Can A36 steel be welded?
Yes. A36 is the reference weldable structural steel: E7018, ER70S-6 or E71T-1 under AWS D1.1, no preheat to 20 mm (3/4"), more as plate gets thicker.
ASTM A36 is the plain carbon structural steel that most welding codes, welder tests and fabrication shops are built around. It is specified by strength, 250 MPa (36 ksi) minimum yield and 400-550 MPa (58-80 ksi) tensile, with a chemistry limit of about 0.25-0.29% carbon depending on product and thickness. At that level it welds with every common process: SMAW with E7018 (or E6010 and E6011 for roots and dirty work), GMAW with ER70S-6, FCAW with E71T-1, and submerged arc with a 70 ksi flux-wire combination. It is a prequalified base metal under AWS D1.1, so a shop can weld it to a prequalified WPS without procedure qualification testing, provided the joint details, filler and preheat stay within the code.
Preheat depends on thickness and on the hydrogen level of the process, and the D1.1 minimum preheat table is the reference. With low-hydrogen processes (E7018, GMAW, FCAW, SAW), no preheat is required up to 20 mm (3/4") as long as the steel is above 0 °C (32 °F); about 10 °C (50 °F) applies from 20 to 38 mm (3/4-1.5"), 66 °C (150 °F) from 38 to 65 mm (1.5-2.5"), and 107 °C (225 °F) above that. Non-low-hydrogen stick electrodes such as E6010 need higher preheats on thick material. Preheat is set by the thickest part in the joint, and below 0 °C the steel is warmed to at least 21 °C (70 °F) before welding. Post-weld heat treatment is not required for strength; a stress relief at 595-650 °C (1100-1200 °F) is used when a weldment will be machined to tight tolerances.
The problems on A36 come from what surrounds the steel. Mill scale, rust, oil and primers cause porosity with GMAW and must be ground or blasted off near the joint; galvanized A36 must have the zinc removed from the joint area, both for weld quality and to avoid zinc fume. Heavy plate welded in T and corner joints can suffer lamellar tearing when the weld pulls through the plate thickness, which joint design and, if needed, through-thickness-tested plate avoid. Chemistry varies more than the name suggests: A36 plate is often dual-certified to A572 Grade 50, and the heaviest plates allow up to 0.29% carbon, so check the mill cert when welding thick, restrained joints. For thin sheet and long weldments, distortion, not metallurgy, sets the procedure.
Welding for A36 parts: where to send them
What to specify
- Code and WPS: AWS D1.1, prequalified or qualified WPS, and welders qualified to it; CWI inspection where the contract requires it
- Filler: E7018 (AWS A5.1), ER70S-6 (AWS A5.18), E71T-1 (AWS A5.20), or a 70 ksi submerged-arc combination (AWS A5.17)
- Weld symbols per AWS A2.4, with CJP or PJP groove welds and fillet sizes called out
- Minimum preheat by the thickest member per the D1.1 table: with low-hydrogen processes none to 20 mm (3/4"), 10 °C (50 °F) to 38 mm (1.5"), 66 °C (150 °F) to 65 mm (2.5"), 107 °C (225 °F) above
- Surface prep: remove mill scale, rust, oil, paint and galvanizing within 25 mm (1") of the joint; weld-through primer only if the WPS covers it
- Inspection: visual to D1.1 acceptance criteria, UT (or RT) on CJP groove welds as the contract requires, MT on critical fillets
- Stress relief at 595-650 °C (1100-1200 °F) before finish machining if the weldment carries precision features
Pitfalls
- Ignoring preheat on thick base plates and column bases: a 50 mm (2") plate welded cold, especially with damp electrodes, can crack at the toe
- MIG welding over mill scale or galvanizing: porosity, lack of fusion and zinc fume; grind or blast first
- Lamellar tearing under large welds on thick plate loaded through its thickness; detail the joint to avoid it
- Assuming all A36 has the same chemistry: dual-certified and heavy plate can run higher carbon and strength; check the cert on thick joints
- Distortion on thin sheet and long beams from unbalanced welding: sequence, fixture, and avoid oversized welds
- Machining features before welding and expecting them to stay in tolerance
Frequently asked questions
- What welding rod is used for A36 steel?
- E7018 is the standard stick electrode, with E6010 or E6011 for root passes and rusty or painted work. ER70S-6 is the usual MIG wire and E71T-1 the usual flux-core wire. All are 70 ksi (480 MPa) class fillers that overmatch A36.
- Does A36 need preheat before welding?
- Not up to 20 mm (3/4") thick if the steel is above 0 °C (32 °F) and a low-hydrogen process is used. Thicker plate needs the AWS D1.1 minimums: about 10 °C (50 °F) to 38 mm, 66 °C (150 °F) to 65 mm and 107 °C (225 °F) above.
- Is A36 the same as 1018 for welding?
- Both weld easily. A36 is a structural plate and shape specification set by strength, with looser chemistry and up to 0.29% carbon in heavy plate; 1018 is a chemistry grade usually bought as cold-drawn bar. A36 is the one listed as a prequalified base metal under AWS D1.1.
