Can You Stick Weld Stainless Steel with 7018: Explained Clearly

Many welders, especially those accustomed to working with mild steel, often wonder about the versatility of their go-to electrodes when facing different materials. A common question that arises is whether a standard electrode like the 7018, renowned for its strength and all-position capabilities, can be effectively used on stainless steel. While 7018 is an excellent choice for many carbon steel applications, its suitability for stainless steel is not straightforward and comes with significant caveats.

In short, while you can you stick weld stainless steel with 7018 in a pinch or for non-critical applications, it is generally not recommended as the primary or preferred method. The metallurgical differences between stainless steel and carbon steel, coupled with the specific properties of the 7018 electrode, lead to several potential issues that compromise weld quality and corrosion resistance.

Understanding 7018 Electrodes

The 7018 electrode is a low-hydrogen, iron powder type electrode designed primarily for welding mild and low-alloy steels. Its designation breaks down as follows:

• 70: Indicates a minimum tensile strength of 70,000 pounds per square inch (psi).
• 1: Signifies that it can be used in all welding positions (flat, horizontal, vertical, and overhead).
• 8: Denotes the type of coating, which is low-hydrogen, iron powder, and typically uses DCEP (Direct Current Electrode Positive) polarity.

The low-hydrogen coating is crucial because it reduces the risk of hydrogen embrittlement, a common problem in welding high-strength steels. Hydrogen embrittlement can lead to delayed cracking in the weld or heat-affected zone (HAZ). The iron powder in the coating increases deposition rates, making welding faster and more efficient. These characteristics make 7018 a popular choice for structural welding, heavy equipment repair, and applications where high strength and ductility are required.

Why 7018 Isn’t Ideal for Stainless Steel

The core reason 7018 is not recommended for stainless steel lies in the fundamental differences between the two materials and the electrode’s composition. Stainless steel is an iron-based alloy containing a minimum of 10.5% chromium, which provides its corrosion resistance by forming a passive oxide layer on its surface. Nickel and other elements are also often added to enhance properties like ductility and further improve corrosion resistance.

Metallurgical Incompatibility

When you weld stainless steel with a 7018 electrode, you are essentially introducing carbon steel filler metal into a stainless steel base metal. This creates a mixed weld deposit that lacks the necessary chromium content to be truly “stainless.”

• Loss of Corrosion Resistance: The primary purpose of using stainless steel is its corrosion resistance. A weld made with 7018 will have a significantly lower chromium content than the surrounding stainless steel. This area will become a preferential site for corrosion, essentially creating a weak point in the material’s protective barrier. This is particularly problematic in environments where stainless steel is chosen specifically for its resistance to rust, acids, or other corrosive agents.
• Galvanic Corrosion: Introducing dissimilar metals can lead to galvanic corrosion. When two different metals are in electrical contact in the presence of an electrolyte (like moisture), the less noble metal (in this case, the carbon steel weld metal) will corrode preferentially. This accelerates degradation of the weld joint.
• Carbide Precipitation: Stainless steels, especially certain grades, are susceptible to carbide precipitation in the heat-affected zone (HAZ) when exposed to elevated temperatures during welding. This phenomenon, often called “sensitization,” occurs when chromium carbides form at grain boundaries, depleting the surrounding area of chromium and making it vulnerable to intergranular corrosion. While 7018 doesn’t directly cause this, the heat input from welding can contribute, and the non-stainless weld metal offers no protection against it.

Mechanical Property Mismatch

While 7018 provides excellent strength for carbon steel, its mechanical properties may not perfectly match those of stainless steel. Stainless steels often have different coefficients of thermal expansion and yield strengths. A mismatch can lead to:

• Residual Stresses: Differences in thermal expansion between the weld metal and base metal can induce significant residual stresses upon cooling. These stresses can lead to distortion, cracking, or reduced fatigue life, especially in thicker sections or constrained joints.
• Ductility Issues: While 7018 is ductile for carbon steel applications, the mixed weld metal might not exhibit the same ductility or toughness as a proper stainless steel weld, potentially making the joint more brittle and prone to failure under stress.

Appearance and Finish

A weld made with 7018 on stainless steel will look different. The color will be closer to that of carbon steel, and it will likely rust over time, contrasting sharply with the surrounding stainless material. This is often unacceptable for aesthetic applications or those requiring a uniform finish.

When Might Someone Consider Using 7018 on Stainless Steel?

Despite the strong recommendations against it, there are a few very specific, non-ideal scenarios where a welder might consider using 7018 on stainless steel. These are almost always driven by necessity, lack of proper materials, or a complete misunderstanding of the implications.

• Emergency Repairs (Temporary): In a dire emergency where no stainless steel electrodes are available, and a temporary, non-structural, non-critical repair is absolutely necessary to get a piece of equipment running for a very short period, a 7018 might be used. However, this weld should be considered a temporary fix and replaced with a proper stainless steel weld as soon as possible. The repaired part should not be subjected to corrosive environments or significant stress.
• Non-Critical, Non-Corrosive Applications: If the stainless steel part is being welded to carbon steel, and the application is purely structural, not exposed to any corrosive elements, and aesthetics are irrelevant, a 7018 might technically join the two. However, even in this scenario, a specialized dissimilar metal electrode (like E309L) would be a far superior choice to minimize issues.
• Training/Practice (with caution): A beginner might try to run a bead on stainless steel scrap with 7018 just to understand how stainless steel reacts to heat, but this should be done with full awareness that the resulting weld is not a functional stainless steel weld. It’s a poor substitute for practicing with actual stainless steel electrodes.

It is crucial to reiterate that these are exceptions born out of constraint, not best practice. Relying on 7018 for stainless steel welding will almost always lead to premature failure, corrosion, or compromised integrity.

The Correct Approach: Stainless Steel Electrodes

For any application involving stainless steel, the correct approach is to use filler metals specifically designed for stainless steel. These electrodes are formulated to match the metallurgical properties, corrosion resistance, and mechanical characteristics of the stainless steel base metal.

Types of Stainless Steel SMAW Electrodes

Stainless steel electrodes are typically designated with an “E” followed by three digits and sometimes additional letters (e.g., E308L-16, E316L-17). The three digits indicate the specific grade of stainless steel the electrode is designed for, often matching the AISI (American Iron and Steel Institute) designation of the base metal.

• E308/E308L: This is the most common electrode for welding 304 and 304L stainless steel. The “L” denotes low carbon content, which helps prevent carbide precipitation and intergranular corrosion, especially important for applications where the weld will be exposed to corrosive environments or elevated temperatures.
• E316/E316L: Used for welding 316 and 316L stainless steel, which contains molybdenum for enhanced corrosion resistance, particularly against pitting and crevice corrosion in chloride environments.
• E309/E309L: Often referred to as a “dissimilar metal” electrode. It has a higher alloy content than 308L and is excellent for joining stainless steel to carbon steel or low-alloy steel. It can also be used for welding 309 stainless steel.
• E347: Used for welding stabilized stainless steels like 321 and 347, which contain niobium (columbium) or titanium to prevent carbide precipitation.
• E410: For welding 410 stainless steel, a martensitic grade. These welds often require preheating and post-weld heat treatment.

Key Characteristics of Stainless Steel Electrodes

• Matching Chemistry: The filler metal closely matches the base metal’s chemical composition, ensuring similar corrosion resistance and mechanical properties.
• Controlled Microstructure: Electrodes are designed to produce a weld microstructure that resists common stainless steel welding issues like hot cracking and sensitization.
• Low Carbon (L-grades): Many stainless steel electrodes are “L-grades” (low carbon) to minimize carbide precipitation and maintain corrosion resistance.
• Flux Coatings: The flux coatings on stainless steel electrodes are specifically formulated to handle the unique metallurgical challenges of stainless steel, such as managing chromium oxides and ensuring proper arc stability.

Practical Considerations for Welding Stainless Steel

Beyond choosing the correct electrode, several other factors are critical when welding stainless steel to ensure a high-quality, corrosion-resistant joint.

Cleanliness is Paramount

Stainless steel surfaces must be meticulously clean before welding. Any contaminants like oil, grease, paint, or even carbon steel dust can compromise the weld’s corrosion resistance and lead to defects. Use dedicated stainless steel brushes and grinding wheels to avoid cross-contamination from carbon steel tools.

Heat Input Control

Controlling heat input is vital to prevent issues like carbide precipitation, distortion, and loss of corrosion resistance. Stainless steel has a lower thermal conductivity and a higher coefficient of thermal expansion than carbon steel, meaning it heats up faster and distorts more easily.

• Lower Amperage: Generally, you’ll use lower amperage settings than you would for carbon steel of similar thickness.
• Faster Travel Speed: Move quickly to minimize the heat-affected zone.
• Interpass Temperature Control: Allow the weld to cool between passes to prevent excessive heat buildup.
• Skip Welding/Backstep Welding: Techniques to distribute heat more evenly and reduce distortion.

Shielding Gas (for TIG/MIG) and Electrode Coatings (for SMAW)

While this article focuses on SMAW (stick welding), it’s worth noting that for TIG and MIG welding of stainless steel, specific shielding gases (typically argon with a small percentage of CO2 or helium for MIG, or pure argon for TIG) are used to protect the weld puddle and prevent oxidation. For SMAW, the electrode coating performs this function, but proper technique is still required to ensure adequate shielding.

Post-Weld Cleaning and Passivation

After welding, the weld area should be thoroughly cleaned to remove slag, heat tint, and any surface contaminants. Heat tint (the discoloration around the weld) indicates chromium depletion and should be removed. This can be done mechanically (brushing with a stainless steel brush, grinding, or sanding with clean abrasives) or chemically (pickling pastes). Following cleaning, passivation is often recommended. Passivation is a chemical treatment (typically with nitric acid or citric acid solutions) that restores the passive chromium oxide layer on the stainless steel surface, maximizing its corrosion resistance.

Distortion Control

Due to its high thermal expansion, stainless steel is prone to distortion. Strategies to minimize distortion include:

• Tack Welding: Use frequent and strong tack welds to hold parts in alignment.
• Clamping and Fixturing: Use robust clamps and fixtures to restrain the material.
• Balanced Welding: Alternate weld passes to distribute heat evenly.
• Peening: Light peening can sometimes relieve residual stresses, though it must be done carefully.

Comparing 7018 to Stainless Steel Electrodes

To summarize the stark differences, consider the following table:

Feature	7018 Electrode (Carbon Steel)	Stainless Steel Electrode (e.g., E308L-16)
Primary Use	Mild and low-alloy steels	Stainless steels (matching grade)
Weld Metal Chemistry	Carbon steel (low chromium)	Stainless steel (high chromium, nickel, etc.)
Corrosion Resistance	Poor on stainless steel (prone to rust)	Excellent (matches base metal)
Galvanic Corrosion Risk	High when joined to stainless steel	Low (similar metals)
Mechanical Properties	Optimized for carbon steel strength/ductility	Optimized for stainless steel strength/ductility
Appearance	Carbon steel color, will rust	Stainless steel color, resists rust
Cost	Generally lower	Generally higher
Availability	Very common	Common in welding supply stores

This comparison clearly illustrates why using a 7018 electrode for stainless steel is a compromise that fundamentally undermines the very properties for which stainless steel is chosen.

Best Practices for Stainless Steel Welding

When approaching a stainless steel welding project, I always recommend the following steps:

1. Identify the Stainless Steel Grade: Knowing the specific grade (e.g., 304, 316, 309) is crucial for selecting the correct filler metal.
2. Select the Appropriate Electrode: Choose a stainless steel electrode that matches the base metal or is suitable for dissimilar metal joints (e.g., E309L for stainless to carbon steel).
3. Ensure Cleanliness: Prepare the joint meticulously, removing all contaminants. Use dedicated stainless steel tools.
4. Control Heat Input: Use appropriate amperage, travel speed, and interpass temperatures to minimize distortion and metallurgical issues.
5. Proper Post-Weld Treatment: Clean and, if necessary, passivate the weld area to restore full corrosion resistance.
6. Ventilation: Welding stainless steel can produce fumes containing chromium and nickel, which are hazardous. Always ensure excellent ventilation and use appropriate personal protective equipment (PPE), including a respirator.

Frequently Asked Questions About Welding Stainless Steel with 7018

Can 7018 be used to tack weld stainless steel temporarily?

While it might technically create a temporary bond, it’s strongly advised against. Even a small tack weld with 7018 introduces carbon steel into the stainless steel, creating a point of corrosion and potential weakness. For tacking, use the correct stainless steel filler metal, even if it’s just for a temporary hold.

What happens if I weld stainless steel with 7018

Even if corrosion resistance isn’t a primary concern, using 7018 on stainless steel can lead to other issues. The mechanical properties of the weld might not match, potentially causing cracking or premature failure under stress. Distortion can also be more severe due to thermal expansion differences. The weld will also look different and may be harder to finish uniformly.

Is there any scenario where 7018 is better than

No, there is no scenario where a 7018 electrode is metallurgically or functionally superior to a properly selected stainless steel electrode for welding stainless steel. Any perceived “advantage” (e.g., lower cost, greater availability) is immediately outweighed by the compromised integrity and performance of the weld.

Can I use 7018 to weld stainless steel to carbon

While 7018 can join carbon steel to carbon steel, and it can physically join stainless steel to carbon steel, it is not the recommended or best practice. When joining dissimilar metals like stainless steel and carbon steel, a specialized stainless steel electrode like E309L or E309LMo is the correct choice. These electrodes are specifically designed to accommodate the differences in chemistry and thermal expansion, producing a much more robust and corrosion-resistant joint than 7018 would.

Will a 7018 weld on stainless steel pass an inspection?

For any critical application, structural component, or pressure vessel, a weld made with 7018 on stainless steel would almost certainly fail inspection. Welding codes and standards (like AWS D1.6 for structural stainless steel) specify the use of appropriate filler metals that match the base material’s properties. A 7018 weld on stainless steel would not meet these requirements due to its compromised corrosion resistance and mechanical incompatibility.

Conclusion

In conclusion, while it is physically possible to strike an arc and deposit weld metal when you can you stick weld stainless steel with 7018, it is a practice that should be avoided for almost all applications. The 7018 electrode is formulated for carbon and low-alloy steels, and its use on stainless steel will inevitably lead to a weld that lacks the essential corrosion resistance, proper mechanical properties, and aesthetic consistency characteristic of stainless steel. For any durable, reliable, and corrosion-resistant stainless steel fabrication or repair, always select a filler metal specifically designed for stainless steel, such as E308L, E316L, or E309L, and adhere to best practices for stainless steel welding.