Other countries in the world mainly use Cr Ni and Cr Ni Mo carbon steel. Compared with Mn Cr steel which is commonly used in mechanical gears in our country, it has greater advantages in strength and toughness. In our country, 18 Cr Mn Ti, 20 Cr Mn Ti and 20 MN VB are commonly used in small power machinery. In recent years, 18 CR 2 Ni 4 W and 20 CR 2 Ni 4 W are mostly used The main reason is that not only its toughness and hardenability are relatively high, but also it has the advantages of high wear resistance and hardness after quenching. The impact toughness at low temperature is relatively good, and the machinability after normalizing is relatively good. In addition, the service life of 18 CR 2 Ni 4 W and 20 CR 2 Ni 4 steel gears is longer than that of 8 Cr Mn Ti, 20 Cr Mn Ti and 20 MN.

The above two kinds of steel gear have chromium, nickel, manganese and other elements, among which chromium can improve the hardenability of steel, nickel can reduce the probability of excessive carbon concentration on the steel surface and the sharp change of equilibrium concentration, which can also greatly improve the strength and toughness of carbon steel. Compared with chromium, manganese can not only improve the strength and toughness of carbon steel, but also improve the hot working of carbon steel Ability also has a greater role in improving.

The main function of molybdenum element is to dissolve austenite to form carbon compound, so as to achieve the goal of solid solution strengthening and precipitation strengthening, and make the carbon steel still have high toughness, at the same time, the strength can be further improved.

There are two main technical requirements for mechanical gears, one is the general working conditions of pulsating cyclic stress, bending stress and surface friction stress, the other is the special working conditions including short-term overload and irregular impact load. Therefore, the gear is required to have high strength and good overload capacity and impact toughness. Secondly, the limitation of working space requires that the size of gear should not increase too much with the increase of power of mechanical tools, otherwise, the surface contact fatigue stress and bending stress of gear will increase. Therefore, in addition, the contact fatigue and bending fatigue performance of material must be ensured.