×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Cronidur 30 Etch

Cronidur 30 Etch

Cronidur 30 Etch

(OP)
I have a part that came in for a metallurgical inspection made of Cronidur 30 (aka N360 Iso-Extra and AMS 5898). We have tried etching in both Nital and Vilella's, our standard etchants for most materials. Neither reveals much of a structure and the part also seems to have scratches afterward. Can anyone recommend a microstructure etchant for this corrosion resistant material?

Aidan McAllister
Metallurgical Engineer
Automotive Enthusiast

RE: Cronidur 30 Etch

You might find the excerpt from the book below interesting for background information, and it does provide a description of the microstructure for Cronidur 30 bearings.

http://books.google.com/books?id=VQOVbmvTyxQC&pg=PA137&lpg=PA137&dq=metallographic+etchant+for+Cronidur+30&source=bl&ots=Wg9yRUl8WS&sig=XqhHNquj4V6vO-dF32fr9WHWtKQ&hl=en&ei=kmMATPj0JJPyM-7F4JYM&sa=X&;oi=book_result&ct=result&resnum=2&ved=0CBMQ6AEwAQ#v=onepage&q&f=false

I did not find much information regarding etchants for this HNS martensitic stainless steel. I would recommend you contact Buehler, specifically, George Vandervoort for etchant techniques/recommendations.

http://www.buehler.com/
 

RE: Cronidur 30 Etch

(OP)
Thank you very much. I couldn't find much information myself on Cronidur 30. That helps some. I will try to get in contact with Mr. Vander Voort, I have seen much of his work in various magazines and books before.

Thanks

Aidan McAllister
Metallurgical Engineer
Automotive Enthusiast

RE: Cronidur 30 Etch

Aidan,

I'm not sure if you or metengr noticed, but the authors of the article from the above link described the etchant that was used (2nd to last paragraph on page 137).  I have not personally used HF + molybdic acid (MoO3) as an etchant, so I cannot give any advice as to its usefulness for this alloy, but boiling HF is not your everyday lab chemical.

I don't think nital by itself will etch this alloy, but maybe adding some HCl to it would improve the response.  I would try 5-10% nital + 5-10 mL HCl.  Another option would be to revisit the Vilella's etch, but to use a different ratio, such as the one suggested by Struers in the following Application Note:

http://www.struers.com/resources/elements/12/101820/Application%20Notes%20Stainless%20Steel%20English.pdf

One suggestion from GVV and Buehler for etching martensitic stainless steel is modified Fry's reagent (150 mL H2O + 50 mL HCl + 25 mL HNO3 + 1 g CuCl2).  Here is a link to some of their technical information on etching:

http://www.buehler.com/technical_information/Buehler%20Book/etching.pdf


By the way, I am not sure that GVV works for Buehler any more.  The latest issue of Industrial Heating has an article authored by him, but it shows his affiliation as a consultant to Struers.  I haven't tried to contact him to confirm his whereabouts, so if anyone else does, please share with the group.
 

RE: Cronidur 30 Etch

My color metalography reference text shows the following for stainless steels (all types):

5-10ml HCL (35%)
1-3ml selenic acid
100ml ethyl alcohol (95%)

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources