F. A. O.
An abbreviation of “finish all over”; it designates that a forging must have sufficient size over the dimensions given on the drawing so that all surfaces may be machined in order to obtain the dimensions shown on the drawing. The amount of additional stock necessary for machining allowance depends on the size and shape of the part, and is agreed on by the vendor and the user.
Flat-Die Forging (Open-Die Forging)
Forging worked between flat or simple contour dies by repeated strokes and manipulation of the workpiece. Also known as “hand” or “smith” forging.
Forging
The hot mechanical forming of metals by use of hammers, presses, or forging machines.
Forging Quality
Term describing stock of sufficiently superior quality to make it suitable for commercially satisfactory forgings.
Forging Plane
The plane that includes the principle die face and that is perpendicular to the direction of the ram stroke when the parting is flat. The forging plane coincides with the parting line.
Forging Reduction
Ratio of the cross-sectional areas before and after forging.
Forging Stresses
Elastic residual stresses induced by forging or by cooling from the forging temperature.
Fracture
The irregular surface produced when a piece of metal is ruptured or broken.
Fracture Test
Breaking a piece of metal for the purpose of examining the fracture surface to determine the structure of the metal or the presence of internal defects.
Free Ferrite
Ferrite that is structurally separate and distinct, such as may be formed without the simultaneous formation of carbide when cooling hypoeutectoid austenite down to the lower critical temperature.
Fullering
Reducing the cross section of a forging between ends of stock, permitting the metal to move outward. The fullering impression is often used in conjunction with an edger (or edging impression).
Grain
The characteristic crystalline structural unit or metals and alloys.
Grain Flow
Fiber-like lines appearing on polished and etched sections of forgings that are caused by orientation of the constituents of the metal in the direction of working during forging. Grain flow can improve required mechanical properties of forgings.
Grain Growth
An increase in the size of grains of a metal with the reduction of the number of grains usually affected during heating at elevated temperatures.
Grain Size
An expression that rates the number of grains per unit area of cross section as determined by metallographic examination.
Grinding
Process of removing metal by abrasion from bar or billet stock to prepare stock surfaces for forging. Occasionally used to remove surface irregularities and flash from forgings.
Hairline Cracks
Fine, tightly-adhering cracks in steel; flakes or thermal flakes.
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 by repeated blows.
Hand Forging
A forging made by hand on an anvil or under a power hammer without dies containing an exact finishing impression of the part. Such forgings approximate each other in size and shape but do not have the commercial exactness of production die forgings. Used where the quantity of forgings required does not warrant expenditure for special dies.
Hardenability
The characteristic of steel that determines its relative depth of hardening when quenched from above the transformation temperature range.
Hardening
Any process for increasing the hardness of a metal. A heat treatment consisting of heating an alloy to a temperature within or above the critical range, maintaining that temperature for the prescribed time, then quenching or otherwise rapidly cooling. For age-hardening alloys, a two-stage process consisting of solution heat treatment and aging.
Heat (Forging)
Amount of forging stock placed in a batch-type furnace at one time.
Heat Treatment
A combination of controlled heating, holding, and cooling operations applied to a metal or alloy in the solid state to produce desired properties.
Hub
A boss that is in the center of the forging and forms a part of the body of the forging.
Impact Testing
Tests to determine the energy absorbed in fracturing a test bar at high velocity. See also Charpy Impact Test, Izod Impact Test.
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.
Inclusion
Impurities in metal, usually in the form of particles in mechanical mixture.
Iron-Carbon Phase Diagram
A diagram showing the relationships existing among constituents in the iron-carbon system when examined under conditions of thermal equilibrium.
Isothermal Annealing
A heat treatment process in which steel is heated above the transformation temperature range, after which it is cooled to and held at a temperature such that the austenite transforms to a relatively soft ferrite-carbide aggregate.
Isothermal Transformation Diagram (IT Diagram, TTT Diagram)
In essence, a concise graphic summary of the process and results of austenite transformation at consistent non-equilibrium temperatures. It is a time-temperature plot showing the time required (log scale), in the case of the specific steel composition depicted, for the austenite to begin, proceed, and complete its transformation at constant sub-critical temperatures.
Izod Impact Test
A type of impact test in which a specially notched specimen, gripped vertically at one end, is broken by the impact of a falling pendulum. See Charpy Impact Test.
Macroetch
A testing procedure for conditions such as porosity, inclusions, segregations, carburization, and flow lines from hot working. After applying a suitable etching solution to the polished metal surface, the structure revealed by the action of the reagent can be observed visually.
Macrostructure
The structure and condition of metals as revealed on a suitably prepared and etched sample and visible without the use of a microscope.
Magnaglo
A type of magnetic-particle testing where the magnetic power is fluorescent and the inspection is preformed under black light. See also Magnetic Particle Testing. Trade name of Magnaflux Corp.
Magnetic Particle Testing
A nondestructive test method of inspecting areas on or near the surface of ferromagnetic materials. The metal is magnetized, then iron powder is applied. The powder adheres to lines of flux leakage revealing surface and near-surface discontinuities. Magnetic particle testing is used for both raw material acceptance testing and product inspection. Quality levels are usually agreed on in advance by the producer and purchaser.
Mandrel Forging
The process of rolling and forging a hollow blank over a mandrel in order to produce a weldless, seamless ring or tube.
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; for example, the modulus of elasticity, tensile strength, and fatigue limit. Mechanical properties are dependent on chemical composition, forging, and heat treatment.
Microstructure
The structure and internal condition of metals as revealed on a ground and polished (and sometimes etched) surface when observed at high magnification over 10 diameters.
Pearlite
The lamellar aggregate of ferrite and carbide resulting from the direct transformation of austenite.
Photomacrograph
A photographic reproduction of a macro specimen.
Photomicrograph
A photographic reproduction of a structure revealed by the microscope.
Physical Properties
Properties familiarly discussed in physics, excluding those described under mechanical properties, for example, density, electrical conductivity, and coefficient of thermal expansion.
Pickling
The process of removing oxide scale from forgings by treating in a heated acid bath.
Pierce
In ring rolling, the process of providing a through hole in the center of an upset forging as applied to ring blank preparation.
Piercing
See Drifting.
Planing
Machining a straight surface with a single point tool used with a machine called a planer used in reciprocal motion.
Planishing
A finishing operation using frequent, light, forging strokes for the purpose of obtaining closer tolerances or removing trim lines from forgings. Usually done by hammering or pressing, hot or cold.
Precipitation Hardening
A process for hardening an alloy in which a constituent precipitates from a supersaturated solid solution. See also Age Hardening.
Precision Forging
A forging produced to closer tolerances than normally considered standard by the industry.
Preform
The forging operation in which stock is preformed or shaped to a predetermined size and contour prior to subsequent die forging operations; the operation may involve drawing, bending, flattening, edging, fullering, rolling, or upsetting.
Preheating
A preliminary heating of ingots, billets, or forgings to reduce the hazards of thermal shock upon subsequent heating to higher temperatures.
Press Forging
The shaping of metal between dies by mechanical or hydraulic pressure. The action is that of kneading the metal by relatively slow application of force as compared with the action of hammering. Usually this is accomplished with a single work stroke of the press for each die station.
Punch (Punching)
A shearing operation to remove a section of metal as outlined by the inner parting line in a blocked or finished forging; the operation is generally performed on a trim press using a punch die. A tool used in punching holes in metal. The movable die in a press or forging machine. See also Drifting.
