KUJ7 steel is a new type of steel developed by K0Y0 based on GCr15, in which Cr, Mo and Si are added. At an ambient temperature of 200°C, the service life of the bearing is greatly improved, and it is particularly suitable for use on bearings with a medium temperature (≤180°C). Medium carbon steel with specific composition using carburizing or CN co-infiltration, a large amount of fine carbides, extremely high hardness and more residual austenite (30%~35%) can be obtained in the infiltration layer. Under these conditions, the service life of the bearing can be extended by 6 times compared with GCr15 steel. Japan calls it TF technology. There are four types of TF series steel: TF, HTF, STF and NTF, they have good wear resistance and grip, and have a stable size between the steel surface and the hardened steel.