# Influence of Different Base Materials on the Microstructure and Properties of Clad Rebar
## 3 Results and Discussions
### Analysis of the Bonding Performance of the Composite Interface  
Table 6 shows the test results regarding the bonding performance of various rebar composite interfaces (the test was repeated 10 times). From the table, it is clear that the bonding strength of the 20 MnSiV/316L rebar composite interface (384 MPa) is higher than those of the 45#/316L rebar and 55#/316L rebar. As the carbon content in the base layer increases, the amount of carbon-chromium compounds in the composite interface  
Figure 11: Macroscopic morphology of the tensile fractures for various rebars: (**a**) 20 MnSiV/316L rebar; (**b**) 35#/316L rebar; (**c**) 45#/316L rebar; (**d**) 55#/316L rebar. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Rebar Type** & **Yield Strength (MPa)** & **Tensile Strength (MPa)** & **Elongation (\%)** \\ \hline
20 MnSiV/316L & 455 & 628 & 26.3 \\
35#/316L & 335 & 575 & 23.6 \\
45#/316L & 363 & 638 & 16.2 \\
55#/316L & 380 & 650 & 14.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Results of tensile experiments on various rebars. increases. However, during shearing, the carbon-chromium compounds can easily develop concentrated stress, leading to the premature initiation of fractures on the interface and a decrease in the bonding strength. Interestingly, although the carbon content of the 35#/316L rebar composite interface is significantly lower than those of the 45#/316L and 55#/316L rebars, the bonding strength of the 35#/316L rebar is not higher than the above two kinds of rebars. Analysis of the metallographic images of the rebar composite interfaces suggests that the grain size of the 35#/316L rebar composite interface is larger than those of the 45#/316L and 55#/316L rebars, leading to a relatively smaller area of the grain boundary, reduced deformation resistance of the metal, and lower bonding strength of the interface. To confirm this, EBSD examination was performed on the rebar composite interface to obtain quantitative statistics on the grain size of all the composite interface microstructures. Because the composite interface consists mainly of austenite and ferrite, this study only considers the grain sizes of austenite and ferrite. Figure 11 shows the EBSD images and the distributions of grain size for all the rebars. Calculations revealed that the ferritic and austenite grains of the 35#/316L rebar composite interface had the largest average sizes of 5.35 and 14.25 \(\upmu\)m, respectively. Therefore, it can be concluded that the bonding strength of the rebar composite interface depends not only on the amount of carbide, but also on the grain sizes of the various microstructures of the interface. The larger the grain sizes at the interface, the lower the bonding strength is. Figure 12 also indicates that although the rolling procedure of every rebar was exactly the same as that of the cladding material (316L stainless steel), certain differences in the average austenitic grain size existed. Among the four types of materials studied, the average austenitic grain size in the 55#/316L rebar (6.67 \(\upmu\)m) was notably smaller than those in the others due to the high carbon content in the base layer of the 55#/316L rebar, which led to the extensive diffusion of carbon to the side of stainless steel and its reaction with chromium to form a large number of carbon-chromium compounds. Carbon-chromium compounds could easily form a series of nucleus droplets during the dynamic recrystallization process of stainless steel, leading to an increase in the number of austenitic nuclei and improved grain refinement. Moreover, when studying a stainless-steel composite plate, [PERSON] et al. discovered that carbides could act as anchors during the formation of the composite interface and inhibit the movement of the grain boundary, leading to slow growth of grains [24].