Metallographic inspection standard of carburized and hardened gears for locomotive traction
1 Subject content and application scope
This standard specifies the allowable ranges of carburized and hardened case structure, core structure, internal oxide layer and surface decarburized layer of gears, as well as their corresponding rating charts, inspection and acceptance methods.
This standard is applicable to metallographic inspection of carburized and hardened gears for locomotive traction made of steels such as 20CrMnMo, 20CrMnTi, 12CrNi3 and 15CrNi6.
2 Normative references
GB 9450 Determination and verification of the effective depth of carburized and hardened cases of steel parts
3 Terms
3.1 effective depth of hardened case of carburized gear
vertical distance measured from the surface to the place where the Vickers hardness is 550HV1 (or 515HV5), on the normal section of the gear tooth in the middle of the tooth width, along the direction perpendicular to the tooth surface at the half height of the tooth after carburizing, quenching and tempering of the gear or specimen
Where,
HV1——the Vickers hardness under the test load of F=9.81N;
HV5——the Vickers hardness under the test load of F=49.03N.
3.2 internal oxidation of surface
process of generating oxide, which exists on the grain boundary of metal, through oxygen penetration into the surface layer of metal and chemical reaction with alloy elements in metal during carburizing heat treatment
3.3 surface decarburized layer
