Metal Grain Direction Test? 5

[luket]

Is there a test that can be done to determine grain direction of stainless 301 1/4 hard sheet? A part has been installed, but grain direction is not known. Specifically, is there a test that could be done installed - meaning tests that don't involve bending the sheet, etc.?

Thanks,
Luke

 

[MikeMet]

You can perform insitu field metallography if you have access to the sheet and room for a man to polish the surface.

 

[EdStainless]

What difference does it make? I don't know why 304 sheet would have a significant preferred orientation.

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[luket]

MikeMet - thanks - that is what we are doing.

EdStainless - my reference, MMPDS, has 301 1/4 Hard with very different properties for Fcy. Do you have data to the contrary?

 

[EdStainless]

In order to have different properties in different directions you not only need elongated grains but the crystal orientation of the grains need to be non-random.
Are you talking about compressive yield?
How on earth can you measure that in sheet?
I suspect that the test is inaccurate.

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[TVP]

Ed,

Yes, the OP is referring to compressive yield strength. MMPDS-01 is the successor to MIL-HDBK-5, and is considered one of the most reliable sources of mechanical property data for metals. I checked the section on austenitic stainless steels and Type 301 specifically, and indeed it shows a considerable variation in the compressive yield and tensile yield strengths for cold worked Type 301: for the particular example of Type 301 1/4 hard, the reported Fcy and Fty are 44 ksi and 69 ksi, respectively.

I must admit, I was not aware that such anistropy existed for cold worked austenitic stainless steels, so I did a quick Google search for "Bauschinger effect stainless steel" and found many hits. Here are two with freely available .pdfs that describe the Bauschinger effect in some amount of detail, including how compressive yield strength is measured in thin sheet materials:

STAINLESS STEEL – PLASTICITY AND CONSTITUTIVE MODELLING

http://www.worldstainless.org/NR/rd...sssteelplasticityandconstitutivemodelling.pdf

MICROHARDNESS TESTING AS A METHOD OF EVALUATING BAUSCHINGER PHENOMENA IN COLD FORMED 301 AUSTENITIC STAINLESS STEEL SHEET USED IN AUTOMOTIVE HEAD GASKETS

http://tptc.iit.edu/Center/Papers/Bauschinger-301SS.pdf

The references for the second paper probably show some of the definitive work that has been performed on this subject.

 

[luket]

Ed - thanks for the input

TVP - thanks for clarifying for me and for the input and the papers. I am looking at them now, although they are a little above my materials pay-grade...

Now, it gets interesting. We had a lab examine some samples, and they send back this:

"The subsequent metallurgical examination revealed each plate to be cross-rolled with the grain structure recrystallized, i.e relatively equiaxed grains were observed. A grain size of 7 or finer per ASTM E112 was observed."

So, based on the equiaxed grains, are the properties the same in both directions? And, if yes, which properties are they - the original L or LT?

 

[luket]

TVP - I just realized you're talking about the difference in Fcy and Fty. I'm talking about the difference in Fcy L and Fcy LT.

 

[CoryPad]

luket,

Same thing, really. Anisotropy can manifest in multiple directions, but it is due to the same cause - preferred orientation of structure formed during thermomechanical processing.

 

[EdStainless]

Rather than grain isotropy I would suspect that residual stresses play a major roll in this. What are the L and T tensile strengths? If the grain structure is equiaxed then the strengths should be the same.

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[luket]

CoryPad - thanks - I think I see your point.

Ed - I think you're right. According to my reference, MMPDS, the tensile strengths are almost the same. The only real difference is the Fcy in the L direction.

I know after 10 posts, the question starts losing it's charm, but if anyone is still interested, here is a picture of the grain structure. Given this pic, is there anyway to know which direction the reduced Fcy is in?

 

[CoryPad]

The L direction is left to right (horizontal) in the image. So, if MMPDS-01 lists Fcy in the L direction to be low, the resistance to compressive stress will be low in the horizontal direction.

 

[luket]

Corypad - thanks, can you give me your rationale? Are you basing this on the horizontal marks across the surface, or something based on the grain structure itself?

 

[CoryPad]

The horizontal lines are grooves that form during etching (was this chemical or electrical?) that follow chemical segregation and other structural irregularities that form during thermomechanical processing.

 

[EdStainless]

Cory, I think that the L direction is in-out of the page. The top-bottom is definitely the thickness of the sheet. But the strain lines would tell me that the left-right dimension is the width of the sheet
I don't see any grain deformation in this photo.
Maybe they took the wrong section?

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