7018 is a widely used stick electrode known for its high strength, low hydrogen content, and excellent weld quality, making it a staple in structural steel welding, pressure vessel fabrication, and other applications requiring strong, crack-resistant joints. For those seeking a flux core wire equivalent, the search centers on finding options that match 7018's key properties-specifically, tensile strength, low hydrogen levels, and versatility across materials and positions.
Key Properties of 7018 to Match
To identify an equivalent flux core wire, it's critical to first outline 7018's defining characteristics. The "70" in its name indicates a minimum tensile strength of 70,000 psi (483 MPa), while the "18" signifies it can be used in all welding positions (flat, horizontal, vertical, overhead) and uses a low-hydrogen flux. This low-hydrogen feature is vital for preventing hydrogen-induced cracking, especially in high-strength steels or thick sections. 7018 also produces smooth, easy-to-clean welds with good penetration and ductility, making it reliable for both structural and critical applications.
Flux Core Wires That Rival 7018
E71T-8 is widely recognized as the closest flux core wire equivalent to 7018. Like 7018, it offers a minimum tensile strength of 70,000 psi, aligning with the "70" strength class. It is a low-hydrogen flux core wire, categorized as an H4 or H8 (depending on the specific formulation), meaning it contains 4 or 8 milliliters of hydrogen per 100 grams of weld metal-well within the low-hydrogen range needed to avoid cracking in high-stress applications.
E71T-8 is designed for all-position welding, matching 7018's versatility. It performs well on carbon steel and low-alloy steel, the same materials 7018 is commonly used for, and produces welds with good ductility and impact resistance. This makes it suitable for structural welding, bridge construction, and heavy equipment repair-applications where 7018 is traditionally relied upon. Additionally, E71T-8 does not require a shielding gas (it is a "self-shielded" flux core wire), which adds flexibility for outdoor or remote work where gas cylinders are impractical, while still maintaining 7018-level performance.
Another option, E81T1-Ni1, can be considered for applications needing slightly higher strength. While it has a higher tensile strength (80,000 psi), it shares 7018's low-hydrogen properties and all-position capability. It is often used as a stronger alternative in scenarios where 7018 meets basic requirements but extra strength is desired, such as in heavy machinery or offshore structures.
Why These Wires Work as Equivalents
The equivalence stems from how these flux core wires replicate 7018's core functions. Low hydrogen content is achieved through careful formulation of the flux core, which binds to moisture and prevents hydrogen from entering the weld pool-just as 7018's coating does. This is critical for welding thick materials or steels with high carbon content, where hydrogen trapped in the weld could cause cracking during cooling.
All-position capability is another shared trait. E71T-8 and similar wires are engineered with a flux that controls the weld pool's viscosity, allowing it to solidify quickly enough for vertical or overhead welding without sagging-matching 7018's ability to produce clean, uniform welds regardless of position. Their tensile strength also ensures that welded joints can withstand the same loads as those made with 7018, making them interchangeable in structural specifications.
Limitations and Considerations
While E71T-8 and related flux core wires are strong equivalents, they have subtle differences from 7018. 7018's welds often have a slightly smoother surface finish, as the stick electrode's coating produces less spatter than some flux core wires. Flux core wires may also leave more slag, requiring extra cleaning time-though modern formulations have reduced this issue significantly.
In terms of material compatibility, 7018 is primarily used for carbon and low-alloy steels, and its flux core equivalents mirror this focus. Neither 7018 nor these flux core wires are ideal for non-ferrous metals like aluminum or stainless steel, as their flux formulations are not designed to protect against oxidation in these materials.
Shielding is another distinction: 7018 relies on its coating for shielding, while self-shielded flux core wires like E71T-8 generate their own shielding gas. This makes flux core wires better suited for windy or outdoor environments than 7018 (which can suffer from slag disruption in drafts), but it also means flux core welders must ensure proper wire feed speed to maintain consistent shielding-adding a layer of equipment control not required with stick welding.
Conclusion
E71T-8 self-shielded flux core wire is the closest equivalent to 7018, matching its tensile strength, low hydrogen content, all-position capability, and suitability for structural steel applications. It offers the added benefit of portability (no need for shielding gas), making it a practical alternative for outdoor or remote work. While minor differences in finish and slag cleanup exist, E71T-8 meets the core performance requirements that make 7018 a industry standard. For those needing slightly higher strength, E81T1-Ni1 is a viable step up, but E71T-8 remains the go-to choice for a direct 7018 equivalent in flux core form.
