Metallurgy and Recycling: Iron and Steel PDF

Metallurgy and Recycling: Iron and Steel 5: Basic Oxygen Furnace Hauke Springer 11.06.2024 Production of ferrous materials Key steps (1) Reduction (2) Melting (3) „Alloying“ (4) Solidification (→ TMT → Products) Three routes 1800 o conventional BF-BOF (C-b...

Metallurgy and Recycling: Iron and Steel 5: Basic Oxygen Furnace Hauke Springer 11.06.2024 Production of ferrous materials Key steps (1) Reduction (2) Melting (3) „Alloying“ (4) Solidification (→ TMT → Products) Three routes 1800 o conventional BF-BOF (C-based) steel (liquid) iron (liquid) o „green steel“ (H)DR + EAF o recycling scrap + EAF 1400 Temperature / °C 1000 600 200 steel [solid] ore [solid] Mn, Si, Cr, Ni, … 0 5 10 15 20 25 30 O in Fe / wt.% 2 Three routes 𝟐𝑭𝒆𝟐 𝑶𝟑 + 𝟑𝑪 → 𝟒𝑭𝒆 + 𝟑𝑪𝑶𝟐 (1) Conventional route o blast furnace → raw iron o BOF → conversion to raw steel 1800 iron (liquid) 1400 Temperatur / °C Why and how to turn raw raw iron iron into raw steel? (liquid) 1000 600 200 ore [solid] 5 4 3 2 1 0 5 10 15 20 25 30 C in Fe / wt.% O in Fe / wt.% 3 Content Lecture topics o Introduction o Applied fundamentals o Raw materials and preparation o Conventional production Basic Oxygen Furnace as part of the integrated mill Development and construction Steps, reactions and mechanisms o Recycling o Transformation Exercises and coordination [email protected] Exam o Voluntary E-Tests for checking progress, potential improvement o Written exam 90 min, calculator 4 Integrated mill Further processing into steel: complex, coordinated, efficient chain of processes steel making oxygen converter raw steel Sec. Met. raw iron ore Sinter/Pell. Casting Rolling steel additionals Mixing charge Blast furn. slag coal Coaking coke Energy Hot wind Energy 5 From raw iron to raw steel Output blast furnace: Fe – 4.5C – 0.6Si – 0.8Mn – 0.08P – 0.04S (avg. wt.%) Tapping: why is that no steel yet? → strategy of conversion? 6 Conversion – motivation Output blast furnace: Fe – 4.5C – 0.6Si – 0.8Mn – 0.08P – 0.04S (avg. wt.%) Too much carbon – limited formability (graphite/cementite) Usable as cast iron? 7 Conversion – motivation Output blast furnace: Fe – 4.5C – 0.6Si – 0.8Mn – 0.08P – 0.04S (avg. wt.%) Problems in liquid or solid state? 8 Abbasi et al. Conversion – motivation Output blast furnace: Fe – 4.5C – 0.6Si – 0.8Mn – 0.08P – 0.04S (avg. wt.%) GJL with 1 wt.% P: Fe-Fe3P-C eutectic → consequences? Solubility? „Steadit“ 9 Abbasi et al. Conversion – motivation Output blast furnace: Fe – 4.5C – 0.6Si – 0.8Mn – 0.08P – 0.04S (avg. wt.%) P in GJL: embrittlement (RT) 10 Abbasi et al. Conversion – motivation Output blast furnace: Fe – 4.5C – 0.6Si – 0.8Mn – 0.08P – 0.04S (avg. wt.%) Even small amounts critical in both steels and cast irons: grain boundary segregations Low energy intercrystalline fracture 11 Kim et al. Conversion – motivation Output blast furnace: Fe – 4.5C – 0.6Si – 0.8Mn – 0.08P – 0.04S (avg. wt.%) Hot shortness Low melting eutectics at hot forming temperature: hot cracking by forming stresses eutectics Also with Cu! 12 Conversion – motivation Output blast furnace: Fe – 4.5C – 0.6Si – 0.8Mn – 0.08P – 0.04S (avg. wt.%) Typically non-critical – depending on final product examples? 13 Conversion – motivation Output blast furnace: Fe – 4.5C – 0.6Si – 0.8Mn – 0.08P – 0.04S (avg. wt.%) Typically non-critical – depending on final product Steels designated for machining Mn-sulfides to capture sulfure and acting as designated fracture points during machining (short flakes) 14 Conversion Output blast furnace: Fe – 4.5C – 0.6Si – 0.8Mn – 0.08P – 0.04S (avg. wt.%) reduce: depending on ferrous material adapt: depending on ferrous material minimise: always (usulally) as low as possible Rotbruch Strategy Eutektikum mit Schmelztemperatur im Umformbereich: Heißrisse durch Umformkräfte How? Three separate steps 15 From raw iron to steel Right after blast furnace tapping: raw iron treatment Desulphurisation with lime Coke as dominant [S] + (CaO) + [C] → (CaS) + {CO} sulfur source Slag forming and removal Alternatives: Mg, Na2O, CaC2 16 From raw iron to steel Right after blast furnace tapping: raw iron treatment Desulphurisation with lime [S] + (CaO) + [C] → (CaS) + {CO} Major parts already captured within blas furnace slag (additionals) the rest during transport 17 From raw iron to steel Right after blast furnace tapping: raw iron treatment Desulphurisation with lime Si [S] + (CaO) + [C] → (CaS) + {CO} C Vorteil: Begleitelemente erhöhen Schwefel- aktivität P Mn Major parts already captured within blas furnace slag (additionals) the rest during transport 18 Basic Oxygen Furnace Arrival at the steel works – basic oxygen furnace as major conversion device function? 19 Basic Oxygen Furnace Function Removal of unwanted elements via their reaction with oxygen stemming from o Air or in pure form (→) o Combustion off-gas (CO2 – Boudouard) o Solid oxides Reactions? Products? 20 Basic Oxygen Furnace Function Removal of unwanted elements via their reaction with oxygen stemming from o Air or in pure form (→) o Combustion off-gas (CO2 – Boudouard) o Solid oxides Reactions o „refining“: [C] + O → {CO}; + ½ {O2} → {CO2} o combustion: 2[P] + 5O → (P2O5) o Conversion to slags: [Si] + 2O → (SiO2) [Mn] + O → (MnO) Does that make sense? Oxidation right after reduction? 21 Basic Oxygen Furnace Oxidation of unwanted elements → transformation into gases and slag Iron also oxides, but lower driving force → Technical realisation? Fe C Mn Si 22 Basic Oxygen Furnace Technical development Starting with puddle-furnaces … Manual (!) stirring of the melt under an oxidising atmosphere → ensure intermixing and removal of solid lumps (solidification without lowering the temperature?) 23 Basic Oxygen Furnace Technical development Starting with puddle-furnaces … Manual (!) stirring of the melt under an oxidising atmosphere → ensure intermixing and removal of solid lumps → Increasing liquidus temperature with carbon removal 24 Basic Oxygen Furnace Technical development … via Bessemer/Thomas … (when?) Injection of air through the bottom („Thomasbirne“) ☺ Steel fully liquid → increase hmogeneity = higher performance and lifetime of products ☺ No additional fuel neccessary (why?)  High nitrogen uptake  Acidic refractories meant only usable for low-phosphorous steels 25 Basic Oxygen Furnace Technical development … to the LD-Converter (origin name?) = Basic Oxygen Furnace Basic refractories More flexible with ores Top-blowing of pure oxygen How to produce that? → Advantages/disadvantages? 26 Basic Oxygen Furnace Technical development … to the LD-Converter (origin name?) = Basic Oxygen Furnace Basic refractories More flexible with ores Top-blowing of pure oxygen How to produce that? Advantages/disadvantages ☺ Easier temperature control  Worse intermixing (→) 27 Basic Oxygen Furnace Modern BOF o Top blowing with pure oxygen through water cooled Cu lance → maximum ~ 2300°C 600 Nm3/min o Formation of foamy slag emulsion via CO (increasing reaction surface/interfaces) O2 wassergekühlte Blaslanze 28 Basic Oxygen Furnace Modern BOF o Top blowing with pure oxygen through water cooled Cu lance → maximum ~ 2300°C 600 Nm3/min o Formation of foamy slag emulsion via CO (increasing reaction surface/interfaces) o Bottom injection of inert gas (Ar) to promote mixing o Changing slag composition via additionals Reactions and mechanisms? O2 Water cooled lance tip 29 Basic Oxygen Furnace Compositional changes? Not strictly following driving force (Si – Mn – C – P – Fe) but parallel due to strong intermixing within the slag emulsion (local equilibria) 30 Basic Oxygen Furnace Reactions within the BOF o Effective removal of Si (highest driving force) o Strongly exothermal: Si + O2 → SiO2 -911 kJ/mol → sometimes deliberately start with high Si content in raw iron (how?) to use as heat source C Concentration / wt.% S P Mn Si 0 2 4 6 8 10 12 Time / min 31 Basic Oxygen Furnace Reactions within the BOF o Continuous removal of manganese, „hump“ by re-reduction out of the slag possible C Concentration / wt.% S P Mn Si 0 2 4 6 8 10 12 Time / min 32 Basic Oxygen Furnace Reactions within the BOF o Continuous refining of carbon: first limited by Si removal, towards the end lower chemical potential → how „deep“ decarburisation is pushed depends on final steel grade and cost of iron losses o Also strongly exothermal (see blast furnace), CO2 source! C Concentration / wt.% S P Mn Si 0 2 4 6 8 10 12 Time / min 33 Basic Oxygen Furnace Reactions within the BOF o Slow removal of phosphorous: complex reactions depending on the slag composition → oxidising atmosphere and lime required to stabilise P2O5 (otherwise re-reduction) o P as an important raw material C Concentration / wt.% lime S P Mn Si 0 2 4 6 8 10 12 Time / min 34 Basic Oxygen Furnace Reactions within the BOF Adapting the slag composition: adjusting basicities, activities (and interaction with vessel lining) Ca. 15 t lime for 300 t raw iron Possible downcycling to blast furnace slag 35 Basic Oxygen Furnace Reactions within the BOF Lime additions lead to parallel desulphurisation – can be unwanted → Gases? Temperature? lime C Concentration / wt.% S P Mn Si 0 2 4 6 8 10 12 Time / min 36 Basic Oxygen Furnace Reactions within the BOF o Process autothermal („chemical heating“) → cooling via scrap additions Multiple charges possible 1600 C Concentration / wt.% 1500 Temperature / °C S 1400 P 1300 Si Mn 1200 0 2 4 6 8 10 12 Time / min 37 Basic Oxygen Furnace Reactions within the BOF o Process autothermal („chemical heating“) → cooling via scrap additions o Oxygen enrichment, possible nitrogen contamination (solubility increases with temperature) 1600 C Concentration / wt.% 1500 Temperature / °C S 1400 Effects of nitrogen in steels? P 1300 Si Mn N2 1200 0 2 4 6 8 10 12 Time / min 38 Basic Oxygen Furnace Reactions within the BOF Raw iron Raw steel after ca. 15 min? 1600 4: wt.% Si, C, Mn, P C 1500 3 Temperature / °C 0.075: wt.% S S 1400 2 0.050 0.02: wt.% N P 1300 1 0.025 0.01 Si Mn N 1200 0 0 2 4 6 8 10 12 Time / min 39 Basic Oxygen Furnace Reactions within the BOF Real process conditions o Blow time ca. 15-20 min (incl. Changing oxygen rates, lance distances etc.) o Total time between charges of about 200- 300t ca. 45 min (incl. filling, positioning, scrap charging, analysis, tapping etc.) How to separate slag from raw steel? Getting ever closer to the final product – thorough separation more and more important! 40 Basic Oxygen Furnace Reactions within the BOF Separation via various techniques possible Valves, plugs (incl. detectors), or floats 41 Basic Oxygen Furnace Output blast furnace: Fe – 4.5C – 0.6Si – 0.8Mn – 0.08P – 0.04S (avg. wt.%) conversion slag (wt.%) o 45-53 CaO o 20-31 FeXOY high iron concentration o 11-18 SiO2 (oxidised) → possible recover with blast furnace (recycling) Output basic oxygen furnace: Fe – 0.03C – 0.05Si – 0.30Mn – 0.008P – 0.008S (avg. wt.%) done? 42 From raw iron to liquid steel Adaption of chemical and physical properties in three separate steps (1) Treatment/desulphurisation of raw iron in the ladle (2) Conversion in the basic oxygen furnace (3) Secondary metallurgy Final adjustment before solidification (casting) Whats left to be done, and how to do it? 43 Summary Steel production in the integrated mill o In three steps from BF raw iron to liquid steel: melt treatment in transport, conversion within BOF, secondary metallurgy to finalise o Critical role of elements: phase diagrams for first insights what effect they can have on metallurgical processing, thermo-mechanical treatments and/or ferrous materials Basic Oxygen Furnace: from raw iron to raw steel o Removal/reduction of unwanted elements by oxidation: conversion to gas (refinement of C – CO2 source!) or slag (P, S, Mn, Si etc.) with higher driving force than Fe-oxidation o Top blowing of pure oxygen within basic lining for P-rich raw iron, inert gas bottom injection for mixing, reaction primarily within foamy slag suspension o Process autothermal: exothermal combustion compensates increasing liquidus temperature from C-removal, scrap for cooling Next step to the final (liquid) product → secondary metallurgy 44 Thank you for our attention Questions? 45