Metal grain in various materials 1

[Manifolddesigner]

Hello all,
I'm interested to know which direction the grain goes in most common structural materials.

Flat Billets & sheet metal->Look at it, ok, along the grain. Got it.

Round Rod - Along the axis? perpendicular to it in hoops? or perpendicular to it straight?

Tubing?
Welded-Made from sheet steel-Which direction though?
DOM-I understand is spiral welded and then Drawn-Over-Mandrel?
Seamless?

My mechanical engineering text is awfully vague about this and just says "orienting the grain properly can be up to 50% stronger". Machinery handbook is hiding.

It seems like it would be convenient to have something 50% stronger (or lighter). Is there published tensile strength data for most common metals oriented both along and against their grain? I understand most book tensile strengths are the weakest side.

Does anyone have any suggestions for determining the grain orientation in some random block of metal?

If these questions are answered in a book, please recommend.


Jason Minahan
J Minahan Designs
JMinahan.com
Auto-Engineer.

 

[gariartola]

A good way to determine grain orientation is finding a lab with an Scanning Electron Microscope and asking them to EBSD (Electron Backscattered Diffraction) your sample and plot the grain orientation map. It can take about a working day (optimistic) to prepare the sample, run the EBSD analysis and get the data processed and sent back to you (provided tehre is free SEM time in the lab and your part can get through straight away).
Anyhow you can asume an orientation provided you know the deformation and thermal story of your material. Cold rolled materials will prefereably align their grains in rolling direction, hot rolled materials too but might have some new grains from recrystallization processes. If you heat treat the material after having deformed it, you an dissolve the internal structure so... it depends...
I hope you can find sth useful in this post!

 

[CoryPad]

Round rod has grain orientation in the axial (longitudinal) direction.

Welded tubing can be made from sheet curled in either direction, which means grain orientation can be circumferential or axial (longitudinal).

DOM tubing usually is not spiral welded, rather it is longitudinally welded.

Seamless tubing can be made by different processes, including a rotary piercing method. This can produce complex orientation patterns.

Static strength is not going to vary by 50 % based on grain orientation. Fatigue strength may vary by this much.

In a random block of metal, EBSD can be used to determine grain orientation. Microscopic examination of the block after sectioning on three orthogonal planes also can be used.

 

[EdStainless]

If the material has been annealed after the forming there is no grain orientation. The grain pattern will be uniform and random. This is why materials have the same properties in all directions.
There are special cases where you want grain orientation, but in most cases it can be bad.

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Plymouth Tube

 

[Wrenchbender]

In answer your question on billets, sheet metal, rods, and tubing - Logically enough, grains in wrought metals become elongated in the working (rolling, drawing, forging) direction.

Also any impurities (always present in commercial products) become elongated as evident in macroetch inspections (e.g. ASTM E381). It may be possible to take a random block of metal that you mentioned and apply this type of inspection. The impurities outline the grain flow; the metal grains themselves may be too small or not clearly visible macroscopically, esp in ferrous alloys. In weldments (castings), grains are usually more ‘equiaxed’ and their geometry depends on cooling rate and direction of solidification.

“50% stronger” is optimistic, but impact strength and elongation are better in the longitudinal direction because of the impurity factor. UTS and YS are much less affected.

It may be interesting to note special cases – single grain turbine blades and amorphous metal which has no grains.

Some good reads, as your requested, are
Metals Handbook, 2nd Desk Ed., p. 88(Crystal Structure of metallic Elements)
ASM Tool Steels
Internet searches on ‘Crystallographic texture’, ‘mechanical texture’

 

[EdStainless]

In same materials such at Ti which are a hexagonal structure (not cubic) you can get some odd properties. Ti sheet is rolled to 0.020" from 14" slab with no recrystallization anneal. The result has such strong grain texture and preferred orientation that the modulus in the longitudinal direction and transverse are different by 1.5-2 million psi. This is over 10%.

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Plymouth Tube

 

[Manifolddesigner]

Great info guys,

RE: ASTM E381, Without spending $40 on a white paper, could you give me the gist of it? I’m guessing: Surface grind the specimen, etch it w/ acid, look at it w/ standard 40x optical microscope?

Still trying to wrap my head around this whole grain thing. It’s getting late, sorry if I’m rambling halfbaked ideas out..

How anisotropic can you make a steel or aluminum specimen w/ grain structure? EdStainless mentions HCP structure’s modulus can be 10% different. How about the tensile strengths? Maximum of 50% in extreme situations like my text was saying?

How would you make ^more^ grain if you wanted it? Lots of cold working in that direction?
Example.
I’ve got a mild steel tensile test sample and I want crystals to run the entire length of the part, like a piece of cable. More, smaller wires in cables are stronger that a few coarse ones, I assume this would hold true wrt grains. Super long, thin impurities would probably not be that bad as long as they didn’t cross the middle of the crystals…
Say I start w/ a piece of Q&T Steel rod or bar (no grain orientation…but still grain cells?), then partially shear it or squish it along the axis a billion times (planishing hammer?). And finally roll the narrow section in the middle. Since it’s along the axis, how would the strength properties be affected?
Would this be an ideal situation or would some other fiberglass weave style thing be more “ideal”?
Would the sample then become ductile in one direction but brittle in another? Which ones?

Could I induce grain growth in a finished sample by heating the part evenly, then holding a piece of dry ice to one end?

Jason

 

[CoryPad]

The gist of ASTM E 381 is immerse the sample in hot acid, wash then observe the specimen without magnification or maybe up to ~ 10X. There are reference images you can purchase separately from ASTM International for comparison purposes.

Anisotropy affects ductility most, strength not as much. For common steels and Al alloys, you aren't going to see much difference - maybe 20 %, not likely 50 %.

Yes, lots of cold working along a single axis will produce the highest preferred orientation or metallurgical texture. Wire is a good example. When you develop this high texture, you reduce the ductility a lot.

You induce grain growth by heating the part evenly and allow for recovery, recystallization and grain growth. The dry ice is not necessary.

 

[EdStainless]

elongation of grains only causes small changes in properties. If the elongation also causes a preferential grain orientation then you might get 25% variation in strength, but that would be extreme.

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Plymouth Tube

 

[Robertmet]

"50 % stronger" ,I question that. There are two things involved with grain orientation. First is the anisotropy, second is the non-metallic inclusions. In the 'old days' inclusions made a big difference but today with modern steel making methods it isn't nearly as significant.Another thing is grain size which can be very important.