Fig. 1. (a) The equipment for pulsed electric current treatment. (b) The temperature-time paths for the pulsed process.

Fig. 2. (a)-(i) The ductile-brittle transition curves of simulated steels under various states. (a) Tempered, (b) 100 h, (c) 250 h, (d) 500 h, (e) 1000 h, (f) Tempered+PEC, (g) Tempered+PEC+1000 h, (h) 1000 h+PEC+1000 h, (i) 1000 h+PEC. (j), (k) The variation of DBTT and USE during the aging-pulsing cycle. It can be seen that DBTT(1000 h) > DBTT(1000 h+PEC+1000 h) and USE(1000 h) < USE(1000 h+PEC+1000 h), which means that the lifetime of simulated materials can be extended at least doubled. Meanwhile, the DBTT(1000 h+PEC) ≈ DBTT(100 h), indicating the lifetime of simulated materials can be recovered by almost 90% after the pulsed treatment, it's like a centenarian turning ten again. (l), (m) The variation of DBTT and USE of the tempered and tempered+PEC samples. By comparing the slope of the orange and green lines, the embrittlement rate of the sample trained by pulsed electric current will be delayed in the followed aging process.

Fig. 3. The advantages of pulsed electric current over annealing treatment. The pulsed treatment requires the RPV to be connected with a power supply for several minutes, which only takes almost a thousandth of annealing time to achieve or even exceed the traditional method.

Fig. 4. Fracture morphologies of simulated steel under several typical states. It can be used to judge the fracture mode by evaluating the size and proportion of the dimples and the cleavage planes in different areas including the fibrous zone, radical zone and shear lip zone.

Fig. 5. The typical TEM bright field images of the aged sample before (a) and after (g) the pre-stretched process. The HRTEM images of the aged sample before (b) and after (h) the pre-stretched process. (c), (i) The lattice fringes of the nanocluster in (b) and (h), respectively. The strain distributions inside the nanocluster in the aged sample before (d)-(f) and after (j)-(l) the pre-stretched process calculated by geometric phase analysis. The nanocluster precipitates on the dislocation line in the aging process. After the pre-stretched process, the pre-existed or new formed dislocation will cut into the nanocluster and induce the adjacent positive and negative dislocations into it.

Fig. 6. Schematic diagrams of nanocluster and dislocation in (a) aged and (b) pre-stretched samples.

Fig. 7. TEM images of (a) aged, (b) aged+PEC, (c) aged+pre-stretched and (d) aged+pre-stretched+PEC samples.

Fig. 8. SEM images of (a) the aged and (b) the pulsed samples. The grain size is basically unchanged after the pulsed electric current.

Fig. 9. (a) The X-ray diffraction pattern of the tempered, tempered+PEC, 1000 h and 1000 h+PEC samples. (b) The FWHMs of the tempered and tempered+PEC samples. (c) The FWHMs of the 1000 h and 1000 h+PEC samples. By comparing the FWHMs of all the peaks from 40° to 120°, it can be known that the FWHMs of both tempered and 1000 h samples decrease after the pulsed treatment, which means the reduction of dislocation density.

Fig. 10. The TEM images of dislocation configuration in the (a) tempered, (b) tempered+PEC, (c) 1000 h and (d) 1000 h+PEC samples under the fixed belt axis [110] and the double-beam condition.