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Questions and Answers
What is the main constituent of ferrous alloys?
What is the main constituent of ferrous alloys?
Which type of steel can be heat treated to improve mechanical properties?
Which type of steel can be heat treated to improve mechanical properties?
What is a key feature of stainless steels?
What is a key feature of stainless steels?
What is the primary microconstituent in martensitic stainless steels?
What is the primary microconstituent in martensitic stainless steels?
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What is a common application for high carbon steels?
What is a common application for high carbon steels?
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How does the carbon content in cast iron typically compare to that in steel?
How does the carbon content in cast iron typically compare to that in steel?
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What is a characteristic of low carbon steels?
What is a characteristic of low carbon steels?
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Which factor contributes to the brittleness of some cast irons?
Which factor contributes to the brittleness of some cast irons?
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What allows gray iron to provide good damping of vibrational energy?
What allows gray iron to provide good damping of vibrational energy?
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What characterizes the microstructure of ductile (nodular) iron?
What characterizes the microstructure of ductile (nodular) iron?
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What property makes white iron unsuitable for most applications?
What property makes white iron unsuitable for most applications?
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What is a primary application of malleable iron?
What is a primary application of malleable iron?
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How does compacted graphite iron differ in graphite formation compared to gray iron?
How does compacted graphite iron differ in graphite formation compared to gray iron?
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What is a common characteristic of copper alloys?
What is a common characteristic of copper alloys?
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Which alloying element is predominantly found in brasses?
Which alloying element is predominantly found in brasses?
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What limits the use of aluminum despite its desirable properties?
What limits the use of aluminum despite its desirable properties?
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What unique property does titanium possess that differentiates it from many other metals?
What unique property does titanium possess that differentiates it from many other metals?
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What are refractory metals primarily known for?
What are refractory metals primarily known for?
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Which application is most suitable for superalloys?
Which application is most suitable for superalloys?
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What is a disadvantage of magnesium alloys?
What is a disadvantage of magnesium alloys?
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Which noble metal is commonly used in laboratory equipment?
Which noble metal is commonly used in laboratory equipment?
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What is the effect of adding magnesium and cerium to molten iron?
What is the effect of adding magnesium and cerium to molten iron?
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Study Notes
Ferrous Alloys
- Iron is the primary constituent of ferrous alloys
- Ferrous alloys are abundant due to the availability of iron-containing compounds in the earth’s crust
- Ferrous alloys are economical to extract, refine, alloy, and fabricate
- Ferrous alloys are versatile materials
- Ferrous alloys have limitations, including high density, low electrical conductivity, and susceptibility to corrosion
Steel
- Steels are iron-carbon alloys with other alloying elements and less than 1.0 wt% carbon
- Low carbon steels:
- Contain less than 0.25 wt% carbon
- Not responsive to heat treatments to form martensite
- Strengthened by cold work
- Microstructure is ferrite and pearlite
- Relatively soft, weak, and ductile
- Used in automobile body components, structural shapes, and sheets
- High-strength low-alloy steels:
- More resistant to corrosion than plain carbon steels
- Have higher tensile strengths than plain carbon steels
- Ductile and formable
- Alloying elements include Cu, V, Ni, and Mo up to 10 wt%
- Medium carbon steels:
- Contain 0.25 to 0.60 wt% carbon
- Can be heat treated to improve mechanical properties
- Used in railway tracks, gears, crankshafts, and machine parts
- High carbon steels:
- Contain 0.60 to 1.4 wt% carbon
- Hardest, strongest, and least ductile of the carbon steels
- Typically hardened and tempered for wear resistance and sharp cutting edge
- Used in knives, razors, hacksaw blades, springs, and wire
- Stainless steels:
- Highly corrosion resistant, especially in ambient atmosphere
- Contain at least 11 wt% Cr, with additions of Ni and Mo
- Martensite is the primary microconstituent in martensitic stainless steels
- Alpha ferrite (BCC) is the primary constituent in ferritic stainless steels
- Ferritic and austenitic stainless steels can be hardened by cold work
- Austenitic stainless steels are the most corrosion resistant due to high Cr and Ni
- Applications include high-temperature environments, gas turbines, steam boilers, furnaces, aircraft, missiles, and nuclear-power-gathering units
Cast Irons
- Cast irons have a carbon content above 2.14 wt%, typically between 3.0 and 4.5 wt%
- Cast irons have a lower melting temperature than steels, allowing them to be easily melted and cast
- Cast irons can be brittle, making casting the most convenient fabrication method
- Cementite can dissociate into BCC iron and graphite
- Graphite formation is promoted by the presence of more than 1 wt% Si and slower cooling rates
- The microstructure and mechanical behavior of cast irons depend on composition and heat treatment
- Gray iron:
- Contains 2.5 to 4.0 wt% C and 1.0 to 3.0 wt% Si
- Contains graphite flakes in an alpha-ferrite or pearlite matrix
- Weak and brittle in tension due to stress concentration at graphite flakes
- Strong and ductile under compression
- Effective in damping vibrational energy
- Resistant to wear
- High fluidity in the molten state allows for intricate castings
- The least expensive metallic material
- Ductile (nodular) iron:
- Contains Mg and Ce added before casting
- Graphite forms as nodules or sphere-like particles in a pearlite or ferrite matrix
- Stronger and more ductile than gray cast iron
- Used in valves, pump bodies, crankshafts, and gears
- White iron:
- Contains more than 1 wt% Si and cooled rapidly
- Carbon exists as cementite
- Fracture surfaces have a white appearance
- Thick sections have a surface layer of white iron with an interior region of gray iron
- Extremely hard and brittle due to cementite content making it difficult to machine
- Used for applications requiring a hard wear-resistant surface without high utility
- Malleable iron:
- White iron heated between 800 and 900°C for long durations, causing cementite to decompose into graphite clusters in a pearlite or ferrite matrix
- Has a microstructure similar to nodular iron, leading to high strength and ductility
- Used for rods, transmission gears, flanges, pipe fittings, and heavy-duty valve parts
- Compacted graphite iron:
- Contains 3.1 to 4.0 wt% C and 1.7 to 3.0 % Si
- Graphite exists in worm-like shapes and some nodules
- Has a pearlite or ferrite matrix
- High strength and ductility
- Pearlitic matrices have higher strength and lower ductility
- Higher thermal conductivity and better resistance to thermal shock
- Used in diesel engine blocks, exhaust manifolds, gearbox housings, brake discs, and flywheels
Nonferrous Alloys
- Classified based on the base metal or specific characteristics
- Cast alloys are too brittle to be shaped by significant deformation
- Wrought alloys can be mechanically deformed
- Copper:
- Unalloyed copper is too soft and ductile to machine properly but has unlimited cold workability
- Highly resistant to corrosion
- Copper alloys cannot be hardened or strengthened by heat treatments
- Mechanical properties can be improved by cold working and solid solution alloying
- Brasses are copper alloys with zinc as the primary alloying element
- Bronzes are copper alloys with various alloying elements, such as Sn, Al, Si, and Ni
- Aluminum:
- Aluminum and its alloys have relatively low density, high electrical and thermal conductivities, corrosion resistance, and high ductility
- Aluminum’s FCC structure permits it to retain ductility at low temperatures
- Low melting point is a significant limitation
- Strength can be improved by cold working and alloying, but this reduces corrosion resistance
- Principle alloying elements include Cu, Mg, Mn, and Zn
- Magnesium:
- Lowest density of structural metals, making it ideal for applications requiring light weight
- Relatively soft and has an HCP structure
- Difficult to deform at room temperature, fabrication is commonly done by casting or hot working
- Mg and its alloys are chemically unstable and susceptible to corrosion in marine environments
- Both cast and wrought forms exist, some are heat treatable
- Have replaced engineering plastics due to higher stiffness, recyclability, and lower cost
- Used in handheld devices, computer and communications equipment, and luggage
- Titanium:
- Relatively low density, high melting point, extremely strong, highly ductile, and easily formed
- Alpha phase (HCP) is used for high-temperature applications, not heat-treatable
- Beta phase (BCC) is highly forgeable and has high fracture toughness
- V, Nb, and Mo reduce the temperature for the transformation between alpha and beta phases
- Highly chemically reactive at elevated temperatures
- Used in airplane structures, space vehicles, and surgical implants
- Refractory metals:
- Have extremely high melting temperatures
- Ni, Mo, W, and Ta are examples
- Extremely strong interatomic bonding contributes to high melting points, strengths, and hardness
- Mo alloys are used for extrusion dies and space vehicle structures
- W alloys are used for light filaments, X-ray tubes, and welding electrodes
- Ta is immune to chemical attack in any environment below 150°C
- Superalloys:
- Used in severe oxidizing environments and high temperatures
- Primarily Fe-Ni, Ni, and Co alloyed with refractory metals
- Applications include turbines, nuclear reactors, and petrochemical equipment
- Noble metals:
- Expensive and characteristically soft, ductile, and oxidation-resistant
- Examples include Ag, Au, Pt, Pd, Ru, Rh, Ir, and Os
- Au and Ag can be strengthened by alloying with Cu
- Pt is used for laboratory equipment and thermocouples
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Description
This quiz covers the essential characteristics of ferrous alloys and various types of steel, including their composition, production, and applications. Explore the advantages and limitations of these materials, especially in comparison to alternative options in metallurgy.
