Performance characteristics of steel bars

The process performance of steel bars includes many items, and different requirements can be put forward based on the characteristics of different products. For example, ordinary steel bars require bending and reverse bending (reverse bending) tests, and some prestressed steel materials require repeated bending, torsion, and winding tests.

The form of all these tests simulates to varying degrees the processing methods that may be involved in actual use of materials. For example, ordinary steel bars need to be hooked or bent, and prestressed steel wires sometimes need to be wound. The purpose is to assess the material's ability to handle these specific plastic properties. The ultimate bearing capacity of deformation and therefore the process performance are also plastic requirements for the material, and are consistent with the above-mentioned ductility (elongation) requirements. Generally speaking, steel with a large elongation has good process performance.

However, compared with the unidirectional stress state during tension, the stress state in the process performance test is much more complicated. The type and size of the deformation of the sample are different in each direction (axial and radial directions). The microstructure and crystal structure of the steel are also different. Grain size, harmful residual element content, especially any internal and surface defects that affect continuous deformation such as cracks, inclusions, etc. may affect and lead to failure of the test. So in a sense, when it comes to assessing the quality of steel, it can be said that process performance testing is more stringent.

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. Then brittle at room temperature.

Since steel bars often need to be bent and formed for use, plastic deformation has already occurred. If the material becomes brittle, the structure cannot withstand the external load (such as an earthquake) that causes plastic deformation of the steel bars. Therefore, the reverse bending test is regarded as a test at home and abroad. Important technical requirements are included in steel bar standards, and the nitrogen content of steel is limited (no more than 0.012%).

Research shows that some elements used in the microalloying of steel, such as vanadium, titanium, niobium, etc., especially vanadium, have a good affinity with nitrogen. Adding vanadium to steel can effectively combine with free nitrogen, and the combination of vanadium and nitrogen can be further improved. Enhance the strengthening effect of vanadium on steel, so some standards also indicate that "if there are enough elements combined with nitrogen, the nitrogen content can be higher than the standard requirement."

Because the anchoring agent is formulated with high-strength materials as aggregates, cementitious materials as binding agents, and supplemented by high-fluid micro-expansion anti-segregation and other substances, its ingredients are mainly inorganic materials, supplemented by organic materials, and are not suitable for steel bars. No rust effect. Therefore, a certain anchoring force can be generated within a few hours. It has the characteristics of rapid setting, rapid hardening, high strength, no shrinkage, high shear strength and low penetration resistance. This construction method is suitable for the support of surrounding rock bolts within 3m of all mine tunnels, tunnels, water conservancy, slope support and other projects.