MIG Welding

How To MIG Weld Stainless Steel

Table of Contents > 1. Exploring Key Factors to Consider Before MIG Welding Stainless Steel
2. Targeting Specific Weld Puddle Characteristics
3. Stainless Steel Joints: Applying Perfect MIG Welding Techniques
4. Developing A Stainless Steel Welding Strategy
5. How To MIG Weld Stainless Steel - FAQ

As cited several times by this very website, stainless steel is an exceptionally tough metal. We think of the alloy family as having a high hardness rating and superior loading-bearing properties. Those attributes alone should make the alloy daunting to weld. Not to worry, MIG welding (Metal Inert Gas) handles stainless steel projects with ease, making it the preferred jointing method for many welders. It’s a fine solution, one that generates a high-temperature arc capable of melting the alloy so that strong weld joints are consistently achieved time-after-time.

MIG Welding for stainless steel

MIG Welding For Stainless Steel
Source: https://www.alphaweld.com.au/blog/56-best-types-of-mig-welding-wire-for-stainless-steel

Come with us today as we learn how to MIG weld one of the toughest alloys known to man. The fundamentals will be covered first, then we’ll cover the more intricate foibles associated with this welding process and the hard metal we’ve chosen as today’s formidable project metal. Don’t be daunted, stainless steel, a dense, durable family of super-hard alloys, is as weldable as any other metal when the right equipment and techniques are employed.

Exploring Key Factors to Consider Before MIG Welding Stainless Steel

First things first, stainless steel melts at a formidably hot temperature of 1530°C, so welders working with the alloy will require a deep understanding of this natural resistance to heat if they’re to successfully and repeatedly create strong joints. To counter this reluctance to melt, the right equipment is essential. A Tooliom MIG TL-135M 3-in-1 welding machine is a natural choice as a MIG welding tool when working on a stainless steel job. 

MIG/Stick/TIG Multi-Process Welder TL-135M 3 in 1 IGBT DC Inverter|Tooliom

MIG/Stick/TIG Multi-Process Welder TL-135M 3 in 1 IGBT DC Inverter|Tooliom

The weld zone is prepped before transporting in the welding gear. A wire brush carefully scours away the surface layer of weld-inhibiting chromium oxide. All dirt and oils are eliminated, metal conductivity is high, and a thumbs up is given to the welder. Now it’s time to focus on the job at hand. The rugged Tooliom equipment is made on-site ready.  

Metal prep with wire brush

Metal prep with wire brush

Source: https://tooliom.com/blogs/tooliom/aluminum-mig-welding-for-beginners

Machine settings are especially critical here, for heat resistance isn’t the only problem welders will encounter when they pick up their welding gun. For one thing, that wire-fed filler metal needs consideration. To do so, the microcrystalline structure of the stainless steel workpiece needs to be recognized. There’ll be more on this subject later in the post. The selection of an incorrect match will cause negative joint characteristics. Intergranular carbide precipitation is one common issue when filler selectivity is a problem. It’s a welding complication that can weaken stainless steel joints and result in a matching loss of workpiece corrosion resistance.

The key takeaway, then, is that the grade of stainless steel being worked upon should lead the welder when selecting a suitable filler wire. Similarly, the choice of shield gas cylinder is essential. Typically, high helium tri-mixes are ideal. A 90% helium blend with around 7% of inert argon is popular. The third member of this atmospheric shielding trio is generally CO2 (Carbon Dioxide). Again, the precise ratio of the shielding gas mix will depend on the composition of the stainless steel workpiece. When employing that Tooliom MIG TL-135M 3-in-1 welding machine, a slight variation in the quantity of CO2 present in the cylinder blend is expected, as the carbon in that gas can be absorbed into the surface of stainless steel metals, which leads to a change in the chemical composition of the alloy in and around the weld zone. 

MIG/Stick/TIG Multi-Process Welder TL-135M 3 in 1 IGBT DC Inverter|Tooliom

MIG/Stick/TIG Multi-Process Welder TL-135M 3 in 1 IGBT DC Inverter|Tooliom

The most controllable, fine-tunable part of the job is the equipment settings panel. Here, dominated by an easy to read smart digital display, the mode selection control is set to MIG welding. To the right, the voltage and current knobs sit one above the other. Wire travel speed is also set here. Assuming a 308LSi solid feed wire has been picked by the welder, which is the right wire grade for welding some of the more popular stainless steel types, such as 302 and 304L, then  a final pre-check should be run through by the equipment operator before the arc is induced. Is the polarity of the gear set to DCEP (Direct Current Electrode Positive) on the front panel? Cables should be configured accordingly and the ground clamp should be secured on a clean, conductive spot on the stainless steel workpiece.TL-135 setting panel

TL-135 equipment setting panel

Targeting Specific Weld Puddle Characteristics 

The settings on the control panel, the selection of filler wire and shield gas cylinder, all of these pre-weld configuring steps exist to enable welders to achieve their chosen goal, which is a strong, splatter-free joint that’s fully fused all the way down to the root. Even with those parameters set, though, there’s more to evaluate.

There’s the chemical composition of the stainless steel component to review. Be it a vehicle support being worked upon in a small garage or a piece of thick sheet metal on some distant construction site, the metal’s properties need identifying. Besides mechanical strength, stainless steel is an alloy with a reputation for corrosion protection and chemical resistance. The filler components and shield gas blend support and reinforce those properties. Carbon content is kept low in both the filler and the gas so that the element doesn’t seep into the alloy piece and alter its chemistry. 

The relationship between corrosion resistance and strength for the common stainless steelsThe relationship between corrosion resistance and strength for the common stainless steels.

Source: https://www.carpentertechnology.com/blog/selecting-new-stainless-steels-for-unique-applications

Of equal importance, puddle fluidity is maximized by the filler so that the high-temperature arc manipulates the pool easily. This is a particularly important feature when we consider the amount of thermal energy being distributed throughout the heat affected zone (haz). If that energy isn’t quickly manipulated, it’ll likely cause mechanical damage, which might include distortion, the bane of all welding projects. Denser stainless steel grades are susceptible to distortion, and this problem will only grow worse if the part being welded experiences a transition in thickness. 

Stainless Steel’s high coefficient of thermal expansion and low thermal conductivity makes it distort easily when welding.

Stainless Steel’s high coefficient of thermal expansion and low thermal conductivity makes it distort easily when welding.

Source: https://weldinganswers.com/5-common-mistakes-made-welding-stainless-steel/

Experienced welders consider these and every other contributing factor when learning how to MIG weld stainless steel. On the control panel, voltage is set high, travel speed/amperage is tuned to minimize thermal expansion effects. The combination of shield gas and solid wire filler similarly contributes to a strong, aesthetically pleasing weld joint. Puddle fluidity encourages bead manipulation in the desired weld position, root penetration is likewise maximized, and the surface tension of the pool forms in such a way that slag production tapers off significantly, to the point that the visual and mechanical quality of the weld is perfectly realized.

The effects of welding variables for the GMAW welding processes.

The effects of welding variables for the GMAW welding processes.

Source: https://www.facebook.com/CiproAhmedHamada/photos/a.222424291214469/3083360305120839/

Stainless Steel Joints: Applying Perfect MIG Welding Techniques

One potential drawback of a fine-tunable welding setup is the possibility of unpredictable results. Granted, it’s a wonder of modern technology, this ability to tweak every panel setting. Add to that the choice of multiple filler wire types and numerous options for shield gas blends, and we have a wealth of routes to take when manipulating a bead/puddle in a stainless steel welding job. As a job-protecting tip, the best way forward is to leave the work to the side for the moment. Instead of creating an opportunity for a mistake that can’t be corrected, such as parts distortion, carry out the work on a scrap piece. For this tip to work, it must be a piece of stainless steel that exhibits the same mechanical and chemical properties as the target workpiece.

Focusing on that scrap metal for the moment, try to select a piece with similar dimensions as the job piece. In other words, if the job is working on a thin section of sheet metal, pick out a scrap piece of metal that’s just as thin. If the work is being done on a component that’s thicker, likely to absorb more thermal energy, then a thick piece of scrap stainless steel would be chosen. It’s an obvious tip, but it’s one that’s still worth mentioning.

2mm Vs. 3mm stainless steel metal welding penetration

2mm Vs. 3mm stainless steel metal welding penetration

Source: https://www.mig-welding.co.uk/clarke-90.htm

Welding on thin sheet steel, that high-temperature melting point is an unavoidable issue. Still, it’s not unsolvable. To minimize thermal expansion, use a stitching technique so that the bead criss-crosses. Again, the Tooliom MIG TL-135M 3-in-1 welding machine comes to the rescue. A hobbyist working on a thin sheet metal weld likely gets the best out of a 0.8mm spool of solid wire. If that’s not enough to create a wide stitching bead, there’s the option to install 0.9mm wire instead. Frankly, the equipment will cover the demands of most hobbyist to light fabrication stainless steel welding work, and the option to select two different wire diameters can only increase the range of its stainless steel welding aptitude.

MIG/Stick/TIG Multi-Process Welder TL-135M 3 in 1 IGBT DC Inverter|Tooliom

MIG/Stick/TIG Multi-Process Welder TL-135M 3 in 1 IGBT DC Inverter|Tooliom

Working above thin stainless steel project work, the next area of application is on thicker, heavier gauge stainless steel work. A push method is employed when this level of alloy denseness is encountered. Relatively fast weld gun travel is advised. As the pool turns to a superheated fluid under the MIG arc, the bead is ‘pushed’ by the action of the welder, who has positioned the weld gun behind the weld puddle. The advantage here is deeper penetration and more control over bead travel. This ‘stringer’ bead also generates less carbide precipitation, meaning a cleaner, stronger weld. Note, such precipitates are common in austenitic stainless steels. They weaken welds, reduce overall corrosion resistance, and are susceptible to cracks.

Push Method In Welding
Push Method In Welding

Developing A Stainless Steel Welding Strategy

Whichever bead manipulating welding technique is employed, welders still need to ‘bookend’ their jointing strategies. Stainless steel has a vast number of grades and families. The prep work begins with cleaning, either with a stainless steel brush or with a powered circular cleaning tool. Knowledge in the austenitic and ferritic/martensitic alloys is made available. In this way, the welder becomes aware of chromium content and of nickel, manganese and all other possible trace elements. Of equal importance, the ratio of carbon and how it has been heat treated to create special crystalline forms is also researched. 

common mig welding patterns

Common MIG Welding Patterns

Source: https://www.earlbeck.com/welding-blog/stainless-steel-properties

Why should this knowledge be of any importance? Essentially, all of those added elements, the trace metals and heat treated carbon chemistry, all impact stainless steel weldability. No problems are likely if a corresponding filler wire and shielding gas are employed. If that’s not the case, if a welder doesn’t know his stainless steel grades and gauges, then all kinds of issues will ensue. Cracking, carbide buildups, corrosion resistance impairment and mechanical strength drop offs, they all become possible if not probable. Use the correct equipment settings, the correct filler/shield gas, and the correct bead laying techniques to ensure a mechanically strong and attractive stainless steel weld. By the way, if the job includes small parts, they might move when the arc generates copious quantities of heat. Use braces to immobilize the parts. A small gap may be required when this is done, one that exists solely to facilitate bead progress and strengthen the final weld. 

When the job’s done, a follow up with a post job-weld strategy is recommended by welding professionals. Yes, the welding is finished, the joint is strong, but the work isn’t quite finished, not yet. Looking at the joint, it’s perhaps tarnished, besmirched with slag and other intrinsically unattractive weld site impurities. The Tooliom gear has done a superb job, but there’s still some spatter in evidence. A pickling paste and/or a steel wire brush soon tidies up the area, ready for inspection.

MIG Welding Spatter

MIG Welding Spatter

Source: https://waterwelders.com/how-to-reduce-spatter-when-mig-welding/

Other possible defects, blemishes that  are related specifically to stainless steel work, include a loss of corrosion resistance strength and an irregular finish. A polishing disc on a powered circular tool takes care of the latter problem while what’s known as a passivation chemical solution quickly deals with the lack of a surface finish that provides much desired oxidation protection. 

From pre-weld surface cleaning strategies to bead manipulation techniques, from weld pool fluidity to post-weld care and attention, stainless steel MIG welding requires attention to detail, plus some basic knowledge of stainless steel properties, including the austenitic and ferritic families that can complicate an otherwise straightforward MIG welding process. If all of this is kept firmly in mind, there's no reason why strong, professionally applied welds can't consistently be achieved.



The opening

Talks about stainless steel as a hard, tough to work family of alloys. MIG welding is introduced.

Pre-weld consideration

Weighing weld-inhibiting factors behind the alloy. Proper cleaning and preparation practices.Equipment settings, filler wire, and shielding gas blends. 

The weld puddle

Explaining weld puddle fluidity and the need for an easy-to-manipulate bead that’s ready to be weaved/stitched or pushed.

Weld technique

Equipment settings and bead laying techniques are discussed as they apply to thin and thicker stainless steel welding projects.

Post-welding stainless steel strategies

Learn about the unique properties of stainless steel, including its corrosion resistance and composition. Knowing those chemical characteristics, post weld completion procedures are utilized.

Shielding Gas For TIG Welding - FAQ

Q: What is MIG welding and why is it preferred for stainless steel projects?

A: MIG welding stands for Metal Inert Gas welding. It is the preferred method for stainless steel projects due to its ability to generate a high-temperature arc that can melt the tough alloy, resulting in consistently strong weld joints.

Q: Why is proper preparation of the weld zone essential before welding?

A: The weld zone needs to be properly prepped to remove surface layers of weld-inhibiting chromium oxide, dirt, and oils. This enhances metal conductivity and ensures a clean surface for welding.

Q: How can the "push" method be advantageous in welding thicker stainless steel?

A: The "push" method involves positioning the weld gun behind the weld puddle, allowing for deeper penetration and more control over bead travel. This method reduces carbide precipitation and leads to cleaner, stronger welds.

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