Characteristics of Metallic Materials

1. Characteristics of Metallic Materials Chapter 9

2. 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

3. 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

4. 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

5. 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

6. Major Metals Major Alloys Steel Brass Bronze • Aluminum • Copper • Iron • Lead • Tin • Magnesium • Nickel • Titanium • Zinc

7. Brass • Copper and zinc • Steel • Iron, carbon, magnesium, vanadium, nickel and chromium • Carbon is not a metal

8. 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

9. Physical Properties 4 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

10. 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

11. 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

12. 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

13. 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)

14. 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

15. 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

16. 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)

17. 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

18. 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)

19. 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

20. 2. Nonferrous Metals • Metals with no iron content • Resistant to corrosion • Aluminum • Copper • Lead • Magnesium • Nickel • Zinc • Fig 9-4 (pg 137)

21. 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

22. 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

23. 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

24. 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)

25. 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

27. Determining the Type of Steel • Usually impossible to look at stock and determine which type of steel it is • 3 basic techniques: • American Iron and Steel Institute (AISI)and Society of Automotive Engineers (SAE) developed a simple labeling system • Tags or engraved on stock

29. 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

30. 1020 Steel • 1 – type = carbon steel • 0 – percentage of alloy = 0% alloy • 20 – carbon content = .20% carbon

31. 3. Color code system • End of stock is painted • Alloy steel is normally painted with 2 colors • 1020 steel is painted brown

32. 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