The Relationship Between Welding Speed And Weld Quality
Aug 13, 2025
The relationship between welding speed and weld quality must be understood dialectically, without neglecting either. This is primarily reflected in the heating and crystallization stages.
In the heating stage, during high-frequency straight seam welded pipe processing, the edge of the tube billet is heated from room temperature to welding temperature. During this period, the tube billet edge is completely exposed to the air without any protection. This inevitably causes a violent reaction with oxygen and nitrogen in the air, significantly increasing nitrogen and oxides in the weld. Measurements show that the nitrogen content in the weld increases by 20-45 times, and the oxygen content by 7-35 times. At the same time, alloying elements such as manganese and carbon, which are beneficial to the weld, are burned and evaporated in large quantities, resulting in a decrease in the weld's mechanical properties. Therefore, in this sense, the slower the welding speed, the worse the weld quality.
Furthermore, the longer the edge of the heated tube is exposed to air-in other words, the slower the welding speed-the deeper non-metallic oxides will form. These deep-seated non-metallic oxides are difficult to completely squeeze out of the weld during the subsequent extrusion crystallization process. After crystallization, they remain in the weld as non-metallic inclusions, forming a distinct, fragile interface, disrupting the weld microstructure and reducing weld strength. Faster welding speeds, on the other hand, shorten the oxidation time, resulting in fewer non-metallic oxides produced and confined to the surface layer. These oxides are easily squeezed out of the weld during the subsequent extrusion process, resulting in fewer residual non-metallic oxides and higher weld strength.
Crystallization Stage
According to metallurgical principles, to achieve high-strength welds, the grain size of the weld structure must be as fine as possible. The fundamental approach to grain refinement is to form a sufficient number of crystal nuclei within a short period of time, allowing them to contact each other before significant growth, thus completing the crystallization process. This requires increasing the welding speed to quickly remove the weld from the heated zone, allowing for rapid crystallization at a greater degree of undercooling. Increasing the undercooling significantly increases the nucleation rate while minimizing the growth rate, thereby achieving finer weld grains.
Thus, whether considering the heating phase of the welding process or the post-weld cooling phase, as long as basic welding conditions are met, the faster the welding speed, the better the weld quality.
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