Q1: What are the precautions for the welding process of Q345B steel pipe?
Before welding Q345B steel pipe, the oil and rust on the groove and the surrounding area must be thoroughly removed to prevent pores and slag inclusions. It is recommended to use low-hydrogen electrodes (such as J507) or submerged arc welding (H10Mn2 welding wire + SJ101 flux) to reduce the risk of cold cracks. The preheating temperature is usually controlled at 100~150℃ (when the plate thickness is >20mm), and the interlayer temperature does not exceed 250℃. After welding, post-heat treatment (such as dehydrogenation treatment) is recommended to reduce residual stress. For important structures, 100% ultrasonic testing is required to ensure the quality of the weld.
Q2: How to weld Q345B steel pipe with dissimilar steel (such as 304 stainless steel)?
Transition layer welding materials (such as E309L) should be used for dissimilar steel welding to avoid brittle areas caused by carbon migration. The heat input should be controlled during welding to prevent the formation of hardened structure on the Q345B side. TIG welding or pulse MIG welding is recommended to obtain a more stable fusion line. PT (penetrant testing) is required after welding to check the crack tendency. In practical applications, such joints are mostly used for non-pressure pipes, and direct welding of dissimilar steels should be avoided as much as possible for load-bearing structures.
Q3: What is the cold bending performance of Q345B steel pipes?
The cold bending radius of Q345B steel pipes is usually not less than 2 times the pipe diameter. Too small may cause thinning or cracking of the outer wall. Annealing treatment is required before cold bending (if the hardness is >HRB80) to improve the plastic deformation capacity. After bending, magnetic particle testing (MT) is recommended to check surface microcracks. For thick-walled pipes (>10mm), hot bending process (heating to 800~900℃) is recommended to reduce deformation resistance. The processed steel pipe needs to be rounded to ensure that the ovality does not exceed the standard allowable value (such as 1%).
Q4: How to choose tool parameters when cutting Q345B steel pipes?
It is recommended to use carbide tools (such as YG8) with a front angle of 10°~15° to reduce cutting force. The cutting speed is controlled at 80~120m/min and the feed rate is 0.1~0.3mm/r to avoid work hardening. Use water-soluble cutting fluid for cooling to reduce tool wear and thermal deformation. For deep hole processing, it is necessary to withdraw the tool in stages to prevent chip blockage. The surface roughness after processing can reach Ra3.2~6.3μm, and precision parts need further grinding.
Q5: What are the key points of thermal cutting (flame/plasma) of Q345B steel pipe?
Use propane or natural gas for flame cutting, the cutting oxygen pressure is 0.7~1.1MPa, and the flame is preheated with a neutral flame. The plasma cutting current is adjusted according to the thickness (such as 30A/mm), and the incision inclination must be controlled within 3°. After cutting, the hardened layer (about 0.5mm deep) needs to be polished to remove it, otherwise it will affect the welding quality. For Q345B with a thickness of more than 50mm, it is recommended to preheat to 100℃ before cutting to prevent cracks. The slag on the cutting edge needs to be cleaned with a carbon arc gouging and the groove should be processed.
