A572 Grade 70 Structural Steel WPS Under AWS D1.1:2025
ASTM A572 Grade 70 sits at the top of the A572 spectrum with a 70 ksi minimum yield. Learn how its WPS differs from Grade 50, what filler metal matching requires, and where the prequalified path ends.
ASTM A572 covers five yield-strength grades: 42, 50, 55, 60, and 70. The 50 ksi version dominates structural steel production and gets the most attention in welding procedure literature. Grade 70 — with a 70 ksi minimum yield and 90 ksi minimum tensile strength — sits at the top of the spectrum, occupying a practical space between commonplace Grade 50 work and the highly restricted quenched-and-tempered A514.
Most CWI/QC managers who routinely weld A572 Grade 50 encounter Grade 70 only occasionally, typically on heavy plate built-up girders, transfer beams, or dense connection zones where a designer chose it to reduce section size. When Grade 70 shows up on a job, the WPS in use for Grade 50 will not automatically cover it.
Why Grade 70 Is Not Just "Stronger Grade 50"
The ASTM A572 specification controls chemical composition and minimum mechanical properties, but it does not guarantee identical alloy content across grades. As yield strength increases within the A572 family, producers typically raise carbon and/or manganese content, add micro-alloying elements (vanadium, columbium, or nitrogen strengthening agents), or adjust rolling practice. The net effect for welding is a higher carbon equivalent — the composite measure AWS D1.1 uses to assess hydrogen-assisted cold cracking risk.
A572 Grade 50 typically runs carbon equivalents well below 0.45; Grade 70 can approach or exceed that threshold depending on heat chemistry. At higher CE, the HAZ becomes more hardenable, hydrogen cracking risk increases, and the preheat requirement climbs. Treating a Grade 70 WPS as a copy of a Grade 50 WPS with only the base metal description changed is a common shop error that an inspector or auditor will flag immediately.
Prequalified Status and Its Limits
AWS D1.1:2025 lists A572 Grade 70 among approved base metals for prequalified WPS use. This means a shop can use Grade 70 under a prequalified WPS without conducting a PQR, provided every other prequalified requirement is met — joint geometry within the Clause 5 joint detail limits, approved filler metal, preheat at or above code minimums, heat input within the prequalified range, and so on.
The prequalified path does not, however, mean low effort. Three constraints tighten materially compared to Grade 50:
Filler metal classification. AWS D1.1 requires that filler metal tensile strength meet or exceed the base metal tensile strength for matching-strength joints. A572 Grade 70 has a 90 ksi minimum tensile requirement. E70XX electrodes — the most common class in structural shops — produce nominal weld metal tensile strengths near 72 ksi. This falls below the 90 ksi base metal tensile, making E70XX an undermatch. While undermatching filler is permitted for some joint configurations under specific code provisions, it is not the default, and a prequalified WPS for Grade 70 work in tension-critical connections requires 80 ksi class filler.
Preheat requirements. AWS D1.1:2025 tables tie minimum preheat to base metal specification, yield strength, and section thickness. For A572 Grade 70 at thicknesses above 3/4 in [19 mm], preheat requirements are meaningfully higher than for Grade 50. At 1-1/2 in [38 mm] and above, preheat of 200°F [95°C] or more is typical, and the exact value depends on the welding process and heat input. Shops accustomed to 50–100°F preheat for their Grade 50 work need to adjust heat-up procedures and equipment.
Process and heat input. High heat input can degrade HAZ toughness in high-strength steels. If CVN toughness is specified — as it commonly is for cyclic or seismic applications — the WPS must stay within the heat input envelope that the test program validated. Even on a prequalified WPS, running parameters outside the reasonable range for Grade 70 invites HAZ coarsening and toughness loss.
Table 6.6 Essential Variables — What Triggers Requalification
Once a Grade 70 WPS is established — whether prequalified or PQR-backed — changes that require requalification under AWS D1.1:2025 Table 6.6 are the same as for any other structural steel. The following are the most consequential for Grade 70 work:
Row 1 — Base metal specification change. Switching from A572 Grade 70 to A572 Grade 50 (or to any other ASTM specification) is an essential variable change. The existing WPS does not cover the new base metal unless both specifications are listed and covered by the same supporting PQR. On the flip side, a WPS written for Grade 70 may qualify lower-strength A572 grades, but verify this against Table 6.6 row 1 language rather than assuming coverage.
Rows 4–6 — Filler metal classification. Moving from an E80XX SMAW electrode to any E70XX class changes the filler classification and triggers requalification. This is the most common error: a shop running out of E8018 rods and substituting E7018 "for the fill passes" has invalidated the WPS for Grade 70 work.
Heat input range (for CVN-critical applications). Where the WPS is PQR-backed and the PQR includes Charpy testing, heat input limits are part of the qualification. Running beyond those limits requires a new test.
When a PQR Is the Better Choice
Even though the prequalified route is available for A572 Grade 70, a PQR-backed WPS has advantages in practice. A PQR provides documented mechanical test results — tensile specimens, guided-bend tests, and Charpy CVN tests if specified — that demonstrate actual weld performance on Grade 70 material. On AISC-certified fabricator audits, a PQR-backed procedure for high-strength steel tends to generate fewer questions than a prequalified WPS applied at its limits.
The cost of qualifying a single PQR is modest relative to the value of the downstream work it supports. For a shop that regularly works Grade 70 on large projects, one well-documented PQR program that covers groove welds in all required positions, with full mechanical testing, pays for itself quickly in audit confidence and re-order eligibility.
Filler Metal Options for A572 Grade 70
For SMAW, the AWS A5.5 classification system covers low-alloy electrodes: E8018-C1, E8018-C2, E8018-C3, and E8018-G are all used for high-strength structural work. The trailing letter designation controls alloy composition and intended application. For Grade 70 structural work without CVN supplementary requirements, E8018-G (low-alloy, general purpose) is commonly specified.
For FCAW-G, E8XT-x classifications under AWS A5.29 apply. Consult the electrode manufacturer for data sheets confirming tensile strength, CVN impact values (if needed), and preheat guidance. For SAW, a wire-flux combination tested to 80 ksi class deposit is needed, and the combination must be tested together — the wire specification alone is insufficient.
Practical Documentation Checklist
When drafting or reviewing a WPS for A572 Grade 70, confirm each of the following:
Base metal listed as A572 Grade 70 (not simply "ASTM A572" or "A572 Gr. 50")
Filler metal classification explicitly 80 ksi class or higher, with AWS designation written out
Preheat minimum per AWS D1.1:2025 for the applicable thickness and process
Interpass temperature maximum noted (often 500°F [260°C] for structural; lower if CVN testing required)
Pass schedule with amperage, voltage, travel speed, and calculated heat input per pass
Edition disclaimer: see WPS compliance guidance for a tool that pre-populates these fields correctly
Any WPS revision that adjusts filler classification, base metal, or preheat values must be re-authorized and re-dated. A revision that downgrades filler to E70XX class for a Grade 70 WPS is not a minor change — it invalidates the procedure for use on 90 ksi tensile base metal in strength-critical joints.
Summary
ASTM A572 Grade 70 is a legitimately prequalified base metal under AWS D1.1:2025, but the prequalified route is not a shortcut. Higher yield strength means higher required filler metal tensile class, stricter preheat requirements based on carbon equivalent, and careful heat input control when CVN toughness is specified. Shops familiar with Grade 50 work who occasionally encounter Grade 70 need a distinct, reviewed WPS — not an edited copy of the Grade 50 document with the base metal field changed.
Rule library based on AWS D1.1:2025. Verify against your governing edition — some projects specify the 2020 edition or an earlier version, and preheat tables and base metal approvals differ between editions.
FAQ
Frequently asked.
Is ASTM A572 Grade 70 on the AWS D1.1:2025 prequalified base metal list?
Yes, A572 Grade 70 appears on the AWS D1.1:2025 approved base metal list for prequalified WPS use. However, the prequalified route imposes matching filler metal and preheat requirements that are more restrictive than those for Grade 50. Verify your specific configuration against the published code table — the list has been updated through recent editions.
What filler metal class do I need for A572 Grade 70?
Matching-strength welds require E80XX class SMAW electrodes (such as E8018-C3 or E8018-G per AWS A5.5) or 80 ksi class continuous electrodes for FCAW-G or GMAW. Undermatching with E70XX is sometimes acceptable for joints where weld strength governs in tension only if engineering analysis supports it, but this requires justification beyond a prequalified WPS.
Does A572 Grade 70 require higher preheat than Grade 50?
Yes. The higher carbon equivalent and yield strength of Grade 70 push required preheat upward, particularly for thicker sections. AWS D1.1:2025 preheat tables reflect the steel's susceptibility to hydrogen-assisted cold cracking. For sections above 1-1/2 in [38 mm], preheat in the range of 200°F [95°C] or higher is common depending on process and heat input. Always calculate or look up preheat for the specific thickness and base metal specification.
Where does A572 Grade 70 fall short of A514 in terms of welding restrictions?
A514 is a quenched-and-tempered steel with yield strengths of 90–100 ksi — a full strength tier above A572 Grade 70. A514 is explicitly excluded from the prequalified base metal list and requires a PQR. A572 Grade 70, by contrast, is a normalized or as-rolled steel produced to a composition limit, and its welding, while demanding, does not carry the same heat input sensitivity as a Q&T microstructure.