Glossary of forging terms


Alloy Steel

Steel that, in addition to carbon, contains one or more elements in sufficient amounts to appreciably alter properties compared with those of carbon steel. Materials are alloyed to enhance physical and mechanical properties such as strength, ductility, and hardenability.



Austenitic Steels

Steels containing such proportion of an alloying element or elements that the austenitic structure is retained at room temperature.



Also often called a bloom. A semifinished product of square, rectangular, or even round cross section, hot rolled, or forged. Producing billets or blooms from ingots by forging is called cogging, while by rolling it is called blooming.


A disc-type forging produced by upsetting and rounding starting stock.



Machining a hole or enlarging an existing one with the objective of producing a more accurate hole than by drilling.

Bottom Poured Ingot

An ingot produced by pouring molten steel into a vertical trumpet where the steel flows down the trumpet, through runners, and then enters the ingot mold from the bottom. This method provides substantially improved surface quality and internal soundness, as well as ingot yield advantages, over top-poured ingots.

Brinell Hardness

A measurement of a metal hardness (or ability to resist penetration). A steel ball is forced into the surface of the material tested under a specific load. The diameter of the depression is measured, and the hardness is the ratio of load to spherical area of the impression.


Camel Back

A rectangular step down bar that has the high point near the center.

Camel Back

Carbon Steel

Steel that owes its properties chiefly to various percentages of carbon with only residual amounts of alloying elements (except those added for composition control such as silicon and manganese).


Process of pouring molten metal into a prepared mold cavity of a desired shape and allowing the metal to solidify.

Centrifugal Casting

Casting process that consists of pouring molten metal into the cavity of a rotating mold, which can be made of various materials.

Charpy Impact Test

An impact test in which a specially V-notched specimen is broken by the impact of a falling pendulum. The energy absorbed in fracture is a measure of the impact strength or notch toughness of the sample.

Closed-Die Forging

Also called Impression Die Forging. A forging that is formed to the required shape and size by machined impressions in specially prepared dies that exert three-dimensional control on the workpiece.


The reducing operation in working the ingots into a billet or bloom by the use of forging hammer or a forging press.


Objects or part features having a common center.

Contour Torch Cutting

Torch cutting or flame cutting a part to achieve a specific shape or contour.



A forging die is a steel block with a flat or contoured working face, which is used in a hammer or press for shaping metal.


The property of a metal that enables it to stretch before rupturing.


A step down forging with two heads.




A step down forging where the journals do not share the same center with the head.


Electrical Conductivity

Rate at which electrons move through atoms causing current to flow.


The amount of permanent stretch in a tensile test specimen before rupture.


Employee Stock Ownership Plan, describing the employee ownership of a company.



A part produced by any of a number of fabricating processes such as forming, rolling, punching or welding, but especially associated with weldments, the joining of two or more individual pieces by welding.

Fatigue Resistance

The ability of a metal to withstand repeated and varying loads without weakening.


Metals that contain iron as the major alloying element.

Flat Bar

A forged bar with a rectangular cross section and the four corners are at right angles (90°).

Flat bar

Flat Head Spindle

A spindle with a rectangular head(s).

Flat Head Spindle


Process of working metal to the desired shape by impact or pressure from hammers, presses or forging machines. The metal object so produced is termed a forging.

Flanged (hollow)

A hollow forging with one or more protruding ribs or flanges on the outside diameter.


Gear Weldment

A semi-finished gear fabrication including the outer ring, inner hub, and torch cut stiffening plates.

Grain Size



Hammer Forging

The mechanical forming of metal by means of a hammer. The action of the hammer is that of an instantaneous application of pressure in the form of a sudden blow.


The ability of a metal to resist penetration, defined in terms of the measurement (Brinell, Rockwell, etc.).

Hardness Test

A test used to determine the relative resistance to indentation or displacement of metals by pressure, or by resistance to abrasion. Common methods of testing include Brinell, Rockwell, and Vickers tests.

Largest point of a forging.


Heat Treatment

An operation or combination of operations involving the heating and cooling of a metal or alloy in the solid state to attain certain desired microstructure or properties.

Hollow Forging

The process of producing circular hollow, tube-like parts by expanding or lengthening the hot workpiece over a mandrel.



Part that has been upset forged using loose tools. This process produces a shape with a smaller diameter projection from either one or both sides of the major diameter of the part.




A casting suitable for working or remelting; the basic starting stock for the forging process.

Intergranular Corrosion

Corrosion of a metal along its grain boundaries.

ISO 9001

An international family of specifications and standards for quality assurance management systems involving a third party for inspection and registration.



A hardenability test for steel to determine the depth of hardening obtainable by a specified heat treatment.


The smaller diameter (size) of a cylindrical forging.




Process to remove excess or unwanted stock by the use of machine tools for rough or finish turning, boring, drilling, or milling.

Magnetic Particle Inspection

A nondestructive method of inspection for determining the existence and extent of possible defects in ferro-magnetic materials. Finely divided magnetic particles, applied to the magnetized part, are attracted to and outline the pattern of any magnetic leakage fields created by discontinuities.


A bar used to retain the cavity or enlarge the bore during hollow forging.


A mechanical device for handling an ingot or a billet during forging.

Mechanical Properties

Those properties of a material that reveal the elastic and inelastic reaction when force is applied, or that involve the relationship between stress and strain. Mechanical properties are dependent on chemical composition, forging, and heat treatment.

Metallographic Examination

Study of the microscopic features of material surfaces that have been specially prepared by cutting, grinding, polishing, and etching.


Science of metals and alloys devoted to the study of engineering materials.

Microhardness Testing

Testing technique used for measuring the hardness of the constituents in the microstructure of a metal.


The process of producing machined surfaces by progressively removing a predetermined amount of material from the work piece which is fed to a rotating milling cutter.



Transition point when going from one size to another in a forging.



Refers to the operation of cutting a groove of predetermined depth in a work piece.

Nondestructive Testing

Any type of testing performed on an object that leaves it unchanged.


Metals that do not contain iron as the major alloying element.


Commonly used heat treatment that decreases pearlite interlamellar spacing and refines grain size. The process consists of heating steels above the transformation temperature range, holding at temperature, and then cooling in air.


Open Die Forging

The mechanical forming of metals between flat or shaped dies, where flow of the metal is not completely restricted.

Open Die Press, Hydraulic

A forging press with a hydraulically operated ram.


Peeled Bar

A round bar that has been centerless machined to remove its outer surface. The peeling process takes less than one-fourth the time of conventional lathe-turning operations.



Planishing Mill, Bar

A custom-designed, computer controlled GFM single-stand bar mill. After an initial forging process, bars are sent through a series of reversing passes on the planishing mill where they are rolled to a smooth surface in less than five minutes.

Pneumatic Hammer

A forging hammer that uses compressed air both to drive the hammer down for a working blow to the workpiece and reposition it for the next blow.

Press Forging

Mechanical forming of metals by means of a press. The action is that of kneading the metal by relatively slow application of force as compared with the action of hammering.

Profiled Rolled Ring

A forged rolled ring with a contoured or profiled cross section achieved during the rolling process.



Rapid cooling of a heated metal, generally by immersion in liquids, to increase strength and hardness. Quenching is always followed by a temper to increase ductility.


Ring Mill

Equipment used to produce forged rolled rings. A metal ring preform is rolled between two rolls that move toward each other to form a continuously reducing gap.

Ring Preform

Material that has been upset and pierced to form a hollow "donut." This is the starting stock needed to produce a rolled ring.

Rolled Ring

A forged seamless ring produced on a ring mill.

Rolled Ring

Rough Machining

A machining operation that allows stock for subsequent finish machining.


Saw Cutting

Metalworking process used to cut starting ingot or billet stock to length in preparation for the forging process and also to trim forged parts to size.


Oxidation that forms on the outside of hot metal and forms a crust. The appearance and amount of scale is depended on the grade of steel and the time it is in the furnace before processing.

Secondary Processing

As used in this reference, all metalworking processes that follow the forging process. Typical secondary processes are heat treating, rough machining, trimming, torch cutting, and testing.

Service Center

Company that warehouses and markets semifinished metal products, such as bars, plate, sheet or structurals.

Shot Blasting

A metal cleaning or finishing process in which a fluid blast blows abrasive steel balls against the surface.

Spectrochemical Analysis

Test performed to verify a material chemistry.


Also referred to as a stepdown shaft. A longitudinal bar-type product with more than one diameter or cross section size.


Square Bars

A forging that has four equal sides and the four corners are at right angles (90°).

Step-down Shaft

Also referred to as a spindle. A longitudinal bar-type product with more than one diameter or cross section size.

Step-down Shaft


Stock is the amount of additional material above the rough turn print sizes. The more stock, the greater the chance the work piece will still be acceptable even with surface defects in present.


Tartan Bars®

Round bars 6" to 16" diameter with a forged center and rolled bar surface produced only by Scot Forge.


A device consisting of two different conductors (usually metal alloys, termed “bi-metallic”) that produce a voltage proportional to a temperature difference, between either end of the two conductors. Thermocouples are a widely used type of temperature sensor for measurement and control.


Heat treat process performed after quenching or normalizing. The forging is heated to a temperature below the critical temperatures and cooled at a suitable rate. Tempering steel after hardening to relieve quenching stresses ensures dimensional stability and obtains specified mechanical properties.

Tensile Strength

The maximum load per unit of initial cross-sectional area obtained before rupture in a tension test.

Tensile Test

A tension-testing machine mechanically or hydraulically applies a tensile load to a specimen. The test establishes ultimate strength, yield strength, and ductility (elongation and reduction of area).

Torch Cutting

The cutting or parting of steel objects with a torch using a flame with excess oxygen to completely oxidize or "burn" the steel directly in the path of the flame; flame cutting.

Toughness Testing

Test used to assess the resistance of metals to brittle fracture propagation (spreading) in the presence of stress raisers.


Removing metal from the outside of a part by means of a tool in a lathe or similar machine tool.


Ultrasonic Testing

A method of nondestructive testing of solid metal for internal flaws utilizing high frequency sound waves.


Working metal so that the cross-sectional area of a portion or all the stock is increased.



A die having two working surfaces at equal opposing angles to the vertical.