Analysis on Bending Fracture of 316L Stainless Steel Electric Heating Tube

- Apr 23, 2020-

The production process of 316L steel electric heating tube is generally as follows: stainless steel plate is bent and drawn and welded into a tube →Heat treatment, surface treatment → heating wire winding → resistance wire welding electrode → threading powder (MgO powder) → packaging → pressure measurement → bending forming → assembly and storage. The bending process in the production process often causes the steel pipe to break, which reduces the production yield and restricts the development of high-quality steel pipe electric heaters. Carrying out research on the cause of bending fracture of 316L electric heating tube and improvement of production process have become one of the key process
issues.

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After the 316L stainless steel electric heating pipe bends, the fracture is torn, and the amount of deformation on the inside and outside of the bending process is inconsistent, and the inside wall of the bend is significantly thicker than the outside. After the coiled tube is welded, the uneven force on the tube wall causes uneven deformation of the tube wall during the continuous drawing process. The grains in the middle of the tube wall are significantly smaller than those in the edge of the tube wall. After the same tube was annealed at 1080 ℃, the grain size of the entire wall area was uniform, indicating that the 1080 ℃ annealing process can significantly improve the microstructure of the 316L stainless steel tube after welding and drawing, avoiding the welding and deformation processing of the 316L stainless steel structure. Impact. In the actual production process, a small part of the 316L stainless steel pipe after annealed will break during the bending process. We selected multiple sets of bending and fractured pipe samples for analysis, and found that during the process of bending the pipe, the weld zone is on the outer side of the bend (tensile deformation side). Before annealing at 1080 ℃, the weld zone has obvious as-cast microstructure and irregular coarse dendrite shape. After annealing at 1080 ℃, the grain size decreases slightly and the dendritic as-cast structure is still retained Appearance. The coarse cast structure in the weld zone has low impact toughness and flexural strength, and is prone to fracture during bending.