In order to further improve the tribological properties of gears made of carbon steel,the commonly used 45 steel gears were treated by sulfur and nitrogen infiltration technology,and their friction and wear properties under dry friction conditions were studied.The gear wear test was carried out at room temperature without using any liquid lubricant,and different surface treatments such as nitriding,carburizing and quenching,high-frequency quenching,and sulfatizing+nitriding were carried out on the 45 carbon steel gear with the same parameters.The gear tester was used to measure the distance between shafts after the gear test,and the change was taken as the wear amount.The friction coefficients of various surface treatments were measured by using a friction and wear tester,and the tooth surface states of six kinds of gears after 4 h test were observed.The results show that compared with other surface treatment technologies,the wear of gears treated by sulfur and nitrogen infiltration is obviously smaller,while the surface hardness is equivalent to or lower those that of other treatments; the composite surface treatment of sulfur-nitrogen infiltration and nitridation has the lowest wear amount; the thickness of sulfide layer formed by sulfatizing is about 1 μm,which is much lower than the wear amount after 4 hours,but the effect of sulfide layer on lubrication still exists after wear.Therefore,by using the sulfatizing+nitridation composite surface treatment,the solid lubrication performance of carbon steel gears in normal temperature air can be effectively improved.