Welding Rod Types: A Comprehensive Guide

Welding rods can be classified according to various methods.

Classification by Application

In China, there are two current methods for classifying welding rods. One is specified by national standards, and the other is determined by the “Sample of Welding Material Products” compiled by the former Ministry of Machinery Industry.

There is no essential difference between the two; the difference lies in their expression. The former is represented by model numbers, while the latter is represented by commercial brand names. The latter is more detailed and has been in use for a long time, appearing frequently in many technical documents and literature.

According to national standards, welding rod models are divided into 7 categories, while welding rod brands are classified into 10 categories based on their applications, as shown in Table 2-9.

Table 2-9 Classification and Designation of Welding Rod Types and Grades

Welding rod designationWelding rod designation
Welding rod category (classified by chemical composition)Welding rod category (classified by application)
National Standard NumberNameDesignationCategoryNameDesignation
LettersChinese characters
GB/T 5117-2012Non-alloy Steel and Fine Grain Steel Welding RodsE1Structural Steel Welding RodsJ
GB/T 5118-2012High Strength Steel Welding RodsE1Structural Steel Welding RodsJ
2Molybdenum and Chromium Molybdenum Heat-Resistant Steel Welding RodsR
3Low Temperature Steel Welding RodsW
GB/T 983-2012Stainless Steel Welding RodsE3Stainless Steel Welding RodsG
4A
GB/T 984-2001Hardfacing Welding RodsED5Hardfacing Welding RodsD
GB/T 10044-2006Cast Iron Welding RodsEZ6Cast Iron Welding RodsZ
7Nickel and Nickel Alloy Welding RodsNi
GB/T 3670-1995Copper and Copper Alloy Welding RodsTCu8Copper and Copper Alloy Welding RodsT
GB/T 3669-2001Aluminum and Aluminum Alloy Welding RodsE9Aluminum and Aluminum Alloy Welding RodsL
10Special Purpose Welding RodsTS

Various types of welding rods can be further divided into several subcategories based on their main properties. For example, low-alloy steel welding rods can be divided into low-alloy high-strength steel welding rods, low-temperature steel welding rods, heat-resistant steel welding rods, and welding rods for corrosion-resistant steel in seawater. Some welding rods can serve multiple purposes.

Classification by Slag Characteristics

The main classification is based on the basicity of the flux, which is the ratio of alkaline oxides to acidic oxides in the flux. Welding rods are divided into two major categories: acidic and alkaline.

(1) Acidic Welding Rods

The flux contains a large amount of acidic oxides such as SiO2, TiO2, and a certain amount of carbonates. The basicity B of the flux is less than 1. Acidic welding rods have good welding process performance and can be used with both AC and DC power sources, abbreviated as AC/DC. The arc is soft, with minimal spattering, good slag fluidity, easy slag removal, and an aesthetically pleasing weld appearance.

However, due to the presence of a significant amount of silicates, iron oxides, and titanium oxides in the flux, the oxidizing nature is strong, resulting in higher alloy element burn-off, leading to lower plasticity and toughness of the deposited metal.

The intense oxidation of carbon during welding causes boiling of the weld pool, facilitating the escape of gases, thus preventing the formation of pores caused by rust, oil, and water. Acidic welding rods include titanium-type, titanium-calcium type, ilmenite type, and iron oxide type welding rods.

(2) Alkaline Welding Rods

The flux contains a large amount of alkaline slag-forming substances such as limestone and fluorite, as well as a certain amount of deoxidizers and alloying agents. These welding rods primarily rely on carbonates (e.g., CaCO3 in limestone) to decompose into CO2 as a shielding gas.

In the arc column atmosphere, the partial pressure of hydrogen is low, and the fluorite in the flux combines with hydrogen at high temperatures to form hydrogen fluoride (HF), thereby reducing the hydrogen content in the weld. Alkaline fluxes contain a high amount of CaO, providing strong desulfurization capability and good resistance to hot cracking in the deposited metal.

Due to the low oxygen and hydrogen content in the weld metal, and fewer non-metallic inclusions, it exhibits higher plasticity, toughness, and better resistance to cold cracking. However, due to the high content of CaF2 in the flux affecting gas ionization, alkaline welding rods generally require the use of DC power sources with reverse polarity for welding. Only when stabilizers are added to the flux can they be welded using AC power sources.

Alkaline (low hydrogen) welding rods are generally used for critical welding structures, such as those subjected to dynamic loads or with high rigidity, due to the excellent mechanical properties of the weld metal, especially its high impact toughness.

However, their drawback is a tendency to produce porosity during welding, and they are sensitive to oil, water, and rust. Preheating at high temperatures (300-450°C) is required before use, and their slag removal performance is relatively poor.

Table 2-10 provides a comparison of the process performance of these two types of welding rods, which should be carefully considered during application.

Acidic Welding RodAlkaline Welding Rod
①Strong complexity of flux composition①The reducing property of the flux composition is strong.
②Not highly sensitive to moisture or rust, the welding rod can be used without baking if not damp, otherwise, it should be baked at 150-200°C for 1 hour before use②It is highly sensitive to water and rust, requiring the welding rod to be preheated at 300-400℃ for 1-2 hours before use.
③Arc can be moved, suitable for both AC and DC welding③Due to the fluoride content in the flux, it deteriorates the stability of the electric arc, requiring the use of direct current for welding. Only when arc stabilizers are added to the flux can it be used with both direct and alternating currents.
④Requires higher welding current④The welding current is relatively small, about 10% smaller than that of the same specification acidic welding rod.
⑤Suitable for long arc operation⑤Short arc operation is necessary, otherwise, it is prone to causing porosity.
⑥Poor transition effect for alloying elements⑥The transition effect of alloy elements is good.
⑦Good weld bead formation, except for ferroalloy types, shallow penetration⑦The weld bead formation is good, easily achieving a higher build-up and deeper penetration.
⑧Glassy slag structure⑧The slag structure is crystalline.
⑨Relatively easy slag removal⑨The first layer of slag removal in the groove is relatively difficult, while subsequent layers are easier to remove.
⑩Average weld and low-temperature impact performance⑩The weld bead often exhibits higher low-temperature impact toughness.
⑪Except for ferroalloy types, relatively poor crack resistance⑪ It has good crack resistance.
⑫High hydrogen content in the weld, prone to hydrogen-induced cracking, affecting ductility⑫ The hydrogen content in the weld bead is low.
⑬Low smoke and fumes during welding operations⑬ There is a relatively high amount of smoke and dust during welding.

Classification by Main Flux Components

Welding rods can be classified into several types based on the main components of the flux, as listed in Table 2-11.

Types of Flux CoatingMain Components of Flux Coating (by mass fraction)Types of Current
Titanium typeTitanium dioxide ≥35%Direct current (DC) or alternating current (AC)
Titanium-calcium typeTitanium dioxide above 30%, calcium and magnesium carbonates below 20%Direct current (DC) or alternating current (AC)
Ilmenite typeIlmenite ≥30%Direct current (DC) or alternating current (AC)
Iron oxide typeSignificant amounts of iron oxide and a considerable amount of manganese iron deoxidizerDirect current (DC) or alternating current (AC)
Cellulose typeOrganic materials above 15%, titanium dioxide around 30%Direct current (DC) or alternating current (AC)
Low hydrogen sodium typeSodium, calcium, magnesium carbonates, and fluoriteReverse polarity for direct current (DC)
Low hydrogen potassium typePotassium, calcium, magnesium carbonates, and nitrateAlternating current (AC) or direct current (DC)
Graphite typeSignificant amount of graphiteDirect current (DC) or alternating current (AC)
Basic (alkaline) typeChlorides and fluoridesDirect current (DC)

Due to differences in flux formulations, the slag characteristics, welding process performance, and weld metal properties can vary significantly among different types of flux. Even for the same type of flux, significant differences in welding process performance can arise due to variations in flux composition and proportions used by different manufacturers.

For example, low hydrogen fluxes are divided into low hydrogen potassium type and low hydrogen sodium type based on the use of different stabilizers and binders. In terms of welding power sources, the former can be used with both AC and DC, while the latter requires DC reverse polarity. Table 2-12 lists the types and main characteristics of welding rod fluxes.

Table 2-12: Types of Welding Rod Coatings and Their Main Characteristics

Serial NumberCoating TypesTypes of Power SupplyMain Characteristics
0Unspecified TypeUnspecifiedSome welding rods use a new slag system composed of zirconium oxide, hematite, etc., which has not yet formed a series.
1Titanium Oxide TypeDC (Direct Current), AC (Alternating Current)Containing a large amount of titanium oxide, the welding rod exhibits excellent process performance, stable arc, easy re-ignition, minimal spattering, shallow penetration, good slag coverage, easy slag removal, and exceptionally aesthetic weld ripples. It is suitable for all-position welding, especially for thin plate welding. However, the weld’s plasticity and crack resistance are slightly inferior. Depending on variations in the dosage of potassium, sodium, and iron powder in the coating, it is classified as high-titanium potassium type, high-titanium sodium type, or iron powder titanium type.
2Titanium Calcium TypeDC,ACWith a titanium dioxide content of over 30% and a carbonate content of calcium and magnesium below 20%, the welding rod demonstrates good process performance, good slag fluidity, moderate penetration, stable arc, aesthetically pleasing welds, easy slag removal, and is suitable for all-position welding. For instance, J422 belongs to this type. It is currently the most widely used type of welding rod for carbon steel.
3Titanium Iron Ore TypeDC,ACContaining at least 30% titanium iron ore in the coating, the welding rod has a fast melting speed, good slag fluidity, deep penetration, easy slag removal, neat weld ripples, stable arc, and good performance for flat and horizontal fillet welding, albeit slightly inferior for vertical welding. The weld exhibits good crack resistance.
4Iron Oxide TypeDC,ACWith a high content of iron oxide and manganese deoxidizer in the coating, the welding rod has a large penetration, fast melting speed, higher welding productivity, stable arc, easy re-ignition, but is relatively challenging for vertical and overhead welding, with some spattering. The weld exhibits good resistance to hot cracking and is suitable for welding medium-thick plates, particularly suitable for outdoor operations. If a certain amount of iron powder is added to the coating, it becomes an iron powder iron oxide type.
5Cellulose TypeDC,ACContaining over 15% organic matter and around 30% titanium oxide, the welding rod exhibits good welding process performance, stable arc, strong arc force, deep penetration, minimal slag, and easy slag removal. It can be used for vertical down welding, deep penetration welding, or single-side welding for double-sided formation welding. It performs well for vertical and overhead welding and is suitable for welding thin plate structures, oil tank pipelines, vehicle bodies, etc.
6Low Hydrogen Potassium TypeDC,ACDepending on the variation in stabilizer and binder content in the coating, it is divided into high-cellulose sodium type (used with reverse polarity DC) and high-cellulose potassium type.
7Low Hydrogen Sodium TypeDCThe coating’s composition is primarily carbonate and fluorite. The welding rod needs to be baked at 300-400°C before use. It exhibits moderate welding process performance with a short arc operation and is suitable for all-position welding. The weld shows good crack resistance and comprehensive mechanical properties, making it suitable for welding critical structures. Depending on the dosage of stabilizer, iron powder, and binder in the coating, it is classified as low-hydrogen sodium type, low-hydrogen potassium type, or iron powder low-hydrogen type.
8Graphite TypeDC,ACContaining a large amount of graphite, it is typically used for cast iron or hardfacing welding rods. When used with low carbon steel cores, the welding process performance is relatively poor, with more spatter and greater smoke, and it is suitable for flat welding. When used with non-ferrous metal cores, its process performance can be improved, but the current should not be too high.
9Basic TypeDCContaining a large amount of chloride and fluoride, it is mainly used for aluminum and aluminum alloy welding rods. It has strong hygroscopicity and needs to be dried before welding. The coating has a low melting point and fast melting speed. When using a DC power supply, the welding process performance is relatively poor, requiring short arc operation, and the slag is corrosive, necessitating post-weld cleaning with hot water.

Classification based on the performance characteristics of welding rods

Welding rods can be classified based on their performance characteristics into low dust low toxicity rods, iron powder high efficiency rods, ultra-low hydrogen rods, vertical downward welding rods, base layer welding rods, cover welding rods, moisture-resistant welding rods, underwater welding rods, gravity welding rods, and horizontal welding rods.

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