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Welding Stainless Steel – Hints and Guidelines

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Stainless steel contains a minimum of 10.5% chromium which imparts it corrosion resistance by forming an oxide layer on the surface. The most common stainless steel is the austenitic type (300 series) which contains chromium and nickel as alloying elements. Other types include ferritic, martensitic and duplex stainless steels. Most stainless steels are considered to have good weldability characteristics. Most common processes used for welding stainless steel are TIG (GTAW) and MIG (GMAW). But, stick welding (SMAW) is also utilized.

Differences in Properties:

The properties of stainless steel differ from mild steel, and these differences need consideration when welding as below:

• Higher coefficient of expansion, 50% more for austenitic – this results in more distortion
• Lower coefficient of heat transfer – welding requires lower heat input as it is conducted away slowly
• Lower electrical conductivity – using the correct and consistent stick-out distance is more critical when using MIG/TIG, higher wire speed for the same current is required when MIG welding

Why segregated work area?

Welding of stainless steel is carried out in a work area segregated from carbon steels. Moreover, tools dedicated for use with stainless steel must not be used to work on carbon steels. These tools include brushes, hammers, clamps, grinders etc. The segregation of work area and tools safeguard the contamination from carbon steels, which may cause welding defects and corrosion (rust) on stainless steel. You must also wear gloves when working with stainless steel as this will prevent oil from the hands passed onto the stainless steel.

Preparation is key!

With stainless steel, it is important that the joint surfaces are thoroughly cleaned before welding to remove any dirt, grease, oil etc. The filler wire also needs to be completely clean.

Additionally, the joint design including the joint gap must cater to the higher expansion rate of stainless steels.

Filler Material Selection:

Filler materials used generally are the same as the base metal. Special considerations are required to select a filler material if welding dissimilar stainless steels or stainless steels where no identical filler material exists. Furthermore, filler materials are selected to reduce the risk of intergranular corrosion and hot cracking.

Welding Considerations:

It is essential to protect the weld during welding using a mainly inert gas. Additionally, the weld root needs to be purged using a pure inert gas.

When welding austenitic stainless steels, it is important to restrict the heat input to a level which is just sufficient to ensure a good weld. The interpass temperature is limited to 350 F. Preheating is not carried out on austenitic stainless steels. Very low carbon grades (suffixed with L e.g. 304L, 316L) are used to prevent the formation of chromium carbides in the heat affected zones which causes intergranular corrosion.

Martensitic stainless steels are generally used as wear resistant materials in overlaying applications. To avoid cracking, accurate preheat needs to be applied and a minimum interpass temperature maintained.

Ferritic stainless steels are used mostly in automotive applications. The heat input in these steels during welding needs to be limited, and a maximum interpass temperature of 300 F is recommended. This will ensure that the grain growth in the material is controlled and the strength is maintained.

With duplex stainless steels, the heat input also needs to be restricted.

Cleaning and Passivation:

Stainless steel welds must be cleaned and passivated after completion to ensure corrosion resistance and good appearance. This is performed manually by mechanical (brushing, grinding, blasting), chemical (applying pickling agents and other chemicals) or electrochemical means.

Red-D-Arc has a wide range of equipment suitable for stainless steel welding for rent including the following:

Multi process welders capable of stick, TIG, MIG, submerged arc, air carbon arc cutting, flux core, up to 1500 A

MIG welding units up to 750 A

TIG welding units up to 750 A

Stick welding units – up to 625A

Also 4 and 6 Paks of welders available

Orbital welders – suitable for stainless steel pipe/tube welding

Various brands including Miller, Lincoln, Red-D-Arc

Have a look at our complete range of welding products.

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Fast, Efficient Flux-Cored Welding with Semi-Automatic Wirefeeders

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By guest blogger David H.

Some years back I was working in a shipyard in San Francisco. The yard had several small repair jobs going, plus a fairly large project building six ocean-going barges. The supervisor who was in charge of the barge-building project was looking for volunteers to operate semi-automatic wire feeders, using flux-cored wire, to weld stiffeners to the skin of the barges. I had never used a wire feeder before, so I volunteered out of curiosity.

After a very short training period, possibly all of 30 minutes but I think a bit less, I was off and running. I was impressed by the quality of the welds and the speed at which they were deposited. Without question I was outpacing anything that could be done by stick welding, and I felt it was easier to maintain a uniform weld size too. The machine itself was light enough and small enough to move without difficulty, and the spools of wire lasted long and were quick and easy to replace when the spool of welding wire was finished.

Red-D-Arc has nearly a dozen semi-automatic wire feeders available for almost any application. We also carry fully automatic wire feeders, which are faster still and appropriate in certain circumstances – like building storage tanks –  especially for large-deposition welds.

Red-D-Arc Welderentals

Red-D-Arc Welderentals™ an Airgas company rents and leases welders, welding positioners, welding-related equipment, and electric power generators – anywhere in the world. Our rental welders, positioners and specialty products have been engineered and built to provide Extreme-Duty™ performance and reliability in even the harshest environments, and are available through over 70 Red-D-Arc Service Centers, strategically located throughout the United States, Canada, the United Kingdom, France, and the Netherlands, as well as through strategic alliances in the Middle East, Spain, Italy, Croatia, and the Caribbean. From our rental fleet of over 60,000 welders, 3,700 weld positioners, and 3,700 electric-power generators, we can supply you with the equipment you need – where you need it – when you need it.

www.red-d-arc.com/