How to Weld Stainless Steel: The Ultimate Guide


Stainless steel is becoming more and more popular as a material in manufacturing. In 2016, 45.8 million metric tons of stainless steel was manufactured worldwide. By 2018, that number rose to 50.7 million. With an increasing amount of stainless steel on the market, stainless steel welding has ramped up as well. The material is strong and attractive looking, but famously difficult to work with. How can you master welding stainless steel? Stay tuned. 

How do you weld stainless steel? There are many methods of welding stainless steel, including MIG, GTAW, TIG, and stick welding. There are advantages and disadvantages of all the methods, but before you decide, you’ll first have to determine what type of stainless steel you’re working with. Stainless steel can be austenitic, martensitic, ferritic, duplex or precipitation hardened. 

Understanding the different methods and materials for welding stainless steel can help you to get dramatically better results. We’ll cover the methods and the materials. But first, let’s talk about why you’d want to use stainless steel in the first place. 

Why Stainless Steel? 

Stainless steel has risen in popularity largely due to its gorgeous appearance. Stainless steel is incredibly shiny and has a mirrorlike reflective finish. This material looks attractive in numerous applications including, kitchenware, appliances, jeweler, and home décor. 

Stainless steel, however, is more than just a pretty face. The material is strong, durable, and adaptable. It has a strong resistance to corrosion. Stainless steel applications are built to last. The material is also fairly workable, making it easy to use for a large number of applications. It is this adaptable property and its resistance to corrosion that actually make it more difficult to work with. 

To avoid contaminating the alloy and causing it to lose its most attractive properties, you need to make sure that all your tools and your workspace are totally clean and free of debris. This adds a bit of extra preparation and a more involved process than welding other metals. However, the strength and appearance of properly treated stainless steel make it well worth the extra effort. 

Types of Stainless Steel

Before you can even begin welding, you have to understand the material you’re working with. Stainless steel isn’t a single material but an umbrella term for a range of different metal alloys. All stainless steel types will share some defining characteristics including those we’ve discussed already, but each has its own unique character, and you may need to work it differently. 

Austenitic

Austenitic stainless steel, also called 300 series, is the most common stainless steel used for welding. This is because it is relatively easy to work. Austenitic steel is formable, highly resistant to corrosion, non-magnetic, and has high tensile strength. Austenitic steels contain high levels of chromium and nickel and low levels of carbon. 

The austenitic range of steels are distinguished by their face-centered cubic (FCC) grain structure. In this structure, there is one atom at each face, as well as one at each corner of the cube. This type of crystal structure forms when there is a large quantity of nickel (8–10 percent) in a steel alloy with 18 percent chromium.

When welding with austenitic stainless steel, it’s important that the filler material matches the base metal. For example, when welding with 304L, use 304L for the filler as well as the base. After welding, austenitic steel can be cold worked to improve strength and durability. 

Applications by Steel Grade

304 and 304L (standard grade):

  • Tanks
  • Storage vessels and pipes for corrosive liquids
  • Mining, chemical, cryogenic, food and beverage, and pharmaceutical equipment
  • Cutlery
  • Architecture
  • Sinks

309 and 310 (high chrome and nickel grades):

  • Furnace components
  • Kiln components  
  • catalytic converter components

318 and 316L (high moly content grades):

  • Chemical storage tanks
  • pressure vessels
  • piping

321 and 316Ti (“stabilized” grades):

  • Afterburners
  • Super heaters
  • Compensators
  • Expansion bellows

200 Series (low nickel grades):

  • Dishwashers and washing machines
  • Cutlery and cookware
  • In-house water tanks
  • Indoor and nonstructural architecture
  • Food and beverage equipment
  • Automobile parts

Ferritic

Ferritic stainless steel, or 400 series, is another very popular steel used for welding. Ferritic steel is known for having good ductility, being resistant to corrosion, and being resistant to cracking. Ferritic steel is high in chromium, low in carbon, and contains little to no nickel. 

In contrast to austenitic steels, ferritic steels have a body-centered cubic (BCC) grain structure. The crystal structure is composed of a cube of atoms, with an atom at the center. This structure is what gives ferritic steel its magnetic properties. 

Ferritic steel is generally very weldable and workable. It doesn’t require any pre-weld or post-weld heat treatments. If the ferritic steel is blended with martensitic structures, it may require a post-weld heat treatment to restore ductility. These metals cannot be hardened by heat treatment. They can be cold worked and softened by annealing. Plan to match filler material to the base material. 

There are five grades of ferritic stainless steel. There are three families of standard grade ferritic steel—409/410L, 430, and 430Ti/439/441—as well as two families of specialty grade steels—434/436/444 and 446/445/447. 

Applications by Steel Grade

Group 1 (Type 409/410L)

  • Automotive exhaust systems
  • Automotive exhaust tubing
  • Catalytic converter casings
  • Containers
  • Buses
  • LCD monitor frames

Group 2 (Type 430)

  • Replacement for austenitic grade 304
  • Interior appliances
  • Kitchen sinks
  • Cutlery and other kitchen utensils
  • Indoor panels

Group 3 (Type 430Ti/439/441)

  • Replacement for austenitic grade 304
  • Sinks
  • Exhaust tubes
  • Exhaust systems
  • Washing machines

Group 4 (Type 434/436/444)

  • Hot water tanks
  • Solar water heaters
  • Exhaust system parts
  • Electric kettles
  • Microwave oven elements
  • Corrosive outdoor environments

Group 5 (Type 445/446/447)

  • Highly corrosive coastal and offshore environments

Duplex

Duplex or austenitic-ferritic stainless steel is made of approximately an equal mix of austenitic and ferritic steels, providing some of the properties of each. Duplex steel has good mechanical properties, making it easy to work and weld, as well as strong corrosion resistance. When it comes to stress corrosion cracking, duplex is one of the best materials available. 

Because duplex is made from a mix of austenitic and ferritic metals, its grain structure has a mix of face-centered and body-centered cubic structures. 

Duplex steels are strong and hard. Duplex stainless steels have roughly twice the yield strength of their austenitic grade counterparts. This means that significantly thinner gauge material can be used in construction. Less weight of material can provide the same or greater strength and support. 

Applications by Steel Grade

Standard Duplex ( PREN Range 28-38)

  • Chemical processing, transport and storage – pressure vessels, tanks, piping, and heat exchangers
  • Oil and gas exploration and processing equipment – piping, tubing, and heat exchangers
  • Marine and other high chloride environments
  • Effluent scrubbing systems
  • Pulp and paper industry – digesters, bleaching equipment, and stock-handling systems
  • Cargo tanks for ships and trucks
  • Food processing equipment
  • Biofuels plants

Super-duplex (PREN Range 38-45)

  • Oil and gas storage and transportation
  • Chemical storage
  • Deepwater offshore oil production

Lean Duplex grades (PREN Range 22-27)

  • Building and construction
  • Bridges
  • Pressure vessels
  • Tie bars

Martensitic

Martensitic steel is used for it’s high durability and resistance to wear. The metal resistant to corrosion (although less so than other stainless steel grades) and can be heat treated post-weld to variable hardness levels, giving it a great degree of flexibility and a wide range of applications.

The basic grade of martensitic steel, 410, was created by Harry Brearly in 1913. This was the first stainless steel or “rustless steel” ever produced. Martensitic stainless steel holds an important place in the history of stainless steels.  

Having little to no nickel, martensitic steel contains a large amount of chromium and can be high or low in carbon. Martensitic stainless steel can be hardened through heat treatment after welding. Quenching and stress relieving or quenching and tempering are good ways to accomplish this.

Preparation/Basics

For you to be successful in stainless steel welding, it’s important that you start off by appropriately preparing your welds and your workspace. Getting sloppy on the preparation side of things can lead to welds that aren’t fully bonded, increased chance of cracking or breakage, rusting of the metal, or reduction of desirable properties in the metal. 

Clean Your Workspace and Base Metal

It’s absolutely crucial that your workspace, base metal, and tools are free of debris or metal dust and shavings leftover from other projects. Carbon steel dust, even suspended in the air, can cause stainless steel to rust and corrode. It’s advisable to perform carbon steel welding and stainless-steel welding in separate areas entirely. 

Scrub the surface of your base metal with a wire brush to ensure a clean surface for the weld to adhere to. Applying a layer of acetone can then chemically clean away any remaining debris. Once you’ve got the base metal clean, begin welding as soon as possible to avoid any buildup on the surface from the air. The base metal can also be power brushed, degreased, pickled, or grinded to fully prepare the surface for welding.

To clean your base metal, follow these steps:

  1. Remove moisture by heating or blowing with dry air. Moisture can collect on metal overnight in high humidity conditions and can cause rusting or deformities in the weld. 
  2. Eliminate organic and chemical contaminants such as paints, anti-spatter compounds, grease pencil marks, cutting compounds, adhesives, and soap. 
  3. Remove any contaminants leftover after beveling and machining.
  4. Avoid zinc contamination from any tools that have been used on galvanized steel. These will cause cracking.
  5. Avoid using copper hold-down fixtures as these will cause copper contamination

Use the Right Tools

Because stainless steel can be so sensitive to even the smallest amount of carbon steel. It’s important to have a separate set of tools for each material. If you’ve used a brush or hammer on carbon steel, you cannot use it to weld stainless steel. Cross-contaminating your metal through use of the same tools will result in rusted welds.

Safety

When welding, you’ll be handling metal at extremely high temperatures. The importance of taking proper safety precautions cannot be overstated. Wear protective clothing on all parts of your body. Use a welding mask that will allow you to see what you’re doing while sparing your eyes from the blinding brightness of the welding arc. 

Some welding processes will generate dangerous fumes. Be sure to work in a well-ventilated area and use a fume hood when necessary. Taking the time to ensure that you are properly prepared for any potential safety concerns will ensure that you stay safe and unharmed while welding. 

Joint Design

Before you begin welding, you need to determine what type of weld you’ll be performing. Choosing the right joint design will ensure a strong and enduring weld. When mapping out your joint design, you’ll want to consider joint accessibility, metal thickness, welding position, and final strength required. There are five basic weld types that can be used in infinite combinations.

Tee Welding Joint

A tee weld is formed when the narrow edge of one component is placed flat against the broad edge of another, forming two 90-degree angles. This type of weld is used when a pipe or tube is welded against a base plate.  

Lap Welding Joint

A lap weld is used when two components are placed flat against each other. This joint is used most often when welding together pieces of two different thicknesses. A lap weld can be made on one or both sides. 

Edge Welding Joint

An edge weld is used when two components are placed side by side and welded on the same edge. This weld is most common in joints where a piece of sheet metal is flanging away from another sheet. Sometimes when the components are heavier, filler metal will be added to melt or fuse the edge completely, creating a heavily reinforced plate. 

Corner Welding Joint

Corner welds are formed when two pieces are placed against each other at the corner to form an L. This is one of the most common joints in welding and is used to create outer edges, boxes, box frames, and similar. 

Butt Welding Joint

Butt welds, also known as square groove welds, are used to attach two components at their narrowest ends. This is most commonly used for welding sections of pipe together, but can also be used for flanges, valves, fittings, etc. 

Stainless Steel Welding Processes

There are many different processes for welding stainless steel. Each process has its own strengths and weaknesses. Understanding what type of welding is appropriate for what type of project and what the general process of each is will help you better understand how to approach your project. We’ll be exploring some of the most common processes for welding stainless steel. 

MIG or GMAW

Metal inert gas (MIG) or gas metal arc welding (GMAW) is very popular for thin-gauge metal plate welding. The process is semi-automated, resulting in clean welds and little post-weld cleanup. With MIG welding, Heat is produced by an arc between the base metal and continuously fed filler metal. 

There are several types of MIG welding, the most common being short circuit transfer and spray transfer. With short circuit transfer, each drop of metal interrupts the arc, and then it restarts, creating rabid bursts of arcing. This makes the welds very even and easy to control and is used for thinner gauges requiring a shallow weld. 

In spray transfer, metal is carried across the arc, and fine droplets of metal are sprayed across the base metal, eventually forming the weld. 

When MIG welding, follow these steps:

  1. Setup a Fume Extractor: MIG welding can produce dangerous fumes. Setting up a hood can ensure that you have a safe, clean space to work. 
  2. Attach a Ground Clamp: Attach the ground to any unpainted metal surface. This is a required step, skipping it may cause you to risk electrocution. 
  3. Turn the Gas On: An argon rich gas will prevent oxidation of the weld. Open the valves to allow the shielding argon gas to flow. 
  4. Determine Welding Settings: Wire size, gas composition, and material thickness will determine how to set your voltage and wire speed. There will likely be a chart provided with the welding unit. 
  5. Check the Amount of Wire on the Welding Torch: You want about ¼” of wire exposed. If there’s more, clip it shorter.
  6. Put on Safety Gear: Put on welding gloves, a welding helmet, closed-toed shoes, and a welding coat to protect your eyes, face, and body. Safety first. 
  7. Weld: Turn on the machine, check the settings, and get welding. 

GTAW or TIG

Gas tungsten arc welding (GTAW), also known as tungsten inert gas (TIG) welding is one of the most popular forms of stainless steel welding. This is due to its versatility and gorgeous appearance of the finished weld. For welds that will be seen and need to look great, GTAW is an excellent option. 

GTAW welding uses a non-combustible tungsten electrode to deliver current to the welding arc. Filler is used for buildup and reinforcement. Filler wire is not required for welding with this method. The TIG machine produces an electric torch as the welder feeds filler rod into the molten puddle. The torch is then applied to the weld. 

The big advantage of GTAW welding is that you can weld at low heat and control the amount of electricity going into the arc. Some welders will even attach a foot pedal to have even greater control. Having direct control over the heat can allow a welder a great degree of precision and flexibility in welding. 

Here’s how to GTAW weld:

  1. Grind the Electrode: You’ll be able to weld more precisely if your tungsten rod is ground to a fine point. As you weld, the rod will become rounded. This will cause the arc to become less focused and directed and dance around a bit on the weld. Avoid this by grinding it down before each weld.
  2. Insert the Correct Electrode into the Collet: Ensure that you’re using the correct electrode for the alloy you’re welding with. Your TIG will generally come with the proper electrode, but it’s good to double-check. Then insert the electrode about ¼” away from the protective sheath.
  3. Choose Your Settings: The welder will have a number of different settings. Including amperage, penetrating, and electricity options. Make sure that these are set appropriately for your materials and project. 
  4. Turn the Gas On: You’ll want to protect the weld from oxidation while it’s at high heat. For stainless steel, use pure argon or argon mixed with carbon dioxide.
  5. Put on Safety Gear: Put on welding gloves, a welding helmet, closed-toed shoes, and a welding coat to protect your eyes, face, and body. Safety first. 
  6. Weld: Hold the electrode about an inch away from the metal without ever touching. Start on the edge and move steadily to avoid warping.  

Stick Weld or SMAW

Stick Welding or shielded metal arc welding (SMAW) is the oldest arc welding process. This process is fully manual, allowing a wide range of flexibility in allowing for a wide range of materials to be welded. Stick welding generates an arc between a covered metal electrode and the base metal. The electrode covering provides shielding. 

Stick welding is one of the most popular forms of welding because the equipment is the most inexpensive, making it the most accessible technique. Electrodes may result in some imperfections such as slag coating and stub loss, which will need to be removed. However, in spite of this, there isn’t a great deal of post-processing required. 

Here’s how to stick weld:

  1. Attach a Ground Clamp: Attach the ground to any unpainted metal surface. A poor ground will make it difficult to complete the circuit and create an arc. 
  2. Select the Correct Rod for Your Project: You want to make sure that the rod and amperage range are appropriate for what you’re trying to accomplish. The material your welding and thickness of that material will affect what type of rod to use. Place the electrode in the stinger. Make sure that the conductive ends are touching. 
  3. Turn on the Welding Machine: You should immediately hear a humming noise.
  4. Put on Safety Gear: Put on welding gloves, a welding helmet, closed-toed shoes, and a welding coat to protect your eyes, face, and body. Safety first. 
  5. Weld: Hold the stinger in your dominant hand a few inches from the weld. Tap the tip against metal and then immediately pull back to create the electric arc. Then move along the path you want to weld. Try to move your hand at a consistent speed. 
  6. Clean the Weld: Use a metal brush to remove slag and finish the weld.

FCAW

Flux-cored arc welding (FCAW) is similar to MIG welding, but instead of a solid wire consumable, a metal powder is used as filler material. This type of welding provides shielding, deoxidization, and arc stabilization. The metal powder is contained within a hollow wire allowing it to be fed into the welding unit. 

The shielding provided from the flux core allows for welding outdoors, in windy conditions, which can be difficult when relying on shielding from applied gas. FCAW is the easiest and fastest of the manual welding processes.

When welding with FCAW, the electrode creates a short circuit with the metal and heats up until the electrode and the metal begin to melt. This metal will then melt the flux core, creating a shield from the air. The welder can then control this process to selectively weld the material. 

Here’s how to do it:

  1. Setup a Hood Ventilator: If you aren’t welding outside. A ventilation hood will ensure that you don’t end up building up a bunch of dangerous fumes in your workspace. 
  2. Turn on the Welder and Choose Settings: Flip the switch and make sure you’ve got everything set correctly. Consider metal gauge and material. You’ll want to increase voltage and wire speeds as the thickness of the metal increases. 
  3. Put on Safety Gear: Put on welding gloves, a welding helmet, closed-toed shoes, and a welding coat to protect your eyes, face, and body. Safety first.
  4. Tack Weld All the Corners: Fuse the metal together at each corner to hold the entire piece together. 
  5. Clean the Tack Welds: Remove any slag generated from the tack welds with a wire brush.
  6. Fill in between the Tack Welds with Bead Welds: Fill in the spaces in between the tack welds with more precise bead welds. Pay attention to your speed, angle, and stickout distance. Try to be consistent all the way across. 
  7. Fully Clean the Piece: Once you’ve finished welding everything together, there’ll be a bunch of spatter and slag left over from the flux. Use the chipping hammer and wire brush to fully clean off the weld.

Wrap-up

There are a great many things to consider when welding stainless steel. There are many different kinds of metal and many different processes to consider. Hopefully, now you’re more prepared to tackle whatever your next welding project may be.

Alexander Berk

A bit about myself: I am a certified international welding engineer (IWE) who worked in different welding projects for TIG, MIG, MAG, and Resistance Spot welding. Most recently as a Process Engineer for Laser and TIG welding processes. To address some of the questions I frequently got asked or was wondering myself during my job, I started this blog. It has become a bit of a pet project, as I want to learn more about the details about welding. I sincerely hope it will help you to improve your welding results as much as it did improve mine.

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