characteristics of metallic materials

CHARACTERISTICS OF METALLIC MATERIALSChapter 9

6 top employment sectors per NAICS• Primary metals• Fabricated metal products• Machinery• Computers and electronics• Transportation equipment and manufacturing• Electrical equipment, appliances, and component

manufacturing

Structure of Metallic Materials• Metals can survive drastic changes in the environment

they used in• Extreme heat, can remain strong and rigid enough to support

heavy loads• Frigid environments, can remain flexible and still be easily formed• Few materials can retain their essential properties when subjected

to the same range of hot and cold

Pure metals• Found in nature• Few are used in their natural form

• Too hard, or too soft• Too expensive

Alloys• Blend of metals and other elements• More complex structure than pure metals

• New elements are discovered when new synthetic products are caused by artificial nuclear reactions

• All man-made elements are radioactive• Short “half-life”

Half-life – the gradual exponential decay where the element exhibits only half of it’s initial values

Major Metals

• Aluminum• Copper• Iron• Lead• Tin• Magnesium• Nickel• Titanium• Zinc

Major Alloys

• Steel• Brass• Bronze

• Brass• Copper and zinc

• Steel• Iron, carbon, magnesium, vanadium, nickel and chromium

• Carbon is not a metal

Why is Alloying Important?• Best attributes of the base metal enhanced by addition of

another element• Brass is stronger than copper and zinc by themselves

• Alloys can be created to withstand exposure to just about any environment• 25,000 types of steel• 200 types of copper alloys

Physical Properties4 basic physical properties:• Weight• Color• Conductivity• Reaction when exposed to heat

• Some metals can be identified by these properties• Lead is dense and heavy• Platinum, gold and silver can be recognized by color

• Physical properties often more important than mechanical properties (next)

Specific Heat• The amount of energy necessary to raise one gram of

material 1°C

Thermal Conductivity• Ability of a substance to conduct heat

• Measured by the rate heat flows through a substance• Good thermal conductivity means good electrical conductivity

Thermal Expansion• Change in volume of a product at different temperatures

• Most molten metals shrink during solidification and cooling• Shrinkage, how much a material shrinks• Must take into account when designing tools

Superconductors• Material able to conduct electricity with no resistance to

the flow of current• Happens at absolute zero (0 Kelvin, -273.15°C)• Increase in heat increases electrical resistance

Mechanical Properties• How parts or products will withstand continued use of

abuse in the user’s work environment• Measured using standardized testing procedures

Tensile Strength• Ability of material to resist being pulled apart

Hardness• Resistance to penetration

Fatigue• Breaking of a metal after stress is continually removed

and reapplied• Fold a thin sheet of metal then straighten repeatedly until it cracks

Creep• Elongation that occurs when exposed to elevated temps

while under stress• Will eventually separate or rupture (creep failure)

Plasticity• The ability to change shape or size as a result of force

being applied• Helpful in shaping materials

Ductility• Ability to be formed plastically, without breaking.

• If material is not ductile, it’s difficult to form

Classifications of Metals (4 types)1. Ferrous Metals• Contain Iron

• Most commonly used metals

• Types of iron:• Wrought iron

• Tough and ductile• Contains very little carbon• Easy to bend (even without heating)• Ornamental iron-work

• Cast Iron• High carbon content• Pouring molten iron into molds• Hard• Brittle• High compression strength

• Good corrosion resistance• Make engine blocks, machine parts, gear cases

• Gray Iron• Easy to cast• Less expensive than other cast irons• Made from pig iron (refined wrought iron) and scrap iron or steel

• White Cast Iron• Very hard• Parts that must combat fatigue and extreme wear and abrasion

• Malleable Iron• Made by heating white cast iron to a specific temperature then

cooling it slowly (called annealing)

• Ductile Cast Iron• One of the newest forms of cast iron• Replaced a lot of use of white iron• Heat-treatable• Crankshafts, connecting rods, camshafts

• Steel• Iron and carbon• Other additives used to make harder and tougher steel

Carbon Steels• Low-carbon steel of mild steel

• .05%-.30% carbon• Very soft• Easily formed and machined• Doesn’t heat treat well

• Medium-carbon steel• .30%-.60% carbon• More difficult to bend and shape• Can be heat treated (can make it brittle)

• High-carbon steel (tool steel)• .60%-1.50% carbon• Difficult to bend• Very hard• Can be heat treated• Used to make tools, dies, molds, screwdrivers, milling cutters

2. Nonferrous Metals• Metals with no iron content• Resistant to corrosion

• Aluminum• Copper• Lead• Magnesium• Nickel• Zinc

• Fig 9-4 (pg 137)

3. High-Temperature Superalloys• Ability to survive, without degradation in temperatures as

great as 2200°F (1200°C) for reasonable periods in nonloadbearing structures

• 1800°F (1000°C) under loads• Developed after WWII• Used in space-related industries

• Classified according to the base metal• Usually Iron, nickel, or cobalt• Sometimes chromium, titanium, aluminum or tungsten

4. Refractory Metals• High temperature metals• Withstand heat and maintain strength at temps ranging

from 4474°F (2468°C) for niobium, to 6170°F (3410°C) for tungsten• Tungsten highest known melting point• Used to make light filaments, welding rods, rocket engines

Nature of Industrial Stock• Steelmaking industry forms molten steel into many

shapes• Ingots for creating:

• Bars• Plates• Hot-rolled strip• Round or hex rod• Tubing• Wire• Angle stock

• Billets• Feedstock for long products with small cross sections

• Bar stock, angles, I-beams, plates• Hot-rolled steel - squeezed between rollers while hot (bluish surface

coating)• Cold-rolled steel – rolled while cold (shiner surface)

• Powder• Used for:

• Casting• Metal Injection Molding• 3D printing

• Sheet form• Sold by gage number, smaller the number the thicker the stock• Not all sheet types have the same numbering system

Determining the Type of Steel• Usually impossible to look at stock and determine which

type of steel it is• 3 basic techniques:

1. American Iron and Steel Institute (AISI) and Society of Automotive Engineers (SAE) developed a simple labeling system

• Tags or engraved on stock

Designation Properties

P Mild and low carbon steels

F Carbon/Tungsten and special purposes steels

L Low alloy/special purpose

M Molybdenum alloy and high speed steel

T Tungsten alloy and high speed steel

H Hot working, chromium, tungsten, and/or molybdenum

D Die steel, air-hardened, and high chromium steel

A Air-hardened steel

O Oil-hardened steel

S Shock-resistant steel

W Water-hardened steel

Unified Numbering System (UNS)• More accurate• Also developed by AISI and SAE• 4 or 5 digits• Classifies steel according to their primary alloying element

• First number stands for the type of metal• Second number indicates the percentage of alloy• Last 2 digits tell how much carbon in 100ths of a percent

1020 Steel• 1 – type = carbon steel• 0 – percentage of alloy = 0% alloy• 20 – carbon content = .20% carbon

UNS Number Type of Steel

1 Plain carbon steel (no alloy)

2 Nickel steel

3 Chromium and nickel steel

4 Molybdenum steel

5 Chromium steel

6 Chromium and vanadium steel

7 Tungsten steel

8 Nickel, chromium, and molybdenum steel

9 Silicon and manganese steel

3. Color code system• End of stock is painted• Alloy steel is normally painted with 2 colors

• 1020 steel is painted brown

When no information is available• Sometimes identification tags or markings can be lost• Then has to be identified by it’s properties

• Pattern and color of sparks when ground• Takes training and experience