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INME4007-14.ppt

Sep 10, 2015

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INME4007-14.ppt

  • Metals and AlloysProperties and Applications

  • Ferrous alloysPlain carbon steelsAlloy steelsStainless steelsCast irons

  • Low-carbon steelsContain less than 0.25%CNot very responsive to heat treatmentssoft, weak, tough and ductileMachinable, weldable, not expensiveYS~275 MPa, TS~415-550MPa, 25% el.

  • High strength low alloy steels(HSLA steels)Contain alloying elements such as Cu, V, Ni, Mo in combined concentrations of >10 wt%Stronger than plain low-C steelsDuctile, formable and machinable

  • Medium-carbon steelsContain 0.25-0.60 wt.% carbonCan be heat-treated but only in thin sectionsStronger than low-C steels but less ductile and less toughGood wear resistanceRailway wheels & tracks, gears

  • High carbon steels0.60 -1.4 wt.% CHardest, strongest, least ductile of all steelsAlmost always used in tempered conditionEspecially wear resistantForm hard and wear resistant carbides with alloying elementsUsed in cutting tools, dies, knives, razors, springs and high strength wires

  • Stainless steelsHighly resistant to corrosion in many environmentsPredominant alloying element is at least 11% ChromiumCorrosion resistance may be enhanced by Ni and Mo additions4 classes: ferritic, austenitic, martensitic and precipitation-hardeningUsed at high temperatures (upto ~ 1000 C) and severe environmentsGas turbines, steam boilers, aircraft, missiles

  • Cast ironsTheoretically contains > 2.14 wt.% carbonUsually contains between 3.0-4.5 wt.% C, hence very brittleAlso 1-3 wt.% siliconSince they become liquid easily between 1150 C and 1300 C, they can be easily castInexpensiveMachinable, wear resistant4 types: gray cast iron, nodular cast iron, white cast iron, malleable cast iron

  • Nonferrous alloysAluminum alloysCopper alloysMagesnium alloysNickel alloysTitanium alloysRefractory metalsSuperalloys

  • Aluminum alloysLow density - 2.7 gm/ccHigh electrical and thermal conductivitiesHigh ductilityLow melting point and strengthsCast or wroughtTemper designation

  • Age hardening

  • Copper alloysSoft, ductile, difficult to machineHighly resistant to corrosionExcellent electrical & thermal conductivityCan be alloyed to improve hardnessCold worked to get the maximum hardnessCu-Zn = brass; Cu-X = bronzes

  • Magnesium alloysLowest density of all structural metals= 1.7 gm/ccRelatively soft and low elastic modulus (45 GPa)Have to be heated to be deformation processedBurns easily in the molten and powder statesSusceptible to corrosion in marine environmentsCompeting with plastics

  • Nickel alloysQuite ductile and formableHighly corrosion resistant, especially at high temperatureEssential part of austenitic stainless steelsUsed in pumps, valves in seawater and petroleum environments

  • Titanium alloysLow density, high melting pointHigh specific strength and elastic modulus superior corrosion resistance in many environmentsAbsorb interstitials at high temperaturesHighly reactive with other materials and hence non-conventional processing techniques have been developedHighly used in aerospace applications

  • Refractory metalsThese are extremely high melting metalsNb, Ta, Mo, WVery high strengths and hardnessVery high elastic modulusW alloys used in x-ray tubes, filamentsTa & Mo used with stainless steels for corrosion resistanceTa is virtually immune to all environments below 150 C