Numerical Simulation of Heat Treatment Process by Incorporating Stress State on Martensitic Transformation to Investigate Microstructure and Stress State of 1045 Steel Gear Parts

This work concurrently investigates the microstructure evolution and stress state during continuous cooling of 1045 steel gear parts. A finite element algorithm was developed by two-way coupling of microstructural and thermal fields. Thermal coefficients were correlated to microstructural evolution, and a phase transformation kinetics model was considered to be both temperature and time dependent. Magee's rule was chosen for martensitic transformation modeling to incorporate the effect of stress state on microstructural field. The dilation curves for the benchmark sample show that martensite starting temperature increases when the stress state is considered in microstructure modeling. To determine the validity of the presented model, a cylindrical specimen was quenched in water and oil media, and their predicted microstructures were compared with experimental results. A reasonable harmony between simulated and experimental results was observed. The simulation was then performed for internal gear parts quenched in oil and water media. The simultaneous monitoring of microstructure and stress evolution during continuous cooling of an internal gear part was conducted. It was shown that simultaneous and separate transformations occurring between the tooth and root region have a determining role in the sign of stress for internal gear parts. Lastly, based on monitoring of different phase transformation scenarios occurring during water and oil quenching, a hybrid quenching was proposed to increase martensite volume fraction at the tooth region of an oil-quenched sample without altering the microstructure at root region.

Automated summary

By developing a finite element algorithm, this study investigates the microstructure evolution and stress state during continuous cooling of 1045 steel gear parts. It was found that considering stress state in microstructure modeling affects martensite starting temperature, and a hybrid quenching method was proposed to increase martensite volume fraction in oil-quenched samples.