20# steel and 45# material are usually suitable for seamless steel pipe, 45# is a common material for machining.

The contents of C, Si, Mn, P and S in 20# steel pipe and 45# steel pipe are different, and 45# steel is higher than 20# steel. 20# steel pipe has low hardenability, plasticity, toughness and weldability. It has better toughness after hot rolling or normalizing. 20# steel can make small and medium-sized carburizing, carbonitriding and forging parts, such as lever shaft, gearbox fork, gear, heavy mechanical pull rod, shackle, etc.

45# steel is commonly used medium carbon steel. It has good comprehensive mechanical properties, low hardenability and easy to crack during water quenching. Small parts should be treated by quenching and tempering, and large parts should be treated by normalizing. 45# steel is mainly used to manufacture high-strength moving parts, such as turbine impeller and compressor piston. Shaft, gear, rack, worm, etc.