Investigating Extra Carbon in Steel Using SEM

In summary, the SEM results showed that the sample had a 2% carbon content, which was much higher than what should be present in a steel of this type. It is unclear why this occurred, but it may be related to the fact that the sample was from a fracture surface. Chromium carbide precipitated inside the sample, possibly due to the high carbon content. This information may be useful in the future when analyzing fracture surfaces.
  • #1
lancashire liuyu
5
0
when i was using Scanning Electron Microscope to investigate fracture surface of a metal sample,the results of composition of it appeared so different to what the composition should be, that sample contains 2% carbon comparing to normally 0.1%. i thought there are 3 ways of doing that:
1.hand--i need to use my hand to handle the operation during the process.
scurf and sweat may pollute the sample surface.
2.Enviroment--instrument;air with high content of carbon dioxide;
residual grease.
3.Chemical reaction--with all possible source.
what is the major reason of that happened? any possibility else?
it's about my project,thank you!
 
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  • #2
... the 1st question that comes to my mind is what were you actually analyzing from the fracture surface? Fracture surfaces often have concentrations of various alloying, impurity etc. elements (which contribute to the fracture process and as a result often reside there, and are the focal point of analysis), so is there a chance you are analyzing something which shouldn't have the nominal composition of the steel?
 
  • #3
It might be possible that the facture is along the grain boundaries (intergranular fracture) which have chromium carbide (Cr23C6) precipitates.
 
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  • #4
PerennialII said:
... the 1st question that comes to my mind is what were you actually analyzing from the fracture surface? Fracture surfaces often have concentrations of various alloying, impurity etc. elements (which contribute to the fracture process and as a result often reside there, and are the focal point of analysis), so is there a chance you are analyzing something which shouldn't have the nominal composition of the steel?
i was using the normal type of steel,which contains normally 0.1%carbon in itself. and the same situation happened in other materials which should not have any carbon inside, like aluminum,copper.
 
  • #5
Astronuc said:
I might be possible that the facture is along the grain boundaries (intergranular fracture) which have chromium carbide (Cr23C6) precipitates.
and why there is chromium carbide precipitated inside?? theoretically i used pure materials,like copper,aluminum...
 
  • #6
lancashire liuyu said:
i was using the normal type of steel,which contains normally 0.1%carbon in itself. and the same situation happened in other materials which should not have any carbon inside, like aluminum,copper.

What kind of an analyzer were you using in your SEM (and with what sort of analysis parameters if there is something unusual or so in them)? Sample preparation might be one, how was it done and were there any steps which might result in carbon 'contamination'? If you're getting the result (with the analyzer) consistently irrespective of the sample, might the analyzer / SEM unit have gotten contaminated itself (like by some other user)? Sometimes we have problems when someone studies unclean samples, especially samples which have been in corrosive etc. environments.
 
  • #7
An SEM itself will not give you a composition analysis - it takes an EDAX attachment to get that info.

Now really, unless the OP provides more specifics on the measurement, any discussion is quite a waste of time.

First, it was said that the high C content was measured in a steel (what grade??). Later, we find out that this was also seen in "theoretically" pure metals (again, no description of grade). There is no mention of sample history (notably, type of fracture), preparation or instrumentation.
 
  • #8
and why there is chromium carbide precipitated inside??
I was thinking of Stainless Steel with about 0.08%C or higher, and chromium carbides will precipitate based on thermal treatment. It is one reason to develop low carbon SS, with =< 0.03% C.

What does one mean by 'normal' steel? There are structural steels or various types, and stainless steels of various types.

e.g. http://www.keytosteel.com/default.aspx?ID=CheckArticle&NM=64

As PerennialII and Gokul questioned, what sample prep did on use. Any grinding with SiC, for example, and grinding liquid? Any type of etchant, or cleaning with alcohol or other carbon-bearing material? If one is sampling 'pure' materials, maybe there is cross-contamination in one's procedures.

Also, as Gokul alluded, does the SEM process involve another analysis? XRF? or EDAX? See for example - http://www.edax.com/

One find this useful in the future:
http://www.keytosteel.com/default.aspx?ID=Articles
 
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  • #9
The few times I've used EDX compositional analysis on fracture surfaces using an SEM (failed combustion engine components), I've generally found false carbon peaks to be down to oil contamination.
 
  • #10
for instance,i broke using tensile mechine steel sample A first, and i did not do any preparation,i.e coating, before place it into SEM,the result of its composition comes out by EDAX on carbon is 2.74% comparing to theoretical value 0.1%...basicly same things happened to copper and aluminum...
 

Related to Investigating Extra Carbon in Steel Using SEM

1. What is the purpose of investigating extra carbon in steel using SEM?

The purpose of this investigation is to determine the amount and distribution of extra carbon in steel samples. This can help in understanding the quality and properties of the steel, as well as identifying any potential issues or defects.

2. How does SEM help in studying extra carbon in steel?

SEM (Scanning Electron Microscopy) is a powerful tool for studying the microstructure of materials. It uses a focused beam of electrons to create high-resolution images of the sample, allowing for the visualization of the distribution of extra carbon in the steel at a microscopic level.

3. What are the steps involved in investigating extra carbon in steel using SEM?

The first step is preparing the steel samples, which involves cutting, grinding, and polishing them to a smooth surface. Next, the samples are coated with a thin layer of conductive material to prevent charging. The samples are then placed in the SEM and scanned using the electron beam. Finally, the images and data collected can be analyzed to determine the distribution of extra carbon in the steel.

4. What are the advantages of using SEM for this investigation?

SEM provides high-resolution images and allows for the examination of a wide range of materials, including steel. It also offers quantitative analysis of the distribution of extra carbon, providing more accurate and reliable results compared to other techniques. Additionally, SEM is non-destructive, meaning the samples can be reused for further analysis.

5. How can the results of this investigation be applied in the industry?

The results of this investigation can be used to improve the quality and strength of steel products in the industry. By understanding the distribution of extra carbon in steel, manufacturers can adjust their production processes to ensure consistent and optimal levels of carbon in their products. This can result in stronger and more durable steel, leading to better performance and customer satisfaction.

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