1. Finite element model
According to the geometric diagram in Figure 1, the three-dimensional software is used for modeling, as shown in Figure 2 (a). Considering the longitudinal symmetry characteristics of the gear shaft, 1 / 14 of the gear shaft is taken for modeling, and the automatic meshing method is adopted. As shown in Figure 2 (b), the number of cells is 40 280 and the number of nodes is 9464.
2. Carburizing quenching coefficient
In the numerical simulation of carburizing, the selection of diffusion coefficient is the key factor to determine the accuracy of the simulation process. The diffusion coefficient of carbon in austenite is not only related to temperature, but also closely related to carbon content. The diffusion coefficient of carbon is shown in the table.
| Carbon content / wt% | 1203 K | 1100 K | 1050 K | 1010 K | 1000 K |
| 0.2 | 16． 390 | 4． 3780 | 2． 1010 | 1． 1082 | 0 |
| 0.4 | 19． 233 | 5． 1377 | 2． 4656 | 1． 3005 | 0 |
| 0.6 | 22． 571 | 6． 0291 | 2． 8934 | 1． 5262 | 0 |
| 0.8 | 26． 487 | 7． 0752 | 3． 3954 | 1． 7910 | 0 |
| 1.0 | 31． 082 | 8． 3021 | 3． 9846 | 2． 1017 | 0 |
During quenching simulation, accurate heat transfer coefficient is the basis of microstructure evolution in the simulation process. Figure 3 shows the heat transfer coefficient between 17CrNiMo6 steel gear shaft and kr128 oil.
