ERW steel pipe welding process is the use of high-frequency current generated by the skin effect of the principle of the edge of the hot-rolled coil, which is heated to a molten state and then by mechanical extrusion welding. Through this process of its production of steel pipe weld fusion center will be a white line, fusion line both sides of the heat affected zone will produce from the central to the direction of extension and external surfaces of the metal flow lines. ERW steel pipe is used as the base material as a welding material, so the performance of the weld and base metal significant performance relationship. In general, the base metal and weld Charpy impact test values of absorbed energy difference is small. In contrast, in high toughness materials, there are large differences in impact toughness was significantly inferior to the base material, but significantly better than ordinary materials welds. From this center, ERW steel pipe weld toughness is generally lower than the base metal toughness, even with high toughness materials, although the toughness of the weld is improved, but not completely improved impact toughness of weld center.
ERW pipe is used as the base metal welding materials, physical and chemical properties of raw materials thus directly determines the physical and chemical properties of the weld. In order to study chemical composition of different materials, the impact of parent metal and weld performance by the impact of changes in chemical composition, the use of two different chemical composition of steel material after Charpy impact test. In order to exclude the results of the test tube during the impact, all samples were normalized condition. ERW steel pipe in the welding process, due to mechanical pressure effect, on both sides of the weld heat affected zone will produce by the middle of the inner and outer surface plate metal flow lines extending in a direction close to the center of the weld metal flow direction of a line substantially parallel to the weld line coincides with the weld line. Hot metal flow lines are along the rolling direction of the steel strip extending organizations and inclusions, the thickness of the metal flow lines and the raw material grain size and the number of the non-metallic inclusions. The larger grain size of raw materials or non-metallic inclusions, the more thicker the metal flow lines more obvious. When the non-metallic inclusions and showed a more uniform distribution of the base metal segregation serious. High-frequency welding, the pressing force of the press roller under the effect of segregation with large non-metallic inclusions within the metal flow along the wire into the weld fusion zone, hot acid from low magnification segregation can clearly see the sample line at a certain point of intersection of the fusion line. In this case, it will seriously reduce the impact toughness of the weld, so that the impact absorbed energy is greatly reduced. Therefore, the raw material coil smelting, rolling phase should take measures to reduce inclusions and grain refinement process in pipe flow line should also increase the metal angle reasonable control, generally require metal flow line and fusion line clip angle control at 25 ~ 45, is best able to basically symmetrical up and down about.
Affected by ERW steel pipe weld toughness of the basic elements of the analysis can be found in the production practice reasonable control of the relevant factors, the ultimate goal is to reduce the weld oxides and inclusions, grain refinement to improve the impact toughness. Impact toughness demanding production ERW steel pipe, should raw materials, forming, welding and weld heat treatment and other considerations, integrated various factors, so that to achieve the best quality of welding. Through the above aspects of reasonable adjustments, produced by the ERW pipe, parent material and weld toughness, ductile-brittle transition temperature can be roughly the same level.
