Banding in Austenitic Stainless Steel

[a7992]

I recently mounted and etched a 316SS sample and it formed lines across the whole sample. I think it could be banding, can someone give me some information on this phenomena or confirm if this is banding? Also, does anyone know if it would affect the metal's mechanical properties? Finally, how are these 'lines' produced and are they usual or a defect?

Thanks!

 

[metengr]

How did you etch the sample?

 

[arunmrao]

Can the bands be due to mechanical processing marks? These should be seen in unetched condition. An etched stainless steel sample revealing bands I just don't know.

Chocolates,men,coffee: are somethings liked better rich!!
(noticed in a coffee shop)

 

[a7992]

I etched the sample electrolytically using 50% Nitric Acid as the electrolyte. I'm thinking the banding is from cold working the material and might also be known as strain lines. It is seen in a microstructure in the Metals Handbook Vol. 7 but I just wanted somemore information on what happens to the microstructure when forming and what effects it would have on mechanical properties, if any.

Any additional information would be great!

 

[CoryPad]

I have seen the "banding" or "lines" appear after chemical or electrolytic etching. It can be due to chemical segregation and/or crystallographic texture issues.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[mfgenggear]

Cory

please advise what you mean by crystallographic texture issues?

Thanks

 

[metengr]

a7992;
I question your etching procedure. If you have access to ASM Handbooks, I would suggest you review the various choices for macro etchants and etchants for microexmination in Volume 9 for stainless steel.


60 mL HNO3 and 40 mL H2O

Electrolytic etch to reveal austenite grain boundaries (but not twins) in austenitic grades. With stainless steel cathode, use at 1.1 V dc, 0.075–0.14 A/cm2 (0.48–0.90 A/in.2), 120 s. With platinum cathode, use at 0.4 V dc, 0.055–0.066 A/cm2 (0.35–0.43 A/in.2), 45 s. Will reveal prior-austenite grain boundaries in solution-treated (but not aged) martensitic precipitation-hardenable alloys and maraging steels



This web site is also handy

http://www.kaker.com/steel/demo/list/chemical.html

 

[a7992]

Well...I'm pretty sure my etching procedure is fine. I've looked it up as well in the ASM Handbook and from LECO's website. HNO3 is nitric acid...my etchant has 50ml H20 and 50ml HNO3 and I used a stainless steel cathode.

The strain lines do etch and are supposed to but I'm wondering why? You can still see the microstructure but you have to be at a higher magnification.

 

[unclesyd]

Why not use 10% Oxalic acid electrolytically. This method will reveal most anything you need to know about an Austenitic Stainless Steel sample. You will see twinning from cold working and you will see in this paper layered appearance will come from Delta Ferrite.

http://www.struers.com/resources/elements/12/74400/Application Notes Stainless Steel English.pdf

 

[Maui]

Can you post the microstructure that you obtained so that we can see what you are describing?

Maui

 

[CoryPad]

mfgenggear,

Crystallographic texture (also known as preferred orientation) refers to a microstructural feature of what crystal planes are prevalent in a particular section. Just as the crystal structure provides variation of the mechanical properties, it also can lead to variation in chemical or electrolytic etching response. The "strain" effect is an example of this.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[mfgenggear]

Cory

Thank you

A7992 & all others

I had a sample of MarAging with the same issue with Banding
of a micro section.

Looks like the same issues.
I was lurking.

Thanks

 

[a7992]

I've attached the two pictures below. I did try 10% Oxalic on the 316SS but it over etched it and produced a really un-even etch. I don't think this has anything to do with how I etched the sample. I've seen these strain bands in pictures but it doesn't give any information about what effects it would have on the properties of the metal.

Thanks for the help!

 

[TVP]

I'm inclined to believe these are effects due to crystallographic orientation. Take a look at the microstructure image in the following paper, which is for a cold drawn (highly strained) stainless steel wire after electrolytically etching:

http://www.sei.co.jp/tr_e/pdf/industrial/60-4.pdf

 

[metengr]

I reviewed the micrograph in the attached file by a7992. I agree with others that these unidirectional bands are a combination of delta ferrite stringers and crystallographic effects from working the material. I would expect these bands would have little to no effect on bulk mechanical properties for this material.

 

[unclesyd]

Look a figure 9 in the Struers paper.

http://www.struers.com/resources/elements/12/74400/Application Notes Stainless Steel English.pdf

 

[EdStainless]

The banding is real. Mostly from strain effects. You see it in all SS sheet products. Then you get either delta ferrite (304 and 316) or intermetallics (6% Mo grades) in addition.
The lines are real, I would suggest that the 'worm tracks' are polish/etch artifacts.
If your oxalic over etched then you need to control the power better.

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