Welding Seam Toughness Impact of Erw Steel Pipe

Through this process of production of steel pipe weld fusion center will appear as a white line on both sides of the heat affected zone will produce fusion line extending from the middle toward the surface and the inner and outer metal flow lines. Since ERW steel pipe is used as the base material using welding materials, so its properties of the weld and base metal properties have a greater relationship. Figure 1 is a common material with high toughness material, weld and base metal ductile-brittle transition temperature curve. In ordinary materials, Charpy impact test weld and base metal absorbs very little difference in the energy value. In contrast there are large differences between high toughness material, weld toughness significantly inferior to the base metal, but much better than ordinary weld material. ERW welded steel pipe weld toughness can be seen in the general case is below the center of the base metal toughness, even with high toughness materials, although the toughness of the weld is improved, but not a radical improvement in the impact toughness of weld center. 
Impact properties affected by changes in the chemical composition, the use of two different chemical composition of the material were made after Charpy impact test pipe. In order to exclude the impact of process pipe on the test results, all samples were carried normalizing. ERW steel pipe welding process, due to the mechanical pressing action, in both sides of the weld heat affected zone generated by the extension of the surface direction of the central inner and outer sheet metal flow line, the direction of the metal flow lines substantially near the center of the weld fusion line parallel to and coincident with the fusion line. Metal flow lines are banded and inclusion of hot-rolled steel plate extending along the rolling direction, the thickness of the metal flow lines and raw grain size and the degree of non-metallic inclusions much about. The larger grain size of the raw materials or more non-metallic inclusions, the thicker the metal flow lines more obvious. When the non-metallic inclusions and showed a more uneven distribution, the base metal segregation serious. When high-frequency welding, the pressing force in the action of the squeeze roll, a large number of non-metallic inclusions in the segregation band will enter the metal flow along the welding line to the fusion zone, the hot acid from the sample may fold lower apparent segregation lines an angle at the intersection of the weld line. In this case, it will seriously reduce the impact toughness of the weld, so that the impact absorbed energy is greatly reduced. Therefore, in coils of raw materials smelting, rolling stage should take measures to reduce inclusions and grain refinement process in pipe flow lines should also rise angle metal reasonable control. 
Metal flow lines of the weld and heat affected zone can be eliminated by heat treatment method. Welding is under the same conditions, the impact of heat treatment and after heat treatment without the sample weld toughness two differences, two samples were taken, a heat treatment, the metal flow lines disappeared, another group without heat treatment, there is a significant flow of metal. One important factor is water-cooled heat treatment conditions on the starting temperature. Pipe weld heat after heat treatment, to go through a long distance air-cooled, air-cooled section in order to shorten the distance and prevent pipe deformation after sizing, sizing prior to entering the water-cooled steel pipe. If the water cooling initiation temperature is too high, bainite is generated, thereby reducing the impact toughness of the weld. As can be seen from the figure the water cooling initiation temperature should be controlled below 400  appropriate.