JP3870627B2 - Method for producing high phosphorus extra low carbon steel - Google Patents
Method for producing high phosphorus extra low carbon steel Download PDFInfo
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- JP3870627B2 JP3870627B2 JP28370299A JP28370299A JP3870627B2 JP 3870627 B2 JP3870627 B2 JP 3870627B2 JP 28370299 A JP28370299 A JP 28370299A JP 28370299 A JP28370299 A JP 28370299A JP 3870627 B2 JP3870627 B2 JP 3870627B2
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- 229910001209 Low-carbon steel Inorganic materials 0.000 title claims description 11
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 title claims description 9
- 238000004519 manufacturing process Methods 0.000 title claims description 8
- 229910052698 phosphorus Inorganic materials 0.000 title claims description 8
- 239000011574 phosphorus Substances 0.000 title claims description 7
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 67
- 229910000831 Steel Inorganic materials 0.000 claims description 58
- 239000010959 steel Substances 0.000 claims description 58
- 229910052742 iron Inorganic materials 0.000 claims description 33
- BHEPBYXIRTUNPN-UHFFFAOYSA-N hydridophosphorus(.) (triplet) Chemical compound [PH] BHEPBYXIRTUNPN-UHFFFAOYSA-N 0.000 claims description 30
- 238000009628 steelmaking Methods 0.000 claims description 26
- 238000005261 decarburization Methods 0.000 claims description 22
- 238000007670 refining Methods 0.000 claims description 20
- 239000002893 slag Substances 0.000 description 15
- 238000009849 vacuum degassing Methods 0.000 description 14
- 238000000034 method Methods 0.000 description 9
- 238000010079 rubber tapping Methods 0.000 description 9
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 8
- 239000002184 metal Substances 0.000 description 8
- 229910052751 metal Inorganic materials 0.000 description 8
- 229910052760 oxygen Inorganic materials 0.000 description 8
- 239000001301 oxygen Substances 0.000 description 8
- 229910000976 Electrical steel Inorganic materials 0.000 description 6
- 229910045601 alloy Inorganic materials 0.000 description 5
- 239000000956 alloy Substances 0.000 description 5
- DPTATFGPDCLUTF-UHFFFAOYSA-N phosphanylidyneiron Chemical compound [Fe]#P DPTATFGPDCLUTF-UHFFFAOYSA-N 0.000 description 5
- 238000006243 chemical reaction Methods 0.000 description 4
- 230000004907 flux Effects 0.000 description 4
- MYMOFIZGZYHOMD-UHFFFAOYSA-N Dioxygen Chemical compound O=O MYMOFIZGZYHOMD-UHFFFAOYSA-N 0.000 description 3
- 229910001882 dioxygen Inorganic materials 0.000 description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 3
- ODINCKMPIJJUCX-UHFFFAOYSA-N Calcium oxide Chemical compound [Ca]=O ODINCKMPIJJUCX-UHFFFAOYSA-N 0.000 description 2
- 238000007664 blowing Methods 0.000 description 2
- 230000000052 comparative effect Effects 0.000 description 2
- 238000009749 continuous casting Methods 0.000 description 2
- 150000004767 nitrides Chemical class 0.000 description 2
- 230000003647 oxidation Effects 0.000 description 2
- 238000007254 oxidation reaction Methods 0.000 description 2
- 150000003568 thioethers Chemical class 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 229910000975 Carbon steel Inorganic materials 0.000 description 1
- 229910000640 Fe alloy Inorganic materials 0.000 description 1
- 229910017082 Fe-Si Inorganic materials 0.000 description 1
- 229910017133 Fe—Si Inorganic materials 0.000 description 1
- 238000003723 Smelting Methods 0.000 description 1
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- 230000000996 additive effect Effects 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 235000012255 calcium oxide Nutrition 0.000 description 1
- 239000000292 calcium oxide Substances 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 238000005266 casting Methods 0.000 description 1
- 239000011162 core material Substances 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 238000005520 cutting process Methods 0.000 description 1
- 238000006477 desulfuration reaction Methods 0.000 description 1
- 230000023556 desulfurization Effects 0.000 description 1
- 230000001627 detrimental effect Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000005188 flotation Methods 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 239000011261 inert gas Substances 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 230000001590 oxidative effect Effects 0.000 description 1
- 238000010992 reflux Methods 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 238000003756 stirring Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 230000007704 transition Effects 0.000 description 1
- 238000005303 weighing Methods 0.000 description 1
- 239000013585 weight reducing agent Substances 0.000 description 1
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- Treatment Of Steel In Its Molten State (AREA)
Description
【０００１】
【発明の属する技術分野】
本発明は、転炉等の製鋼炉及びＲＨ真空脱ガス装置を用いてＰを０．０５ｗｔ％以上含有する高燐極低炭素鋼を製造する方法に関し、詳しくは、高燐極低炭素鋼のＴｉ濃度を安定して低く抑えることができる製造方法に関するものである。
【０００２】
【従来の技術】
近年、材料の用途拡大や軽量化等により、極低炭素鋼であり、鉄心材料等に使用される電磁鋼板では、鉄損値、磁束密度等の磁気特性の向上に対する要求が年々高まっている。この磁気特性は結晶粒の成長性と関連があり、粒成長を阻害する要因として窒化物、硫化物、酸化物等が挙げられ、磁気特性向上のためにこれら介在物の低減が望まれている。
【０００３】
ＭｎＳに代表される硫化物に関しては脱硫用フラックスを用いた精錬により鋼中Ｓ濃度を１０ｐｐｍ以下にしてその析出を防止し、酸化物に関してはＲＨ真空脱ガス装置における脱酸後の攪拌時間の延長や環流用不活性ガス流量の増大により、酸化物の浮上分離を促進して無害化を図っている。
【０００４】
窒化物に関しては特開昭５５−９７４２６号公報に開示されるように、鋼中に０．１ｗｔ％以上のＡｌを含有させ、粒成長の妨げとならない比較的大きなＡｌＮを析出させる方法があるが、Ｓｉ濃度が１ｗｔ％未満の比較的低級な電磁鋼板では、このような多量のＡｌ添加はコスト増を招くと云う弊害があり、実施されることは少ない。更に、Ａｌを添加させない場合には電磁鋼板の硬度を維持するために、Ｐ濃度を０．１ｗｔ％程度まで増加させることが一般的であり、成分調整のための合金鉄として燐鉄（フェロホスホルとも云う）が用いられている。
【０００５】
ところで、極低炭素鋼の製造には溶鋼を未脱酸状態とした真空脱炭処理が必要であり、この真空脱炭処理時の酸化による添加成分の歩留まり低下を防止するために、極低炭素鋼においては合金鉄を用いた成分調整は真空脱炭処理後に行われることが一般的である。又、真空脱炭処理が可能なＲＨ真空脱ガス装置等の二次精錬設備には、ホッパー、秤量機、切り出し装置等の合金鉄添加装置が備わっており、従って、成分調整は、真空脱炭処理に引き続いて二次精錬炉において行われることが一般的である。
【０００６】
しかしながら、真空脱炭処理後に燐鉄を用いてＰ濃度を調整すると、燐鉄中にはＴｉが２ｗｔ％前後含まれているため、Ｔｉが溶鋼中に溶解してＴｉＮを生成し、電磁鋼板の粒成長に悪影響を及ぼして磁気特性を劣化させる。従って、Ｓｉ濃度が１ｗｔ％未満の比較的低級な電磁鋼板の磁気特性を向上させるためには、燐鉄から持ち越されるＴｉの低減対策が必要である。尚、燐鉄以外にＰ濃度を調整することのできる物質として不純物含有量の少ない赤燐があるが、赤燐は高価でありコスト増を招くため、製鋼プロセスでは通常使用されない。
【０００７】
【発明が解決しようとする課題】
本発明は上記事情に鑑みなされたもので、その目的とするところは、０．０５ｗｔ％以上のＰを含有する電磁鋼板用の高燐極低炭素鋼のＴｉ濃度を安定して低く抑えることができる製造方法を提供することである。
【０００８】
【課題を解決するための手段】
溶鋼中のＴｉを除去するには、下記の（１）式に示すようにＴｉを酸化させて、Ｔｉ酸化物の形態でスラグ中に取り込んでしまう方法が考えられる。
３Ｔｉ＋５Ｏ＝Ｔｉ3Ｏ5 ……（１）
【０００９】
そのためには溶鋼中の溶存酸素が高い時期に燐鉄を添加する必要がある。ＲＨ真空脱ガス装置の真空脱炭処理中は溶鋼は未脱酸状態で溶存酸素が高く、従って燐鉄を添加する１つのチャンスである。そこで、本発明者等は、ＲＨ真空脱ガス装置の真空脱炭処理中に燐鉄を添加して溶鋼中のＴｉの挙動を調査した。しかしながら真空脱炭処理時には溶鋼中のＴｉ濃度は１０ｐｐｍ以下まで低減するが、真空脱炭処理後に成分調整用のＳｉを添加すると溶鋼中溶存酸素が低くなるため、一旦生成してスラグに取り込まれたＴｉ酸化物が解離して、Ｔｉが再び溶鋼中に戻るケースがあることを確認した。従って、燐鉄中のＴｉを効率良く除去するためには、溶鋼が取鍋に入る以前に燐鉄を添加することが重要であるとう云う知見を得た。
【００１０】
本発明は上記知見に基づきなされたもので、本発明による高燐極低炭素鋼の製造方法は、製鋼炉にて精錬して得た溶鋼を取鍋に出湯した後、ＲＨ真空脱ガス装置を用いて取鍋内溶鋼の真空脱炭処理及び成分調整を行い、０．０５ｗｔ％以上のＰを含有する高燐極低炭素鋼を製造する方法において、Ｐ濃度を調整するための燐鉄を製鋼炉内にて全量添加し、製鋼炉内溶鋼のＰ濃度を所定値まで上昇させ、製鋼炉出湯後には燐鉄を添加しないことを特徴とするものである。
【００１１】
本発明では燐鉄を製鋼炉内で添加する。本発明における製鋼炉とは転炉、電気炉等、溶銑に酸素ガスを供給して精錬する機能を持つものであればどのような精錬炉であっても良く、その中で転炉が最も一般的である。これらの製鋼炉で精錬中の溶鋼又は製鋼炉精錬直後の溶鋼では溶存酸素が高く、燐鉄中のＴｉはＴｉ酸化物になり、製鋼炉内のスラグ中に取り込まれる。そして、製鋼炉からの出湯時にＴｉ酸化物を取り込んだスラグが取鍋内に持ち込まれないようにする、若しくは取鍋に出湯後、取鍋内に持ち込まれたスラグを取鍋から排出することで、溶鋼がＳｉにより脱酸されてもスラグからのＴｉの戻りを防止することができる。更に、製鋼炉からの出湯後には燐鉄を添加しないので、取鍋内のスラグにはＴｉ酸化物が実質的に含まれないため、溶鋼がＳｉにより脱酸されてもＴｉが再び溶鋼中に戻ることがない。
【００１２】
本発明においてＰ濃度が０．０５ｗｔ％以上のＰ含有鋼を対象とする理由は以下の通りである。即ち、溶銑を製鋼炉で精錬すると、この精錬中に脱燐反応が起こり、精錬後の溶鋼のＰ濃度は高々０．０４ｗｔ％程度にしかならず、Ｐ濃度が０．０５ｗｔ％以上の溶鋼を製造する際には合金鉄として燐鉄が必ず必要になるからである。尚、本発明における極低炭素鋼とはＣ濃度が０．００５ｗｔ％以下の鋼である。
【００１３】
【発明の実施の形態】
高炉から出銑された溶銑を、必要により、一般的に行われている溶銑予備処理設備にて脱硫処理し、転炉、電気炉等の製鋼炉に装入する。製鋼炉では溶銑に酸素ガスを吹き付け、所謂、酸素吹錬して脱炭精錬する。この製鋼炉での精錬中に燐鉄を添加する。燐鉄の添加時期は脱炭精錬の末期とすること、若しくは、炭素濃度が所定値まで低下した脱炭精錬終了後とすることが好ましい。未脱酸状態の溶鋼では溶鋼中溶存酸素濃度は溶鋼中Ｃ濃度に逆比例し、従って、脱炭精錬の末期及び脱炭精錬終了後では溶鋼中の溶存酸素が高く、燐鉄中のＴｉが迅速にＴｉ酸化物になってスラグ中に移行すると共に、添加したＰの酸素吹錬による酸化ロスが減少するためである。
【００１４】
そして、目標とするＰ濃度とするために必要な燐鉄の全量を製鋼炉内で添加する。燐鉄の添加量は、目標とする電磁鋼板のＰ濃度、精錬終了時の溶鋼中Ｐ濃度、及び燐鉄の歩留まりから算出することができる。Ｐ濃度を正確に調整するため、燐鉄の歩留まりは予め試験操業して求めておくことが好ましい。このようにして、製鋼炉内溶鋼のＰ濃度を所定値まで上昇させる。尚、脱炭精錬終了時の溶鋼中Ｃ濃度は０．０２〜０．０５ｗｔ％程度で良い。又、生成されるＴｉ酸化物を迅速に吸収させるために、製鋼炉内にはスラグ分となるフラックスを添加すること、若しくは前ヒートの精錬で生成されたスラグを製鋼炉内に残留させておくことが好ましい。
【００１５】
次いで、この溶鋼を未脱酸状態のまま取鍋に出湯する。出湯時に製鋼炉内のスラグが大量に取鍋内に排出されないように、例えばスラグ検知装置等を用いて注意深く出湯する。スラグが取鍋内に排出された場合には、出湯後、真空除滓装置等を用いて取鍋内のスラグを取り除くこと、又は、生石灰や合成フラックス等を取鍋内に添加してスラグ中のＴｉ酸化物濃度を希釈しておくことが好ましい。
【００１６】
出湯後、未脱酸状態の溶鋼のまま、溶鋼を収容した取鍋をＲＨ真空脱ガス装置に搬送する。ＲＨ真空脱ガス装置では最初に真空脱炭処理を行う。溶鋼が未脱酸であるので、ＲＨ真空脱ガス装置の真空槽内へ溶鋼を環流させるだけで脱炭反応が起こるが、脱炭反応を促進させるために真空槽内に酸素ガスを吹き込んでも良い。
【００１７】
脱炭反応により溶鋼中のＣ濃度が所定値まで低下したならば真空脱炭処理を終了し、Ｆｅ−Ｓｉ合金等のＳｉを含有する合金鉄を溶鋼に添加して溶鋼をＳｉ脱酸する。更に必要により、Ｍｎやその他の成分等の成分調整を行い、真空槽を大気圧に戻してＲＨ真空脱ガス装置による精錬を終了する。ＲＨ真空脱ガス装置における真空脱炭処理後には溶鋼にはＡｌを添加しない。その後、溶鋼を連続鋳造設備や普通造塊設備等の鋳造設備に搬送して鋳造し、電磁鋼板用の鋳片若しくは鋼塊とする。
【００１８】
Ａｌを含有せず、０．０５ｗｔ％以上のＰを含有する電磁鋼板用の高燐極低炭素鋼をこのようしにて製造することにより、Ｔｉ濃度を安定して低く抑えることができ、その結果、電磁鋼板の磁気特性を向上させることが可能となる。
【００１９】
【実施例】
高炉から出銑された溶銑を溶銑予備処理にて脱硫し、この溶銑を転炉で精錬して約２５０トンの溶鋼を得、転炉内で燐鉄（Ｐ含有量：２５ｗｔ％）を添加した後、溶鋼を取鍋に出湯した。燐鉄の添加量は溶鋼トン当たり、Ｐ純分で０．８〜１．０ｋｇとした。出湯時の溶鋼成分はＣ：０．０２〜０．０５ｗｔ％、Ｓｉ：０．０５ｗｔ％以下、Ｍｎ：０．２〜０．４ｗｔ％、Ｐ：０．０９５〜０．１０５ｗｔ％であった。その後、未脱酸状態のまま溶鋼をＲＨ真空脱ガス装置に搬送し、ＲＨ真空脱ガス装置にて真空脱炭処理してＣ濃度を２０ｐｐｍ前後まで低下し、更にＳｉ、Ｍｎを調整してＲＨ真空脱ガス装置の精錬を終え、その後、連続鋳造機で鋳造してスラブ鋳片とした。転炉出湯時の溶鋼成分値と鋳片の成分分析値とを比較して、溶鋼中のＴｉ濃度の推移を調査した。又、比較として転炉では燐鉄を添加せずにＲＨ真空脱ガス装置で燐鉄を添加し、その他の条件は同一とした比較例も実施した。表１に、転炉出湯時の成分値及び鋳片成分値の代表例の調査結果を示す。
【００２０】
【表１】
表１で明らかなように、転炉で燐鉄を添加した実施例では鋳片のＴｉ濃度は０．００１ｗｔ％以下であり、極めて低かったが、ＲＨ真空脱ガス装置で燐鉄を添加した比較例では、燐鉄からのＴｉのピックアップが発生し、鋳片のＴｉ濃度は０．００３〜０．００４ｗｔ％であった。又、実施例ではＰ濃度は転炉出湯から鋳片まで変わることなく安定していた。一方、比較例では転炉出湯時のＰ濃度は転炉精錬により０．０１２〜０．０１５ｗｔ％まで低下していた。
【００２２】
【発明の効果】
本発明では、０．０５ｗｔ％以上のＰを含有する電磁鋼板用の高燐極低炭素鋼を製造する際に、Ｐ濃度調整用の燐鉄を製鋼炉内で全量装入するので、燐鉄中に含まれるＴｉのピックアップが防止され、Ｔｉ濃度を安定して低く抑えることができ、その結果、電磁鋼板の磁気特性を向上させることが可能となり、工業上有益な効果がもたらされる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a high phosphorus extremely low carbon steel containing 0.05 wt% or more of P using a steelmaking furnace such as a converter and an RH vacuum degassing apparatus. The present invention relates to a manufacturing method capable of stably keeping the Ti concentration low.
[0002]
[Prior art]
In recent years, due to expansion of use of materials and weight reduction, electromagnetic steel sheets that are extremely low carbon steels and are used for iron core materials and the like have been increasing year by year to improve magnetic properties such as iron loss value and magnetic flux density. This magnetic property is related to the growth of crystal grains, and factors that inhibit grain growth include nitrides, sulfides, oxides, etc., and reduction of these inclusions is desired to improve magnetic properties. .
[0003]
For sulfides represented by MnS, S concentration in steel is reduced to 10 ppm or less by refining using desulfurization flux. For oxides, the stirring time after deoxidation in RH vacuum degassing equipment is extended. In addition, by increasing the flow rate of the inert gas for reflux, flotation separation of the oxide is promoted to make it harmless.
[0004]
Regarding the nitride, as disclosed in JP-A-55-97426, there is a method in which 0.1 wt% or more of Al is contained in the steel and a relatively large AlN that does not hinder grain growth is precipitated. In a relatively low-grade electrical steel sheet having a Si concentration of less than 1 wt%, such a large amount of Al addition has a detrimental effect of increasing costs and is rarely performed. Furthermore, when Al is not added, in order to maintain the hardness of the electrical steel sheet, it is common to increase the P concentration to about 0.1 wt%. Phosphorus iron (ferrophosphol is also used as an alloy iron for component adjustment) Is used).
[0005]
By the way, the production of ultra-low carbon steel requires a vacuum decarburization process in which the molten steel is in a non-deoxidized state, and in order to prevent a decrease in the yield of additive components due to oxidation during this vacuum decarburization process, In steel, the component adjustment using iron alloy is generally performed after vacuum decarburization treatment. In addition, secondary refining equipment such as RH vacuum degassing equipment that can be vacuum decarburized is equipped with alloy iron addition equipment such as hoppers, weighing machines, and cutting equipment. It is common to carry out in a secondary smelting furnace following processing.
[0006]
However, when the P concentration is adjusted using phosphorous iron after vacuum decarburization treatment, Ti is contained in the phosphorous iron around 2 wt%, so that Ti dissolves in the molten steel to generate TiN, It adversely affects grain growth and degrades magnetic properties. Therefore, in order to improve the magnetic properties of a relatively low-grade electrical steel sheet having a Si concentration of less than 1 wt%, it is necessary to take measures to reduce Ti carried over from phosphorous iron. In addition to phosphorus iron, there is red phosphorus with a low impurity content as a substance capable of adjusting the P concentration. However, red phosphorus is expensive and causes an increase in cost, so it is not usually used in a steelmaking process.
[0007]
[Problems to be solved by the invention]
The present invention has been made in view of the above circumstances, and the object thereof is to stably keep the Ti concentration of a high phosphorus extremely low carbon steel for electrical steel sheets containing 0.05 wt% or more of P low. It is to provide a manufacturing method that can be used.
[0008]
[Means for Solving the Problems]
In order to remove Ti in molten steel, a method of oxidizing Ti as shown in the following formula (1) and taking it into the slag in the form of Ti oxide is conceivable.
3Ti + 5O = Ti 3 O 5 (1)
[0009]
To that end, it is necessary to add phosphorous iron when the dissolved oxygen in the molten steel is high. During the vacuum decarburization process of the RH vacuum degasser, the molten steel is undeoxidized and high in dissolved oxygen, and is therefore one chance to add phosphorous iron. Therefore, the present inventors investigated the behavior of Ti in the molten steel by adding phosphorous iron during the vacuum decarburization process of the RH vacuum degassing apparatus. However, during vacuum decarburization treatment, the Ti concentration in the molten steel is reduced to 10 ppm or less, but when Si for component adjustment is added after the vacuum decarburization treatment, the dissolved oxygen in the molten steel becomes low, so it was once generated and taken into the slag. It was confirmed that there was a case where the Ti oxide was dissociated and Ti returned again into the molten steel. Therefore, in order to efficiently remove Ti in the phosphorous iron, it has been found that it is important to add the phosphorous iron before the molten steel enters the ladle.
[0010]
The present invention has been made on the basis of the above knowledge, and the method for producing a high phosphorous ultra-low carbon steel according to the present invention is that the molten steel obtained by refining in a steelmaking furnace is poured into a ladle, and then an RH vacuum degassing apparatus is used. In the method of producing high phosphorus extra low carbon steel containing 0.05wt% or more of P by vacuum decarburization treatment and component adjustment of molten steel in the ladle, steel making phosphorous iron for adjusting P concentration The total amount is added in the furnace, the P concentration of the molten steel in the steelmaking furnace is increased to a predetermined value, and phosphorous iron is not added after the steelmaking furnace tapping.
[0011]
In the present invention, phosphorous iron is added in a steelmaking furnace. The steelmaking furnace in the present invention may be any refining furnace, such as a converter, electric furnace, etc., as long as it has a function of supplying oxygen gas to the hot metal and refining, and the converter is most commonly used. Is. In these steelmaking furnaces, the molten steel being refined or the molten steel immediately after refining the steelmaking furnace has high dissolved oxygen, and Ti in the phosphorous iron becomes Ti oxide and is taken into the slag in the steelmaking furnace. And, the slag that took in Ti oxide at the time of tapping from the steelmaking furnace is not brought into the ladle, or after draining into the ladle, the slag taken into the ladle is discharged from the ladle. Even if the molten steel is deoxidized by Si, it is possible to prevent Ti from returning from the slag. Further, since phosphorous iron is not added after tapping from the steelmaking furnace, Ti slag is substantially not contained in the slag in the ladle. Therefore, even if the molten steel is deoxidized by Si, Ti is again contained in the molten steel. Never come back.
[0012]
The reason why the P-containing steel having a P concentration of 0.05 wt% or more in the present invention is as follows. That is, when hot metal is refined in a steelmaking furnace, a dephosphorization reaction occurs during the refining, and the P concentration of the molten steel after refining is only about 0.04 wt%, and a molten steel with a P concentration of 0.05 wt% or more is produced. This is because in some cases, phosphorous iron is always required as an alloy iron. The ultra-low carbon steel in the present invention is a steel having a C concentration of 0.005 wt% or less.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
If necessary, the hot metal discharged from the blast furnace is desulfurized in a generally performed hot metal pretreatment facility and charged into a steelmaking furnace such as a converter or an electric furnace. In a steelmaking furnace, oxygen gas is blown into the hot metal, so-called oxygen blowing and decarburization refining. Phosphorus iron is added during refining in this steelmaking furnace. It is preferable to add the phosphorous iron at the end of the decarburization refining or after the end of the decarburization refining when the carbon concentration is reduced to a predetermined value. In the undeoxidized molten steel, the dissolved oxygen concentration in the molten steel is inversely proportional to the C concentration in the molten steel. Therefore, the dissolved oxygen in the molten steel is high at the end of decarburization and after the decarburization refining, and the Ti in the phosphorous iron is high. This is because it quickly becomes Ti oxide and moves into the slag, and oxidation loss due to oxygen blowing of the added P is reduced.
[0014]
Then, the entire amount of phosphorous iron necessary for achieving the target P concentration is added in the steelmaking furnace. The addition amount of phosphorous iron can be calculated from the target P concentration of the electromagnetic steel sheet, the P concentration in the molten steel at the end of refining, and the yield of phosphorous iron. In order to accurately adjust the P concentration, it is preferable to obtain the yield of phosphorous iron in advance through a test operation. In this way, the P concentration of the molten steel in the steelmaking furnace is increased to a predetermined value. The C concentration in the molten steel at the end of decarburization refining may be about 0.02 to 0.05 wt%. In addition, in order to quickly absorb the generated Ti oxide, a flux as a slag is added to the steelmaking furnace, or the slag generated by refining the preheat is left in the steelmaking furnace. It is preferable.
[0015]
Next, this molten steel is poured out into a ladle in an undeoxidized state. In order to prevent a large amount of slag in the steelmaking furnace from being discharged into the ladle at the time of the hot water, the hot water is carefully discharged using, for example, a slag detector. If the slag is discharged into the ladle, remove the slag from the ladle using a vacuum remover after pouring the hot water, or add quick lime, synthetic flux, etc. into the ladle. It is preferable to dilute the Ti oxide concentration.
[0016]
After the tapping, the ladle containing the molten steel is conveyed to the RH vacuum degassing apparatus with the molten steel in an undeoxidized state. In the RH vacuum degassing apparatus, first, vacuum decarburization processing is performed. Since the molten steel is not deoxidized, the decarburization reaction occurs only by circulating the molten steel into the vacuum tank of the RH vacuum degassing apparatus, but oxygen gas may be blown into the vacuum tank to promote the decarburization reaction. .
[0017]
If the C concentration in the molten steel is lowered to a predetermined value due to the decarburization reaction, the vacuum decarburization process is terminated, and an alloy iron containing Si such as Fe-Si alloy is added to the molten steel to deoxidize the molten steel. Further, if necessary, the components such as Mn and other components are adjusted, the vacuum chamber is returned to the atmospheric pressure, and the refining by the RH vacuum degassing apparatus is completed. After the vacuum decarburization process in the RH vacuum degassing apparatus, Al is not added to the molten steel. Thereafter, the molten steel is transported to a casting facility such as a continuous casting facility or a normal ingot forming facility, and cast into a slab or a steel ingot for an electromagnetic steel sheet.
[0018]
By producing a high phosphorous ultra-low carbon steel for electrical steel sheets that does not contain Al and contains 0.05 wt% or more of P in this way, the Ti concentration can be stably kept low. As a result, it is possible to improve the magnetic properties of the electromagnetic steel sheet.
[0019]
【Example】
The hot metal discharged from the blast furnace was desulfurized by hot metal pretreatment, and this hot metal was refined in a converter to obtain about 250 tons of molten steel, and phosphorous iron (P content: 25 wt%) was added in the converter. Later, the molten steel was poured out into a ladle. The amount of phosphorous iron added was 0.8 to 1.0 kg in terms of pure P per ton of molten steel. Molten steel components at the time of tapping were C: 0.02 to 0.05 wt%, Si: 0.05 wt% or less, Mn: 0.2 to 0.4 wt%, and P: 0.095 to 0.105 wt%. Thereafter, the molten steel is transported to an RH vacuum degassing apparatus in an undeoxidized state, vacuum decarburized by the RH vacuum degassing apparatus, the C concentration is reduced to about 20 ppm, and Si and Mn are further adjusted to adjust the RH. After refining the vacuum degassing device, it was cast with a continuous casting machine to form a slab slab. The transition of Ti concentration in the molten steel was investigated by comparing the molten steel component value at the time of converter tapping with the component analysis value of the slab. As a comparison, a comparative example was also carried out in which the phosphor iron was added by the RH vacuum degasser without adding phosphor iron in the converter, and the other conditions were the same. Table 1 shows the survey results of representative examples of component values and slab component values during converter tapping.
[0020]
[Table 1]
As is apparent from Table 1, in the example in which phosphorous iron was added in the converter, the Ti concentration of the slab was 0.001 wt% or less, which was extremely low, but the comparison in which phosphorous iron was added by the RH vacuum degassing apparatus. In the example, Ti pickup from phosphorous iron occurred, and the Ti concentration of the slab was 0.003 to 0.004 wt%. In the examples, the P concentration was stable without changing from the converter tapping to the slab. On the other hand, in the comparative example, the P concentration at the converter tapping was reduced to 0.012 to 0.015 wt% by converter refining.
[0022]
【The invention's effect】
In the present invention, when producing high phosphorus extra low carbon steel for electrical steel sheets containing 0.05 wt% or more of P, the entire amount of phosphorous iron for adjusting P concentration is charged in a steelmaking furnace. The pickup of Ti contained therein is prevented, the Ti concentration can be stably kept low, and as a result, the magnetic properties of the electromagnetic steel sheet can be improved, and an industrially beneficial effect is brought about.
Claims (1)
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| JP28370299A JP3870627B2 (en) | 1999-10-05 | 1999-10-05 | Method for producing high phosphorus extra low carbon steel |
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| JP28370299A JP3870627B2 (en) | 1999-10-05 | 1999-10-05 | Method for producing high phosphorus extra low carbon steel |
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| US7981224B2 (en) | 2003-12-18 | 2011-07-19 | Nippon Steel Corporation | Multi-phase steel sheet excellent in hole expandability and method of producing the same |
| CN108611462B (en) * | 2016-12-12 | 2020-03-27 | 上海梅山钢铁股份有限公司 | Method for controlling inclusions in ultra-low carbon steel |
| CN110537314A (en) * | 2017-04-24 | 2019-12-03 | 松下知识产权经营株式会社 | Electric motor assembly, motor, device |
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