Austenite Grain Refinement and Homogenization Control of the Flexspline for Industrial Robot Harmonic Drive

The austenite grain refinement and homogenization control strategies of the flexspline were investigated, including microalloying with V and Ti, the evolution of austenite grain size and homogenization during forging processes and multiple times of heat treatment. The results show that the grain growth rate during high temperature was lowered obviously which leads to the grain refinement, owing to the addition of microalloying elements V and Ti. After holding at 1200 °C for 40 min, the average grain size of 0.05%V+0.0045%Ti steel was reduced by 39% compared with 0.04%V+0.0025%Ti steel. During the manufacturing process of the flexspline from induction reheating to quenching and tempering, the austenite grain was gradually refined from 340.0-380.7 to 9.3-9.8μm. The grain size and homogenization were improved obviously in the first two times during the multiple times of normalizing. After multiple times of quenching and tempering, the size and homogenization of the grain were gradually improved. The exponential relationship between grain size and multiple times of normalizing and the linear relationship between grain size and multiple times of quenching and tempering were also obtained, respectively.