Stick Electrode Specification: E7018 vs E6013 — Tensile Strength, Impact Toughness and AWS Class

Overview #

The specification parameter that most procurement teams get wrong when sourcing stick electrodes from China is not the tensile strength classification — it’s the low-hydrogen moisture content and lot-to-lot flux coating consistency, both of which directly determine weld quality in structural and pressure vessel applications. E7018 and E6013 are the two most commonly sourced SMAW electrodes from Chinese manufacturers, and they serve fundamentally different structural roles. Treating them as interchangeable based on price is one of the most common and costly sourcing errors we see in incoming inspection. Before committing to volume orders from any Chinese supplier, the first document to request is not the product brochure — it’s three consecutive batch COAs showing moisture content, flux coating eccentricity, and mechanical property test results against AWS A5.1.

AWS Classification, Tensile Strength and Mechanical Property Benchmarks #

The AWS A5.1 classification system encodes the minimum mechanical properties directly into the electrode designation. For E7018, the “70” prefix specifies a minimum tensile strength of 480 MPa (70,000 psi), a minimum yield strength of 400 MPa, and a minimum Charpy V-notch impact toughness of 27 J at −46°C. For E6013, the “60” prefix specifies a minimum tensile strength of 415 MPa (60,000 psi), with no mandatory low-temperature impact requirement in the base classification. That difference in impact toughness specification is not a minor footnote — it is the engineering reason why E7018 is mandated for structural steel, pressure vessels, and low-temperature service, while E6013 is appropriate for general fabrication, sheet metal, and non-critical joints.

The flux coating type drives the mechanical outcome. E7018 uses a low-hydrogen iron powder coating (H-suffix designation), which limits diffusible hydrogen to ≤8 mL/100g of deposited weld metal under AWS A5.1 H8 classification, and ≤4 mL/100g under H4. E6013 uses a rutile-based coating, which produces a softer arc, easier slag removal, and better cosmetic bead appearance — but does not control diffusible hydrogen to the same level. In hydrogen-induced cracking (HIC) sensitive applications, this distinction is non-negotiable.

Most Western buyers do not realize that GB/T 5117 — the Chinese national standard governing carbon steel covered electrodes — uses the same minimum tensile strength thresholds as AWS A5.1 for equivalent grades, but the flux coating eccentricity tolerance and moisture re-baking requirements are specified differently. A Chinese supplier can deliver a product that is fully GB/T 5117 compliant and still fail your AWS H4 hydrogen requirement if you have not explicitly specified the H-suffix designation on the purchase order.

For related sealing and fluid-system components used in welding fixture assemblies, see pump valve seals for compatible hardware specifications.

Flux Coating Quality, Moisture Control and Lot Consistency #

This is where most sourcing decisions go wrong, and it is the section of the specification that Chinese supplier datasheets almost universally omit in English.

E7018 electrodes are hygroscopic. The low-hydrogen flux coating absorbs atmospheric moisture, and once moisture content exceeds the threshold — typically 0.4% by weight for standard H8 classification — diffusible hydrogen in the weld deposit rises above the 8 mL/100g limit, creating conditions for hydrogen-induced cold cracking in medium and high-carbon steels. AWS A5.1 mandates that E7018 electrodes be supplied in hermetically sealed containers and re-baked at 260–430°C for 1–2 hours if the container has been open for more than 4 hours in humid conditions. In our qualification program, we have seen Chinese suppliers pass initial sample approval with sealed-can product and then deliver bulk orders in non-hermetic cardboard packaging with no desiccant. The moisture content on incoming inspection tested at 0.6–0.8% — well above the H8 threshold — and the buyer’s structural welds on S355 steel showed cold cracking at the root that was not detected until post-weld NDT.

Flux coating eccentricity is the second parameter to verify. AWS A5.1 limits coating eccentricity to a maximum of 7% for electrodes ≥3.2 mm diameter. Eccentric coating causes arc deflection, uneven penetration, and inconsistent bead geometry. In our supplier qualification program, we reject batches where coating eccentricity exceeds 5% — tighter than the AWS minimum — because production-volume welding on automated fixtures cannot tolerate the arc instability that borderline-compliant eccentricity introduces.

Three out of five Chinese suppliers we evaluated for E7018 in the 4.0 mm diameter could not produce lot-to-lot consistency data across six months of production showing stable Charpy impact values at −46°C. The variation was not in tensile strength — that parameter is easy to control and easy to verify. The variation was in impact toughness, which is sensitive to flux chemistry batch variation at the raw material compounder level.

For buyers sourcing abrasive and cutting consumables alongside welding electrodes for fabrication operations, the abrasives-cutting category covers compatible grinding and finishing specifications.

Diameter Selection, Current Settings and Deposition Efficiency #

Electrode diameter selection is a function of base metal thickness, joint geometry, and welding position — not a procurement variable. However, the diameter specified on the purchase order directly determines which mechanical property test applies, and this is where specification errors occur.

For E7018 at 3.2 mm diameter, the recommended welding current range is 80–130 A (DC+). At 4.0 mm, the range is 130–190 A. Deposition efficiency for E7018 iron powder coating runs 105–115% — meaning the iron powder in the flux contributes to deposited weld metal, giving a higher deposition rate than the core wire alone. At 4.0 mm and 160 A, expect a deposition rate of approximately 1.8–2.2 kg/h under standard conditions. E6013 at the same diameter runs 1.5–2.0 kg/h with deposition efficiency of 85–95%.

Most procurement teams focus on unit price per kilogram of electrode when sourcing from China. The variable that actually drives total cost is deposition efficiency and stub loss — a 10% difference in deposition efficiency between two nominally equivalent E7018 products translates directly to 10% more electrode consumed per kilogram of deposited weld metal. At production volume, that difference accumulates faster than any unit price differential.

The AWS A5.1 mechanical property tests are conducted on weld pads deposited under controlled conditions: 125 A for 3.2 mm, 175 A for 4.0 mm, flat position, on ASTM A36 or equivalent base plate. If a Chinese supplier’s COA shows tensile and impact data but does not specify the test current, position, and base plate, the data cannot be compared against the AWS classification requirement.

Compliance Documentation and Certification Requirements #

For structural steel applications governed by ISO 2560 (the international equivalent of AWS A5.1 for covered electrodes), the classification system uses a different alphanumeric format but maps to comparable mechanical property tiers. An electrode classified as ISO 2560-A E 46 4 B 42 H5 corresponds approximately to an AWS E7018-H4 in tensile class and hydrogen designation. Buyers specifying to European fabrication codes — EN 1011, EN 1090 — should verify that the Chinese supplier’s product is certified to ISO 2560, not only to GB/T 5117, since the two standards are not identical in all test conditions.

For pressure vessel and boiler applications, the relevant qualification framework is ASME Section IX (Welding and Brazing Qualifications), which requires that the filler metal classification be documented on the Welding Procedure Specification (WPS) and Procedure Qualification Record (PQR). A Chinese supplier’s CE mark or GB/T certificate does not substitute for ASME SFA-5.1 classification documentation if your end application is ASME-governed.

The English technical content available for Chinese-manufactured welding electrodes is almost entirely produced by Western brand owners — Lincoln Electric, ESAB, Böhler — not by Chinese suppliers. Chinese manufacturers producing equivalent products rarely publish English-language technical data sheets with the same depth of mechanical property data, hydrogen test results, and application guidance. That documentation gap is precisely why specification errors happen at the sourcing stage: the buyer assumes the Chinese product meets the same standard because it carries the same AWS classification number, without verifying the test documentation behind that classification.

Practical Guidance for Buyers #

When sourcing E7018 or E6013 stick electrodes from China, the first specification to request from suppliers is not the tensile strength — every supplier will show 480 MPa on a datasheet. Request the diffusible hydrogen test certificate (mL/100g per AWS A5.1 Annex A or ISO 3690) and the Charpy V-notch impact test report showing individual specimen values at −46°C, not just the average. Most buyers ask for the hardness and tensile data because it is easy to read. The impact toughness data is what separates a structurally qualified electrode from a general fabrication product.

The most common sourcing mistake is accepting E7018 in non-hermetic packaging for humid-climate storage. Moisture content above 0.4% by weight in the flux coating will push diffusible hydrogen above the H8 threshold, and the resulting cold cracking in S355 or higher-strength steel will not appear until post-weld NDT — after the joint is already in service. Specify hermetically sealed cans with desiccant, and require re-baking documentation if the supplier’s lead time means product will be in transit or storage for more than two weeks in tropical or coastal environments.

Before committing to volume order, require three consecutive batch COAs showing Charpy impact values at −46°C and flux coating eccentricity measurements. If a supplier cannot produce six months of lot consistency data for these two parameters, do not qualify them for structural or pressure vessel applications regardless of unit price.

Frequently Asked Questions #

Q1: What is the minimum Charpy impact toughness required for E7018 per AWS A5.1?
A: 27 J at −46°C, tested on individual specimens — not an average. Any COA showing only an average value without individual specimen data does not fully satisfy the AWS A5.1 reporting requirement.

Q2: Can E6013 be substituted for E7018 in structural steel applications?
A: No. E6013 has a minimum tensile strength of 415 MPa versus 480 MPa for E7018, and carries no mandatory low-temperature impact requirement. For applications governed by structural codes — AWS D1.1, EN 1090, or ASME Section IX — the substitution is not permitted without a new procedure qualification. The 65 MPa tensile strength difference is not the primary issue; the absence of hydrogen control and impact toughness certification is.

Q3: What is the most common quality failure when sourcing E7018 from Chinese suppliers at production volume?
A: Moisture ingress from non-hermetic packaging. This is where most sourcing decisions go wrong. The threshold is 0.4% moisture by weight in the flux coating — above that, diffusible hydrogen exceeds the H8 limit of 8 mL/100g and cold cracking risk in medium-carbon and high-strength steels becomes significant. We have seen this failure mode on incoming inspection after suppliers passed initial sample approval with sealed-can product.

Q4: What certification documentation should I require before approving a Chinese E7018 supplier for pressure vessel work?
A: Request the full mechanical property test report per AWS A5.1 or ISO 2560, the diffusible hydrogen certificate per ISO 3690 showing ≤4 mL/100g (H4) or ≤8 mL/100g (H8), and the ASME SFA-5.1 classification letter if the application is ASME-governed. A GB/T 5117 certificate alone is not sufficient for ASME or EN 1090 applications.

Q5: Is a higher deposition rate always better when comparing E7018 products from different Chinese suppliers?
A: Not without verifying deposition efficiency and stub loss together. A supplier quoting 2.4 kg/h deposition rate at 4.0 mm means nothing if their stub loss is 15% higher than a competitor’s — the net deposited metal per kilogram purchased will be lower, and the total cost per joint will be higher despite the better headline rate.

Published by sinoraw.com Technical Team | Request a sourcing consultation