Amongst my small collection of silversmithing tools is a Dixon t-stake with
the words 'semi steel' cast into the base. Does anyone out there know what
this material is?. The stuff is fairly soft and dents easily with a raising
hammer, although it seems to take a pretty high polish and is obviously
More idle curiosity, thanks.
Cast iron (not steel) of increased strength, obtained by using a large
percentage of steel scrap with the pig iron. The quality varies, but if a
known amount of good steel is added, like rail croppings, the resulting
product will have more ductility and strength than cast iron alone. Used for
casters, machine frames and other items where toughness is needed in a cast
In most cases, it refers to a material, made in a cupola furnace, that's
melted from scrap cast iron and a large percentage of scrap steel. It's
considered a high-quality version of cast iron: somewhat freer of
impurities, and with lower overall carbon, and with very little *free*
carbon. It contains a lot of cementite (iron carbide), but it's almost as
ductile and malleable as cast steel. How hard it is depends on how, or
whether, it's been heat-treated. The object in making most of it is to
achieve higher ductility than gray cast iron, so it's generally left soft
and not heat-treated at all.
It was commercialized in high volumes during WWI and has been used in making
machinery parts, mostly, up until recent years. I believe that ductile cast
iron has replaced a lot of it, but I haven't checked in a couple of decades.
If you have a historical interest, be aware that it hasn't always meant
exactly the same thing. In Bessemer's day he called steel with *lower* than
normal carbon content "semi steel." This was a very soft product
intermediate between steel (minimum around 0.08% carbon) and "soft iron,"
which had less carbon still, down close to zero percent. It also has
virtually no sulfur and most other impurities have been oxidized out along
with the sulfur. Basically, it's steel that's been oxidized to a very high
degree, producing carbon levels that are below those normal for steel.
How much of that latter product was ever commercialized, I don't know. But
what you have is almost certainly the first version of "semi steel" that I
described above: cast iron made with a high percentage of steel scrap. It
has *more* total carbon than steel does, but less than typical cast irons.
As the previous poster have said, "semi-steel" refers to a type of gray iron
with a large amount of the charge composed of steel scrap. It is an obsolete
term, although you will still find it on the material specs on blueprints.
These days, most foundries use at least a portion of their charge makeup in
steel scrap and the term is made even more meaningless by the way people
specify castings by tensile class (Class 20, 30, 40 ,50). That being said,
when I get a request for quote from a customer with semi-steel called out on
the print, I generally quote in Class 35 or 40.
Not the same thing, Harold, although you're on the right track in terms of
Ductile iron is an alloy (iron plus magnesium or some other metal, which I
forget). Semi-steel is plain iron/carbon. In semi-steel, the ductility is
the result of the carbon percentage being reduced by adding scrap steel to
the melt, and by much of the remaining carbon being tied up in the form of
iron carbide -- few or no free flakes, unlike the case of gray iron. In
ductile iron, on the other hand, the ductility is the result of the graphite
being converted from flakes to nodules.
I think that most semi-steel applications have been taken over by ductile
iron. Maybe someone can confirm that.
Yeah, in some cases, but not in others. "Cast iron" is generic. Gray iron is
what we usually mean by "cast iron," but not necessarily.
Nodular iron is a name sometimes used for ductile iron. But the automobile
industry, in particular, has drawn a distinction between nodular and ductile
for its own purposes. What the distinction is, I don't know. Maybe just a
slightly different alloy. We ran an article on it in _Machining_ a couple of
years ago but I didn't read it. (Sometimes I don't read everything in
Maleable is a specific material. It's a form of cast iron (white iron, I
think) which is heat treated for an exended time: something like 48 or 72
hours, IIRC, to nodularize the graphite flakes.
There are stainless alloys of ductile iron, and chilled iron (sometimes used
as an alternate name for white iron), and wrought iron, and soft iron
(extremely low carbon, used in the past for transformer and motor armature
stampings; high-silicon, low-carbon iron is used for that today). And there
Ferrous alloys fill entire books.
BTW, Meehanite is not a grade of iron. It's a process. The Meehanite company
uses specific, proprietary iron alloys to make its products, but the iron
itself isn't "Meehanite."
Semi-steel is basically a high grade of gray iron. Gray irons, no mattern
how they are made, have virtually no ductility. The improvement one sees in
a semi-steel gray cast iron is the result of low %'s of phos and sulfur. In
a standard cupola iron made in the 1900's- 1950, tensile strengths were
often quite low, as the charge materials were typically all cast iron and
the resulting iron had phos contents ~.15-.25% and sulfur content >.08.
Using large amounts of steel in the charge reduced these levels by dilution
dramatically and greatly improved the quality of the iron. Another concept
that aided gray iron metallurgy was the concept of carbon equivalent (CE),
which is defined as CE= %C+ ((%Si +%P)/3). Tensile strength and hardness
are generally inversely proportional to CE.
In some cases yes, that is true, but in general, casting buyers generally
rely on the ASTM A48 specification when calling out material specs on gray
iron castings. Some companies get even more specific when specifying gray
iron requirements, calling out graphite flake morphology, flake size and the
percentage of ferrite vs. pearlite. One must keep in mind that ductile irons
have greater tensile strengths and the property of ductility, they are not a
good choice on applications that require vibration-damping and certain
Good point Ed! I get lots of calls from buyers asking me if we produce
Meehanite, as that is the material spec on their prints. I have to tell them
that this is a trademarked name and patented process and that I can't offer
them Meehanite, as we do not have a Meehanite license ( very expensive I
might add!) IMHO, the whole Meehanite marketing process is one of the bigger
scams I've seen.
Meehanite's original research in the need for inoculation and control of
undercooling in the 1930's, laid the foundation for the consistent
production of quality gray irons in the present day. But the Meehanite
process is basic knowledge to most foundrymen today!
Note: Meehanite is the registered trademark of Meehanite Metal Corp. All
references below to Meehanite refer to the one and the same company.
Hmm....there are Meehanite licenced foundries, but as far as I know, there
are no "Meehanite-owned" foundries. Basically any foundry is eligible to
become a Meehanite-licensed foundry, if they are willing to pay the
licensing fees and abide by the "rules" put out by Meehanite. These not
only include the processing techniques but the foundry is subject to audit
of their processes, and because the license may sometimes involves a fee on
the tonnage produced then they have to open their shipment figures to
Meehanite. There are marketing advantages as well.
At one point in time Meehanite also had company in the U.S. that made the
inoculants (i.e. the iron alloys mentioned above) to Meehanite
specifications, but that company does not exist any more. Meehanite is
world-wide, so there may be licensed companies to make the inoculants (iron
The Meehanite Process was conceived in the USA by Meehan and Smalley in the
Wedge testing of iron is one important part of the process measurement
techniques that Meehanite foundries would use. There are also A.S.T.M.
specifications (I think A367) that describe wedge testing of iron. The main
point of Meehanite is that the "process" of making the iron is controlled.
One should never attempt to control the making of iron by chemistry alone
(as with steel, aluminum, bronze, brass, etc.) Graphite structure control
is the single most important thing about producing quality iron.
The basic difference in all major families or cast iron: gray, ductile (aka
nodular, or spheroidal iron), malleable, and white irons is all about the
basic structure of the carbon. Gray and Ductile irons can also be heavily
alloyed, with Nickel, Copper, and Chrome and Molybdenum but the graphite
will still be either "Flake-like" for gray iron or "ball-shaped" for ductile
iron. The alloys mentioned above substitute for the element Fe to increase
corrosion resistance, or increase useable working temp, etc. So there are 5
basic families if you classify the last one as Alloyed irons.
With Meehanite's very good marketing campaigns of the past, they were able
to convince designers that the key to good casting design was to specify
"Meehanite" on their blueprints. This also meant that legally if you are
making a part with the "Meehanite" description on the blueprint, you had to
use a Meenanite-licensed foundry.
Once designers' designs worked well with "Meehanite" castings, it is hard to
convince them that an "non" Meehanite-licensed foundry can produce the same
or better quality level castings. But they can.
Not taking a position one way or the other on Meehanite....I have worked for
Meehanite and non-Meehanite foundries.
Here's the UK website:
White iron production can take several different approaches. The
compositional limits you give will give a white iron suitable for
malleablizing. However, many white irons are produced for non-malleable
usages by adding 5 to 28% Cr, depending on specification and section size.
Also, castings can be produced with a white iron outer layer and a
traditional gray iron core by using a iron chill to form the outer surface
of the casting. The chill promotes extremely rapid solidification in the
outer sections, while providing a normal gray iron microstructure in the
core of the casting. Very useful for as-cast gears and sprockets.
Thanks, all. That's all very interesting and informative, but what about the
forest? Can someone guess, based on the on-going discussion, how the
properties of semi-steel make it a good material for a silversmithing stake?
What would make semi-steel preferable to, say, all-steel or non-steel
"Semi-steel" does not exist except as a marketing term, and at one time
_might_ have described a slightly superior cast iron. It is only describing
that the foundry melted some steel to make the cast iron. Once melted into
a cast iron base melt the steel no longer exists as steel.
Good quality cast iron (or "semi-steel") would be better than "ordinary"
cast iron (i.e. that which was made by just throwing a lot of pig iron into
a furnace, melting and pouring) because the silversmithing stake would be
less likely to break.
Good quality cast iron (or "semi-steel") would be preferred over steel for
the reason is that it's less costly than steel for many reasons, the raw
materials themselves, because it's easier to cast gray iron than steel
(leading to lower cost), etc. Good quality cast iron is easier to machine.
Also the good quality cast iron will tend to absorb the vibrations of the
hammer a little better than the steel, which will "ring".
The downside of the good quality cast iron is if you hit the silversmithing
stake too hard it will fracture, and cast irons are harder to weld than
steels. But usually this would mean the cracking is coming from abuse not
You already mentioned that the anvil will dent when hammered. If this is
ordinary hammering and it's objectionable then you should buy a steel one,
preferably hardened, and it will not dent as easily. It may cost a lot
more. Also when a steel one does dent you could weld up the dents I
You probably already know from experience (I assume you've used the anvil)
whether it works OK or not.
If you have a choice between buying one in any of the materials buy the
lowest cost one that gets the job done. Don't worry about the semi-steel
nomenclature cast into the base. It's cast iron. Think of it as somebody
selling a cola. Do you want Pepsi-Cola, Coca-Cola, RC, or ??? They are all
colas just different brands, quality levels, prices, etc. But if you have a
choice between cast iron (i.e. regular, "semi-steel", "Meehanite", or ???)
vs. steel, then that would be like a choice between a cola and a root beer.
Hope to not confuse it but there could be a dozen grades of steel that steel
anvils are made of, then there's heat treating the casting, etc.