What is the chemical composition of 20# steel?
The chemical composition of 20# steel mainly includes carbon (C: 0.17%-0.24%), silicon (Si: 0.17%-0.37%), manganese (Mn: 0.35%-0.65%), phosphorus (P≤0.035%) and sulfur (S≤0.035%). Its low carbon content gives it good plasticity and welding properties, while manganese improves the strength and toughness of the material. Compared with Q235 steel, 20# steel has a slightly higher carbon content but fewer alloying elements, so the cost is moderate and it is widely used in the fields of mechanical manufacturing and fluid transportation.
What are the mechanical properties of 20# steel pipe?
The tensile strength of 20# steel pipe is 410-550MPa, the yield strength is ≥245MPa, the elongation is ≥25%, and the Brinell hardness is about 120-160HB. Its mechanical properties are between Q235 and Q345, and it is suitable for medium-loaded structures and piping systems. After cold working, the strength can be increased by 10%-15%, but the plasticity will be reduced accordingly. Compared with 16Mn steel, 20# steel has lower high temperature strength, but has better comprehensive performance at room temperature.
What is the welding performance of 20# steel pipe?
20# steel pipe has excellent welding performance, and can be welded by manual arc welding (J422 welding rod), gas shielded welding (ER50-6 welding wire) and other welding methods. Preheating is generally not required during welding, but it is recommended to preheat to 100-150℃ when welding in low temperature environment (<0℃) or thick plates. Heat treatment is usually not required after welding, but important structural parts can be stress-relieved annealed (600-650℃). The weld strength can reach more than 90% of the parent material, which is suitable for pressure vessels and pipeline connections.
What are the heat treatment processes for 20# steel pipes?
Common heat treatment processes for 20# steel pipes include normalizing (900-930℃) and annealing (880-900℃), which are mainly used to improve the uniformity of the structure and eliminate residual stress. Due to the poor hardenability of 20# steel, the quenching process is generally not used. The steel pipe after cold processing can be recrystallized annealed (650-700℃) to restore plasticity. The cooling method after heat treatment is usually air cooling, and furnace cooling can be used when special requirements are required.
What is the difference between 20# steel pipe and other carbon steels (such as Q235, 45# steel)?
Compared with Q235 steel, 20# steel has a slightly higher carbon content and higher strength (yield strength 245MPa vs 235MPa), but slightly lower plasticity. Compared with 45# steel, 20# steel has a lower carbon content (0.17%-0.24% vs 0.42%-0.50%), so it has better weldability and cold processing performance, but lower hardness. In terms of price, 20# steel is slightly higher than Q235, but more economical than 45# steel. It is suitable for occasions that require both strength and processing performance.
