AWS D1.1:2025 Table 6.9 organizes structural steel base metals into numbered groups by composition and strength tier. This classification directly controls WPS qualification scope: when a project uses a steel from a different group than the one in your PQR, you likely have a qualification gap. Understanding how the groups work — and where the boundaries are — is a daily reality for CWI and QC managers in structural fab.
Rule library based on AWS D1.1:2025; verify against your governing edition.
Why a base metal grouping system exists
Qualifying a separate PQR for every ASTM steel designation a shop might encounter would be unworkable. There are dozens of structural steel specifications, and many of them share nearly identical weldability characteristics.
Table 6.9 solves this by clustering steels with similar chemical composition and strength ranges into groups. A PQR run on one steel within a group qualifies a WPS for all steels in that group — reducing the total number of PQRs the shop must maintain while still ensuring meaningful qualification boundaries.
The grouping is not about equivalency of mechanical properties. It is about weldability: steels in the same group behave similarly enough in a PQR qualification test that the results are transferable.
Table 6.9 group structure
The groups progress from lower-strength carbon steels to high-strength quenched and tempered grades. Each group lists the ASTM designations that belong to it, with note columns for any restrictions or special conditions.
Group I covers common low-carbon structural steels. ASTM A36, A53, A500, A501, and A709 Grade 36 are Group I examples. Minimum yield strength is typically at or below 40 ksi. These steels have the lowest preheat requirements, the widest range of compatible filler metals, and full access to prequalified WPS provisions. The vast majority of general fab work runs on Group I steel. For a complete worked example, see the SMAW WPS for ASTM A36 walkthrough.
Group II covers the medium-strength structural steels that now dominate the market. ASTM A572 Grade 50, A992, and A709 Grade 50 are Group II examples. Minimum yield strength is typically in the 50–65 ksi range. A992 wide-flange shapes and A572 plates account for the majority of beams, columns, and connection plates in modern structural steel construction. FCAW and GMAW spray transfer on Group II material are the most common qualifications shops carry. See FCAW WPS for A992 wide-flange steel for a Group II example.
Group III covers higher-strength structural steels that require closer procedural attention. ASTM A913 Grades 65 and 70 fall in this tier. These grades are produced by quench and self-tempering (QST), which gives them high yield strength with good toughness — but also makes the heat-affected zone sensitive to excessive heat input and interpass temperature. Projects involving seismic demand-critical welds or AISC 341 applications frequently involve Group III steels.
Group IV covers quenched and tempered high-strength steels, primarily ASTM A514 (Fy = 90–100 ksi) and A517. These are the most demanding structural steels to weld:
- Prequalified WPS provisions do not apply — a PQR is required in all cases.
- Maximum interpass temperature limits are lower than for mild steel; overheating tempers the microstructure and degrades yield strength.
- Hydrogen cracking risk is highest; low-hydrogen processes and strict electrode storage are essential.
- CVN toughness testing is typically required for PQR qualification.
For a focused discussion of A514 qualification requirements, see WPS for high-strength A514 steel.
Base metal group as an essential variable
Table 6.6 of AWS D1.1:2025 lists the PQR essential variables for SMAW, SAW, GMAW, FCAW, and GTAW. Among those essential variables is the base metal group.
If you change from the group listed on the PQR to a different group, the PQR no longer supports the WPS for that new combination. You must either run a new PQR on the higher group or obtain a PQR that already covers it.
The most common gap in structural fab: a shop qualifies on Group I (A36) and later wins a project using Group II (A572 Grade 50 or A992). The processes, joint designs, and filler metals may be identical — but the base metal group change requires a new PQR before the existing WPS can be used.
For a broader view of essential variable categories and how Table 6.6 is organized, see AWS D1.1:2025 Table 6.6 explained.
Prequalified WPS and group eligibility
Prequalified WPS provisions under AWS D1.1:2025 apply only to steels listed in Table 6.9. Steels outside the table require qualification by testing (PQR route).
Within the table, Group IV steels (A514 and similar) are explicitly excluded from prequalified provisions — a PQR is required regardless of joint geometry or process. Groups I through III are eligible for prequalified WPS, subject to all other prequalified criteria being met (joint detail from Annex B, preheat per prequalified minimums, compatible filler metal, and process restrictions — GMAW short-circuit transfer is never prequalified regardless of base metal group).
Dissimilar base metal welds and Table 6.9
Welding two different base metals — a common scenario at column splices, beam-to-column connections, or heavy plate-to-tube joints — requires the WPS and PQR to address both base metals.
AWS D1.1 requires the PQR to be run on the higher-group material, or for the PQR to explicitly cover both base metals in the combination. The filler metal must be compatible with both base metals: when a Group I plate welds to a Group II wide-flange, the filler metal tensile strength must meet the requirements of the Group II steel.
Preheat and interpass temperature should follow the requirements of the higher-strength base metal in the joint. Do not relax preheat to the Group I requirement when the other member is Group II.
For additional detail on dissimilar base metal WPS documentation, see dissimilar base metal WPS under AWS D1.1.
Practical checks for audits and submittal packages
When preparing or reviewing WPS packages for an AISC certification audit or owner submittal:
- Look up every base metal on the WPS in Table 6.9 and confirm its group designation.
- Check the PQR test plate — the ASTM spec for the PQR coupon must be the same group as, or a higher group than, the base metals listed on the WPS.
- Flag all dissimilar welds — both base metals in the joint must appear on the WPS, with a single PQR or combination of PQRs that covers both groups.
- Identify Group IV steel early — if A514 appears anywhere in the project, confirm a PQR backs every WPS that covers it. No prequalified route exists.
- Check change orders — late material substitutions that swap steel grades between groups are a common source of after-the-fact qualification gaps.
A digital procedure library that stores the Table 6.9 group for each base metal on each WPS and automatically flags PQR coverage gaps eliminates most of these manual audit steps. See WeldingWPS pricing for how the platform structures this tracking.
Common mistakes
Using the A36 PQR on all carbon steel. A36 is Group I, not a universal structural steel. A572 Grade 50 is Group II. Inspectors and project managers sometimes treat these as interchangeable because both are "common structural steel" — but from a WPS qualification standpoint they are not.
Accepting a mill substitution without checking groups. A572 Grade 50 is often substituted for A36 by the steel mill (Grade 50 exceeds Grade 36 requirements). If the WPS only covers Group I, that substitution creates a qualification gap even though the actual steel is stronger. The QC manager should review any base metal substitution letter against the WPS coverage.
Failing to list the group on the WPS form. The WPS should explicitly call out the Table 6.9 group number alongside the ASTM designation. An auditor will check both, and a WPS that only says "ASTM A36" without the Group I designation misses a required documentation element in many audit protocols.