In foreign countries, the carburized gear steel initially used is basically manganese steel and manganese chromium steel. For example, the Japanese mainly use smn420 and SMN C420, while the Germans mainly use 16MnCr5 and 20mncr5. This kind of steel is cheap and has good comprehensive properties. At that time, from an economic point of view and considering the limitations of resource conditions, their quality was not stable enough, their strength and toughness fit was poor, their strength index was often qualified, but their toughness could not meet the requirements, and their grain coarsening tendency was large. Therefore, it has been rarely used in foreign automobile industry, and has been gradually replaced by chromium steel, chromium molybdenum steel and nickel chromium molybdenum steel. German ZF company once added boron treatment on the basis of mn2cr steel to form a distinctive ZF steel series, and its performance in all aspects has been greatly improved.
The application status of carburized gear steel in various countries is as follows:
Japan: mainly chromium steel and chromium molybdenum steel. For example, chromium steel scr415, SCr420 and chromium molybdenum steel SCM415, scm418, SCM420, scm421 and scm822 are widely used in Japanese automobile industry. Chrome steel is mostly used for transmission gears of small cars. SCM415, scm418, SCM420 and scm421 steels with low molybdenum content in chromium molybdenum steel are mostly used for transmission gears of medium-sized vehicles and driving and driven gears of rear axle of light vehicles. Scm822 with high Mo content is used for driving and driven gears of rear axle of medium-sized vehicles. Followed by nickel chromium molybdenum steel, such as sncm415 and sncm420, which are mainly used in heavy vehicles requiring high hardenability and high core toughness to replace nickel chromium steel snc415 and snc815 without mo.
United States: the gearbox of cars is mainly made of molybdenum steel 4023. Ni2cr2mo steel grades 8620 and 8720 with lower Ni content are mainly used for medium-sized automobile transmission gears and rear axle driving and passive gears, while ni2cr2mo steel 4320 with higher Ni content and ni2cr2mo steel 8822 with higher Mo content are used for heavy-duty automobile gears. Some heavy truck gears are made of ni2cr2mo2b steel 94b17.
UK: traditional Ni steel is still used, such as en35 steel of ni2mo, en36 steel of ni2c and EN352 steel of ni2cr2mo for light and medium-sized vehicles. En355 with high ni2cr2mo content is adopted for heavy vehicles.
Germany: 14nicr10, 14nicr4 and 14nicr18 steels are mainly used for heavy vehicles. At present, ZF series is gradually replacing mn2cr series steel 16MnCr5, 20mncr5, etc. for light and medium-sized vehicles.