The two-step sintering method is to heat the product to a specific temperature (T1) to eliminate the subcritical pores in the green body, and then reduce it to a lower temperature (T2) to make the green body compact. In the low-temperature sintering stage of the two-step junction method, the activation energy required for grain boundary migration is higher than that for grain boundary diffusion. Therefore, this stage is mainly based on grain boundary diffusion. Therefore, in the second stage of the two-step sintering method, the green body is continuously dense, but the grains will not grow too fast. In the low-temperature sintering stage of the two-step sintering method, the prerequisite for complete compaction of the green body is that the pores in the green body gradually become closed pores during the shrinkage of the green body.