Subject: Grain Structure

From: [email-masked] (Mark McDade x6841)
Date: Tue, 10 Jan 1995 16:14:03 GMT

Can an amateur with a microscope and common chemicals prepare a 
steel surface and see the grain structure - can I see the changes
induced by heat treatment?  How about other metals (does grain
structure even matter with other metals)?

Mark McDade
[email-masked]

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From: [email-masked] (William Judson Ready)
Date: 10 Jan 1995 13:03:36 -0500

>structure even matter with other metals)?
=================================
Yeah, its easy.....You can do either a macroetch (which reveals the flow
patterns of the piece and doesn't require a microscope or polishing).  Or,
you can polish it (you didn't say anything about polishing equipment),
down to say 0.05 micron and microetch it.  What's the maximum
magnification of the microscope??  What chemicals do you consider common?

Keep posting, we'll help.

 - Jud Ready

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From: [email-masked] (Kuzmack)
Date: 12 Jan 1995 02:52:33 -0500

In article <[email-masked]> Mark McDade asks:

>Can an amateur with a microscope and common chemicals
>prepare a steel surface and see the grain structure - can I see
>the changes induced by heat treatment?

Jud Ready in <[email-masked]> responded:

>You can either do a macroetch (which reveals the flow patterns
>of the piece and doesn't require a microscope or polishing).  Or,
>you can polish it (you didn't say anything about polishing
>equipment) down to say 0.05 micron and microetch it.

The macroscopic or deep etch won't show grain structure, but it
will show changes from heat treatment.  The specimen is treated
with a mixture of equal parts (by volume) of hydrochloric (muriatic)
acid (available at hardware stores) and water at 160 degrees F for
20-30 minutes depending on the type of steel alloy it is.  

To see gain structure requires a microscopic etch.  The specimen
needs to be highly polished, but the amatuer without polishing
equipment can do an adequate job by hand with enough patience
and elbow grease.  First make sure that the specimen fits under 
your microscope with the target flat surface face up toward the
objective.  Start the polishing process (by grinding) with 150 grit 
paper face up on a flat surface and move up through paper with
220, 320, 400, and 600 grit.  Change to the next finer grade when 
the marks from the previous grade are no longer visible.  Be sure
to clean up abrasive dust between grades.  Then polish with 0.05 
micron aluminum oxide if available (plain white paper has been 
used with satisfactory results, but takes longer).

The polished surface is then washed with absolute alcohol.  The 
etch is done with 0.2 - 2.0 percent nitric acid in absolute alcohol 
for a few seconds to a few minutes and washed with running water 
followed by absolute alcohol.  Denatured absolute alcohol is 
available as a painting supply at most hardware stores.  Nitric acid 
may be more of a problem to come by (it can be prepared, but
that is another story).  

The etched surface is examined under the microscope at powers
>from  400 to 800 or 1000.  Depending on the heat treatment of the
specimen, the characteristic structures of ferrite, pearlite, 
cementite, martensite, and combinations of them should be readily 
identified.  A good metallurgy text should provide pictures that will
help you understand what you are seeing, but experience is the
best teacher.  

Rich Kuzmack     ([email-masked])

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From: [email-masked] (Ian P Kemp)
Date: Sat, 21 Jan 95 09:19:53 GMT

>structure even matter with other metals)?
...yes, certainly.  The main hassle is that you need to prepare a
fairly highly polished surface, preferably which is flat over a
reasonably large area.  Normal procedure in metallography would
be to use silicon carbide paper ('wet & dry'), wet, to abrade
suitable area - remove enough material to expose the metal, away
>from  'surface effects'.  Then abrade with succesively finer grit
SiC paper to remove the scratches from the coarse paper.  Finish
up with say 400 grit, then change to polishing, with a nap cloth
impregnated with diamond or alumina paste and an oil lubricant.
For best results you need to use a sequence of succesively finer 
grade polishes, say 14-micron, 6-micron then 3-micron.  3u will
produce a fine enough polish to reveal the main features of the
structure; for better results go on to 1-micron and 1/4 micron.

When you have a highly reflective surface to look at, etch it
with 2% nital (i.e. wash the sample with a solution of 2% nitric
acid in ethanol) for a few seconds, then check it under a 
microscope at say 100x or more mag.  Oh, after applying the
etching solution, wash it off with pure ethanol, then rapidly
evaporate this with a hair drier, then use the microscope.
if you can't see any grain structure, etch for a bit longer,
and repeat as necessary.

The 'black art' is all in the polishing!

Same procedure for other metals, but use a different etching
solution.  Softer metals (e.g. copper alloys) are more difficult
to polish without scratching!

By the way, if you want to easily see the grain structure of
a metal, have a look at a galvanised garbage bin, or
galvanised steel lamp-post, if they use these near where you live.

Good luck!

>[email-masked]

///\   Ian Kemp, BHP Steel, Port Kembla, NSW, Australia
\///   [email-masked]

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From: [email-masked] (Norman Billingham)
Date: 22 Jan 1995 14:05:00 GMT

Ian P Kemp ([email-masked]) wrote:
: [email-masked] (Mark McDade   x6841) writes:

: >Can an amateur with a microscope and common chemicals prepare a 
: >steel surface and see the grain structure - can I see the changes
: >induced by heat treatment?  How about other metals (does grain
: >structure even matter with other metals)?

DELETED

: When you have a highly reflective surface to look at, etch it
: with 2% nital (i.e. wash the sample with a solution of 2% nitric
: acid in ethanol) for a few seconds, then check it under a 
: microscope at say 100x or more mag.  Oh, after applying the

I'm sure this is authoritative advice.  However, be extremely careful if
mixing nitric acid with ethanol.  I don't know what the limits are, but
these mixtures can expolode violently if there is too much acid.  I have
twice seen windows blown out of a laboratory by someone accidentally
pouring nitric acid into ethanol.

Norman Billingham
Sussex University
England

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From: [email-masked] (Andrew Y. Kim)
Date: Sun, 22 Jan 1995 16:03:06 UNDEFINED

>pouring nitric acid into ethanol.

Make the nital in small quantities, carefully adding the acid to the solvent, 
do not store it away, do not put it in closed containers, use an open 
container with a fume hood.

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From: [email-masked] (J. Kimberlin)
Date: 22 Jan 1995 18:20:50 -0800

>pouring nitric acid into ethanol.

Really!  There is no reaction at all in mixing nitric acid with ethanol.  
You just take 98 ml of ethanol and add 2 ml of conc nitric with an 
eyedropper and the stuff doesn't even get hot.  Done it a hundred times.

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From: [email-masked] (MadMat9)
Date: 24 Jan 1995 23:59:52 -0500

Yes, there usually is no reaction.  But in other concentrations and larger
volumes, there is an explosion hazard.  I was in school when two grads
were working with sponge metal particles.  They wanted to 'degrease' then
in ethanol, but they also wanted to etch them.  Thinking they were dry,
they put the ethanol-laden pieces in a beaker of nitric.  They soon
smelled something funny, and went into the next room to investigate.  Its
lucky they did -- the explosion blew out the fume hood completely.

Never make more than 10 ml or so.
NEVER NEVER store this stuff.

The poster may have done it 100 times, but you may not be so lucky.  There
IS a reaction when nitric and ethanol (as well as many other organics)
come together in the right proportions.

Mat

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From: [email-masked] (J. Kimberlin)
Date: 25 Jan 1995 16:09:44 -0800

>come together in the right proportions.

No point in storing anything these days that can be made so simply.  Your 
explosion was not a result of simple mixing but just plain stupidity.  
Sponge metal, especially palladium, is very dangerous.  But nital is not 
dangerous when made and used as an etchant for polished surfaces.  Much 
more dangerous is picral, also used as an etchant.

JerryK