Welding Wire 101: Functions, Types, and Features

The Role of Welding Wires

Welding wires are the primary welding materials used in submerged arc welding, gas shielded welding, electroslag welding, and gas welding. They are mainly used for filling metal or for conducting welding current. Additionally, at times, alloying elements are transitioned to the weld seam through the welding wire. For self-shielded flux-cored welding wires, they also play a role in protection, deoxidation, and denitration during the welding process.

Classification and Characteristics of Welding Wires

There are many classification methods for welding wires. They can be categorized into solid wires and flux-cored wires based on their structural shape. Based on the welding process, they can be classified as submerged arc welding wires, gas shielded welding wires, electroslag welding wires, hardfacing welding wires, and plasma transferred arc welding wires.

Furthermore, based on the material of the base metal, they can be classified as carbon steel welding wires, low-alloy steel welding wires, stainless steel welding wires, cast iron welding wires, and non-ferrous metal welding wires.

Currently, the most commonly used classification methods are based on structural shape and welding process.

Classification and Characteristics of Solid Wires

Solid wires are the most commonly used welding wires, produced by processing hot-rolled wire rods through drawing. To prevent rusting, the surface of the welding wire (except for stainless steel welding wires) needs special treatment. Currently, the primary method is copper plating, including electroplating, copper immersion, and chemical copper plating.

Solid wires include welding wires used for submerged arc welding, electroslag welding, CO2 gas shielded welding, argon arc welding, gas welding, and hardfacing. The classification and application characteristics of solid wires are outlined in Table 3-1.

Table 3-1 Classification and Application Characteristics of Solid Welding Wires

ClassificationSubclassificationCharacteristics
Submerged arc welding and electroslag welding wiresWelding wire for low carbon steelFor submerged arc welding and electroslag welding, high current is required, so coarse welding wire with a diameter of 3.2 to 6.4mm is used.
Welding wire for low alloy high strength steel
Welding wire for Cr-Mo heat-resistant steel
Welding wire for low temperature steel
Welding wire for stainless steel
Welding wire for surface claddingDue to the high carbon or alloy content, welding wire is difficult to process and manufacture. Currently, it is mainly produced in small batches using the liquid metal casting and drawing method.
Gas shielded welding wiresTIG welding wireGenerally, no filler wire is added. For manual feeding, the wire is cut into specific lengths, while for automatic feeding, spooled wire is used.
MIG/MAG welding wireMainly used for welding low alloy steel, stainless steel, etc.
CO2 welding wireThe welding wire composition should contain a sufficient amount of deoxidizers such as Si, Mn, Ti, etc. Insufficient alloy content and deoxidation can lead to the formation of porosity in the weld, resulting in a significant decrease in the mechanical properties of the weld (especially toughness).
Self-shielded welding wireIn addition to increasing the content of C, Si, and Mn in the welding wire, strong deoxidizing elements such as Ti, Zr, Al, Ce, etc., should also be added.

(1) Welding Wires for Gas Shielded Welding

The welding methods for gas shielded welding include non-melting electrode inert gas shielded welding, abbreviated as TIG welding; melting electrode inert gas shielded welding, abbreviated as MIG welding; and melting electrode active gas shielded welding, abbreviated as MAG welding.

Inert gases mainly use Ar, while active gases mainly use CO2. Pure Ar is used for TIG welding; MIG welding generally uses Ar+2%O2 or Ar+5%CO2; and for MAG welding, CO2, Ar+CO2, or Ar+O2 are used. When welding with pure CO2, there is more spattering, poor appearance and forming of the weld bead, and it is difficult to operate when welding thin plates. To improve the process performance of CO2 welding, generally, a mixed gas of Ar+CO2 is used.

(2) Welding Wires for Submerged Arc Welding

Welding wires for submerged arc welding are mainly used as filler metals. According to the different chemical compositions of the welding wires, they can be roughly divided into low carbon steel welding wires, high-strength steel welding wires, Cr-Mo heat-resistant steel welding wires, low-temperature steel welding wires, stainless steel welding wires, and welding wires for surface buildup.

(3) Welding Wires for Electroslag Welding

Electroslag welding is mainly used for welding low carbon steel, 490MPa and 590MPa grade high-strength steel, and chromium-molybdenum heat-resistant steel. Therefore, the corresponding welding wires for electroslag welding are only low carbon steel welding wires, high-strength steel welding wires, and chromium-molybdenum heat-resistant steel welding wires. The composition of welding wires for electroslag welding is mainly filler metal.

(4) Welding Wires for Surface Buildup

Welding wires for surface buildup include corrosion-resistant buildup welding wires and wear-resistant buildup welding wires, such as low-alloy steel welding wires, stainless steel welding wires, and hard alloy welding wires.

(5) Solid Welding Wires for Self-shielded Welding

Utilize the alloy elements contained in the welding wire to deoxidize and denitrate during the welding process, to eliminate the adverse effects of oxygen and nitrogen entering the weld pool from the air. Therefore, in addition to increasing the content of C, Si, and Mn in the welding wire, strong deoxidizing elements such as Ti, Zr, Al, and Ce are also added.

Classification and Characteristics of Flux-cored Welding Wires

Flux-cored welding wire is a welding wire that encapsulates flux powder in a thin steel strip, which is then processed into different cross-sectional shapes through rolling and drawing. Flux-cored welding wire is also known as powder-core welding wire, tubular welding wire, or folded welding wire, and is used for gas shielded welding, submerged arc welding, and self-shielded welding, making it a promising welding material.

The function of flux-cored welding wire powder is similar to the flux coating of welding rods. The difference lies in the fact that the flux coating of the welding rod is applied to the outer layer of the welding core, while the powder of the flux-cored welding wire is encapsulated within the core of the wire. Flux-cored welding wire can be supplied in spool form, making it easy to achieve mechanized welding.

Flux-cored welding wires can be used as welding materials for both melting electrodes (MIG, MAG) and non-melting electrodes (TIG) gas shielded welding.

The classification of flux-cored welding wires is complex. Based on the structure of the welding wire, flux-cored welding wires can be divided into seamed welding wires and seamless welding wires. Seamless welding wires can be copper-plated, with good performance and low cost, and have become the direction for future development.

① Classified by whether external shielding gas is used, flux-cored welding wires can be divided into self-shielded (without external shielding gas) flux-cored welding wires and gas-shielded (with external shielding gas) flux-cored welding wires.

The process performance and impact resistance of the weld metal of gas-shielded flux-cored welding wires are superior to self-shielded flux-cored welding wires, but self-shielded flux-cored welding wires have certain wind resistance and are more suitable for outdoor or high-rise structural site use.

② Classified by the cross-sectional structure of the flux-cored welding wire. The cross-sectional shape of the flux-cored welding wire has a significant impact on the welding process performance and metallurgical properties.

According to the different cross-sectional shapes, flux-cored welding wires can be divided into seamed flux-cored welding wires and seamless flux-cored welding wires. Seamed flux-cored welding wires can be divided into simple cross-section O-shape and complex cross-section folded shapes, which can further be categorized into plum blossom shape, T-shape, E-shape, and middle filling shape, etc.

The cross-sectional shapes of flux-cored welding wires are shown in Figure 3-2.

Figure 3-2 Cross-sectional diagram of flux-cored welding wire
Figure 3-2: Cross-sectional diagram of flux-cored welding wire

Generally speaking, the more complex and symmetrical the cross-sectional shape of flux-cored welding wire, the more stable the arc and the more thorough the metallurgical reaction and protective effect of the flux core. However, as the diameter of the welding wire decreases, this difference gradually diminishes. When the wire diameter is less than 2mm, the influence of the cross-sectional shape becomes less significant.

Currently, for small diameters (not exceeding 2.0mm), flux-cored welding wires generally adopt an O-shaped cross-section, while for large diameters (≥2.4mm), flux-cored welding wires mostly use complex folded cross-sections such as E-shaped and T-shaped.

Seamless flux-cored welding wires are all O-shaped, allowing for surface copper plating, excellent rust resistance, prevention of moisture absorption by flux, and suitability for long-distance wire feeding, expanding their range of use.

③ By classifying the filling powder in the core, flux-cored welding wires can be divided into two types: flux powder type and metal powder type. Flux powder type flux-cored welding wires incorporate powders such as slag formers, deoxidizers, arc stabilizers, alloying agents, and iron powders.

During the welding process, these powders form slag, which can improve the welding process and the mechanical properties of the weld metal, hence they are also known as slag-forming flux-cored welding wires. Based on the type of slag formers and the basicity of the slag, they are further categorized as titanium type (also known as rutile type), titanium-calcium type (also known as rutile-basic type), and calcium type (basic type).

Self-shielding flux-cored welding wires also belong to the flux powder type. Metal powder type flux-cored welding wires contain almost no slag formers; they mainly consist of metal powders (such as iron powders) and a small amount of arc stabilizers. Their welding characteristics are similar to solid wires, but with higher current density.

They produce very little slag during welding, reducing spatter significantly and increasing the deposition rate noticeably. Compared to flux powder type flux-cored welding wires, their slag production is reduced by over 60%, allowing for continuous multi-pass welding without slag removal, improved crack resistance, and deposition efficiency.

Additionally, they produce less welding fumes, reducing to the level of solid wires, approximately half that of flux powder type flux-cored welding wires, and they exhibit superior surface formation in the weld compared to solid wires.

Currently, in China, the product varieties of flux-cored welding wires mainly consist of titanium type gas-shielded, basic gas-shielded, and hardfacing (mainly submerged arc hardfacing) three major series, suitable for welding carbon steel, low-alloy high-strength steel, stainless steel, etc., generally meeting the welding requirements for typical engineering structures.

In terms of product quality, there has been a breakthrough in the product quality of E71T-1 titanium type gas-shielded flux-cored welding wires used for welding structural steel, while the product quality of basic flux-cored welding wires still needs further improvement.

In gas-shielded arc welding, the use of flux-cored welding wires instead of solid wires represents a significant technological advancement. The similarities between flux-cored welding wires and solid wires are as follows:

  1. Compared to manual shielded metal arc welding, high-efficiency welding is achievable.
  2. Easily adaptable for automated and mechanized welding.
  3. The arc is visible, making it easy to control the welding process.
  4. Weaker wind resistance, with a risk of poor protection.

Compared to solid wires, flux-cored welding wires have the following characteristics:

  1. Flux-cored welding wires have a higher deposition rate than solid wires, especially in all-position welding, allowing for the use of high currents, thus improving welding efficiency.
  2. Strong adaptability for welding various types of steel. Adjusting the composition and proportion of the flux is extremely convenient and easy, enabling the provision of the required chemical composition for the weld metal.
  3. Soft arc with minimal spatter.
  4. Excellent welding characteristics, resulting in flat and aesthetically pleasing weld beads.
  5. Increased generation of welding fumes.
  6. When slag is produced, it must be removed.

Compared to solid wires, flux-cored wires have been highly regarded due to their good welding characteristics, low spatter, aesthetically pleasing weld bead formation, and the ability to use high currents for all-position welding, resulting in high deposition efficiency. In recent years, the use of fine-diameter flux-cored welding wires for all-position welding has increased sharply.

These wires are mostly of the titanium slag type and exhibit excellent welding process performance. Many problems that were difficult to solve with solid wires in the past, such as high spatter, poor formation, and hard arcs, have been eliminated when using fine-diameter flux-cored welding wires.

Due to the high efficiency and good welding process performance of flux-cored welding wires, they have received high praise from various industries and are considered the most promising welding materials.

Flux-cored welding wires can be used for welding low carbon steel, low-alloy high-strength steel, atmospheric corrosion-resistant steel, Cr-Mo heat-resistant steel, low-temperature steel, stainless steel, and for hardfacing. Additionally, there are flux-cored welding wires specifically designed for gas-electric welding, mainly used for welding low carbon steel and 490MPa and 590MPa grade high-strength steel.

A comparison of the welding performance of various flux-cored welding wires is shown in Table 3-2.

Table 3-2: Comparison of Welding Performance of Various Flux-Cored Wires

projectType of fill powder
Titanium typeCalcium titanium typeCalcium oxide-calcium fluoride typeMetal powder type
Welding PerformanceWeld AppearanceBeautifulFairSlightly poorFair
Weld ShapeSmoothSlightly convexSlightly convexSlightly convex
Arc StabilityGoodGoodGoodGood
Droplet TransitionFine droplet transitionDroplet transitionDroplet transitionDroplet transition (short-circuit transition at low current)
SpatterFine, very fewFine, fewLarge, manyFine, very few
Slag CoverageGoodSlightly poorPoorVery little slag
Slag RemovalGoodSlightly poorSlightly poorSlightly poor
Smoke EmissionFairSlightly moreManyFew
Weld Joint PerformanceNotch ToughnessFairGoodExcellentGood
Diffusible Hydrogen Content (mL/100g)2~102~61~41~3
Oxygen Mass Fraction (10-6)600~900500~700450~650600~700
Crack ResistanceFairGoodExcellentExcellent
X-ray InspectionGoodGoodGoodGood
Porosity ResistanceSlightly poorGoodGoodGood
Deposition Efficiency (%)70~8570~8570~8590~95

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