CO₂ Gas Shielded Welding Wire

A1: CO₂ gas shielded welding wire is a welding material used in conjunction with CO₂ gas shielded welding. It is divided into solid core and flux-cored. The solid core wire relies on CO₂ gas to isolate air and deoxidizing elements (manganese, silicon) to prevent oxidation; the flux-cored wire has a flux core inside, which can assist deoxidation and slag removal. It is mainly used for welding carbon steel and low-alloy steel.

A2: In structure, solid core wire is a solid metal wire, while flux-cored wire is a hollow wire with flux inside. In performance, solid core wire has high welding efficiency and low spatter, suitable for precision welding; flux-cored wire has strong deoxidation and slag removal ability, suitable for welding rusty or dirty base metals. In application, solid core wire is used for clean workpieces and indoor welding; flux-cored wire is used for outdoor, thick plates or workpieces with poor surface conditions.

A3: For ordinary carbon steel (such as Q235, tensile strength 375-500MPa), choose ER49-1 (tensile strength ≥490MPa); for low-alloy high-strength steel (such as Q355, tensile strength 490-630MPa), select ER50-6 (≥500MPa); for high-strength steel (such as Q460, tensile strength ≥460MPa), use ER55-G (≥550MPa) to ensure the joint strength is not lower than the base metal.

A4: The matching of welding parameters is the key: too high current or voltage will increase spatter; the wire feeding speed is unstable, causing arc fluctuation and spatter; the purity of CO₂ gas is insufficient (such as water content >0.05%), which will cause arc instability; the distance between the contact tip and the workpiece is too large (exceeding 15mm) will also increase spatter.

A5: Remove oil, rust, and paint on the surface of the base metal—mechanical methods (wire brush, grinder) can be used for rust removal, and organic solvents (acetone, gasoline) can be used for degreasing; for thick plates (thickness >10mm), preheat to 80-150℃ if necessary to prevent cold cracks; for flux-cored wire, the cleaning requirement can be appropriately reduced, but severe rust and oil stains must still be removed.

A6: Common defects include spatter (affecting appearance and increasing cleaning workload), pore (caused by moisture, oil stains, or insufficient gas protection), cold cracks (mostly in low-alloy steel thick plates, caused by high hydrogen content and large restraint intensity), and incomplete fusion (due to low heat input or fast welding speed).

A7: Adjust the current and voltage to the optimal matching range (the arc is stable, and the molten pool is quiet); use a welding wire with a smooth surface to ensure stable wire feeding; select high-purity CO₂ gas (purity ≥99.5%) and control the gas flow (15-25L/min for solid core wire); install a spatter inhibitor (anti-spatter spray) on the workpiece surface in advance.

A8: For solid core wire: when welding thin plates (thickness <3mm), the flow rate is 10-15L/min; for medium and thick plates (3-10mm), it is 15-20L/min; for outdoor or windy environments, increase by 5-10L/min. For flux-cored wire: the flow rate is generally 20-25L/min, because the flux core reaction requires better gas protection.

A9: Store in a dry and ventilated warehouse with a relative humidity not exceeding 60% and a temperature of 10-30℃; the packaging must be sealed to prevent moisture (moisture will cause pore and hydrogen-induced cracks); flux-cored wire should be used within 6 months after opening, and unused wire should be sealed and stored in a moisture-proof cabinet.

A10: For ordinary carbon steel structural parts, post-weld heat treatment is not required; for low-alloy steel thick plates (thickness>20mm) or workpieces with high restraint intensity, stress relief annealing at 550-650℃ can be performed to reduce residual stress and prevent cold cracks; for pressure vessels, heat treatment must be carried out according to design specifications.

A11: Not recommended. CO₂ is an oxidizing gas, which will cause chromium oxidation in stainless steel, reducing corrosion resistance; stainless steel welding requires inert gas (argon) or argon-carbon dioxide mixed gas, and special stainless steel welding wire should be used instead of ordinary CO₂ gas shielded welding wire.

A12: For thin plates (thickness 1-3mm), choose 0.8-1.0mm diameter wire; for medium plates (3-10mm), use 1.2-1.6mm wire; for thick plates (≥10mm), select 1.6-2.0mm wire. The wire diameter should also match the welding machine's current range—small-diameter wire is suitable for low current, and large-diameter wire requires high current.

A13: The wire feed wheel pressure is too high, causing the wire to deform; the wire feed hose is bent, blocked by debris, or the inner wall is worn; the welding wire diameter is uneven or there are burrs on the surface; the contact tip aperture is too small, which does not match the wire diameter.

A14: Tensile test: measure the tensile strength, yield strength, and elongation of the joint; impact test: detect the toughness of the weld (especially for low-temperature and high-strength steel); bending test: check the plasticity of the joint (bend 180° without cracks indicates good performance); hardness test: evaluate the hardness distribution of the weld and heat-affected zone.

A15: First, use a grinder to remove the 气孔 and the surrounding 5mm range of the weld; clean the repair area with acetone to remove oil and debris; adjust the welding parameters (increase gas flow, reduce current appropriately) and re-weld with low hydrogen type welding wire if necessary; after repair, check with penetration testing to ensure no residual 气孔.

A16: Use a wind shield to block the wind (wind speed >2m/s will destroy the gas protection); increase the CO₂ gas flow rate by 30-50% to compensate for the gas blown away by the wind; choose flux-cored wire, which has stronger anti-wind ability than solid core wire; avoid welding in open areas with strong winds, or choose indoor welding.

A17: Slightly damp solid core wire can be used after drying at 150-200℃ for 1-2 hours; severely damp wire (with obvious rust or white spots) may cause a large number of 气孔 and must be scrapped. Flux-cored wire is more sensitive to moisture—slightly damp wire needs to be dried at 250-300℃ for 2-3 hours, and severely damp wire is recommended to be scrapped.

A18: Use low-hydrogen type welding wire (such as ER50-6 with hydrogen content <5ml/100g); strictly clean the base metal to remove oil, rust, and moisture (sources of hydrogen); preheat the base metal to 80-150℃ (the thicker the plate, the higher the preheating temperature); perform post-weld heat treatment in time to eliminate hydrogen.

A19: High moisture content will cause hydrogen to enter the molten pool, leading to hydrogen-induced cracks; it will also cause arc instability, increase spatter, and make the weld surface rough; in severe cases, white smoke will appear during welding, and the weld will have dense 气孔. Therefore, the moisture content of CO₂ gas should be controlled below 0.05%.

A20: Choose solid core wire for clean workpieces, high appearance requirements, and indoor welding (such as automobile body welding); select flux-cored wire for workpieces with rust, oil stains, or outdoor welding (such as construction site steel structure); flux-cored wire is preferred for all-position welding of thick plates, while solid core wire is more cost-effective for flat welding of thin plates.

A21: In process, CO₂ gas shielded welding uses gas protection, while submerged arc welding uses flux protection; in efficiency, submerged arc welding is suitable for thick plate flat welding with high deposition rate, and CO₂ gas shielded welding is suitable for all-position welding with flexible operation; in application, CO₂ gas shielded welding wire is used for medium and thin plates and small structural parts, and submerged arc welding wire is used for large-scale equipment (such as pressure vessels, ship hulls).

A22: The welding speed should be matched with current and wire feeding speed: too fast will cause incomplete fusion and shallow penetration; too slow will lead to excessive heat input, large deformation, and coarse grains. For thin plates (1-3mm), the speed is 150-300mm/min; for medium plates (3-10mm), it is 100-200mm/min; for thick plates with grooves, it is 80-150mm/min.

A23: The welding speed is unstable (fast and slow); the wire feeding speed fluctuates, causing current changes; the welding gun moves unevenly (such as shaking); the groove is asymmetric, leading to uneven distribution of molten metal.

A24: Remove the oxide layer and spatter on the weld surface (mechanical grinding or pickling); paint the weld surface (such as anti-rust paint, galvanizing) to form a protective layer; for workpieces in humid environments, choose a welding wire with trace alloy elements (such as copper-plated wire, which has better corrosion resistance than ordinary wire).

A25: Choose a flux-cored welding wire with good flowability (such as E71T-8) or a solid core wire with special processing; use small-diameter wire (0.8-1.2mm) and low current to control the molten pool; adopt short-circuit transition mode to avoid molten metal sagging; maintain a stable welding gun angle (vertical or slightly inclined to the workpiece).

A26: First, check whether the flux core is evenly distributed (uneven flux core will cause local slag inclusions); increase the welding current appropriately to ensure the slag floats up; clean the slag between welding passes (especially for multi-layer welding); adjust the welding gun angle to avoid slag being trapped in the weld.

A27: Unopened welding wire can be stored for 2 years under standard storage conditions; opened solid core wire should be used within 1 year, and flux-cored wire should be used within 6 months (flux core is easy to absorb moisture); if the surface is oxidized (rusty) or the flux core is damped (hardened), the service life is terminated, and it should be scrapped.

A28: Use large-diameter wire (1.6-2.0mm) and high current (250-400A) to ensure penetration; adopt multi-layer multi-pass welding, and clean the slag between layers; preheat the base metal to 100-150℃ to reduce cold crack risk; use a U-shaped or X-shaped groove to increase the fusion area.

A29: Too long a stick-out (＞15mm) will cause unstable arc, increased spatter, and reduced penetration; too short (＜5mm) will cause the contact tip to be heated and worn, and the weld may be blocked by the tip. The appropriate stick-out is 10-15mm, which can ensure stable current transmission and gas protection.

A30: Ensure the groove is clean and free of oxides, rust, and oil stains; adjust the heat input (increase current or reduce welding speed) to ensure the base metal edge melts; maintain a proper welding gun angle (10-15° forward inclination) to direct the arc to the fusion zone; for thick plates, use a bevel to increase the fusion area.

A31: Copper-plated wire has a layer of copper on the surface, which improves electrical conductivity and reduces wire feeding resistance, suitable for high-speed wire feeding occasions (such as automobile production lines); non-copper-plated wire is cheaper, but has higher requirements for wire feeding equipment. Copper-plated wire has better corrosion resistance in storage, but the copper layer may fall off if the plating is poor, causing blockage.

A32: Check the surface: no rust, oil stains, or burrs, and the copper plating (if any) is uniform; check the diameter: use a caliper to measure, and the tolerance should be within ±0.02mm; for flux-cored wire, bend the wire to check if the flux core is continuous and free of powder leakage; perform a trial welding to observe arc stability, spatter, and weld formation.

A33: High humidity (＞70%) will cause the welding wire and base metal to absorb moisture, increasing the risk of 气孔 and hydrogen-induced cracks; it will also reduce the effectiveness of CO₂ gas protection (moisture in the air reacts with the gas). In high humidity environments, dehumidify the workplace, preheat the base metal, and use low-hydrogen welding wire.

A34: Select welding wire with low-temperature impact toughness (such as E81T1-Ni1, -40℃ impact energy ≥27J); choose flux-cored wire with better crack resistance than solid core wire; the welding wire should have low hydrogen content (＜5ml/100g) to prevent cold cracks; preheat the welding wire and base metal to room temperature (＞15℃) before use.

A35: Adopt symmetrical welding sequence (weld from both sides of the workpiece alternately) to balance stress; use intermittent welding instead of continuous welding to reduce heat accumulation; pre-set reverse deformation (calculate the deformation direction in advance and bend the workpiece oppositely); use fixtures with strong rigidity to clamp the workpiece during welding; cool the weld with a heat sink (such as a copper block) after welding.