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Selecting steel for steel stamps


#1

I will be teaching a class in making steel stamps soon. Although I
can order water-quenched annealed tool steel (actually, drill rod
blanks) and have it cut to length, it would be cheaper to use old
tools, such as Allen wrenches or push rods from car engines. I prefer
to water quench rather than oil quench since I will be working inside
in a classroom. I understand I’ll have to anneal the old tools and
then let them cool slowly in sand or ash for several hours. My
question for the metallurgists out there is: does it matter whether
the old tool was originally oil or water quenched? Does the annealing
process essentially take you back to the original grain structure and
enable you to use either method of quenching, or is there some
residual effect from the original quenching that requires you to
continue to use the same type of quenching media? If so, how would I
know whether oil or water was used to originally quench (during
hardening and tempering) the tool I’m now modifying?

Also, after heating to the annealing temperature, can I cool the
steel in a kiln that has been heated to the proper temperature and
then shut off so that it cools slowly, or is there a problem with the
air coming into contact with the cooling steel?

Thanks!
Emie Stewart


#2

Hi Emie:

Err…I’m not sure about random spare tools really being cheaper. I
just did a term on chasing and repusee with my folks, and we got 1/4"
square W1 (water quenching) drill rod. A 4" tool blank worked out to
about 75 cents. (I got them from MSC, they’re calling it “Square bar
cold drawn tool steel” Page 1735 of the catalog. 3 foot stick =
$6.25) I got them as 3 foot sticks, and chopped them down into 4"
blanks from there.

Annealing in a kiln, and letting them cool with the kiln is a really
good way to do it. The oxygen may scale the outside a bit, but it
shouldn’t be a problem with any of the alloys you’d want to be
playing with.

Now for the fun part: yes, it still matters what the quenching
medium the steel was designed for. Oil steels will never like water,
no matter what you do to them. It’s a function of some of the
components that make up the steel, not anything they may have ever
been quenched in before. Oil steels are liable to crack if quenched
in water. God help you if you run into any air quenching steels.
Those will make your day really interesting.

The problem with valve stems, pushrods & etc is that they can be
anything. They don’t even have to be all one thing or another. Some
of the modern valve stems are air-hardening steel friction welded
onto mild steel bits, so one bit won’t harden at all, and the other
won’t really ever soften. Engine components are made from all sorts
of odd things these days, and there’s no telling what that piece of
steel in your hand is actually intended to harden in, if at all. It
could be case-hardened, just to make your life complicated. Once you
really get to know the zen of steel, then you can play with scrap
much more confidently, but until the point where you can spot the
difference between hi and low carbon by their sparks, and have a
good sense of what W1 sparks like, as opposed to O1 or A2, I wouldn’t
try to teach a class depending on scrap.

Once you count all the scrounging and fussing with random god-knows-
what, 75 cents for annealed, known material is starting to look
pretty good.

Regards,
Brian Meek.


#3

Emie, the method of quenching is dependent on several factors.
Number one is carbon content. Higher carbon steel needs to be
quenched in oil, else it will crack or shatter. Medium carbons are
fine in water. Lower carbons can be quenched in a saturated brine
solution, which is slightly more aggressive than plain water. Also,
some tool steels are formulated to be water hardening, some oil
hardening, and some air hardening. If you get an air hardening steel,
you will most assuredly crack or shatter it in water. There is
functionally no way to know how existing tools were hardened, nor the
carbon content, other than a spark test, or by experimenting around.
Unless you happen to be real lucky, you’ll probably be better off
buying known tool steel new.

You can anneal via the method you mention, leaving it cool slowly
inside the kiln. You can also use a pail full of Vermiculite, that’s
how I anneal. Yes, annealing will make the steel as soft as you can
get it. Bear in mind that after you create the stamp, you will want
to harden and then temper it.

Michael
www.radharcknives.com


#4
Number one is carbon content. Higher carbon steel needs to be
quenched in oil, else it will crack or shatter. Medium carbons are
fine in water. 

Hey Michael while it is the alloying elements that determine how fast
the steel needs to be quenched to retain the martensite structure
that makes it hard it is not the carbon but the other elements that
determine quench speed. High carbon content can be air quenching (A2
0.95-1.05% C), water quenching ( W1 0.70-1.50% C), or oil quenching (
O1 0.85-1.00 % C )

you'll probably be better off buying known tool steel new. 

You are absolutely right.

Emie, buy your tool steel so you know how to treat it. Also I would
not use water hardening drill rod which is W1 for a punch. I would
use O1 as it is somewhat less shock sensitive and less likely to
fracture when struck.

Jim

James Binnion
James Binnion Metal Arts


#5

most of the steel I worked with was oil quenced. If it goes
vise-versa it can crack the piece. Drill rod is pretty cheap and
ready to work/ grind to shape. Messing around with old push rods &
allen wrenches Involves much more work imho.

Cutting off the parts of the tool you don’t need, heating up past
magnetic, cool down, re-grind / shape, re-heat, polish, temper. With
drill rod, chose a close diameter, shape/ grind to suit, heat and
quench & polish.

my $.02
mtlctr


#6

Hi Ernie,

As a Jeweler Who also teaches in an c.c. art department with little
to no tool or repair budget( I gather you’re in a similar situation)
I recommend gathering and testing scrap steel to make chasing tools,
chisels and design stamps. Your post indicates you’ve already
identified Allen wrenches and pushrods as tool steel sources ; how
about old worn out files and cheap poorly made files from china( the
steel in these tends to be ok quality and can be purchased new
inexpensively). Prowl pawnshops and junk stores for files. don’t
spend more than a dollar for a large file and if the bin in which
the files/ Allen wrenches is full, offer the proprietor a cheaper by
the pound price. You should also check out the local fencing
academy/club if there’s one near. Broken foils and sabers are made of
excellent steel and have unusual and interesting cross sections with
which to make interesting design stamps.

After acquiring enough used steel for your needs use a small cutoff
wheel attached to a high speed tool like a dremmel to notch the blank
material at the appropriate length for whatever kind of tool your
making. I usually then snap the blank off in a vice with a cloth
towel covering the area to be broken. This prevents any shards of
steel from flying about. Pack your blanks into a steel can salvaged
from the kitchen and completely cover them with clean sand to prevent
excess oxidation. Place the can(s) into a kiln and bring the
temperate up to 1250 degrees Fahrenheit and soak at the annealing
temperature for 30 to 45 minutes. I use several smaller diameter soup
cans rather than say a larger diameter coffee can to keep the heating
cycle shorter; their smaller mass requires less soak time to insure
the core temperature reaches the annealing target temperature. After
soaking at annealing temperature simply turn off the kiln and let it
cool with the door closed (4-6hrs.).This should yield a whole mess of
well annealed blanks with which to create tools. I usually prepare
several stamps from the varied scrap tool steel and harden it so I
know that it’s high carbon and useable for the students. I only use a
water quench. Occasionally I run across some cheap stuff that wasn’t
actually tool steel and is unhardenable or even more rarely some
special purpose steel that is unannealable. Making a few hardened
tools insures that the stuff I’m giving to the students will work and
prepares several items for the tempering step which the students
generally need to see a couple of times to properly discern temper
colors on steel.

Don’t forget to torch anneal a couple of tool blanks in front of
your students at the demonstration; I explain that they need to
understand torch annealing of steel so they can do it if they only
need a single tool blank or if they have a torch but no kiln
available. I also explain I’VE ALREADY annealed the class tool blanks
so our limited fuel gas budget is not totally consumed by annealing
steel tool blanks.

Remind your student to do the reading and point out that there is an
operational difference between ferrous and nonferrous annealing. I
always get comments like " It’s all just metal isn’t it? How could it
be different?". Remind them to wear safety glasses and Good Luck.

Mike Edwards
Associate Faculty
Collegeof the Redwoods
Art Department- Jewelry


#7
Does the annealing process essentially take you back to the
original grain structure 

There’s been a lot of good advise for Ernie already - to the degree
that I remember it, I’ll go back a little farther for anyone. This
comes under the heading of “stuff you learned but then after you
understood it you forgot some details because all you needed was an
understanding of it.”

It’s not really “grain structure”. In a nutshell, a piece of fully
annea= led tool steel is a mixture of iron and carbon (maybe not
precisely, but good enough for here and now). When you heat that
steel to a certain temperature, the crystalline structure changes
from ferrite (simple iron) to austenite, which is another structure.
In that process, since there’s carbon present, it also forms solid
solutions with it: Martensite, pearlite, cementite, bainite… All
of which is quite complex and can be explained better than I am
doing…

If you do that and then quench the metal, those structures and
solutions become frozen in the metal - it retains the same state it
had when it was hot… And those structures and solutions are what
makes the steel hard. When you heat it up again, the same things
happen, but if you let it cool slowly the carbon comes OUT of
solution, the crystalline structure goes back to ferrite and the
steel goes soft again. Complex but simple to understand in general.

Otherwise: I wouldn’t teach a class with stray bits and pieces and
sizes of mystery metal, but that’s just me. Teaching them that
there’s plenty to be had out in the world is a good thing, but
they’re paying you.

To some degree it qualifies as “not rocket science”. Much of the
stuff of steel specs is about arcane engineering problems and
strength under load and stuff. Just about any hardness of any steel
will make a decent stamp… I’d vote for W1 drill rod, myself. It’s a
fine steel…

http://www.donivanandmaggiora.com


#8

There are also the S series of tool steels, some are affordable.
Emie, S series means shock resistant tool steel.

Michael
www.radharcknives.com


#9
I only use a water quench. 

This is potentially dangerous for your students. Many of the tool
steels in things like allen wrenches are oil hardening. While a water
quench may not result in immediate fracture it can produce a tool
that is so highly stressed that it cracks in use, sending little bits
of sharp hardened steel flying around the room. For scrap steel first
try oil quenching and see if it gets hard enough, then if not try
water quenching. It is much safer that way. Corn oil or other
vegetable oils will work well for the size tools you make by hand.

James Binnion
James Binnion Metal Arts


#10
Does the annealing process essentially take you back to the
original grain structure 

In a word, no it does not take it back to some original structure.

When you heat basic carbon steel (iron-carbon alloy) to between
727-912 C or 1341-1673 F It changes its crystal structure to become
austenite a face centered cubic or FCC crystal. This pretty much
obliterates the previous crystal structure of the steel. This is a
radical change in structure from the body centered crystal BCC
structure of lower temperature steel. You must heat to above the
austenite transformation temperature to harden the steel. One way to
test this is that austenite is not ferro magnetic so steel that is
hot enough to harden is no longer attracted to a magnet. Once you go
through this austenite phase transformation you can cool it in such
a way as to cause it to transform to martensite. This is a fine
needle shaped grain structure that is the hardest form of steel that
is also quite brittle, for a micrograph of the martensite grain
structure go to

http://en.wikipedia.org/wiki/File:Steel_035_water_quenched.png.

In basic carbon steel you need to cool or “quench” the steel at a
rate in the neighborhood of 1000C per minute to freeze the steel in
the martensite crystal structure. This almost has to be done in water
as other quenching media are too slow.

If you allow the steel to cool at a slower rate then it will
transform to a mixture of one or more of these other structures
pearlite, bainite, ferrite (pure iron), or cementite (iron
carbide).Pearlite is a lamellar (layered) structure of 88% ferrite
and 12% cementite See

for a micrograph of pearlite, the pearlite is the striped crystals.
Bainite is a lamellar structure as well but the layers are too thin
to be seen with a light microscope and can only be resolved with an
electron microscope. The proportions of these crystals in the
quenched steel will vary depending on cooling rate and alloy
composition.

If you succeed in cooling the steel fast enough to make martensite
you need to temper it. By heating to a specific temperature some of
the martensite transforms to a mixture of bainite, pearlite, ferrite
and cementite. This makes the steel softer tougher and increases the
grain size. The temperature you need to heat to and time to be held
at that temperature is going to depend on the use of the item and the
alloy composition of the steel. There are lots of references to
approximate temperatures for various uses in many of the jewelry
texts so I will not go into them here. But often these texts do not
cover time at temperature. For the best results holding the tool at
the tempering temperature for an hour or so will make for a much
longer lived tool, it takes time for the carbon to diffuse in the
steel matrix. Just a quick trip to the desired temperature will
provide only a partial transformation of the martensite to the other
forms of steel crystal structure and can mean that the tool will be
more brittle than desired.

Ok so for plain carbon steel you need that really fast cooling rate
to capture the martensite structure. When other elements are added to
the steel for various property enhancements the speed of
transformation changes and typically it becomes slower as other
elements are added to the steel alloy. This is where we get oil and
air hardening tool steels. The alloy additions have slowed the
transformation of martensite to other structures to the point that a
slower quench sometimes even air cooling will still capture the
martensitic structure. The mechanics get much more complicated when
talking about alloy steels and I will not go into them but the thing
you need to know is that martensite is a highly stressed structure
and in some of these alloy steels using too fast a cooling method
will stress them to the point of self destruction. Many steels in
their martensitic state will fracture if you drop them some will
fracture if you allow them to sit around at room temperature before
tempering them so you allow them to cool to 150 F then take them
right into the tempering oven. The upshot is that if you don’t know
what kind of steel you are working with you can easily ruin it if the
wrong cooling rate or tempering process is used. There are literally
hundreds of alloy steels in regular use by manufacturers 40 or 50
years ago you could count on finding scrap steel that had fairly
simple characteristics that you could easily repurpose but modern
manufactured goods are much more likely to have more complex steels
in them. Known quality alloy tool steel is easily purchased in a wide
variety of shapes and sizes. why put a bunch of work into steel that
you have no idea of what its composition is or its suitability for
your use.

Hope this helps and doesn’t confuse things too much,

Jim

James Binnion
James Binnion Metal Arts


#11

I missed the original posting on this, but I’ll chime in anyway! I
highly recommend the use of center punches or nail sets as raw
materials for making stamps. I used to get mine at a swap meet, but
now I’ve found them online. It’s good steel and works with water.
They often come in sets of 4 or 5, in different sizes- very handy!
My favorite aspect is the knurled or checkered surface on the shaft.
The key thing in stamping is to put it right where you want it, and
being able to grip the shaft securely helps a whole bunch. You’re
limited by size at the upper end, but I’ve often used larger types of
punches for bigger stamps.

Allan
www.silvermason.com


#12

I found 36" lengths of inch annealed O1 drill rod for sale at
mcmaster.com for less than $2.80 USD. I found them as part number
8893K36.

Again, the usual caveat. not pitching them, but the price seems
reasonable.

Mike DeBurgh, GJG
Henderson, NV


#13

Thanks so much to everyone for the detailed answers. It’s been about
30 years since my college metallurgy course, but my foggy memories
do recognize some of the concepts discussed in the answers. You
confirmed my instincts: know what type of steel you are starting
with, which indicates buying the steel already annealed. Thanks
again, and maybe I can slip in so physics of metallurgy to my
students!

Emie