Help on microstructure identification

[Salvatio]

Dear all,

I have 3 different steel samples in which I have taken a microstructure photo of them as the link below. I was only given the specifications of the steels, but not the chemical composition. My questions is, are these steel martensitic steel (tempered), with precipitations? The application of these steels are to use as strapping material, which is subjected to high load, tensioning, and probably relatively high impact load.

Thank you.

Jeffrey

Sample 1 -

http://www.flickr.com/photos/82669020@N00/247288926/

Sample 2 -

http://www.flickr.com/photos/82669020@N00/247290706/

Sample 3 -

http://www.flickr.com/photos/82669020@N00/247290707/

 

[TVP]

What etchant was used to obtain the micrographs? When you say that you were given the specifications, what exactly were you given? Do you have a standard number such as SAE, ISO, etc.?

 

[Salvatio]

the etchant used was 2% nital. basically the specs given are only the mechanical properties, nothing more. however, about the etchant, I dont really know if it's the suitable one, because the longer i etch it, the precipitate like particles will only grow darker, without any significant signs of clear grain boundries. Perhaps that's why I said that it might be a tempered martensite. However, according to the supplier, the carbon content is in the range of medium-high.

 

[Goahead]

The purpose of microstructure identification is not clear.
Could you have your samples hardness tested?
Can you determine if the material is magnetic?
If it is indeed tempered martensitic microstructure then what is the conclusion you would like to reach?

http://www.welding-advisers.com/

 

[Salvatio]

well..basically i've done some mechanical testing, which also includes hardness. the HRB value is about 104. Why i need to identify is that, due to some reason, i may need to change another supplier. However, the new supplier's material is made from cold-rolling steel, which may give a similar hardness reading. I am definetely sure that the sample material is magnetic. We use magnetic car to dispose them as scrap.
so anyone, any idea what structure is that?
Thanks.

 

[metengr]

Salvatio;
Samples 2 and 3 look more like mixed microstructures containing ferrite/carbides/and bainite. The carbides appear to be arranged in colonies of fine pearlite (dark islands) at least in samples 2 and 3.

Sample 1 looks like a tempered martensite structure containing islands of ferrite.

I agree with the above. There is not enough information to determine if samples 1-3 should be used as strapping material.

 

[arunmrao]

There is so much of carbides in the microstructure that it deceives me into thinking it is a Cr containing high carbon material.

 

[redpicker]

Trying to analyze a microstructure without knowing the composition and heat treatment is a dicey proposition, at best.

Based on what you have described, however, I'd say you are looking at a plain carbon steel (~.4-.6 %C)that has been annealed and cold rolled. The differences in the microstructures reflect differences in the microstructures prior to cold rolling (which, perhaps, are adjusted by the supplier based on the amount of cold rolling and the desired tensile properties).


Just a WAG.

rp

 

[NickE]

HRB is not valid over 100, if you use a steel indenter then you ball is flatted, if carbide it might be cracked. I would do all the normal tests before doing mettalography. IE: arc/spark for chemistry, hardness testing in the proper scale.


Nick
I love materials science!