Welders prefer stainless steel for their welding purposes mainly because they are highly resistant to rust and corrosion as it contains high levels of chromium. Most welders consider welding stainless steel as a great skill as it gives them the desired output although it is more complicated when compared to other processes.
Stainless steel was first introduced by Harry Brearley in 1913 as it was highly resistant to corrosion when compared to carbon steel. Over the years, metallurgists have experimented with a lot of alloying materials and have enhanced the performance of stainless steel to a great extent.
But when you look at the techniques between welding stainless steel and carbon steel, there is not much difference though except for the fact that while welding chromium, the welders have to be more cautious to control the welding process. It is also important to use proper filler materials to alloy steel before welding for the right output. In this article, you will learn about the types of stainless steel, how to weld stainless steel and other important information when it comes to MIG welding stainless steel.
Types of Stainless Steel
Contents
Stainless steel can be broadly classified into five categories namely:
- Austenitic Stainless Steel
- Ferritic
- artensitic stainless steel
- Duplex
- Precipitation Hardening
Austenitic:
Austenitic stainless steel is the ones with the highest levels of corrosion resistance as it comes with a composition of 18% chromium and 8% nickel. These are the most commonly used stainless steel covering 70% of the whole production. They can’t be hardened through normal heat treatment methods but can be work-hardened. The widely used stainless steel is the Type 304 stainless steel as they are also referred to as surgical stainless steel as it contains a maximum of 20% of chromium and 10% of nickel.
Ferritic:
Ferritic stainless steel is the cheapest form of steel and hence it is favored for manufacturing automotive exhaust components. Along with 17% of chromium, they also contain iron in it. When compared to Austenitic steel, the ferritic steel is more ductile but similar to Austenitic, they also cannot be easily hardened by normal heat treatment methods.
Martensitic:
Martensitic stainless steel is another type of stainless steel that is mostly used in high-wear applications. It can also be transformed into Austenitic steel when it is quenched and cooled below 450 degrees Fahrenheit. But the steel is brittle when compared to other types and hence most of the time they are hardened before use.
Duplex Steel:
This type of steel is made using a combination of both Ferritic and Austenitic microstructures making it much stronger than the other two. And since the steel is very strong, it is also very difficult to work with.
Precipitation Hardening Steel:
Another type of stainless that is formulated to steel so that it can be supplied easily in a condition that that is easily workable as they come solution-treated and can be hardened quickly. This stainless steel possesses good weldability features and provides moderate resistance to corrosion.
Preparing to Weld
It is highly important to clean the metal before any type of welding and cleaning helps get rid of all the dust and other particles before welding stainless steel. And one thing to remember is that you should refrain from using the same brush that is used for cleaning carbon steel because the residue carbon left in the brush can get embedded over the stainless steel and starts rusting it in no time.
Also when you are grinding or cutting carbon steel, make sure that any stainless steel is not kept close to the grinding process as carbon steel dust will get suspended in the air during the grinding process. If there is any stainless steel nearby, then carbon steel dust can settle over the stainless steel and lead to rusting. It is better to have a separate workplace for both stainless metal and carbon steel.
Another important aspect that needs to be watched before preparing to weld stainless steel is to check whether you are having the proper filler material. Better go with the same number of filler material as the base metal. So if you are using a base metal of 316L, then use 316L filler metal for getting the desired outputs.
Other major factors that you need to consider before starting the welding process are:
- Get to know the type of metal to be welded.
- The thickness of the metal
- Whether the workpiece is cleaned
- What type of metal-transfer mode is available?
- Whether the MIG welding machine is correctly setup etc.
Procedures for Using MIG To Weld Stainless Steel
When it comes to MIG welding stainless steel, the procedure uses constant voltage power outputs so that it energizes the electrode to produce the electric arc. In this kind of constant voltage power output, the voltage always remains at a constant level whereas resultant heat and the current fluctuates. Keep in mind that arc length changes have a direct impact on the current and resultant heat and hence a shorter arc is better to produce higher current. High heat is needed because stainless steel has a low thermal conductivity, so for stronger weld and deeper penetration, you need more heat.
In MIG welding machines, DC current is used along with electrode positive power supply (DCEP) or else AC current is used in conjunction with negatively charged electrodes. Even though MIG welding stainless steel doesn’t require a lot of professional years to master it, still you need to have an understanding of the common welding skills and the settings that are used for MIG welding. When it comes to MIG welding settings these 3 important settings play a huge role in providing a better output which includes voltage setting, wire feed,
MIG Settings for Stainless Steel Welding
Most of the MIG welding machines often come with a table that is affixed to the machine that explains the amount of power supply, type of wires, shielding gases to be used, electrode size and the wire feed rates, etc. Hence, MIG welding stainless steel is largely a simple task for professional welders as they don’t need to go for a trial and error by testing test bits to calculate the machine settings. All they need to do is get the thickness of the metal and the size of the electrode wire and based on that look at the average value in the table and set the machine accordingly.
The values may slightly differ from one manufacturer to the other. Sometimes, the machine comes with detailed user manuals that provide you with all the details including the gas flow rates as well. If you do not have a manual, you can use this table as a quick guide for your settings.
| Thickness | Wire speed (ipm) | Wire Size | Gas | Amps |
| 18 ga | 120-150 | .035 | Helium+Argon+Co2 | 50-60 |
| 16 ga | 180-205 | .035 | Helium+Argon+Co2 | 70-80 |
| 14 ga | 230-275 | .035 | Helium+Argon+Co2 | 90-110 |
| 12 ga | 300-325 | .035 | Helium+Argon+Co2 | 120-130 |
| 3/16 | 350-375 | .035 | Helium+Argon+Co2 | 140-150 |
| ¼ | 400-425 | .035 | Helium+Argon+Co2 | 160-170 |
Even though most of the welding machine manufacturers have included a table of materials and voltage settings in the machine, it is highly important for you to pick the right kind of gas and electrode wire to be used for MIG welding stainless steel. Alternative gases that you can use are 98% Argon and 2% Co2 or 98% argon and 2% oxygen mix.
Mode of Metal Transfer
When it comes to MIG welding thin stainless steel, it is important how the metal is transferred to the workpiece. Generally, the metal transfer is done in three modes namely,
- Spray Transfer
- Short-Circuit Transfer
- Globular Metal Transfer
Spray Transfer
One of the most popular metal transfers is the spray transfer method, where the electrode metal is transferred through a voltage electric arc. The resultant weld is high-quality and clean. Another method is the pulsed spray transfer where the metal is melted and falls on the workpiece as droplets due to the pulsing current that is passed over the metal.
Short-circuit Transfer
This kind of metal transfer occurs when the feed rate is slower, and the molten filler spans the gap between the workpiece and the electrode and create a short circuit and even extinguishes the arc for a second or two.
Globular Metal Transfer
In this mode of metal transfer, there occurs a large blob at the end of the electrode and when it becomes bigger, it naturally falls onto the workpiece.
Potential Issues & Problems
It is always important that you gain experience practicing with less expensive metals before start MIG welding 316 stainless steel for example. You can always use carbon steel to hone your skills and once you are confident, then you can switch over to more exclusive materials. The reason many say that MIG welding stainless steel is difficult is that without proper training you can easily ruin the base metal. The main thing that you want to keep an eye on is that you do not want the base metals to become too hot, because then the carbon will mix with chromium forming chromium carbide which is not corrosion-resistant.
MIG Welding Stainless Steel Tips
When it comes to welding stainless steel, professionals make the job look much simpler than you think as they learn some tips here and there from their many years of experience. Say, for example, it is extremely important that you clean the stainless steel before you start welding as it will help in removing all kinds of chromium buildup, dirt, debris, grease, and oils.
Get a Better Ground Clamp
This may sound pretty odd to some, but do you know that this is one of the most important tips that many miss out during MIG welding stainless steel. It’s quite common when you hear sound like a drive-by shooting when newbie welders are operating the MIG welders. Do you know what’s the reason? It is highly possible that it is due to a bad ground. Even after hearing those annoying sounds, many don’t know that it may be caused by the ground clam. When compared to the ground clamps available now, the copper clamps that were used a few years back were much better, so I would advise you to use a quality one.
Watch Your Stickout
The next important tip that beginners need to take a look at is the
Conclusion
If you already have some experience in the world of welding, you should be completely capable
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Hope you enjoyed this post, and if you have any questions, feel free to drop a comment below.
Check out this post as well about shielding gas cost.
