Salt bath
carburizing - See Carburizing.
Salt bath
heat treatment Heat treatment carried out in a bath of molten
salt.
Salt bath
nitriding - See Nitriding.
Salt bath
nitrocarburizing - See Nitrocarburizing.
Salt spray
test - Accelerated testing of corrosion properties of metallic
coatings
Sand
- In metalcasting, a loose, granular material high in SiO2,
resulting from the disintegration of rock. The name sand refers
to the size of grain and not to mineral composition. Diameter
of the individual grains can vary from approximately 6 to 270
mesh. Most foundry sands are made up principally of the mineral
quartz (silica). Reason for this is that sand is plentiful, refractory,
and cheap; miscellaneous sands include zircon, olivine, chromite,
CaCO3, black sand (lava grains), titanium minerals
and others.
Sand Casting
- Metal castings produced in a green sand, dried sand or core
sand mold.
Sand Control
- Procedure whereby various properties of foundry sand, such
as fineness, permeability, green strength, moisture content, etc.,
are adjusted to obtain castings free from blows, scabs, veins,
and similar defects.
Sand Porosity
- Volume of the pore spaces or folds in sand. Not synonymous with
permeability.
Saponification
number A number given to quenching oils that reflects the
oils amount of compounding with fatty materials, which thereby
helps evaluate the condition of these oils in service. See neutralization
number.
Scab
- An expansion discontinuity defect on the surface of a casting
which appears as a rough, slightly raised surface blemish, crusted
over by a thin porous layer of metal under which is a honeycomb
or cavity that usually contains a layer of sand.
Scaling
(Scale) - Surface oxidation, partially adherent layers of
corrosion products, left on metals by heating or casting in air
or in other oxidizing atmospheres.
Scanning
probe microscopy (SPM) An extremely accurate and versatile
technique for measuring structures or surface forces. A very fine
sensor tip mounted to the end of a small deflecting spring, known
as a cantilever, is brought into contact with the sample surface
to be investigated. The sensor tip is moved across the surface
in numerous line scans. Due to the surface roughness (topography),
the tip and the cantilever move up and down. This movement can
be measured with high resolution and the resulting data allows
imaging of the surface structure. Also called atomic
force microscopy.
Scanning
Tunneling Microscopy - Technique to directly observe individual
atoms on surfaces. In STM a solid specimen in air, liquid or vacuum
is scanned by a sharp tip located very close to the surface. A
quantum -mechanical tunneling current flows between atoms on the
surface and those on the tip. The magnitude of the current depends
upon the separation between the surface and tip atoms, so that
it is possible to obtain surface topography with atomic resolution.
Scarfing
- Cutting off surface projections such as gates and risers from
casting by means of gas torch.
Scoring
- A severe form of wear characterized by the formation of extensive
grooves and scratches in the direction of sliding.
Scrap Metal
- Metal to be remelted; includes scrapped machinery fabricated
items such as rail or structural steel and rejected castings.
Scratching
- The mechanical removal or displacement, or both, of material
from a surface by the action of abrasive particles or protuberances
sliding across the surfaces.
Screen
Analysis - Distribution of particle size sand expressed in
terms of the percentage of weight retained on each of a series
of standard screens decreasing in mesh size and the percentage
passed by the screen of finest mesh.
Sealant,
Sealer - A preparation of resin or wax type materials for
sealing the porosity in coatings.
Sealing
- A process which, by absorption of a sealer into thermal spray
coatings, seals porosity and increases resistance to corrosion
of the underlying substrate material.
Seam - A defect on the surface of a metal which appears
as a crack. Experience indicates that most seams are created during
the cooling or reheating of cast structures.
Secondary hardness - The higher hardness developed by certain
alloy steels when they are cooled from a tempering operation.
This should always be followed by a second tempering operation.
Selective
heating Intentionally heating only certain portions of a
work piece.
Selective
quenching Quenching only certain portions of an object.
Self-bonding
coatings - A name given to thermal spray coatings that are
capable of bonding to clean smooth surfaces. Bond and "one-step"
coatings are normally in this group. These are particularly important
where grit blasting or surface roughening processes must be omitted.
Self-hardening
steel See preferred term, air-hardening
steel.
Semi-killed steel - Incompletely deoxidized steel which
contains enough dissolved oxygen to react with the carbon to form
carbon monoxide to offset solidification shrinkage.
Sensitization In austenitic
stainless steels, the precipitation of chromium carbides, usually
at grain boundaries, on exposure to temperatures of about 540
to 845°C (1000 to 1550°F), leaving the grain boundaries
depleted of chromium and therefore susceptible to preferential
attack by a corroding (oxidizing) medium.
Severity
of quench Ability of quenching medium to extract heat from
a hot steel work piece; expressed in terms of H value.
Shaker-hearth
furnace A continuous-type furnace that uses a reciprocating
shaker motion to move the parts along the hearth.
Shear
- A type of deformation in which parallel planes in the metal
crystals slide so as to retain their parallel relation.
Shear Modulus
(G) - In a torsion test, the ratio of the unit shear stress
to the displacement caused by it per unit length in the elastic
range. Units are Pa or psi.
Shear Strain
- Elastic displacement produced by pure shear loading.
Shear Strength
- Maximum shear stress a material is capable of withstanding without
failure.
Shell hardening
A surface-hardening process in which a suitable steel work piece,
when heated through and quench hardened, develops a martensitic
layer or shell that closely follows the contour of the piece and
surrounds a core of essentially pearlitic transformation product.
This result is accomplished by a proper balance among section
size, steel hardenability, and severity of quench.
Shell Molding
- A process for forming a mold from resin-bonded sand mixtures
brought in contact with pre-heated (150-250°C / 300-500°F)
metal patterns, resulting in a firm shell with a cavity corresponding
to the outline of the pattern.
Shift
- A casting defect caused by mismatch of cope and drag or of cores
and mold.
Shim
A thin piece of material placed between two surfaces to obtain
a proper fit, adjustment, or alignment. The piece can also be
analyzed to measure furnace carbon potential (that is, because
while in the furnace it will quickly carburize to a level equal
to the furnace carbon potential).
Shot peening
- The bombardment of a component surface with steel or ceramic
shot. Produces a residual compressive stress in the surface and
improves fatigue and stress corrosion performance.
Shrinkage
- A decrease in dimensions of a coating during processing.
Shrinkage
stress - The residual stress in a coating caused by shrinkage
during processing.
Shroud
- A gaseous and/or mechanical or physical barrier placed around
the spraying process designed to reduce the ingress of air into
the system and so reduce oxidation of the particles being sprayed.
Sieve Analysis
- Distribution of particle size sand expressed in terms of the
percentage of weight retained on each of a series of standard
screens decreasing in mesh size and the percentage passed by the
screen of finest mesh.
Sieve classification
- That portion of a powder sample which passes through a standard
sieve of specified number and is retained by some finer sieve
of specified number.
Sigma phase
A hard, brittle, nonmagnetic intermediate phase with a tetragonal
crystal structure, containing 30 atoms per unit cell occurring
in many binary and ternary alloys of the transition elements.
The composition of this phase in the various systems is not the
same, and the phase usually exhibits a wide range in homogeneity.
Alloying with a third transition element usually enlarges the
field of homogeneity and extends it deep into the ternary section.
Sigma-phased
embrittlement Embrittlement
of iron-chromium alloys (most notably austenitic stainless steels)
caused by precipitation at grain boundaries of the hard, brittle
intermetallic sigma phase during long periods of exposure to temperatures
between approximately 565 and 980°C (1050 and 1800°F).
Sigma-phase embrittlement results in severe loss in toughness
and ductility and
can make the embrittled material structure susceptible to intergranular
corrosion. See also sensitization.
Signal-to-noise
ratio Ratio of the average response to the root-mean-square
variation about the average response. Ratio of variances associated
with the two parts of the performance measurement.
Silica
Sand - Sand with a minimum silica content of 95% used for
forming casting molds.
Silicon (Si) - is one of the principal deoxidizers with
the amount used dependent on the deoxidization practice. It slightly
increases the strength of ferrite without a serious loss of ductility.
In larger quantities, it aids the resistance to scaling up to
500°F in air and decreases magnetic hysteresis loss.
Siliconizing Diffusing silicon into solid metal, usually
steel, at elevated temperature.
Silver
plating - The electrodeposition of silver for electrical,
decorative or anti-fretting properties.
Simulation
- A procedure which describes, numerically, a given flow regime.
The solution of the numerical method should replicate the real
life flow characteristics.
Single
Port Nozzle (Plasma) - Constricted nozzle with only one internal
bore, concentric with the longitudinal axis of the tungsten electrode.
The shape and design accuracy of this single orifice is decisive
for arc stability in plasma welding.
Sintering
The bonding of adjacent surfaces in a mass of particles by molecular
or atomic attraction on heating at high temperatures below the
melting temperature of any constituent in the material. Sintering
strengthens a powder mass and normally produces densification
and, in powdered metals, recrystallization.
Size analysis
- Analysis of the size of the particles being deposited by spraying
processes.
Size distribution
- The distribution of sizes within a size analysis. The distribution
may be normal or skewed in some way due to the powder manufacturing
process.
Skewed
Tolerances - Tolerances which are non-symmetrically distributed
about the design parameter.
Skim Core
(Skimmer) - A flat core or tile placed in a mold to skim a
flowing stream of metal. Commonly used in pouring basins, it holds
back slag and dirt while clean metal passes underneath to the
downsprue.
Skim Gate
- A gating arrangement which changes the direction of flow of
molten metal and prevents the passage of slag and other undesirable
materials into the mold cavity.
Skimming
- Removing or hold back dirt or slag from the surface of the molten
metal before or during pouring.
Skin
- A thin surface layer different chemically or structurally from
the main mass of a metal object.
Skin-Drying
- Drying the surface of the mold by direct application of heat.
Slack quenching
The incomplete hardening of steel due to quenching from the
austenitizing temperature at a rate slower than the critical cooling
rate for the particular steel, resulting in the formation of one
or more transformation products in addition to martensite.
Slag Inclusion
- Nonmetallic solids entrapped in solid metal.
Slag Trap
- An enlargement, dam, or extrusion in the gating or runners system
in a mold for the purpose of preventing molten slag particles
from entering the mold cavity.
Slicking
(Sleeking) - Smoothing the surface of molds.
Slot furnace
A common batch furnace where stock is charged and removed through
a slot or opening.
Slurry
- A term loosely applied to any clay-like dispersion. It may be
use to wash ladles or other refractory linings to impart a smooth
surface; as a bonding addition to molding sand; as a thin loam
over specially made molds or as a mixture to fine joints or cracks
of a core, etc.
Smelting
- A metallurgical thermal process in which a metal is separated
in fused form from nonmetallic materials or other undesired metals
with which it is associated.
Snap temper
A precautionary interim stress-relieving treatment applied to
high-hardenability steels immediately after quenching to prevent
cracking because of delay in tempering them at the prescribed
higher temperature.
Soaking
Prolonged holding at a selected temperature to effect homogenization
of structure or composition.
Soft temper
Same as dead soft
temper.
Solution
heat treatment Heating an alloy to a suitable temperature,
holding at that temperature long enough to cause one or more constituents
to enter into solid solution, and then cooling rapidly enough
to hold these constituents in solution.
Sorbite
(obsolete) A fine mixture of ferrite and cementite produced
either by regulating the rate of cooling of steel or by tempering
steel after hardening. The first type is very fine pearlite difficult
to resolve under the microscope; the second type is tempered martensite.
Spalling
A chipping or flaking of a surface due to any kind of improper
heat treatment or material dissociation.
Specific
Gravity - A numerical value representing the weight of a given
substance as compared with the weight of an equal volume of water
at 3.9°C (39°F), for which the specific gravity is taken
as 1,000 kg/m3.
Specific
Heat - Equivalent to thermal capacity, or the quantity of
heat required to produce a unit change in the temperature of a
unit mass.
Specific
Volume - Volume of one gram of a substance at a specific temperature,
usually 20°C (68°F).
Spinodal
hardening See aging.
Spheroidite
An aggregate of iron or alloy carbides of essentially spherical
shape dispersed throughout a matrix of ferrite.
Spheroidizing
Heating and cooling to produce a spheroidal or globular form
of carbide in steel. Spheroidizing methods frequently used are:
- Prolonged
holding at a temperature just below Ae
1
- Heating
and cooling alternately between temperatures that are just
above and just below Ae
1
- Heating
to a temperature above Ae
1 or Ae3
and then cooling very slowly in the furnace or holding at
a temperature just below Ae1
- Cooling
at a suitable rate from the minimum temperature at which all
carbide is dissolved, to prevent the reformation of a carbide
network, and then reheating in accordance with method 1 or
2 above. (Applicable to hypereutectoid steel containing a
carbide network.)
Spinodal
structure A fine homogeneous mixture of two phases that
form by the growth of composition waves in a solid solution during
suitable heat treatment. The phases of a spinodal structure differ
in composition from each other and from the parent phase but have
the same crystal structure as the parent phase.
Spray chamber
- A chamber in which the spraying process is carried out. It may
merely be an acoustic chamber for plasma spraying or a vacuum
chamber for vacuum plasma spraying.
Spray dried
powder - Powder formed by the spray drying process.
Spray-fused
coatings - A process in which the coating material is deposited
by flame spraying and then fused into the substrate by the addition
of further heat. This can be applied by flame induction heating
or by laser.
Spray
quenching A quenching process using spray nozzles to spray
water or other liquids on a part. The quench rate is controlled
by the velocity and volume of liquid per unit of time of impingement.
Spring
temper A temper
of nonferrous alloys and some ferrous alloys characterized by
tensile strength and hardness about two-thirds of the way from
full hard to extra
spring temper.
Sputtering
- This is a glow discharge process whereby bombardment of a cathode
releases atoms from the surface which then deposit onto a nearby
target surface to form a coating.
Stabilizing
treatment (1) Before finishing to final dimensions, repeatedly
heating a ferrous or nonferrous part to or slightly above its
normal operating temperature and then cooling to room temperature
to ensure dimensional stability in service. (2) Transforming retained
austenite in quenched hardenable steels, usually by cold
treatment. (3) Heating a solution-treated stabilized grade
of austenitic stainless steel to 870 to 900°C (1600 to 1650°F)
to precipitate all carbon as TiC, NbC, or TaC so that sensitization
is avoided on subsequent exposure to elevated temperature.
Stainless
Steel - A wide range of steels containing chromium or chromium
and nickel, exhibiting high resistance to corrosion.
Standard
Deviation - A statistical quantity used to describe the variation
of a measurable attribute about some average value.
Statistical
process control The application of statistical techniques
for measuring and analyzing the variation in processes.
Statistical
quality control The application of statistical techniques
for measuring and improving the quality of processes and products
(includes statistical process control, diagnostic tools, sampling
plans, and other statistical techniques).
Steads
brittleness A condition of brittleness that causes transcrystalline
fracture in the coarse grain structure that results from prolonged
annealing of thin sheets of low-carbon steel previously rolled
at a temperature below about 705°C (1300°F). The fracture
usually occurs at about 45° to the direction of rolling.
Steam tempering
- The production of a stable oxide on steel parts by treatment
in steam at about 300°C. Improves corrosion performance and
reduces friction.
Steel
- An alloy of iron and carbon that may contain other elements
and in which the carbon content does not exceed about 1.7%; it
must be malleable at some temperature while in the as-cast state.
Step
aging Aging at two or more temperature, by steps, without
cooling to room temperature after each step. See aging, and compare
with interrupted
aging and progressive
aging.
Sticker
- A lump on the surface of a casting caused by a portion of the
mold face sticking to the pattern. Also, a forming tool used in
molding.
Strain
- A measure of the extent to which a body is deformed when it
is subjected to a stress.
Strain-age
embrittlement A loss in ductility accompanied by an increase
in hardness and strength that occurs when low-carbon steel (especially
rimmed or capped steel) is aged following plastic deformation.
The degree of embrittlement is a function of aging time and temperature,
occurring in a matter of minutes at about 200°C (400°F)
but requiring a few hours to a year at room temperature.
Strain
aging Aging following plastic deformation.
Strand casting - Operation in which a cast shape is continuously
drawn through the bottom of the mold as it solidifies. The length
is not determined by mold dimensions.
Streamlines - A streamline is a line of fluid particles,
the velocity of each particle is tangential to the line, the particle
can not cross the streamline.
Stress
- The force per unit area on body that tends to cause it to deform.
It is a measure of the internal forces in a body between particles
of the material of which it consists as they resist separation,
compression, or sliding.
Stress-Corrosion
Cracking - Spontaneous failure of metals by cracking under
combined conditions of corrosion and stress, either residual or
applied.
Stress
equalizing A low-temperature heat treatment used to balance
stresses in cold-worked material without an appreciable decrease
in the mechanical strength produced by cold working.
Stress relieve temper - A thermal treatment to restore
elastic properties and to minimize distortion on subsequent machining
or hardening operations. This treatment is usually applied to
material that has been heat treated (quenched and tempered). Normal
practice would be to heat to a temperature 100°F lower than
the tempering temperatures used to establish mechanical properties
and hardness. Ordinarily, no straightening is performed after
the stress relieve temper.
Stress, Relieving - A heat treatment to reduce residual
stresses followed by sufficiently slow cooling to minimize development
of new residual stresses.
Stress,
Residual - Those stresses setup up in a metal as a result
of nonuniform plastic deformation or the unequal cooling of a
casting.
Strike-Off
- Operation of removing excess sand from top or core box or
flask.
Stripping
- Removing the pattern from the mold or core box from core.
Structurals
- Steel product group that includes I-beams, H-beams, wide-flange
beams and sheet piling. These products are used in the construction
of multi-story buildings, industrial buildings, bridge trusses,
vertical highway supports, and riverbank reinforcement.
Structure
(Cast Structure) - The size and disposition of the constituents
of a metal as cast.
Subcritical
annealing A process anneal performed on ferrous alloys at
a temperature below Ac1.
Submerged-electrode
furnace A furnace used for liquid carburizing of parts by
heating molten salt baths with the use of electrodes submerged
in the ceramic lining. See immersed-electrode
furnace.
Substrate
- The parent or base material to which the coating is applied.
Sulfidation
- The reaction of a metal or alloy with a sulfur containing species
to produce a sulfur compound that forms on or beneath the surface
of the metal or alloy.
Sulfur (S) - A nonmetallic element, melting point 444°C
(831.2°F) occurring as an undesirable tramp (trace) element
in most ferrous alloys. Detrimental to transverse strength and
impact resistance. It affects longitudinal properties to a lesser
degree. Existing primarily in the form of manganese sulfide stringers,
sulfur is typically added to improve machinability.
Supercooling Cooling below
the temperature at which an equilibrium phase transformation takes
place, without actually obtaining the transformation.
Superheating
Heating above the temperature at which an equilibrium phase
transformation should occur without actually obtaining the transformation.
Surface
Coating Operations - All operations involving the application
of protective, decorative, adhesive or strengthening coating or
impregnation to one or more surfaces, or into the interstices
of any object or material, by means of spraying, spreading, flowing,
brushing, roll coating, pouring, cementing or similar means; and
any subsequent draining or drying operations, excluding open-tank
operations.
Surface
Hardening - Conferring a superficial hardness to a steel while
maintaining a relatively soft core.
Surfacing
- Depositing a filer metal on a metal surface by any method to
obtain certain desired properties or dimensions.
Surface
Texture - The roughness, waviness, lay or other characteristics
of the surface of a part.
Surfacing
- The application of a coating or cladding to a surface to impart
a change in its surface behavior.
Stress-Corrosion
Cracking - Spontaneous failure of metals by cracking under
combined conditions of corrosion and stress, either residual or
applied.
Surface
energy - Surface energy exists because the molecules of a
condensed phase are attracted to each other, which is what causes
the condensation. The force required for the removal of molecular
contact from above a surface, i.e. for the bond-breaking, is the
surface energy.
Surface
Finish (or Surface Texture) - A measure of the roughness of
a surface by expressing the average deviation of the peaks and
valleys from the mean line (denoted Ra).
Surface
hardening A generic term covering several processes applicable
to a suitable ferrous alloy that produces, by quench hardening
only, a surface layer that is harder or more wear resistant than
the core. There is no significant alteration of the chemical composition
of the surface layer. The processes commonly used are carbonitriding,
carburizing,
induction
hardening, flame
hardening, nitriding,
and nitrocarburizing.
Use of the applicable specific process name is preferred.
Surface
parameter Ra - Arithmetical mean roughness: is the arithmetical
average value of all departures of the surface profile from the
mean line throughout the sampling length.
Surface
parameter Rmax - It is the largest single peak-to-valley height
within five adjoining sampling lengths 'le'.
Surface
parameter Rt - Maximum roughness depth: is the distance between
the highest and the lowest points of the surface profile within
the evaluation length Lm.
Surface
parameter Rz - Mean peak-to-valley height: is the average
of the single peak-to-valley of five adjoining sampling lengths
'le'.
Surface
preparation - Cleaning and roughening the surface to be sprayed,
usually by grit or bead blasting. This is to increase the adhesion
of the coating to the substrate.
Surface
topography - The geometrical detail of a surface, relating
particularly to microscopic variations in height.
Surface
Treatment - General term denoting a treatment involving a
modification of the surface: superficial heat treatment, diffusion
treatment, conversion coating (consisting of a compound of the
surface metal by chemical or electrochemical treatment).
Surfacing
- The application of a coating or cladding to a surface to impart
a change in its surface behavior.
Swell
- A casting defect consisting of an increase in metal section
due to the displacement of sand by metal pressure.
Synthetic
Molding Sand - Any sand compounded from selected individual
materials which, when mixed together, produce a mixture of the
proper physical and mechanical properties from which to make foundry
molds.
System
Sand - Foundry sand used in making molds and which eventually
becomes the bulk of the sand used in the mechanical system or
mechanized unit.
