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A lamellar tear is a form of fracture caused by high stress in the short-distance transverse direction (thickness direction), which can be extended over a long distance. The lamellar tear is roughly parallel to the surface of the rolled product, usually originating from the same planar strip. Metal inclusions, areas of the parent metal with a high rate of tearing. Generally, the elongation of the Z-direction (thickness direction) of the low-alloy steel is 30% to 40% lower than that of the L direction (rolling direction). Therefore, when Z is expected to have tensile stress, it is easy to cause inclusion cracks distributed along the layer. Layered tearing is different from the formation of hot cracks and cold cracks, and is a special steel structure welding crack. As can be seen from the cross section of the welded joint, the distinct difference between the lamellar tear and the other crack is that the crack has a stepped shape consisting of a platform of a substantially parallel rolled surface and a shear wall substantially perpendicular to the platform.

The danger of a layered tear is its concealment and delayed destructiveness. The lamellar tear does not occur on the weld of the steel structure, but only in the heat-affected zone or the inside of the base metal, and there is no sign on the surface, even the existing non-destructive testing technology for steel structures is difficult to find. The lamellar tear can be formed either during the welding process, cracking and spreading after the end of welding, or even delayed until use, and is basically impossible to repair, so lamellar tearing usually causes huge economic losses.

Layered tear control measures

1. Reasonable choice of steel

2. Determine the best welding process

3. Using small current welding and multi-layer multi-pass welding

4. Welding method and welding sequence, select the low hydrogen welding method with high deposition rate, and use the small wire capacity to avoid the concentration of restraint stress of the welded joint. Use a reasonable welding sequence to minimize the welding residual stress in the thickness direction. For weldments with symmetric design of steel structure, welds with symmetric arrangement are symmetrically welded, and the welders are symmetrically welded by two welders to balance the strain distribution, reduce strain concentration and reduce deformation caused by weld shrinkage.

5. Preheating, post-heating, and control of interlayer temperature. Proper pre-weld preheating, control of the inter-channel temperature during the welding process, post-heat dehydrogenation treatment, etc., have a certain inhibitory effect on the formation of lamellar tear.

Through the understanding of lamellar tearing and the research on the mechanism of lamellar tearing, the effective method of controlling lamellar tearing was found, which successfully solved the laminar tearing of giant steel structural columns under the design willingness. The problem is to use high-quality Z-direction steel and low-hydrogen welding materials, choose a reasonable groove form, and cooperate with mature and rigorous welding work, which are effective measures to prevent layer tear.