# Corrosion Behavior of Corrosion-Resistant Spring Steel Used in High Speed Railway
## 2 Materials and Methods
### Experimental Methods  
The corrosion-resistant sample size is 60 mm \(\times\) 40 mm \(\times\) 5 mm, and the surface roughness is 0.7 \(\mu\)m. The sample was cleaned by ultrasonic wave with acetone, then washed with anhydride ethanol and blow-dried. After being placed in a dryer for 24 h, the initial mass of the sample was weighed with an electronic balance, with the precision of 0.1 mg. Zqfs-1200 z type periodic infiltrating corrosion test box was used for accelerated corrosion test. The experimental method was based on railway standard TB/T 2375-1993 (test method for periodic infiltrating corrosion of weathering steel for railway use). The test solution was NaHSO\({}_{3}\) solution with a concentration of (1.0 \(\pm\) 0.05) \(\times 10^{-2}\) mol/L, solution temperature (45 \(\pm\) 2) \({}^{\circ}\)C, and humidity (70 \(\pm\) 5)%. NaHSO\({}_{3}\) solution with 0.02 mol/L was used as the make-up solution. The pH value of the solution was controlled within the range of 4.4-4.8 to simulate the corrosive environment of industrial atmosphere. Each cycle of the test was 60 min, with the infiltration time of 12 min, and the rest of the time, it was baked by infrared lamp. After baking, the maximum surface temperature of the sample was (70 \(\pm\) 10) \({}^{\circ}\)C. A total of 360 h was carried out in the test, and samples were taken in cycles of 24 h, 72 h, 144 h, 216 h, and 360 h. After the samples were taken out, they were washed in anhydrous ethanol, then cleaned with acetone and dried by hot air and stored in a dryer.  
The corrosion rate was calculated by weight loss method. At the end of each cycle, the samples were taken out, and the rust layer was removed with a chemical reagent prepared by mixing 250 mL hydrochloric acid +250 mL distilled water +3 g hexamethylenetetramine. After the sample was cleaned, it was washed in anhydrous ethanol, then cleaned with acetone and dried by hot air and then dried in a dryer for 24 h, then weighed and recorded.  
X-ray diffractometer was used for phase analysis of the sample's rust layer. Cu target was selected, and the scanning angle of 2\(\theta\) ranged from 10\({}^{\circ}\) to 70\({}^{\circ}\). The peak positions of the corrosion phases were identified with PDF-2 (2004) database using MDI jade software. FEI QUANTA 600 electron scanning microscope (SEM) was used to observe the surface morphology of rust layer. JEOL JXA -8530F electron probe micro-analyzer (EPMA) was used to analyze the cross-sectional morphology and element-mapping distribution of rust layer with WDS.  
For the determination of the polarization curve and electrochemical AC impedance of the rusty samples, CS2350 double-cell electrochemical workstation was adopted. The motor system was a three-electrode system, and the working electrode was rusty samples. The area with a surface radius of 5 mm of the rusty samples was taken as the measuring work area; reference electrode (SCE), auxiliary electrode (Pt), working electrode, and reference electrode were connected by a salt bridge. The electrolyte of NaHSO\({}_{3}\) solution was 0.01 mol/L, and the solution temperature was 25 \({}^{\circ}\)C. In the experiment, the polarization curve was measured by potentiometric scanning method, and the scanning rate was 0.5 mV/s. The test frequency range of electrochemical impedance spectrum was 10\({}^{-2}\)-10\({}^{5}\) Hz, and a disturbance voltage of 10 mV was applied during the test.  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Sample** & **C** & **Mn** & **Si** & **P** & **S** & **Ni** & **Cr** & **Cu** & **Fe** \\ \hline
60 Si2 Mn-A & 0.557 & 0.812 & 1.542 & 0.013 & 0.003 & - & 0.265 & - & Bal. \\
60 Si2 Mn-B & 0.56 & 0.77 & 1.67 & 0.016 & 0.004 & 0.2–0.4 & 0.3–0.4 & 0.2–0.4 & Bal. \\ \hline \hline \end{tabular}
\end{table}
Table 1: Chemical composition of experimental steels (mass %).