Fig. 1. Setup of corrosion fatigue.

Fig. 2. Cross sectional macroscopic appearance of double-sided FSP IF steel.

Fig. 3. Microstructure of FSP IF steel in different regions: (a) BM (region 1 in Fig. 2), (b) PZ formed by the first pass FSP (region 2 in Fig. 2), (c) PZ formed by the second pass FSP (region 3 in Fig. 2), (d) fine grains of surface layer in the PZ, (e) dislocation of surface layer in the PZ, (f) TMAZ formed by the first pass FSP (region 4 in Fig. 2), and (g) TMAZ formed by the first pass FSP (region 5 in Fig. 2).

Fig. 4. Contour map of microhardness distribution of FSP IF steel.

Fig. 5. Typical fracture surfaces of IF steel after tensile testing: (a) BM specimen, and (b) FSP specimen.

Fig. 6. Log fatigue life vs log stress range curves of the BM and FSP specimens (a) in air and (b) in 3.5 wt% NaCl solution at a stress ratio of R = 0.1 and 10 Hz loading frequency.

Fig. 7. Typical fracture surfaces of the BM specimen (on the left side) at ΔS = 220 MPa, Nf = 2.144 × 106 and FSP specimen (on the right side) at ΔS = 420 MPa, Nf = 0.936 × 106 in air: (a) (b) crack initiation zone; (c) (d) crack propagation zone at low amplification, and (e) (f) crack propagation zone at high amplification.

Fig. 8. Fracture surfaces of the BM specimen in crack propagation zone at ΔS = 220 MPa, Nf = 0.689 × 106 in 3.5 wt% NaCl solution.

Fig. 9. Fracture surfaces of the FSP specimen in crack propagation zone at ΔS = 370 MPa, Nf = 0.397 × 106 in 3.5 wt% NaCl solution: (a) at low amplification, and (b) at high amplification of region A in (a).

Fig. 10. Surfaces topography of (a) BM fatigue specimen failed at ΔS = 230 MPa, Nf = 0.411 × 106 and (b) FSP fatigue specimen failed at ΔS = 350 MPa, Nf = 0.513 × 106 in 3.5 wt% NaCl solution.

Fig. 11. Potentiodynamic polarization curves of the BM and FSP specimens in 3.5 wt% NaCl solution.

Fig. 12. Nyquist plots of the BM and FSP specimens in 3.5 wt% NaCl solution.