Glossary | S (The vocabulary of the coating and heat-treating industries—explained)

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Salt Bath Carburizing

See carburizing.

Salt Bath Heat Treatment

Any heat treatment carried out in a bath of molten salt.

Salt Bath Nitriding

See nitriding.

Salt Bath Nitrocarburizing

See nitrocarburizing.

Salt Spray Test

The accelerated testing of the corrosion properties of metallic coatings.


In metalcasting, a loose, granular material high in SiO2—the end result of disintegration of rock. A material is termed ‘sand’ based on the property of grain size, and not mineral composition. Diameters of individual grains can vary from approximately 6 to 270 mesh. Most foundry sands are made up principally of the mineral quartz (silica), because sand is plentiful, refractory and cheap. Some example sands are zircon, olivine, chromite, CaCO3, black sand (lava grains) and titanium minerals.

Sand Casting

The production of metal castings in a mold of green sand, dried sand or core sand.

Sand Control

Procedure whereby various properties of foundry sand (including fineness, permeability, green strength, moisture content, etc.) are adjusted to obtain castings free from blows, scabs, veins and similar defects.

Sand Porosity

The 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. This helps evaluate the condition of these oils in service. See neutralization number.


An expansion discontinuity defect on the surface of a casting, appearing as a rough and slightly raised surface blemish crusted over by a thin, porous layer of metal. Under it lies 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 (STM)

A technique used to directly observe individual atoms on surfaces. 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 atoms of the surface and the tip, making it possible to obtain surface topography with atomic resolution.


Using a gas torch to cut off surface projections, such as gates and risers, from a casting.


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.


The mechanical removal and/or displacement of material from a surface, using the action of abrasive particles or protuberances sliding across the surfaces.

Screen Analysis

Distribution of particle-sized 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/wax-type materials used to seal the porosity in coatings.


A process which, by absorption of a sealer into thermal spray coatings, seals porosity and increases resistance to corrosion of the underlying substrate material.


A defect on the surface of a metal, appearing 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

Intentionally quenching only certain portions of a work piece.

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 should not or cannot be implemented.

Self-Hardening Steel

A less-preferred term for air-hardening steel.

Semi-Killed Steel

Incompletely deoxidized steel that contains enough dissolved oxygen for the oxygen to react with the carbon, forming carbon monoxide. This reaction offsets solidification shrinkage.


In austenitic stainless steels, the precipitation of chromium carbides (usually at grain boundaries) upon exposure to temperatures from ~540°C–845°C (~1000°F–1550°F), leaving the grain boundaries depleted of chromium and therefore susceptible to preferential attack by a corroding (oxidizing) medium.

Severity of Quench

A quenching medium's ability 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.


A type of deformation in which parallel planes in the metal crystals slide, but remain parallel to one another.

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

The maximum amount of 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 metal patterns pre-heated to 150°C–250°C (300°F–500°F), resulting in a firm shell with a cavity corresponding to the outline of the pattern.


A casting defect caused by mismatch of cope and drag or of cores and mold.


A thin piece of material that is placed between two surfaces to obtain a proper fit, adjustment or alignment. The piece can also be analyzed to measure furnace carbon potential. 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.


A decrease in the dimensions of a coating during processing.

Shrinkage Stress

The residual stress in a coating; caused by shrinkage.


A gaseous and/or mechanical/physical barrier placed around the spraying process and designed to reduce the ingress of air into the system, to prevent oxidation of the particles being sprayed.

Sieve Analysis

-Distribution of particle-sized sand, expressed in terms of the percentage of weight retained on each of a series of standard sieves decreasing in mesh size as well as the percentage passed by the sieve of finest mesh. Compare to screen analysis.

Sieve Classification

The portion of a powder sample that 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 alloy 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

The 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 from ~565°C–980°C (~1050°F–1800°F). Sigma-phase embrittlement results in severe loss in toughness and ductility, and can make the embrittled material structure susceptible to intergranular corrosion. Also see 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)

An element, and 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.


Diffusing silicon into solid metal, usually steel, at elevated temperature.

Silver Plating

The electrodeposition of silver for electrical, decorative or anti-fretting properties.


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.


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

In spraying processes, the analysis of the size of the particles being deposited.

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 not 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.


Removing or holding back dirt or slag from the surface of the molten metal before or during pouring.


A thin surface layer that is different, chemically or structurally, from the main mass of a metal object.


Drying the surface of a mold via the 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, there for the purpose of preventing molten slag particles from entering the mold cavity.

Slicking (Sleeking)

Smoothing the surface of a mold.

Slot Furnace

A common batch furnace where stock is charged and removed through a slot or opening.


A term loosely applied to any clay-like dispersion. It may be used 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.


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.


Prolonged holding at a selected temperature to effect Homogenization of structure or composition.

Soft Temper

Another name for 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.


An obsolete term for 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, and the second type is tempered martensite.


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, which is usually 20°C (68°F).


An aggregate of iron or alloy carbides, of essentially spherical shape, dispersed throughout a matrix of ferrite.


Heating and cooling to produce a spheroidal or globular form of carbide in steel. Spheroidizing methods frequently used are:
(a) prolonged holding at a temperature just below Ae1,
eating and cooling alternately between temperatures that are just above and just below Ae1,
(c) heating to a temperature above Ae1 or Ae3 and then cooling very slowly in the furnace or holding at a temperature just below Ae1, and
(d) 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. This is applicable to hypereutectoid steel containing a carbide network.

Spinodal Hardening

See aging.

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 a spraying process is carried out. It may merely be an acoustic chamber for plasma spraying or a vacuum chamber for vacuum plasma spraying.

Spray Quenching

A quenching process that uses 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.

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.

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.


This is a glow discharge process whereby bombardment of a cathode releases atoms from the surface, which are deposited 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°C–900°C (1600°F–1650°F) to precipitate all carbon as TiC, NbC, or TaC so that sensitization is avoided on subsequent exposure to elevated temperatures.

Stainless Steel

A wide range of steels containing chromium and sometimes 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).

Stead's 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° angle compared to the direction of rolling.

Steam Tempering

The production of a stable oxide on steel parts by treatment in steam at about 300°C. This improves corrosion performance and reduces friction.


An alloy of iron and carbon that may contain other elements, and in which the carbon content does not exceed ~1.7%; it must be malleable at some temperature while in the as-cast state.

Step Aging

Aging at two or more temperatures by steps, without cooling to room temperature after each step. Compare with interrupted aging and progressive aging.


(defect) A lump on the surface of a casting, caused by a portion of the mold face sticking to the pattern.
(object) A forming tool used in molding.


A measure of the extent to which a body is deformed when it is subjected to a stress.

Strain Aging

Aging that follows plastic deformation.

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.

Strand Casting

An 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.


A streamline is a line of fluid particles. The velocity of each particle is tangential to the line, which the particle is unable to cross.


The force-per-unit area on a work piece that tends to cause it to deform. It is a measure of the internal forces in a body between particles of its material as they resist separation, compression and/or sliding.

Stress Equalizing

A low-temperature heat treatment used to balance stresses in cold-worked material without an appreciable decrease in the mechanical strength that cold working produces.

Stress Relieve Temper

A thermal treatment to restore elastic properties and to minimize distortion on subsequent machining/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-Corrosion Cracking

Spontaneous failure of metals by cracking under combined conditions of corrosion and stress, either residual or applied.


An operation to removing excess sand from top or core box or flask.


Removing the pattern from the mold, or core box from core.


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 in liquid carburizing. It heats molten salt baths with the use of electrodes submerged in the ceramic lining. Compare to immersed-electrodes furnace.


The parent or base material to which a coating is applied.


The reaction of a metal or alloy with a sulfur-containing species to produce a sulfur compound, which forms on or beneath the surface of the metal or alloy.

Sulfur (S)

A nonmetallic element, melting point 444°C (831.2°F), that occurs as an undesirable tramp (trace) element in most ferrous alloys. It is detrimental to transverse strength and impact resistance and, to a lesser degree, also affects longitudinal properties. It exists primarily in the form of manganese sulfide stringers. Sulfur is typically added to improve machinability.


Cooling below the temperature at which an equilibrium phase transformation takes place without actually obtaining the transformation.


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 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 name of the specific applicable process is preferred.

Surface Parameter Ra

See surface finish.

Surface Parameter Rmax

Maximum peak-to-valley height—the length of the largest individual peak-to-valley height within five adjoining sampling lengths ‘le’.

Surface Parameter Rt

Maximum roughness depth—the distance between the highest and lowest points of the surface profile within the evaluation length Lm.

Surface Parameter Rz

Mean peak-to-valley height—the average of the heights of all individual peak-to-valley instances that lie within five adjoining sampling lengths ‘le’.

Surface Preparation

Prior to spraying, cleaning and roughening the surface to be sprayed, using usually 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 the modification of a surface, including superficial heat treatment, diffusion treatment and conversion coating (consisting of a compound of the surface metal by chemical or electrochemical treatment).


The application of a coating or cladding to a surface to impart a change in its surface behavior.


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 that, 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.

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