Look up the minimum preheat and interpass temperature for welding reinforcing steel bars per AWS D1.4/D1.4M:2018 Table 7.2. Enter the carbon equivalent (CE) and select the bar size.
Applies to SMAW with low-hydrogen electrodes, GMAW, FCAW, and GTAW. All processes share the same requirements.
SMAW with low-hydrogen electrodes, GMAW, FCAW, or GTAW. When welding rebar to structural steel, also check D1.1 preheat requirements and use the higher value.
| Carbon Equivalent (CE) | Bar Size | °F | °C |
|---|---|---|---|
| Up to 0.40 | Up to #11 [#36] | None | None |
| Up to 0.40 | #14 and #18 [#43 and #57] | 50 | 10 |
| 0.40 to 0.45 | Up to #11 [#36] | None | None |
| 0.40 to 0.45 | #14 and #18 [#43 and #57] | 50 | 10 |
| 0.45 to 0.55 | Up to #6 [#19] | None | None |
| 0.45 to 0.55 | #7 to #11 [#22 to #36] | 50 | 10 |
| 0.45 to 0.55 | #14 to #18 [#43 to #57] | 200 | 90 |
| 0.55 to 0.65 | Up to #6 [#19] | 100 | 40 |
| 0.55 to 0.65 | #7 to #11 [#22 to #36] | 200 | 90 |
| 0.55 to 0.65 | #14 to #18 [#43 to #57] | 300 | 150 |
| 0.65 to 0.75 | Up to #6 [#19] | 300 | 150 |
| 0.65 to 0.75 | #7 to #18 [#22 to #57] | 400 | 200 |
| Over 0.75 | Up to #6 [#19] | 300 | 150 |
| Over 0.75 | #7 to #18 [#22 to #57] | 500 | 260 |
Rebar to structural steel: When steel reinforcing bars are welded to structural steel, the preheat requirements of D1.1 also apply. Use the higher preheat requirement of D1.4 Table 7.2 and D1.1 Table 5.11. Extreme caution is needed when welding rebar to quenched and tempered steels.
Cold weather: When the base metal is below 32°F (0°C), preheat to at least 70°F (20°C) and maintain during welding.
Cooling: After welding, bars must cool naturally to ambient temperature. Accelerated cooling is prohibited.
Carbon equivalent: CE = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15. When chemical composition is not available, see D1.4 Clause 1.5.4. Use our Carbon Equivalent Calculator to compute CE from MTR data.
D1.4 uses the standard IIW carbon equivalent formula: CE = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15. This value determines the hardenability of the reinforcing steel and directly maps to the preheat requirement in Table 7.2. Mill test reports (MTRs) typically include CE, or you can calculate it from the listed chemical composition.
Table 7.2 covers SMAW with low-hydrogen electrodes, GMAW, FCAW, and GTAW. All four processes share the same preheat requirements — unlike D1.1, D1.4 does not differentiate preheat by welding process. Non-low-hydrogen SMAW is not addressed in this table.
When reinforcing bars are welded to structural steel, both D1.4 Table 7.2 and D1.1 Table 5.11 apply. Use the higher preheat requirement of the two tables. If the structural steel requires a higher preheat than the rebar, that higher temperature governs. Extreme caution is needed when welding rebar to quenched and tempered steels.
When Table 7.2 shows 'none', no minimum preheat temperature is required for that combination. However, if the base metal temperature is below 32°F (0°C), you must still preheat to at least 70°F (20°C) and maintain that temperature during welding. After welding, bars must cool naturally — accelerated cooling is prohibited.