Fig. 2 is the curves of DL-EPR and

Fig. 2 is the curves of DL-EPR and metallography of samples after DL-EPR experiment. The Ra is shown in Table 1. It can be clearly seen that the Ra of S1-4 is the highest, which means that the pre- cipitated carbides are the most. The increase of carbides makes it easier to aggregate and grow, presenting a continuously dis- tributed structure. This is consistent with the continuous distribu- tion of carbides found in Fig. 1. It can also be seen from Fig. 2 that after DL-EPR, S1-4 has the deepest corrosion pits and corrosion grooves. This is inseparable from the formation of continuous carbides.