6 Metals and Alloys Flashcards
- How are steels classified?
- What are their subfamilies?
- What are the main strengthening mechanisms?
- Where is steel used?
- steels are classified according to their carbon content and other alloying elements.
- subfamilies: carbon steels and alloy steels
- Main strengthening mechanisms: eutectoid (equilibrium) or martensitic (metastable) transformations
- cars, ships, trains, skysrapers, bridges, etc.
(iron density: 7,87 g/cm3, young’s modulus: ~219 GPa)
- How does the eutectoid transformation look like?
- What does α, δ, γ, CM stand for?
- What is Hypoeutetoid, Eutectoid, and Hypereutetoid?
- What does Pearlite mean?
- See presentation 6 slide 4
- α= ferrite, δ=delta iron, γ=austentite, CM=cementite
- Ferrite+Pearlite= Hypoetuetoid
100% Pearlite= Eutectoid
Cementite+Pearlite=Hypereutetoid - Es ist ein Phasengemisch aus Ferrit und Zementit, das durch gekoppelte Kristallisation in Eisen-Kohlenstoff-Legierungen bei Kohlenstoffgehalten zwischen 0,02 % und 6,67 % auftritt. Der eutektoide Punkt (100%ige Umwandlung zu Perlit) liegt bei 723 °C und 0,83 % C. Bis 2,06 % C liegt der Perlit als separater Gefügebestandteil vor, oberhalb von 2,06 % C ist er Bestandteil des Ledeburits II
What are low carbon steels?
Low carbon steels:
%C below 0,2
Low cost, the highest volume used in the world.
Not heat treated, typical equilibrium microstructure: ferrite and pearlite
Hardening by cold work only
Tough and ductile, easy to machine, weldable
Typical mecanical properties LE ca. 275 MPa, R ca. 415 - 550 MPa, A% ca. 25
What are medium carbon- low alloy steels?
%C 0,25-0,6%
Higher strength, lower ductility and toughness.
Hardened by heat treatment (martensitic transformation -> to be seen 3rd year)
Low contents of Cr, Ni y Mo (-> low alloy) to facilitate heat treatment
What are high carbon steels?
%C 0,6-1,4
High strength and hardness, low ductility.
Wear resistance (cutting and forming materials)
Usually with high alloy content of Cr, V, W y Mo, to form carbides (very hard to increase further wear resistance -> tool steels)
Do you want to see a table of compositions of selected AISI-SAE steels? (Carbon and low-alloy steels)
Yes, you want. So look at the presentation 6 slide 6!
- What is the definition of stainless steel?
2. What are the different categories of stainless steels (ss)?
- stainless steel: a group of ferrous alloys that contain at least 11% Cr, providing extraordinary corrosion resistance.
- Ferretic (magnetic)
Martensitic (hardest, but lowest corrosion resistance, magnetic)
Austenitic (high Ni, high corrosion resistance, most used)
Precipitation-Hardening (PH) (good combination of strength and corrosion resistance)
Duplex (ferrite+austenite microstructure), good combination of props.)
->See pictures on slide 7
Do you want to see typical compositions and properties of stainless steels this time?
Of course you want, you little nerd. So check out presentation 6, slide 8
- What is the definition of cast irons?
- Which reactions can be found in cast irons?
- Which types of cast irons exist?
- What is the iron-carbon phase diagram showing?
- Cast iron: ferrous alloys containing sufficien carbon so that the eutectic reaction occurs during solidification
- Eutectic and Eutectoid
- gray cast iron, white cast iron, malleable cast iron, ductile or nodular, compacted graphite
- It shows the relationship between the stable iron-graphite equilibria (solid lines) and the metastable iron-cementite reactions (dashed lines). slide 9
How does the schematic drawings of the five types of cast iron: (a) gray iron, (b) white iron, (c) malleable iron, (d) ductile iron, and (e) compacted graphite iron look like?
Just kidding. You will find the pictures on slide 10. a graphite flakes b Fe3C and Pearlite c Graphite nodules d Graphite spheroids (nodules) e compacted (vermicular) graphite
What are the main characteristics of gray cast iron?
Main characteristics:
- Brittle
- Fracture gray in appaearance
- Higher UTS in compression
- Low cost
- Vibration damping capacity
- Low wear
- Good castability
You want to see more: photomicrograph of the flake graphite in gray cast iron? click on slide 11
What are the main characteristics of white cast iron?
Main characteristics:
- Low C, low Si, high cooling rate
- Very brittle (cementite)
- Fracture white in appearance
- Very hard
- Difficult to machine
- Very low wear
slide 12 microstructure of white cast iron with eutectic cementite and pearlite
What are the main characteristics of malleable cast iron?
Main characteristics:
- Obtained from white cast iron after prolonged heat treatment
- High ductility
- Strength depending on the matrix microstructure
slide 13 malleable cast iron showing graphite nodules in ferrite matrix
What are the main characteristics of ductile or nodular cast iron?
Main characteristics:
- Mg or Ce added to nucleate graphite spheroids
- Higher strength and ductility than gray iron
- Strength similar to equivalent steels (depending on the matrix)
slide 14: (1) annealed ductile iron with a ferrite matrix, (2) As-cast ductile iron with a matrix of ferrite (white) and pearlite, (3) normalized ductile iron with a pearlite matrix
A table of typical properties of cast irons is fun, right?
You are so stupid, to think that, but here you are: slide 15, presentation 6.
- What are aluminium alloys?
- What are the main characteristics?
- Where do we use this material?
1. Light alloy of extended use Density: 2,70 g/cm3 (1/3 of steel!!!) Young’s modulus: ~70 GPa 2. Main characteristics: - Good corrosion resistance - High electrical and thermal conductivity - Main strengthening mechanisms: cold work &/or precipitation hardening (age hardening-> 3rd year) 3. planes, chair, car, ship, arenas...
- Here we are again, is a table about the effect of strengthening mechanisms in aluminium and aluminium alloys interesting for you?
- Not enough, you also want tho see a table of the designation system for aluminum alloys?
- You want to see more? This time the temper designations for aluminum alloys?
- Next, a table of the properties of typical aluminum alloys?
Vale, I give up. Look on slide 17, presentation 6.
- check out slide 18, if you want to get bored as f***.
- What is wrong with you? slide 19
- no words. slide 20
How do the microstructures of aluminum alloys look like? (casting alloys)
(a) Sand-cast 443 aluminum alloy containing coarse silicon and inclusions.
(b) Permanent-mold 443 alloy containing fine dendrite cells and fine silicon due to faster cooling.
(c) Die-cast 443 alloy with a still finer microstructure ( 350).
slide 21, presentation 6
- What are magnesium alloys?
- What are the main characteristics?
- For what do you use it?
- You want to see an exciting table about the properties of typical magnesium alloys?
- Lightest of structural alloys
Density: 1,80 g/cm3 (2/3 of aluminium!) - Main characteristics:
- Bad corrosion resistance
- Good strength but low elastic modulus (~45 GPa)
- HCP structure: difficult to form
- Main strengthening mechanisms: cold work &/or precipitation hardening (age hardening) - They are used aerospace applications, high-speed machinery, and transportation and materials handling equipment.
- Yes, on slide 23, presentation 6
handlebar, mobilephone, laptop, carseat, rim of wheel
- What are titanium alloys?
- What are the main characteristics?
- What 3 things are titanium alloys used for?
- a nice table about the properties of selected titanium alloys sounds good?
- Best compromise in lightness and strength of all alloys
Density: 4,50 g/cm3
Young`s modulus: ~110 GPa. - Main characteristics:
- Excellent corrosion resistance. Biocompatibility
- Best strength to density ratio of metals.
- Very costly. - Titanium’s excellent corrosion resistance provides applications in chemical processing equipment and marine components,.
- Titanium is an important aerospace material, finding applications as airframe and jet engine components.
- Titanium alloys are considered biocompatible (i.e., they are not rejected by the body) and biomedical implants such as hip prostheses.
- Titanium’s excellent corrosion resistance provides applications in chemical processing equipment and marine components,.
- There is nothing more exciting than on slide 25, presentation 6
Let’s have a closer look on titanium alloys, okay?
- Both the grain boundary precipitate and the Widmanstätten plates are alpha.
- Microstructure of the alpha-beta titanium alloys. The structure contains primary a (large white grains) and a dark β matrix with needles of a formed during aging
- What are copper alloys?
- What are their main characteristics?
- Where do you use it?
- First of metals to be used
Density: 8,96 g/cm3 E ≈ 100 GPa - Main characteristics:
- Good corrosion resistance
- High electrical and thermal conductivity
- Main hardening mechanisms: cold work, solid solution, age hardening (with Be or Cr or Zr). - money, statues, cable
- How do the binary phase diagrams of copper alloys look like?
- You want to see the properies of typical copper alloys obtained by different strengthening mechanisms?
Binary phase diagrams for:
(a) copper-zinc (brasses)
(b) copper-tin (bronzes)
(c) copper-aluminium, (aluminium bronces)
(d) copper-beryllium
answer on slide 28
- slide 29
- What are zinc alloys?
- What are the main characteristics?
- How does the eutectic and hypereutecitc version look like?
- table of zinc wrought (forging) alloys or zinc cast alloys?
1. Low melting point metal with relatively low strength Density: 7,13 g/cm3 2. Main characteristics: - Low corrosion resistance, but is use to give corrosion protection to steels (galvanising) - Forging and cast alloys available. - Easy to cast. - Low cost. 3. slide 31 4. slide 32
- What are nickel and cobalt alloys used for?
- What are superalloys?
- super interesting table about compositions, properties, and applications for selected nickel and cobalt alloys?
- Nickel and cobalt alloys are used for corrosion protection and for high-temperature resistance, taking advantage of their high melting points and high strengths.
Density: ~8,9 g/cm3 - Superalloys - A group of nickel, iron-nickel, and cobalt-based alloys that have exceptional properties:
- Excelent heat resistance.
- Outstanding oxidation (high temperature) resistance.
- Exceptional creep resistance.
-… but very expensive - slide 34
