Metals and Alloys: Steels, Cast Irons, and Nonferrous Alloys

Vocabulary practice flashcards covering alloy classifications, steel designation systems, heat/surface treatments, cast irons, nonferrous alloys, and metal fabrication processes based on lecture material.

Steel vs. Cast Iron Carbon Threshold

The carbon concentration dividing line between steels and cast irons, where alloys containing less than $2.11\,\text{wt\% C}$ are classified as steels and those containing $2 - 4.5\,\text{wt\% C}$ are classified as cast irons.

AISI/SAE Steel Designation System

A four-digit nomenclature system where the first two digits identify the major alloying elements and the last two or three digits specify the carbon content in hundredths of a weight percent ($\text{wt\% C} \times 100$).

Plain Carbon Steel

A carbon steel classified under SAE designation $10XX$ containing manganese up to a maximum of $1.00\%$, without significant intentional alloy additions.

High-Strength Low-Alloy (HSLA) Steel

A low-carbon steel ($< 0.25\,\text{wt\% C}$) containing alloy additions such as chromium ($Cr$), vanadium ($V$), nickel ($Ni$), and molybdenum ($Mo$) to enhance strength while retaining ductility for structural applications like bridges and towers.

Annealing (Steels)

A recrystallization heat treatment performed on steels containing less than $0.25\,\text{wt\% C}$ to eliminate the strain-hardening effects caused by cold working.

Carburizing

A surface-hardening process in which carbon is diffused into the surface layer of a low-carbon steel at temperatures above $A_3$, forming a hard, high-carbon martensitic case upon quenching and tempering.

Nitriding

A surface-treatment process in which nitrogen is diffused into the surface of steel to increase surface hardness and wear resistance.

Carbonitriding

A case-hardening technique where both carbon and nitrogen are diffused simultaneously into the surface of steel by generating gas mixtures containing $CO$ and $NH_3$.

Stainless Steel

A corrosion-resistant high-alloy steel containing a minimum of $11\,\text{wt\% Cr}$, which enables the formation of a protective passive chromium oxide coating.

Ferritic Stainless Steel

A non-heat-treatable, ferromagnetic stainless steel containing up to $30\,\text{wt\% Cr}$ and less than $0.12\,\text{wt\% C}$ that provides good strength and moderate ductility.

Martensitic Stainless Steel

A heat-treatable stainless steel containing less than $17\,\text{wt\% Cr}$ and $0.1 - 1.0\,\text{wt\% C}$ that can achieve high hardness and strength for applications like knives and ball bearings.

Cast Iron

An iron-carbon-silicon ferrous alloy containing $2 - 4.5\,\text{wt\% C}$ and $0.5 - 3\,\text{wt\% Si}$ that undergoes a eutectic reaction during solidification.

White Cast Iron

A hard and brittle cast iron produced by rapid cooling, in which carbon remains bound as cementite ($Fe_3C$) mixed with pearlite.

Ductile Cast Iron

A cast iron formed by adding small amounts of magnesium ($Mg$) or cerium ($Ce$) to melt, causing graphite to solidify as spherical nodules rather than flakes.

Malleable Cast Iron

A cast iron produced by heating white cast iron at approximately $700^\circ\text{C}$ for more than $30\,\text{hours}$, decomposing cementite into irregular graphite rosettes ($G_r$).

Brass

A copper alloy where zinc ($Zn$) acts as a substitutional impurity, providing enhanced corrosion resistance for decorative jewelry, coins, and fittings.

Bronze

A copper alloy in which tin ($Sn$), aluminum ($Al$), silicon ($Si$), or nickel ($Ni$) serve as substitutional impurities, commonly used in bushings and landing gear.

Refractory Metals

A category of metals characterized by extremely high melting temperatures, consisting of niobium ($Nb$), molybdenum ($Mo$), tantalum ($Ta$), and tungsten ($W$).

Noble Metals

A group of precious metals including silver ($Ag$), gold ($Au$), and platinum ($Pt$) that show high resistance to oxidation and corrosion.

Forging

A mechanical deformation process where a metal workpiece is shaped by compressive forces applied through hammering or stamping, often at high temperatures.

Extrusion

A metal-forming operation in which a billet is forced through a shaped die orifice by a ram to form continuous shapes with uniform cross-sections like rods or tubes.

Drawing (Metal Fabrication)

A forming process in which a rod, wire, or tube is pulled through a tapered die using tensile forces to reduce its cross-sectional area.

Sand Casting

A casting method where molten metal is poured into a mold cavity created by packing sand around a pattern, widely used for large parts like automobile engine blocks.

Investment Casting

A casting technique involving a wax pattern surrounded by a plaster or ceramic slurry, where the wax is melted out to leave a hollow cavity into which molten metal is cast.

Die Casting

A high-volume manufacturing process in which molten metal with a low melting temperature is forced under pressure into a permanent, reusable steel die cavity.

Continuous Casting

A processing method where molten metal is continuously solidified while passing through a water-cooled mold to create long, semi-finished shapes such as slabs and billets.

Powder Metallurgy (Sintering)

A processing route for metals with low ductility where fine metal powders are compacted under pressure and heated below their melting point to achieve densification via diffusion.

Additive Manufacturing

A manufacturing methodology, commonly known as 3D-printing, that builds solid three-dimensional objects layer by layer according to a digital CAD model.

Fused Deposition Modeling (FDM)

An additive manufacturing technique that extrudes heated thermoplastic polymer filaments through a nozzle layer by layer to construct 3D objects.

Selective Laser Sintering (SLS)

A powder bed fusion 3D-printing process that utilizes a high-power laser to selectively fuse powdered plastics, metals, or ceramics into solid objects.

Blast Furnace Refinement

The chemical process of refining iron ore ($Fe_2O_3$) into molten iron using coke (coal), limestone, and air heat generation ($C + O_2 \rightarrow CO_2$), reduction ($3CO + Fe_2O_3 \rightarrow 2Fe + 3CO_2$), and flux purification ($CaO + SiO_2 + Al_2O_3 \rightarrow \text{slag}$).

Iron-Iron Carbide Phase Diagram

The phase diagram showing phase equilibria for iron-carbon mixtures up to $6.7\,\text{wt\% C}$, highlighting key invariant reactions such as the eutectoid at $0.76\,\text{wt\% C}$ ($727^\circ\text{C}$) and eutectic at $4.30\,\text{wt\% C}$ ($1148^\circ\text{C}$).