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BRIEF HISTORY:

Wrought Iron dates back to the ancient Egyptian Empire. Very small blooms of iron were produced in forges using charcoal.  In 500 BC, the Etruscans were producing 10,000 pounds of iron per year on the western shore of Italy using short cupolas with bellows made from animal skins to produce the air source.  Once the burn was complete, the short furnaces made of stone were disassembled and the resulting mass of iron and impurities were removed and further refined by heating and hammering.  The charcoal making process deforested most of western Italy.  The iron ore was brought to the furnaces on sailing ships.  The extraction method that the Etruscans used was so poor that the tailings were mined during both world wars to produce steel.  Wrought iron was produced throughout Europe in late BC to early AD.  In the magnificent buildings of the Greeks and Romans, the stones were held together with butterfly-shaped pieces of iron coated with lead.

The first steel was produced by the Celts, ca. AD 200.  They cut wrought iron into small strips and stacked the strips in a wrought iron container with burnt bone and carbon and then heated the iron in a charcoal-fired furnace for 10-12 hours at high heat.  In the process, carbon was absorbed into the surface of the metal.  They then forge welded the pieces together and produced blades.  This was the forerunner of pattern-welded blades as we know them and which we erroneously call "Damascus."  Damascus steel was produced in Pakistan about the same time in the form of Wootz billets and sent to Syria to be made into Damascus blades.  As near as we can tell (since the exact process is unknown), pure iron ore and carbon were placed in a ceramic crucible and actually melted, producing carbon steel containing about 1.5% carbon.  The steel was very difficult to forge since it had to be worked at a red heat.  Any hotter and it would shatter.  The Celt's steel process was copied by the Vikings and Germans to produce pattern-welded steel blades through about 1050.  From then until about 1400, both countries produced steel blades by family-protected, secret processes.

During that time period, they started making their furnaces taller and taller.  At this point they were no longer producing wrought iron.  The iron finally melted, and as it ran down through the charcoal, it dissolved some of the carbon into the iron.  The resulting iron contained 3-4% carbon, was not forgeable, and was very brittle.  It could only be used for casted items and was not useful for blades or wagon parts.  Also during this time period, most of the forests in England and Europe were disappearing because of building and charcoal making.  The King of England ruled at one point that the forests could no longer be cut for making charcoal.  This forced the steel makers to come up with a process to make coke out of coal by driving out the volatile oils.

To get wrought iron in quantity, the English developed a puddling process; they mixed molten cast iron with molten iron silicate and iron oxide.  Iron silicate is a component of wrought iron.  They called this coal-fired furnace a "finery."  When a worker (the rabbler) stirred this mixture, the iron oxide would combine with the carbon forming iron and carbon dioxide.  The resulting iron had a much higher melting point and would float to the top of the puddle.  The rabbler would move the pieces into larger lumps weighing 200-300 pounds.  Another worker, using a pair of large tongs and an overhead track, would grab the pieces (called "blooms") and place them in a press to squeeze out some of the iron silicate.  The pressed blooms would then be run through a rolling mill and turned into muck bars.  The muck bars were cut into short pieces, wired together, and placed in a coal-fired soak pit where they were heated to a welding heat.  The muck bars were run through the rolling mill again and turned into a merchant bar.  This process was used not only throughout Europe but in the eastern United States as well.

To make steel, thin rolled merchant bars were placed in a coal-fired soak pit, covered with carbon and burnt bone, and heated at a high temperature for several days.  The carbon would be absorbed into the iron forming blister steel.  The name "blister" comes from the appearance of the bars when they were removed from the pit-they were covered with "blisters."  The bars were then folded over and re-welded together to be used as steel.  None of the steel was of very good quality as it had iron silicate inclusions.

England needed good quality steel to make springs for timepieces so that their fleet could navigate the oceans.  One enterprising Englishman noticed that glassmakers were able to get very high temperatures in their glass furnaces.  He took pieces of blister steel, placed them in ceramic crucibles, and set them in a glass furnace.  When the steel melted, iron silicate floated out and the carbon remained, making a good quality steel.  Unfortunately for him, too many people observed the process and he was unable to keep it secret and thereby profit from the discovery.  This process was further developed and produced quality steel called "cast steel" or "crucible steel."  It is still used today to produce small quantities of differing steels.  Many old tools made in the USA are marked "cast steel".  Some mistakenly believe that these tools were "cast" as the name implies.

Steel making got its greatest boost when the Bessemer process was developed.  There is a great argument as to whether it was invented in England or the United States.

Wrought Iron was produced in quantity by Beyers Steel through 1950 and was used in large construction projects such as the Grand Coulee Dam because wrought iron is impervious to rusting.  It will only rust down to the iron silicate and then stop.

Mixing of alloys with iron occurred in the early 1900's when manganese, chrome, nickel, etc. were added in gas-fired open hearth furnaces.  The progress of alloying was very slow since it is a hit-or-miss experimental process.  The real push for alloying metal occurred during WWII when greater strength alloys were required for the weapons of war.  Since then, great strides have been made in developing different steels.

IRON & STEEL:

Wrought Iron: Wrought Iron is pure iron mixed with iron silicate. When rolled through the mills a few times, its structure takes on the characteristics of wood, having a definite grain structure. It is forged at a yellow heat. Lower heats will result in the metal shattering like a wood board unless it has been refined several times. If it does split, it is easily welded together at a yellow heat. Iron silicate acts a flux in this process. Holes drilled through wrought iron will split out lengthwise under load. Therefore, the end where the hole is drilled should be folded across the grain and forge welded. Since there is no carbon in wrought iron, it will not burn like carbon steel, even at a yellow heat. Wrought iron is no longer commercially produced. It can still be found in structures built a century or more ago. Old bridges have been a good source of wrought iron.

Carbon steels: Most carbon steels contain less than 1.5% carbon. Mild steel, as we once knew it, was labeled 1018-1020 and contained .18% and .20% carbon respectively. Today this is only true for steels smaller than 1/4" thick and over 4" in width. Most of the hot-rolled steel today is made from scrap and is categorized as A-36, having a guaranteed tensile strength of 65,000 psi. Since it contains numerous other alloys, the carbon content can vary up to .29% at which level it is not very suitable for forging. Metal with that carbon content develops black hardness which results in cracking and breaking. A-36 is also made in a continuous pour process. As a result, it contains inclusions which will cause it to split when you work with it.

Sulfur or Lead is added to low carbon steel to improve machineability. This is usually found in cold-drawn mild steels and is no good for forging at all as it has a tendency to crumble at forging temperatures. It is usually designated as 1118 or 11L18.

The more carbon added to the iron, the stronger the tensile strength until it becomes brittle. The optimum strength is achieved at .40% to .45% carbon. In order to achieve hardness, the steel has to be heated to a cherry red, quenched in warm salt brine, and then tempered.

Carbon steels with a carbon content of .60% to 1.4% are designated as W-1, W-2, etc. The "W" indicates that they can be hardened in water. This is somewhat misleading as only small pieces such as chisels and punches can be safely hardened in water. When water boils, it causes steam bubbles which result in uneven cooling, causing cracking on larger pieces of carbon steel. Most of the time, the coolant used is warm salt brine. With the best quench, the depth of the hardness goes in less that 1/4" leaving the core soft. The cherry red color of the core can be observed in a dark area with no outside lighting. Blacksmiths of old used a blackened bucket to find this red color. For people who are colorblind, this temperature occurs when the steel is no longer magnetic. 

Tempering: Once the steel is quenched, it has to be tempered using heat. This is done by first cleaning the piece down to bright metal and then slowly heating it, watching for the color of the metal to change. The proper temper is reached according to the chart below and then the metal is further cooled in water.

Alloy steels: Since carbon steels can only be hardened to a depth of 1/4", large pieces of hardened steel were not available to industry. The most important alloying metal is chrome. Chrome does two things: It allows for deeper hardening and for increased resistance to deforming at elevated temperatures. Other metals that improve strength and deep hardening are molybdenum, vanadium, nickel, and tungsten. Since we now have deep hardening during quenching, we can no longer use water or brine because the cooling is too fast and high stresses in the metal cause cracking or breakage. We must now quench with oil or air. Quenching oils are organic and specifically developed for quenching. Motor oil can be used but fumes from the oil are toxic and results are not predictable since quenching rates are unknown.

Some useful steels that blacksmiths can find at the local junkyard: