Stainless steel can be welded using a range of processes. Which one is suitable depends on far more than material thickness.
The deciding factors include:
material grade
component geometry
type of joint
material thickness
accessibility
required weld appearance
heat input
permissible distortion
batch size
surface and post-weld finishing requirements
A process that works beautifully on a thin-walled visible component can be needlessly laborious on a large welded structure. There is no such thing as the best welding process – only the right process for the component in hand.
Why is stainless steel demanding to weld?
Stainless steel differs from unalloyed steels in several respects. Depending on the material group, the following come into play:
thermal expansion
thermal conductivity
changes to the microstructure
oxidation of the weld zone
distortion
corrosion resistance after welding
choice of filler metal
On thin-walled components in particular, heat input can have a marked effect on geometry. At the same time, a technically sound weld must not lose the surface properties it was meant to have through unsuitable handling or post-weld treatment.
TIG welding of stainless steel
TIG stands for tungsten inert gas welding. The arc is struck between a non-consumable tungsten electrode and the workpiece; filler metal can be added separately, although not every application requires it. The process allows the welder to keep very close control of what is happening.
Typical advantages
excellent control of the weld pool
high-quality, comparatively clean welds
well suited to thin material thicknesses
good control of heat input
suitable for demanding visible welds
an excellent fit for many stainless steel structures
Typical drawbacks
comparatively low welding speed
greater manual effort
not always economical on long welds
high demands on the welder’s qualification
When does TIG make sense?
thin-walled stainless steel structures – where heat input and weld quality need to be closely controlled
vessels and process components – where high-quality welded joints are called for
visible welds – where weld appearance matters
complex one-off work – with small batch sizes and changing geometries
pipework and connections – where controlled weld quality and sound root penetration are required
With stainless steel, the visible face of the weld is not the only thing that counts. The weld root on the reverse side oxidises heavily if it comes into contact with oxygen. Back purging shields that area with a suitable gas while welding is in progress, which markedly reduces oxidation on the root side. This matters in particular for:
pipework
vessels
hygienic applications
demanding product-contact welds
components whose interior is difficult to finish later on
Back purging protects the weld exactly where the welder often cannot reach it afterwards.
MIG welding of stainless steel
In MIG welding, a consumable wire electrode is fed continuously. This allows higher welding speeds and deposition rates than manual TIG welding.
Typical advantages
higher welding speed
higher deposition rate
well suited to larger weld volumes
economical given suitable designs and batch sizes
readily mechanised
Typical challenges
heat input can be higher
weld appearance is not ideal for every visible application
spatter and rework can weigh more heavily, depending on how the process is run
not always the first choice for very fine, thin-walled work
When does MIG make sense?
larger welded assemblies
heavier material sections
longer welds
frames and load-bearing structures
components with a higher weld volume
recurring production work
The design itself remains decisive: on some components TIG is the more economical answer despite its lower speed, simply because less rework is needed.
MIG or MAG – where is the difference?
In practice the two terms are often used interchangeably. The basic difference lies in the shielding gas: MIG (metal inert gas) uses a largely inert shielding gas, while MAG (metal active gas) works with gas mixtures containing active components.
Which process variant and which shielding gas suit a particular stainless steel depends on the base material, the filler metal and the result required. A specification should therefore never stop at “MIG or MAG” but cover the complete welding process, including shielding gas and filler metal.
Laser welding of stainless steel
Laser welding introduces energy into the component in a highly concentrated form. The result is a narrow weld zone and, compared with many conventional processes, often a lower heat input into the component as a whole.
Typical advantages
high welding speed
low heat input
narrow heat-affected zone
little distortion
high repeat accuracy
readily automated
suitable for complex, precise assemblies
In return, component preparation has to be precise
High precision comes with a consequence: joint gap, positioning, fixtures, component tolerances, weld geometry and access for the laser all matter. Where a manual process can absorb minor deviations, the laser calls for components prepared to a repeatable standard.
When is laser welding worthwhile?
thin-walled components
demanding requirements for low distortion
precision enclosures
complex three-dimensional geometries
recurring assemblies
applications calling for high repeat accuracy
For one-off parts or geometries with very poor access, a manual process may well be the more flexible option. 3D laser welding at stainlesstec
TIG, MIG or laser? A rough guide
Requirement
TIG
MIG
Laser
Thin sheet
excellent
limited to good
excellent
Visible weld
excellent
good
excellent
High welding speed
moderate
good
excellent
High deposition rate
moderate
excellent
depends on the task
Low heat input
good
moderate
excellent
Low distortion
good
moderate
excellent
Flexible one-off work
excellent
good
depends on the fixture
Automation
possible
good
excellent
High gap tolerance
comparatively good
good
rather low
Recurring small batches
good
good
excellent with a suitable design
This table is deliberately no more than a rough guide. The actual choice always depends on the component.
And what about longitudinal seam welding?
Longitudinal seam welding is less a welding principle in its own right than a mechanised way of producing a long, straight weld repeatably. Typical applications are:
vessel shells
tube bodies
elongated enclosures
shell components
cylindrical assemblies
Mechanical guidance keeps the process even over a greater weld length, with benefits for weld appearance, speed, repeatability and geometry. Longitudinal seam welding
The material grade has a say
“Stainless steel” is not a single material. An austenitic grade such as 1.4301 makes different demands from, for example:
1.4404
duplex 1.4462
high-alloy special grades
non-magnetisable special materials
Duplex steels in particular call for controlled heat management, because unfavourable welding conditions can affect the microstructure and with it the properties of the material. The welding process is therefore never chosen in isolation from the specific stainless steel grade.Working with stainless steel
Choosing the right filler metal
The filler metal, too, has to match the base material and the application. What matters here:
chemical composition
corrosion resistance
mechanical properties
welding process
loads in service
temperature range
On demanding applications, the filler metal should form part of the agreed welding procedure specification or project specification.
Heat changes the component
Welding creates high local temperatures. The material expands, stresses build up, the weld contracts as it cools and the component can deform. The thinner and the larger a structure is, the more pronounced the effect.
Planning a weld is therefore not only about how the parts come together – but also about what the whole component looks like once it has cooled.
How can welding distortion be reduced?
a suitable welding sequence
welding symmetrically
controlled heat input
suitable clamping
tacking strategy
mechanised processes
laser applications
straightening afterwards
Which measures make sense depends very much on the design.
Heat tint and post-weld treatment
Welding stainless steel can leave visible heat tint around the heat-affected zone. It shows that the surface has been thermally oxidised. Depending on the application, these areas need appropriate treatment – particularly in hygienic applications, on components exposed to corrosion, in food and pharmaceutical process technology and wherever high-quality visible surfaces are involved.
Mechanical grinding – works back weld reinforcement, surface defects or visible transitions.
Pickling – chemically removes certain oxide layers and metallic contamination.
Passivation – helps restore a suitable passive surface condition on the stainless steel.
Which combination is required depends heavily on the application and the surface specification. There is no one-size-fits-all treatment for every stainless steel weld. Preventing rust contamination on stainless steel
When does the surface matter most?
Food processing technology
Where cleanability and product-contact surfaces are involved.
Welding processes are tools – what counts is which one fits the component
stainlesstec has a range of processes available for welded stainless steel assemblies – from manual TIG and MIG welding through mechanised longitudinal seam welding to CNC-controlled 3D laser welding.
Our services page shows how we put these processes to work in production. Or perhaps you already have a specific design in hand:
Send us your drawing or CAD data by email – together with material, batch size and your requirements. We will come back to you with a sound assessment.
