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MMET Lecture 3
| Question | Answer | |
|---|---|---|
| What are the 2 principles of iron ores? | Hematite (Fe_2O_3) & magnetite (Fe_3O_4) | |
| What is taconite? | Siliceous rock containing fairly low-volume concentrations of iron. | |
| What is pelletizing? | When rocks are sintered into small balls about 1/2 in in diameter. Iron %: 70% or greater. | |
| What is a blast furnace & what does it do? | A multistory heated reaction vessel to reduce iron ore to steel (1st step). Iron freed from most impurities. Charged with iron ore, limestone, & coke. Slag protects from oxygen. | |
| What are the equations of the production of the reducing gas? | C (coke) + O_2 (air) -> CO_2 (carbon dioxide) CO_2 +C (excess coke )-> 2CO (carbon monoxide) | |
| What are the equations of the reduction of the iron oxide? | 2 Fe_2O_3 (ore) +3C (coke) -> 4Fe + 3CO_2 Fe_2O_3 + 3CO (carbon monoxide) ->2Fe (iron) + 3CO_2 (carbon dioxide) | |
| What is pig iron? | Impure, high carbon content, & not suitable for making engineering materials because it would be extremely brittle & weak. Has 3-5% carbon, rest is iron & some impurities. | |
| What are direct reduction processes? | ||
| What is the iron carbide process? | ||
| What is a basic oxygen furnace (BOF) furnace? | A steelmaking process that reduces impurities in steel. Charged with scrap, pig iron, & hot metal. Cheaper. Continuous. | |
| What is steel? | An alloy of iron & carbon 0.06%-2.0%. combination of iron & carbon. | |
| What is pure iron? | Soft, ductile, & weak. Used for magnetic devices & enameling steels. | |
| What is the lowest carbon content for steels? | 0.06% | |
| What are cast irons? | Have more than 2% C. | |
| What happens if alloys have high carbon content? | It makes them too brittle for any fabrication techniques besides casting. | |
| What is oxidation? | Removes impurities from pig iron. | |
| What is an electric arc furnace (EAF)? | Uses heat & charged with scrap or pig iron. Better, but expensive | |
| What is continuous casting? | Skips the ingot step. Used for tool steels. Produces rounds, squares, slabs, & plates. Improved yield, quality, productivity, & cost efficiency. 2 hrs | |
| What are inclusions? | Oxides, silicates, sulfides, or aluminas that form during conventional melting & refining. | |
| What is vacuum degassing? | Removes dissolved gases from steels. | |
| What is deoxidation? | removal of oxygen from molten steel | |
| What is ladle heating? | Restores heat to the metal in the ladle. | |
| What is vacuum arc remelting (VAR)? | Involves casting of steels from the BOF or electric furnace into cylindrical ingots. Removes inclusions. | |
| What is vacuum induction melting (VIM)? | Melts solid scrap/liquid charges. | |
| What is electron beam refining? | Vaporizes impurities so that they can be removed as vapors in the vacuum. | |
| What is the AOD process? | ||
| What is electroslag refining? | Similar to VAR, but w/out the vacuum. | |
| What is purification? | Accomplished when melting metal from the ingot passes through a molten flux that acts like a welding electrode slag to remove impurities. | |
| What is segregation? | A variation in chemical composition. | |
| What is pipe? | A cavity in the top of an ingot. | |
| How is pipe formed? | By volumetric shrinkage of the metal as it transforms from liquid to solid. | |
| What is rimmed steel? | Ingots that solidify w/ a skin that is purer than the center. Slightly deoxidized steels that solidify w/ outer shell on the ingot which is low in impurities. Can retain a good finish after severe forming because of the surface cleanliness. | Very ductile & malleable - can be shaped. |
| What are killed steels? | Less prone to problems. Strongly deoxidized by chemical additions to the melt. Very few inclusions & little porosity. | |
| What metal is always killed/deoxidized? | Continuous cast steels | |
| What are concerns with continuous cast steels? | Inclusions, porosity, segregation, & grain size | |
| What are strands? | Solidify w/ a grain structure | |
| What is a dendrite? | 3-D treelike structure. Nature's way of solidifying. A significant part of the basic metallurgy. Can form from nuclei that can be a single atom, impurity, or protrusion from the mold wall, etc. | |
| What is a grain boundary? | When grains/crystallites meet. | |
| Grain size relates to? | Strength | |
| Small grain size = | Higher strength | |
| Large grains = | Weaker strength | |
| What are equiaxed grains? | Grains that have the same shape in the x, y, & z directions. | |
| How are steels shaped? | By hot rolling, or hot/cold-finished from a steel mill | |
| What shapes can hot rolling produce? | Billets, blooms, & slabs | |
| What is the metallic bond? | Atoms that are held together by an electron cloud | |
| What is plastic deformation? | By atomic movement (slip) in each crystal/grain that is in the metal shape | |
| What is solidification? | Dendrites -> crystals | |
| What is a phase? | Homogeneous component of a solid/liquid/gas that is separated from other phases by an interface. Happens after solidification. More dendrites & grains will be formed. | |
| Billets can become? | Bars, rods, or tube rounds | |
| Bars are used for? | Cold-drawn bars | |
| Rods are used for? | Wire | |
| Tube rounds are used for? | Seamless pipes | |
| Blooms can become? | Tube rounds, structural shapes, or rails | |
| Rails are used for? | Cold-rolled sheet & strip | |
| Slabs can become? | Skelps or plates; Hot-rolled sheet & strip for tin mill products | |
| Skelp is used for? | Welded pipe & tubing | |
| Plates are used for? | Large-diameter pipe | |
| What is recrystallization? | Grains grow back when the steel is red hot after being squashed. Occurs in annealing. | |
| The more the grains are squashed..? | The harder the steel gets | |
| Fracture will occur if..? | Additional reduction/shaping is attempted | |
| What is hot finishing? | Ingots/continuous cast shapes are rolled in the red-hot condition to smaller shapes such as blooms or billets. Makes steels soft, but mechanical properties are very low. | |
| What is cold finishing? | Much stronger mechanical properties & better surface finish than hot finished steels. | |
| Hot finished, low carbon steel may have a tensile strength of? | 60 ksi | |
| A full, hard, cold finished steel may have a tensile strength of? | 120 ksi | |
| What is a carbon steel? | Steel with a carbon as the principal hardening agent. All other alloying elements are present in small %s. Max %: Maganese - 1.65%, Silicon - 0.60%, Copper - 0.60%, Sulfur & Phosphorus - 0.05% | |
| What is an alloy steel? | Steels w/ total alloy additions of less than ~5%. Used for structural applications/ | |
| How are killed steels produced? | Elements are added to the steel, such as aluminum & silicon, that remove dissolved oxygen from the molten metal & alter the ingot solidification characteristics to minimized segregation. | |
| What are galvanized steels? | Zinc-coated steel. Zinc is applied by hot dipping. | |
| What are galvannealed steels? | Zinc-coated & heat-treated steels. Has an oxide layer that allows better paint adhesion. | |
| What is a free machined steel? | Steels w/ additions of sulfur, lead, selenium, or other elements in sufficient quantity that they machine more easily. | |
| What is Commercial Quality? | Steels produced from standard rimmed, capped, concast, or semiskilled steel. | |
| What are H steels? | Made to guarantee ability to harden to a certain depth in heat treatment, | |
| What are B steels? | Steels w/ small boron additions as a hardening agent. | |
| What is pickling? | Use of acids to remove oxides & scale on hot-worked steels | |
| What is temper rolling? | Involves a small amount of roll reduction to eliminate stretcher strains | |
| What is temper? | The amount of cold reduction in rolled sheet & strip | |
| What are E steels? | Melted by electric furnace | |
| What is the product of the blast furnace? | Pig iron | |
| What is the 1st step of steelmaking? | Iron ore must be reduced from its oxide form in a blast furnace | |
| Iron ore is the source of the..? | Iron oxide | |
| What is C + O_2 -> CO_2? | Combustion creating heat | |
| What is the source of the pure carbon? | Coal/Coke | |
| What is CO_2 + C -> 2CO | Produces the carbon monoxide that when combined w/ the iron oxide in Fe_2O_3 + 3CO -> 2Fe + 3CO_2 preferentially bonds with the oxygen thus yielding more iron & carbon dioxide | |
| Limestone is added to the blast furnace for what purpose? | It forms slag that helps draw out impurities that can be removed. | |
| A blast furnace & a basics oxygen furnace do the same thing? | False | |
| Chemical segregation during ingot solidification usually leads to a variation of mechanical properties across the cooled ingot. | True | |
| An allotropic material can have 2 or more crystalline forms in the same phase. | True | |
| The charpy impact test is used to determine the sensitivity of a metal's impact strength to changes in _? | Temperature | |
| A basic oxygen furnace must have a change of molten metal, can use recycled steel & used an oxygen lance to make steel? | True | |
| As carbon content increases in steel, the strength & ductility increase. | False | |
| What is low carbon alloy steel? | 0-30 pts of carbon | |
| What is alloytropism? | The conversion to FCC or BCC | |
| What is the key to MMET-207? | Carbon | |
| What is a body centered cubic (BCC)? | Pearlite, holds less carbon | |
| What is a face centered cubic (FCC)? | More brittle, above AC_3, holds more carbon, stronger & harder | |
| How do you get BCC -> FCC -> BCT? | Quench | |
| What is a BCT? | Martensite | |
| An electric arc furnace & a basic oxygen furnace make? | Steel | |
| What are raw materials? | Iron ore mined & crushed into tiny pieces | |
| What is limestone? | Serves as flux, cleans out impurities & floats to the surface. | |
| What is coke? | Coal, pure form of carbon, supplies heat for smelting iron in blast furnaces, hard, brittle substance consisting of carbon | |
| What is steel refining? | Uses basic oxygen furnace (BOF) or electric arc furnace (EAF). May use pig iron, liquid pig iron, or scrap steel | |
| Oxygen process | After scrap & hot metal are charged into furnace, dust cap is put on, & oxygen blown through the lance to the surface of the molten metal in order to burn out impurities. | |
| Steel scrap | BOF uses this. Integrated producer. | |
| Electric arc furnace (EAF) processes | Can produce more than 800 tons of steel in 24 hrs, electricity used for production of heat, uses 3 carbon electrodes for direct arc, circular furnace shape which can be tilted to pour molten steel into ladle | |
| Cast steel | Made by molten steel casts in molds | |
| What is the sequence of the type of steels from least refinement to most refinement? | Rimmed - Capped - Semikilled - Killed | |
| What are capped steels? | Thin low carbon rim, remainder of cross section approaches degree of semikilled steels | |
| What are semikilled steels? | Intermediate in deoxidization between killed & rimmed, composition more uniform than rimmed steels | |
| What are killed steels used for? | Forging, piercing, carburizing, heat treatment, or continuous cast | |
| What are the steps of casting? | 1. Tundish to feed liquid steel to mold. 2. Primary/secondary cooling zone to generate solidified outer shell/the strand 3. Unbending & straightening 4. Severing unit to cut solidified strand | |
| What are the different processes? | Vacuum degassing, ladle stirring injection, & ladle furnace reheating | |
| What do vacuum furnaces & degassing produce? | High quality steel aloys | |
| What are the advantages of vacuum furnaces & degassing? | Less expensive, decreased amounts of hydrogen, oxygen, & nitrogen in finished product, improved mechanical properties, close heat control, & better hot & cold workability | |
| Example of hot workability? | Recrystallization | |
| Example of cold workability? | Dent your truck | |
| What is ladle degassing? | Ladle of molten steel placed in tank & then air removed from tank, exposing it to vacuum | |
| What are special refining processes? | Vacuum arc remelting (VAR), vacuum induction melting (VIM), electron beam refining, & electroslag melting (ESR) | |
| What is Vacuum arc remelting used for? | Super-alloys & extra clean steels | |
| What is vacuum induction melting used for? | Specialty alloys | |
| What is electron beam refining used for? | Purify specialty alloys | |
| What is electroslag melting used for? | Tool steels & special-purpose steels. Molten slag acts as a cleansing flux | |
| What is a consumable electrode vacuum arc melting? | Refining process for steels prepared by other methods. Steel electrodes or predetermined composition are remelted by an electric arc in air-tight, water-cooled crucible | |
| What is vacuum induction melting? | Charge melted in furnace within airtight, water cooled steel chamber | |
| What are the advantages of vacuum induction melting? | Freedom from air contamination, close control of heat, & few air inclusions | |
| What is cold work? | Residual stress, heated below AC_3 | |
| What is hot work? | element alignment, heated above AC_3 | |
| What is forging? | Reduces metal to desired shape, usually done with steam hammer, recrystallizing grains | |
| What is drop forging? | Piece of roughly shaped metal placed between die-shaped faces of exact form of finished piece - metal forced to take form by drawing dies together | |
| Metalworking processes are..? | All about the grain | |
| What are metalworking processes? | Shape & improve its characteristics: Forging & rolling. Destroy the cast structure. | |
| What do metalworking processes do to steels? | Make steels stronger, more ductile, & better shock resistance. | |
| What is steel rolling? | Steel wants to go back to equilibrium when energy (heat) is added creating rust/iron-carbide. Grains are oriented in direction of rolling. | |
| What is hot rolling? | Finished at temps between 900-2400 degrees F, black iron | |
| What is cold rolling? | Finished at room temperature, coated w/ Zinc (galvanized), tin (tin plate), tin & lead | |
| What is piercing? | Bar to pipe | |
| What does rolling in the x direction do? | Best strength & ductility | |
| What does rolling in the y direction do? | 30% reduction in strength & ductility | |
| What does rolling in the z direction do? | Lower strength, no ductility | |
| What is drawing? | Operation of reducing cross section & increasing length of metal bar/wire | |
| What is extrusion? | Forming by pressing through an opening, obtain perfectly round rods, metal places in closed chamber fitted w/ opening at 1 end & piston at the other end |
Created by:
Texi Rae