strathSEEA

SEM Results

As was the case with XPS, only select samples could be examined using the SEM due to time restrictions. The selected samples were; SS 254, SS 353 and Inconel 617 K33.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Stainless Steel 353 was selected as one of the samples to be analysed due to the interesting results previous investigations gave. Because the expanded austenite layer was difficult to measure due to the different focal points; SEM was used to verify the results. Figure 63 depicts the measured expanded austenite layer depth on the polished side to be around 15.56 µm which just falls short of the minimum error of the optical microscope measurement, 17.12 ± 1.26 µm.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Further SEM investigations were carried out on the top surface of SS 353. This was in search of visual proof that there were carbides being formed on the surface, confirming up claims form optical microscopy analysis. Figure 64 and Figure 65 show alloys SS 353 and SS 254 respectively. It can clearly be seen that the surface of SS 353 presents obvious features when compared to 254, a sample which did not seem to show any carbides on the polished face in the XRD investigations. This image provides solid more possible evidence that carbides were in fact formed during the carburisation procedure, which attributes to what seems to be its unexpected hardness. The fact that carbides were formed, suggests a lower diffusivity and so lesser solubility within SS 353, which makes the formation of carbides more likely. However due to the inability to perform an XPS analysis, the exact nature of these carbides could not be identified.

 

Alloys SS 2343 and Inconel 617 (K33 treated) cross sections were also analysed under the SEM. Both expanded austenite layer depths reflected the results from the optical microscope.

 

EDX Results: SS 353

 

As the equipment available cannot read the carbon results reliably, EDX could not be used to verify whether there are carbides present in the sample. Therefore EDX was only used to confirm the chemical composition of SS 353. To allow for a comparison, the carbon concentration was omitted.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table of Elements Present and Atomic Percentage in SS 353 via EDX

 

 

 

 

 

 

 

The results of SS 353 from EDX (Table 18) correlate very well with the approximate chemical composition expected from this material, shown earlier in Table 1 in section 6.1. Although not a direct comparison, as Table 1 contains given weight percentages, whereas the elemental concentrations are measured by EDX, the fact that the four main elements present are all of a very similar atomic weight still allows for a justifiable comparison.  This is good as there are no unexpected compositions causing the unusual results from the other investigations. Had the EDX carbon detector been fully functioning then EDXit would have been a good method in verifying the depth of the carburised layer and also if there were any carbides present in the sample.

 

SEM Summary

 

The SEM imaging appeared to show that theconfirm the presence of carbides near the surface morphology of Stainless Steel 353 showed more prominent features than Stainless Steel 254, with a good possibility that this was due to presence of carbides. This could not be seen in the XRD results, but had been expected throughout the investigations. The carburised layer depths of samples SS 2343 and Inconel 617 (K33) were also confirmed through the use of SEM, as was the elemental composition of SS 353.