Welding Rods Explained: Their Crucial Role in Fabrication

The electrode and welding wire are integral components of the entire welding circuit. During the welding process, the welding core and wire not only conduct electricity but also serve as an electrode that generates an arc with the workpiece. Additionally, the welding core and wire act as fillers for the metal.

The heat energy used to heat and melt the electrode (or welding wire) during welding includes resistance heat, arc heat, and chemical reaction heat (generally, chemical reaction heat accounts for only 1% to 3%). Under the influence of the welding heat source, the welding core or wire is heated and melted, forming droplets that enter the molten pool, combining with the molten base material to form the weld seam.

The welding materials used in submerged arc welding and electroslag welding are flux and welding wire (or strip electrode, strip). The role of the welding wire is equivalent to the welding core in the electrode, and the role of the flux is similar to the coating on the electrode. During the welding process, the function of the flux is to isolate air, protect the metal in the welding area from air intrusion, and carry out metallurgical treatments.

Therefore, the coordinated use of welding wire and flux is a crucial factor in determining the chemical composition and mechanical properties of the weld metal.

When using low-carbon steel welding wire for unprotected welding in the air, significant changes occur in the composition and properties of the weld metal compared to the base metal and welding wire. Due to the interaction of the molten metal with the surrounding air, the content of oxygen, nitrogen, and hydrogen in the weld metal increases significantly.

The nitrogen content can reach 0.105% to 0.218%, which is 20 to 50 times higher than the nitrogen content in the welding wire; the oxygen content can reach 0.14% to 0.72%, which is 7 to 35 times higher than the oxygen content in the welding wire. At the same time, alloy elements such as manganese and carbon decrease due to burning and evaporation.

At this point, the plasticity and toughness of the weld metal sharply decrease, but due to the strengthening effect of nitrogen, the change in weld strength is relatively small.

When using solid welding wire, the arc is unstable, resulting in a large number of gas pores in the weld. Therefore, this type of solid welding wire without protection has no practical value. The primary task of the coating on the electrode, flux, and shielding gas is to strengthen the protection of the metal in the welding area to prevent harmful effects from the air.

In order to improve the quality and performance of the weld metal, when manufacturing important metal structures using fusion welding methods, it is necessary to minimize the content of harmful impurities and the loss of alloy elements in the weld metal, ensuring that the weld metal has the appropriate chemical composition.

Most fusion welding methods have been developed and improved based on the concept of strengthening protection. The protection methods for fusion welding methods are outlined in Table 1-2.

Table 1-2: Protection methods for fusion welding

Protection MethodsWelding Methods
SlagShielded metal arc welding, submerged arc welding, electroslag welding, flux-cored arc welding with gas shielding
GasOxy-fuel welding, CO2 gas shielded welding, argon arc welding (TIG, MIG), mixed gas shielded welding (MAG)
Slag and GasShielded metal arc welding with gas-forming components, flux-cored arc welding with gas shielding
VacuumVacuum electron beam welding
Self-protectionWelding using self-shielded wires containing deoxidizers

The protective effects of various methods differ. Submerged arc welding utilizes flux and the slag formed after melting to isolate and protect the welding area from air. The protective effect of the flux depends on its composition and particle size. The protective effect of gas shielded welding depends on the properties and purity of the shielding gas.

In general, inert gases (such as argon and helium) have better protective effects and are suitable for welding alloy steel, chemically active metals, and their alloys.

The coating on welding rods and the core of welding wires generally consist of gas-forming agents, slag-forming agents, and ferroalloys, which collectively form a slag-gas combined protection during welding. The slag-forming agent melts to form slag, covering the surface of the molten droplets and pool to isolate them from the air.

After solidification, a slag shell forms on the weld, preventing the high-temperature weld metal from contacting the air. Upon heating, the gas-forming agent decomposes, releasing a large amount of gas to isolate the welding area from the air. The protective effect of welding rods and cored wires depends on the content of the protective materials, the nature of the slag, and the welding process parameters.

Self-shielded welding is a method of welding in the air using specially designed solid or flux-cored wires. It does not rely on mechanical isolation from the air to protect the metal. Instead, it involves adding deoxidizers and denitriding agents to the wire or core, allowing the oxygen and nitrogen from the air to enter the slag rather than the molten metal, hence the term “self-shielded.”

Because solid self-shielded wires provide inadequate protection, resulting in lower plasticity and toughness of the weld metal, they are currently rarely used in production.

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