ppt on Metallurgical Engineering PPT.pptx

presentation created for presenting in NIT calicut material science department

1. Metallurgical Engineering (MT2006D)

2. Course Evaluation Policy Mid Exam: 30 Marks Quiz/Assignment: 30 Marks End Exam: 40 Marks Relative grading

3. According to 2020 statistics, 1.9 billion tons of steel is produced globally. India produced around 115 million tons of steel in 2020 Entire Asia produced 1.3 billion tons of steel in 2020. If we consider India’s population as 134 crores, then the percapita steel consumption will be ≈ 80 115∗10 6 ∗10 3 𝐾g 134∗10 7 𝑃𝑒𝑟𝑠𝑜𝑛 Most of the developed countries would be consuming atleast Kg/person. 200-300

4. Iron is available in abundance in the earth’s crust relative to copper, zinc etc. Iron is available in the form of hematite (Fe 2 O 3 ) or Magnetite (Fe 3 O 4 )

5. Ferrous Extraction Iron is made in the blast furnace using these raw materials, iron ore , coke , Flux , and hot air : Iron ores (hematite, magnetite) – iron oxides with earth impurities (>10 mm) Sinter/pellets Coke, which is both reducing agent and fuel, providing heat for melting the metal and slag (coal 🡪 coke through carbonization) Flux: Limestone, calcium carbonate, is used to remove impurities. Iron is produced in a blast furnace , schematically shown in the picture

6. Counter current reaction

7. Blast Furnace It is a shaft type furnace consisting of a steel shell lined with refractory bricks. The top of the furnace is equipped with the bell-like or other system, providing correct charging and distribution of the raw materials (iron ore, coke, limestone). Air heated to 2200 °F (1200 °C) is blown through the tuyeres at the bottom. Oxygen containing in air reacts with the coke, producing carbon monoxide: 2C + O 2 = 2CO Hot gases pass up through the descending materials, causing reduction of the iron oxides to iron according to the following reactions: 3Fe 2 O 3 + CO = 2Fe 3 O 4 + CO 2 Fe 3 O 4 + CO = 3FeO + CO 2 FeO + CO = Fe + CO 2 FeO + C = Fe + CO Indirect reduction (65%) Direct reduction (35%) Ratio of direct to indirection reduction is 1:2 (combustion)

8. Iron ore contains impurities of silicon dioxide (sand). In the blast furnace the intense heat causes the calcium carbonate to decompose into calcium oxide and carbon dioxide. CaCO 3 = CaO + CO 2 The calcium oxide reacts with the sand impurities to form a substance called slag (calcium silicate) which can there be removed. CaO + SiO 2 = CaSiO 3

9. Charging system:

10. Charging raw materials in a blast furnace is a crucial step in the iron making process Efficient utilization of heat: the heat generated during combustion of coke at the bottom of the furnace rises through the stack, preheating the raw materials as it ascends. The preheating of raw materials helps in reducing the overall energy consumption of the blast furnace Iron ore reduction: the reduction process is more effectively controlled when the materials are layered, allowing for better contact between reducing agents and iron oxides Controlled combustion Uniform distribution of load Optimizing gas flow

11. Refractory lining: Alumino-silicates (Fire-clay brick) Carbon (Near hearth region) Failure of refractory lining can be due to CO attack ( in stack region ) High temperature ( near the Tuyeres ) Abrasion of solid charge ( in stack region ) Attack/reaction by molten slag or hot metal ( in hearth and bosh ) Ordinary (40 – 45% Al2O3) Near Stack/Shaft region Super-duty (>60% Al2O3) Near Belly and bosh region

12. Combustion of coke C + O 2 🡪 CO 2 ΔG= -394100 – 0.84T J/mol C + 1/2O 2 🡪 CO ΔG= -111700 – 87.65T J/mol C + CO 2 🡪 2CO (Boudouard reaction/ Gassification reaction) Thermodynamics

13. Output from Blast Furnace Molten iron Molten slag Top gases (N 2 + CO+ CO 2 )

14. Iron in the form of a spongy mass moves down and its temperature reaches the melting point at the bottom regions of the furnace where it melts and accumulates. The gangue, ash and other fractions of ore and coke are mixed by fluxes, forming slag which is capable to absorb Sulphur and other impurities. The furnace is periodically tapped and the melt (pig iron) is poured into ladles, which are transferred to cast iron and steel making furnaces. Pig iron usually contains 3-4% of carbon, 2-4% of silicon, 1-2% of manganese and 1-1.2% of phosphorous.

15. Major constituents of slag SiO 2 (30-35%), Al 2 O 3 (1.8-2.5%) CaO (28-25%), MgO (1-6%) MnO, P 2 O 5 The viscosity of the slag should be less for easy removal Major Minor

16. Major impurities in pig iron Silicon This element comes from the sand or other minerals mixed with the iron ore. It can make the iron brittle and hard to work with. In the blast furnace, silicon reacts with limestone (CaCO3) to form calcium silicate (CaSiO3), which floats on top of the molten iron as slag Carbon Sulfur This element can come from iron ore or the coke. It makes the steel hot-short (high temperature). In the blast furnace, sulfur reacts with calcium oxide (CaO) from the limestone to form calcium sulfide (CaS), which goes into slag Phosphorous this element can make the steel cold-short (low temperature). It is usually removed by adding manganese to the molten iron, which forms manganese phosphate that goes into the slag Manganese

17. SiO 2 + C 🡪 SiO + CO SiO2 + 3C 🡪 SiC + 2CO SiO+ 2C SiO + [C] 🡪 [Si] +CO 2SiO 🡪 SiO 2 + [Si] FeO + SiO 🡪 [Fe] +SiO 2 How to decrease the Si in the hot metal? High blast pressure Silicon (Si) CO [] 🡪 dissolved state Le Chatelier’s principle

18. P 2 O 5 + 5C = 2P + 5CO MnO + C = Mn + CO Pig iron Wrought iron Steel Cast iron

19. Cast iron manufacturing process Cast iron is manufactured by re-melting pig iron with coke and limestone This is done in a furnace known as cupola furnace Cupola furnace was first built in china in the warring states period (403-221 BC) Generally cupolas are not worked continuously like blast furnaces but are run only when required.

20. Cupola furnace Charge: Pig iron, coke, limestone Combustion zone: C + O 2 = CO 2 + heat Si + O 2 = SiO 2 + heat 2Mn + O 2 = 2MnO + heat Reducing zone: C + CO 2 = 2CO + heat Melting zone: 3Fe + 2CO = Fe 3 C + CO 2

21. Cupola shell is made of steel and has a lining of refractory brick The bottom of the shell is lined with clay and sand mixture and it is a temporary lining. Parts of cupola furnace Cylindrical shell: It is the outermost part of the furnace. It is made up of steel and other parts of this furnace are present inside this shell Legs: Legs are provided at the bottom of the furnace to support the furnace

22. Sand bed: It is in tapered form so that the melted iron can flow easily Slag hole: it is present at the opposite side of the hole from which cast iron comes out. It is present near the elevated part of the sand bed. It is used to remove slag formed on melted iron due to impurities. Air pipe and Tuyers: Air pipe is provided to allow the air to reach inside the furnace through the tuyers. Spark arrestor or cap of furnace: it is present at the top of the furnace. It is used to capture the burning particles and only allow the gas to pass to the environment.

23. Charging door: it is present near the top of the furnace. The charge in this furnace are pig iron, coke and limestone. Coke is used for combustion and limestone is used as flux Well: the part of the furnace from sand bed to lower part of tuyers is known as well. Molten iron is stored in well and comes out from the tapping hole. Combustion zone: Combustion takes place in this zone. The air from tuyers reacts with carbon to form carbon di oxide. It is also known as oxidizing zone. Reducing zone: it is above the combustion zone. In this zone carbon reacts with carbon dioxide to form carbon monoxide.

24. Melting zone: in this zone iron melts and the molten iron comes out of the tap hole. The temperature of this zone is very high nearly 1600 ℃ . Preheating zone: the metal to be melted is preheated in this zone. The temperature in this zone is around 1090 ℃ Stack zone: In this zone the charge is staked in layer form.

25. Advantages of cupola furnace Simple in construction Wide rage of materials can be melted Less floor space is required Very skilled operators are not required Low cost of operation Low cost of maintenance Low cost of construction

26. Disadvantages of cupola furnace Very hard to control the temperature in the furnace Some metals are converted to their oxide which are not suitable for casting

27. Conventional route for making steel consists of sintering or pelletization plants, coke ovens, blast furnaces. Coking coke is needed to make coke strong enough to support the burden in the blast furnace. This requires high capital expenses and raw materials of stringent specifications. The coke ovens and sintering plants in an integrated steel plant are polluting and expensive units.

28. Over years, the hot metal production from the blast furnace has decreased due to the unavailability of high grade coke. Alternative iron production is feasible in the places where high grade coal (coking coal) is not available but low grade coal (non- coking coal) or natural gas is available

29. Alternative routes of iron making Solid iron Liquid iron DR: Direct reduced Retort processes Shaft furnace processes Fluidized bed processes COREX process FINEX process According to reduction reactor type Rotary kiln based processes Shaft furnace based processes Rotary hearth furnace based processes

30. From DRI, iron is produced from direct reduction of iron ore (in the form of lumps, pellets or fines) by a reducing gas (H 2 , CO) produced from natural gas or coal. DR process convert iron ore into sponge iron at temperature below the melting point of iron. DR process differ from conventional blast furnace in two ways Solid metallized product is produced A wide variety of reductants can be used in the place of high grade coke

31. Sponge iron production in rotary kiln Coal-based sponge iron process

32. Rotary kiln inclination: 2.5° Speed of kiln: 0.2 – 1.0 rpm 1000-1100 ℃ 950 ℃

33. Coal based direct reduction rotary kiln process was developed for converting iron ore directly into metallic iron without melting. Hence the produced iron has highly porous structure and gives a sponge appearance. As iron ore is in direct contact with the reducing agent throughout the reduction process, it is called direct reduced iron. Raw material mix consisting of iron ore, dolomite and non-coking coal is fed at one end of the rotary kiln and is heated by coal burner to produce DRI. The produced DRI along with char is taken out from the other end of the kiln.

34. Process control parameters Feed rate Kiln temperature Control of gaseous atmosphere Kiln speed, inclination Retention time of charge Waste gas temperature and composition Fe Total 90 – 94% Fe Metallic 83 – 90 % Metallization 92 – 96 % C 1.0 – 2.5 % P 2 O 5 0.005 – 0.9 % S 0.001 – 0.03 % Gangue 2.8 – 6 %

35. Ring formation in rotary kilns Raw mix chemistry Coal fineness to be controlled Low fusion temperature of coal ash Incomplete calcination of raw metal Kiln speed too low High burning zone temperature Frequent change in secondary air temperature Volatile recycling

36. Advantages of coal based process They does not require high grade coal which is scarcely available They can use non-coking coal They can be installed at lower capacity They can be easily installed at center where small reserves of coal and iron ore are available Dis-advantages of coal based process Coal based processes have lower economy of scale High energy consumption (16 to 21 GJ/t) Low carbon content in the production (< 1%) Lower productivity Hot feeding to the steel making furnace is not possible, due to the presence of residual char and ash

37. Gas-based sponge iron process (MIDREX process)

38. In the gas based reduction process, a vertical shaft kiln is used in which iron ore is fed into the top of the kiln and finished sponge iron is drawn off from the bottom after cooling so as to prevent it from re-oxidation. High methane containing natural gas is the most commonly used gas. Natural gas is reformed to enrich with H 2 and CO mixture. This enriched and reformed gas mixture is preheated and sent to the shaft furnace Gas based process is simple to operate and involves three major steps Iron ore reduction Gas preheating Natural gas reforming

39. The reduction reaction takes place both with H 2 and CO in a gas based DRI process. Reactions with H 2 3Fe 2 O 3 + H 2 = 2Fe 2 O 4 + H 2 O (Exothermic reaction) Fe 3 O 4 + H 2 = 3FeO +H 2 O (endothermic reaction) FeO + H 2 = Fe+H 2 O (endothermic reaction) Reactions with CO 3Fe 2 O 3 + CO = 2Fe 3 O 4 + CO 2 (Exothermic reaction) Fe 3 O 4 + CO = 3FeO + CO 2 (Endothermic reaction) FeO + CO = Fe + CO 2 (Exothermic reaction) Gas based DRI is not subjected for any magnetic separation since no contamination with non magnetic materials is possible

40. Advantages of gas based process over coal based process Less capital cost High productivity Better quality Energy efficiency Better plant availability Environmental pollution

41. Corex process

42. COREX consists of two reactors, the reduction shaft and the melter-gasifier. The reduction shaft is placed above the melter-gasifier and reduced iron material descends by gravity. The volume of the reduction shaft is 600 m 3 and the melter- gasifier is 2000 m 3. Iron ore, pellets and additives (limestone and dolomite) are charged into the reduction shaft from the top of the shaft. Some amount of coke is also added to the shaft to avoid clustering inside the shaft due to sticking of the ore/pellets and to maintain adequate bed permeability. The reduction gas from the melter-gassifer is injected into the reduction shaft at 850 ℃ and over 3 bar pressure.

43. The gas moves in the counter current direction to the top of the shaft and exists at around 250 ℃ from the shaft. The iron bearing material gets reduced to over 95% metallization in the shaft. The hot DRI at around 600 – 800 ℃ is discharged from reduction shaft into the melter-gasifier Oxygen plays a vital role in COREX process for generation of heat and reduction gases. Oxygen gasifies the coal char and generates CO. The sensible heat of the gases is transferred to the char bed which is utilized for melting iron and slag. The hot metal and slag are collected in the hearth.

44. Reactions in reduction shaft: Reduction of iron oxide by CO and H 2 and transforming the iron oxides to metallic iron Fe 2 O 3 ---> Fe 3 O 4 ---> FeO ---> Fe Calcination of limestone and dolomite CaCO 3 ---> CaO + CO 2 3Fe + 2CO ---> Fe 3 C + CO 2 CaO + H 2 S ---> CaS + H 2 O MgO + H 2 S ---> MgS + H 2 O

45. Reactions in melter-gasifier: Devolatilisation of coal at 200 to 950 ℃ liberates methane and higher hydrocarbons. Due to high temperature, hydrocarbons are cracked into hydrogen and elementary carbon C n H m = nC + (m/2)H 2 2C + O 2 = 2CO 2CO + O 2 = 2CO 2 C + CO 2 = 2CO

46. Advantages: Reduces investment cost compared with conventional blast furnace COREX export gas can be used for a wide range of applications Use of wide variety of iron ores and coals Elimination of coking plants Hot-metal quality suitable for all steel applications

47. Limitations: Use of high grade raw material The system is maintenance oriented, including cooling gas compressor for recycling part of COREX gas for cooling the hot gases from the melter-gasifier. Hot DRI transfer and hot gas recycling are hazardous especially during their maintenance periods

48. O 2 +CaO C + O 2 🡪 CO 2 Si + O 2 🡪 SiO 2 4P + 5O 2 🡪 P 4 O 10 SiO 2 + CaO 🡪 CaSiO 3 P 4 O 10 + 6CaO 🡪 2Ca 3 (PO 4 ) 2

49. Effect of chemical elements in steel Carbon : It is the most important element in steel and can be present up to 2%. Increased amount of carbon increase hardness and tensile strength, as well as response to heat treatment. Increased amounts of carbon will reduce weldability. Sulphur: It is usually undesirable impurity in steel rather than an alloying element. If exceeds 0.01% it tends to cause brittleness and reduce weldability. Alloying addition of sulphur in amounts of 0.1 to 0.3% will tend to improve machinability of steel. Phosphorous: it is also undesirable impurity in steel. It is normally found in amount up to 0.01% in most carbon steels. In hardened steels, it may tend to cause embrittlement. In low-alloy high strength steel, it is added up to 0.1% to improve strength and corrosion resistance. Zirconium: It is added to modify the shape of the inclusions resulting in improved toughness and ductility.

50. Effect of chemical elements in steel Silicon: Only small amount (0.2%) is present and it is used as a deoxidizer. Silicon dissolves in iron and tends to strengthen it. Weld metal usually contains 0.5% silicon as a deoxidizer. Manganese: Steel usually contain atleast 0.3% manganese because it assists in the deoxidation of the steel, prevents the formation of iron sulfide and inclusions and promotes greater strength by increasing the hardenability of steel. Chromium: it is powerful alloying element in steel. It strongly increases the hardenability of steel, improves corrosion resistance of alloys in oxidizing media. Stainless steel may contain in excess of 12% chromium. Molybdenum: molybdenum is a strong carbide former and is usually present in amounts less than 1%. It increases hardenability and strength. In austenitic stainless steel it improves pitting corrosion. Titanium: it helps to keep grain size smaller and also helps manage inclusions by making them rounder

51. Effect of chemical elements in steel Nickel: it is added to steel to increase hardenability. It often improves the toughness and ductility of the steel even with the increases strength and hardness. Aluminium: it is added in a very small amounts as a deoxidizer. It also acts as grain refiner for improved toughness. Vanadium: it helps remove oxides and thus increases yield strength and tensile strength. At greater than 0.05% there may be tendency for the steel to become embrittled during thermal stress relief treatment. Nitrogen: high levels of nitrogen will make welding difficult by increasing embrittlement in the heat affected zone. Copper: it will improve atmospheric corrosion resistance and has a small impact on hardenability. Niobium: it is a key grain refinement element which improves strength, toughness of the material Boron: it is added to achieve finer grains to increase hardenability.

52. Liquid salts which contain cyanide compounds such as NaCN

53. Fe(CO) 5 , Ni(CO) 4 Fe(CO) 5 🡪 Fe(S) + 5CO Ni(CO) 4 🡪 Ni + 4CO

54. For complete combustion one mole of acetylene requires 2.5 moles of oxygen Overall reaction: C 2 H 2 + 5/2O 2 🡪 2CO 2 +H 2 O + ΔH

55. No sound Hissing sound Roaring sound

56. Assignment Tensile test Compression test Hardness test Impact test Fatigue test Creep test