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Patented Apr. 5, 1949
Wilhelm Ekmanland Giista Erik Hildebrand
. Hildebrand, Fagersta, ‘Sweden
No Drawing. Application June 22, 1945, Serial
‘No. 601,070. In Sweden July 10, 1944 ‘
= 4 Claims.
(C1. 75-51)
gestions of solving this problem have already’been
made earlier. For 1 example, it has been sug
> 'gested to effect the blowing with an oxidizing, gas
There is a clear difference in certain ‘properties
between acid Bessemer or Thomas‘s'teel produced
a in a converter (hereinafter called converter steel),
von the one hand, and steel produced according to
other methods,- e. g. Martin-steel, on~theiother
hand. It has appeared from comparative tests
that the higher nitrogen content of the converter
steel occasions this difference in the properties
also in steel with the same chemical analysis of
the other constituents. The high nitrogen con
tent depends on the method of production. Of
course, ‘a strong absorption of nitrogen takes
place in the process as hitherto usually carried
out when the air current is pressed through the
steel at the blowing. This is clear from nitrogen
analyses showing the following values: Martin
- mixture with low nitrogen content,- or to bring
' the melt to boil by adding oxidizing matter after
?nished or almost ?nished blowing whereby the
‘ nitrogen content would be reduced.
The nitrogen content of a steel which'is ‘in
-‘ equilibrium with a gas phase, is directly propor
tionalwith the square root of the partial pressure
of the nitrogen in the gas mixture. In order to
‘ prevent or delay the absorption of nitrogen in the
steel by changing the composition of the gas phase
‘ or simply obtain ‘a lowering of the nitrogen con
tent of ‘the steel from> an earlier higher-value
(denitratiom‘ it. is, thus, necessary to lower the
nitrogen content of the gas mixture. In the gas
?owing through the steel in the converter at
nitrogen, converter steel
0.010-0.030% nitrogen.
normal blowing the nitrogen content lies at about
The special properties which the high nitrogen
‘70%. In order to obtain a denitration the aver
age content must vbe very much lower. vAt con
content gives the converter steel over e. g. Martin
steel, are for example: greater strength (about '7
kgs./mm.2), higher yield limit, greater ageing
tents between the normal one (about 70%) and
the one necessary for the denitration the absorp—
tion rate for the nitrogen is reduced more and
(are also in?uenced by the nitrogen content. 25 more with sinking nitrogen content.v
Under certain circumstances, e. g. in the produc
As already mentioned, it is known that a low
‘ partial pressure for nitrogen in the gas phase
tion of some kinds of tool steel, automatic steel,
can be obtained by in?uencing the composition
tubes and railway rails, some of these properties
of the blast air admitted into the converter prior
might be desirable. However, as a'rule they are
not desirable. In the normal production of mere; 30' to the blast contacting the steel, which’ can be
e?ected e. g. by enriching the blast air with
chant iron the high nitrogen content of the con
verter steel is most often detrimental, particu
larly with regard to the fact that-the nitrogen
- The object of the present invention is to in?u
liability, and greater hardness and brittleness
after cold treatment. The hardening‘properties
causes a hardness and brittleness of the steel after
‘ ence the composition of the gas phase not until
cold treatment which is greater than of other
steel, e, g. Martin-steel, after ‘the same degree
of cold treatment; this has appeared to be a great
disadvantage for the converter steel, inter alia
in cold-drawing of wire and deep-pressing of
it has contacted the steel by adding an oxidizing
agent, e. g. iron ore, in the converterone or more
times in the course'of the blowing. "However, in
sheet metal.
order that a denitration or at least a considerable
delay of the nitrogen absorption shall be obtained
40 by such addition it is necessary that according to
However, it has become apparent that‘ a con
verter steel, produced with a lower nitrogen con
the invention the supply of the blast air or of
the‘ blast air gas mixture at least after the addi
tent than normally, in the way according to this
invention does not show the said speci?c proper
ties but is completely comparable with e. g. a
prime Martin-steel.
‘tion is arranged in such a way that the blast air
> passes only through a certain part of the melt
The problem of lowering the nitrogen content
of the converter steel has on a larger technical
scale hitherto been solved in such a way that
after finished blowing the converter steel has been
conveyed to another steel production furnace,
generally an open hearth or electric steel furnace,
and been subjected to a further re?ning in the
said furnace. Among other things a lowering of
the nitrogen content has been obtained in this _ '
second step of the duplex process.
It would, of course, be of great economical im
whereas the other part is not subjected to the
. direct in?uence of the blast air or of'the blast air
gas mixture.
Several methods of e?ecting a partial [blowing
through according to the invention are possible.
In a converter provided with the bottom hitherto
used this blowing through is obtained by such
. tilting of the converter that the larger part of the
. meltlies on the furnace wall and only a smaller
' ‘part is in contact with the furnace bottom and
thus is flowed through by the blast air. It'may
also be proceeded in such a way that the blast air
is admitted only through part of the furnace
bottom or through the wall of the furnace.
portance if such a duplex process could be avoided
By addition of oxidizing agent substantially
and a steel with low nitrogen content could be
produced directly in a converter. Various sug 60 silicium, manganese, carbon and iron and in a
demandzwcanl: -be covered; according to earlier
known .methods, blast:vv air being admitted also
basic methodalspphosphorusz-areioxidized. . Only
in the'acar-b‘on oxidation the reactioniproduct is a
gas, by the supply of which to the gas phase a
reduction of the partial pressure of the remain
above the surface of the bath, 1. e. by blowing in
1?an oblique direction or via special twyers in the
furnace walls. This can also be effected by ad
w'mi'ttingf'bla's’t.~'air.;lto"the steel bath at such a low
ing components, among themthat of the nitro-‘
gen, can be obtained. It’is‘antadvaintageous, al-'
though not determinant factor‘o‘f'th'e process that
‘ ‘depth ben'e'athi‘ts surface that the oxygen of the
blast air has ‘no time to be consumed during the
1-=passage1through" the steel bath. The oxygen
the contents of other substances than carbon and
iron are held as low as caniberde'em'edfsuitable
from other points of view. For theiri*reaction; 10 -.=lwhi'ch'i;inisome of these ways is admitted above
the surface of thesteel bath, partially combusts
products are not included in the gas phase,,and
,itnerormed carbon monoxide within the converter
thus they do not contribute ‘to lowering 'the ‘par
tial pressure of the nitrogen. Particularly ‘in the
and gives ‘a su'?icient heat quantity for the above
acid Bessemer method it is moreover :desiralble, : mentioned reduction.
By the method according to the invention a
although not necessary, that the contents of these
converter ‘steel can- be. produced-.whichthas the
. substances are low as thereby the boiling which
a~~condition for the denitration or the delay-of wsame-properties asva ‘Martin-steel of thecorre
:sponding- analysis. HAt *tests made ' it. has been
the nitrogen absorption, more quickly gets into
spossible to ?reducesthe :vnitrogen-content ofthe
1 working-orderand its intensity becomes stronger.
At addition of oxidizing agent at normal blow-;-, converter steel torsuch values as are character
wing, i.‘ e.-when. the blastx-air ?ows practically
through the whole melt; no denitrationv is; ob
»itained'in spite of the addition, possibly only a
. :istic of normal ‘Martin-‘steel.
. The method according to the invention “camiof I
~ course, be used with. ‘advantage :also in such a
. v:slight reduction'of .the nitrogen absorption rate. ~: method inwhichtan oxidizing gas mixture poorer
. The explanation’of- it is that the volume of the, :; in nitrogen ‘is ‘blown *through instea-dof air.
:f'carbon monoxide ‘formedper .unit of time-at'the
I ‘oxidation . is
slight‘ in’ comparison vwith
Having/now described» ouriinvention; what we
-,claim ‘as. new rand-desire "to secure by Letters
:volumeof'the blastairadmitted to thesteel bath
: :Patentis:
.roxide formed: ‘thereof. 1 .The lowering- of the
.-1 1; .In'atmethod of producing steel? by‘ blowing a
metal melt in'a converter with-a continuous'blast
, partial .pressure'of the :nitrogen' in‘ the gas phase
. of a'i-gasli-containing :air ‘but ‘being otherwise. free
t rthen ‘becomes too small to considerably in?uence
“ ‘theinitrogen content of. the steel. Consequently,
yanv already known suggestion :of- lowering e» the
a o?-nitrogen-compounds, ‘the steps. of. adding to. the
melt in the converter prior .tor‘the scom‘pletion-bf
“the. blowing, a nitrogen-free oxidizing agent‘, “and
. ,duringthe ‘same time :and 0f .the f'carbon'mon
vrnitrogencontent at Thomas blowingvbyf‘ore ‘addi-s » ethent‘continuing the blowing without interruption,
:tion. during, the ~ dephosphorizing'period does not
*while retaining the entire melt in ethenconverter,
"bring" about: any considerablexlowering of‘ the
pnitrogen‘v content.
v.However,- when theaddition of the “oxidizing
agent is combined with a'partial'blowing through
.-in§ such a‘manne'r that-the gas. flows through-part
.-of~lthemelt-onlyvsosthat ?nal oxidation, withxsi
. .‘multaneousL denit-ration, is ‘eifectedby the added
oxidizing agent, the ‘part 'of’ the'melt traversed by
~~the~blast§gas after addition‘of .the oxidizingagent
" according to the invention things are --di?ferent,
:‘being proportioned Eto ‘maintain a su?icient rate of
‘ .for in this case two oxidizing {processes which are
:vrdi-?erent but which merge :in ‘one another, will
' ‘take place in the ‘melt.
: oxidation.
Part of the melt is oxi
- 2.-=-A~m'ethod-asclaimed‘inclaim Lin which: the
w‘dized by blast air'as well as by the specially added ,1 blast gas is air.
' oxidizing. agent. :In another part through which
- l3.-.-A-met;hodsas claimed in vclaim 1-' in whichthe
.xblast gas isanair-gas mixture.
the blast air does not flow, the oxidation is- caused
substantially by the specially‘ added oxidizing
4.2-1 A method as claimedin ‘claim 1 ‘in which ‘iron
iniagen't. There is, of course, nosharp limit-be
‘ore is used as 'an oxidizing agent.
tween these-parts.
lnqthe ?rst mentioned part of the vmelt the
..;nitrogen content'of the "gas phaseis ‘relatively
‘high, and there are thus factors existent :to
render the. absorption of nitrogen‘feasiblea ‘In
The i'follo'w‘ing references are of 'reco'rd‘in the
1-the vother part ofthe melt thei'gasphasezsubstan- -,
Thus deni
:tration: can take ‘place'in the said phase. .In
.1. order-‘to 'obtain low nitrogen contents it should
?le of this patent:
' tially ‘consists of ‘carbon monoxide.
melt to which no blast air is ‘admitted, is pro-7
. portionally . large.
‘ ‘ ' Number
- consequently be seen to it that that partofthe
However, the other part in
4. 51,401
‘ Date
‘ {Bessemer ___'__'____~__ Dec.75, 1865
' Phillips _______ __'.__._ Feb.» 9, 1869
which the blast air passes, must not be too small,
Reese ____________ __~J-u1y 24, I877
’ >McDOn'ald _____..__._; Nov. "6, 1883
- either, because in- such a case the oxidation rate
’ Sherk et‘aL _._' ____ __'Féb. ‘4,1896
Brassert -_- ________ __ "June 3,1941
; becomes too ‘low. .‘Moreover, .as regards the
..‘specially added oxidizing agent its oxidizing in-r 65
.‘=fluence ‘is-reduced if vthatagitation of the melt
» which is caused by the blast air fails to-‘come- on.
‘.At theme of someoxidizin'g agents, e. g.xiron
- tore, considerable heatiquantities are required .for
".fl'ihe :reduction 1 of the oxidizingv agent. ' , 1This...heat
v'Lellep _____- ______ __- Nov. 9, ;17943
I 2,390,346
'iBayer ~__~___g-______-__g Dec. 4,1945
...'I-'l'ie*Journa-l ‘of: theeIron‘ ‘and Steel'rInsti'tute
LCBritishl- yo'lumeCVILNo. 1,1923, pages-‘665, 1666.
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