45# seamless steel pipe and 20# seamless steel pipe are commonly used materials for machining. The C, Si, Mn, P, and S contents of 45# seamless steel pipe and 20# seamless steel pipe are different, and 45# seamless steel pipe is higher grade than 20# seamless steel pipe.

20# seamless steel pipe has low hardenability, good plasticity, toughness, and weldability. 20# seamless steel pipe has better toughness after hot rolling or normalizing. 20# seamless steel pipe can be used to produce less important medium and small carburizing, carbonitriding parts, and forging parts. Such as lever shafts, gear shift forks, gears, heavy machinery levers, shackles, etc.

45# seamless steel pipe is a commonly used medium carbon quenched and tempered steel with good comprehensive mechanical properties, low hardenability, and cracks easily during water quenching. Small parts should be quenched and tempered, and large parts should be normalized. 45# seamless steel pipe is mainly used to manufacture high-strength moving parts, such as turbine impellers and compressor pistons, shafts, gears, racks, worms, etc.