IMPROVING CONTACT FATIGUE STRENGTH OF CARBONITRIDING GEAR STEEL 25MnTiBR WITH RETAINED AUSTENITE

A study was made of the behaviour of retained austenite to improve the contact fatigue strength of the carbonitriding gear steel 25MnTiBR by means of the contact fatigue test, the fracture mechanics analysis of spalling on contact surface and the energy estimation of crack tip plastic zone The retained austenite deformation induces the martensite transformation, which absorbs energy more than one half of the strain energy of material It may retard the propagation of fatigue cracking and may improve the contact fatigue strength of the carbonitriding steel 25MnTiBR with retained austenite The proper material together with a reasonable technique chosen for production practice may be available to obtain more and not very stable retained austenite in the surface layer of the gear, especially, it may improve the gears under heavy load.