Current Iron/Steel making
What are the furnaces used in Steel making? (Full names only)
Basic Oxygen Furnace
Electric Arc furnace
Why are S and O bad in plain carbon steels?
Diffuse too and collect at grain boundaries, weakening them and making the mat more brittle.
What are the four types of stainless steel?
Austenitic, Ferritic, Martensitic, and Precipitation hardened.
What is the secret 6th reason for alloying metal?
Solid solution strengthening the metal
What elements are added to the blast furnace to reduce hematite (Fe2O3) to Fe during the iron smelting process?
C (coke and carbon monoxide), and Calcium (Limestone)
What is pig iron?
Iron fresh out of the blast furnace, ab 4 wt% C
What are the five reasons for alloying metal?
1. React with impurities
2. Lower surface energy of the liquid.
3. To form strong precipitates
4. to improve corrosion resistance
5. Slow the speed of phase transitions
What is white iron?
Iron with 2.5-4.5% C & 2% Si
What are the best aluminum alloys to be heat treated? What's their designation?
- Mg + Si (6)
- Mg + Zn (7)
- Lithium, Tin, Zirconium, Iron (8)
Why is oxygen added to molten iron during steel making in a BOF?
Oxygen reacts with carbon to make CO2 and reduce carbon content.
Describe the process of ingot and continuous casting
Ingot - Molten iron is poured into a mold
Continuous - Molten iron is directed into a water cooled mold and rolled through several rolls until solidified.
What is the direct reduction process (DIR), why do people want to switch to it, and why is there resistance to switching to it?
Reduction process that uses pure H or H heavy gasses (ex: CH4)
It's a carbon free production, therefore emitting less greenhouse gasses.
Its slow, produces little, and is very expensive
What effect do graphite flakes have on cast iron
softens metal, damps vibrations, improves thermal conductivity, reduces shrinkage
List and describe the three primary reasons for adding Si to steel.
1. to react with and dissolve oxygen to form solid SiO2 particles
2. To lower surface tension of molten steel.
3. To prevent the formation of Fe3C and promote the formation of graphite flakes.
What phases are found in bainite?
From what solid phase of steel does bainite from?
Ferrite and Fe3C
Austenite
What are the three additives to iron making and what is their purpose?
Coke - To supply heat and produce CO to reduce ore
Limestone - To bond with and remove impurities
Hot Gasses - To burn coke, generate heat, and reduce ore?
pptys of Dual phase and TRIP steels
- 1-20% Mn, Ti, V, Nb
- alpha ferrite + gamma austinite + martensite
- High strength and high ductility
Why is nickel added to some stainless steels?
it stabilizes the gamma phase and makes FCC gamma phase at RT possible
What does it mean to say pure titanium is allotropic?
T>882 = BCC (beta) -> stronger, brittle
T<882 = HCP (alpha) -> weaker, ductile
What is martensite and when does it form?
Martensite is metastable iron phase (BCT structure). BCT is a highly stretched and brittle and is formed when quickly quenched from gamma phase to room temp.
What ores do you extract iron from?
Hematite, magnetite, cementite, siderite
Why did the titanic sink?
They didn't add Mn or Si to make the plain carbon steel more ductile.
What are the three ways to fix Sensitization and describe each one.
1. Use a very low carbon content steel
- prevents chromium carbides from forming
2. Solution Treatment
- heat to 980-1040 to eliminate Cr depletion zones, cool rapidly through 800-400 to avoid them forming
3. Stabilization
- use alloy elements that react with the carbon so the chromium doesn't
Coherent vs incoherent precipitates
Coherent - Continuous across precipitate, Elastic strain extends from precipitate
Incoherent - Discontinuous across precipitate, Elastic strain doesn't extend from precipitate
Explain how and why Nickel alloys containing 𝑁𝑖3𝐴𝑙 ordered inter-metallics have very good mechanical properties at high temperature
Ni3Al has a microstructure with highly regular atomic compositional order; namely, three Ni atoms for every one Al atom. Plastic deformation in such an ordered crystal is very difficult because the motion of dislocations, causes the fixed atomic order to be disrupted. The result is that Ni3Al has very high yield strength and very low ductility (i.e. its brittle) at room temperature however at elevated temperature, where the increased atomic vibration allows the fixed atomic order to be easily re-established after a dislocation moves through the crystal, Ni3Al displays very good ductility while still retaining high yield strength. Nickel alloys can be heat treated to create very large coherent Ni3Al precipitates which are very stable at high temperature. These are the reason why Ni3Al inter-metallic “Superalloys” are the metal of choice for structural applications at very high temperatures, T > 800oC.