# Microscopic Analysis of Structure and Wear for Metallic Materials Using SEM
## 3 Results  
Microscopic analysis was performed on four materials cut from different pipe diameters. For better evaluation, the cuts from a pipe, which has not been in service yet, were used as a standard reference sample. The other samples of pipe were from service where there was water medium flowing through them for a certain period of time. Individual parts of the materials were cut out for connection and riser pipes to the radiators. Metallographically, they were prepared so that it was possible to study the surfaces on the inside and outside of the tube (labeled as Samples 1, 2, 3, and 4). All samples (Figure 1) for microscopic analysis were prepared as transverse sections. The samples were cleaned in isopropyl alcohol in an ultrasonic cleaner for 20 min [7]. The cleaned samples were examined with an electron microscope--VEGA 2 TESCAN. Before the microstructure evaluation, the samples were etched. Each sample was examined in detail from the external surface to the internal surface and attention was mainly paid to the nature of the material microstructure as well as purity and the chemical composition of inclusions, corrosion products, and internal surface deposits. The first observation and analysis were performed for sample No. 1 (no service--seamless steel pipe 21.3 mm \(\times\) 2.65 mm, DN 15) from material 11 353 (according to STN 42 0250--for threading and welding) [20]. The tube was not protected with any painting. A detail of the technological manufacturing defect on the surface of the pipe magnified 300\(\times\) is shown in Figure 2. It can be seen that the outer surface has a relatively large roughness and indentations (indicated by arrows), which were apparently caused by a tool in the manufacture of pipes. In a detailed examination of the inner surface at vol. 2000\(\times\) (Figure 3), its broken integrity was highlighted, which could have been caused by the molding technology. Further, Figure 3 shows visible distinct initiation scratches (marked with arrows), passing into cracks towards the material. Such unevenness can be the reason for the development of not only corrosion, but also cavitation. At this magnification, inclusions can also be seen, such as black dots in the microstructure of the material. The inner surface did not show the appearance of corrosion layers or deposits, as it was an unused pipe. The composition of the steel was controlled in the site, which was tightly close to the internal surface (Figure 4). Chemical analysis confirmed that from the qualitative aspect, it is common plain steel that had not been micro-alloyed or surface treated [7]. The guaranteed chemical composition of pipes in [%] is processed from the manufacturer's technical sheet in Table 1.  
Figure 1: Samples from selected areas of metal pipes [7]. Figure 2: Detail of the non-uniformity on the external surface (300\(\times\) zoom) of sample No. 1 [7]. Figure 4: Results of chemical analysis for the edge of the internal surface m2—inclusions: sample No. 1 [7]. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multicolumn{2}{c}{**Standard**} & \multicolumn{1}{c}{**C**} & \multicolumn{1}{c}{**Mn**} & \multicolumn{1}{c}{**Si**} & \multicolumn{1}{c}{**P**} & \multicolumn{1}{c}{**S**} & \multicolumn{1}{c}{**Cu**} & \multicolumn{1}{c}{**Cr**} & \multicolumn{1}{c}{**Ni**} \\ \hline Min. & 0.07 & 0.35 & 0.17 & & & & & \\ \hline Melting number & Max. & 0.15 & 0.60 & 0.35 & 0.040 & 0.040 & 0.25 & 0.25 & 0.25 \\ \hline
84328 & & 0.07 & 0.42 & 0.19 & 0.013 & 0.006 & 0.14 & 0.06 & 0.06 \\ \hline
84591 & & 0.08 & 0.43 & 0.23 & 0.014 & 0.005 & 0.20 & 0.07 & 0.07 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Chemical composition of seamless, cold-drawn steel pipes, material 11 353 in %. Figure 3: Internal surface with inclusion (2000\(\times\) zoom) of sample No. 1 [7]. Sample No. 2 is a seamless steel pipe (21.3 mm \(\times\) 2.65 mm, DN 15) made of 11 353 material class, according to STN 42 0250 (for threading and welding).