Acid Embrittlement
A form of hydrogen embrittlement that may be induced in some metals by acid treatment.
Age Hardening (Aging)
An aging process that results in an increase in hardness and strength with, usually, some loss of ductility. It is generally induced by a low-temperature treatment following a relatively rapid cooling from some elevated temperature. Aging tends to restore equilibrium in the metal and eliminate any unstable condition induced by a prior operation. See also Precipitation Hardening and Solution Heat Treatment.
Air-Hardening Steel
An alloy steel that does not require a liquid quench to harden, but hardens simply by cooling in air from above its transformation temperature range.
Aircraft Quality
Denotes stock of sufficient quality to be forged into highly stressed parts for aircraft or other critical applications. Such materials are of extremely high quality, requiring closely controlled, restrictive practices in their manufacture in order that they may pass rigid requirements, such as magnetic particle inspection (Ref: Aerospace Material Specification 2301).
Air Quenching
A heat-treating process consisting of heating steel above the transformation temperature range and then cooling in agitated air. The process is a type of normalizing but with more rapid air circulation.
Alloy
A material that exhibits metallic properties and is composed of two or more chemical elements with at least one being metallic. In practice, the word is commonly used to denote relatively high-alloy grades of material—for example, “alloy” steels as differentiated from “carbon” steels. Materials are alloyed to enhance physical and mechanical properties such as strength, ductility, and hardenability.
Alloying Element
An element added to a metal that remains within the metal and changes its properties.
Alloy Steel
Steel that, in addition to carbon, contains one or more elements in sufficient amounts to appreciably alter the mechanical or physical properties when compared with those of carbon steel.
Aluminum-Treated Steel
Steel to which aluminum has been added to deoxidize it, or to control grain size, or to modify mechanical properties by subsequent precipitation hardening or nitriding.
Annealing
A heat-treating operation wherein metal is heated to a temperature above its critical range, held at that temperature long enough to allow full crystallization, then slowly cooled through the critical range. Annealing reduces hardness, improves machinability, increases ductility, facilitates cold working, or produces a desired microstructure.
Auxiliary Operations
Additional processing steps performed on forgings to obtain properties, such as surface conditions or shapes, not obtained in the regular processing operation.
Backward Extrusion
Forcing metal to flow in a direction opposite to the motion of a punch or die.
Bar
A section hot rolled from a billet to a form, such as round, hexagonal, octagonal, square, or rectangular, with sharp or rounded corners or edges, with a cross-sectional area of less than 16"; a solid section that is long in relation to its cross-sectional dimensions, having a completely symmetrical cross section and whose width or greatest distance between parallel faces is 3/8" or more.
Bend
Operation to preform (bend) stock to approximate shape of die impression for subsequent forging.
Bend or Twist (Defect)
Distortion similar to warpage, but resulting from different causes; generally caused in the forging or trimming operations. When the distortion is along the length of the part, it is called “bend”: when across the width, it is called “twist”.
Billet
1) A semi-finished section hot-rolled from a metal ingot, with a rectangular cross section ranging from 16" to 36", the width being less than twice the thickness. Where the cross section exceeds 36", the word “bloom” is properly but not universally used. Sizes smaller than 16" are usually termed “bars”. 2) A semi-finished, cogged, hot-rolled, or continuous-cast metal product of uniform section, usually rectangular with radiused corners. Billets are relatively larger than bars.
Blank
A piece of stock (also called a “slug” or “multiple”) from which a forging is to be made.
Blast Cleaning (Blasting)
A process for cleaning or finishing metal objects by use of an air jet or centrifugal wheel that propels abrasive particles (grit, sand, or shot) against the surfaces of the workpiece at high velocity.
Block
The forging operation in which metal is progressively formed to general desired shape and contour via an impression die (used when only one block operation is scheduled).
Blow
The impact or force delivered by one work-stroke of the forging equipment.
Bore Sonic Testing
A method of examining bored forgings ultrasonically from the inner surface.
Boring
Machining a hole or enlarging an existing one.
Boss
A relatively short protrusion or projection on the surface of a forging, often cylindrical in shape.
Box Annealing
A heat-treating process whereby metal to be annealed is packed in a closed container to protect its surfaces from oxidation.
Brinell Hardness Testing
A test to determine the hardness of a metal made by forcing a hard steel, or carbide ball of specified diameter, at a known pressure (10-mm ball, 500-kg load for aluminum alloys). The result is expressed as the Brinell Hardness Number (BHN), which is the value obtained by dividing the applied load in kilograms by the surface area of the resulting impression in square millimeters.
Burning
Permanently damaging a metal or alloy by heating so as to cause either incipient melting or intergranular oxidation.
Burst
An internal discontinuity caused by improper forging.
Carbon Steel
Steel containing carbon up to about 2.0 percent, but usually under 1.0 percent, and only residual amounts of other alloying elements, except for those added for composition control (silicon usually limited to 0.60 and manganese to 1.65 percent, maximum).
Carbonitriding
A process of case hardening a ferrous material in a gaseous atmosphere containing both carbon and nitrogen.
Case
The surface layer of an alloy that has been made substantially harder than the interior by some form of hardening operation.
Case Hardening
A heat treatment or combination of processes in which the surface layer of a ferrous alloy is made substantially harder than the interior. Carburizing, cyaniding, nitriding, and heating and quenching techniques are commonly used. Case hardening can provide a hard, wear-resistant surface on a forging, while retaining a softer, tougher core.
Cast Steel
A product made by pouring molten steel into molds to obtain a desired shape.
Centerline Segregation
Chemical segregation occurring in a zone along the axis of an ingot.
Charpy Impact Test
An impact test in which a specially V-notched specimen is broken by the impact of a pendulum. The energy absorbed in fracture is a measure of the impact strength or notch toughness of the sample.
Check Analysis
A supplemental chemical analysis, sometimes called product analysis, obtained from the semi-finished or finished product.
Chipping
Removing seams or other defects from a surface with a chisel or gouge. Chipping may also by used to remove excess metal.
Chop
A die forging defect; metal sheared from a vertical surface and spread by the die over an adjoining horizontal surface.
Cleaning
The process of removing scale, oxides, or lubricant—acquired during heating for forging or heat treating—from the surface of the forging. See also Blasting, Pickling, Tumbling.
Closed Die Forging
See Impression Die Forging.
Closing In
The forging operation of locally reducing diameters in hollow forging.
Coarse Grain Size
An austenitic grain size generally less than ASTM 5.
Cogging
The reducing operation in working the ingot into a billet by the use of a forging hammer or a forging press.
Coining
The process of applying necessary pressure to all or some portion of the surface of a forging to obtain closer tolerances or smoother surfaces or to eliminate draft.
Cold Inspection
A visual (usually final) inspection of the forgings for visible defects, dimensions, weight, and surface condition at room temperature.
Cold Shut
A defect characterized by a fissure or lap in the surface of a forging that has been closed without fusion during the forging operation.
Cold Working
Plastic deformation of a metal at a temperature low enough to induce strain hardening.
Columnar Structure
A structure of elongated parallel crystals formed during solidification of steel by growth taking place perpendicular to the mold surface.
Conventional Forging
A forging characterized by design complexity and tolerances that fall within the broad range of general forging practice.
Core
The softer interior portion of an alloy piece that has been surface (case) hardened; or that portion of a forging removed by trepanning or punching.
Critical (Temperature) Range
Temperatures at which changes in the phase of a metal take place. Changes are determined by absorption of heat when the metal is heated, and liberation of heat when it is cooled.
Decarburization
The loss of carbon from the surface of steel by heating above lower critical temperature or by chemical action. Decarburization is usually present to a slight extent in steel forgings. Excessive decarburization can result in defective products.
Descaling
The process of removing oxide scale from heated stock prior to or during forging operations, using such means as extra blows, wire brushes, scraping devices, or water spray.
Die
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.
Differential Heat Treatment
A heat treating process by which the temperature is varied within the object being treated so that after cooling different portions may have different properties.
Draft
1) Taper on the sides of a forging (and the forging die impression) that is necessary for removal of the workpiece from the dies. 2) As applied to open-die forging, draft is the amount of relative movement of the dies toward each other through the metal in one application of power.
Drawing
1) Referring to a heat treating operation. See Tempering. 2) Referring to a forging operation in which the cross section of a forging stock is reduced and the stock lengthened between flat or simple contour dies. See also Fullering.
Drawing out
A forging operation which produces elongation by mechanical working.
Drifting
In forging the operation of forming or enlarging a hole by the use of a tapered pin. See also Punching.
Drop Forging
A metal form or shape wrought in closed or impression dies under a drop or steam hammer.
Ductility
The property of a metal that enables it to stretch before fracturing.
Dye-Penetrant Testing
A method of inspecting for surface discontinuities in forgings by applying a dye to a liquid penetrant.
