heat resulting in the formation of large
volumes of intermetallics. Some success has been found through the use of laser welding
due to its precise, localized heat input capabilities which allows for small heat affected
zones, however, the joints still suffer from brittle intermetallic formation.

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Laser fusion welded dissimilar joints between stainless steel 316 and titanium grade 2 have
been investigated as a simplified model for the NiTi - stainless steel dissimilar material pair.
Tensile strengths of the joints are observed to be lower than the base materials with failure
occurring through brittle fracture.

EDX and EBSD analysis indicated the formation of coarse intermetallic TiFe dendrites within
a β-Ti matrix in the main weld pool and single-phase supersaturated β-Ti(Fe) in the lower
weld zone.

Fracture surface analysis suggests that smooth interdendritic fracture between dendrites
oriented perpendicular to the tensile load is the predominant mechanism of failure in the
main weld pool while alternating failure along the SS-weld and Ti-weld interfaces was
observed in the lower weld zone. Significantly greater surface area formation was observed
in the lower portion of the weld suggesting that the single-phase supersaturated β-Ti(Fe)
structure may be beneficial for fracture resistance.

The specific fracture morphologies observed and preferential cracking within the coarse
dendritic microstructure observed near the stainless-steel base material in the main weld
pool suggests that control over the weld pool geometry, heat flow, and quench rate may
allow for robust dissimilar metal welds between titanium and stainless steel.

On the other hand, several problems arise when welding dissimilar steels, related mainly to
the different physical, chemical and mechanical properties of the welded materials.
Austenitic stainless steel and low carbon steel possess a good combination of mechanical
properties, formability, weldability and resistance to corrosion. This combination of steels is
extensively used in the power generation industry. Research on welding is carried out at
various research institutions. The aim of our paper is to analyze and compare the properties
of resistance spot welds of low carbon steel and austenitic stainless steel. Optical
microscopy, microhardness measurements and EDX analysis were used to analyze the
properties of the spot welded joints.

The macrostructure of the welded joint produced by using a welding current of 7.5 kA is
documented in Figure 2. As the macrostructure suggests, the welded joint is asymmetrical.
The fusion zone size on the stainless steel side is larger than the fusion zone on the low
carbon steel side. Similar results were also observed in welds produced with welding
currents of 7 and 8 kA. The heat-affected zone (HAZ) of the DC 01 steel is broader due to
the higher thermal conductivity of the low carbon steel sheet. On the basis of macrostructure
analysis, it can be stated that the higher the welding current that is used, the larger the
fusion zone.

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Figure 2: The macrostructure of a selected dissimilar resistance spot weld (IW = 7.5 kA) .

The microstructure of low carbon steel is fully ferritic. Grain refining was observed in the low
temperature HAZ of carbon steel (see Figure 3). Some amounts of pearlite were also
present.

Figure 3: HAZ – DC 01 steel interface.

References

1. Joining Dissimilar Metals, The Fabricator, 1991, Accessed Nov 2015

2. Welding dissimilar metals, ASSDA Technical FAQ No9, Accessed Sept 2016

3. B. I. Mendoza, Z. C. Maldonado, H. A. Albiter, P. E. Robles: Dissimilar Welding of

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4. G. Satoh, Y. Lawrence Yao, C. Qiu: Strength and Microstructure of Laser Fusion Welded
Ti-SS Dissimilar Material Pair, Proceedings of NAMRI/SME, Vol. 39, 2011

5. L. Kolařík, M. Sahul, M. Kolaříková, M. Sahul, M. Turřna, M. Felix: Resistance Spot

Welding Dissimilar Metals: Dos and Don'ts

Chances are, you’ve heard the horror stories about welding dissimilar metals. Taking the
right precautions during these dangerous welds can mean the difference between improving
your process piping system and causing long-term headaches.

Luckily, if you take a few minutes now to understand the hazards and advantages of welding
different metals, you can save time, money, and productivity in the future.

In this article, we dig into the nitty-gritty of the welding process and outline the dos and
don’ts of welding dissimilar metals.

Why Is Welding Important?

When done right, welding can be miraculous. It allows you to alter structures in the field and
support new pipe runs without having to completely replace piping. If you need to connect
metal, expand a piping system, or redirect pipe flow, welding may be your best option.

Still, it’s important to keep welding to a minimum whenever possible. Welds slice into your
piping system. That means these welded areas, although valuable, add weak spots to pipes,
and they can be vulnerable to corrosion.

Why Weld Dissimilar Metals?

You may already understand the dangers of combining dissimilar metals. Because metal can
have wildly different properties, fusing the wrong dissimilar metals together can cause
corrosion or flimsy connections.

However, the very fact that metals have different properties often inspires welders to connect
dissimilar metals. In some cases, it’s cost-effective or convenient to mix and match different
metals.

For instance, you may use aluminum in your system because it’s light and resistant to
corrosion. However, aluminium tends to be more expensive than other strong metals, such
as steel. So you may decide to weld steel to aluminum in order to save on costs or add
durability.

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Regardless of the combination, welding different metals can be a way to get more out of a
metal’s unique properties.

What to Consider When Welding Dissimilar Metals

Welding dissimilar metals is a touchy process. If you don’t weld with care, you could end up
with destroyed piping or massive corrosion problems. Here are some factors to consider
when welding dissimilar metals.

Melting point: Dissimilar metals can melt at drastically different temperatures. For instance,
steel generally won’t melt until it heats up to around 1,370°C (2500°F) . Aluminium, on the
other hand, starts melting around 660°C (1220°F). In most cases, you’ll want to modify your
welding technique to make sure metals are melting and fusing together smoothly.

Thermal expansion rates: When they heat up or cool down, different metals will expand and
contract at different rates. If the two welded metals’ thermal expansion rates are too
different, it could increase the welded point’s residual stress. That means your connection
will be up against extra pressure and be more highly vulnerable to breaks.

Galvanic corrosion: Galvanic corrosion can spread quickly and destroy metal. This
electrochemical reaction kicks off when metals with different anodic and cathodic properties
get together. That’s why it’s important to separate reactive metals with a buffer, neutral joint,
or nonmetallic support.

End environment: A metal’s environment can drastically affect its durability. For instance, if
unprotected metal, such as carbon steel, is left in salt-heavy air, it can cause corrosion. It’s a
good idea to consider where a metal will be operating and all of the corrosive elements that it
will be up against. In some cases, metal may need protective coatings or galvanizing to
avoid corrosion.

Use Transition Materials

If the metals you’re welding have different electrochemical properties, you may want to
separate them with a transition material. This will keep noble metal from pulling electrons out
of more basic metals.

Limit Welding

As helpful as welding is, it’s a good idea to remember that with every weld, you’re upping the
potential for weak spots and corrosion in your piping system. In some instances, you can
use supports, such as repads, to limit welds. In other cases, it may be possible to use pipe
shoes, wear pads, or other supports to bypass welding altogether.

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Research Metals

Not sure if the materials you’re working with are compatible? Stop and take a minute to do
some research before you weld. Here are some groups that provide standards for welding
materials:

American National Standards Institute (ANSI)

American Society of the International Association for Testing and Materials (ASTM
International)

American Society of Mechanical Engineers (ASME)

Don’t ...

Directly Connect Incompatible Metals

If you directly connect metals that have different electrochemical properties, it could cause
galvanic corrosion. If metals are incompatible, it’s important to use a buffer or surface
protection to keep metal from corroding.

Underestimate Metallic Properties

Remember, metals can have different melting points, conductivity, strengths, and
malleability. All of these factors can contribute to the durability of your weld and the
performance of your piping system.

Rule Out Alternatives to Welding

In many cases, welding may seem like a simple solution. However, before melting your
piping system’s metallic surfaces, it’s worth asking if there are adjustable supports or other
creative alternative products that can strengthen your system.

https://www.appmfg.com/blog/welding-dissimilar-metals-dos-and-donts

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 Welding Dissimilar Metals Using 309 Stainless Steel

How To Weld Dissimilar Metals?

Most welders experience difficulty welding dissimilar metals. An example of it is weld fusion
on ferritic-to-carbon-steel joints - the welds do not seem to be fusing with the carbon steel.
This problem is not uncommon when welding stainless steel (SS) to carbon steel. In many
cases, it can be resolved simply by removing any mill scale or surface impurities from the
base materials. Keep in mind that the surface of stainless steel has a tough oxide layer that
makes it passive to environmental attack. This oxide can sometimes cause welding
difficulties.

In the present article, we will focus on the potential problems welding dissimilar metals such
as ferritic to carbon steel. We will also discuss welding dissimilar metals using 309 stainless
steel.

Let us consider a case where the welder is experiencing issues welding ferritic stainless
steel and other grades of stainless steel (SS) with carbon steel.

The Case: Welding Dissimilar Metals

The welding team commonly builds and welds carbon steel parts with a standard ER 70S-6
wire using a 98 percent argon/2 percent carbon dioxide shielding gas. Recently they have
begun manufacturing parts that combine carbon steel, ferritic stainless steel, and other
grades of stainless steel (SS) using a 309LSi grade of wire with GMAW (Gas Metal Arc
Welding). The welders are struggling with weld fusion on the ferritic-to-carbon-steel joints -
the welds do not seem to be fusing with the carbon steel. The welding team is looking for
suggestions on it.

The Solution

In most cases when welding dissimilar metals or, more specifically, carbon to SS, we
recommend you use a 309 filler metal because of its higher ferrite content. This higher ferrite
content can minimize weld dilution and prevent weld cracking. The 309LSi grade of wire has
a low carbon content and a higher silicon content, hence the "LSi" in the designator. The
lower carbon content is ideal for applications that have a risk of intergranular corrosion
cracking. The higher silicon content serves as a deoxidizer and helps remove weld impurities
and increase weld puddle fluidity.

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When welding carbon steel to SS, be some weld dilution from the sides of the joint will occur.
The small amount of base material dilution in the weld metal will provide a better match to
each of those respective base materials. You should not have difficulties welding on the
ferritic side of the joint as stainless-to-stainless welding should fuse relatively well. If there
are problems, check to ensure the welding machine is set up correctly with good work lead
connections.

The 309LSi weld issues on the carbon steel may be the result of contamination. Try cleaning
the steel with an approved cleaner to remove any grease, oil, or paint. Grinding the mill scale
½ inch back from the weld joint may also help.

Last, the 98 percent argon/2 percent CO2 may not be aggressive enough to allow for proper
weld bead wetting on the carbon steel side of the joint. You want to keep the CO2 low to
minimize carbon pickup in the weld joint and prevent the welds from oxidizing too much.
However, since there is already cross-contamination from welding on the carbon steel, using
a higher-CO2 mix, such as 90/10 or even 85/1, may provide the necessary oxidizing action
to allow the weld to tie in properly.

https://esab.com/us/nam_en/esab-university/blogs/welding-dissimilar-metals-using-309-
stainless-steel/

Dissimilar Metals Welding

Performing dissimilar metals welding is a common occurrence, especially when dealing with
applications where advanced alloys are needed due to the mechanical, physical or corrosion
properties that the components will need to exhibit.

Due to economic factors, different metals give optimum performance in different parts of a
system. They do however need to be joined to each other. When welding is the best joining
technique, then our dissimilar metals welding problem raises its head.

Desired Dissimilar Metals Welding Outcomes

When joining two different metals by fusion welding, we are melting together three different
constituents:

1. Base metal 1
2. Base metal 2
3. Welding filler metal. (In some instances, no filler metal is added. This is called
autogenous welding)

When performing dissimilar metal welds, we are interested in the following final outcomes:

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 That the weld metal composition formed is stable from a metallurgical point of view:
Some metal compositions will form brittle intermetallic phases, or some metals will
quite simply not mix. Obviously such compositions are to be avoided. The simplest
way of avoiding this is to use combinations that have been used successfully before.
This can simply be done by looking up suitable filler metals for different base metal
combinations from existing tables. These are freely available on the internet from
most filler metal suppliers. See Figure 1 below for an example recommended filler
metal table from "Special Metals".

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Figure 1: Dissimilar metals welding recommended filler table. This table comes from a
"Special Metals" catalogue. They produce the industry standard "Inconel" branded nickel
based filler metals, hence the emphasis on these consumables in the table.

 That the weld metal formed has a microstructure that provides us with the necessary
mechanical properties: Even if we are using a filler metal recommended in a table,
we may still end up with a microstructure that is not suitable for our specific
application. It is therefore important to establish what the microstructure is going to
be, to be able to choose the best filler metal from a selection of different materials.
The best way of doing this for the typical combinations of base metals is to use the
Schaeffler diagram. See Figure 2 below for an example of a Schaeffler diagram.
(Lower down the page we will go into the details of how to use and interpret this
diagram when performing dissimilar metals welding.)

Figure 2: Schaeffler Diagram - Used in dissimilar metals welding to predict the weld
metal composition and properties.

 Any possible difficulties we may have during the welding process: Certain types of
weld metal may pose different challenges during the welding process. So for
instance, a 100% austenitic weld metal is prone to suffer hot cracking, while a
martensitic weld metal is prone to be brittle and suffer from hydrogen assisted cold
cracking. (HACC) By understanding the composition and structure of the weld metal,
we can try to prevent any such problems. Once again, the Schaeffler diagram comes
in handy for this purpose.

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Using The Schaeffler Diagram

To most easily explain the use of the Schaeffler diagram for dissimilar metals welding, I will
explain the use and show it as an example at the same time.

Let us assume that we will be welding the following materials:

 A carbon steel: Designated "Parent metal 1", with chemical composition of: C:0.25%;
Si:0.3%; Mn:1%
 To a duplex stainless steel: Designated "Parent metal 2", with a chemical
composition of: C:0.03%; Si:0.6%; Mn:1.5%; Cr:22%; Mo:3%; Ni:5%
 Using a duplex stainless steel filler: Designated "Filler metal" with a chemical
composition of: C:0.02%; Si:0.5%; Mn:1.5%; Cr:23%; Mo:3%; Ni:9%. - Note that this
filler metal is not listed in the "Inconel" table above, but is often used when joining
these materials.

To use the Schaeffler diagram, the following steps need to be taken:

Calculate the Chrome and Nickel Equivalents for parent metal 1. (Cr Equivalent = 0.45; Ni
Equivalent = 8 – Calculate these by applying the Cr and Ni equivalent formulas shown on
the axes of the Schaeffler diagram)

Plot the point on the diagram. (See P1 on the diagram below.)

Calculate the Chrome and Nickel Equivalents for base metal 2. (Cr Equivalent = 25.9; Ni
Equivalent = 6.65 – Calculate these by applying the Cr and Ni equivalent formulas shown on
the axes of the Schaeffler diagram)

Plot the point on the diagram. (See P2 on the diagram below.)

Draw a line between these two points. (See red line joining P1 and P2.)

Based on the ratio of base metal melted from each of the two base metals, mark a position
along the line. We are assuming a 15% dilution from parent metal 1 and 15% dilution from
parent metal 2 and 70% dilution from the filler metal. Because the dilution of parent metal 1
and parent metal 2 are the same, the position we mark is exactly half way between P1 and
P2 on the red line joining them. (See the red box on the line joining P1 and P2 in the
diagram below.)

Calculate the Chrome and Nickel Equivalents for the filler metal. (Cr Equivalent = 26.75; Ni
Equivalent = 10.35)

Plot the point for the filler metal on the diagram. (See F on the diagram below.)

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Draw a line between the point identified on the P1 – P2 line (the red box) and the point for
the filler metal. (point F) (See red line joining F and the red box in the diagram below.)

Based on the ratio of metal melted from the parent metals and the filler metal, mark a
position along this line. Assuming a 30% dilution from the parent metals and 70%
contribution from the filler metal, we will plot this point 30% along the line from point F. (See
the point marked W on the diagram below.)

The point W on the diagram below is then the anticipated composition of the weld metal.

Its location on the diagram also gives an indication of the microstructure that is anticipated,
as well as how sensitive it is to dilution. In this case we see that it will be between 20 – 40%
ferrite with the rest austenite. Because point W is relatively close to the austenite +
martensite + ferrite line, we can see that it is relatively sensitive to dilution from the parent
metal, so we would have an instruction on the welding procedure that low dilution welding
techniques are to be used.

Figure 3: Schaeffler Diagram Application Example.

Some Notes to the Dissimilar Metals Welding Example

The Schaeffler diagram is not very accurate for modern duplex stainless steel parent metals,
because it does not take account of the effect of Nitrogen as an alloying element. It is
however accurate enough for our purposes because the welding filler metals and weld
metals are low in Nitrogen, so their positions are more accurate for weld metals than the
parent metals.

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An Excel spreadsheet is available for performing these calculations automatically. This
spreadsheet is freely available when you sign up to receive the free WelderDestiny
newsletter. The spreadsheet also allows calculations to be performed for overlay welding.
Click on the prominently displayed subscribe button to sign up for the newsletter.

The fact that there is going to be quite a bit of ferrite in the weld metal (Around 20 - 40%)
means that it will not be very sensitive to hot cracking. We will look at these issues in future
web pages.

https://www.welderdestiny.com/dissimilar-metals-welding.html

Conclusions - Intergranular corrosion of dissimilar austenitic weld

Investigations of heat treatment by annealing influence as well as quality of dissimilar

The time of heat treatment duration has more significant influence on transformation rate in
relation on heat treatment temperature.

The most part of delta-ferrite transformation take place already after 2 hours annealing
regardless off temperature.

The specimens with larger amount of delta-ferrite in as welded state (welded by consumable
material quality of AWS E 316L) show the highest transformation degree what was specially
expressed at prolonged duration time of 10 hours.

Analysing the influence of heat treatment by annealing on intergranular corrosion favour of

Significant influence of the annealing parameters:

temperature and time duration on inergranular corrosion rate.

Specifically, the time duration influence more than temperature on corrosion rate.

Regarding to use austenitic dissimilar weld quality, the highest corrosion rate is present at
joints welded with AWS E 316L, as well as the lowest at AWS E 309L joints.

Filler Metals For Welding Stainless Steel

https://tubingchina.com/Filler-Metals-For-Welding-Stainless-Steel.htm

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