Improved fatigue prop. of powertrain comp. by reduced internal oxidation and interrupted quenching
Purpose and goal
The aim has been to increase the fatigue resistance, by at least 25%, of carburized transmission components by introducing two methods; (1) interrupted quenching and (2) a modified heat treatment process in order to minimize a negative effect caused by internal oxidation in connection to atmospheric carburizing. The maximum increase in fatigue strength, 16%, was obtained for steel 16MnCr5 by introducing the two methods. The increase in fatigue strength should correspond to a triple service lifetime. Reference is casehardening and and normal quenching in the applied quenching oil.
Expected results and effects
Two industrially implementable processes; (1) interrupted quenching and (2) a modified heat treatment process in order to minimize a negative effect caused by internal oxidation in connection to carburizing have been analyzed. Steel 16MnCr5 showed a 16% increase in fatigue strength. Further adaptation to different steel grades depending on Ms is necessary to achieve maximum effect and productivity for interrupted quenching. The increase in strength allows for lightweight components or that higher torque/longer life can be taken out of existing designs without redesign.
Planned approach and implementation
Interrupted quenching and the modified heat treatment process to control/suppress a negative effect of internal oxidation was performed on specimens and gears in steel 16MnCr5, V2158 and Ovako 158Q. All experiments were performed in industrial batch furnaces at Bodycote and GKN Driveline. Rotating-bending tests and pulsating testing were performed on specimens and gears. Various parameters for how the interrupted quenching and modified process would be carried out were examined. A final process was selected and used for all the heat treatments of the fatigue testing specimens.