How to weld stainless steel | Complete step by step guide

As you know, the way to join stainless steel parts , either for repair work or even for craft projects, is welding . But what type of welding is best for stainless steel? Before continuing with the article, it is recommended that you take a look at our article Types of welding: TIG vs MIG vs Electrode vs Arc , where we explain the different welding methods, and the advantages and disadvantages of each of them.

So, in this article we explain the different ways of welding stainless steel , and the most appropriate methods to do so. From these options, each one must choose the most appropriate process according to the application that will be given. Let’s go there!

0. Before you start

In this complete guide we will go step by step . And there are some things you should know before you start welding, and that are necessary to be able to choose the best welding method to meet your needs.

0.1. Identify the type of stainless steel you want to weld

Stainless steel is composed of Iron (Fe), Carbon (C) and Chrome (Cr) . The fundamental element is iron, but it is chromium that makes steel stainless. For this, the minimum proportion of chromium must be 11.5%.

Stainless steels are divided into three main groups (there are others that are not used as much) , and each type is identified by the three digits that are usually printed on the steel:

  • Martensitic stainless steel : It is the steel whose chromium ratio is between 11.5% and 18%. It is used for wear resistant projects. It is magnetic and produces long white sparks with few forks. Some examples are AISI 410, 416, 420, 431, 501 and 502 steels.
  • Ferritic steel : It is the steel that contains between 17-18% and 27% chromium. It is very common, and its high carbon content makes it magnetic. When it is milled, it produces white or red sparks with few forks. Examples of ferritic steel are AISI 405, 409, 432, 439, 442 and 446.
  • Austenitic steel : The total nickel and chromium content is at least 23%. They are essentially non-magnetic in the annealing condition and do not harden by heat treatment. It is a fairly common type of steel, and they usually start with the digit 3.

0.2. Choose the right filler metal for your type of steel

Depending on the type of stainless steel you have to weld, you have to choose a filler metal accordingly . If the metals that you must join are different, you have to choose it based on the one that has less chance of cracking and which one is the most compatible with the base metal.

In the following tables we help you choose the filling material for your stainless steel:

Contribution metal for martensitic stainless steels

AISI steel Recommended input metal Alternative input metal
403 410 308, 347, 309
410, 410S 410 308, 347, 309
414 410 410 NM, 309
420 420 309
431 410 309, 310
440A 312 309

Contribution metal for ferritic stainless steels

AISI steel Recommended input metal Alternative input metal
405 410 308L, 309, 410NM
409 409CB 430, 309LSi
430 430 308L, 309L
442 308L 309L
446 308L 309L

Contribution metal for austenitic stainless steels

AISI steel Recommended input metal Alternative input metal
201, 202, 205 240 308, 347, 309
301, 302, 302B 308 347, 309
304, 304L 308L 347, 309
304H 308H 347, 309
303, 303SE 312 309MO
316, 309S 309 309CB, 310
310, 310S, 314 310 310CB, 310MO
316, 316L 316, 316L 309MO, 317
316H 316H 309MO, 317
317 317 317L, 309MO, 318
321 347 309CB, 310CB, 321
347, 348, 347H 347 309CB, 310CB
320 320LR 320
330 330
904L 385

If you are not sure of the type of stainless steel you have, the 309 works well in most situations .

0.3. Choose the type of joint you need to weld

Depending on how you need to join the pieces together, you will need to make one type of joint or another . Each joint can be welded in different ways, depending on the thickness and shape of the joint.  The most common junctions are the T-joint, the overlap joint, the edge joint, the corner joint and the top joint .

0.4. Secure the parts you are going to weld

Place the pieces you are going to weld on a work surface where you can work with stainless steel . Put the two pieces as you want to join them by means of different accessories that usually bring the welding tables.

If you have a normal table, you can secure them with sarjentas or cheaters as firmly as possible so that they do not move while welding.

0.5 Clean the base stainless steel

Use a specific wire brush for stainless steel to clean the metal. Rub the brush to remove all impurities , and review with a wet rag of acetone to finish cleaning all debris. This makes welding better.

If necessary, sandpaper and grinders can also be used to clean the steel and remove all impurities.

0.6. Type of welding for stainless steel

The most suitable processes for welding stainless steel are MIG and TIG . Although arc welding can also be used to weld stainless steel, it is not the most appropriate method, so we recommend that you opt for TIG or MIG welding.

Among the MIG and TIG processes, TIG welding is more appropriate for small parts and delicate but strong welds. Instead, MIG welding is used to weld large parts . If you need more information about these two types of welding, in our article where we compare the different types of welding you can find it.

0.7. Gas for welding stainless steel with MIG or TIG

The gas we need for our project depends on the type of welding we are going to use (MIG or TIG), and depending on that, the type of stainless steel we have or the filler material we use.

In the following table we show you with which gas the stainless steel is welded in each case:

Filling material / steel type Basic and rutile tubular thread Solid thread and metallic filler
Martensitic 68% Argon, 20% Helium, 12% Dioxide c. 63% Argon, 35% Helium, 2% Dioxide c. 70% Argon, 30% Helium
Ferritic 68% Argon, 20% Helium, 12% Dioxide c. 63% Argon, 35% Helium, 2% Dioxide c. 70% Argon, 30% Helium
Austensitic 68% Argon, 20% Helium, 12% Dioxide c. 63% Argon, 35% Helium, 2% Dioxide c. 98% Argon, 2% Helium

Although these are the ideal gases, other mixtures can also be used. A gas with the mixture 90% Helium, 7.5% Argon and 2.5% Carbon Dioxide can be used for MIG welding of stainless steel, and a gas mixture of 98% Argon and 2% Carbon Dioxide for TIG stainless steel welding.

0.8. One last step before starting welding: Protection

During welding, sparks can always jump and that is why it is important to use as much protection as possible. The use of gloves and darkening helmets is of vital importance, and should be the minimum protection to be used for any welding work.

Welding apron, respiratory mask and safety shoes are also recommended. But, if you don’t have them, you should at least wear a long-sleeved shirt and long pants to avoid exposing the skin to any dangerous situation.

1. TIG welding for stainless steel or How to weld stainless steel with TIG

As we have mentioned before, TIG welding will be used to weld stainless steel of little thickness , approximately up to 6 mm. From then on, TIG welding will not be economical.

In TIG welding ( Tungsten Inert Gas) , also known as GTAW (Gas Tungsten Arc Welding), the electric arc is established between the base metal and a non-consumable Tungsten electrode . All this is done in a protective atmosphere that is created by the inert gas chosen for the project. This gas is used to protect the metal we are melting for air welding.

The trouble is that TIG welding equipment is a little more complicated to use than MIG welders , and the welding process is also slower. But, on the contrary, it can create stronger and more durable joints than MIG welds when done correctly.

And it is that the cords that are created with TIG welding are of a very high quality , and there is no slag presence when using non-consumable electrodes. Because of this, in addition to thin materials, TIG welding is also used when an excellent quality finish is needed. In this article you can find all the necessary information about TIG welders .
So, here we show you how to weld stainless steel with TIG :

1.1. First steps

Insert the sharp tungsten rod into the torch , and then start the gas. Then, open the electrode by turning the torch, and put the tungsten rod of the appropriate diameter in the center of the cylinder. Adjust the rod , letting it protrude a little.

1.2. Turn on and configure the soldering iron

Turn on the soldering iron, setting it to DC (Continuous Current) mode . You need to put it in this configuration to weld the stainless steel properly.

In other inverter welders, which have possibilities to use different functions and types of welding, it is sufficient to put it in TIG mode, or TIG LIFT.

1.3. Get ready to start welding

Light the TIG torch and put it next to the joint you wish to weld . Hold the torch about 2 or 3 centimeters from the junction of the pieces, and at an angle of 75 degrees. Hold the torch at this distance and in this position while welding.

1.4. TIG welding process   in stainless steel

To activate the torch, they usually have a pedal, which light the torch when pressed . You have to keep the torch still in one place until you see the metal melt, and when this happens you have to move it to weld the entire joint.

You have to make sure that the metal does not splash , and if it does, you should raise the welder’s amperage. It is a sign that the torch does not have enough strength. On the contrary, if you have too much energy or strength, you will melt too much metal.

1.5. Fill the gasket while moving the rod

Hold the rod with one hand and the torch with the other . Pass the filler rod in the molten metal to fill the joint and create the cord along the entire joint.

1.6. Let it cool

Before moving the new part you just welded, let it dry . The union has to solidify completely before moving it. In addition, the torch must also be cooled before storing it, since if it is still hot it can cause a fire.

1.7. Video

If you want to see on video how the welding of stainless steel with TIG is done correctly, we leave you a video so you can do it:

2. MIG welding for stainless steel or How to weld stainless steel with MIG

MIG welding, also known as gas metal arc welding (GMAW), is used when we have to weld thick pieces . This welding is faster than TIG welding, and easier to do , so you don’t have to be an experienced welder to get a good weld. The bad thing is that the union that is created is not so durable, it is more fragile. So for those who ask if you can weld stainless steel with MIG , the answer is YES.

This MIG welding process, and the MAG (Metal Active Gas) process, are used to protect the welding with inert gas , since an electric arc is established between a consumable electrode and the stainless steel part that we are going to weld. In addition, the MIG torch has the filling material inside, so it can be welded with one hand . To achieve better arc action, active gases such as carbon dioxide, oxygen or hydrogen are usually used, but this will depend on the gas mixture you have chosen.

If you are going to weld stainless steel using MIG welding, in this article you have all the information you need about MIG welding machines .

Without lengthening more, let’s do it, here we show you how to weld stainless steel with MIG :

2.1. First steps

The first thing to do is to pass the filler wire through the reel of the MIG machine , and take it out through the tip of the torch. This wire has to be a little protruding from the torch, about half a centimeter. Once you have put the wire in the correct position, you only have to activate the gas to weld stainless steel with MIG to start welding.

2.2. Hold the torch at 30 ° above the weld joint

You have to hold the torch at a 30º angle to the pieces that you must join. You have to have the torch in a position that allows you to reach the edge of the two pieces, so that the flame heats the pieces. In this way a weld bead is formed in the joint with the liquid metal that was created when melted .

To do it correctly, the metal cannot splash, and if it does, it is a sign that you need to use more power. And on the contrary, if the metal melts too quickly, you must lower the power, in order to achieve a smooth liquid cord so that you can easily control it .

2.3. Move the torch over the edge to join the entire joint

You have to move the torch little by little keeping the angle of 30º along the entire edge of the pieces to fill the joint. Do it at a constant speed, so that the welding is uniform throughout the joint. This way you will create a weld bead throughout the entire joint.

Before moving the torch forward, you have to make sure that the gasket has been filled smoothly and evenly. And if you move very fast, the steel will not melt enough, and the union will be very weak. And otherwise, you will melt too much metal, which is also not convenient.

2.4. Let the solder cool

When you have finished passing the torch all over the edge, the welding will be finished . At this time, do not forget to turn off the gas.Once you finish, you must let both the welding and the torch cool down .

Normally with MIG welding this usually happens very fast, so you don’t have to wait long.

2.5 Video

Finally, I leave you with a video where you can see how the welding of stainless steel is performed:

I hope you found the article useful! You can write us with any questions!

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