5C.1.3 Describe and explain the conversion of iron into steel using the basic oxygen converter. C.1.4 Describe alloys as a homogeneous mixture of metals or a mixture of a metal and non-metal.C.1.5 Explain how alloying can modify the properties of metals.C.1.6 Describe the effects of heat treatment of steel. (Effects should include tempering, annealing and quenching)C.1.7 Describe the properties and uses of iron and steel.
6The molten iron produced in the blast furnace contains impurities. The main impurity is carbon, but there are also small amounts of other elements.ElementApprox. %Carbon4 - 5 %Silicon1 – 2 %ManganeseTraceSulphurPhosphorous
7These impurities make the resulting iron very brittle when it cools down. Some is used to make cast iron goods (e.g. cylinder blocks for cheaper cars)
8This impure iron is known as “pig iron” Which entirely coincidentally is the name of an album by The Anti Nowhere League.You will not be tested on the album!
12This causes impurities in the pig iron to oxidise. C + O2 CO2 (escapes as a gas)Si + O2 SiO2S + O2 SO2 (escapes as a gas)4P + O2 P4O10
13Quicklime is also added. This reacts with the impurities to form “slag” –e.g. Calcium Silicate CaSiO3 and Calcium Phosphate Ca3(PO4)26CaO + P4O10 2Ca3(PO4)2
14Some additional notes: The crude steel formed is around 1.5% carbon.It also contains dissolved oxygen. This can be removed by adding controlled amounts of silicon and aluminium.Other elements can be added to the steel to modify its properties. More about this later. . .The oxidation is exothermic. Old scrap steel is added cold to control the temperature.
15AlloysPure iron is a shiny, soft, ductile malleable metal of high strength (typical transition metal properties!)It rusts easily to form hydrated iron(III) oxide.4Fe + 3O2 + xH2O 2Fe2O3.xH2OThis crumbles easily, and allows oxygen and water to penetrate it and continue the corrosion process.Iron is easily shaped (“wrought iron”) and is used for many ornamental purposes (gates, fences etc.) It is also used for bridges and as a catalyst in . . .The Haber process!
16Most iron is used to make steel – which is an alloy. An alloy is a homogeneous mixture of metals, or a mixture of a metal and a non-metal.Or in English . . .An alloy must be 2 or more elements – at least one of which must be a metal. If a non-metal is involved, then the metal must be the main component.Alloys are made by mixing the required element with the molten metal and then cooling the mixture.
17How do alloys work?Remember metallic structures?
18They are a regular lattice where the atoms can slide past each other. Adding different sized atoms or atoms with different numbers of valence electrons, disrupts the lattice.This alters properties such as hardness, melting point and conductivity.
20Low carbon (mild steel) Steel is not just one material. There are many different types of steel:Type of steel% CarbonPropertiesUsesLow carbon (mild steel)0.07 – 0.25Easily cold workedCar bodiesHigh carbon (tool steel)0.85 – 1.2Wear resistantCutting tools, railway lines
21Properties given to steel Alloying elementProperties given to steelUsesCobaltEasily magnetisedMagnetsMolybdenumHigh strength at high temperatureHigh speed drillsManganese (10 – 18% manganese)ToughSafes, earth moving machineryTitaniumWithstands high temperaturesTurbines, spacecraft, aircraftVanadiumStrong, hardHigh speed toolsStainless steel (20% chromium, 10% nickel)Resists corrosionCutlery, surgical instruments, car accessories
22The properties of steel can also be modified by heating and cooling it under carefully controlled conditions.You need to be aware of annealing, quenching and tempering.
23AnnealingThe steel is slowly heated to about half its melting point (1040 °C ?) and then let cool slowly.This modifies the metallic crystals in the steel and makes it more malleable and ductile.
24Artificially coloured scanning electron microscope picture of tungsten crystals at magnification x 2275
25Quenching If a very hard steel is needed, the steel is quenched. The hot steel is cooled rapidly using cold water or oil.This traps the crystal structure which was present at high temperatures.The steel is hard but brittle and is used in cutting tools.
26Water quenched steel etched to show crystal structure Water quenched steel etched to show crystal structure. Magnification x 400
27Tempering Quenched steel can be made more malleable by tempering. The quenched steel is heated to about 300°C and cooled slowly (or 600 °C – depending on which book you read!)The resulting steel is still quite hard, but is now more malleable and ductile.
28High impact toughness means that the metal is less brittle High impact toughness means that the metal is less brittle. NB You don’t need to know this graph!
29ReviewC.1.3 Describe and explain the conversion of iron into steel using the basic oxygen converter.Reasons for getting rid of carbonDraw the basic oxygen converterEquations for all the main reactions
30Review C.1.7 Describe the properties and uses of iron and steel. Be able to name several uses of steels
31ReviewC.1.4 Describe alloys as a homogeneous mixture of metals or a mixture of a metal and non-metal.Or even describe them in English!
32Review C.1.5 Explain how alloying can modify the properties of metals. Draw the pictures and talk the talk!
33ReviewC.1.6 Describe the effects of heat treatment of steel. (Effects should include tempering, annealing and quenching)Describe each one. No equations needed; no pictures need!