Which base metal governs preheat when welding dissimilar metals under D1.1?

The more demanding base metal governs. Apply the preheat requirement of the higher-carbon-equivalent material to the entire joint — both sides. For a weld between A36 and A514, the A514 side dictates minimum preheat (often 200°F [95°C] or higher depending on thickness and heat input), even though A36 by itself would require little or no preheat at the same thickness.

Do you need a separate PQR for each dissimilar-metal combination?

Not necessarily. If both base metals fall within material groups covered by existing PQRs, and the filler metal is qualified for both, a new test coupon may not be required. If one base metal falls outside any qualified group, or the combination creates unusual metallurgical behavior — dilution issues with alloy steel, HAZ hardening from one side affecting the other — qualify a new coupon representing the actual combination.

What filler metal do you use for A36-to-A514 welds?

A low-hydrogen filler that satisfies the design requirement for the connection. Where the A514 side carries the design load, undermatching to A36-level UTS is not appropriate. AWS E11018-M-H4 or E12018-M-H4 per A5.5 is commonly specified for A514. Always confirm filler selection with the engineer of record — CVN requirements, heat input constraints, and service temperature affect the choice.

How does Table 6.6 apply when the two base metals are in different groups?

Each base metal must be within the qualified range from the PQR. The Table 6.6 row for base metal group or category applies to each side independently. If the combination puts one base metal outside the qualified envelope, the WPS is not supported. Either extend qualification through a new PQR coupon representing the actual combination, or split the joint into two WPSs with a butter-layer approach.

Dissimilar metal welding: writing the WPS under AWS D1.1

Welding A36 to A514 or mild steel to high-strength alloy requires a WPS that covers both base metals. Procedure qualification strategy under AWS D1.1:2025.

Most WPS work targets a single base metal: A36 to A36, A572 Gr. 50 to A572 Gr. 50. Production fab shops regularly encounter dissimilar-metal joints — base plates of A36 welded to A572 Gr. 50 beam webs, A514 crane girder flanges connected to mild-steel stiffeners, or high-strength gussets welded into standard W-shapes. The WPS for these joints requires deliberate decisions on preheat, filler metal, and procedure qualification that a single-base-metal WPS can gloss over.

Defining the dissimilar-metal case

Under AWS D1.1, a dissimilar-metal joint is any groove or fillet weld where the two base metals differ in grade, specification, material group, or strength level. The joint doesn't have to span exotic alloy families. A36-to-A572 Gr. 50 is the most common dissimilar structural joint and is usually straightforward — both are in low-carbon territory, preheat requirements are similar, and filler selection is simple. A36-to-A514 is more demanding: yield strength differs by nearly 50 ksi, carbon equivalent diverges, and HAZ hardenability on the A514 side requires careful preheat control.

The same principles apply across the spectrum. Recognize the dissimilar-metal condition early in WPS development rather than discovering it during a procedure review.

Preheat: apply the more demanding requirement

AWS D1.1 preheat requirements are base-metal-specific. The tables in Annex I and the body code give minimum preheat by material category and thickness. For a dissimilar joint, apply the more demanding preheat of the two base metals — across the entire joint, both sides.

If A514 Gr. Q requires 200°F (95°C) minimum preheat for a 1.25-in plate, that temperature applies to the A36 side as well. The joint is a single thermal unit during welding. Preheating only the A514 side to the required temperature while leaving the A36 side cold will not deliver the intended interpass temperature or slow the cooling rate adequately on the A514 HAZ.

Document the governing preheat on the WPS and note which base metal drives the requirement. That notation is a documentation aid for the welder, the inspector, and the auditor — it eliminates guesswork when the WPS is reviewed months after it was written.

For carbon equivalent calculations and preheat derivation, see carbon equivalent and preheat under AWS D1.1 and preheat and interpass temperature on a WPS.

Filler metal selection

Match to the design requirement, not just the lower base metal's strength. Where the higher-strength base metal carries the design load, undermatching to the lower base metal's UTS is a structural deficiency, not a conservative choice.

For A36-to-A514 joints in a load-carrying connection:

An E70XX filler matched to A36 (65 ksi minimum UTS) would undermatch the A514 side (nominal UTS 115–130 ksi depending on grade and thickness)
E11018-M-H4 or E12018-M-H4 per AWS A5.5 satisfies the A514 side; the resulting weld metal will overmatch A36, which is acceptable for most joint configurations
CVN toughness: check the design-basis temperature. Many A514 applications carry CVN requirements; the filler must match.

H4 or H8 designation is mandatory when any A514, A517, or other quenched-and-tempered high-strength alloy is in the joint — even if only one side is high-strength. See low-hydrogen electrode conditioning: H4, H8, H16 on a WPS for conditioning requirements.

Always confirm filler selection with the engineer of record. Filler choices for dissimilar joints sometimes require engineering analysis beyond what a standard WPS checklist covers.

Essential variables under Table 6.6

AWS D1.1:2025 Table 6.6 lists the essential variables for SMAW, SAW, GMAW, FCAW, and GTAW procedures. For dissimilar-metal joints, the rows that most often require attention:

Base metal group or category. Table 6.6 contains rows that trigger requalification when the base metal group changes. If the two base metals in a dissimilar joint are in different groups, the PQR must qualify both — either with a coupon that represents the combination, or with separate PQRs whose qualified ranges together cover both sides.

Base metal UTS range. Some essential variable rows tie qualification limits to the base metal's UTS or yield strength tier. A PQR coupon welded from A36 does not automatically cover A514; the strength tiers and HAZ thermal responses are categorically different.

Preheat and interpass temperature range. A PQR coupon welded at A36-level preheat (50°F/10°C) does not cover production conditions requiring A514-level preheat (200°F/95°C). The qualified preheat envelope must span the actual production preheat.

See AWS D1.1:2025 Table 6.6 explained for the full row-by-row breakdown and WPS essential variables vs. nonessential for how to classify each parameter on your WPS.

PQR strategy for dissimilar joints

Two approaches are available:

1. Qualify the actual combination. Weld a test coupon from production-representative material — one side A514, one side A36 — using the production process, filler, preheat, position, and heat input. Run tensile, bend, and CVN specimens. This is the clearest path for high-consequence joints.

2. Cover by analogy. If you hold separate PQRs whose qualified envelopes individually cover each base metal, and the combination doesn't create anomalous metallurgical behavior, the EOR may accept the combination without a new coupon. Get written acceptance before assuming this path is available. It isn't always, and the acceptance decision belongs to the engineer, not the fabricator.

For primary structural members under cyclic loading, option 1 is almost always the right call. A514's HAZ response is sensitive to heat input and preheat; coupon welding from production heat provides the most accurate mechanical test data. See what is a PQR and when does a PQR require requalification for the broader qualification framework.

How to write the WPS document

Identify both base metals explicitly:

Base Metal 1: ASTM A514, Gr. Q, 1.25 in [32 mm]
Base Metal 2: ASTM A36, 1.0 in [25 mm]
Governing preheat: A514 requirement, 200°F [95°C] minimum
Governing interpass max: 400°F [205°C] — A514 requirement
Filler: E11018-M-H4 per AWS A5.5
PQR support: PQR-07 (A514/A36 combination, 1.25 in plate)

Leave no ambiguity about which material is which, which requirement governs each essential variable, and which PQR supports the WPS. An auditor should be able to answer these questions from the WPS face alone without referencing external documents.

Common deficiencies found in dissimilar-metal WPSs during third-party audits:

WPS identifies only one base metal specification, treating the joint as single-material
Preheat on the WPS is listed at the lower base metal's requirement with no note that the higher controls
PQR support is from a single-base-metal coupon that doesn't represent the production combination
No H designation on the filler, despite one side being A514

Any of these will generate an audit finding. The WPS fix is straightforward; the repair of a hydrogen crack after the structure is erected is not.

High-strength-to-high-strength joints

The dissimilar case also arises between two high-strength steels — A572 Gr. 65 to A572 Gr. 50, or A709 Gr. 70W to A588. The principles are the same: use the more demanding preheat, ensure the filler satisfies the stronger base metal, and confirm PQR coverage spans both material tiers. For details on A514 and other quenched-and-tempered steels in structural applications, see high-strength steel WPS requirements for A514.

Manage procedure qualification for dissimilar joints alongside your full WPS library at wpswelding.com/pricing.

Rule library based on AWS D1.1:2025; verify against your governing edition.