JP6674093B2 - Mold powder for continuous casting of steel and continuous casting method - Google Patents
Mold powder for continuous casting of steel and continuous casting method Download PDFInfo
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- 239000000843 powder Substances 0.000 title claims description 65
- 229910000831 Steel Inorganic materials 0.000 title claims description 57
- 239000010959 steel Substances 0.000 title claims description 57
- 238000009749 continuous casting Methods 0.000 title claims description 26
- 238000000034 method Methods 0.000 title claims description 9
- 239000000203 mixture Substances 0.000 claims description 68
- 229910004298 SiO 2 Inorganic materials 0.000 claims description 35
- 229910018072 Al 2 O 3 Inorganic materials 0.000 claims description 22
- 229910004261 CaF 2 Inorganic materials 0.000 claims description 16
- 229910018068 Li 2 O Inorganic materials 0.000 claims description 12
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 7
- 229910052799 carbon Inorganic materials 0.000 claims description 6
- 239000012535 impurity Substances 0.000 claims 1
- ODINCKMPIJJUCX-UHFFFAOYSA-N Calcium oxide Chemical compound [Ca]=O ODINCKMPIJJUCX-UHFFFAOYSA-N 0.000 description 70
- 238000002425 crystallisation Methods 0.000 description 69
- 230000008025 crystallization Effects 0.000 description 69
- 230000008859 change Effects 0.000 description 39
- 239000000292 calcium oxide Substances 0.000 description 35
- 235000012255 calcium oxide Nutrition 0.000 description 35
- 239000002893 slag Substances 0.000 description 33
- 229910001678 gehlenite Inorganic materials 0.000 description 18
- 230000000052 comparative effect Effects 0.000 description 15
- 239000011734 sodium Substances 0.000 description 13
- 238000005266 casting Methods 0.000 description 9
- 239000003245 coal Substances 0.000 description 9
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 8
- 238000002844 melting Methods 0.000 description 8
- 230000008018 melting Effects 0.000 description 8
- 238000012360 testing method Methods 0.000 description 8
- 230000003628 erosive effect Effects 0.000 description 7
- 239000013078 crystal Substances 0.000 description 6
- 239000002436 steel type Substances 0.000 description 6
- 230000004907 flux Effects 0.000 description 5
- 239000000463 material Substances 0.000 description 5
- 239000002994 raw material Substances 0.000 description 5
- 238000006243 chemical reaction Methods 0.000 description 4
- 239000011449 brick Substances 0.000 description 3
- 238000005336 cracking Methods 0.000 description 3
- 239000008187 granular material Substances 0.000 description 3
- 239000000377 silicon dioxide Substances 0.000 description 3
- 238000010583 slow cooling Methods 0.000 description 3
- 229910052708 sodium Inorganic materials 0.000 description 3
- FUJCRWPEOMXPAD-UHFFFAOYSA-N Li2O Inorganic materials [Li+].[Li+].[O-2] FUJCRWPEOMXPAD-UHFFFAOYSA-N 0.000 description 2
- 229910000954 Medium-carbon steel Inorganic materials 0.000 description 2
- KKCBUQHMOMHUOY-UHFFFAOYSA-N Na2O Inorganic materials [O-2].[Na+].[Na+] KKCBUQHMOMHUOY-UHFFFAOYSA-N 0.000 description 2
- CDBYLPFSWZWCQE-UHFFFAOYSA-L Sodium Carbonate Chemical compound [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 description 2
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 2
- 230000033228 biological regulation Effects 0.000 description 2
- 229910052681 coesite Inorganic materials 0.000 description 2
- 229910052593 corundum Inorganic materials 0.000 description 2
- 229910052906 cristobalite Inorganic materials 0.000 description 2
- XUCJHNOBJLKZNU-UHFFFAOYSA-M dilithium;hydroxide Chemical compound [Li+].[Li+].[OH-] XUCJHNOBJLKZNU-UHFFFAOYSA-M 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000011156 evaluation Methods 0.000 description 2
- 229910052731 fluorine Inorganic materials 0.000 description 2
- 150000002222 fluorine compounds Chemical class 0.000 description 2
- 239000010439 graphite Substances 0.000 description 2
- 229910002804 graphite Inorganic materials 0.000 description 2
- 238000007654 immersion Methods 0.000 description 2
- 238000005461 lubrication Methods 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 2
- 235000012239 silicon dioxide Nutrition 0.000 description 2
- PUZPDOWCWNUUKD-UHFFFAOYSA-M sodium fluoride Chemical compound [F-].[Na+] PUZPDOWCWNUUKD-UHFFFAOYSA-M 0.000 description 2
- 238000007711 solidification Methods 0.000 description 2
- 230000008023 solidification Effects 0.000 description 2
- 229910052682 stishovite Inorganic materials 0.000 description 2
- 229910052905 tridymite Inorganic materials 0.000 description 2
- 229910001845 yogo sapphire Inorganic materials 0.000 description 2
- BVKZGUZCCUSVTD-UHFFFAOYSA-L Carbonate Chemical compound [O-]C([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-L 0.000 description 1
- 239000005909 Kieselgur Substances 0.000 description 1
- 235000019738 Limestone Nutrition 0.000 description 1
- 229910001566 austenite Inorganic materials 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 238000009529 body temperature measurement Methods 0.000 description 1
- WUKWITHWXAAZEY-UHFFFAOYSA-L calcium difluoride Chemical compound [F-].[F-].[Ca+2] WUKWITHWXAAZEY-UHFFFAOYSA-L 0.000 description 1
- 239000003575 carbonaceous material Substances 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 239000004568 cement Substances 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 239000000470 constituent Substances 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 229910001610 cryolite Inorganic materials 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 239000010436 fluorite Substances 0.000 description 1
- 238000007429 general method Methods 0.000 description 1
- 230000020169 heat generation Effects 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 239000006028 limestone Substances 0.000 description 1
- 229910052744 lithium Inorganic materials 0.000 description 1
- XGZVUEUWXADBQD-UHFFFAOYSA-L lithium carbonate Chemical compound [Li+].[Li+].[O-]C([O-])=O XGZVUEUWXADBQD-UHFFFAOYSA-L 0.000 description 1
- 229910052808 lithium carbonate Inorganic materials 0.000 description 1
- 230000001050 lubricating effect Effects 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 239000000155 melt Substances 0.000 description 1
- 229910052697 platinum Inorganic materials 0.000 description 1
- 230000008569 process Effects 0.000 description 1
- 230000001737 promoting effect Effects 0.000 description 1
- 229910052761 rare earth metal Inorganic materials 0.000 description 1
- 238000006479 redox reaction Methods 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 238000006722 reduction reaction Methods 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 238000010405 reoxidation reaction Methods 0.000 description 1
- 239000004576 sand Substances 0.000 description 1
- 229910000029 sodium carbonate Inorganic materials 0.000 description 1
- 239000011775 sodium fluoride Substances 0.000 description 1
- 235000013024 sodium fluoride Nutrition 0.000 description 1
- 239000007921 spray Substances 0.000 description 1
- 230000009466 transformation Effects 0.000 description 1
- 229910052727 yttrium Inorganic materials 0.000 description 1
- 229910000859 α-Fe Inorganic materials 0.000 description 1
Description
本発明は鋼の連続鋳造用モールドパウダーに関し、更に詳細には、中炭高Ａｌ含有鋼(鋼中Ｃ含有量０．０７〜０．２５質量％、鋼中Ａｌ含有量≧０．２０質量％)の連続鋳造で発生し得る、拘束性ブレークアウト、鋳片の縦割れ、溶融スラグ層の過剰増大、スラグベアの肥大化等の種々のトラブルを抑制しつつ、高品質な鋼を得ることができる鋼の連続鋳造用モールドパウダーおよびそれを使用した鋼の連続鋳造方法に関するものである。 The present invention relates to a mold powder for continuous casting of steel, and more particularly, to a medium-coal high Al-containing steel (C content in steel: 0.07 to 0.25% by mass, Al content in steel ≧ 0.20% by mass) )), It is possible to obtain high quality steel while suppressing various troubles such as restraint breakout, vertical cracking of slab, excessive increase of molten slag layer, enlargement of slag bear, etc. which can occur in continuous casting of). The present invention relates to a mold powder for continuous casting of steel and a continuous casting method of steel using the same.
鋼の連続鋳造用モールドパウダー（以下、「モールドパウダー」と記載する）は、鋼の連続鋳造において水冷鋳型（以下、「モールド」と記載する）内の溶鋼表面に添加され、溶鋼からの受熱により溶融し、酸化物融体(以下、溶融スラグ)となってモールドと凝固シェルの間隙に流れ込みながら消費される。モールドパウダーは添加されてから消費される間に以下の役割を果たす：（１）モールドと凝固シェルの潤滑；（２）凝固シェルの冷却速度(抜熱速度)のコントロール；（３）溶鋼から浮上する介在物の吸収除去；（４）溶鋼の保温；（５）溶鋼の再酸化防止。前述の５つがモールドパウダーの主要な役割である。 Mold powder for continuous casting of steel (hereinafter, referred to as "mold powder") is added to the surface of molten steel in a water-cooled mold (hereinafter, referred to as "mold") during continuous casting of steel, and is subjected to heat from the molten steel. It is melted and consumed as an oxide melt (hereinafter, molten slag) flowing into the gap between the mold and the solidified shell. The mold powder plays the following roles between the time of addition and consumption: (1) lubrication of the mold and the solidified shell; (2) control of the cooling rate (heat removal rate) of the solidified shell; (3) floating from the molten steel. (4) Keeping molten steel warm; (5) Preventing reoxidation of molten steel. The above five are the main roles of the mold powder.
一般的なモールドパウダーは、ＣａＯ、ＳｉＯ２、Ａｌ２Ｏ３、Ｎａ２Ｏ、ＭｇＯ、Ｌｉ２Ｏ、Ｂ２Ｏ３、Ｋ２Ｏ、Ｆ、Ｃ等多くの成分で構成され、例えばＳｉＯ２：２０〜４５質量％、ＣａＯ：２０〜４５質量％、Ａｌ２Ｏ３：０．５〜１０質量％、ＭｇＯ：０．１〜８質量％、Ｎａ２Ｏ：１〜２０質量％、Ｌｉ２Ｏ：０．１〜１０質量％、Ｆ：２〜１５質量％、Ｃ：２０質量％以下の組成を有する。 Common mold powder, CaO, SiO 2, Al 2 O 3, Na 2 O, MgO, Li 2 O, B 2 O 3, K 2 O, F, is composed of C and many other components, for example, SiO 2 : 20 to 45 wt%, CaO: 20 to 45 wt%, Al 2 O 3: 0.5~10 wt%, MgO: 0.1 to 8 wt%, Na 2 O: 1~20 wt%, Li 2 O: 0.1 to 10% by mass, F: 2 to 15% by mass, C: 20% by mass or less.
本発明の対象となる中炭高Ａｌ含有鋼の連続鋳造では、２つの大きな課題を有している。１つ目は、鋼中のＣ含有量が０．０７〜０．２５質量％の中炭素鋼は、凝固過程でδ相(フェライト)からγ相(オーステナイト)への包晶変態が生じ、凝固収縮が大きいことから鋳片縦割れが発生し易い特徴がある。鋳片縦割れを抑制するには、（２）の働きによって凝固シェルからモールドへの抜熱速度を制御し、均一な凝固シェルを形成する必要がある。一般的な方法としては、凝固シェルを緩やかに冷却すること(以下、「緩冷却」と記載する)であり、モールドと凝固シェルの間に流れ込んだ溶融スラグのフィルム(以下、「スラグフィルム」と記載する)がモールドによって冷却される際に生成する結晶晶出温度(結晶化温度)を高くすることである。２つ目は、一般的に溶融スラグ中のＳｉＯ２が溶鋼中Ａｌと（１）式に示す酸化還元反応を生じることによって、溶融スラグ中のＳｉＯ２が減少（ＣａＯ／ＳｉＯ２比が上昇）し、Ａｌ２Ｏ３が増加する（以下、「組成変動」と記載する）。
４Ａｌ＋３ＳｉＯ２→２Ａｌ２Ｏ３＋３Ｓｉ・・・（１）
The continuous casting of the medium-coal high Al-containing steel, which is the subject of the present invention, has two major problems. First, medium carbon steel with a C content of 0.07 to 0.25 mass% in steel undergoes peritectic transformation from δ phase (ferrite) to γ phase (austenite) during the solidification process, Since the shrinkage is large, there is a feature that a slab vertical crack is easily generated. In order to suppress the vertical cracks in the slab, it is necessary to control the heat removal rate from the solidified shell to the mold by the operation of (2) to form a uniform solidified shell. As a general method, to slowly cool the solidified shell (hereinafter, referred to as `` slow cooling ''), a film of molten slag flowing between the mold and the solidified shell (hereinafter, `` slag film '' and (To be described) is to increase the crystallization temperature (crystallization temperature) generated when cooled by the mold. Second, SiO 2 in general molten slag and molten steel Al by producing an oxidation-reduction reaction shown in equation (1), SiO 2 is reduced in the molten slag (CaO / SiO 2 ratio is increased) However, Al 2 O 3 increases (hereinafter, referred to as “composition variation”).
4Al + 3SiO 2 → 2Al 2 O 3 + 3Si (1)
上述のように中炭高Ａｌ含有鋼は、鋼中Ａｌが多いために反応量が多く、一般的な中炭素鋼と比較して溶融スラグ中のＡｌ２Ｏ３およびＣａＯ／ＳｉＯ２比が非常に高くなる特徴がある。特に、鋼中Ａｌ量が０．２０質量％以上の鋼種では組成変動が大きく、モールドパウダー特性に与える影響が大きくなる。 As described above, the medium-coal high Al-containing steel has a large amount of reaction due to a large amount of Al in the steel, and the Al 2 O 3 and CaO / SiO 2 ratios in the molten slag are much higher than those of general medium-carbon steel. There is a feature that becomes higher. In particular, in a steel type in which the Al content in steel is 0.20% by mass or more, the composition variation is large, and the influence on the mold powder characteristics is large.
上述のような組成を有するモールドパウダーで一般鋼を鋳造する際は、通常スラグフィルム中にカスピダイン（３ＣａＯ・２ＳｉＯ２・ＣａＦ２）と呼ばれる結晶が晶出する。しかしながら、高Ａｌ含有鋼のように組成変動が大きい場合はカスピダインの晶出が弱まり、ゲーレナイト（２ＣａＯ・ＳｉＯ２・Ａｌ２Ｏ３）が晶出するようになる。ゲーレナイトの融点は１５９３℃、カスピダインの融点は１４０７℃であり、組成変動によりゲーレナイトが晶出し易い組成に近づくことで、結晶化温度が過剰に高くなるため、（ｉ）スラグベアの肥大化；（ｉｉ）溶融スラグの潤滑性の低下により、モールドパウダーの溶融速度が消費速度を上回ることで、溶融スラグ層厚みが過剰に増大；（ｉｉｉ）拘束性ブレークアウトの発生に繋がる。また、モールド内は場所によって温度や溶鋼流動状況が異なるため組成変動量は一律ではない。そのため、モールド内の場所によってゲーレナイトの晶出状況が異なり、（ｉｖ）モールド内で結晶化温度に差が生じることで、凝固シェルが不均一に成長し、鋳片縦割れに繋がる。 When casting general steel with the mold powder having the above-described composition, a crystal called cuspidyne (3CaO.2SiO 2 .CaF 2 ) is usually crystallized in the slag film. However, when the composition variation is large, as in the case of high Al content steel, crystallization of caspidine is weakened, and gehlenite (2CaO.SiO 2 .Al 2 O 3 ) is crystallized. The melting point of gehlenite is 1593 ° C., and the melting point of caspidyne is 1407 ° C. The crystallization temperature becomes excessively high by approaching a composition in which gehlenite tends to crystallize due to composition fluctuation. ) The molten lubricating property of the molten slag is reduced, so that the melting rate of the mold powder exceeds the consumption rate, so that the thickness of the molten slag layer is excessively increased; (iii) restraint breakout is caused. In addition, since the temperature and the flow state of the molten steel vary depending on the location in the mold, the composition variation amount is not uniform. For this reason, the crystallization state of gehlenite differs depending on the location in the mold, and (iv) a difference in crystallization temperature occurs in the mold, whereby the solidified shell grows unevenly, which leads to a vertical crack in the slab.
高結晶化温度を有するゲーレナイトが晶出することは、緩冷却の面から必ずしも悪影響を与える訳では無いが、組成変動によりモールド内で結晶化温度差が生じる状況では、鋳片縦割れを発生させる要因となる。これらの対策として、これまで様々なモールドパウダーが提案されてきた。
例えば、特許文献１には、ＣａＯ、ＳｉＯ２、Ｌｉ２Ｏおよびフッ素化合物を基本成分とするモールドパウダであって、さらに、Ｎａ２ＯおよびＫ２Ｏのうちの１種以上、ならびにＡｌ２Ｏ３を含有し、ＳｉＯ２の含有率が１０〜３０質量％、フッ素化合物を構成するＦの含有率が４〜２５質量％、Ｎａ２ＯおよびＫ２Ｏの合計の含有率が１．５質量％以下であり、かつ、これらＣａＯ、ＳｉＯ２、Ｌｉ２Ｏ、Ｆ、Ｎａ２Ｏ、Ｋ２ＯおよびＡｌ２Ｏ３の含有率で表される、下記（イ）式、（ロ）式および（ハ）式によって規定される指標ａが０．４７〜０．７、指標ｂが０を超え０．４以下、および指標ｃが０．１〜０．５であることを特徴とする連続鋳造用モールドパウダが開示されている：
ａ＝(%CaO)h／{(%CaO)h＋(%SiO2)h＋(%Al2O3)h}・・・（イ）
ｂ＝(%Al2O3)h／｛(%CaO)h＋(%SiO2)h＋(%Al2O3)h}・・・（ロ）
ｃ＝(%CaF2)h／{(%CaO)h＋(%SiO2)h＋(%CaF2)h}・・・（ハ）
ここで、(%CaO)h＝{WCaO−(%CaF2)h×0.718}・・・（ニ）
(%CaF2)h＝（WF−WLi2O×1.27−WNa2O×0.613−WK2O×0.404）×2.05・・・（ホ）
(%SiO2)h＝WSiO2および(%Al2O3)h＝WAl2O3であり、WCaO、WSiO2、WAl2O3、WLi2O、WNa2OおよびWK2Oは、モールドパウダ中に分析されるＣａ、Ｓｉ、Ａｌ、Ｌｉ、Ｎａ、Ｋが全てそれらの酸化物であるとして換算した含有率（質量％）であり、WFは、分析されるＦの含有率（質量％）である。
特許文献１は、高Ａｌ含有鋼特有の大きな組成変動により引き起こされる溶融スラグの粘度や結晶化温度の過剰な上昇、それに伴うスラグ潤滑不良による拘束性ブレークアウトや鋳片品質悪化の課題に対して、組成変動に関与するモールドパウダー中のＳｉＯ２を低位(１０〜３０質量％)に抑え、かつ上述の（１）式の反応を抑制するＬｉ２Ｏを適用し、組成変動を抑えることで、ゲーレナイト生成を抑制する。カスピダインを晶出させることで結晶化温度や粘度の上昇を抑制しようとするものである。
The crystallization of gehlenite having a high crystallization temperature does not necessarily have a negative effect on the aspect of slow cooling, but in a situation where a crystallization temperature difference occurs in a mold due to composition fluctuation, a slab vertical crack is generated. It becomes a factor. As a countermeasure for these, various mold powders have been proposed.
For example, Patent Document 1 discloses a mold powder containing CaO, SiO 2 , Li 2 O and a fluorine compound as basic components, and further includes one or more of Na 2 O and K 2 O, and Al 2 O 3 , the content of SiO 2 is 10 to 30% by mass, the content of F constituting the fluorine compound is 4 to 25% by mass, and the total content of Na 2 O and K 2 O is 1.5% by mass. % Or less, and expressed by the content of these CaO, SiO 2 , Li 2 O, F, Na 2 O, K 2 O and Al 2 O 3 , the following formulas (a), (b) and (C) Continuous casting characterized by the index a defined by the equation being 0.47 to 0.7, the index b being greater than 0 and less than or equal to 0.4, and the index c being 0.1 to 0.5. Mold powder for is disclosed:
a = (% CaO) h / {(% CaO) h + (% SiO 2 ) h + (% Al 2 O 3 ) h} (a)
b = (% Al 2 O 3 ) h / {(% CaO) h + (% SiO 2 ) h + (% Al 2 O 3 ) h} (b)
c = (% CaF 2 ) h / {(% CaO) h + (% SiO 2 ) h + (% CaF 2 ) h} (c)
Here, (% CaO) h = {W CaO − (% CaF 2 ) h × 0.718} (d)
(% CaF 2 ) h = (W F −W Li2O × 1.27−W Na2O × 0.613−W K2O × 0.404) × 2.05 ・ ・ ・ (e)
(% SiO 2) h = W SiO2 and (% Al 2 O 3) is h = W Al2O3, W CaO, W SiO2, W Al2O3, W Li2O, W Na2O and W K2O are analyzed during mold powder Ca, Si, Al, Li, Na, and K are the contents (% by mass) calculated as being oxides thereof, and WF is the content (% by mass) of F to be analyzed.
Patent Literature 1 addresses the problem of excessive increase in viscosity and crystallization temperature of molten slag caused by large compositional variation unique to high Al content steel, and associated restraint breakout due to poor slag lubrication and deterioration of slab quality. By suppressing SiO 2 in the mold powder involved in the composition fluctuation to a low level (10 to 30% by mass) and applying Li 2 O for suppressing the reaction of the above formula (1), the composition fluctuation is suppressed. Suppresses the formation of gehlenite. The purpose is to suppress the rise in crystallization temperature and viscosity by crystallizing caspidyne.
また、特許文献２では、高Ａｌ、Ｙまたは希土類元素を含有する鋼に使用する連続鋳造用モールドフラックスにおいて、ＣａＯ：２５．０〜４５．０ｗｔ％、Ａｌ２Ｏ３：１０．０〜１７．０ｗｔ％、ＳｒＯ：１０．０〜２５．０ｗｔ％とし、これらが総量で５５．０〜８５．０ｗｔ％からなり、かつこれにＦ：５．０〜２０．０ｗｔ％を含み、これらの主成分に溶融速度調整剤として炭素を１０．０ｗｔ％以下含有せしめ、その他原料中から混入する不可避的組成を含み、該不可避的組成から混入するＳｉＯ２を２．０ｗｔ％以下に規制したことを特徴とする連続鋳造用モールドフラックス（請求項１）が開示されている。更に、特許文献２のモールドフラックスは、ＬｉＦを５．０ｗｔ％以下の量で含有したり（請求項２）、ＭｇＯを１０．０ｗｔ％以下に規制したり（請求項３）、ＬｉＦを５．０ｗｔ％以下の量で含有し且つＭｇＯを１０．０ｗｔ％以下に規制したり（請求項４）、ＬｉＦを５．０ｗｔ％以下の量で含有し且つＬｉ２Ｏ＋Ｎａ２Ｏを４ｗｔ％以下に規制したり（請求項５）、ＬｉＦを５．０ｗｔ％以下の量で含有し、Ｌｉ２Ｏ＋Ｎａ２Ｏを４ｗｔ％以下に規制し且つＭｇＯを１０．０ｗｔ％以下に規制できること（請求項６）が開示されている。特許文献２のモールドフラックスは、Ａｌをはじめとするパウダースラグ還元元素を含む鋼の連続鋳造に対して、拘束性ブレークアウトや鋳片品質低下を抑制するために、ＳｉＯ２の代わりにＳｒＯを使用し、ＳｉＯ２は不可避的成分として２．０ｗｔ％までに留めることで組成変動を抑制し、ゲーレナイトを抑制。それにより、結晶化温度や粘度の上昇を抑制しようとするものである。 In Patent Document 2, in the high Al, Y or continuous casting mold flux for use in steel containing rare earth elements, CaO: 25.0~45.0wt%, Al 2 O 3: 10.0~17. 0 wt%, SrO: 10.0 to 25.0 wt%, these are composed of 55.0 to 85.0 wt% in total, and further contain F: 5.0 to 20.0 wt%, and these main components are included. Containing 10.0 wt% or less of carbon as a melting rate adjusting agent, and containing other unavoidable compositions mixed from the raw materials, and restricting SiO 2 mixed from the unavoidable composition to 2.0 wt% or less. The present invention discloses a mold flux for continuous casting (Claim 1). Further, the mold flux of Patent Document 2 contains LiF in an amount of 5.0 wt% or less (Claim 2), regulates MgO to 10.0 wt% or less (Claim 3), and regulates LiF to 5.0 wt% or less. 0 wt% or less of in amounts and or regulation of MgO below 10.0 wt% (claim 4), regulating the and Li 2 O + Na 2 O contained below 4 wt% with an amount of less than 5.0 wt% of LiF or (claim 5), a LiF in an amount of less than 5.0 wt%, to the regulation and and MgO the Li 2 O + Na 2 O below 4 wt% can be restricted below 10.0 wt% (claim 6) It has been disclosed. Mold flux of Patent Document 2, the continuous casting of steel comprising a powder slug reduction elements, including Al, to suppress restricted breakout and slab quality degradation, using SrO in place of SiO 2 However, SiO 2 is suppressed to 2.0 wt% as an unavoidable component to suppress composition fluctuation and suppress gehlenite. Thereby, the crystallization temperature and the viscosity are suppressed from increasing.
しかしながら、特許文献１に記載されている連続鋳造用モールドパウダーでは、中炭高Ａｌ含有鋼のように鋳片縦割れが発生し易い鋼種では、組成変動前後の結晶化温度差が大きくなり、鋳片縦割れが発生するため不十分であった。
また、特許文献２に記載されているモールドフラックスは、ＳｉＯ２を極端に低減したことにより、晶出結晶種が安定せず、抜熱速度の制御が困難となり高Ａｌ含有中炭素鋼においては鋳片縦割れの観点から不十分であった。
これらの特許文献を以ってしても、種々の問題を解決することができないのが現状である。
However, in the mold powder for continuous casting described in Patent Document 1, in a steel type in which slab longitudinal cracks are likely to occur, such as medium-coal high Al-containing steel, the crystallization temperature difference before and after the composition change becomes large, and This was insufficient because one-sided vertical cracks occurred.
Further, the mold flux described in Patent Document 2 has an extremely reduced amount of SiO 2 , so that the crystallized crystal seed is not stable, and it is difficult to control the heat removal rate. It was insufficient from the viewpoint of one-sided cracking.
At present, various problems cannot be solved even with these patent documents.
従って、本発明は、中炭高Ａｌ含有鋼の連続鋳造時における、大きな組成変動を起点とした拘束性ブレークアウト、パウダー溶融層厚みの過剰な増大、スラグベアの肥大化、鋳片縦割れといったトラブルを抑制することができるモールドパウダー並びにそれを使用した鋼の連続鋳造方法の提供することを目的とする。 Therefore, the present invention has problems such as restraint breakout starting from a large composition variation, excessive increase in the thickness of a powder molten layer, enlargement of a slag bear, and vertical cracks in a slab during continuous casting of a medium-coal high Al-containing steel. It is an object of the present invention to provide a mold powder capable of suppressing the occurrence of a crack and a method of continuously casting steel using the same.
上述のような種々の問題を抑制するには、組成変動前の結晶化温度を鋳片縦割れが発生しない程度(実績より１０００℃以上)に設定し、組成変動後の結晶化温度を拘束性ブレークアウト、パウダー溶融層厚みの過剰な増大、スラグベアの肥大化が発生しない程度の結晶化温度(実績より１３００℃以下)に設定する必要がある。更に、モールド内は場所によって温度や溶鋼流動状況が異なるため組成変動量が一律ではなく、モールド内の場所によってゲーレナイトの晶出状況が異なる。それにより、モールド内で結晶化温度に差が生じ、凝固シェルが不均一に成長することで鋳片縦割れに繋がる。
そこで、本発明者らは、中炭高Ａｌ含有鋼の連続鋳造時における溶融パウダーの組成変動が抑えられなくても、何らかの方法で組成変動前後の結晶化温度差を小さくすることができれば、鋳片縦割れを抑制することができるのではないかと考えた。組成変動後にＣａＦ２(融点１４１８℃)の晶出を促進させてＣａＦ２を主結晶とすることでゲーレナイトが晶出しても結晶化温度の過剰な上昇を抑制でき、また、組成変動前においても主結晶の一つとしてＣａＦ２を晶出させることで、必要な結晶化温度を確保しつつ、組成変動前後の結晶化温度差が小さくでき、鋳片縦割れを抑制できることを見出した。
In order to suppress the various problems as described above, the crystallization temperature before the composition change is set to such an extent that vertical cracks of the slab do not occur (1000 ° C. or more from the actual results), and the crystallization temperature after the composition change is restricted. It is necessary to set a crystallization temperature (1300 ° C. or less based on actual results) at which breakout, excessive increase in the thickness of the powder molten layer, and enlargement of the slag bear do not occur. Further, since the temperature and the flow state of the molten steel vary depending on the location in the mold, the composition variation is not uniform, and the crystallization state of gehlenite varies depending on the location in the mold. As a result, a difference in crystallization temperature occurs in the mold, and the solidified shell grows unevenly, which leads to a vertical slab crack.
Therefore, the present inventors have proposed that, even if the composition variation of the molten powder during continuous casting of medium-coal high Al content steel cannot be suppressed, if the crystallization temperature difference before and after the composition variation can be reduced by any method, the casting We thought that one-sided vertical cracking could be suppressed. By promoting the crystallization of CaF 2 (melting point 1418 ° C.) after the composition change and making CaF 2 the main crystal, an excessive increase in the crystallization temperature can be suppressed even when gehlenite crystallizes, and also before the composition change. It has been found that, by crystallizing CaF 2 as one of the main crystals, the difference in crystallization temperature before and after the composition change can be reduced while maintaining the required crystallization temperature, and vertical slab cracks can be suppressed.
これらの条件を満たすためには、Ｆを１６〜２５質量％、ＣａＯ／ＳｉＯ２質量比を１．０〜１．８、Ａｌ２Ｏ３を５質量％以下（ゼロを含む）、ＭｇＯを１．５質量％以下（ゼロを含む）とすることで、達成できることを見出した。 In order to satisfy these conditions, F is 16 to 25% by mass, CaO / SiO 2 mass ratio is 1.0 to 1.8, Al 2 O 3 is 5% by mass or less (including zero), and MgO is 1%. It has been found that it can be achieved by adjusting the content to 0.5% by mass or less (including zero).
即ち、本発明のモールドパウダーは、Ｆ量が１６〜２５質量％、ＣａＯとＳｉＯ２の質量比（ＣａＯ／ＳｉＯ２）が１．０〜１．８、Ａｌ２Ｏ３量が５質量％以下（ゼロを含む）及びＭｇＯ量が１．５質量％以下（ゼロを含む）であることを特徴とする。 That is, the mold powder of the present invention has an F amount of 16 to 25% by mass, a mass ratio of CaO to SiO 2 (CaO / SiO 2 ) of 1.0 to 1.8, and an Al 2 O 3 amount of 5% by mass or less. (Including zero) and the amount of MgO is 1.5% by mass or less (including zero).
また、本発明の鋼の連続鋳造方法は、上記モールドパウダーを用いて、中炭高Ａｌ含有鋼(鋼中Ｃ含有量＝０．０７〜０．２５質量％、鋼中Ａｌ含有量≧０．２０質量％)を連続鋳造することを特徴とする。 Further, in the continuous casting method for steel of the present invention, using the above-mentioned mold powder, a medium-coal high Al-containing steel (C content in steel = 0.07 to 0.25 mass%, Al content in steel ≧ 0. (20% by mass) is continuously cast.
本発明のモールドパウダーと、それを用いた鋼の連続鋳造方法により、中炭高Ａｌ含有鋼の連続鋳造時における、大きな組成変動を起点とした拘束性ブレークアウト、パウダー溶融層厚みの過剰な増大、スラグベアの肥大化、鋳片縦割れを回避することができるという効果を奏するものである。 Due to the mold powder of the present invention and the continuous casting method of steel using the same, at the time of continuous casting of medium-coal high-Al-containing steel, restraint breakout originating from a large compositional variation and excessive increase in the thickness of the powder molten layer. In addition, it is possible to prevent the slag bear from being enlarged and the slab from being vertically cracked.
本発明のモールドパウダーにおいて、Ｆ量は１６〜２５質量％の範囲内であり、好ましくは１８〜２５質量％の範囲内である。Ｆ量が１６質量％未満の場合、組成変動後の結晶化温度が高くなり、組成変動前後の結晶化温度差が大きくなることで鋳片縦割れが発生するため好ましくない。また、Ｆ量が２５質量％より高い場合、Ｆは浸漬ノズルの溶損を助長する元素であることから、多量添加による浸漬ノズルの折損に繋がるため好ましくない。高Ａｌ含有鋼のように組成変動が大きな鋼種では、スラグ中のＡｌ２Ｏ３、ＣａＯ／ＳｉＯ２が大きく上昇し、ゲーレナイトが晶出し易くなる。しかし、Ｆ量を上記範囲内とすることにより、ＣａＦ２の晶出が促進されるのに対して、ゲーレナイトの晶出が抑制されるので、組成変動後の過剰な結晶化温度上昇を抑制することできる。 In the mold powder of the present invention, the F content is in the range of 16 to 25% by mass, and preferably in the range of 18 to 25% by mass. If the F content is less than 16% by mass, the crystallization temperature after the composition change becomes high, and the crystallization temperature difference before and after the composition change becomes large, so that the vertical slab cracks are not preferable. On the other hand, if the amount of F is higher than 25% by mass, F is an element that promotes the erosion of the immersion nozzle, and therefore, it is not preferable because the addition of a large amount leads to breakage of the immersion nozzle. In a steel type having a large composition variation such as a high Al content steel, Al 2 O 3 and CaO / SiO 2 in the slag increase significantly, and gehlenite is easily crystallized. However, by setting the F content within the above range, the crystallization of CaF 2 is promoted, whereas the crystallization of gehlenite is suppressed, so that the excessive increase in the crystallization temperature after the composition change is suppressed. I can do it.
また、本発明のモールドパウダーにおいて、ＣａＯとＳｉＯ２の質量比（ＣａＯ／ＳｉＯ２）は１．０〜１．８の範囲内であり、好ましくは１．２〜１．６である。ＣａＯ／ＳｉＯ２が１．０未満の場合、組成変動前の結晶化温度が低くなり、組成変動前後の結晶化温度差が大きくなることで鋳片縦割れに繋がるため好ましくない。また、ＣａＯ／ＳｉＯ２が１．８より高い場合、組成変動後の結晶化温度が過剰に高くなり、拘束性ブレークアウトやパウダー溶融層厚みの過剰な増大、スラグベアの肥大化の問題が発生し、更に、組成変動前後の結晶化温度差が大きくなることで鋳片縦割れが発生するため好ましくない。なお、本発明におけるＣａＯ量はモールドパウダーに含まれるＣａ成分が全てＣａＯとして存在するものとして求めた値である。このため、例えばＦ成分としてＣａＦ２を含有する場合も、そのＣａ成分はＣａＯ量に含まれる。 In the mold powder of the present invention, the mass ratio of CaO to SiO 2 (CaO / SiO 2 ) is in the range of 1.0 to 1.8, and preferably 1.2 to 1.6. When CaO / SiO 2 is less than 1.0, the crystallization temperature before the composition change becomes low, and the crystallization temperature difference before and after the composition change becomes large, which is not preferable because it leads to the vertical crack of the slab. Further, when CaO / SiO 2 is higher than 1.8, the crystallization temperature after the composition change becomes excessively high, and problems such as restraint breakout, excessive increase in the thickness of the powder molten layer, and enlargement of the slag bear occur. Further, since the crystallization temperature difference before and after the composition change becomes large, slab vertical cracks occur, which is not preferable. The CaO amount in the present invention is a value obtained assuming that all Ca components contained in the mold powder are present as CaO. Therefore, for example, when CaF 2 is contained as the F component, the Ca component is included in the CaO amount.
なお、本発明のモールドパウダーにおいて、ＣａＯ量は２０〜６０質量％、好ましくは２５〜５５質量％の範囲内である。ここで、ＣａＯ量が６０質量％より高い場合、ＣａＯ／ＳｉＯ２が１．８より高くなるだけでなく、スラグとして溶融しにくくなるために好ましくない。また２０質量％より低い場合、ＣａＯ／ＳｉＯ２が１．０より低くなるだけでなく、結晶化温度が低下して緩冷却機能を果たすことができなくなるために好ましくない。 In addition, in the mold powder of the present invention, the CaO content is in the range of 20 to 60% by mass, preferably 25 to 55% by mass. Here, when the CaO amount is higher than 60% by mass, not only CaO / SiO 2 becomes higher than 1.8 but also it becomes difficult to melt as slag, which is not preferable. On the other hand, when the content is lower than 20% by mass, not only is CaO / SiO 2 lower than 1.0, but also the crystallization temperature is lowered so that a slow cooling function cannot be achieved, which is not preferable.
更に、本発明のモールドパウダーにおいて、Ａｌ２Ｏ３量は５質量％以下（ゼロを含む）であり、好ましくは３質量％以下（ゼロを含む）である。Ａｌ２Ｏ３量が５質量％より高い場合、組成変動前はカスピダインやＣａＦ２の晶出が抑制されることで組成変動前の結晶化温度が低くなり、組成変動後はゲーレナイトの晶出が促進されるため結晶化温度が高くなる。そのため、組成変動前後の結晶化温度差が大きくなり、鋳片縦割れが発生するため好ましくない。 Further, in the mold powder of the present invention, the amount of Al 2 O 3 is 5% by mass or less (including zero), preferably 3% by mass or less (including zero). When the amount of Al 2 O 3 is higher than 5% by mass, crystallization of caspidyne and CaF 2 is suppressed before the composition change, so that the crystallization temperature before the composition change is lowered, and after the composition change, crystallization of gehlenite is prevented. As a result, the crystallization temperature increases. For this reason, the difference in crystallization temperature before and after the change in the composition becomes large, and vertical cracks in the slab occur, which is not preferable.
本発明のモールドパウダーにおいて、ＭｇＯ量は１．５質量％以下（ゼロを含む）であり、好ましくは１．０質量％以下（ゼロを含む）である。なお、ＭｇＯ量が高くなると、ゲーレナイトが晶出し易くなり、組成変動後の結晶化温度が上昇する傾向があるため、ＭｇＯはできるだけ排除することが望ましい。 In the mold powder of the present invention, the amount of MgO is 1.5% by mass or less (including zero), and preferably 1.0% by mass or less (including zero). When the amount of MgO increases, gehlenite tends to crystallize, and the crystallization temperature after a change in composition tends to increase. Therefore, it is desirable to eliminate MgO as much as possible.
また、本発明のモールドパウダーにおいて、Ｎａ２ＯやＬｉ２Ｏはパウダースラグの粘度調整や結晶化温度調整に必要な成分である。しかし、Ｎａ２Ｏ量やＬｉ２Ｏ量を多くすると、結晶種の変化や重要なＦ量が制限されるため、Ｎａ２Ｏ量とＬｉ２Ｏ量は合計で２０質量％以下（ゼロを含まず）、好ましくは１５質量％以下（ゼロを含まず）とすることが好ましい。 In the mold powder of the present invention, Na 2 O and Li 2 O are components necessary for adjusting the viscosity of the powder slag and adjusting the crystallization temperature. However, when the amount of Na 2 O or the amount of Li 2 O is increased, the change of crystal seeds and the amount of important F are limited, so that the total amount of Na 2 O and the amount of Li 2 O is 20% by mass or less (including zero). ), Preferably 15% by mass or less (excluding zero).
本発明のモールドパウダーの構成原料としては、例えば、セメント、石灰石、生石灰のようなＣａＯ原料、珪砂、珪藻土のようなＳｉＯ２原料、蛍石のようなＣａＦ２原料、炭酸リチウムのようなＬｉ２Ｏ原料、炭酸ナトリウム、フッ化ナトリウム、氷晶石のようなＮａ２Ｏ原料を用いることができる。 The constituent materials of the mold powder of the present invention include, for example, CaO materials such as cement, limestone and quick lime, SiO 2 materials such as silica sand and diatomaceous earth, CaF 2 materials such as fluorite, and Li 2 materials such as lithium carbonate. O raw materials, Na 2 O raw materials such as sodium carbonate, sodium fluoride and cryolite can be used.
また、本発明のモールドパウダーにおいて、溶融速度の調整のために炭素原料を必要に応じて配合することができる。炭素原料としてはグラファイト、黒鉛などを用いることができる。なお、Ｃ量は、２０質量％以下、好ましくは１５質量％以下である。Ｃ量が２０質量％より高くなると、モールドパウダー溶融速度が遅く、溶融スラグ層厚みが不足して拘束性ブレークアウトに繋がるため好ましくない。 Further, in the mold powder of the present invention, a carbon material can be blended as needed for adjusting the melting rate. Graphite, graphite, and the like can be used as the carbon raw material. The C content is 20% by mass or less, preferably 15% by mass or less. If the C content is higher than 20% by mass, the mold powder melting rate is low, and the thickness of the molten slag layer is insufficient, which leads to restrictive breakout.
また、本発明のモールドパウダーの形状は特に限定されるものではなく、例えば、粉末、押し出し成形顆粒、中空スプレー顆粒、撹拌造粒など様々な形状で使用することができる。 In addition, the shape of the mold powder of the present invention is not particularly limited, and for example, it can be used in various shapes such as powder, extruded granules, hollow spray granules, and agitated granules.
なお、本明細書におけるモールドパウダーの「結晶化温度」は、１３５０℃で溶融状態のパウダースラグ１２０ｇを４℃／分の速度で降温しながら温度を記録し、結晶化に伴うパウダースラグの発熱開始温度を結晶化温度と定義して測定したものである。 The “crystallization temperature” of the mold powder in the present specification is a temperature at which the temperature of 120 g of powdered slag in a molten state at 1350 ° C. is lowered at a rate of 4 ° C./min, and the temperature is recorded. The temperature was defined as the crystallization temperature and measured.
次に、本発明の鋼の連続鋳造方法は、上述のような構成を有する本発明のモールドパウダーを用いて中炭高Ａｌ含有鋼(鋼中Ｃ含有量＝０．０７〜０．２５質量％、鋼中Ａｌ含有量≧０．２０質量％)を連続鋳造することからなる。モールドパウダーは鋼の連続鋳造においてモールド内の溶鋼表面に添加され、溶鋼からの受熱により溶融し、溶融スラグとなってモールドと凝固シェルの間隙に流れ込みながら消費され使用される。本発明のモールドパウダーを使用する連続鋳造操作において、鋳造速度は０．６〜３．０ｍ／分、好ましくは１．０〜２．５ｍ／分の範囲内である。鋳造速度が０．６ｍ／分未満であると、鋳造速度が遅く経済的でないために好ましくない。また、鋳造速度が３．０ｍ／分を超えるとブレークアウトの危険性が増すため好ましくない。 Next, the continuous casting method of the steel of the present invention uses the mold powder of the present invention having the above-described structure to produce a medium-carbon, high-Al-content steel (C content in steel = 0.07 to 0.25% by mass). (Al content in steel ≧ 0.20% by mass). The mold powder is added to the molten steel surface in the mold in continuous casting of steel, melts by receiving heat from the molten steel, and is consumed and used as molten slag flowing into the gap between the mold and the solidified shell. In a continuous casting operation using the mold powder of the present invention, the casting speed is in the range of 0.6 to 3.0 m / min, preferably 1.0 to 2.5 m / min. If the casting speed is less than 0.6 m / min, it is not preferable because the casting speed is low and it is not economical. If the casting speed exceeds 3.0 m / min, the risk of breakout increases, which is not preferable.
以下の実施例により、本発明品の連続鋳造用モールドパウダーをさらに説明する。
表１及び２に本発明品を示し、表３に比較品を示す。
The following examples further describe the mold powder for continuous casting of the product of the present invention.
Tables 1 and 2 show the products of the present invention, and Table 3 shows comparative products.
表１及び表２中の組成（質量％）は、組成変動前のモールドパウダーの組成および組成変動後のパウダースラグの組成を示しており、組成変動後の組成は（１）式に示す化学反応を組成変動前のモールドパウダーに与えた場合の組成に調整した値を示したものである。即ち、中炭高Ａｌ含有鋼(Ｃ＝０．１２質量％、Ａｌ=０．６質量％)の鋳造時に採取したパウダースラグの分析結果では、元の溶融スラグ組成に対してＡｌ２Ｏ３量が約２０質量％増加していた。そこで、増加した約２０質量％のＡｌ２Ｏ３量は全てが（１）式の反応に従ったと考え、Ａｌ２Ｏ３量を１８〜１９質量％増加し、ＳｉＯ２量を１５〜１７質量％減少した組成を模擬したパウダースラグを調製して変動後の組成としたものである。なお、組成の和が１００質量％を超えるのは、Ｆ成分としてＣａＦ２、ＡｌＦ、ＬｉＦ等を全て酸化物として換算しているためである。なお、ＣＯ２は、原料として炭酸塩を使用することに起因するものである。 The composition (% by mass) in Tables 1 and 2 shows the composition of the mold powder before the composition change and the composition of the powder slag after the composition change, and the composition after the composition change is the chemical reaction shown in the equation (1). Is adjusted to the composition in the case where is given to the mold powder before the composition change. That is, according to the analysis result of powder slag collected at the time of casting of medium-coal high Al content steel (C = 0.12 mass%, Al = 0.6 mass%), the amount of Al 2 O 3 was compared with the original molten slag composition. Was increased by about 20% by mass. Therefore, it is considered that the increased Al 2 O 3 amount of about 20% by mass all followed the reaction of the formula (1), and the Al 2 O 3 amount was increased by 18 to 19% by mass, and the SiO 2 amount was increased by 15 to 17% by mass. The powder slag simulating the composition reduced by% was prepared to be a composition after fluctuation. Note that the sum of the compositions exceeds 100% by mass because CaF 2 , AlF, LiF, and the like are all converted into oxides as the F component. Note that CO 2 is derived from using a carbonate as a raw material.
＜結晶化温度測定＞
本発明品及び比較品のモールドパウダーの結晶化温度測定は以下のように行った：
加熱には電気炉を用い、各モールドパウダー試料を白金製るつぼに装填し、るつぼごと１３５０℃の炉内に装入した。モールドパウダーが溶融した後、熱電対をパウダースラグ中に挿入し、パウダースラグの温度が安定するまで１０分間待機した。続いて、パウダースラグの温度を測定しながら電気炉温度を４℃／分の速度で降温し、パウダースラグの結晶化に伴う発熱開始温度を測定し、この温度を結晶化温度とした。
結晶化温度差については、比較品１のモールドパウダーで鋳片縦割れが発生したことから結晶化温度差が１２０℃以上のモールドパウダーについては「×」、１２０℃未満１００℃以上については「○」、１００℃未満については「◎」として評価した。
＜侵食試験評価＞
侵食試験は、高周波炉を用い１５８０℃の溶銑を作成し、溶銑上に５００gのパウダースラグを作製してその中にＺｒＯ２−Ｃレンガを９０分浸漬させ、溶損量を比較したものである。実機試験でノズル溶損が問題にならなかった比較品１をベースに溶損速度が５％以上上昇したものを「×」、５％未満に収まった、もしくは溶損速度が低下したものを「○」と評価した。
<Measurement of crystallization temperature>
The crystallization temperature measurement of the mold powders of the present invention and the comparative product was performed as follows:
An electric furnace was used for heating, each mold powder sample was charged into a platinum crucible, and the entire crucible was charged into a furnace at 1350 ° C. After the mold powder was melted, a thermocouple was inserted into the powder slag and waited for 10 minutes until the temperature of the powder slag was stabilized. Subsequently, while measuring the temperature of the powder slag, the temperature of the electric furnace was lowered at a rate of 4 ° C./min, and the heat generation starting temperature accompanying the crystallization of the powder slag was measured, and this temperature was defined as the crystallization temperature.
Regarding the crystallization temperature difference, “×” was given for mold powder having a crystallization temperature difference of 120 ° C. or more because a slab vertical crack occurred in the mold powder of Comparative Product 1, and “○” was given for a mold powder of less than 120 ° C. and 100 ° C. or more ”And below 100 ° C were evaluated as“ ◎ ”.
<Erosion test evaluation>
In the erosion test, hot metal of 1580 ° C. was prepared using a high-frequency furnace, 500 g of powder slag was prepared on the hot metal, and ZrO 2 -C brick was immersed therein for 90 minutes, and the amount of erosion was compared. . Based on the comparative product 1 in which nozzle erosion did not become a problem in the actual machine test, the case where the erosion rate increased by 5% or more was evaluated as “x”. ○ ”.
表２中、比較品８は特許文献１の範囲内の組成を持つモールドパウダーを用いた例であり、Ｆ量が本発明よりも少なくゲーレナイトの晶出によって組成変動後の結晶化温度が高くなり、組成変動前後の結晶化温度差が大きくなった。
比較品１および２も比較品８と同じくＦ量が少なく、ゲーレナイトの晶出によって組成変動後の結晶化温度が大きくなり、組成変動前後の結晶化温度差が大きくなった。
比較品３は組成変動前後の結晶化温度差は問題無いものの、Ｆ量が多いため、ＺｒＯ２−Ｃレンガの溶損が助長され、侵食試験でＺｒＯ２−Ｃレンガの溶損速度が速くなった。
比較品４はＡｌ２Ｏ３量が多く、組成変動後にゲーレナイトが晶出し易くなり、組成変動後の結晶化温度が高くなったことで組成変動前後の結晶化温度差が大きくなった。
比較品５はＣａＯ／ＳｉＯ２が低く、組成変動前の結晶であるＣａＦ２やカスピダインの晶出が抑制され、結晶化温度が低くなり組成変動前後の結晶化温度差が大きくなった。
比較品６はＣａＯ／ＳｉＯ２が高く、ＣａＯ量が多いことから組成変動後においてＣａＦ２晶出後でも溶融スラグ中にゲーレナイトが晶出するためのＣａＯが多く残ることで結晶化温度が高くなり、組成変動前後の結晶化温度差が大きくなった。
比較品７は組成変動後の結晶化温度が高くなり、組成変動前後の結晶化温度差が大きくなった。ＭｇＯ量が１．５質量％より多くなると、ゲーレナイトの晶出を促進して結晶化温度差が大きくなった。
比較品９はＮａ２Ｏ＋Ｌｉ２Ｏが２０質量％より多く、組成変動前後の結晶化温度差が大きくなった。
In Table 2, Comparative Product 8 is an example using a mold powder having a composition within the range of Patent Document 1, in which the amount of F is smaller than that of the present invention, and the crystallization temperature after the composition change is increased due to crystallization of gehlenite. In addition, the crystallization temperature difference before and after the composition change was increased.
Comparative products 1 and 2 also had a small amount of F similarly to comparative product 8, and the crystallization temperature after the composition change was increased due to crystallization of gehlenite, and the crystallization temperature difference before and after the composition change was increased.
Although comparative product 3 is the crystallization temperature difference before and after the composition change is no problem, since F amount is large, melting of ZrO 2 -C brick is promoted, erosion rate of ZrO 2 -C bricks faster in corrosion test Was.
Comparative product 4 had a large amount of Al 2 O 3 , gehlenite was easily crystallized after the composition change, and the crystallization temperature after the composition change was increased, so that the crystallization temperature difference before and after the composition change was large.
Comparative product 5 had low CaO / SiO 2 , suppressed the crystallization of CaF 2 and caspidyne, which were crystals before the composition change, reduced the crystallization temperature, and increased the crystallization temperature difference before and after the composition change.
Comparative product 6 has a high CaO / SiO 2 content and a large amount of CaO. Therefore, even after the crystallization of CaF 2 after the composition change, a large amount of CaO remains for the crystallization of gehlenite in the molten slag. In addition, the crystallization temperature difference before and after the composition change was increased.
Comparative product 7 had a higher crystallization temperature after the composition change, and a larger crystallization temperature difference before and after the composition change. When the amount of MgO was more than 1.5% by mass, crystallization of gehlenite was promoted, and the crystallization temperature difference was increased.
In Comparative Example 9, the content of Na 2 O + Li 2 O was more than 20% by mass, and the difference in crystallization temperature before and after the composition change was large.
＜実機試験結果＞
実機試験では本発明品３および９並びに比較品１および８について、評価試験を実施した。
実機試験条件は中炭高Ａｌ含有鋼（Ｃ＝０．０７〜０．２５質量％、Ａｌ＝０．６質量％）のスラブ連鋳機で、モールドサイズが２００×１５００ｍｍ、鋳造速度が１．３ｍ／分での結果を示している。
比較品１および８は鋳片縦割れが発生した。組成変動前後の結晶化温度差が大きいため、凝固シェルの不均一凝固が発生し、鋳片縦割れに繋がったと考えられる。
これに対し、本発明品３および９では鋳片割れは起こらなかった。
このように、本発明品の優位性は明らかである。
<Result of actual machine test>
In the actual machine test, evaluation tests were performed on the products 3 and 9 of the present invention and the comparative products 1 and 8.
The actual machine test conditions were a slab continuous caster of medium carbon high Al content steel (C = 0.07 to 0.25% by mass, Al = 0.6% by mass), a mold size of 200 × 1500 mm, and a casting speed of 1. The result at 3 m / min is shown.
Comparative products 1 and 8 had vertical slab cracks. It is considered that since the crystallization temperature difference before and after the composition change was large, uneven solidification of the solidified shell occurred, which led to vertical cracks in the slab.
In contrast, in the products 3 and 9 of the present invention, no slab cracks occurred.
Thus, the superiority of the product of the present invention is clear.
本発明のモールドパウダーは、中炭高Ａｌ含有鋼(鋼中Ｃ含有量＝０．０７〜０．２５質量％、鋼中Ａｌ含有量≧０．２０0質量％)のように、鋳片縦割れが発生し易い特徴を有する鋼種と、高Ａｌ含有鋼のように大きな組成変動が生じる特徴をもつ鋼種に特に高い効果を発揮する。また、本発明のモールドパウダーは、その他の鋼種に使用しても問題のないものである。 The mold powder of the present invention has a vertical slab crack like medium carbon high Al content steel (C content in steel = 0.07 to 0.25 mass%, Al content in steel ≧ 0.200 mass%). The effect is particularly high for a steel type having a characteristic in which cracks easily occur and a steel type having a characteristic in which a large composition variation occurs, such as a high Al content steel. Further, the mold powder of the present invention has no problem even when used for other steel types.
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