Submerged arc welding (SAW) is widely recognized in industrial manufacturing for its high efficiency and stable welding quality. Temperature, as a core parameter in this process, runs through the entire welding process and directly affects the formation of welds, metallurgical properties, and final mechanical performance. So, what is the specific temperature range of submerged arc welding? And what factors will affect the temperature changes?
Key Temperature Ranges in Submerged Arc Welding
Arc Zone Temperature
The arc zone is the core area where energy is generated in submerged arc welding. The temperature here is extremely high, generally reaching 10,000–15,000°C. Such a high temperature is sufficient to instantly melt the welding wire and the surface of the base metal, forming a molten pool. The arc temperature is mainly maintained by the electrical energy input. Under normal welding conditions, the arc column, as the main part of the arc, has the highest temperature, while the temperature near the anode and cathode is slightly lower but still far exceeds the melting point of most metals.
Molten Pool Temperature
The molten pool is formed by the melting of the base metal and welding wire under the action of the arc. Its temperature is lower than the arc zone but still stays at a high level, usually in the range of 1,500–2,500°C. The specific temperature is related to factors such as the type of base metal, welding current, and welding speed. For example, when welding carbon steel, the molten pool temperature is generally around 1,500–1,800°C; when welding high-alloy steel or thick plates, due to the need for more heat input, the molten pool temperature may rise to 2,000–2,500°C. The temperature of the molten pool directly affects the fluidity of the molten metal and the metallurgical reaction effect. A suitable temperature can ensure that the molten metal fully wets the base metal and reduces the generation of defects such as pores and incomplete fusion.
Slag Temperature
In submerged arc welding, the flux melts to form slag, which covers the surface of the molten pool to protect it from atmospheric pollution. The slag temperature is close to the molten pool temperature, approximately 1,400–2,200°C. The slag not only plays a protective role but also affects the cooling rate of the molten pool through its own heat retention. For example, sintered fluxes with high viscosity usually have better heat retention, which can slow down the cooling rate of the molten pool, while some fused fluxes with low viscosity may cool faster.
Factors Affecting Submerged Arc Welding Temperature
Welding Current
Welding current is the most critical factor affecting welding temperature. Under the condition of other parameters being fixed, the higher the welding current, the greater the heat input, and the higher the arc temperature and molten pool temperature. For example, when the current increases from 500A to 1,000A, the arc temperature can rise by 2,000–3,000°C, and the molten pool temperature can increase by 300–500°C accordingly. Therefore, in actual welding, for thick plates that require more heat to melt, a larger current is often selected; for thin plates, a smaller current is used to avoid excessive melting or burn-through.
Welding Voltage
Welding voltage mainly affects the length of the arc. A higher voltage will lead to a longer arc, and the heat distribution in the arc zone will be more dispersed. Although the maximum temperature of the arc may not increase significantly, the effective heating area of the base metal and welding wire will expand, which can also cause the overall temperature of the molten pool to rise. For example, when the voltage increases from 30V to 40V, the arc length increases, and the molten pool area may expand by 10%–20%, and the average temperature of the molten pool may increase by 100–200°C.
Welding Speed
Welding speed determines the time that the arc acts on a unit area of the base metal. A slower welding speed means that the base metal and welding wire are heated for a longer time, and the temperature of the molten pool will be higher; conversely, a faster welding speed will result in insufficient heating time, and the molten pool temperature will decrease. Taking spiral pipe welding as an example, when the welding speed is increased from 30m/h to 60m/h, the molten pool temperature may decrease by 200–300°C. Therefore, high-speed welding often needs to be matched with a higher current to compensate for the heat loss caused by the fast speed.
Flux Properties
The thermal conductivity and melting point of the flux will affect the heat transfer and retention in the welding area. Fluxes with low thermal conductivity and high melting points (such as some sintered fluxes) can reduce heat loss, making the molten pool maintain a high temperature for a longer time; fluxes with high thermal conductivity (such as some fused fluxes) may accelerate heat dissipation, resulting in a lower molten pool temperature. For example, when using SJ101 sintered flux and HJ431 fused flux under the same current and voltage conditions, the molten pool temperature when using SJ101 is about 100–200°C higher than that when using HJ431.
Base Metal and Welding Wire Thickness
Thicker base metals or welding wires require more heat to melt, so the actual welding temperature (especially the molten pool temperature) needs to be higher. For example, when welding a 20mm thick carbon steel plate, the molten pool temperature is usually 200–300°C higher than when welding a 10mm thick plate under the same process parameters.
Importance of Temperature Control in Submerged Arc Welding
Ensuring Weld Formation
A suitable molten pool temperature can ensure that the molten metal has good fluidity, making it fully fill the weld groove and form a smooth and uniform weld bead. If the temperature is too low, the molten metal may not flow sufficiently, leading to defects such as incomplete fusion and undercut; if the temperature is too high, the molten metal may sag, resulting in an irregular weld shape or even burn-through (especially for thin plates).
Guaranteeing Weld Metallurgical Performance
The temperature of the molten pool and its cooling rate directly affect the metallurgical reactions in the weld, such as the dissolution of alloying elements, the precipitation of inclusions, and the formation of microstructure. For example, in the welding of low-alloy high-strength steel, if the molten pool temperature is too high, grain growth may occur, reducing the toughness of the weld; if the temperature is too low, the alloying elements may not be fully dissolved, affecting the strength of the weld. By controlling the temperature, the microstructure of the weld metal can be optimized, such as refining grains, to balance strength and toughness.
Preventing Welding Defects
High-temperature control can reduce the generation of pores. A higher molten pool temperature is conducive to the escape of gas (such as hydrogen and nitrogen) in the molten metal; if the temperature is too low, the gas cannot escape in time and will form pores in the weld. In addition, for materials sensitive to cold cracking (such as high-carbon steel and low-alloy steel), an appropriate molten pool temperature and slow cooling rate (achieved by controlling temperature) can reduce the residual stress and the risk of cold cracking.
Adapting to Different Welding Requirements
Different welding scenarios have different temperature requirements. For example, in the welding of thick-walled pressure vessels, a higher and more uniform molten pool temperature is required to ensure deep fusion between layers; in the welding of thin-walled pipes, a lower temperature is needed to avoid deformation and burn-through.
Industry experts point out that in actual submerged arc welding production, enterprises should not only pay attention to the setting of current, voltage, and speed but also monitor and adjust the welding temperature according to the type of base metal, welding material, and weld structure. By mastering the law of temperature change and its influence, stable and high-quality welding results can be achieved, providing a solid guarantee for the safety and reliability of industrial products.
