Subject: Directional properties in plate

From: [email-masked] (MR WILLIAM A HOCHELLA)
Date: Sun, 8 Sep 1996 19:41:48, -0500

To All,
All bars, rods and plates have directional variations in their 
physical properties.
All bars, rods, and plates have three major directions.
The X direction is along the length of the piece and is the direction 
of rolling or drawing.
The Y direction is the width and is perpendicular to the rolling or 
drawing direction.
The Z direction is the thickness of a rolled plate.
In square and round sections, Y and Z are the same.
In plate, the direction with the poorest properties is the Z 
direction.
This is beacuse as the original ingot solidifies, the impurities in 
the melt are forced to the center of the ingot. Look at an ice cube 
from the fridge as an example. The walls of the cube are pure ice and 
towards the center is the air that is being rejected from the liqiud. 
Also salt water rejects the saltier water as the pure water freezes 
first.
What does this have to do with what we do?
Well, if you have access to plate and you wish to flame cut something 
out of it, you must pay attention to how you lay out the work.
The best example is a hammer flame cut from plate. If the side view 
of the hammer is layed out on the top of the plate, the punched hole 
for the eye will be in the X or Y direction. The width of the hammer 
is in the Z direction and eye is stressing the plate in the worst 
place. The eye can split out during punching or hardening.
If the top view of the hammer is layed out on the top of the plate, 
the punched eye will be in the Z direction and the stress of punching 
the eye will be handled by the best directions in the plate.

Food for thought,

Hochewa

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From: [email-masked]
Date: Wed, 11 Sep 1996 21:19:45 -0400

This is an interesting post and I felt obliged to comment.  I have heard this
"grain direction" debate for years and still don't have a definitive answer.
 Some tool engineers that I have spoken to swear that steel develops a
direction of grain flow, but steel is crystalline and shouldn't react this
way.  I read a treatise some time back which stated that hot rolling (or
forging) improved molecular structure, but it was due to better distribution
of carbides which occurred under pressure and not to the direction of grain
flow.  In other words, if the alloying elements tended to form molecular
clumps, then the rolling/forging redistributed them and created a more
homogenous material, but it did not have a "grain".  This article said that
any references to grain are left over from wrought iron, which was a mix of
iron and silica and did develop a grain (it will also split if not forged
correctly).  It seems then, that splits in modern steel while forging may not
be so much related to direction of flow but to the quality of the melt when
it is rolled.  I have seen a lot of mild steel with cold shuts which I assume
were from too cold a temp or maybe a flash or slag inclusion.  Having said
all this, I have also seen rolling direction specified with some frequency on
tool steels, especially if certain types of stress are a problem.  Correct
annealing should solve these types of problems, but you never know...Maybe
some of the metallurgists out there can comment.

Hollis

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From: [email-masked]
Date: Thu, 12 Sep 1996 13:51:56 -0400

To All,
I am a Metallurgist and have done work in the lab on the directional
properties of submarine hull plate. Trust me, the "Z" direction is really
lousy as far as ductility, fracture toughness, impact resistance, resistance
to lammelar tearing, etc. Most normal tensile test bars have an inch or so of
3/4" threads on each end and have a gauge length of 2" @ .505" in diameter.
The tensile test bars I ahd to work with were through the thickness. !/4"
long tensile test bars are a bitch to work with. The good news is that nobody
uses plate where the applied tensile stress is in the "Z" direction very much
except if you lay the side view of a hammer out on the surface of a plate
Nobody uses material directky fron the ingot. Forging and hot rolling break
up the as cast structure. Through the repeated heating and working the
operations tend to honogemize the material. The solidification carbides are
"broken" up by working and repeatedly heating. You solidify from the walls of
the mold inward and as the ingot solidifies the junk is forced to the center
of the ingot. A lot of it also gets trapped in the interdendtritic space.
Given the time that it takes to solidify a large ingot, there is ample
opportunity to grow some pretty big carbides. I have followed a single
solidification cardide for over for 2". Remenber that true Damascus steel is.
Slowly cooled,  high carbon steel that is never worked at a temperature where
any of the solidification carbides are dissolved, hence the pattern that is
developed.
Any way, as the section is changed from large to small any nonmetallics and
some of the larger carbides align them selves along the rolling or forging
direction. Modern steel has "grain". It is not as evident as it is in wrought
iron but anyone that tells you differently has not spent time at a
metallograph looking at the stuff.

Hochewa