Bending Metal to Your Will

While forging—the verb—is what a blacksmith does with hot iron, a forge—the noun—is what heats up the metal for the blacksmith to work. Heating metal to make it more malleable dates to prehistoric times, and even though presses and other forging machines have greatly improved the efficiency of the process for large scale modern production, quite a bit of hand forging is still done by craftsmen and craftswomen today.

Traditionally, a forge is a brick or stone-lined furnace where metal is heated to a malleable temperature before being moved by a blacksmith to an anvil to begin the hammering and shaping process. Other metallurgical effects, like annealing, hardening, and tempering can also be accomplished through heating metal in a forge. The fire in a forge is controlled by the blacksmith to suit the job at hand and is adjusted by balancing three factors: the volume of fuel present, the amount of air that is introduced to the flame, and the shape of the fire or the fuel.

The key elements of a forge are the hearth, the place where the burning fuel can be contained; a tuyere, the pipe through which air is forced into the fire; and a bellows or blower for moving the air into the tuyere. The fuel for a traditional forge is usually bituminous coal, industrial coke, or charcoal. While coal is a naturally occurring substance, the other two are manmade products created by heating oil or coal (in the case of coke) or wood (in the case of charcoal) in minimal or no oxygen.

When the metal is sufficiently malleable, the blacksmith uses tongs to move it to an anvil where the craft of hot working the metal begins. While the process itself is called forging, the workpiece that is created by the process is also known as “a forging.” While many metal fabrication processes today may be more science than skill, the craft of the classic blacksmith is still, first and foremost, an art. As someone once said, “Forging is the process of bending metal to your will with a hammer.”

A Glossary of Forging Terms

There are hundreds of different terms associated with forging. Here are several common ones:

Age hardening or aging is a process that changes the properties of a metal by subjecting a forging to a relatively low heat for a specific period following a final heat treatment or cold working operation. Aging helps stabilize a piece of metal following structural changes induced by any prior operations.
An alloy, such as alloy steel, is a hybrid material composed of a metal and at least one other chemical element, usually created to increase a property of the metal such as strength, ductility, or hardenability.
Annealing is a heat-treating process that increases the ductility of metal by raising it to a temperature above its critical range, holding it there long enough to permit full recrystallization, then allowing it to cool slowly.
The anvil is essentially the blacksmith’s workbench, a carefully shaped tool that allows several different hand forging operations to take place, such as using the protruding horn for bending steel.
The designation “as forged” refers to the condition of a completed forging without any subsequent operations.
Austenitic steels are steels containing between 16- 26% chromium and up to 35% nickel, giving them high corrosion resistance, but also rendering them nonmagnetic. They cannot be hardened through heat treatment.
Auxiliary operations are additional steps applied to shape or condition the surface of a workpiece when the forging operation has been completed.
A bellows or a blower are commonly used to force air into a hearth to keep the flame going.
A billet is a semifinished length of metal that has a round or square cross-section and that was created through continuous casting or extrusion or by hot rolling an ingot or bloom.
A blacksmith is someone uses heat, hammers, and specialized tools to forge iron, steel, or similar metals into objects. A smith in general is someone who crafts with metal—such as a tinsmith—while the term blacksmith specifically refers to the black color of heated iron.
A blank is the raw material used in forging, cut from wrought material. Also called a slug, a multiple, or forging stock. “Blank weight” refers to the weight of the blank when it’s been sawed and deburred and is ready for forging.
A blast furnace is a tower-shaped smelting furnace used to make iron by blasting hot, compressed air into the bottom.
Blocker-type forging is an operation that uses an impression die to form the metal progressively into the approximate shape and contour of the final part, which will then usually be machined into its completed shape.
A bloom is a semifinished piece of steel produced from an ingot. Blooms are like billets but are usually larger.
In forging, the term boss refers to a usually cylindrical protrusion extending from the surface of the main body of a forged workpiece.
Carbon steel is steel that contains up to 1.2% of carbon with only residual amounts of alloying elements. Mild steel is a low carbon steel containing less than 0.3% carbon and is very malleable, making it ideal for fabrication work.
Case hardening is a process, usually involving heat treatment, that makes the surface layer of a ferrous alloy substantially harder and more wear-resistant than the core, which remains softer, yet tougher.
Casting is the process of pouring molten metal into a mold where it is allowed to solidify.
A cavity is the hollow impression in a die.
Centrifugal casting refers to a casting process that involves pouring molten metal into a rotating mold.
To chamfer forging stock is to break, grind or otherwise remove sharp edges from it.
Chisels are a common tool of the blacksmith and are made of high carbon steel. While the cutting edge of a chisel is hardened and tempered, the head on the other end is left semi-malleable so that it doesn’t crack when hammered.
A chop is a die forging defect, referring to metal sheared from a vertical surface and spread by a die over an adjoining horizontal surface.
Close-tolerance forging refers to a forging process held to closer than normal tolerances to eliminate most or all the normal post-forging machining. Also known as precision forging.
A coal forge, also known as a coke forge or a charcoal forge, uses coal or another fuel to heat metal, controlling the process by altering the volume of the fuel that is used, the shape of the fuel or fire, and the amount of air that is introduced.
Cogging is an operation in which an ingot is worked into a billet or bloom using a forging hammer or a forging press.
Cold trimming refers to removing excess metal from a forging that is at room temperature.
Cold working, as opposed to hot working or warm forging, is the manipulation of metal without heating it to create a permanent plastic deformation of the material at a temperature low enough to produce strain hardening. Cold working is also known as cold forging and cold forming.
Critical point refers to the temperature at which recrystallization or another phase change takes place in a metal.
A crucible is a container used for melting metals.
Crude iron is a product which is obtained by smelting iron ore. It has a very high carbon content and is often called by the colloquial name “pig iron.”
Decarburization is the loss of carbon from the surface of steel due to heat or chemical action. While it is usually present to a degree in forgings, excessive decarburization can result in a defective part.
Descaling is a process of removing oxide scale from heated stock before or during a forging operation. Methods include scraping devices, wire brushes, a water spray, or the application of extra blows to the stock.
Dies or die blocks are the metal forms or molds, usually used in pairs, that produce the forgings. The forging impressions are machined into their interior surfaces.
A double forging is a single forged workpiece designed to be cut apart and used as two separate pieces.
A draft is a taper on the side of a forging that allows it to be removed from the dies.
Drawing out is the process of making a workpiece longer in one dimension, while thinner in one or both other dimensions.
Drop forging is a process used to shape metal by dropping a die mounted on a heavy hammer or ram onto a workpiece.
Dross is any unwanted byproduct of smelting ore. Also called slag or tailings.
Ductility is the characteristic of a metal that measures what degree it can be stretched before it ruptures.
Elongation is the amount of permanent stretch that can be put into piece of metal before rupture. The percentage of elongation is an indication of ductility.
Extrusion is the process of shaping metal into a specific continuous form by forcing it to flow through a die orifice.
The abbreviation F.A.O. stands for “finish all over” and designates the amount of additional stock needed for the forging to be at the correct dimensions once all surfaces have been machined.
Fatigue resistance refers to the ability of a metal to resist weakening when exposed to repeated loads.
Ferrous metals are those alloys that have iron as their major component.
A fin or feather is a thin projection on the surface of a forging caused by metal under pressure being forced into hairline cracks in dies or the spaces between dies.
Finish refers to the forging operation where the workpiece is forged into its final shape in a finish die. The term “finish” can also refer to the surface condition of a forging following being machined.
Flash refers to excess metal that extends out from the body of the forging as a thin plate at the seam where the dies come together. It is removed by trimming, leaving a faint “flash line” on the forging.
Flat die forging is a forging worked between flat or simple contour dies by repeated strokes and manipulation of the workpiece. Also called open die forging, hand forging or smith forging.
Flattening is a preliminary operation performed on forging stock to flatten it prior to further operations.
Flux is any substance used to prevent oxidation by keeping oxygen away from the surface of a hot piece of metal.
A fold is a forging defect caused by metal folding back on its own surface while flowing into the die cavity.
Forgeability is the relative ability of material to deform without fracturing, rupturing, or developing flaws.
A forging press is a pressing machine that shapes metal into three-dimensional shapes.
Forging stock is raw material used in forging. Also called a slug, a multiple or a blank.
A foundry is a place where metal is cast.
Fullers are forming tools of different shapes, often used in pairs, that can make grooves or hollows in a forging.
A gas forge is easier to operate when compared with a coal forge, making it ideal for use by a beginning blacksmith. Gas forges generally used propane or natural gas as their fuel source and produce a clean, consistent flame.
A grain is the individual crystal or unit of the crystalline structure of a metal or alloy.
A hammer, along with an anvil, are the basic tools of a blacksmith. A variety of handheld hammers are used by blacksmiths in shaping metal, including ball-peen hammers, cross-peen hammers, straight-peen hammers, and sledgehammers. The term hammer can also refer to different powered machines used in forging, like air-lift hammers, drop hammers, and gravity hammers.
Hand forging is a forging made by hand on an anvil or by using a power hammer with dies that are generally flat. Also known as smith forging, flat die forging, or open die forging.
Hardening is the process of making a metal harder, whether by quenching and tempering, hammering, or adding alloys to change its chemical makeup.
Hardness is how resistant a metal is to indentation or penetration. It is measured by a hardness test, such as Brinell, Rockwell, Scleroscope, or Vickers.
A hardy is any type of tool with a square shank that fits in a hardy hole in an anvil. Examples include a fuller tool—used for drawing out metal and making grooves—and a hot cut hardy that can cut hot metal on the anvil.
A hearth is a place in a forge where burning fuel can be contained near the tuyere, the opening through which air is supplied to the fire.
Heat treatment is an operation that combines heating and cooling of a metal or alloy in a solid state to produce specific properties in the structure of the material, like making metal more malleable.
Heat-resistant steel is an alloy steel designed for use in applications at elevated temperatures.
Hollow forging is the process of forging seamless tubes, rings, or other circular hollow parts by expanding or lengthening the hot workpiece over a mandrel.
Hot trimming refers to removing excess metal from a hot part, like a forging.
Hot working, as opposed to cold working or warm forging, is plastically deforming an alloy at a temperature above its recrystallization point to avoid strain hardening, allowing recrystallization to take place simultaneously with the deformation. Hot working is also known as hot forging and hot forming.
Hot-die forging is a process used with difficult-to-forge alloys, where the dies themselves are heated to nearly the forging temperature of the alloy being forged.
Inclusions are impurities like dirt, oxides and other foreign particles that are present in the metal.
Induction heating is a way of heating metals by using an alternating magnetic field.
Ingots are rough metal castings used as stock for forging and other operations, such as extrusion or rolling. They are designed for storage and transportation.
Isothermal forging is a forging process in which a constant temperature is maintained uniformly throughout a workpiece.
A knockout is a mechanism to help release the finished forging from a die.
A lap is a type of a surface defect that appears like a seam or fissure caused by folding over an extrusion like a fin and forging it into the surface of the workpiece.
Lubricant residue is the carbonized residue of lubricant burned onto the surface of a part during forging. The condition of such a forging is called “baked on.”
A mandrel is a blunt-ended tool used to retain or enlarge a cavity in a hollow metal product during a “mandrel forging” operation, producing a seamless tube or ring.
Mill scale is the heavy oxide layer that forms on steel during forging and other extreme heating.
Nonferrous material are metals—like aluminum or copper—or alloys that contain no significant amount of iron.
Normalizing is a common process of heat treatment where a ferrous alloy is heated above its critical range, held at that temperature for a specific amount of time, and allowed to air cool.
An offset is a defect in a forging caused when the dies did not align properly.
Open die forging is a forging produced by working between simple dies where the flow of metal is largely unrestricted. Also called flat die forging, hand forging or smith forging.
A pancake forging is a quickly and easily created rough forged shape that is usually flat.
A parting line is the point where the dies meet on the surface of a forging and flash is formed.
Pickling is the process of using a heated acid bath to removing oxide scale from a forging.
Pig iron is a crude, high-carbon iron formed from smelting. It gets its name from the traditional arrangement of the molds used to create ingots. A shape is formed in sand, with the individual ingot molds arranged in a branching structure at right angles to a central channel called a runner. Someone observed that the configuration resembled rows of piglets being nursed by a sow, and the name stuck.
Precision forging refers to a forging produced to closer tolerances than normally considered standard by the industry, eliminating most or all post-forging machining. Also known as close-tolerance forging.
A punchout is the metal removed from a forging when a hole is punched in it.
Quenching is the process of rapidly cooling hot metal by contact with a lower temperature material like liquid or gas to harden it or otherwise alter its properties. The process is always followed by tempering to increase the metal’s ductility.
Scale is a layer or crust of oxidation that forms on steel when it’s heated, such as mill scale.
Sinking is the operation where an impression is machined into die blocks for a specific forging.
A slack tub is used by a blacksmith to quench hot metal and usually consists of a large water-filled container.
Slag is any unwanted byproduct of smelting ore. Also called dross or tailings.
A slug is a piece of raw stock material used in forging. Also called a blank, a multiple or just forging stock.
Smelting is the process of heating and melting ore to extract metal.
Smith forging is the type of forging commonly performed by blacksmiths. It is a forging worked between flat or simple contour dies by repeated strokes and manipulation of the workpiece. Also called hand forging, flat die forging, or open die forging.
Spheroidizing is a form of annealing so named because it causes the graphite in an iron base alloy to assume a spheroid shape. The process consists of prolonged heating of the alloy slightly below the critical range temperature, followed by relatively slow cooling.
Springback is the tendency of a bent or shaped piece of metal to return to its original shape or contour after undergoing a forming operation.
Stainless steels are steels that contain a minimum of 10% to 12% chromium, making them corrosion and heat resistant.
Straightening is a finishing operation for correcting misalignment in a forging or between different sections of a forging. Straightening may be done by hand, with simple tools, or using a die with forging equipment.
Strain rate is the rate at which metal is deformed.
Strain-rate sensitive alloys are those that can be forged only at low rates of deformation.
Stress relieving is a process that reduces residual stresses in a piece of metal created by machining, welding, quenching, or other operations. The metal is heated to a specific temperature and held there for a set amount of time.
Tailings are any unwanted byproduct of smelting ore. Also called dross or slag.
Tempering is the process of hardening metal by heating and then quenching it.
Tensile strength is the maximum stress that a metal or other material can withstand while being stretched or pulled before it breaks or shows strain.
Tongs are used by a blacksmith for holding hot metals securely. The term can refer to other types of metal holders used to handle hot or cold forgings or other metal pieces. Forging billets and other stock often have a small portion of metal protruding on one end referred to as the “tong hold.”
Tool steel is a hard, high-grade steel that is used to create tools and dies.
Trepanning is the use of a hollow tool to remove a core of metal.
A tuyere is a pipe or tube through which air is forced into the fire of a hearth or furnace.
Warm forging, as opposed to cold working or hot working, is deformation of metal at an elevated temperature, but lower than the recrystallization temperature of the material. The heat allows for lower forces to be used than in cold working.
Warpage is a term that refers to distortion that can occur in a forging during quenching following heat treatment.
Work hardening, also known as strain hardening or stress hardening, is a cold working method for hardening metal through compression or flexing.
Wrought steel refers to steel that has been produced by hot mechanical working. Wrought is an archaic term that means “worked” and in the metal fabrication industry has traditionally been used to mean metal that has been hammered or beaten into shape.
A yield point refers to the stress at which the material is no longer elastic.