Determination of the mechanical properties of surface-modified layer of 18CrNiMo7-6 steel alloys after carburizing heat treatment

A surface-modified layer (SML) can enhance the fatigue life of key components. Material in a SML is inhomogeneous in the depth direction. Therefore the test method for this type of material should differ from that for a homogeneous material. An indentation method with a spherical indenter was developed to measure the elastic modulus of the SML based on the contact theory of a gradient material. The elastic modulus of the SML for 18CrNiMo7-6 steel alloys after carburizing heat treatment was tested by using the proposed method. The elastic modulus and hardness of the SML were evaluated by using the Vickers indentation test on the top surface and on the cross section to verify the proposed method. The elastic modulus of the SML that was generated by the carburizing heat treatment did not change with depth and the SML hardness was improved significantly.