Q1: What should be paid attention to when welding Q275 steel pipe?
Before welding Q275 steel pipe, the surface oil, rust and moisture should be thoroughly removed to prevent pores and slag inclusions. It is recommended to use J422 or J506 welding rods, and low-hydrogen welding rods should be used to reduce the risk of cracks. The welding current should be controlled in a moderate range (such as 110~130A for 3.2mm welding rods) to avoid overheating and coarse grains. For thick-walled pipes, preheat to 100℃~150℃, and slowly cool after welding to reduce residual stress.
Q2: Can Q275 steel pipes be cold-bent?
Q275 steel pipes can be cold-bent, but the bending radius should not be too small (recommended ≥2 times the pipe diameter), otherwise cracking or wrinkling is likely to occur. Annealing is required before cold bending to eliminate internal stress, especially for thick-walled pipes (wall thickness >10mm). After processing, stress relief annealing is recommended (600℃~650℃ for 1 hour). Compared with low carbon steel, Q275 has slightly worse cold formability and needs to be more carefully controlled.
Q3: What is the cutting performance of Q275 steel pipe?
The cutting performance of Q275 steel pipe is medium, and carbide tools (such as YG8) need to be selected and sharp edges should be maintained. The cutting speed is recommended to be 60~100m/min, the feed rate is 0.1~0.3mm/r, and emulsion cooling is used to reduce tool wear. Its cutting resistance is about 15% higher than that of Q235, but lower than that of high carbon steel. Continuous chips are easily generated during processing, and chip breaker design is required.
Q4: What are the heat treatment processes for Q275 steel pipe?
Q275 steel pipe can be refined by normalizing (900℃~950℃ air cooling) to improve the comprehensive mechanical properties. Annealing (slow cooling at 680℃~720℃) is used to eliminate cold working stress, and quenching + tempering (water quenching + 500℃ tempering) can significantly improve strength but reduce plasticity. Surface carburizing can enhance wear resistance, but the cost is high. Hardness and metallographic structure need to be tested after heat treatment to ensure quality.
Q5: What are the connection methods of Q275 steel pipe with other materials?
Q275 steel pipe can be connected with dissimilar materials such as cast iron and copper alloy through threaded connection, flange connection or clamp. Sealant (such as polytetrafluoroethylene tape) needs to be applied for threaded connection, and rubber gasket should be used for flange connection to prevent leakage. Insulating gaskets are required for connection with aluminum to avoid electrochemical corrosion. Transition layer welding materials (such as nickel-based welding rods) need to be used when welding dissimilar materials.
