SURFACE HARDENING CHARACTERIZATION OF TRANSMISSION GEARS

Abstract

This paper is presented to compare the transmission gear products from SME (UKM gear) and
national scale manufacturer (OEM gear) especially on the surface hardening characterization.
Both gears  were  heat  treated with  different methods.  The gear product of SME was  heat
treated by pack carburizing and quenching whereas the OEM gear was predicted to be heat
treated using induction  heating with high frequency. The surface hardening characterization
was conducted by investigating the hardening thickness,  the hardness number  and the
microstructure  observation  on the gear surfaces.  The result  of the hardening thickness
investigation reveals a distinction on the depth of hardening penetration. The heat treatment
using  long interval  pack carburizing  of UKM gear  produces a  deeper  penetration and the
higher hardness number on the gear surface whereas the OEM gear has a thin hardness
penetration and lower hardness number.  The microstructure of  the  both gears  depicts the
different types  of phase. The  SME  gear shows the present of the carbon  infiltration  on the
martensitic phase structure boundary whereas the OEM gear exhibits lower bainite phase on
the gear surface. With this condition the OEM gear is predicted to behave a better contact
stress distribution during operation.
Keywords: gear, heat treatment, surface hardening, microstructure