Characteristics of Metals

AG 221 – Metals and Welding

Metallurgy

Process - The art and science of extracting metals from their ores, refining them, and processing them for use (including compounding alloys)

Physical – behavior of the structure and composition of the metal (shaping, fabricating, heat treating, welding)

Mechanical Properties

Terms Relative to Tensile Strength(Resistance to the act of pulling apart.)

Stress - The load pressure (measured in 1000psi) of a metal before it stretches.

Strain - Elongation that occurs during the pulling action.

Yield Point - Amount of force required to stretch the metal until it is permanently deformed.

Terms Related to Tensile Strength (continued)

Elastic Range of Limit - The maximum stress the metal will support without permanent deformation.

Ultimate Strength - The maximum load the metal will support in tension.

Modulus of Elasticity - The ratio of stress to strain used to compare elasticity of metals.

Other Mechanical Properties

Ductility - The property of a metal to be formed into shapes without breaking (drawn into wire).

Compression strength - The ability of a metal to withstand a compression force before deforming.

Torsion - The ability of metal to withstand a turning or twisting motion.

Shear strength - The ability of metal to withstand shearing pressure.

Physical Properties

Hardness - The characteristic of metal which resists scratching, abrasion or indentation.

Toughness - The ability of a metal to absorb repeated abuse before failing.

Brittleness - The ability of the material to absorb shock or impact.

Physical Properties (continued)

Corrosion Resistance - The ability of a metal to resist chemical action.

Electrical Resistance - The ability of metal to resist carrying an electric current (opposite of conductivity).

Fusability - Measure of ease of melting. Thermal Expansion - Increase in size of metal from

changes in temperature. Cost – not a physical property, but must be considered

Ferrous Metals

Made up of Iron and Carbon Classification is based upon amount of

carbon and the finish process Steel – less than 1.7% Carbon Cast Iron – more than 1.7% Carbon

See Chart on Page 41

Ferrous Metals

Wrought iron - Very ductile, easily worked cold, high corrosion resistance. Rivets, ornamental work

Low carbon steels - tough, ductile,easily formed, machined and welded. Bolts, nails, sheet metal

Ferrous metals cont.

Medium carbon steels - strong and hard, but not as easily forged or welded as low carbon. Ag. machinery, bars, plates

High carbon steels - Respond well to heat treating to obtain any degree of hardness, temper or strength; special welding rods are required. Screw drivers, pliers, drive shafts

Ferrous metals (continued)

Very high carbon - mechanical characteristics are similar to high carbon. Chisels, punches, dies, taps, files, metal

cutting saws.

High speed steel (Alloy Steel) - contains carbon with cobalt, molybdenum and tungsten. Withstands heat from high speed operations. Drills, milling cutters, taps, dies

Gray cast iron - containing free carbon and silicon; brittle, resists rust. Slow cooling – graphite flakes. Ag. machinery, engine blocks

White cast iron - carbon does not separate, very hard, white or silvery when broken, high wear resistance. Quick cooled. Disc bearings

Ferrous metals (continued)

Last of the Ferrous Metals

Malleable cast iron - white cast annealed to produce a steel skin;bends without breaking. High strength Ag. machinery parts, some

tools.

Ductile cast (Nodular) - addition of magnesium increases ductility, high strength. Replaces gray and malleable cast.

Non-Ferrous Metals

Brass - alloy of copper and zinc, harder than copper. Hinges, screws, other hardware

Bronze - alloy of copper and tin, tough, wear resistant, highly corrosion resistant. Machinery parts, bearings

Non-Ferrous cont.

Aluminum - light weight, good strength, high electrical conductivity, excellent heat transfer, corrosion resistant. Trailers, airplanes, food handling equipment

Magnesium - lightest weight, has low strength in pure form, produces magnesium oxides when burned. Wheels, lawn mower frames

Non-Ferrous cont.

Zinc - used for galvanizing, very corrosion resistant.

Nickel - increases hardness and improves resistance to corrosion in steel.

Lead - heavy and soft, considered a health hazard Soldering

Non-Ferrous cont.

Tin - very high corrosion resistant. Solder, brass, bronze and pewter

Copper - excellent conductor of electricity and heat, very workable (ductile). Wire, water pipes, radiators

Tungsten - high melting point, tungsten carbide is very hard. Cutting and piercing tools

Last of the Non-Ferrous

Silver - very soft, excellent conductor of electricity; sterling silver is 92.5% silver and 7.5% copper. Metal alloys

Gold - 24 karats is pure gold. Plating and jewelry

Pg. 41 & 42 characteristics and uses

Affects of Elements on Steel

Element Affect

Chromium Hardness and resistance to wear

Manganese Toughness and ductility

Molybdenum Strength and toughness

Nickel Strength, corrosion and shock resistance

Tungsten Tough, hard, resistant to wear

Cobalt Remain hard at red hot

Vanadium Strength and toughness

Reading Assignment

Metals (Unit III) Iron & Steel and Their Alloys – pages 43-49 Metal Identification – pages 65-71 Drill Bits – pages 76-78 Lab Exercise 6 – page 105 Lab Exercise 7 – page 106