2006-08-22
QUESTIONS FOR REHEARSAL
STEEL MAKING
General
Describe the main properties of the commoniron alloy phases in steel (approximate carbon content, if it is soft/hard/brittle, and if it consists of other phases): austenite, ferrite, cementite, pearlite, ledeburite, bainiteandmartensite
Pretreatment of hot metal
Describe the preconditions to carry out de-sulphurisation of hot metal.
Describe how desulphurisation is carried out (describe processes, chemical agents, chemical reactions etc.)!
De-phosphurisation of hot metal:
Explain/discuss the reasons for de-phosphurisation of hot metal.
Explain the preconditions to de-phosphurisation.
Describe (general outline of process, chemical agent’s chemical reactions etc.) de-phosphurisation of hot metal.
Oxygen converter processes
Describe the steelmaking process in the BOF-process (i.e. from scrap charging until slag tapping).
What additions are normally made during a blowing (in the BOF process)?
What are the reasons for these additions?
Which properties are important for the added agents?
Describe the most important parts of top (LD) and bottom (OBM) blown oxygen converters, respectively!
Explain the course of chemical reactions during a converter blow in:
a) the LD process (both slag and metal reactions)
b) the OBM process
The OBM and LD processes differs in a fundamental way by the method how the oxygen is supplied to the metal.
Explain how that affects the oxidation of carbon, manganese, iron, silicon, phosphorus and sulphur
Discuss also the other differences between OBM and LD processes (post combustion of carbon monoxide, lime additions, refractory wear etc.).
The stirring is of fundamental importance in metallurgical processes. Explain how stirring is accomplished in OBM and LD processes, respectively. What will be affected by a better or worse stirring in the processes?
The progress of oxygen converter processes have gone towards combination between the LD and OBM processes, i.e. combine blowing processes. What are the advantages of combined blowing compared with the LD and OBM processes, respectively? Give examples of combined blowing processes!
Scrap based steelmaking
Explain the scrap based process route! (I.e. from scrap to casted steel.)
Explain the physical heat generation in an electric arc furnace (EAF)!
Explain the consequence of raising the electrode in an EAF! (Electric current, voltage, power factor, electrode wear etc)
Which restrictions are there regarding the voltage and power factors during a melting in an EAF?
An important point of view in the EAF-process is to decrease the electrical energy usedDescribe methods to decrease the electric energy need!
What are the advantages/disadvantages to use DRI compared with ”ordinary” scrap?
Explain the use of an oxy-fuel burner!
How can foaming slag be accomplished in an EAF?
Explain the differences between AC and DC electric arc furnaces.
What are the advantages/disadvantages with DC-furnaces? Why does a DC-furnace have lower electrode consumption than an AC-furnace?
Stainless steelmaking
Explain the mechanism of corrosion resistance in stainless steel and explain why a low carbon content is normally preferable in stainless steels!
Explain how to achieve decarburisation with limited chromium losses in AOD-, CLU- and VOD(K)-process, respectively.
Explain how stainless steelmaking was carried out in the EAF before AOD-, CLU- and VOD(K)-processeswere invented.
Describe the main parts of an AOD-converter and CLU-converter, respectively.
Describe how the stainless steelmaking is carried out (decarburisation, slag reduction, desulphurisation) in these processes!
Describe the course of chemical reactions during an AOD-blowing (i.e. the variations of C-content, Si-content, temperature and CRE-index during the blow)!
Explain CRE-index.
Wastes from iron and steel making
Discuss the possibilities and restrictions different processes (blast furnace, oxygen converters and electric arc furnace) have to process different kinds of waste materials (metal oxides, fine-grained materials, Zn/Pb-containing material, oil containing and/or wet materials).
If Zn-containing dust must be recycled in an integrated ore based iron and steel plant, which process is the best suited to take care of the dust (BF or BOF)?
Describe some processes for treatment of dust.
Slag is the largest group of generated waste material in steelmaking.Which fields of applications are there for slag and give examples of different products?
Why is the utilisation degree higher for BF slag than BOF and EAF slag?
Discuss the necessary properties of slag to be utilised externally (i.e. in applications outside of the steel plant)!