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Weldability of low-carbon steel Due to its low carbon content as well as low levels of manganese and silicon, low-carbon steel generally does not develop severely hardened or quenched microstructures as a result of welding. The welded joints of low-carbon steel exhibit good plasticity and impact toughness. During welding, preheating, control of interlayer temperature, and post-weld heating are generally not required; nor is heat treatment necessary after welding to improve the microstructure. No special process measures are needed throughout the welding process, resulting in excellent weldability. However, in a few cases, difficulties can arise during welding: 1) Converter steel produced using old smelting methods has a high nitrogen content and many impurities, which results in high cold brittleness, increased sensitivity to aging, reduced quality of the welded joints, and poorer weldability. 2) The deoxidation of boiling steel is incomplete, resulting in a high oxygen content; impurities such as P are unevenly distributed, with concentrations exceeding limits in certain areas. It has high sensitivity to aging and cold brittleness, as well as an increased tendency to develop thermal cracks. 3) The use of welding electrodes that do not meet quality standards results in excessive levels of carbon and sulfur in the weld metal, which can lead to cracks. When a factory uses acidic electrodes to weld Q235-A steel, the high carbon content in the manganese iron contained in the electrode coating can cause thermal cracks in the weld. 4) Certain welding methods can reduce the quality of welded joints in low-carbon steel. In processes such as electroslag welding, the high wire energy causes the grains in the coarse-grained region of the heat-affected zone to grow very large, leading to a significant decrease in impact toughness. Normalizing treatment to refine the grain structure is necessary after welding in order to improve impact toughness. In summary, low-carbon steel is the type of steel with the best weldability and is the easiest to weld; all welding methods can be applied to welding low-carbon steel.