# Pitting Corrosion in AISI 304 Rolled Stainless Steel Welding at Different Deformation Levels
## 4 Analysis of Results and Discussion  
Figure 11 shows the correlation between the cold work level (percentage of width reduction) and the number of pits (an indicator of the corrosion degree). The following expression, obtained by a least squares fit, models this correlation:  
\[y=165316+8343e^{0.0585\cdot x},\]  
where:  
y = Pits number/m\({}^{2}\)  
x = Cold work (%) \begin{table}
\begin{tabular}{c c c} \hline \hline
**Cold Work** & **Yield Strength (MPa)** & **Pits Number (10\({}^{3}\)/m\({}^{2}\))** \\ \hline
0\% & 180 & 175 \\
17\% & 360 & 185 \\
33\% & 580 & 225 \\
50\% & 930 & 320 \\
57\% & 1120 & 400 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Yield strength and number of pits per m\({}^{2}\). Figure 10: Pitting at the welding and HAZ zones of a 33% cold work sample. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Cold Work** & **Tensile Strength (MPa)** & **Yield Strength (MPa)** \\ \hline
0\% & 480 \(\pm\) 17 & 180 \(\pm\) 14 \\
17\% & 760 \(\pm\) 20 & 360 \(\pm\) 16 \\
33\% & 800 \(\pm\) 16 & 580 \(\pm\) 15 \\
50\% & 1170 \(\pm\) 25 & 930 \(\pm\) 20 \\
57\% & 1200 \(\pm\) 29 & 1120 \(\pm\) 26 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Resistance characteristics obtained from tensile tests. According to [21], the linear dependence of the pit generation rate on the potential suggests that the pitting process is controlled by an electromechanical breakdown of the passive film. This conclusion could support the correlation found between the cold work level and the number of pits at the present study, that has been represented in Figure 11.  
About the result of the corrosion test, we must first consider that the effectiveness of the surface layer of chromium oxide, which acts as a protective agent against corrosion in stainless steels, can be reduced due to the rolling mechanical effects that could lead to a thickness reduction and/or breakage of this protective layer, as evidenced by the presence of small surface cracks in the cold rolled samples. Furthermore, the study carried out in [33] focused on the welding of 304 L austenitic stainless steel by the shielded metal arc welding process using a standard 308 L electrode, shows that, during sensitization, chromium in the matrix precipitates out as carbides and intermetallic compounds on grain boundary, decreasing the corrosion resistance. Similar results are found in [34], and [35] which associates the precipitation of chromium nitride with the reduction of the corrosion resistance of the nitrided layer. In the AISI 304 stainless steel welding, pitting is concentrated in Cr-depleted regions adjacent to the carbide precipitates [11]. The studies about the effect of microstructural changes in the AISI 304 stainless steel induced by TIG welding, and surely other welding techniques, on the pitting corrosion behavior conclude that the process made the weld metal and HAZ zone more sensitive to the pitting corrosion than the base metal [36]. This work also concludes that high heat-input (and low cooling rate) was likely to induce the segregation of alloying elements and formation of Cr-depleted zones, resulting in decreasing the corrosion resistance [36]. Even more, under [11] study, TIG-welds exhibit lower pitting corrosion resistance than friction and electron beam welds. In fact, austenitic stainless steels are prone to sensitization when subjected to higher temperatures during the manufacturing process. In particular, the study of [27] emphasizes the essential role of temperature-affected variations of the properties of oxide films and their effect on the pitting corrosion in the AISI 304 stainless steel. Figure 11: Graphical representation of the correlation between the cold work and number of pits in a 10% mass solution of FeCl\({}_{3}\)-6H\({}_{2}\)O. The pitting corrosion occurs as a result of a breakdown of the protective passive film on the metal surface [22; 37; 38; 39] and according to [25], the lowest pitting corrosion resistance behavior is shown in the heat affected zone.