METALS

Ferrous Alloys

Ferrous Alloys

Alloys where iron is the primary constituent, widely used in engineering construction due to their abundance, economical production, and versatility in mechanical and physical properties.

Steels

Iron-carbon alloys with various alloying elements, classified into low-, medium-, and high-carbon types based on carbon concentration and heat treatments.

Low-Carbon Steels

Steels with less than 0.25 wt% carbon, offering softness, outstanding ductility, and machinability, commonly used in automobile components and structural applications.

High-Strength, Low-Alloy (HSLA) Steels

Low-carbon alloys with added elements like copper and vanadium, providing higher strengths than plain low-carbon steels and can be strengthened by heat treatment.

Medium-Carbon Steels

Steels with carbon concentrations between 0.25 and 0.60 wt%, often heat-treated to improve mechanical properties, used in applications requiring strength, wear resistance, and toughness.

High-Carbon Steels

Steels with carbon contents between 0.60 and 1.4 wt%, known for hardness and wear resistance, used in hardened and tempered conditions for sharp cutting edges.

Stainless Steels

Highly corrosion-resistant steels with chromium as the predominant alloying element, classified into martensitic, ferritic, and austenitic types based on microstructure.

Martensitic Stainless Steels

Stainless steels capable of being heat-treated to form martensite as the primary microconstituent, offering high wear resistance.

Cast Irons

Ferrous alloys with carbon content above 2.14 wt%, commonly containing 3.0-4.5 wt% C, and various alloying elements, including gray, nodular, white, malleable, and compacted graphite types.

Gray iron

The carbon and silicon contents of gray cast irons vary between 2.5 and 4.0 wt% and 1.0

and 3.0 wt%, respectively.

Mechanically, gray iron is comparatively weak and brittle in tension as a consequence of

its microstructure; the tips of the graphite flakes are sharp and pointed and may serve as

points of stress concentration when an external tensile stress is applied.

Ductile (or Nodular) Iron

Adding a small amount of magnesium and/or cerium to the gray iron before casting

produces a distinctly different microstructure and set of mechanical properties. Graphite

still forms, but as nodules or spherelike particles instead of flakes. The resulting alloy is

called ductile or nodular iron.

White Iron and Malleable Iron

For low-silicon cast irons (containing less than 1.0 wt% Si) and rapid cooling rates,

most of the carbon exists as cementite instead of graphite, A fracture surface of this alloy

has a white appearance, and thus it is termed white cast iron.

Forging

is mechanically working or deforming a single piece of a usually hot metal; this

may be accomplished by the application of successive blows or by continuous squeezing.

Rolling

the most widely used deformation process, consists of passing a piece of metal

between two rolls; a reduction in thickness results from compressive stresses exerted by

the rolls. Cold rolling may be used in the production of sheet, strip, and foil with a high-

quality surface finish. Circular shapes, as well as I-beams and railroad rails, are fabricated

using grooved rolls.

Extrusion

a bar of metal is forced through a die orifice by a compressive force that is

applied to a ram; the extruded piece that emerges has the desired shape and a reduced

complicated cross-sectional geometry; seamless tubing may also be extruded.

Drawing

is the pulling of a metal piece through a die having a tapered bore by means of a

tensile force that is applied on the exit side. A reduction in cross section results, with a

corresponding increase in length. The total drawing operation may consist of a number of

dies in a series sequence. Rod, wire, and c products are commonly fabricated in this

way.

Casting

is a fabrication process in which a completely molten metal is poured into a mold

cavity having the desired shape; upon solidification, the metal assumes the shape of the

mold but experiences some shrinkage.

Sand Casting

probably the most common method, ordinary sand is used as the mold

material. A two-piece mold is formed by packing sand around a pattern that has the shape

of the intended casting. A gating system is usually incorporated into the mold to expedite

the flow of molten metal into the cavity and to minimize internal casting defects. Sand-cast

parts include automotive cylinder blocks, fire hydrants, and large pipe fittings.

Die Casting

the liquid metal is forced into a mold under pressure and at a relatively high

velocity and allowed to solidify with the pressure maintained. A two-piece permanent steel

mold or die is employed; when clamped together, the two pieces form the desired shape.

When the metal has solidified completely, the die pieces are opened and the cast piece is

ejected.

Investment Casting

(sometimes called lost-wax) casting, the pattern is made from a wax or

plastic that has a low melting temperature

Lost foam casting

or expendable pattern) casting. Here, the

expendable pattern is a foam that can be formed by compressing polystyrene beads into the

desired shape and then bonding them together by heating.

Continous

These casting and rolling steps may be combined by a continuous casting (sometimes

termed strand casting) process. Using this technique, the refined and molten metal is cast

directly into a continuous strand that may have either arectangular or circular cross section;

solidification occurs in a water-cooled die having the desired cross-sectional geometry.