When we use the steel structure, we will find that there are many factors affecting the use of the product, such as temperature, load, external force impact and other external factors, human factors also exist, such as problems caused by improper operation. The influence of external factors requires that the steel should have good mechanical properties and processing properties to ensure the safety and reliability of the structure. Because the steel used in the processing process is divided into many kinds due to the different raw materials and processes, the structure also has many requirements for the steel. Let's take a look at the main requirements.
1. Strength
The strength index of steel is composed of elastic limit σ e, yield limit σ y, and tensile limit σ u. The design is based on the yield strength of steel. High yield strength can reduce the self weight of structure, save steel and reduce the cost.
2. Plasticity
The plasticity of steel generally refers to the obvious plastic deformation without fracture when the stress exceeds the yield point. The main indexes to measure the plastic deformation ability of steel are elongation δ and reduction of area ψ.
3. Cold bending performance
The cold bending performance of steel structure steel is to measure the resistance of steel to crack when it is bent to produce plastic deformation under normal temperature. The cold bending performance of steel is to test the bending deformation performance of steel under specified bending degree by cold bending experiment.
4. Impact toughness
The impact toughness of steel refers to the ability of steel to absorb mechanical kinetic energy in the process of fracture under the impact load. It is a mechanical property to measure the resistance of steel to impact load, which may lead to brittle fracture due to low temperature and stress concentration. Generally, the impact toughness index of steel is obtained by impact test of standard specimens.
5. Weldability
The weldability of steel structure steel refers to the welding joint with good performance under certain welding process conditions. Welding performance can be divided into two types: welding performance in welding process and welding performance in service performance. The welding performance in the welding process refers to the sensitivity that the weld and the metal near the weld do not produce hot cracks or cooling shrinkage cracks during the welding process. Good welding performance means that the weld metal and the adjacent base metal do not produce cracks under certain welding process conditions. The weldability in service performance refers to the impact toughness and ductility in the heat affected zone at the weld joint. The mechanical properties of the weld joint and the steel in the heat affected zone shall not be lower than the mechanical properties of the base metal.
6. Durability
There are many factors that affect the durability of steel structure. First of all, the corrosion resistance of steel is poor. Protective measures must be taken to prevent corrosion and rust of steel. The protective measures include: regular maintenance of steel paint, use of galvanized steel, in the presence of acid, alkali, salt and other strong corrosive media, use of special protective measures, so as to achieve the function of protecting steel jacket. Secondly, because the failure strength of steel under the action of high temperature and long-term load is much lower than that of short-term load, the permanent strength of steel under the action of long-term high temperature should be measured. The steel will become hard and brittle automatically with time passing. The impact toughness of steel under low temperature load should be tested.
Therefore, when we use steel structure for work, we must select the steel well, and ensure the quality and performance of the steel, so as to ensure the construction quality of the structure. Of course, we also need to design the structure according to our own actual situation, so as to save some money.