What is Wrought Iron?

In the eighteenth and early nineteenth centuries, blacksmiths
had a very narrow range of materials to work with under the
hammer. There was wrought iron, wonderfully malleable, and
three types of high carbon steel.

Wrought iron isn’t available to smiths today. What we have
instead is a variety of mild steel alloys. These are tougher than
wrought iron, suitable to more applications in this power-tool
age. What the mild steels have lost is wrought iron’s malleability
under the hammer and its resistance to corrosion.

This is an old hardy tool that Molly uses. The maker forge
welded a piece of steel to the wrought iron body. The seam is
visible in the photograph. Early trades’ tools were often made
of wrought iron with pieces of high carbon steel forge welded
onto it for cutting or other purposes. Today, we’d tend to make
the whole tool out of high carbon steel. In the past the body of
an anvil was wrought iron with a relatively thin piece of tool steel
plate forge welded to it for the working surface. Woodworkers’
tools like chisels, axes, hammers, plane irons, and so forth
were made this way with just a small piece of tool steel for the
working surface or cutting edge.

Smiths 200 years ago had three types of tool steel available.
Blister steel, the least expensive, was made by placing large
bars of wrought iron surrounded by leather scraps in huge kilns
where they were heated to high temperatures. The bars were
crudely case hardened and had a blistered appearance but still
retained a wrought iron core. Shear steel was made by reforging
the blister steel bars into a more homogenous product. Cast
steel was the most expensive steel of its time. It was made by
cutting bars of shear steel into small pieces and melting them in
a crucible. This was a truly homogenous material with wonderful
edge-holding properties for tradespersons’ tools. Often quality
tools of the period are marked “Cast Steel.” Here are a couple of
nineteenth century center bits for woodworkers. One is marked
and still has its temper color.

High carbon steels are much more varied today and have
a range of properties unknown to earlier smiths. For tool
making we use W1 or O1 tool steels – water or oil hardening.
These steels we have to anneal (or normalize) after forging
to return the steel to a soft state. This relaxes the tensions in
the steel caused by forging and prevents breaking when it is
hardened. We harden the steel tool in the fire by heating it to
the temperature at which steel loses its magnetic properties.
Then the tool is plunged into its proper quench – brine for W1,
oil for O1. The tool in this state is too hard and we temper it by
reheating it to a much lower temperature, either in the fire or in
the kitchen oven. About 450 degrees is the proper temperature
to temper a woodworking chisel. For a tool like a cold chisel
used to cut steel, the tool is heated to a higher temperature, one
at which the polished metal turns blue, about 550 degrees.

Wrought iron, unlike modern steels, has a grain, much like
wood. This large forged nut shows the grain. In forging wrought
iron, operations would have to be done in consideration of this.
Holes punched near the end of a bar would be liable to break
out. If the bar is spread first, forming a cusp, a hole punched
on the cusp would be less likely to exceed its boundaries.
Many decorative elements in traditional ironwork also serve a
functional purpose.

Because of the weakness of wrought iron and its easy
workability, a smith formed this washer by wrapping a piece of
iron in a circle and forge welding the ends. The overlap is clearly
visible. Ram’s horn nuts are useful, beautiful, and necessary
adaptations for wrought iron’s weakness.

As blacksmiths today we are having to deal with materials
changing. Mild steel, low carbon and low alloy, is difficult to find.
Instead, steel dealers in our area have products like A36 which
are versatile but tough to hand forge and which have a tendency
to form stress cracks when shaped hot. This means that a
sizeable portion of our raw stock has to be purchased from out-
of-state suppliers.

Even though our craft is an ancient one, it is not static, but
continues to evolve in accord with the world’s changing