Fig. 1. Microstructure of 300M steel used in test

Fig. 2. Energy density distribution of Gaussian heat source and surface morphologies of laser remelting layer. (a) Energy density distribution of Gaussian heat source; (b) macro morphology; (c) micro morphology of x-y cross section when P=600 W and S=66 mm/s ; (d) micro morphology of x-y cross section of remelting layer when P=300 W and S=33 mm/s; (e) micro morphology of y-z cross section of remelting layer when P=600 W and S=66 mm/s; (f) mi

Fig. 3. Microstructures of different regions of laser remelting layer in x-y direction for different parameters. (a) P=300 W, S=33 mm/s, weld zone; (b) P=300 W, S=33 mm/s, weld remelting zone; (c) P=600 W, S=66 mm/s, weld zone; (d) P=600 W, S=66 mm/s, weld remelting zone

Fig. 4. CCT curves of 300M steel

Fig. 5. Microhardness contour maps of laser remelting layer for different parameters. (a) P=600 W, S=66 mm/s; (b) P=300 W, S=33 mm/s

Fig. 6. Polarization plots of substrate and remelted samples in 3.5% NaCl solution

Fig. 7. Electrochemical impedance spectra ofsubstrate and remelted samples in 3.5% NaCl solution. (a) Nyquist plots; (b) Bode plots (impedance); (c) Bode plots (phase angle)

Fig. 8. Equivalent circuit of 300M steel in 3.5%NaCl solution

Table 1. Parameters for laser surface remelting

Table 2. Polarization curve fitting results of substrate and remelted samples in 3.5%NaCl solution under different processes

Table 3. EIS fitting results of substrate and remelted samples in 3.5% NaCl solution