The technological properties of reinforcing bars include many items. Different requests can be made according to the characteristics of different products, such as ordinary reinforcing bars requesting to stop bending and reverse bending (reverse bending) experiments, and some prestressing steel requesting to stop repeated bending, changing and winding experiments.
All these experiments simulate the processing methods that the data may touch upon in practice, such as bending or bending forming of ordinary steel bar, winding of prestressing steel wire, etc. The purpose of these experiments is to check the data's ability to accept the limit of these specific plastic deformation. Therefore, the process performance is also a plastic request for the data and is related to the ductility (extension) mentioned above. Length) Requests are common. Generally speaking, steel with high elongation has good technological properties.
However, compared with the unidirectional stress state under tension, the stress state of the process performance test is much more complex. The deformation type of the specimen is different from that of the specimen in all directions (axial and radial). The structure, grain size, harmful residual element content of the steel, especially any defects, such as cracks and inclusions, which affect the continuous deformation both inside and outside, may affect and cause the experiment not to pass through. Therefore, in a sense, it can be said that the process performance test is more rigorous to assess the quality of steel.
In addition, the reverse bending experiment of steel bar is essentially a strain-aging sensitivity experiment, which is due to the fact that the steel usually contains a certain amount of free nitrogen (N), also known as residual nitrogen. When the content is too high, the steel can be brittled at room temperature after plastic deformation.
Because steel bars often need to be used after bending and forming, plastic deformation has been produced. If the material is brittle, the structure can not accept the additional load (such as earthquake) which causes plastic deformation of steel bars. At present, the reverse bending experiment is included in the steel bar code as an important technical request at home and abroad, and the nitrogen content of steel is limited (not exceeding 0.012%).
The study shows that some elements used in microalloying of steel, such as vanadium, titanium, niobium, etc., especially vanadium and nitrogen have excellent affinity. Vanadium in steel can effectively separate free nitrogen. The separation of vanadium and nitrogen can further enhance the strengthening effect of vanadium on steel. Therefore, some codes also indicate that "if there are enough elements separated from nitrogen, the nitrogen content can be higher than the norms".