MIG welding is a versatile welding process that is often considered the best welding method to weld stainless steel.
However, for beginners, MIG welding stainless steel can be a bit challenging. You will need to understand the fundamentals and the technicalities before you are able to create perfect welds.
Hence, to help you out, I will be sharing in-depth details about the MIG welding process of stainless steel.
In this article, I will be discussing everything from essential tools to effective methods that are best suited for this metal.
So, without any further ado, let’s get right to it.
Preparing the MIG Welder for Stainless Steel
To get started, you will need the following tools and equipment:
1. MIG Welder
That seems to be the most obvious piece of equipment. You can choose a good quality MIG welder that is suitable for your needs and budget and comes with appropriate compatibility for stainless steel settings.
2. Welding Wire
There are various types of welding wires available for stainless steel. The choice will depend on what alloy of stainless steel you are welding. Typically, ER308, ER309, and ER316 are used.
3. Shielding Gas
The choice of shielding gas will depend on the specific welding application. You can use pure argon or a blend of argon with helium and CO2 depending on the need. Stainless steel may require the use of trimix blends to get desired results.
4. Welding Gun
If your MIG welder didn’t arrive with the welding gun, then you will have to purchase one separately that is compatible with your MIG welder and well-suited for the task. Make sure the gun has a compatible nozzle and contact tip.
5. Workbench or Ground Clamp
Getting a workbench is very advantageous as it allows you to be more productive and efficient while working. If the piece being welded is too large, then you better get a ground clamp for attaching the workpiece to the ground cable.
6. Other Equipment
Besides this basic welding equipment, you will also need some other gear before you start the welding process.
A dedicated cleaning brush, grinder, and buffer for pre-welding and post-welding cleaning operations must be kept with the rest of the tools to enhance your welding aesthetics as well as the efficiency of the welds.
Adding to this, safety should never be compromised. You must always wear proper safety gear that includes a welding helmet with an auto-darkening lens, welding gloves, protective clothing made of fire-resistant material, and leather shoes.
You can also get other accessories that have the ability to enhance the MIG welding process.
Choosing the Right Type of Stainless Steel
Understanding different types of stainless steel is important as it will allow you to select the best welding wire for your base metal.
Each type of stainless steel is used in specific applications and has different welding parameters for an efficient weld bead.
Here are some of the common types of stainless steel you can find:
This is one of the most widely used types of stainless steel that is known for its excellent corrosion resistance and weldability. You might be familiar with its alloys which include 304, 308, 316, and 321.
Austenitic steel is the most versatile variant with excellent weldability. It is used in various industries.
This type is less corrosion-resistant but more economical. They are easily available and widely used because of their cost-effective nature. Examples include ER430, ER444 and ER447.
Ferritic steel is magnetic and has lower nickel content. So, they are a bit difficult to weld.
This is a less common type of stainless steel that is known for its high strength and hardness. However, this type also comes with reduced corrosion resistance. Examples include ER410, ER420 and ER440.
Martensitic steel has high tensile strength, but they don’t have very vast applications.
This is a blend of two types of stainless steel. The duplex is formed by the mixing of austenitic and ferritic stainless steel.
The resultant blend has excellent corrosion resistance and exceptional strength. Hence, it is widely used in the pipeline industry.
The choice as to which type of stainless steel you will be using will depend wholly on the specific application.
Setting Up Your MIG Welder for Stainless Steel
Once you have gathered all the equipment and tools, next you need to set up the MIG welder for stainless steel.
Here are the important setups that you need to go through to properly set it up.
Welding Wire Selection
The right welding wire is essential for getting strong and reliable welds with stainless steel. Choosing the wrong wire can affect the corrosion-resistant ability of the base metal and also get you weaker welds.
The most common types of stainless-steel welding wires include ER 308, ER309, and ER316.
However, you must keep in mind that the choice of welding wire depends on the composition of the base metal.
Also, you must choose the right wire diameter depending on the thickness of the base metal and the specific welding requirements of the project. The diameter typically ranges from 0.023 to 0.045 inches.
If you cannot find the exact match for filler material or if it is not available, then you can use higher stainless alloy wire.
For example, you can use ER308 to MIG weld 301, 302, 304, and 305.
Once you have selected the right wire, you have to install it in the welder’s spool holder.
Selecting the Shielding Gas
Shielding gas plays a crucial role in MIG welding, especially when it comes to the welding of stainless steel.
The gas is mainly responsible for protecting the weld pool from atmospheric contamination and ensuring cleaner and stronger welds.
When welding stainless steel, you can use a blend of argon with CO2 or Helium, depending on the specific applications. Most commonly, professionals use trimix blends to get the desired results.
However, you must keep in mind that a higher concentration of CO2 can lead to loss of corrosion resistance.
So, you won’t be able to use the usual blend of argon and carbon dioxide which was 75% and 25%.
You will have to keep the concentration of CO2 extremely low. That is why most commonly, trimix blends are used for welding stainless steel.
A blend of 90% helium, 7.5% argon, and 2.5% carbon dioxide is commonly used.
You can also opt for an argon-oxygen mixture that will remove the carbon problem and improve the arc stability during the welding process.
However, you still cannot use a higher concentration of oxygen and will have to keep it as low as just 1-2% because a higher concentration can lead to oxidation.
After selecting the right gas, you should connect the shielding gas cylinder to the welder and set the gas flow rate (typically between 15-25 CFH).
Adjusting the Welding Parameters
Last but not least, you will have to adjust the specific welding parameters depending on the thickness of the metal, the diameter of the welding wire, and the specific requirements of the task.
Adjust the wire feed speed and amperage using either the chart or an online setting calculator. As you become more experienced, you will be able to adjust these settings more naturally.
Once you have gotten an approximate idea, then you can fine-tune your way to the perfect settings using a trial-and-error approach.
Generally, the rule is one amp of power for every 0.001-inch thickness of stainless steel, but this rule is not absolute and can vary from different thickness ranges.
Pre-Cleaning the Base Metal
You must clean the base metal before you start the welding process. The pre-cleaning will help you remove every kind of dirt, debris, and oil from the surface of the metal.
The process also removes the oxide layer from the surface which will ensure that the welding process goes smoothly.
You can use a wire brush, a dedicated one for stainless steel, to clean the base metal. You can also use chemicals like acetone to clean the base metal properly.
Not cleaning the base metal can lead to several issues including weaker weld quality, contamination, and loss of corrosion resistance.
Effective Techniques for MIG Welding Stainless Steel
Now that you are fully ready, let’s get on with the welding process.
Welding stainless steel is pretty much similar to other welding applications of MIG welders. You will be laying beads. There are a few things that you should keep in check.
The Basics: Speed, Angle, and Flow Rate
Getting the right travel speed for the welding gun is going to take a bit of practice. There is just no way to get it right the first time when you are a beginner.
So, you will have to fine tune your way to it. If you move the welding gun too slowly, it can lead to overheating which can cause distortion and warping, that will ruin the base metal.
On the other hand, if you go too fast, then you won’t be able to achieve proper penetration which will lead to weaker welds.
As for angle, you will have to use the push technique for MIG welding stainless steel. As for techniques, professionals recommend going for the stringer movement instead of weaving.
While weaving is more effective for other metals, in the case of stainless steel it can increase the heat build-up which is not good for this metal and can lead to further problems.
You should select the optimum gas flow depending on the specific weld requirement. An important point to keep in mind is the post-flow coverage.
As I mentioned earlier, stainless steel has higher heat retention and low thermal conductivity. It means that the weld bead will remain hot longer when you are done.
So, you have to use post-flow gas coverage to prevent the heated metal from oxidizing.
You should not remove the gas flow immediately when you shut down the arc and leave the gas flow on for a few seconds to prevent contamination and let the metal cool down a bit.
Stainless steel has high thermal expansion and low thermal conductivity. It means it can easily warp and distort especially if you are welding a thin metal sheet.
You must manage the heat input properly to avoid running into any issues. Also, you can limit the base metal size to the smallest possible to ensure that the problem of warping and distorting stays at a minimum.
You can use clamps to hold the metal in place and use techniques like stitching and tack joints instead of going for a large single weld line.
Additionally, for effective heat management, you can use copper backing bars to remove the heat and dissipate it.
However, copper can contaminate the weld. So, ensure that the bars you are using are nickel plated to avoid this contamination.
Welding Stainless Steel Pipes
When you are welding stainless steel pipes, you have to adapt to a special technique known as purging.
Purging means that you protect the other side of the weld joint from contamination just like the side being welded is being protected.
So, you must purge the area on the other side of the weld from any sort of contaminants. This will help you achieve the highest quality welds with MIG welding.
You should keep in mind that stainless steel reacts with oxygen aggressively when heated. So, you must ensure that both sides of the base metal, especially the HAZ, are free from any oxygen excess.
This problem arises when you are welding a stainless steel pipe because the inner part of the pipe is more susceptible to corrosion which results in ruining of the pipe.
You can hire professional pipe purging devices to bridge both sides of the pipe and remove the excess oxygen.
If you want to try a DIY method, you can tape both sides of the pipe and then stick a nozzle inside to fill in the argon gas which will solve your problem.
Common Challenges While MIG Welding Stainless Steel: Problems and Solutions
You can face a lot of challenges when you are MIG welding stainless steel. Let’s discuss a few of them that you come across often:
Distortion can occur when the excessive heat from the welding process can cause the base metal to warp. If you are facing this issue and want to get rid of it, you will have to balance the heat input.
The imbalance can occur because of a number of reasons. The base metal might be unstable, which can be fixed by using clamps or fixtures that will hold it in place.
There might be a problem with your welding technique. To overcome that, you need to practice proper techniques like stitching or backstepping.
You can also lower the amperage and wire feed speed to reduce the overall heat input, but it might also slow down the welding process.
The chances of contamination are always quite high when it comes to MIG welding. The problem is very common with beginners, mostly because they are not able to properly adjust the gas flow rate.
Contamination in the weld bead can lead to weak or brittle welds. There are a number of things you can do to prevent this.
Cleaning the base metal properly with a wire brush can reduce the risk of contamination. This will ensure that the base metal is free from any dirt, grease, or oxides.
If you do not use a dedicated brush for cleaning the base metal, then the carbon content deposited in the brush from earlier cleaning can contaminate the weld and impact it negatively.
You will have to use an appropriate shielding gas that is best suited for stainless steel and the specific welding requirements of the project.
Adding to this, while working with a MIG welding gun, make sure that the contact tip doesn’t get too close to the weld pool, or it might get spatter build-up which will lead to contamination.
Additionally, you must also avoid welding in an environment where there are chances of mild steel dust in the air.
So, if someone else is cutting or grinding mild steel nearby, you have to ensure that you don’t work in that area. The dust particles can deposit on the metal surface and ruin your weld.
Moreover, you must also ensure that the MIG welding gun is a dedicated one for stainless steel. You cannot use the one you have previously used for other metals, because it too can lead to contamination.
Heat tint can form on the surface of stainless steel during the MIG welding process. It is a thin oxide layer that has the ability to affect the corrosion-resistant ability of the base metal.
While the light heat tint can be easily removed by adjusting the gas flow rate and using a wire brush to clean the oxide layer, you won’t be able to remove severe heat tint easily.
If you are experiencing a severe heat tint in your welds, then you will have to use chemical passivation or electropolishing treatments.
Chromium Carbide Formation (Overheating)
One of the most difficult challenges one has to face while MIG welding stainless steel is chromium carbide formation.
We all know that stainless steels are alloys of iron and chromium and the chromium oxide layer on the surface of the steel is the primary reason for its strong defense against corrosion.
This metal retains more heat than carbon steel and also has greater thermal expansion but on the other hand, it has low thermal conductivity.
It means when you are welding, heat will be concentrated on the Heat Affected Zone (HAZ) more and won’t dissipate to the rest of the metal as quickly as it did with mild steel.
So, the higher heat in the joint can lead to certain problems, one of which is chromium carbide formation. So, overheating leads to this issue which reduces the chromium in certain zones of the metal, which leads to loss of corrosion resistance.
Without corrosion resistance, stainless steel is wasted and is equivalent to just mild steel which is cheaper. So, heat input control is important to prevent this issue.
The issue can be easily identified by the coloring of the weld bead. If your weld has turned entirely black, it means that the carbide formation has occurred, and the base metal is ruined.
You must not let the metal get overheated for a longer period of time, or you can ruin the base metal.
Post-Welding Processes for MIG Welding Stainless Steel
Your job is not done just after laying the beads. You need to do some post-weld inspections and processes to ensure that your weld has optimum strength and quality. Think of it like a quality assurance process.
First of all, you must inspect the weld once it has cooled down to ensure that the weld is of good quality and consistency. Look for common defects that can happen if you are a beginner.
These common defects include porosity, cracks, and lack of fusion at certain places. If you find any of these defects, you will have to address them properly before moving on to the post-weld cleaning process.
Once you have completed your inspection, you must move to the post-weld cleaning. It is crucial not only for maintaining corrosion resistance but also for enhancing the appearance of the resultant weld.
The choice is yours. You can simply use a wire brush for the cleaning, or you can opt for a grinding wheel to buff your beads and give a nice finish to your welds.
You can also polish the weld using electrochemical processes to increase their aesthetic appeal.
Frequently Asked Questions
Can you MIG weld stainless steel with regular MIG wire?
No, you cannot MIG weld stainless steel with a regular MIG wire. You will have to use a stainless-steel specific wire for the welding process. The choice of wire will depend on the base metal being welded.
What do I need to weld stainless steel with a MIG welder?
To do this, you will need a MIG welder, stainless steel wire, shielding gas, appropriate safety gear, base metal, workbench or ground clamp, and other necessary equipment as per the specific requirements of the project.
What is the setting for MIG welding stainless steel?
The settings will depend on the specific requirements of the task. They can vary depending on the type of stainless steel being welded, the thickness of the material, and the diameter of the wire being used.
What is the correct shielding gas for MIG welding stainless steel?
Tri-mix gas blends are preferred when MIG welding stainless steel. The reason is that you can only use carbon dioxide in minimum concentration, so the standard Ar-C02 mixture is not suitable for the job.
What happens if you weld stainless steel with MIG?
When you weld stainless steel with a MIG welder, you have a tendency to produce a strong and corrosion-resistant weld. This welding method is ideal for welding stainless steel and has tons of applications.
What is the best MIG wire to weld stainless steel?
The best MIG wire for welding stainless steel is usually ER308, ER309, or ER316, depending on base metal compatibility. If you cannot find an exact match, you can use a higher number of wires for welding lower-grade base metal.
What is the easiest way to weld stainless steel?
MIG welding is a faster and more efficient method of welding stainless steel, also considered the easiest. It is easy to learn, which makes it ideal for beginners. It will take some practice, but it is much easier compared to other methods.
Why is welding stainless steel difficult?
Welding stainless steel is difficult primarily because of its heat sensitivity. The metal has higher thermal expansion and heat retention but low heat conductivity which makes it more susceptible to damage from overheating or high heat input.
MIG welding stainless steel might seem a bit challenging at first, but it is surely an adventurous and enjoyable experience.
With the right knowledge and tools at your disposal, you can create great welds both in terms of quality and appearance on stainless steel.
Following the proper process will help you get to perfection with time. As a beginner, you are bound to make mistakes. So, never be afraid of them, rather learn from them as much as you can.
Learning the proper techniques can help you out with common issues of welding stainless steel with a MIG welder. The techniques help compensate for shortcomings and challenges that one has to face when MIG welding stainless steel.
Remember to always prioritize safety, practice proper technique, and continually learn from wherever you get a chance. If you are stuck, you can always consult a professional.
Let us know about your experience of welding stainless steel in the comments section below.
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