*3.2.1 Optical micrographs*

**Figure 1** shows the optical micrographs of different rebar samples (cross section). **Figures 1(a)** and **(b)** reveals the optical micrographs of the Fe 600 and galvanized rebar samples, respectively, that exhibit intermediate zones with three distinctly separate regions for both the samples. On the other hand, microstructures consisting of equiaxed ferrite grains for stainless steel (**Figure 1(c)**) and ferrite-pearlite type for plain rebar (**Figure 1(d)**) have been observed throughout the samples because these two rebars were processed through the conventional cold rolling process and not subjected to thermomechanical treatments (TMT). The presence of dark peripheral ring (edge/rim) consists of tempered martensite with an intermediate narrow transition zone of bainite with a comparably grey core with ferrite-pearlite microstructure as shown in **Figures 1(a)** and **(b)** [23, 33, 39, 40]. It is imperative to mention here that in the TMT process, quenching of hot-rolled bars


**Table 1.**

*Chemical composition (wt. %) of all the experimental rebar specimens.*

*Study on the Perspective of Mechanical Properties and Corrosion Behaviour of Stainless… DOI: http://dx.doi.org/10.5772/intechopen.101388*

### **Figure 1.**

*Optical micrographs of different rebar samples (a) Fe 600, (b) galvanized rebar, (c) stainless steel and (d) plain rebar.*

**Figure 2.**

*SEM micrographs of Fe 600 rebar sample showing (a) transition zone, (b) core region, (c) outer rim region and (d) pearlite at higher magnification.*

with water jet leads to the formation of martensite at the outer surface of the rebars. The residual heat flow across their bar section during cooling results in the tempering of the initially formed martensite with finer grains, which is self-tempering in nature and also produces ferrite-pearlite with coarser grains or mixed microstructure in the core region [13, 33, 41, 42]. A clear boundary separating the outer ring from the inner core is also visible in the case of TMT rebars (**Figures 1(a)** and **(b)**). This boundary can be considered as the demarcation line between the tempered martensite and ferrite-pearlite microstructures.
