Steel Sheet Metal Supplies

Term

Definition

Adhesion

Force of attraction between the molecules (or atoms) of two different phases, eg, base and coating, metal and paint

Annealing

A process involving heating and cooling applied normally to induce softening, usually in a protective atmosphere. The term annealing is also used to cover treatments used:-
a) to remove stresses
b) to alter mechanical or physical properties
c) to produce a definite microstructure and recrystallisation
d) to remove dissolved gases
e) to subcritical anneal

Ageing

Changes occurring with the passage of time which affect the mechanical properties of a metal or alloy. Usually accelerated by an increase in temperature.

Alloy

A metal containing two or more elements giving it modified properties and a melting point below that of its constituents. Impurities remaining from processes of manufacture are not regarded as part of the alloy.

Anode/cathode

These are terms applied to positively and negatively charged poles to effect the current flow in an electrolytic cell, eg, zinc-coated sheet.

Bead

A run of fusion weld deposit.

Bend Test

A test of ductility where (at ordinary temperature), a test piece must withstand, without fracture, bending through a specified angle around a specified diameter, eg:
0t - flat bend on itself
1t - bend around thickness of sheet

Brittle

Will fracture suddenly, ie, with little or no plastic (permanent) deformation.

Burr

The rough projection left by a cutting operation.

Camber

The greatest deviation of a side edge of sheet or strip from a straight line, the measurement being taken on the concave side with a straight edge in the same plane as the steel.

Carbon Steel

A steel, free from intentionally added alloying elements, depending for its properties substantially upon its carbon content alone. Manganese influences the mechanical properties of carbon steels, but up to a concentration of approximately 1%, is not regarded as removing the steel from the carbon steel into the alloy steel classification. Silicon, up to approximately 0.3%, phosphorus, sulphur, and other elements governed by normal steel making practices, are usually referred to normal impurities.

Cathodic protection

In the case of galvanised steel (ie, zinc coating on steel base) where the base steel may be exposed by a scratch, the zinc becomes the anode (+ve) and corrodes and the steel becomes the cathode (-ve).

Cementite

A form of iron carbide (Fe3C) seen in the microstructure of low carbon steel sheet. It is viewed under a microscope at 500 magnifications.

Coating Pot

The pot that contains the molten zinc or zinc/aluminium through which the heated strip passes to in the hot dip galvanising process.

Cold Rolling

This is the reduction of hot rolled pickled steel strip to a specified thickness, using a series of stands of rolls reducing the thickness progressively. This distorts the grain structure of the steel significantly and therefore a loss of ductility results.

Corrosion

Destruction of a metal by electrochemical reaction with its environment.

Decarburisation

In steel the partial or complete removal of carbon by chemical reaction during heat treatment.

Deep Drawing

A process in which a blank or work piece usually controlled by a pressure plate is forced into and/or though a die by means of a punch to form a hollow component in which the wall thickness of the product is substantially the same as that of the original.

Defect

A condition that impairs the usefulness of an object or a part.

Denitriding

The partial or complete removal of nitrogen by chemical reaction during heat treatment.

Diffusion

Movement of atoms through a phase(s)

Dross

Particles of zinc and impurities formed on the surface of the coating pot due to air turbulence. Dross is regularly skimmed from surface of pot to prevent contact with the strip.

Ductility

Relative ability of a metal to deform from a flat condition into a more complex shape, without fracture; formability; workability.

Elasticity

That property of a material which causes it to resume its original form after removal of a load.

Elastic Limit

The maximum stress to which a material may be subjected without any permanent strain remaining upon complete release of stress.

Electrolyte

A liquid, most often a solution that will conduct an electric current.

Electroplating

Electro depositing metal onto an object.

Elongation

A measure of ductility determined on a tensile test. The percentage increases in gauge length after fracture of a tensile specimen. It is measured as the percentage increase in gauge length after extending a tensile specimen until fractured.

Ferrite

The almost pure form of iron seen in the microstructure of low carbon steel sheet. This is the main constituent of the microstructure of S&CP low carbon steel products.

Finish

Refers to the degree of smoothness of lustre of the sheet.

Flatness

Flatness of sheet metal may be best defined as the absence of any waviness or buckles.

Fluting (Coil Break)

The tendency to form a series of near parallel kinks or creases in sheet metal during curving or bending operations. The creases occur at right angles to the direction of curving and are associated with the non-uniform yielding of metal causing localised deformation.

Formability

The relative ease with which a metal can be shaped through plastic deformation.

Full Annealing

Heating ferrous alloys to and holding at some temperature above the transformation range followed by very slow cooling. The object of full annealing is always associated with the achievement of minimum hardness and/or maximum ductility and freedom from internal stresses (NB full annealing does not take place in galvanising).

Galling

The unintentional roughening or abrasion on rubbing metal surfaces. Often results from relative movement of adjacent sheet or wraps during transport. Some times referred to as "Road Burn".

Galvanising

A process for applying a coating of zinc to the surface of iron or steel to provide a corrosion resistant surface. Zinc coatings may be applied by hot dipping or electroplating.

Grain

Any one of the individual crystals of which a metal is composed.

Grain Size

The size of crystals of ferrite (iron) measured under a microscope at 100 magnifications after polishing and etching the surface and specified using the ASTM grain size system.

Hardness

Is the resistance offered by a metallic material to plastic deformation by indentation or penetration. Common indentation hardness scales and the types of indentors used are:
1) BRINELL- Steel or tungsten carbide ball
2) VICKERS - Square based pyramidal diamond
3) ROCKWELL: Spherical painted conical diamond or steel ball most commonly used: all our hardness products stipulate minimum Rockwell hardness (eg. HA70T).

Heat Treatment

An operation or combination of operations involving the heating and or cooling of a metal or alloy in the solid state for the purpose of obtaining certain desired properties.

Hot-Dipped Coating

Coating applied by means of dipping object to be coated into molten coating metal.

Inert

Unreactive

Ingot

A cast rectangular steel shape for rolling into slab for production of hot rolled strip.

Iron Carbide

The form in which carbon is present in steel. In low carbon steels, the common forms of carbide are cementite and pearlite.

Intermetallic

A crystal phase containing atoms of two or more elements.

Jet Strippers

Jets through which air is blown into the strip to remove (strip) excess molten coating metal.

Inclusions

Particles of insoluble impurities entrapped during solidification of metal or formed by subsequent reaction with the solid metal. Inclusions in steel are usually oxides or sulphides and except when permitted deliberately under careful control in certain special steels, such as to confer free machining properties, they are generally undesirable and sometimes detrimental to mechanical, chemical or other properties.

Lock-forming

The forming of two adjacent edges prior to interlocking.

Lock-seaming

The closing of a tight seam of lock formed edges of sheet metal, for example Pittsburg lock-seam, grooved single lock-seam, Snap Lockseam.

Mandrel Marks

Creases across face of strip created by the jaws of the un-coiler or the re-coiler. Generally more pronounced at the coil ends.

Mechanical Properties

Properties relating to the behaviour of materials being worked, eg, yield strength, tensile strength, elongation, hardness and bends.

Metallography

The science of a constitution and structure of metals and alloys as revealed by the unaided eye or by such tools as the optical microscope, the electron microscope and x-ray techniques.

Metallurgy

The science and technology of metals. Process (chemicals) metallurgy is concerned with the extraction from their ores and with the refining of metals, physical metallurgy with the physical and mechanical properties of metals as affected by composition, mechanical working and heat treatment.

Oil Canning

Description of full centre of flat strip, which resembles, and behaves like the bottom side of an old fashion Oil can.

Oxidation

Combination of metal with oxygen to form an oxide layer.

Paintability

Ability of a material to accept a paint coating, and maintain good adherence.

Passivation

A surface treatment to give greater resistance to storage corrosion in which the protection is afforded by film such as chromates, oxides and phosphates.

Pearlite

A form of iron carbide, sometimes present in S&CP low carbon steel products. It consists of alternate layers of cementite and ferrite and when it is viewed under a microscope at 500 magnifications, it appears to have a "pearly" lustre.

Pickling

Removal of oxide films from metals by immersion in hot acid. The process is applied particularly to scale removal from metal prior to such operations as cold rolling, wire drawing and electroplating and in general is carried out in dilute solutions of the mineral acids often with additions of organic material (inhibitors) to restrain the rate of attack on the metal.

Photomicrograph

A photograph of the surface of a prepared specimen, usually at high magnifications.

Plastic Deformation

Deformation that remains permanent after removal of the load which caused the change.

Porous

Contains fine holes or pores.

Prep Lap Weld

Weld made to join coils at the entry of a continuous galvanising line.

Preheat Furnace

Furnace positioned before the direct fired furnace, which can be used to heat the strip slightly prior to entry to remaining furnace.

Proof Stress

That stress at which a material exhibits a specific limiting permanent set. The proof stress of a material is found by observing, usually from a stress-strain diagram, the stress at which the predetermined permissible elongation (usually of the order of 0.1% or 0.2%) occurs.

Recrystallisation

The reformation to "round" ferrite grains flattened during rolling. This occurs at temperatures above 725º C either immediately after hot rolling or during annealing after cold reduction.

Roll-Forming

Forming sheet or strip by passing it through one or more sets of contoured rolls.

Roller Levelling

The levelling of sheet or strip by passing it through a series of staggered rolls of small diameter (machines combining this function with the levelling are sometimes known as sheet or strip processes).

Rolling Direction

The main direction in which sheet strip has been rolled. Associated terms used are:
a) Longitudinal - in the rolling direction (L)
b) Transverse - right angles to the rolling direction (T)

Rust

A corrosion by product, consisting of hydrated oxides of iron.

Scale

Layers of iron oxide formed on the surface of hot steel when oxygen from the atmosphere combines with iron from the steel.

Seaming

The process of joining two edges of sheets or strip to produce a seam.

Skin Passing

A light cold rolling operation which must not cause significant changes in sheet ductility. This is called skin passing because it was originally thought to be a surface treatment as distinct from temper rolling.
1) Skin passing is a small amount (1-2%) of cold work removes the yield point in steel which otherwise causes coil break, fluting or stretcher strain in subsequent operations.
2) Modifies surface for example, by reducing surface roughness for bright (lustre) qualities or by specially controlled roughening for matt finish for drawing qualities.
3) Also used to improve strip shape (flatness).

Slab

Normally, a rectangular steel shape continuously cast, ranging up to about 300mm thick by 2000mm wide and 6 or 12 metres long. Heated slabs are the feed for hot strip mills.

Spangle

Grain or crystal of zinc, or zinc/aluminium as appearing on hot-dip metallic coated steel.

Springback

The elastic recovery after deformation.

Strain Ageing

Ageing which occurs subsequent to the cold working of an alloy. Strain ageing in steel is predominantly due to the presence of uncombined nitrogen, and results in a marked decrease in ductility.

Stretcher Levelling

The flattening of sheet or strip by stretching in such a way as to impose the minimum permanent extension required to remove distortion.

Stress Relieving

Heating a metal to and if necessary holding at temperature below the recrystallisation range followed by uniform cooling for the sole purpose of removing internal stresses.

Stretcher Strain Markings

Characteristic surface markings, which appear during the early stages of the plastic deformation of mild steel and certain copper base alloys. Their production is associated with the sudden extension at the yield point. In steel they are called alternatively Luders lines or bands.

Strip

A continuously rolled flat product of any width and thickness, supplied rolled up into and stored in coil form. Previously, the official designation was "coil" used for both the strip and the rolled up product.

Substrate

Material on which another component, such as a coating is placed.

Swarf

Shaving chips of filings of metal, usually debris from sawing, grinding or drilling.

Temper

To modify hardness of metals by controlled heating after quenching. Increase of hardness by cold rolling (temper rolling) or drawing by small increments.

Tensile Strength

The maximum strength reached during a tensile test on a material; the maximum load divided by the original cross-sectional area and expressed in MPa for steels.

Tension Levelling

This is a process whereby any shape imperfections in the strip are corrected by passing the strip around a series of rolls to initiate bending and stretching to correct the shape, and then flattening to correct the bend.

Total Coated Thickness

The measurement of thickness of the base metal added to any coating in total. i.e. The combined overall thickness of the product.

Undercutting

Corrosion of the substrate under a paint film. Begins at a score mark or sheared edge where corrosive agents can gain access to the metal.

White Corrosion

Formation of a basic zinc carbonate complex on zinc surfaces in moist atmospheres where unprotected by surface passivation.

Work Hardening

An increase in the hardness and/or mechanical strength of a metal resulting from plastic deformation. According to the nature and extent of the cold work to which an object has been subjected, the work hardening effect may be confined to the surface layer (skin-hardening), as in peening, frictional wear and machining operations, or may extend through the body of metal, as in cold-rolling, drawing and upsetting operation.

Yield Strength

Strength at which steel first exhibits plastic strain.

Yield Point

The stress at which a material permanently deforms.