Steel Forging Glossary Terms

The forging industry has unique terminology when it comes to the process of forging and the finished product. Below is a list of common terminology that you might come across during the forging process.

Aircraft Quality

Stock and forgings used for aircraft applications including Aerospace that require close monitoring during production. This helps reduce flaws both on the surface and internally as well as cracks, inclusions, and segregations of the forging.

Air-lift Hammer

A type of gravity drop hammer that uses an air cylinder to raise the ram and deliver blows to a forging. Because the velocity can be controlled, each blow can vary based on the amount of force needed to properly forge a metal.

Alloy

A steel that contains a small amount of various alloying elements including silicon, molybdenum, manganese, vanadium, nickel, titanium, copper, chromium, and aluminum.

Annealing

Annealing is a heat treatment that alters the physical properties of a material, usually to increase its ductility and reduce its hardness, making it more workable. It involves heating a material to above its recrystallization temperature, maintaining a suitable temperature, and then cooling.

Austenite

A solid combination of iron and at least one alloying element defined by a cubic crystal structure that is face-centered. Most common engineering steels transform into pearlite, bainite, or martensite during the austenite phase when factoring in the cooling rate.

Backward Extrusion

Forcing metal to flow in a direction opposite to the motion of a punch or die.

Batch Furnace

A furnace used for heating forging materials. All loading and unloading of materials is done using a single entrance, door, or slot.

Blank

Often referred to as a "slug" or “mult”, a blank is raw material that has been cut to weight or length and is used to create forged parts; also known as forging stock.

Blast Cleaning

Cleaning and finishing metal process by using high-velocity particles including grit, sand, or shot.

Board Hammer

A type of gravity hammer that uses wood boards to raise the ram.  The wooden boards are lifted up by the contra-rotating rolls and then released.

Carbon Steel

Steel material containing up to 1.2% carbon and only trace amounts of other alloy materials. Higher percentages of silicon and manganese may be added for composition control.

Case Hardening

Also known as surface hardening is the process of hardening a metals surface while allowing the core to remain soft. Methods used include carburizing, carbonitriding, cyaniding, and flame hardening and are used on ferrous alloys.

Close-Tolerance Forging

A metal forging that requires little to no machining because of the close dimensional tolerance during the forging process.

Closed Die Forging

The forging of hot metals that are encapsulated between two dies. These dies come together on all sides, creating the impression of the desired part.

Coining

Slightly deforming a forging in order to create closer tolerances, eliminate draft, or for a smoother surface.

Cold Shut

A surface defect caused by metal folding over itself during the forging process. This typically happens at the intersection of vertical and horizontal surfaces.

Compressive Strength

The max amount of stress a metal can withstand under compression without fracturing or becoming permanently deformed.

Counterblow Forging Equipment

Two rams on opposite sides of a metal forging, striking the piece simultaneously to achieve the proper shape.

Descaling

A process that removes scale from forged stock before or during the forging process. Wire brushes, water spray, scraping equipment, and light blows to the metal are often used.

Die

The tooling or mold in which a piece of metal is placed in order to create a forging.

Die Blocks

Metal blocks with impressions of the desired shape of a metal used during the open and closed-die forging.

Die Life

The duration of a die impression or die block measured by how many forging it has produced before it becomes too worn to use.

Die Lubricant

A product applied during forging that is sprayed to metal in order to reduce friction and to provide thermal insulation.

Die Match

The alignment of the upper and lower forging dies inside a drop hammer or press.

Die Sinking

The process in which an impression is machined into die blocks.

Directional Properties

The varying of mechanical properties when a metal part is being tested.

Draft

Taper or excess material on the sides of a metal forging that is used to remove the part from the dies. This taper is usually between 5 and 7o.

Drawing Out

A forging process in which metal stock is reduced at the cross section and lengthened between flat dies.

Drop Forging

The process of heating metal material and hammering into a specific shape using dies and die blocks by means of a forging hammer.

Drop Hammer

A hammer used to forge metal parts into specific shapes. Blows from the drop hammer are made by gravity, steam, or compressed air.

Ductility

The property of a solid metal deforming when under tensile stress but before it ruptures.

Dye Penetrant Testing

Method for inspecting and detecting flaws in metal surfaces by use of penetrating liquids. This liquid contains dye or fluorescent color in order to identify flaws.

Elastic Limit

The stress limit a metal can withstand before permanent deformation occurs.

Electroslag Remelting (ESR)

A process of refining metal in which metal is remelted through a layer of slag from a consumable electrode form. Alloys that are refined through ESR have better uniformity, are better for forging, and have superior properties to other metals.

Embrittlement

A loss of ductility of a metal material, making it brittle. Often the result of mechanical or chemical defects that occur during forging or exposure to elements.

Fatigue

The cracking or breaking of metals when put through cyclic stresses that are below the ultimate tensile strength of the metal.

Finish Allowance

The amount of stock remaining on the surface of a forging that will be removed by machining for the finished product.

Finisher (Finishing Impression)

A die impression that holds the final shape for a forged part.

Flakes

Internal fissures in ferrous metals that are short and discontinuous and caused by internal stresses when cooled, after being heated.

Flash

Metal that is extruded between dies in a thin layer at the parting line and helps regulate the flow of metal into cavities of the dies. This excess metal is removed by trimming after forging.

Flash Extension

Leftover flash that remains on the forged part after the completion of trimming. This is typically included in the normal forging tolerance allowance.

Flat Die Forging

The process of repeatedly applying blows and manipulation to metal between flat or simple contour dies. This is can also be referred to as hand forging or smith forging.

Forgeability

The ability of a metal or alloy to form and deform without rupture during the forging process.

Hardening

A process or treatment that has the ability to increase the hardness of a metal along with increasing the strength. Heat treatment and cold working are two common ways to achieve hardening.

Grain Flow

A grain pattern that is developed during the forging process. Good forging techniques create good fiber-like grain flow that enhances metal properties.

Grain Size    

The number and size of grains or crystals in a metal material per unit area of a cross section.

Hardenability

The measurement of the capacity a metal has to be hardened. This is measured by depth and degree.

Hardness

The numerical value that expresses the resistance of a metal to indentation. These numbers derive from the measurements on Brinell hardness and Rockwell hardness testing devices.

Heading

A forging process that creates heads on rod or wire ends. These are typically used in bolt or rivet making.

Heat Treatment    

The process of heating and cooling a metal material several times in order to obtain desired properties.

Hot Inspection

A process to ensure quality of a forging. This is a visual examination during the forging process using gauges and other methods that are nondestructive.

Hot Working

The process that deforms a metal beyond its recrystallization point and high enough to prevent strain hardening.

Impression Die Forging

Completely enclosing hot metal on all sides between two die cavities and forming into a desired shape.

Inclusions

Particles in metals that are nonmetallic as well as impurity elements that are present in ingots. These are carried over in wrought products. Inclusions shape and distribution are changed by plastic deformation are can contribute to a metals directionality.

Ingot

The process in which temperature remains constant and uniform.

Lap

A defect on the surface of a metal that appears as a seam. This is caused by folding over or sharp corners and the rolling or forging into the surface.

Machinability

The ease that a material can be drilled or cut.

Macrostructure

The observation of the structure and internal condition of a metal surface that has been polished and etched. This is done with the naked eye or low magnification, up to 10x.

Magnetic Particle Inspection    

Referred to as MPI, Magnetic Particle Inspection is a non-destructive test that detects surface and subsurface discontinuities or breaks in ferromagnetic materials. Materials include nickel, iron, and some alloys.

Malleable

The ability of metal to be formed or deformed by the forging process.

Martensite

A structure within quench-hardened steel that is unstable and has maximum hardness of any austenite product that has been transformed.

Mechanical Properties    

Identification and classification of metal materials. Common properties include strength, hardness, impact resistance, and fracture toughness.

Microstructure

The inspection and examination of a polished and etched metal surface at a high magnification.

Normalizing    

A form of heat treatment used during the forging process by heating metals above the normal transformation temperature for a period of time and then cooling.

Parting Line

The line where the dies meet on the surface of a forging. This is typically the largest cross section of the forged part and where flash is formed.

Press Forging    

The process of forming metal material between dies using a forging press that is operated mechanically or by the use of hydraulics.

Quenching    

The process of rapidly cooling a forged piece of metal using liquids. This is to increase the strength and hardness of the piece.

Reduction in Area

The measurement from a tensile ductility test that is the difference between the original cross sectional area of a metal and the smallest cross section after testing.

Ring Rolling

The process of rolling metal between rotating rolls. This increases the diameter of a metal part and reduces the ring wall section.

Scale    

The "crust" that forms on the outside of a metal forging caused by oxidation. The amount of scale present on a forging is largely dependant on the grade of the metal and how long it was exposed to heat before processing.

Segregation

The distribution of alloying elements in a metal that are non-uniformed. This occurs during shape casting or solidification.

Shrinkage

The thermal contraction of metal after hot forging and during the cooling period. Die impressions are produced to account for precise shrinkage and tolerances that occur during forging.’

Solution Heat Treatment

Heating an alloy to a certain temperature and holding at that temperature, allowing for a second element to form a solid solution with the base metal. Then the metal is rapidly cooled to retain the constituent solution.

Steam Hammer    

A type of forging hammer that uses a piston and fixed steam cylinders to operate.

Stock    

A piece of raw metal material that is used to produce a single forging.

Stress

Internal force reactions on a material when it subjected to a load. This is calculated by dividing the load by the cross-sectional area.

Stress Relieving

The process of reducing stresses in metal using controlled heating and cooling without major changes in the grain structure. This can be done with cold compression or stretching as well.

Superalloys

Referring to iron-base, nickel-base, and cobalt-base alloys that have high temperature mechanical properties and oxidation resistance.

Temper    

A heat treatment process that occurs after quenching. Forgings are heated below critical temperatures and then cooled to relieve stresses caused by quenching. This process helps the forging obtain specific mechanical properties.

Tensile Properties

The mechanical properties of a metal when subject to tension. These properties including tensile strength, yield strength, elongation, proportional limit, and reduction of area.

Tensile Strength   

The maximum amount per unit of the initial resistance required before the rupture a piece of metal material.

Tolerance

The allowance of deviation from a specification for any design characteristics during forging.

Trimming

The process of removing flash and excess metal from a forged part. Trimming can occur hot or at room temperature.

Tumbling

A process for removing scale from forgings using a rotating container and abrasive materials.

Ultrasonic Testing    

A non-destructive test using ultrasonic beams to locate structural discontinuities within a metal material.

Upsetting    

The process of increasing the cross-sectional area of a metal material.

Yield Strength

The stress that a metal reaches a specific amount of permanent deformation.