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Unusual microstructure of martensitic stainless steel

Unusual microstructure of martensitic stainless steel

(OP)
Hi all,

I have prepared an etched martensitic stainless steel and it appears differently from what is expected. This stainless steel was not used in high temperature application.

I have done some research and the microstructure observed could be a highly tempered martensite or annealed spheroid (see Photograph no.1 at 1000X).

Could anyone advise whether it is a highly tempered martensite or annealed spheroid?


Apart from this, there are clumps of particles throughout the microstructure which I have never seen before (see Photographs below, 100X and 400X).





Could anyone advise on this? Is this aggregation of spheroids?

Many thanks.

RE: Unusual microstructure of martensitic stainless steel

What was the etchant that was used?? Some of the above looks like artifacts in the form of etch pits. What is the hardness?? At higher magnification, the carbides above are spheroidized, which would imply an annealed form. Again, check hardness, annealed 410 martensitic stainless steel is approximately 80 HRB scale.

RE: Unusual microstructure of martensitic stainless steel

What is the alloy? What is the actual C level?
What was the heat treatment supposed to be?


By spec these are usually delivered in the annealed condition.
I would like to see some un-etched micros (use polarization or DIC to get some contrast).

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: Unusual microstructure of martensitic stainless steel

(OP)
metengr and EdStainless

Thank you for the comments.

The etchant used was Kalling's No 2. Hardness is yet to be checked. It contains about 15 % Cr, 0.75% Ni and 0.95% Mo. I do not know the actual C level. I think it is an annealed form. What I am puzzled is the cluster of the "dark" particles, which i have no idea what that is. It can be seen throughout the etched microstructure.

RE: Unusual microstructure of martensitic stainless steel

Re-polish and do not etch. These may be etch pits.

RE: Unusual microstructure of martensitic stainless steel

Metallic007, how much time elapsed between when the sample was etched in Kalling's No. 2 and when these images were taken? If the sample was not rinsed off thoroughly, it will continue to etch in areas where the etchant is still present. That appears to be the case here. Those darker pinpoint areas you examined are very likely spots where the Kalling's has continued to etch.

Maui

RE: Unusual microstructure of martensitic stainless steel

I am going with over etched.
To repolish you will have to back to fairly coarse abrasive to cut the etch pits out.
Give us a shot un-etched.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: Unusual microstructure of martensitic stainless steel

(OP)
Metengr: I did repolish at 6 micron and the dark particles appeared to be pits.

Maui: Thank you for the comment. The time elapsed was about 1 minute.


EdStainless: Below is the unetched microstructure at 100X (taken before etching with Kalling's 2). The dark spots observed are inclusions. Hardness is approximately 50HRC.





RE: Unusual microstructure of martensitic stainless steel

The microstructure and hardness do not indicate annealed. It should be quenched and tempered.

RE: Unusual microstructure of martensitic stainless steel

And if it is Q&T (as I also believe) then it look about right.
I don't see any massive structures.
Can you give us a shop polarized or DIC?
Perhaps a less aggressive etch such as Fry's would work better.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

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