The following is an abstract from the book of Mr. David A. Hansen
"Raw steel is saturated with oxygen in the form of both
dissolved gas and as iron oxides.The oxygen can combine with
carbon,also dissolved in liquid steel to form carbon monoxide.The
reaction causing violent boiling during the pouring and solidification
process.By adding an oxygen scavenger such as silicon to the liquid
steel before it is poured,the excess oxygen can be removed as slag.The
resulting material doesnot boil during pouring and cooling,thereby
producing a more homogeneous"killed" steel.Such steels are cleaner and
contain fewer defects than "unkilled" or "wild" steels.ASTM A106
Pipe,A105 forgings and A516 plate are examples of killed carbon steel
products.Cast carbon steel products are also killed,eventhough typical
ASTM specifications for casting do not mention the requirement.
Killing with an oxygen scavenger such as silicon is the
primary method of deoxidation.A less common method is vaccum
degassing,which is usually a secondary measure,employed when very
clean steels are required.Vaccum degassing not only assists in
controlling oxidising gases such as oxygen and carbon dioxide,but will
help to limit non-oxidising gases such as Nitrogen and Hydrogen.
Steels killed with a combination of silicon and aluminum or
aluminium alone leave a fine austenitic grain size.They are preferred
for applications requiring low temperature toughness;ASTM A 516
(plate) is an example.Such steels are usually described in ASTM
specifications as being made to "fine grain practice".Although ASTM
specifications for steel products usually do not indicate a
requirement for aluminium content.Steels killed with aluminium will
have aluminium perecentage in the range of 0.02 to 0.05 wt.
perecentage."
Regards,
Sunil
On Jun 15, 3:18 pm, limesh M <limes...@gmail.com> wrote:
> Dear All,
>
> I have two more doubts , wether we are adding Si and Al in its pure form or
> some other compounds form which contains Si and AL abundantly?Are we
> performing killing operation after making steel(ie, First steel making
> ,second killing operation) or during steel making process everything
> happening(ie, steel making and killing happening at the same time with same
> process)?
>
> Thanks and Regards
>
> On Tue, Jun 15, 2010 at 3:19 PM, Prabhu Kumar L <
>
>
>
> l.prabhuku...@saipem-india.com> wrote:
> > Dear Limesh,
>
> > Silicon & Aluminum are called as deoxidizing elements, which will be
> > added during steel making process for deoxiding and grain refining
> > purpose. Based on the need for end product it can be added together or
> > individual element.
>
> > Killed steel: De-oxidation or killing is a process by which strong
> > deoxidizing element is added to the steel to react with the remaining
> > oxygen (oxygen used of melting purpose) in the liquid bath to prevent
> > any further reaction between carbon and oxygen. Si & Al are high
> > affinity for oxygen and hence produce oxides such as Al2O3 & SiO2 which
> > will be removed from top of the steel ingot. This would eliminate the
> > carbon boil (CO2, CO) and killing the heat and hence the required % of
> > Cabon is retained in the steel.
>
> > Basically pure Oxygen is used for purpose of steel making process which
> > is called basic oxygen furnace.
>
> > Si Killed steel: This type of steel shall have coarse grain structure
> > (grain no. 1 to 5) and will not react for grain refinement.
>
> > Al Killed steel: This will act as deoxidizing and grain refinement as
> > well and then the structure will be fine grain ie. grain no. 6 & above.
> > Al will react with Nitrogen to form aluminum nitride to initiate the new
> > grains at grain boundaries and hence more grains will be formed ie. fine
> > grains. For notch toughness requirements, steel shall have fine grain
> > size and hence it will be treated with Al.
>
> > Si & Al killed steels: This type of steel called silicon killed, fine
> > grain. The later is achieved by addition of Al.
>
> > Hope it clarifies.
>
> > Regards,
>
> > L. Prabhu kumar,
>
> > Sr. Principal Engineer,
>
> > Equipments & Materials Dept.,
>
> > Saipem India Projects Limited,
>
> > Nungambakkam High Road, Chennai - 600 034, India.
>
> > Tel:+91 44 43906588, Ext.: 588, Fax:+91 44 66840345,
>
> > Mobile Ph. No.: +91 9003010978.
>
> > -----Original Message-----
> > From: materials-welding@googlegroups.com
> > [mailto:materials-welding@googlegroups.com] On Behalf Of limesh M
> > Sent: Tuesday, June 15, 2010 2:05 PM
> > To: Materials & Welding
> > Subject: [MW:5599] Silicon&Aluminium Killing
>
> > Dear All,
>
> > What is meant by Silicon&Aluminium killing of steel?Is there any
>
> > significant difference between both process and resulting quality of
>
> > material like grain size and other metallurgical property?
>
> > Thanks and Regards
>
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