The material of the gear shaft is carbon steel and alloy steel. Such as 40, 45, 50, 40Cr, 50Cr, 42CrMoA, etc., the commonly used heat treatment method is tempering, and quenching treatment in important parts. When the requirements are higher, high-quality low-carbon alloys such as 20CrMnTi, 20CrMo, 20MnCr5, 17CrNi5, and 16CrNi can be used for carburizing and quenching treatment to obtain higher surface hardness and higher core toughness, spline shafts.