# Influence of Different Base Materials on the Microstructure and Properties of Clad Rebar
## 3 Results and Discussions
### Analysis on Corrosion Resistance  
To compare the corrosion resistance of the four types of rebars horizontally, salt spray corrosion experiments were performed on all the rebars. The sample specification was \(\Phi\)28 \(\times\) 80 mm, and the corrosion time was 30 d.  
Figure 14 illustrates the end and axial morphologies of various rebars after rust removal. The figure suggests that no corrosion or cracks occurred on the axial faces of the four types of rebars, which can be attributed to the high corrosion resistance of the clad layer of 316L. The end faces of the four rebars were severely corroded due to the absence of cladding, and their composite interfaces also appeared to be detached.  
Figure 15 illustrates the corrosion depth in the composite interfaces of all the rebars. The figure suggests that the corrosion depth in the composite interfaces was remarkably higher than that in the carbon-steel bases. This was attributed to the existence of a certain  
Figure 14: Surface morphologies of various rebars after rust removal: (**a**) 20 MnSiV/316L rebar; (**b**) 35#/316L rebar; (**c**) 45#/316L rebar; (**d**) 55#/316L rebar.  
Figure 13: Shear fracture profiles of clad rebars: (**a**) 20 MnSiV/316L rebar; (**b**) 35#/316L rebar; (**c**) 45#/316L rebar; (**d**) 55#/316L rebar.  
potential difference between carbon steel and stainless steel due to their different properties. Consequently, under salt spray, electrochemical corrosion occurred in the composite interface of each rebar (with the stainless steel as the cathode and carbon steel as the anode). Because the carbon-steel base had no contact with the stainless steel, chemical corrosion occurred. In their research of corrosion behavior on a composite plate, [PERSON] et al. found that the corrosion resistance can be greatly reduced by cracking and spalling the high chromium alloy protective layer, even exceeding the untreated sample in the study concerning the corrosion behavior of 304 austenitic stainless steel [25,26].  
[PERSON] et al. found that the electrochemical corrosion rate of a composite plate (0.728 g/m\({}^{2}\)) was several times that of its chemical corrosion [25].  
Moreover, Figure 15 suggests the existence of obvious differences among the corrosion depths in the composite interfaces of the four rebars. The corrosion depth of the 20 Mn-SiV/316L rebar composite interface was \(\sim\)0.75 mm, while that of the 55#/316L rebar was \(\sim\)2.3 mm (nearly three times higher). The corrosion depth of each composite interface was related to the chromium content in the base. As carbon-chromium compounds were formed in large amounts, the chromium content in the composite interface decreased sharply, resulting in lower corrosion resistance of the interface and a larger corrosion depth.  
Table 7 shows the corrosion rates of the various rebars. The corrosion rates of the 20 Mn-SiV/316L, 35#/316L, 45#/316L, and 55#/316L rebars were 0.61, 0.75, 0.92, and 1.15 g/(m\({}^{2}\)-h), respectively. Thus, the 55#/316L rebar has the highest corrosion rate, which is approximately twice the corrosion rate of the 20 MnSiV/316L rebar. The high corrosion rate of the 55#/316L rebar can be attributed to its severely corroded composite interface.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Rebar Type** & **Corrosion Rate (g/(m\({}^{2}\):h))** \\ \hline
20 MnSiV/316L Rebar & 0.67 \\
35\#/316L Rebar & 0.75 \\
45\#/316L Rebar & 0.92 \\
55\#/316L Rebar & 1.05 \\ \hline \hline \end{tabular}
\end{table}
Table 7: Calculated corrosion rates of the various rebars.  
Figure 15: Illustration of corrosion depths in composite interfaces of various rebars: (a) 20 Mn-SiV/316L rebar; (b) 35#/316L rebar; (c) 45#/316L rebar; (d) 55#/316L rebar.