What is the chemical composition of Q235 steel?
The chemical composition of Q235 steel mainly includes carbon (0.12%-0.20%), silicon (≤0.30%), manganese (0.30%-0.70%), phosphorus (≤0.045%) and sulfur (≤0.045%). This low carbon content design gives it good plasticity and welding properties. Compared with high-strength steel, Q235 does not contain special alloying elements, so the cost is lower. Its chemical composition meets the requirements of GB/T 700 standard and is the most widely used ordinary carbon structural steel.
What are the mechanical properties of Q235 steel pipe?
The tensile strength of Q235 steel pipe is 375-500MPa, the yield strength is ≥235MPa, and the elongation is ≥26%. This combination of mechanical properties makes it suitable for general structural bearing requirements. In terms of hardness, the Brinell hardness of Q235 steel is about 120-160HB. Compared with Q345 steel, it has lower strength but better plasticity. Cold working can improve strength but reduce plasticity, so the amount of cold deformation needs to be controlled.
What is the welding performance of Q235 steel pipe?
Q235 steel pipe has excellent welding performance and can be welded by various methods such as manual arc welding and gas shielded welding. Preheating and post-weld heat treatment are generally not required during welding, which simplifies the construction process. The commonly used welding rod model is J422 (E4303), which has good matching and low cost. However, it should be noted that in low temperature environment (<0℃) or thick plate welding, it is recommended to preheat to about 100℃. The efficiency of the welded joint can reach more than 90%, which is an ideal choice for steel structure connection.
What are the heat treatment processes for Q235 steel pipe?
The commonly used heat treatment processes for Q235 steel pipe include annealing (880-900℃) and normalizing (900-950℃), which are mainly used to eliminate residual stress. Since Q235 is a low-carbon steel, it is generally not quenched because of poor hardenability and easy deformation. For cold-processed steel pipes, recrystallization annealing (650-700℃) can be performed to restore plasticity. The cooling method after heat treatment is usually air cooling, and furnace cooling can be used when special requirements are met.
What is the difference between Q235 steel pipe and other carbon steels (such as Q195, Q345)?
Compared with Q195, Q235 has higher strength (yield strength 235MPa vs 195MPa), but slightly lower plasticity. Compared with Q345, Q235 does not contain microalloying elements (such as Nb, V), has lower strength but better weldability. In terms of price, Q235 is about 15%-20% cheaper than Q345, but about 10% more expensive than Q195. When choosing, you need to consider the strength requirements, welding process and cost factors comprehensively.
