CA1123607A - Process for the treatment of molten iron with simultaneous increase of the scrap rate - Google Patents
Process for the treatment of molten iron with simultaneous increase of the scrap rateInfo
- Publication number
- CA1123607A CA1123607A CA328,531A CA328531A CA1123607A CA 1123607 A CA1123607 A CA 1123607A CA 328531 A CA328531 A CA 328531A CA 1123607 A CA1123607 A CA 1123607A
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- calcium carbide
- molten iron
- carbide
- added
- calcium
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Abstract
ABSTRACT
A process for the treatment of molten iron and for increasing the proportion of scrap in a converter by injecting an oxygen containing treating gas which contains calcium compounds characterised in that the treatment gas charged with calcium carbide is injected by means of a lance onto or into the molten iron. This process provides a complete and uniform reaction. The oxidized calcium carbide is a very highly reactive calcium oxide which accelerates metallurgical reactions (desulphurization, dephosphorization) required anyway. In addition, the lime charge can be substantially reduced which shortens the lime dissolution process.
A process for the treatment of molten iron and for increasing the proportion of scrap in a converter by injecting an oxygen containing treating gas which contains calcium compounds characterised in that the treatment gas charged with calcium carbide is injected by means of a lance onto or into the molten iron. This process provides a complete and uniform reaction. The oxidized calcium carbide is a very highly reactive calcium oxide which accelerates metallurgical reactions (desulphurization, dephosphorization) required anyway. In addition, the lime charge can be substantially reduced which shortens the lime dissolution process.
Description
This invelltion relates to a process for the treatment of molten iron and for simultaneously increasing the scrap rate in a ~converter.
Thc acldi.tioll of up to 25 - 30 wt.',' of scrap to pig iron in the convcrter i.s well lcnown. The combustion heat of the ~ccompanying elements c~rbon, mang~nese, ~ilicon and others in pig iron is ~ufficient to nleJ.t dOWII a certain cllargc of scrnp and to r~ise tl-e tem~ernturc to tlle reqnirecl de~rce for nloltcn stoel, _ ,1_ ~ ' '~. ' ' '' ., ' ' ' , .. . .
~Z~7 In certain cases, however, therc :i~ 6rreat intcrest in furtl-ler increasin~ thc pro~ortion of scra~, ~o .a~ to Ina}ce the steel production capacity flexible ancl to adapt it to marlcet ancl prod~lction requirements. In pa-r~iclllar it would be desirable to permit ~rocessing of cxcess scrap which is more reasonably priced than pig iron. Tt would moreover be useful to make BOF-converters less dependent on tl~e pig iron supply, i.e. it should mitiga*e the eifect of breakdowns in the blast furnace operation on steel malcing. The convent:ional oxygen top blo~in~ technique permits the bath temperature in the con-verter to be increased within very narrow limits only.
Moreover, this measure is connected with a high specific cost, because the after-blow causes increased iron losses~
Consequently ~ays and means have been sGught for a long time to impr,ve the heat balance in the converter by adding an agcnt with a high exothermic reaction to such an extent that addition of greater proportions Or scrap becomes possible.
Processes ha~e been proposed for increasing the scrap rate by, for instance, mixing o~ygen wlth fuel gas in special ~ burners and in this way increasin~ the heat balance of the converter. It is also known to preheat andlor ~.elt down scrap with a flame lance, introducing oxidlzable material such as iron, magnesium, calcium, aluminium and others into the -flame to increase the heat supply.
.
It had also been proposed in the past to use calcium-carbide suspended in combustible organic compounds, to replace a part of these fuels and produce e~othermic heat on the surface of the molten metal.
The commoll feature of all these processes known to-date con-sists of either addin~ or supplying to the o~ygen jet n~ter ` leaving the lance separately, by llleans of a ~pecial jet, another ~as, char~ed if neecl be with an oxidizable solicl, in order to develop combustion energy on impact UpOII the Inolter iron, "
To simpliI`y t~le process, it was also ~ror)osed previously to a(3d ca]ci~lnl carbide to the melt in lllmp form durirl~ the blowin~ process. The thermal energy develo~ed by combustion Or 1 kg carbide should in theory be sufficierlt to raise approxima~e]y G k~ iror~ f`ronl room tenlperat-ure to a temperaturc of 1630 C. This high grade of efficiency required to render the addition of carbide economical was, howe~er, not attained in practice. Moreover, increased foaming of the slag causes considerable mal~unction in the course of operation which by far outweigh possible advantages.
The present invention is concerned, therefore, with finding a method ~or treating molten iron and increasillg the proportion of scrap in the converter, preferably in an BOF converter, wllich elinlinates the current disadvantages and uses an easily carried out technique.
~us the invention provides a process~hich involves blowing an oxygen containing treating gas containing calcium compounds, in which the treating gas is charged with calciurn carbide and is in jected by means of a lance either onto the surface of the n~elt or into it. This ensures a complete and uniform reaction The product of the oxidized calcium carbide is a very highly reactive calcium oxide wllich accelerates metallurgical reactions (desulphurization, dephosphorization) required anyway. This pheno~nenon permits the lilsle charge to b~
substantially reduced, thus shortening the lime dissolution process.
A special advantage of the present process is derived from Usillg o~y~en of lrldustrial purity as treat-ing gas, to which calcium carbide can be added in varying amounts without any problem.
Surprisin~ly, it has been found that even finely particulate calcium carbicle can be harldled to~et~ler wit}~ oxygerl up to a tclnperatllre oL` appro~imately 200 C Wit~lout any risk of the carbicle being destroye;~ by oxidatiorl nnd its efficiellcy im-paired thcreby, ;23~
~urt;hcr improvelnents in recent years regardin~ the ~neurnatic transport and introduction of reacti~e constituents gro~lnd as fine as clust into molten iron havc helped to ~chieve control]ed inject:ion by means of oxygen of finely pRrticulate to grarlular ca]cium carbide on its own or togets~er with other constituents into molten iron at given intervals or respectively in specifiéd amounts per unit time, either from above using a lance or by ~neans of jets known per se through the bottom of the converter.
Since the oxygen lances for top blown converters are water cooled, the tenperature of the o~ygen up to the orifice is as a rule approximately 10 Cl The shape of the nozzle causes the oxygen to expand when it leaves the lance 3 cooling it down further on. Consequently heating up of the gas-solid mixture to a temperature at which a reaction between oxygen and calcium carbide could start, is impossible in a regular operation. Combustion takes place when passing between the orifice of the lance and the surface of the metal.
Ignition is cau3ed by the given temperature of e;g, the pig ~0 iron or the steel bath at the point of impact.
To obtain a complete reaction one works preferably with excess oxy~en.
The calcium carbide is preferably injected in the form of industrial o~ commercial calcium carbide, containing approximately 75 to 83~ CaC2, finely ground or crushed.
The grain si~e of the calcium carbidc to be injected and of any other metals or metal oxides which may have been added can vary widely and lie between 0 and 20 mm. HoweYer, a range of 0 to approximately 1.0 mm is preferred.
Besides llsing commercial carbide~ the use of so-called eutectic car~ide, i.e. carbide with a hi~her proportion of calciuln oxide can also have an ad-rantageous effect, irl that an islcreast~d ~ ~ 3~ ~ 7 - 6 - ' proportion of metalllTrgicc~lly effectlve lime (CaO) can be ofrered tocctller wi-th redllced heatillg action, The aalount of calcium carbide to be injecte~ depends both on the proportion of scrap char~ed or respectively the temperature of the Inelt and the composi-tion of the injected carbide, Generally, 5 - 125 kg and preferably 30 - 60 kg calcium carbide are injected for every 1 t molten iron to be treated. These amounts permit an adequate temperature control of the molten iron e~en when a high proportion of scrap is charged. The amount of calcium carbide metered into the oxygen furtherrnore also permits the oxygen concentration in the l~olten iron to be controlled, and adjustment of the o~ygen concentrQtion in narrower limits than with the convent onal process is obtainecl. Controlled calcium carbide injection enables the oxidation of alloying metals to be inhibited, recovery of effective alloying elements as e,~, also aluminium and silicon to be accurately controlled on tapping, or on the other hand the oxygen to be adjusted in such a way that eertain steel grades as e.g, rimming steel or semi-]cilled steel can be east without fla~s.
Other oxidizable inor~ranic eompounds, in partieular silieon carbide may preferably be added to the calcium carbicle and injected and alloyed simultaneously.
~esides these colupounds which supply only thermal energy also such eonlpounds, espeeially metal oxidesj ean be added to the ealcium earbide in aecordance with the process of the illVCntiOII ~hichl due to reaction processes, e~ereise an ~lloyin~ effeet in the steel bat~l. For this purpose preferrably niclcel o~ide ~Ni-sinter), vanadiuTn pentoxide~
ehromiulrl trio~icle or other oxides or ores are used depending `~ on the desired steel grade, ~ecorclirlg to the inventioll, the Inetal. oxides used for allQying can ~e introdl~ced illto the s-teel bath together with thc o~idi.~able irl~r~allic compouTIds and the calciu carbide. The)r call, ho~rever, also be nletered into t~le . ~ . . .
~23Çi~7 oxygen strean~ d with calci~1nl carbide or on thcir own.
The proportion of these compo~mds or ores can range from O to as much as 5O wt.% of calcium o~-de charged and is e5sential1y governed by the steel grade required and by economic conditions.
.
~inally n1etallurgically active s]ag forming compounds Call also be added to the calcium carbide. These include in particular calcium fluoride, boratesj alumina, lime ~nd mi~tures thereof.
The forming of a suitable slag is of importance in so far as the iron concentration, i.e. the proportion of essentially ~e-II-oxide in the slag should be as low as possible. ~n the other hand the nature of the sla~ must be sucll that an essentially free Y.one can form in the region cr the injection stream through which the reaction gases can escape. This prevents gases being retained in thc slag ~hich would cause it to start foamillg as is the case e.g~ when calcium carbide or silicon carblde is added in lumps.
Dcpclldillg on t~e stage of the melting process or the refining reaction or the concentration of impurities e~g. sulphur in the molten pig iron, the treating gas is charged with more or less calcium`carbide, and slag ~oarning compounds if required (charging in stages~. This calcium carbide addition can be increased or decreased continuously; it can, ho~ever, also be carried out at the same level throughout the entire treatmellt tilne.
~inally, the temperature of the molten pig iron is affected by the alnount Gf scrap added to the ch~rge. 1lere an increase in calci~m carbide and possibly n1etal compounds as e~g, silicon~carbide anlong others can quickly control the process.
In case the temperatur( Or the mclt has dropped excessively, it is quickly and relilbly raised by interlnittently addcd , .. :
.. . . . ..
$~2~
~3 .
doses of calcium carbide or rnixtures of cnlcium carbide a.ncl other heat producing additiolls.
The process according to t-he inventio}l for the treatment of nloltcn iron ~ith :increasing the scrap rate injeeting calcium carbide aeting as fuel as well as other oxidizable eonstituents as required, together with the -treatment gas ean also be applied in bottom blown eonverters~
The faet that in this proeess the injected ealeium earbide or the reaetion produets forrning in the 'creatment gas flow through the entire bath from bottom to top ensures a high degree of reaetion. Undesirable impurities in the steel are rapidly brought do-~n to values close to the reaetion zone to the melt takes plaee wi.th close to 100 ~ effieiency.
The process according to the invention is furtherillustrated by the following examples:
~ .
The invention was tested in a series of 11 melt~, All the figures given are mean values.
(a) reference example-~ eonventional n~ethod:
pig iron 0.... ~.......O............... 78.5 t serap ........ ~0.....,.'................ 15 t lime ,............................ ..... 4.5 t liquid yield ,...~.,....t..l....,. 85.5 tfinal sulphur concentrat:ion ..,,.. 0.021 final phosphorus coneentration .... 0.014~o iron yield ... ,~.......... ,............. 91.5 . .
; ' ' ~ 3~
g (~) nlet}lod accorai~g to the illventiorl pi~ iron ....... O ~ .............. 78 . 5 t scrap ............................ 31 t lime ........... -................. ..........2.1 t carbide ........ ,................. ..~ . 2.8 t liquid ~ield .. 0.~............... approx. 102.5 t final sulphur concentration .......... Ø014 c~O
~inal phosphorus concentration ,...... Ø007 ~
iron yield ........................... 95.5 _alnPle 2 The effect of charging the oxygen stream with calcium carbide on the ~e~ oxide concentrations in the slag and the concentration of dissol~ed oxygen in the steel was exanlinec1 in a series of 4 melts.
To a charge of in each case approx. 100 t liquid steel with concentrations of carbon 0.07 ~t sulphur 0.02 ~o ~nd phosphorus 0.015 '~
(a) 41 t scrap were added and 4 t calcium carbide ~ere blown with oxygen onto the melt ~o (b) 21 t scrap were added and blown with oxygen without calcium carbide additio~.
~esult ` The ~e~ o.~cide concelltration in the slag of the n~elts treated with calciuln carbicle was FeO 11 - 14 ~, and ol the nlelts treated only with oxygen: l~`eO 18 - 23 ~.
' " . :' ' ~ .
.
3~7 ~ o --The oxy~;en concentrations before tappin~ were Or a silnilar nature. In tho liquicl steel treated with calci~1m carbide the oxygen COnCelltrati Oll WQS ~-100 - 600 ppm, in the other melts 800 - 1200 ppm.
xamp].e ~
The erfect of the process according to the invention was examined in a series of ten melts in an 110 t converter operatin~ by the BO~ process.
On a~erage 85 t pig iron with phosphorus of 1.6 7~ were eharged and 2S t scrap were added.
~fter a conventional blowing treatment (oxygen charged with 4 ~ calcium oxide ) lasting approx. 15 minutes the eonverter was tilted, partially slag~ed off and appro~.
another 29 t scrap w~re added~ The amount of lime to be freshly ad(led was redllced to 1 ~. The lime was réplaced by eomrnereial calciu~n carbide and on average a total of 5 t calcium car~ide was blown at a rate of 400 kg/min, ~fter a furt]ler 13 - l6 minutes treatmeIlt time, a carbon eoncentration in the range of 0.3~ - o.36 ~o was met; the 7~ sulpllur eoncentration amounted to 0.011 $ and the phosphorus eoneentration was 0.00~ ~o.
Compared with the usual procedure, the char~ing time was increased by only 3 - 5 minutes. The output/h however rose from l46 t/h to 170 t/h, giving an increase o~ 16.l~ $
with improved ~inal phospllorus and sulphur concentrations eompared with the eonventional procedure, Examp~e 4 The haatiI1~ up ef~oct wJIell operating in ~ccorclance with the iIl~Cllt:iOII W.15 exanlirIed Jor 4 n~elts accordin~ to the LD~C -.2;~
process with 1 lo t tap wei~ht. ~fter working cot1ventionally a temperature which was on average too low by 25 C (1580 C) for tlle desired steel grade with approx~ 0,35 $ carbon g was found.
lo correct the temperature the oxygen stream was charged with comlnercial calciulll carbide immedlately after the last temperature nleasurement, The blowing rate was 40 _ 50 kg calcium carbide/min.; after 5 minutes 2.5 - 3 kg calciurn carbide/t steel had been blown.
In this time the average temperature :inorease tras 28.5 C.
The Fe~ oxide concentration of the slag was reduced by a~ average of 4.5 ~ and the iron yield was consequently increased correspondingly.
~n a series of six melts with a tap weight of 110 t, produced by the LD process the lime charge of approx. 4.5 ~ was reduced to ~ 1 ~o of the steel weight. The oxygen stream was charged with a mixture of finely grainecl ca]cium carbide, doloniite and calcium fluoride in a ratio of 100:15:10; the blo~ing rate was 250 kg llixture/min.
The scrap alno-~nt was raised by 15 t to 44 t. The degree of desulphurisation was increased by this measure from an nveragc of 23 ~o to 59 ~.
The F`e~ o~ide concentration in the slag dropped ~~ 12 ~.
_ ~No definitive statemeIlt can be made after this series regard~ g the improYement in service life of the rerractory lining, but in accordance with the kllOWII correlRtiorls at least a 25 ~ improvelllent in the total service lile is anticipate-l.
; ; ' : J
Thc acldi.tioll of up to 25 - 30 wt.',' of scrap to pig iron in the convcrter i.s well lcnown. The combustion heat of the ~ccompanying elements c~rbon, mang~nese, ~ilicon and others in pig iron is ~ufficient to nleJ.t dOWII a certain cllargc of scrnp and to r~ise tl-e tem~ernturc to tlle reqnirecl de~rce for nloltcn stoel, _ ,1_ ~ ' '~. ' ' '' ., ' ' ' , .. . .
~Z~7 In certain cases, however, therc :i~ 6rreat intcrest in furtl-ler increasin~ thc pro~ortion of scra~, ~o .a~ to Ina}ce the steel production capacity flexible ancl to adapt it to marlcet ancl prod~lction requirements. In pa-r~iclllar it would be desirable to permit ~rocessing of cxcess scrap which is more reasonably priced than pig iron. Tt would moreover be useful to make BOF-converters less dependent on tl~e pig iron supply, i.e. it should mitiga*e the eifect of breakdowns in the blast furnace operation on steel malcing. The convent:ional oxygen top blo~in~ technique permits the bath temperature in the con-verter to be increased within very narrow limits only.
Moreover, this measure is connected with a high specific cost, because the after-blow causes increased iron losses~
Consequently ~ays and means have been sGught for a long time to impr,ve the heat balance in the converter by adding an agcnt with a high exothermic reaction to such an extent that addition of greater proportions Or scrap becomes possible.
Processes ha~e been proposed for increasing the scrap rate by, for instance, mixing o~ygen wlth fuel gas in special ~ burners and in this way increasin~ the heat balance of the converter. It is also known to preheat andlor ~.elt down scrap with a flame lance, introducing oxidlzable material such as iron, magnesium, calcium, aluminium and others into the -flame to increase the heat supply.
.
It had also been proposed in the past to use calcium-carbide suspended in combustible organic compounds, to replace a part of these fuels and produce e~othermic heat on the surface of the molten metal.
The commoll feature of all these processes known to-date con-sists of either addin~ or supplying to the o~ygen jet n~ter ` leaving the lance separately, by llleans of a ~pecial jet, another ~as, char~ed if neecl be with an oxidizable solicl, in order to develop combustion energy on impact UpOII the Inolter iron, "
To simpliI`y t~le process, it was also ~ror)osed previously to a(3d ca]ci~lnl carbide to the melt in lllmp form durirl~ the blowin~ process. The thermal energy develo~ed by combustion Or 1 kg carbide should in theory be sufficierlt to raise approxima~e]y G k~ iror~ f`ronl room tenlperat-ure to a temperaturc of 1630 C. This high grade of efficiency required to render the addition of carbide economical was, howe~er, not attained in practice. Moreover, increased foaming of the slag causes considerable mal~unction in the course of operation which by far outweigh possible advantages.
The present invention is concerned, therefore, with finding a method ~or treating molten iron and increasillg the proportion of scrap in the converter, preferably in an BOF converter, wllich elinlinates the current disadvantages and uses an easily carried out technique.
~us the invention provides a process~hich involves blowing an oxygen containing treating gas containing calcium compounds, in which the treating gas is charged with calciurn carbide and is in jected by means of a lance either onto the surface of the n~elt or into it. This ensures a complete and uniform reaction The product of the oxidized calcium carbide is a very highly reactive calcium oxide wllich accelerates metallurgical reactions (desulphurization, dephosphorization) required anyway. This pheno~nenon permits the lilsle charge to b~
substantially reduced, thus shortening the lime dissolution process.
A special advantage of the present process is derived from Usillg o~y~en of lrldustrial purity as treat-ing gas, to which calcium carbide can be added in varying amounts without any problem.
Surprisin~ly, it has been found that even finely particulate calcium carbicle can be harldled to~et~ler wit}~ oxygerl up to a tclnperatllre oL` appro~imately 200 C Wit~lout any risk of the carbicle being destroye;~ by oxidatiorl nnd its efficiellcy im-paired thcreby, ;23~
~urt;hcr improvelnents in recent years regardin~ the ~neurnatic transport and introduction of reacti~e constituents gro~lnd as fine as clust into molten iron havc helped to ~chieve control]ed inject:ion by means of oxygen of finely pRrticulate to grarlular ca]cium carbide on its own or togets~er with other constituents into molten iron at given intervals or respectively in specifiéd amounts per unit time, either from above using a lance or by ~neans of jets known per se through the bottom of the converter.
Since the oxygen lances for top blown converters are water cooled, the tenperature of the o~ygen up to the orifice is as a rule approximately 10 Cl The shape of the nozzle causes the oxygen to expand when it leaves the lance 3 cooling it down further on. Consequently heating up of the gas-solid mixture to a temperature at which a reaction between oxygen and calcium carbide could start, is impossible in a regular operation. Combustion takes place when passing between the orifice of the lance and the surface of the metal.
Ignition is cau3ed by the given temperature of e;g, the pig ~0 iron or the steel bath at the point of impact.
To obtain a complete reaction one works preferably with excess oxy~en.
The calcium carbide is preferably injected in the form of industrial o~ commercial calcium carbide, containing approximately 75 to 83~ CaC2, finely ground or crushed.
The grain si~e of the calcium carbidc to be injected and of any other metals or metal oxides which may have been added can vary widely and lie between 0 and 20 mm. HoweYer, a range of 0 to approximately 1.0 mm is preferred.
Besides llsing commercial carbide~ the use of so-called eutectic car~ide, i.e. carbide with a hi~her proportion of calciuln oxide can also have an ad-rantageous effect, irl that an islcreast~d ~ ~ 3~ ~ 7 - 6 - ' proportion of metalllTrgicc~lly effectlve lime (CaO) can be ofrered tocctller wi-th redllced heatillg action, The aalount of calcium carbide to be injecte~ depends both on the proportion of scrap char~ed or respectively the temperature of the Inelt and the composi-tion of the injected carbide, Generally, 5 - 125 kg and preferably 30 - 60 kg calcium carbide are injected for every 1 t molten iron to be treated. These amounts permit an adequate temperature control of the molten iron e~en when a high proportion of scrap is charged. The amount of calcium carbide metered into the oxygen furtherrnore also permits the oxygen concentration in the l~olten iron to be controlled, and adjustment of the o~ygen concentrQtion in narrower limits than with the convent onal process is obtainecl. Controlled calcium carbide injection enables the oxidation of alloying metals to be inhibited, recovery of effective alloying elements as e,~, also aluminium and silicon to be accurately controlled on tapping, or on the other hand the oxygen to be adjusted in such a way that eertain steel grades as e.g, rimming steel or semi-]cilled steel can be east without fla~s.
Other oxidizable inor~ranic eompounds, in partieular silieon carbide may preferably be added to the calcium carbicle and injected and alloyed simultaneously.
~esides these colupounds which supply only thermal energy also such eonlpounds, espeeially metal oxidesj ean be added to the ealcium earbide in aecordance with the process of the illVCntiOII ~hichl due to reaction processes, e~ereise an ~lloyin~ effeet in the steel bat~l. For this purpose preferrably niclcel o~ide ~Ni-sinter), vanadiuTn pentoxide~
ehromiulrl trio~icle or other oxides or ores are used depending `~ on the desired steel grade, ~ecorclirlg to the inventioll, the Inetal. oxides used for allQying can ~e introdl~ced illto the s-teel bath together with thc o~idi.~able irl~r~allic compouTIds and the calciu carbide. The)r call, ho~rever, also be nletered into t~le . ~ . . .
~23Çi~7 oxygen strean~ d with calci~1nl carbide or on thcir own.
The proportion of these compo~mds or ores can range from O to as much as 5O wt.% of calcium o~-de charged and is e5sential1y governed by the steel grade required and by economic conditions.
.
~inally n1etallurgically active s]ag forming compounds Call also be added to the calcium carbide. These include in particular calcium fluoride, boratesj alumina, lime ~nd mi~tures thereof.
The forming of a suitable slag is of importance in so far as the iron concentration, i.e. the proportion of essentially ~e-II-oxide in the slag should be as low as possible. ~n the other hand the nature of the sla~ must be sucll that an essentially free Y.one can form in the region cr the injection stream through which the reaction gases can escape. This prevents gases being retained in thc slag ~hich would cause it to start foamillg as is the case e.g~ when calcium carbide or silicon carblde is added in lumps.
Dcpclldillg on t~e stage of the melting process or the refining reaction or the concentration of impurities e~g. sulphur in the molten pig iron, the treating gas is charged with more or less calcium`carbide, and slag ~oarning compounds if required (charging in stages~. This calcium carbide addition can be increased or decreased continuously; it can, ho~ever, also be carried out at the same level throughout the entire treatmellt tilne.
~inally, the temperature of the molten pig iron is affected by the alnount Gf scrap added to the ch~rge. 1lere an increase in calci~m carbide and possibly n1etal compounds as e~g, silicon~carbide anlong others can quickly control the process.
In case the temperatur( Or the mclt has dropped excessively, it is quickly and relilbly raised by interlnittently addcd , .. :
.. . . . ..
$~2~
~3 .
doses of calcium carbide or rnixtures of cnlcium carbide a.ncl other heat producing additiolls.
The process according to t-he inventio}l for the treatment of nloltcn iron ~ith :increasing the scrap rate injeeting calcium carbide aeting as fuel as well as other oxidizable eonstituents as required, together with the -treatment gas ean also be applied in bottom blown eonverters~
The faet that in this proeess the injected ealeium earbide or the reaetion produets forrning in the 'creatment gas flow through the entire bath from bottom to top ensures a high degree of reaetion. Undesirable impurities in the steel are rapidly brought do-~n to values close to the reaetion zone to the melt takes plaee wi.th close to 100 ~ effieiency.
The process according to the invention is furtherillustrated by the following examples:
~ .
The invention was tested in a series of 11 melt~, All the figures given are mean values.
(a) reference example-~ eonventional n~ethod:
pig iron 0.... ~.......O............... 78.5 t serap ........ ~0.....,.'................ 15 t lime ,............................ ..... 4.5 t liquid yield ,...~.,....t..l....,. 85.5 tfinal sulphur concentrat:ion ..,,.. 0.021 final phosphorus coneentration .... 0.014~o iron yield ... ,~.......... ,............. 91.5 . .
; ' ' ~ 3~
g (~) nlet}lod accorai~g to the illventiorl pi~ iron ....... O ~ .............. 78 . 5 t scrap ............................ 31 t lime ........... -................. ..........2.1 t carbide ........ ,................. ..~ . 2.8 t liquid ~ield .. 0.~............... approx. 102.5 t final sulphur concentration .......... Ø014 c~O
~inal phosphorus concentration ,...... Ø007 ~
iron yield ........................... 95.5 _alnPle 2 The effect of charging the oxygen stream with calcium carbide on the ~e~ oxide concentrations in the slag and the concentration of dissol~ed oxygen in the steel was exanlinec1 in a series of 4 melts.
To a charge of in each case approx. 100 t liquid steel with concentrations of carbon 0.07 ~t sulphur 0.02 ~o ~nd phosphorus 0.015 '~
(a) 41 t scrap were added and 4 t calcium carbide ~ere blown with oxygen onto the melt ~o (b) 21 t scrap were added and blown with oxygen without calcium carbide additio~.
~esult ` The ~e~ o.~cide concelltration in the slag of the n~elts treated with calciuln carbicle was FeO 11 - 14 ~, and ol the nlelts treated only with oxygen: l~`eO 18 - 23 ~.
' " . :' ' ~ .
.
3~7 ~ o --The oxy~;en concentrations before tappin~ were Or a silnilar nature. In tho liquicl steel treated with calci~1m carbide the oxygen COnCelltrati Oll WQS ~-100 - 600 ppm, in the other melts 800 - 1200 ppm.
xamp].e ~
The erfect of the process according to the invention was examined in a series of ten melts in an 110 t converter operatin~ by the BO~ process.
On a~erage 85 t pig iron with phosphorus of 1.6 7~ were eharged and 2S t scrap were added.
~fter a conventional blowing treatment (oxygen charged with 4 ~ calcium oxide ) lasting approx. 15 minutes the eonverter was tilted, partially slag~ed off and appro~.
another 29 t scrap w~re added~ The amount of lime to be freshly ad(led was redllced to 1 ~. The lime was réplaced by eomrnereial calciu~n carbide and on average a total of 5 t calcium car~ide was blown at a rate of 400 kg/min, ~fter a furt]ler 13 - l6 minutes treatmeIlt time, a carbon eoncentration in the range of 0.3~ - o.36 ~o was met; the 7~ sulpllur eoncentration amounted to 0.011 $ and the phosphorus eoneentration was 0.00~ ~o.
Compared with the usual procedure, the char~ing time was increased by only 3 - 5 minutes. The output/h however rose from l46 t/h to 170 t/h, giving an increase o~ 16.l~ $
with improved ~inal phospllorus and sulphur concentrations eompared with the eonventional procedure, Examp~e 4 The haatiI1~ up ef~oct wJIell operating in ~ccorclance with the iIl~Cllt:iOII W.15 exanlirIed Jor 4 n~elts accordin~ to the LD~C -.2;~
process with 1 lo t tap wei~ht. ~fter working cot1ventionally a temperature which was on average too low by 25 C (1580 C) for tlle desired steel grade with approx~ 0,35 $ carbon g was found.
lo correct the temperature the oxygen stream was charged with comlnercial calciulll carbide immedlately after the last temperature nleasurement, The blowing rate was 40 _ 50 kg calcium carbide/min.; after 5 minutes 2.5 - 3 kg calciurn carbide/t steel had been blown.
In this time the average temperature :inorease tras 28.5 C.
The Fe~ oxide concentration of the slag was reduced by a~ average of 4.5 ~ and the iron yield was consequently increased correspondingly.
~n a series of six melts with a tap weight of 110 t, produced by the LD process the lime charge of approx. 4.5 ~ was reduced to ~ 1 ~o of the steel weight. The oxygen stream was charged with a mixture of finely grainecl ca]cium carbide, doloniite and calcium fluoride in a ratio of 100:15:10; the blo~ing rate was 250 kg llixture/min.
The scrap alno-~nt was raised by 15 t to 44 t. The degree of desulphurisation was increased by this measure from an nveragc of 23 ~o to 59 ~.
The F`e~ o~ide concentration in the slag dropped ~~ 12 ~.
_ ~No definitive statemeIlt can be made after this series regard~ g the improYement in service life of the rerractory lining, but in accordance with the kllOWII correlRtiorls at least a 25 ~ improvelllent in the total service lile is anticipate-l.
; ; ' : J
Claims (17)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for the treatment of molten iron to increase the proportion of scrap which can be used in a converter, comprising injecting a treatment gas containing oxygen and calcium carbide by means of a lance onto or into the molten iron.
2. The process of claim 1, in which the treatment gas charged with calcium carbide is injected by means of jets through the bottom of the converter.
3. The process of claim 1 wherein the treatment gas further includes at least one of an alloying metal oxide and a metallurgically active slag forming compound.
4. The process of any one of claims 1, 2 or 3, in which oxygen or gaseous compounds containing oxygen are used as treatment gas.
5. The process of any one of claims 1, 2 or 3, in which the calcium carbide used is commercial calcium carbide.
6. The process of any one of claims 1, 2 or 3, in which the calcium carbide used is eutectic calcium carbide.
7. The process of any one of claims 1, 2 or 3, in which 5 - 125 kg, calcium carbide are injected for every 1 t of molten iron to be treated.
8. The process of any one of claims 1, 2 or 3, in which 30-60 kg calcium carbide are injected for every 1 t of molten iron to be treated.
9. The process of any one of claims 1, 2 or 3, in which other oxidizable constituents are added to the calcium carbide.
10. The process of any one of claims 1, 2 or 3, in which compounds exercising an alloying effect in the steel bath are added to the calcium carbide and any other oxidizable constituents added thereto.
11. The process of any one of claims 1, 2 or 3, in which metallurgi-cally effective slag forming constituents or metals which are converted to slag forming constituents by combustion or melting, are added to the calcium carbide.
12. The process of any one of claims 1, 2 or 3, in which a propor-tion of oxidizable constituents is added and varied during the treating process within the range of 0-50 wt. % relative to the calcium carbide.
13. The process of any one of claims 1, 2 or 3, in which the grain size of the compounds to be introduced is in the range of 0-20 mm.
14. The process of any one of claims 1, 2 or 3, in which the grain size of the compounds to be introduced is in the range of 0-1.0 mm.
15. The process of any one of claims 1, 2 or 3, in which the addi-tion of calcium carbide, is carried out stepwise as a function of the progress of the refining reaction.
16. The process of any one of claims 1, 2 or 3, in which the addi-tion of calcium carbide is made intermittently as a function of the temperature of molten iron.
17. The process of any one of claims 1, 2 or 3, used for controlling the temperature of iron melts in a converter.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA328,531A CA1123607A (en) | 1979-05-28 | 1979-05-28 | Process for the treatment of molten iron with simultaneous increase of the scrap rate |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA328,531A CA1123607A (en) | 1979-05-28 | 1979-05-28 | Process for the treatment of molten iron with simultaneous increase of the scrap rate |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1123607A true CA1123607A (en) | 1982-05-18 |
Family
ID=4114302
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA328,531A Expired CA1123607A (en) | 1979-05-28 | 1979-05-28 | Process for the treatment of molten iron with simultaneous increase of the scrap rate |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1123607A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115261546A (en) * | 2021-04-30 | 2022-11-01 | 宝山钢铁股份有限公司 | Method, system, apparatus and medium for determining the most economical scrap ratio in converter steelmaking |
-
1979
- 1979-05-28 CA CA328,531A patent/CA1123607A/en not_active Expired
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115261546A (en) * | 2021-04-30 | 2022-11-01 | 宝山钢铁股份有限公司 | Method, system, apparatus and medium for determining the most economical scrap ratio in converter steelmaking |
| CN115261546B (en) * | 2021-04-30 | 2024-05-14 | 宝山钢铁股份有限公司 | Determination method, system, equipment and medium for most economical scrap ratio in converter steelmaking |
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