Metallurgical Terms
S
S
Chemical symbol for sulphur.
S-Curve
(See Time Temperature Transformation Curve).
Sadden
An operation in which an ingot is given a succession of light reductions
under a hammer or press, or in a rolling mill, with the object of overcoming
initial tenderness.
Salt Bath
A bath of molten salts used for heating steel, for hardening, tempering or
quenching. Salt baths give uniform heating and prevent oxidation. Different
salts are used for different temperatures; for tempering, e.g., sodium and
potassium nitrate, and for hardening, sodium cyanide and sodium, potassium,
barium and calcium chlorides.
Sand-Blasting
A method of cleaning metal surfaces by means of sand directed from a nozzle
at high velocity; also used for forming a key on the surface of various
materials requiring a finish such as enamel.
Sb
Chemical symbol for antimony.
Scale
The oxidized surface of steel produced during hot-working or by exposure to
air or steam at elevated temperature. It consists of partially adherent layers
of corrosion products consisting of iron oxides in the form of FeO, Fe2O3, and
Fe3O4. The scale becomes cracked and may break off during working, and according
to the operation is known as roil-, hammer-, or mill-scale.
Scaling
The formation of scale on the surface of steel, but the term is sometimes
used to describe the removal of scale, i.e., descaling as in pickling.
Scarf
(a) To bevel the edges of skelp in the process of making lap-welded pipe.
(b) To bevel the edges of plates prior to welding.
(c) (See Scarfing).
Scarfing
(Deseaming). A process of burning out defective areas on the surface of
ingots or semi-finished steel, by the oxy-acetylene method. By this means the
surface of the steel is put into such a condition that it can be rolled or
forged to a satisfactory product.
Scrap Process
(See Basic Steel)
Se
Chemical symbol of selenium.
Seam Welding
(See Welding)
Seams
Numerous shallow grooves, or striations, most obvious when the piece is
upended, cross-cut or pickled. They are generally formed by the elongation
during rolling of oxidized surface or sub-surface blowholes present in the
ingot. They may also arise from a badly rippled surface or from recurrent
teeming laps.
Season Cracking
Cracking resulting from combined corrosion and internal stress. It occurs in
severely cold-worked materials. The term is usually applied to the stress
corrosion cracking of brass.
Secondary Hardening
An increase in hardness which takes place when a hardened steel is reheated.
It may be caused by the transformation of retained austenite to martensite (as
in high speed steel) or by the precipitation of an alloy carbide.
Secondary Metals
Metals recovered from scrap, as distinguished from primary metals which are
obtained direct front the ore.
Segregation
The non-uniform distribution of impurities or alloying elements. The degree
of segregation depends not only on the chemical composition of the alloy, but
also on the rate of cooling, both of the ingot as a whole, and of each
individual point within the mass. For example, near the surface, where the rate
of cooling is rapid, the segregated impurities are trapped in the rapidly
growing crystals. Fur- their inside the ingot, where the cooling is slower, the
segregates will collect together and produce the so-called ghosts, or they may
tend to rise to the surface and collect in the scrapped ingot head. In normal
segregation, the constituents with the lowest melting points concentrate in the
last portions to solidify, but in inverse segregation this is reversed. The
segregation tends to form in bands sloping inwards to the top of the ingot (A
segregate) and at the same time, due to shrinkage, it takes a V shape (V
segregate) along the upper part of the ingot axis.
Self Hardening Steel
(See Air Hardening Steel)
Semi-Steel
The name sometimes given to the metal resulting from the addition of mild
steel to the charge of pig iron in the cupola. The term is a misnomer, for the
product is still cast iron although the total carbon content is lower than usual
and the graphite is in a finer state of division.
Sendzimir Mill
A cluster mill in which the backing rolls do not have conventional bearings
but are supported by stationary shafts on which are groups of roller bearings.
High front and back tension is applied to the strip by powered coilers. The
mills are particularly suited to the cold reduction to fine gauges of stainless
steel or other materials having high resistance to deformation.
S.G. Iron
Abbreviation for Spheroidal Graphite Cast Iron (see Cast Iron).
Shatter Cracks
(See Flakes)
Shear Steel
(See Cementation)
Shearing Test
A test applied to metal to determine the stress required to cut it across
its section.
Shell Moulding
Also known as "C" or Croning process, after its inventor. A mixture of sand
and synthetic resin is placed in contact with a metal pattern plate heated at
about 250˚C. The heat causes the resin to set in the immediate neighborhood of
the pattern; in this way a thin-walled half-mould is obtained, two half-moulds
are placed together and supported by some suitable means, e.g., steel shot.
Sherardizing
A method of producing a protective zinc coating on iron and steel articles.
Shielded Inert Gas Are Welding
(See Welding)
Shielding Corrosion
(See Crevice Corrosion)
Shore Scleroscope
An instrument which consists essentially of a small diamond-tipped hammer
which falls freely down a graduated glass tube from a constant height onto the
surface of the sample under test. The hardness is measured by the height of the
rebound. In one form of the instrument the rebounding hammer actuates the
pointer of a scale so that the height of rebound is recorded.
Shorterizing
(See Flame Hardening)
Shot-Blasting
A method of cleaning the surface of metals by abrasion, as in sand-blasting,
the sand being replaced by broken shot or steel grit.
Shot Peening
Superficial cold working by directing a stream of metal shot on to the
surface of a metal article. The fatigue strength is in7proved since the surface
becomes slightly work hardened and acquires a residual compressive stress.
Si
Chemical symbol for silicon
Side-Blown Converter
(See Tropenas Converter).
Siemens-Martin Process
(See Open Hearth Furnace)
Siemens Open Hearth Process.
(See Open Hearth Furnace)
Sigma Phase
Originally a phase in iron chromium alloys containing essentially the
compound FeCr, but the term has been extended to include similar related phases
in other systems. It is formed at temperatures of the order of 900˚C and may
occur in stainless steels where, because of its hard, brittle nature, it is
undesirable.
Sigma Welding
(See Welding)
Silica. (SiO2)
The most common refractory for acid furnaces and an important constituent of
steel making slags. Silica sand is used extensively as a foundry moulding
material.
Silico-Manganese
An alloy added to steel as a deoxidizing agent. It contains up to 25%
carbon, from about 12 to 25% silicon and about 65 to 70% manganese.
Silky Fracture
A steel fracture having a very smooth fine grain or silky appearance.
Silver Steel
A name given to bright carbon steel, containing 095 to 125% carbon with
normal silicon, manganese, sulphur and phosphorus. It has no silver in its
composition.
Sink Head
(See Feeder Head)
Sintered Metal Carbides
(Sec Hard Metals)
Sintering
(a) The process of agglomerating fine iron ore and iron-bearing materials
such as mill scale, with coke breeze so that they may be charged into the blast
furnace without choking it and impairing its efficiency by impeding the up-ward
now of gases.
(b) The bonding of adjacent surfaces of particles in a mass of powder or a
compact by heating to a suitable temperature depending upon the metal concerned
keeping the compact at that temperature for a predetermined time, and then
cooling it.
Skelp
Mild steel strip from which tubes are made by drawing through a welding
bell, at welding temperatures, to produce butt-, or lap-welded tubes. The skelp
is made of a suitable width and thickness to form tube of the required diameter
and wall thickness.
Skin Pass (Pinch Pass)
A very light reduction given by cold rolling annealed sheet or strip to
prevent the formation of stretcher strain markings and the tendency to kinks and
flats on subsequent working.
Slabbing Mill
A rolling mill in which ingots are rolled down to slabs for subsequent
reduction to plates, sheet or strip.
Slag
(a) In the blast furnace, where it is usually referred to as cinder, the
molten non-metallic layer formed by the reaction of the flux and the gangue of
the ore, which floats on the surface of the molten pig iron.
(b) The non-metallic layer covering the molten steel in a steel making furnace.
It is formed from the materials, e.g., lime and ore, added for the purpose of
assisting purification and plays an important part in the refining of steel. An
acid slag consists principally of silica and various metallic oxides whilst a
basic slag is composed chiefly of lime and metallic oxide.
Slag Washing
A process in which steel is refined by being intimately mixed with slag
after the normal steel making process.
Slip
The mechanism of cold deformation wherein one part of a crystal glides over
another part along certain planes known as slip planes.
Slip Bands
A series of parallel lines showing across the individual crystals of a
deformed polished surface.
Smelting
A metallurgical process or series of processes, whereby a metal or compound
is separated in a state of fusion from its ore or other material with which it
is chemically combined or physically mixed. The separation of the impurities
involves the fusion of the ore with suitable fluxes to produce a melt consisting
of two layers, the molten metal sinking to the bottom, whilst the gangue
together with the flux forms a slag which floats on the top. Care should be
taken to distinguish between the terms smelt and melt.
Sn
Chemical symbol for tin
S-N Curve
Stress-number curve showing the number of reversals to rupture for a given
applied stress in a fatigue test.
Snowflakes
(See Flakes)
Soaking Pit
Originally a soaking pit simply consisted of hole in the ground, lined with
fire-brick, in which an ingot was placed for soaking, i.e., to allow the heat
from the still molten steel in its interior to extend to the surfaces and thus
render the temperature of the ingot approximately uniform throughout. Modern
soaking pits are heated. There are several types
(1) The regular reversing regenerative type of pit which operates in much the
same way as the open hearth furnace but the periods of reversal are longer.
(2) The one-way fired recuperative pit where the flame enters at one end and
leaves the pit at the same end but at a lower level.
(3) The bottom-fired recuperative pit where the flame enters from the bottom.
(4) The tangentially-fired circular pit where the flame enters tangentially.
(5) Electrically heated by a current passed through a coke-filled trough at the
bottom, with or without auxiliary oil firing.
Solid Solubility
The extent to which one metal is capable of forming solid solutions with
another. This capacity varies considerably: some metals are almost insoluble in
each other, whilst others are mutually soluble in all proportions.
Solid Solutions
A homogeneous solution of two or more crystallized bodies in the solid
state.
Solidus
A line or surface in a constitutional diagram indicating the temperatures at
which solidification is completed or melting begins in alloys and other melts of
different composition, i.e., the line or surface below which the alloys are in a
solid condition (Cf. Liquidus).
Solution Heat Treatment
A treatment in which an alloy is heated to a suitable temperature and held
at this temperature for a sufficient length of time to allow a desired
constituent to enter into solid solution. It is often followed by rapid cooling
to hold the constituent in solution. The material is then in a supersaturated,
unstable state and may subsequently exhibit age hardening.
Sonim
Abbreviation of Solid Non-metallic Inclusions in
Metal.
Sorbite
A term, which has fallen into disuse, for a micro constituent of steel
consisting of small globules of cementite in a matrix of ferrite. It is obtained
on tempering hardened steel (martensite) at temperatures above about 450˚C.
Space Lattice
The three dimensional geometric pattern in which the atoms of a metal
arrange themselves, and upon which a crystal is built. There are several known
lattice configurations, but most metals crystallize in one of three types:
(1) face centered cubic
(2) body centred cubic
(3) close packed hexagonal.
Spalling.
(a) The cracking off of thin flakes from the surface of a metal, It is also
known as exfoliation and flaking.
(b) A term used to cover a number of different forms of disintegration in
refractories. It has been suggested that spalling is the breakdown of the
structure of a refractory owing to the irregular mechanical strength of a brick
or of a more or less solid mass of brickwork when subjected to thermal shock.
Spark Testing
A method of determining the approximate composition of steel by holding a
sample on a grinding wheel and producing sparks. An experienced operator can
detect differences in the carbon content of steels of 005% in the range up to
035 % and 010% in the range from 033 to 060%. The effects of alloying
elements such as tungsten, molybdenum, chromium, nickel, silicon and manganese
are also recognizable.
Spheroidizing
A process of heating and cooling steel through a selected temperature cycle
within or near the transformation range, in order to obtain the carbide in a
globular form. The process is usually applied to high carbon steels to obtain
improve machinability, to facilitate subsequent cold-working or to obtain a
desired structure for subsequent heat treatment.
Spiegeleisen
(See Ferro Manganese).
Spinning
(a) A process for shaping a circular blank of sheet into a hollow vessel.
The blank while in contact with a rotating former of the required shape is
pressed by tools, mechanically or by hand, so that it assumes the shape of the
former. Annealing may be needed during and/or after the operation to remove the
effects of work hardening.
(b) The feeding of bar or wire through rotating rollers or dies to straighten it
so it can be cut into lengths.
Spoon Sample
A sample of steel taken from the molten bath.
Spot Welding
(See Welding)
Stabilization
(a) The retarding or prevention of a particular reaction by the addition of
a stabilizer or negative catalyst.
(b) A heat treatment, to relieve internal stresses (See Stress Relieving).
(c) A treatment of magnetic material designed to increase the permanency of its
magnetic properties or condition.
Stabilizers
Elements added to austenitic stainless steels, of the type containing 15 to
20% chromium and 12 to 8% nickel, for the purpose of forming a stable carbide,
thus preventing any tendency to intercrystalline corrosion or weld decay. The
stabilizers in most common use are titanium and niobium. (The titanium should be
added to the extent of 4 to 5 times, and niobium 8 to 10 times, the carbon
content).
Stainless Steel (or Iron)
Steel containing between 10 and 35% chromium with or without the addition of
nickel, mangenese, silicon, copper, molybdenum, niobium or titanium. Stainless
steel intended for cutlery contains about 030% carbon and 14% chromium, whilst
in stainless irons the carbon content is less than about 0.10% (See also
Staybrite).
Stamping
(a) A stamping differs from a pressing in that it is made by the impact of a
hammer on metal in dies either in the cold or hot state for drop stamping. (See
Drop Forging).
(b) A process used to cut lines of letters, figures and decorations on smooth
metal surfaces. The impact of a punch with comparatively sharp projecting
outlines impresses the characters into the surface of the metal.
Staybrite
The trade name of a series of stainless steels manufactured by Firth-Vickers
Special Steels Ltd. These steels possess a high degree of corrosion-resistance
and good ductility. They are made in several modifications to meet various
industrial and domestic conditions. The essential constituents are 18% chromium
and 8% nickel.
Steckel Mill
A rolling mill, usually reversible, in which the rolls are not driven, the
material being drawn through by powered reels. This permits greater reductions
per pass and also allows the rolling of finer gauges than would otherwise be
possible with the same roll diameter. The reels may be closed in furnaces to
enable the metal to be rolled hot.
Stitch Welding
(See Welding)
Strain Ageing
The gradual changes in physical and mechanical properties, generally an
increase in hardness, which takes place following cold deformation. At
atmospheric temperatures the change is slow; it may be accelerated by heating to
say 200˚C.
Strain Hardening
The loss of ductility and gain in hardness resulting from strain ageing.
Stress Corrosion.
The term implies a greater deterioration in mechanical properties of
material through the simultaneous action of static stress and exposure to
corrosion than could occur by the separate but additive action of those
agencies. It is often accompanied by cracking.
Stress Number Curve
(See S-N Curve)
Stress Releif Heat Treatment (Stress Relieving)
A process of reducing residual stress in metal by heating to a suitable
temperature e.g., 600˚C to 650˚C and holding for a sufficient time for the
internal stress to be released by creep. After soaking, the metal is allowed t
cool sufficiently slowly to prevent the reintroduction of stress. This treatment
may be applied to relieve stresses induced by casting, quenching, normalizing,
machining, cold-working or welding.
Stress Relieving
(See Stress Relief Heat Treatment)
Stress Strain Curve
A graph in which stress (load divided by the original cross-sectional area
of the test piece) is plotted against strain (the extension divided by the
length over which it is measured).
Stretcher Strains (Luders Lines)
Lines often approximately parallel to one another and appearing on the
surface of some materials, particularly mild annealed steel sheet or strip, on
cold working. The markings can be prevented by temper rolling the sheet after
annealing.
Stud Welding
(See Welding)
Sub-Critical Annealing (Process Annealing)
Heating to, and holding at, some temperature below the transformation range.
Subsequent cooling may be in air.
Sub-Zero Treatment
Subjecting hardened steel to low-temperature treatment in order to complete
the transformation of austenite to martensite. The treatment is best applied
immediately after hardening, since tempering tends to stabilize the austenite
making transformation more difficult Cooling to 78˚C by solid carbon dioxide is
commonly used.
Submerged-Arc Welding process
(See Welding)
Sulfinuz Treatment
Heat treatment in a salt bath containing sulphur to give a surface with
anti-galling properties. A certain amount of surface hardening takes place as a
result of the treatment.
Sulphur Print
A macro graphic method of examination for the distribution of impurities. A
sheet of bromide paper, after being soaked in dilute sulphuric acid, is placed
upon the plane polished surface to be examined. The sulphides in the steel react
with the acid, liberating hydrogen sulphide which reacts with the silver salt in
the paper, leaving a dark brown stain, thus indicating the distribution of the
sulphur.
Superplasticity
A property brought about by heat treatment or controlled work which enables
certain alloys to be extensively deformed by small forces and without risk of
fracture. The alloys exhibiting super plasticity have an extremely fine grain
size. Some non-ferrous alloys can be made super plastic at room temperature, for
others, including steel, high temperatures are needed.
Surface Hardening
This may be achieved by various methods which are described under their
respective headings:
Nitriding, carbon case hardening, gas carburizing,
Flame hardening and induction hardening.
Swaging
A process by which metal is worked into the desired shape by a series of
blows rapidly applied by suitably shaped dies to produce close tolerances in
cylindrical or tapered bars or tubes. In hand swaging, the bar or tube is
rotated. In machine or rotary swaging, the dies, usually two in number but
sometimes four on large machines, reciprocate rapidly as the spindle on which
they are mounted rotates. This means that the finished work must be round, but
within this limitation swaging can be applied to a wide variety of pointing,
tapering, sizing and reducing operations.
Swarf
Fine particles of metal (usually iron or steel) produced in machining or
grinding.