Steel bar performance

The process performance of steel bars includes many items, and different requirements can be proposed based on the characteristics of different products. For example, ordinary steel bars require bending and reverse bending (reverse bending) tests, while some prestressed steel bars require repeated bending, torsion, and winding tests.
All these experimental forms simulate to varying degrees the processing methods that may be involved in the actual use of materials, such as the need for ordinary steel bars to be bent or formed, and the need for prestressed steel wires to be sometimes wrapped. The purpose is to assess the material's ultimate bearing capacity for these specific plastic deformations, and therefore the process performance is also a plastic requirement for the material, which is consistent with the above ductility (elongation) requirements, Generally speaking, steel with high elongation has good processing performance.
However, compared to the unidirectional stress state during stretching, the stress state of the process performance test is much more complex, and the deformation type and size of the sample are different in both directions (axial and radial). The microstructure, grain size, harmful residual element content, especially any internal and surface defects that affect continuous deformation, such as cracks and inclusions, may affect and lead to failure of the test. So in a sense, for assessing the quality of steel, it can be said that the process performance test is more rigorous.
In addition, the reverse bending test of steel bars is essentially a strain aging sensitivity test. This is because molten steel generally contains a certain amount of free nitrogen (N), also known as residual nitrogen. When the content is too high, it can cause the steel to undergo plastic deformation and become brittle at room temperature.
Due to the frequent use of steel bars after bending and forming, plastic deformation has already occurred. If the material becomes brittle, the structure cannot withstand the external loads that cause plastic deformation of the steel bars (such as earthquakes). Therefore, both domestically and internationally, the reverse bending test is included as an important technical requirement in the steel bar standard, and the nitrogen content of the steel is limited (not exceeding 0.012%).
Research has shown that some elements used for microalloying of steel, such as vanadium, titanium, niobium, etc., especially vanadium has good affinity with nitrogen. Adding vanadium to steel can effectively bind free nitrogen, and the combination of vanadium and nitrogen can further enhance the strengthening effect of vanadium on steel. Therefore, some standards also specify that "if there are enough elements that combine with nitrogen, the nitrogen content can be higher than the standard requirements".
Due to the fact that the anchoring agent is composed of high-strength materials as aggregates, cementitious materials as binders, and high flow micro expansion and anti segregation substances, its composition is mainly inorganic materials, supplemented by organic materials, and has no rust effect on steel bars. Therefore, a certain anchoring force can be generated within a few hours. It has the characteristics of rapid solidification, rapid hardening, high strength, no shrinkage, high shear strength, and low penetration resistance. This construction method is applicable to the support of rock bolts in the surrounding rock layer within 3m of all mining tunnels, tunnels, water conservancy, slope support and other engineering projects.