Inadequacies of high-strength steel structure is thermoformed and post-weld heat treatment temperature determination are limited material softening problem. Therefore, in practical applications in order to avoid affecting the thermoforming process on the mechanical properties of the material, the thickness of the smaller material using cold forming technology for cold-formed parts processing is an economical and practical way. In fact, steel shelf applications factors currently affecting small or obvious, because the shelves in steel sheet thickness of application mainly in 4mm or less; but when the thickness of more than 25mm, in cold forming technology for cold-formed parts when processing, part of the material will fracture, fracture fibrous, gray color, there is macroscopic plastic deformation near the fracture, which is part of post-ductile fracture characteristics.
Analysis of the fracture reason, in addition to temperature, loading rate and other external factors have a very important influence on the fracture mode of the material outside the first metallurgical factors in the production of sheet metal, rolled a large quantity of materials, finishing temperature is low, the organization fine, uniform inner and outer layers; and in the heavy plate rolling, rolling times less material, finish rolling temperature is high, loose tissue, the inner and outer layer uniformity is poor. Second, the impact of the stress state of the material of the cold forming process, when the relatively thin sheet material deformation in the thickness direction is relatively easy, small radial strain material, the thickness direction of the stress is smaller, its force is close to a planar state ; and when the slab due to the shrinkage in the thickness direction is greatly restricted, cold bending process, the surface of the cold-formed parts easy to form micro cracks, cracks formed at the three-dimensional stress, the so called plane strain state of the material change brittle, resulting in breakage.
In addition, the temperature of the cold hardening material surface significantly thinner plate, high hardness is caused by the fracture occurred in the processing of cold-formed reason, although part of the material did not break, but its cold-formed surface has obvious cracks, and because of the machined surface work hardening phenomenon, the plastic material is reduced, once used, will also have the strength of the entire cold-formed steel, stiffness, stability a potential danger. In some applications, the test must be cold-formed high-strength structural steel, designed to control the bend radius to meet the basic pass design requirements.
Post time: Oct-29-2019