Controlled quenching at case hardening for optimal performance - QuenchCool
Purpose and goal
The aim has been to understand the mechanisms behind controlled cooling in order to model the process and a PhD work has been carried out with a focus on this. The goal has been to be able to control the production processes in order to quickly adapt to new components and steel alloys to shorten lead times. The project has resulted in an improved understanding of controlled/interupted cooling. A number of different explanatory mechanisms have been studied.
Expected results and effects
By controlling the cooling process as above, 8-10% higher fatigue strength has been reached. No complete model has been reached to explain the mechanisms, but clear differences in microstructure and volume expansion exist for samples cooled at different cooling rates. A sample that cools faster has greater volume expansion during the martensite transformation as well as larger martensite units. A sample that cools more slowly changes the tetragonity of the martensitic during cooling due to carbon depleting.
Planned approach and implementation
The intention has been to relate properties of the wheels, in terms of microstructure and fatigue strength, to effects studied in the dilatometer test rods. The work has been carried out in two main parts: Studies and analysis on dilatometer test rods with different carbon content and cooling sequences Studies and analysis on gears that have been heat treated in industrial processes. These wheels have also been evaluated regarding fatigue gear root testing. Various techniques and methods have been used: Dilatometer testing. In-situ dilatometer HEXRD SEM, EBSD Fatigue testing