Age Hardening
Martensitic stainless steels are hardened by heating
above their critical temperature, holding them at heat
to insure uniform temperature, and cooling them rapidly
by quenching in air or oil.
Alloying Element
The adding of any metallic element in stainless steel
production in order to increase hardness, strength,
or corrosion resistance. Molybdenum, nickel, and chromium
are common alloying elements in stainless steel.
Alloy Surcharge
The producer’s selling price plus a surcharge
added to offset the increasing costs of raw materials
caused by increasing alloy prices.
Annealing (Solution Annealing)
A process of heating cold stainless steel to obtain
maximum softness and ductility by heat treatment which
also produces a homogeneous structure (in austenitic
grades) or a 50/50 mixture of austenite and ferrite
(in duplex grades). It relieves stresses that have built
up during cold working and insures maximum corrosion
resistance. Annealing can produce scale on the surface
that must be removed by pickling.
Austenitic Stainless Steel
Non-magnetic stainless steels that contain nickel and
chromium sufficient to develop and retain the austenitic
phase at room temperature. Austenitic stainless steels
are the most widely used category of stainless steel.
Centerless Grinding
An operation whereby the surface of a bar is ground
without using a lathe.
Chloride Stress Corrosion Cracking
Cracking due to the combination of tensile stress and
corrosion in the presence of water and chlorides.
Chromium (Cr)
An alloying element that is used in stainless steel
to deter corrosion.
Cold Finished Bars
Hot rolled stainless steel bars that are annealed and
cold worked to produce a higher surface quality and
higher strength.
Cold Forming (Cold Working)
Any mechanical operation that creates permanent deformation,
such as bending, rolling, drawing, etc., performed at
room temperature that increases the hardness and strength
of the stainless steel.
Continuous Casting
Processes of pouring stainless steel into a billet,
bloom, or slab directly from the furnace. This process
avoids the need for large, expensive mills and also
saves time because the slabs solidify in minutes rather
than the several hours it takes for an ingot to form.
Corrosion
The attack upon metals by chemical agents converting
them to non-metallic products. Stainless steel has a
passive film created by the presence of chromium (and
often other alloying elements – nickel, molybdenum)
that resists this process.
Corrosion Fatigue
Cracking due to repeating and fluctuating stresses in
a corrosive environment.
Corrosion Resistance
A metal's ability to resist corrosion in a particular
environment.
Crevice Corrosion
Corrosion of stainless steel on the surface that is
fully shielded from air such that the passive film cannot
be created to resist the corrosion.
Cut-to-Length
Cutting flat-rolled stainless steel into desired length
and then normally shipping it flat-stacked.
Duplex
Stainless steel comprised of austenitic and ferritic
stainless steels that contain high amounts of chromium
and nickel. This combination is stronger than both of
the individual stainless steels. Duplex stainless steels
are highly resistant to corrosion and cracking.
Elongation
A measurement of ductility expressed in terms of the
stretch having occurred over a given length on a standard
tensile specimen at time of fracture, usually based
upon an original length of 2 inches.
Erosion-Corrosion
An accelerated loss of material concerning corrosion
and erosion that results from corrosive material interacting
with the material.
Fabricator
An intermediate product producer that purchases materials
and processes them specifically for a particular project.
Fatigue
A condition leading to the eventual fracture of a material
due to constant or repeated stresses that exert less
pressure than the tensile strength of the material.
Ferrite
The body-centered cubic crystalline phase of iron-based
alloys.
Ferritic
Magnetic stainless steels that have a low carbon content
and contain chromium as the main alloying element, usually
between 13% and 17%. It is the second most widely used
stainless steel. Ferritic stainless steels are generally
used in automotive trim and exhaust systems, hot water
tanks, and interior architectural trim.
Ferroalloy
Metal products such as ferrochrome, ferromanganese,
and ferrosilicon that are commonly used as raw materials
to aid various stages in stainless steel making.
Ferrochrome
A common raw material in stainless steel production.
This alloy consists of iron and up to 72% chromium.
Finish
The final condition of the surface after the last phase
of production.
Finishing Facilities
These facilities process semi-finished stainless steel
into ready-made forms that can be used by others. Some
facilities are rolling mills, pickle lines, tandem mills,
annealing facilities, and temper mills.
Flat-Rolled Stainless Steel (Flat
Product)
Category of stainless steel that includes shapes such
as sheet, strip, and plate.
Forming
A process that brings about a change in the shape of
stainless steel by the application of force (i.e. cold
forming, hot forming, wire forming).
Free-Machining
A stainless steel to which a small amount of some relatively
insoluble element (such as sulfur, selenium) is added
to create a minute and widely distributed soft phase
that acts as chip breakers during machining.
Galvanic Corrosion
Accelerated corrosion of a metal because of an electrical
contact with a more noble metal or non-metallic conductor
in a corrosive electrolyte.
Gauge
The thickness of a certain stainless steel.
General Corrosion
General corrosion is the term used to describe the attack
that proceeds in a relatively uniform manner over the
entire surface of a metal. Typically, stainless steels
do not exhibit general corrosion.
Heat Treatment
Altering the properties of stainless steel by subjecting
it to a series of temperature changes. To increase the
hardness, strength, or ductility of stainless steel
so that it is suitable for additional applications.
Hot Forming
Hot forming operations are used widely in the fabrication
of stainless steel to take advantage of their lower
resistance to shape change. High temperature reduces
their yield strengths, and this results in a marked
lowering of the force that is required to bring about
plastic movement or flow from one shape to another (hot
rolling, hot stretching, etc.).
Impact Test
Impact testing is used to measure the toughness of a
material, corresponding to the energy necessary to cause
fracture under shock loading. Low toughness is generally
associated with brittle shear fracture and high toughness
with ductile plastic tearing.
Intergranular Corrosion
Preferential corrosion cracking at or along the grain
boundaries of a metal.
Intergranular Stress Corrosion
Cracking
Stress corrosion cracking in which the cracking occurs
along grain boundaries.
Life Cycle Costing
An accounting method of costing where expenses are allocated
over the life of the product. Life cycle costs are often
lower for stainless steel than for alternatives despite
a higher initial outlay because stainless products generally
last longer and require little maintenance.
Long Products
Category of stainless steel that includes rods, bars,
and structural products that are described as long rather
than flat.
Low-Carbon Stainless Steel
Stainless steel containing less than 0.03% carbon.
Martensite
A hard supersaturated solid solution of iron characterized
by an acicular (needle-like) microstructure.
Martensitic
A small category of magnetic stainless steels typically
containing 12% chromium, a moderate level of carbon,
and a very low level of nickel.
Mechanical Properties (Physical
Properties)
Properties determined by mechanical testing, such as
yield strength, ductility, ultimate tensile strength,
hardness, bendability, impact strength, etc.
Molybdenum (Mo)
An alloying element that enhances corrosion resistance
along with chromium in stainless steels.
Nickel (Ni)
An alloying element used in stainless steels to enhance
ductility and corrosion resistance.
Nickel-Based Superalloys
Alloy metal produced for high-performance, high-temperature
applications such as nickel-iron-chrome alloys and nickel-chrome-iron
alloys.
Passivation
When exposed in air, stainless steels passivate naturally
(due to the presence of chromium), but the time required
can vary. In order to ensure that the passive layer
reforms rapidly after pickling, a passivation treatment
is performed using a solution of nitric acid and water.
Passive
A characteristic condition of stainless steels which
impedes normal corrosion tendencies to the point where
the metal remains virtually unattacked — hence,
passive to its environment.
Pickling
A process that removes surface scale and oxidation products
by immersion in a chemically active solution, such as
sulfuric or hydrochloric acid.
Plate
Stainless steel measuring more than 10 inches wide with
a thickness ranging from 3/16 of an inch and over.
Precipitation Hardening (PH)
A small category of stainless steels resembling martensitic
stainless steels that have great strength and hardness
due to heat treatment.
Service Center
An operation that buys metal, stores it (often processing
it in some way), and then sells it in a slightly different
form than it was purchased from the producing mills.
Shearing
Trimming of the edges of sheet strip to make them parallel.
This is done at either the stainless steel mill or at
the stainless steel processor.
Slab
A very common type of semi-finished stainless steel
which usually measures 6-10 inches thick by 30-85 inches
wide and averages 20 feet long. After casting, slabs
are sent to a strip mill where they are rolled and coiled
into sheet and plate products.
Solution Heat Treatment
Heating a metal to a high temperature and maintaining
it long enough for one or more constituents to enter
the solid solution. The solution is then cooled rapidly
to retain the constituents within.
Specialty Alloys
Metals with distinct chemical and physical properties.
These alloys are produced for very specific applications
and considered to be on the low end of superalloys.
Specialty Steel
Category of steel that includes electric, alloy, stainless,
and tool steels.
Stainless Steel
Group of corrosion-resistant steels containing at least
10.5% chromium which may also contain other alloying
elements. These steels resist corrosion and maintain
their strength at high temperatures.
Strength
The ability of stainless steel to oppose applied forces
when considering resistance to stretching, forming,
compressing, etc.
Stress Corrosion Cracking (SCC)
Slowly developing cracks that form in stainless steel
due to mechanical stress and exposure to a corrosive
environment.
Vacuum Oxygen
Decarburization (VOD)
A refinement of stainless steel that reduces carbon
content. Molten, unrefined stainless steel is heated
and stirred by an electrical current while oxygen enters
from the top. Many undesirable gases escape from the
stainless steel and are evacuated by a vacuum pump.
Alloys and other additives are then mixed in to refine
the molten stainless steel further.
Vanadium (V)
A gray metal that is normally used as an alloying agent
for iron and stainless steel. It is also used as a strengthener
of titanium-based alloys.
Width
The lateral dimensions of rolled stainless steel, as
opposed to the length or the gauge. If width of the
stainless steel strip is not controlled during rolling,
the edges must be trimmed.
