During the welding process of the high-frequency welded pipe, due to the mechanical pressurization, the metal flow line extending from the middle of the steel plate to the inner and outer surfaces in the heat-affected zone on both sides of the welded pipe weld, the direction of the metal flow line near the center of the welded pipe weld It is basically parallel to the fuse and coincides with the weld line. The metal streamline is the band structure and inclusions extending along the rolling direction during hot rolling of the steel sheet. The thickness of the metal streamline is related to the grain size of the welded pipe raw material and the amount of non-metallic inclusions.
. The larger the grain size of the welded pipe raw material or the more non-metallic inclusions, the coarser the metal flow line is. When the non-metallic inclusions are large and unevenly distributed, the base material is segregated severely. In high-frequency welding, the pressing force of the pressing roller is large, and a large amount of non-metallic inclusions in the segregation zone will enter the welding fusion zone along the metal flow line, and the segregation line can be clearly seen from the low-temperature hot acid sample. Converging at a certain angle on the fusion line.
In this case, the impact toughness of the welded pipe weld will be seriously reduced, and the impact absorption work will be greatly reduced. Therefore, measures should be taken to reduce inclusions and refine grains during the smelting and rolling stage of the welded steel pipe, and the metal streamline rise angle should be properly controlled during the pipe making process.
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