For a long time, truck gears most commonly used steel 20CrMnTi. This was the 50 's of the last century in China from the former Soviet Union to introduce midsize cars geared 18XTr steel (20CrMnTi steel). The steel grain fine, carburizing and grain likely small, carburizing and quenching with good performance, can direct quenching after carburizing. In literature, by 1980, our carburizing alloy steel (20CrbinTi steel) steel factory-only steel chemical composition and determination of the mechanical properties of the sample, but often when car production chemical and mechanical performance of gear shaft of steel, due to hardenability can range is too large and affect the quality of products. If, for example, 20CrMnTi low hardenability of carburizing steel, gears made of carburized hardened core hardness lower than the specification values, fatigue test, gear fatigue life lower half; if high hardenability, gears carburized and hardened inner-hole shrinkage after excessive gear Assembly.