MP415 Theory

Thermodynamic considerations of Fe-Mn alloys

• reduction of higher Mn-oxides to MnO is exothermic

• C-reduction of MnO to Mn highly endothermic and thermodynamically unfavourable

• MnO reduction substantially completed in liquid slag in contact with solid C but maintains less than 10e-17 pO2 levels at 1400 ºC

Thermodynamic considerations of Fe-Cr alloys

• endothermic reduction of both Fe and Cr oxides from chromite spinel

• partial chromite dissolution into liquid slag as both Cr2O3 and CrO by CO reduction from MgO.Cr2O3 under 10e-14 pO2 levels at 1400 ºC

• liquid phase mass transfer of oxides is required to effect reduction; proximity of solid C with liquid oxide under 10e-15 pO2 levels to produce alloy between 1400-1600 ºC

reverbatory furnace

• long flat bath

• 1200 ºC

• charged one end

• heated by burner at one end

• slag tapped from opposite end

• matte tapped from sides

complicatins of Cu smelting

• iron sulphide soluble in matte

• copper oxide soluble in slag

• richer copper matte means more copper oxide in slag

magnetite problem in Cu smelting

• solid magnetite makes slag viscous

  • inhibits efficient separation

  • Cu entrainment

• solid magnetite denser than matte and slag

  • tends to settle and build-up, reducing production capacity

• magentite combines with other oxides (eg. Cr2O3) to produce solids of densities between matte and slag

  • form false bottom which obstructs separation

minimization of magnetite formation

• high temp increases solubility of magnetite in liquid slag

• avoid using recycled converter slag and over-roasted feed

converting of copper matte

• matte from smelting charged to Peirce-Smith converter to produce blister copper and slags

• molten matte oxidized via blowing hot air through tuyeres

  • removes iron, sulphure, other impurities and produces metallic copper

• slag forming: FeS oxidized to FeO and SO2, resulting in molten matte containing Cu2S and trace FeS, and slag containing metal-oxides

• copper making: sulphur defficient Cu2S forms as Cu2S1-x; subsequent air blowing causes second liquid phase to appear; sulphide phase disappears

uses of PGMS

auto catalyst; jewellery; electronics

ironmaking

reduction of Fe oxide

steps in BF

1. deulsphurisation

2. pre-reforming

3. steam reforming

4. shift conversion

5. PSA

ironmaking steps

reduce iron ore to iron, melt iron

steelmaking steps

remove unwanted impurities, alloy wuth wanted elements, cast steel into semi finished shape

iron from BF

pig iron, not useful due to high carbon content

steelmaking process principle

oxidation of impurities and formation of slags as mechanism for refinement

removing Si in steelmaking

• Si hot metal removed by injecting oxidising agent like mill scale

• accompanied by lime to help produce neutral slag

• soda ash also used

removing sulphur in steelmaking

lime, calcium carbide, magnesium commonly used desulphurising reagents

removing phosphourous in steelmaking

• done under oxidising conditions and in presence of highly basic slag

• all Si must be removed first

• if basicity falls, P reverts back to metal phase

• activity of P2O5 decreased using strong and excess external basic flux

primary property of stainless steel

corrosion resistance due to addition of Cr

austenitic stainless steels

• Ni containing

• most common

• excellent corrosion resistance

• suitable for wide range of applications

• non-magnetic

duplex stainless steels

• mixed ferrite-austenitic crystal structure

• higher levels of Cr, lower levels of Ni

• contains nitrogen

• high strength and good corrosion resistance

• weldable

ferritic stainless steel

• plain Cr steels but with low C levels

• cant be strengthened by heat treatment

• poor weldability with exception of utility grades

martensitic stainless steels

• plain Cr stainless steels

• can be strengthened by heat treatment

making ss: AOD

• low gas content

• low S

• high yield

making SS: CLU

• bottom blowing with oxygen-steam mix

• high Cr slag formation

• high Si consumption for reduction

• high hydrogen content

making ss: combined blowing

• bottom and top blowing with O2

• lime injection

• post combustion

• very high rate of scrap use