High-strength steel can be used for long-span bridge steel structure engineering and super-high-rise steel structure houses as well as strength-controlled components in extra-high and heavy-duty steel structures to save steel, but not in general industrial and civil buildings and structures. The most adopted, this is because when selecting materials in steel structure design, it should not be unilaterally pursued high strength, but should fully consider whether the selected steel materials can meet the requirements of reliable structure, economical rationality and convenient construction. However, the following unfavorable factors exist in high-strength steel, which requires us to pay attention to the construction of steel structure engineering;
1. Because high-strength alloy steel contains more alloying elements, it is more difficult and less stable than carbon-structured steel and low-alloy structural steel in the production process of smelting and processing steel. In particular, it must be subjected to a heat treatment process with low production efficiency and high cost. The material price and processing cost of high-strength steel are about 1.5-2.0 times that of carbon structure.hot dip galvanized steel coil
2. The fatigue strength of high strength steel is not high. It has been proved by experiments that this is closely related to the sudden change of section and the surface machining accuracy and the shape of the weld surface. It is more sensitive than carbon structural steel and low alloy structural steel. Some extruding forms of high strength riveting The fatigue strength is close to or even lower than that of ordinary carbon, which is mainly caused by the concentration of dry stress and high residual stress.
3. Poor toughness. The toughness of steel is essentially a measure of the ability of steel to break. High strength results in low toughness and is particularly prominent in low-light conditions. The tendency to create a gap is more attractive because it is used in high-strength pots. The requirements for toughness are also stricter.
4. Poor welding performance: Due to the large number of alloys contained in the high-strength steel, the splicing process is difficult. There are more opportunities for welding to produce cracks. Due to the poor plasticity of high-strength steels, the high residual stress during the splicing is low in the ability to redistribute, which sometimes seriously affects the reliability of steel structure engineering. At the same time, when the welding is subjected to heat treatment, due to uneven heating and rapid smelting of the steel, different steel transitions will occur in the steel near the weld, some form quenched structures, and some will be softened by high tempering to reduce the strength. 30% of these are one of the important reasons that hinder the widespread promotion of high-strength steel.
5. It is difficult to process and manufacture. For example, the cutting, correction, pre-weld preheating, post-weld cooling, and component correction of the materials are all difficult. If they are not worthwhile, they will have adverse effects on the steel structure engineering.
6. The tensile strength of high-strength alloy steel is large, but the yield ratio (yield strength/limit strength) is also high. When it is not quenched and tempered, its elongation is low, brittleness, plasticity is poor, and stress is heavy. Low distribution capacity.
7. The construction of steel structure with high-strength steel has poor stability and performance, and the performance is low. High-strength steel has high strength. However, the elastic modulus is the same as that of carbon structural steel and low-alloy structural steel. Therefore, when the strength is fully utilized, the elastic deformation is large and it is easy to buck. Especially when the length of the member is relatively large, the shaft The pressure stability factor is reduced too much. When the input is 100, the axial stability coefficient of the high-strength steel is about 50% lower than that of the carbon structural steel.