Material selection and microstructure of hardened gear

Due to the differences in stress conditions and working environment, the materials and heat treatment processes of gears used in different vehicles are also quite different.

At present, most vehicle gears are carburized and quenched, and the carburizing atmosphere has oxidation to Cr, Mn, Si, Al and other elements. These elements are internally oxidized under the surface layer, which reduces the content of alloy elements in the surface layer, leads to the reduction of hardenability, and forms an incomplete quenching layer at a depth of about 10 ~ 20 mm. This phenomenon has a great impact on the fatigue strength. The countermeasures are to reduce the content of elements in the steel that lead to the formation of the above oxides and add non oxidizing elements such as Ni and Mo, which can improve the hardenability. Carburized steel shall be selected for carburized gears of vehicles.

Vehicle gears are generally strengthened by carburizing and quenching, but carburizing and quenching will bring large deformation and affect the gear accuracy. Induction heat treatment has fast heating speed and small deformation. Medium carbon steel or medium carbon alloy steel is selected, such as 45, 55, 40Cr, 42SiMn, 35CrMo, 42crmoh, 40CrMnMo and 40CrNiMo. The hardened layer on the gear surface is medium carbon tempered martensite, and the gear surface has high hardness, high wear resistance, high fatigue strength and toughness to ensure that it can withstand large bending stress and impact force in use.

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