10208-15101387124325Secondary Steel Making Overview

8/3/2019 10208-15101387124325Secondary Steel Making Overview

1/13

econdary steel making

econdary steel making: Overview

n completion of primary steel making (either in the Basic Oxygen Furnace or Electric Arc Furnace), the molten steel is 'tapped'to a ladle and transported to the casting facility. While in the ladle, the steel may be subjected to a number of differenteatments, such as composition adjustments, stirring, degassing and reheating. Collectively this stage in the overall steel makingocess is called secondary steel making

econdary steel making module - outline

Where secondary steel making fits in the overall production process.What secondary steel making is all about - description of bits of plant and what they do.Simulation exercise to convert a ladle of steel from BOS/EAF at a given composition and temperature to one of three specifiedmpositions at a temperature and time ready for casting.

Detailed exercises ondeoxidationdesulfurizationclean steelsdehydrogenationdecarburizationalloy additionreheating

equence of stages in the production processelow are some of the individual stages involved in steel making Place them in the correct sequence starting top left.

econdary steel making simulationthis simulation you will play the role of plant metallurgist in charge of secondary steel making operations. You will take chargea 250 tonne ladle of molten steel from the Basic Oxygen Furnace (BOF), and attempt to deliver it to the appropriate caster at

e specified time, composition, temperature and inclusion content (cleanness). You should also aim to complete the simulationminimum processing cost.

this simulation you will play the role of plant metallurgist in charge of secondary steel making operations. You will take chargea 250 tonne ladle of molten steel from the Basic Oxygen Furnace (BOF), and attempt to deliver it to the appropriate caster at

e specified time, composition, temperature and inclusion content (cleanness). You should also aim to complete the simulationminimum processing cost.

le:///D|/reform%20of%20processes/steel/Secondary%20steel%20making.htm (1 of 13)2008/12/14 06:16:03 .


2/13




3/13




4/13




5/13


here are four different steel grades from which to choose, each requiring a different processing route. As a relativelyndemanding grade, a general purpose construction steel for beams and columns is recommended for novice users. A TiNbtra-low carbon (ULC) steel for automotive strip requires different processing in order to remove carbon. A line pipe steel for oil

nd gas distribution is a much more demanding grade as it requires very low levels of sulfur and hydrogen. Finally, a heat-eatable medium-carbon CrMo engineering steel provides an example of a more highly alloyed grade.



6/13


o achieve your objectives, you will need to make decisions based on alloy and slag additions, stirring, vacuum degassing andheating. The sequencing, timing and quantity of additions and applications of stirring, degassing and/or reheating practices will critical to the successful completion of the simulation.

t the end of the simulation, the user is given feedback on whether the composition, temperature, inclusion level and deliveryme were within the specified values, together with the total operating cost.

econdary steel making operationsecondary steel making involves some of the following options. The selection of which are available in any particular steel

aking shop depends on the types of steel being made and the availability of space within the factory.

*Stirring*Lance1. Bottom porous plug2. Electromagnetic Stirring (EMS)*Ladle furnace*Ladle injection1. Powder2. Wire*Degassing1. Tank Degasser

2. Stream Degasser3. RH Degasser4. DH Degasser*CAS-OB*AOD

eel grades used in simulation

his page provides some information about the steel grades used in the secondary steel making simulation.

niversal beams for building construction



7/13


icrostructureerrite + ~15% Pearlite, mean grain size 6.6m.

X200

ypical Composition C 0.14

Si 0.26Mn1.22P0.019maxS0.018maxAl0.022Nb 0.033

echanical PropertiesS 429 MPaTS 537 MPaEl 25



8/13


Nb ultra-low carbon (ULC) steel for automotive strip

icrostructure

ypical CompositionC 0.003Si 0.21Mn 0.75P 0.01maxS 0.012maxNb 0.01Ti 0.01

echanical PropertiesS 180-280 MPaTS 310 -375 MPavalue 0.16 - 0.2

El 34 - 40

ne pipe Steel

pes carrying gas or oil require good weldability and a high toughness to withstand cracks. As higher capacity pipes have led toe development of steels with higher yield strength. Deep (170m) water usage requires heavy-wall pipes to withstand buckling,hile low temperature conditions (e.g. Alaska, Russia) require special toughness. The transport of sour gas and oil demandseel with resistance to hydrogen-induced cracking and corrosion.



9/13


ypical CompositionC %Si %Mn %P %S07 0.18 1.05 0.012max 0.003max

echanical Properties X65S 448 MPaS 530 MPaEl 23.5

ngineering Steel

medium carbon, heat treatable steel for applications requiring high strength in combination with toughness, such asmponents for engines, drives, equipment, transmissions, and tools, etc.

ypical CompositionC 0.415Si 0.4Mn 0.75P0.035maxS0.035max

Al0.0225Ni0.3Cu0.35Cr1.05Mo 0.225

echanical PropertiesS 1250 MPaTS 1450 MPaEl 2

eoxidation: Overview



10/13


eoxidation is one of the most important processes in secondary steel makingearning Outcomes for this Sectionfter completing this module, you should be able to:

Explain why the control of oxygen is importantDescribe the chemical reactions, thermodynamics and kinetics for the removal of oxygen from liquid steelExplain the interactions between liquid steel, slag, refractories and the atmosphere that underpin the control of the oxygenntent of steel

Apply this understanding to the control of oxygen content in a simulation of the secondary steel making processentify the origins of oxygen in steel

Why deoxidize?

he oxygen content of liquid steel in the ladle at the start of the secondary steel making process is 400-1000 ppm (0.04 - 0.1%).he solubility of oxygen in liquid steel is 0.16% but in solid steel it is only 0.003%.herefore, steps have to be taken to reduce the oxygen content (deoxidize) of the steel before it solidifies in order to preventowhole formation during casting and a porous product being created or large quantities of FeO being precipitated.

ources of oxygen

xygen enters the liquid steel in a number of different ways.

Which of these sources of oxygen do you think is the dominant one?

educing oxygen content

he addition of a strong oxide forming element is the most commonly used method of reducing the oxygen content of liquid steel.se the Ellingham diagram to help you decide which of the following may be suitable (cheapest) choices for this.



11/13


eoxidation reactions

luminum, silicon and manganese are the most common deoxidisers used in steel making The chemical reactions associatedith their use are:

licon and manganese are often used in conjunction with one another.

B.

Square brackets [] denote component present in molten steel;Parentheses () denote component present in slag;



12/13


Thus [Al] represents aluminum in molten steel but (Al2O3) refers to aluminum oxide in slag;Temperature (T) is on the Kelvin scale.

he reference state for the solute metal activities in all the thermodynamic values listed is the 1% solution, that is the values oftivity and mass % are about equal for low-alloyed steels (see Table I below).

ffectiveness of deoxidizers

quilibrium concentrations of dissolved oxygen under different concentrations of manganese, silicon and aluminum

eel cleanness

here are a variety of sources of inclusions:

indigenous (small):deoxidation product and MnSexogenous (large)reoxidation (reaction with air or slag)

entrainment of slageroded refractories

clusions are formed by chemical reactions (deoxidation, reoxidation and precipitation) or by physical conditions (turbulance orear).



13/13


ffect of inclusions on downstream processing and properties and performance

ost inclusions have a detrimental effect on properties. Solid oxides (alumina or certain calcium aluminates) can cause nozzleockage during continuous casting and disrupt the process and have to be burnt out. Some inclusions can cause cracking andfects, slivers and delamination in rolled products and also fracture during hot/cold forming and wire drawing.

eoxidation: Summary

aving completed this section, you should be now able to:

Explain why the control of oxygen is importantDescribe the chemical reactions, thermodynamics and kinetics for the removal of oxygen from liquid steelExplain the interactions between liquid steel, slag, refractories and the atmosphere that underpin the control of the oxygenntent of steelApply this understanding to the control of oxygen content in a simulation of the secondary steel making processIdentify the origins of oxygen in steel

eference :Web site http://ilsap.matter.org.uk/

ack
http://ilsap.matter.org.uk/http://ilsap.matter.org.uk/

10208-15101387124325Secondary Steel Making Overview

Documents

Transcript of 10208-15101387124325Secondary Steel Making Overview