JP4705381B2 - Manufacturing method of low yield ratio steel - Google Patents
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本発明は,高層建築物などの鋼構造物に用いられる効率的な低降伏比鋼材の製造方法に関する。 The present invention relates to an efficient method for producing a low yield ratio steel material used for a steel structure such as a high-rise building.
近年の高層建築物には,巨大地震に見舞われた場合を想定して,柱や梁部材の塑性変形により地震エネルギーを吸収させて大崩壊を回避するという人的安全性を重視した限界状態設計法が適用されているが,それには降伏応力(YP)と引張強さ(TS)の比で示される降伏比(YR)の低い鋼材を使用することが有効であるとされている。 For high-rise buildings in recent years, assuming a case of a huge earthquake, a limit state design that emphasizes human safety by absorbing earthquake energy and avoiding major collapse by plastic deformation of columns and beam members Although the method is applied, it is considered effective to use a steel material having a low yield ratio (YR) indicated by the ratio of yield stress (YP) to tensile strength (TS).
一般に,鋼材の低降伏比化は,ミクロ組織を軟質のフェライト相と硬質のベイナイト相またはマルテンサイト相とからなる混合組織とすることにより達成されることが知られている。低降伏比鋼材の製造方法としては,例えば特許文献1,特許文献2等に記載されているように,熱間圧延終了後,フェライト+オーステナイトの二相域まで空冷した後に加速冷却する方法がある。しかし,このような製造方法は,空冷時に生成するフェライトが粗大化するため,一般に靭性が劣化する傾向があることに加えて,鋼材長手方向の材質均一化が困難であり,また生産性も顕著に低下してしまう,という問題がある。
In general, it is known that a reduction in the yield ratio of steel is achieved by making the microstructure a mixed structure composed of a soft ferrite phase and a hard bainite phase or a martensite phase. As a method for producing a low yield ratio steel material, for example, as described in Patent Document 1,
他の製造方法としては,特許文献3に見られるように,圧延終了後フェライト+オーステナイトの二相温度域で熱処理を施す方法がある。しかし,この方法も,二相域加熱によってミクロ組織が粗大化するため靭性が劣化するとともに,熱処理工程が増える分,生産性が大幅に低下してしまう,という問題がある。
As another manufacturing method, as shown in
そこで,本発明は,このような問題に鑑みてなされたもので,その目的は,生産性の低い複雑な熱間圧延工程や熱処理工程を必要とせずに,低降伏比鋼材を効率的に製造することが可能な,新規かつ改良された低降伏比鋼材の製造方法を提供することにある。 Therefore, the present invention has been made in view of such problems, and the object thereof is to efficiently produce a low yield ratio steel material without requiring a complicated hot rolling process or heat treatment process with low productivity. It is an object of the present invention to provide a new and improved method for producing a low yield ratio steel that can be used.
本発明者らは,上記課題を解決すべく鋭意検討を重ねた結果,通常の加熱,圧延,冷却,熱処理工程により,フェライト分率を20%以上とした後,低温で軽圧下圧延を施すことにより,鋼材のTSや伸び(EL)を低下させずにYPのみを低下させて,容易に低降伏比化を達成できることを見出した。 As a result of intensive studies to solve the above-mentioned problems, the present inventors set the ferrite fraction to 20% or more by normal heating, rolling, cooling, and heat treatment processes, and then performing light reduction rolling at a low temperature. Thus, it was found that the yield ratio can be easily reduced by reducing only YP without reducing TS and elongation (EL) of the steel material.
本発明は,かかる知見に基づき,さらに検討を加えてなされたものであり,その手段とするところは下記の通りである。
(1) 0.01〜0.20質量%のCと,0.02〜1.0質量%のSiと,0.20〜2.5質量%のMnと,0.025質量%以下のPと,0.020質量%以下のSと,0.002〜0.10質量%のAlと,0.0010〜0.0080質量%のNと,残部として,Feおよび不可避不純物とからなり,かつ,フェライト分率が20%以上である鋼材を,100℃以上,かつ,時効が生じない温度で,圧下率0.1〜0.5%で軽圧下圧延を行うことを特徴とする,低降伏比鋼材の製造方法。
(2) 0.05〜1.5質量%のCu,0.05〜1.0質量%のCr,0.05〜0.5質量%のMo,0.05〜0.5質量%のW,0.05〜0.5質量%のTa,0.05〜3.5質量%のNi,0.003〜0.050質量%のNb,0.003〜0.10質量%のTi,0.005〜0.10質量%のV,0.0003〜0.0030質量%のB,0.0003〜0.0050質量%のCa,0.0005〜0.0060質量%のMg,及び0.0005〜0.0060質量%のREMからなる群より選択される1種または2種以上をさらに含有することを特徴とする,(1)に記載の低降伏比鋼材の製造方法。
(3) 前記時効が生じない温度Tは,下記数式1を満足する温度であることを特徴とする,(1)または(2)に記載の低降伏比鋼材の製造方法。
T≦250−26000*[(N%)−(Ti%)/3.4−(Al%)/29](℃)
(但し,[(N%)−(Ti%)/3.4−(Al%)/29]<0の場合は,T=0とする。また,Tiが含まれていない場合には,(Ti%)=0とする。)
・・・(数式1)
The present invention has been made on the basis of such findings and has been further studied, and the means thereof is as follows.
(1) 0.01-0.20 mass% C, 0.02-1.0 mass% Si, 0.20-2.5 mass% Mn, 0.025 mass% or less P 0.020% by mass or less of S, 0.002 to 0.10% by mass of Al, 0.0010 to 0.0080% by mass of N, and the balance being Fe and inevitable impurities, and Low yield, characterized by rolling a steel material with a ferrite fraction of 20% or more at a temperature of 100 ° C or more and at a temperature at which aging does not occur at a rolling reduction of 0.1 to 0.5%. A method for producing a specific steel material.
(2) 0.05 to 1.5 mass% Cu, 0.05 to 1.0 mass% Cr, 0.05 to 0.5 mass% Mo, 0.05 to 0.5 mass% W 0.05 to 0.5 mass% Ta, 0.05 to 3.5 mass% Ni, 0.003 to 0.050 mass% Nb, 0.003 to 0.10 mass% Ti, 0 0.005 to 0.10 mass% V, 0.0003 to 0.0030 mass% B, 0.0003 to 0.0050 mass% Ca, 0.0005 to 0.0060 mass% Mg, and The method for producing a low yield ratio steel according to (1), further comprising one or more selected from the group consisting of 0005 to 0.0060 mass% REM.
(3) The method for producing a low yield ratio steel material according to (1) or (2), wherein the temperature T at which the aging does not occur is a temperature that satisfies the following mathematical formula 1.
T ≦ 250-26000 * [(N%) − (Ti%) / 3.4− (Al%) / 29] (° C.)
(However, if [(N%)-(Ti%) / 3.4- (Al%) / 29] <0, T = 0. If Ti is not included, Ti%) = 0.)
... (Formula 1)
本発明の低降伏比鋼材の製造方法によれば,時効が生じない低温域で軽圧下圧延してYPのみを低下させることで,生産性を低下させる熱間圧延後の温度待ちや熱処理工程を必要とせずに,低降伏比鋼材を効率的に得ることができる。 According to the manufacturing method of the low yield ratio steel material of the present invention, the temperature waiting after the hot rolling and the heat treatment process to reduce productivity can be achieved by reducing only YP by light rolling in a low temperature region where aging does not occur. Low yield ratio steel can be obtained efficiently without the need.
以下に添付図面を参照しながら,本発明の好適な実施の形態について詳細に説明する。 Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.
本発明者らは,鋼材のミクロ組織のフェライト中に可動転位を導入することにより,TSやELを低下させずにYPのみを大きく低下させることが可能であるとの知見に基づき,まず,鋼材のフェライト分率について検討した。その結果,鋼材のフェライト分率が20%以上であれば好ましいことが判明した。つまり,フェライト分率が20%未満であると,フェライト中に可動転位を導入出来たとしても,その絶対量が少ないため鋼材のYPの低下が少なく,YRの低下が小さいために,フェライト分率を20%以上,好ましくは50%以上とするものである。 Based on the knowledge that by introducing movable dislocations in the ferrite of the microstructure of the steel material, it is possible to greatly reduce only YP without reducing TS and EL, The ferrite fraction was examined. As a result, it was found that it is preferable if the ferrite fraction of the steel material is 20% or more. In other words, if the ferrite fraction is less than 20%, even if movable dislocations can be introduced into the ferrite, the absolute amount is small, so the decrease in YP of the steel material is small, and the decrease in YR is small. Is 20% or more, preferably 50% or more.
ここで,フェライト分率が20%以上の鋼材を得るためには,生産性を阻害するような複雑な熱間圧延や熱処理によってミクロ組織を精緻にコントロールする必要はなく,最終的な圧延を行う前の段階で,フェライト分率を20%以上にしておけばよい。例えば,1000〜1300℃に加熱した鋼片をAr3〜1100℃,累積圧下率50%以上で圧延し,次に,空冷してもよく,あるいは高強度化を図るために,Ar3以上の温度から,20℃/s以下の冷却速度で,または,400℃以上の温度まで加速冷却してもよい。更に,強度,靭性,伸び等を調整することを目的として,650℃以下の温度で熱処理してもよい。
Here, in order to obtain a steel material having a ferrite fraction of 20% or more, it is not necessary to precisely control the microstructure by complicated hot rolling or heat treatment that hinders productivity, and final rolling is performed. In the previous stage, the ferrite fraction should be 20% or more. For example, a steel slab heated to 1000 to 1300 ° C. may be rolled at
また,軽圧下圧延の圧下率を0.1〜0.5%の範囲で圧延を行う必要がある。これは,圧下率が0.1%未満であると,上記フェライトに可動転位を均一かつ十分な量導入することができず,YRが低下しないからである。一方,圧下率が0.5%を超えると,転位密度が過剰になるため加工硬化が生じ,YP,およびYRが上昇に転じることに加えて,ELの低下が顕在化してくるからである。ここで,軽圧下圧延の圧下率とYRとの関係を図1に示した。なお,図1において,横軸は圧下率(%)であり,縦軸はYR(%)である。 In addition, it is necessary to perform rolling in a light rolling reduction range of 0.1 to 0.5%. This is because if the rolling reduction is less than 0.1%, a uniform and sufficient amount of movable dislocations cannot be introduced into the ferrite, and YR does not decrease. On the other hand, when the rolling reduction exceeds 0.5%, the dislocation density becomes excessive, so that work hardening occurs, and in addition to YP and YR starting to increase, a decrease in EL becomes apparent. Here, the relationship between the rolling reduction of light rolling and YR is shown in FIG. In FIG. 1, the horizontal axis represents the rolling reduction (%), and the vertical axis represents YR (%).
また,軽圧下圧延時の鋼材温度については,時効が生じない温度範囲内で圧延を行う必要がある。これは,軽圧下圧延によりフェライトに可動転位が導入されたとしても,時効によってYPが元に戻り,YRが上昇する場合があり,これを回避するためである。ここで,軽圧下圧延を実施した温度と数式1の上限温度との差と,YRとの関係を図2に示した。なお,図2において,横軸は軽圧下圧延を実施した温度と数式1の上限温度との差(℃)であり,縦軸はYR(%)である。また,時効が生じない温度領域であっても,100℃以上であると,圧延の負荷を軽減できるので好ましい。 In addition, regarding the steel material temperature during light rolling, it is necessary to perform rolling within a temperature range in which aging does not occur. This is to avoid the possibility that even if movable dislocations are introduced into the ferrite by light rolling, YP may return to the original due to aging and YR may rise. Here, the difference between the temperature at which the light rolling is performed and the upper limit temperature of Formula 1 and the relationship with YR are shown in FIG. In FIG. 2, the horizontal axis represents the difference (° C.) between the temperature at which the light rolling is performed and the upper limit temperature of Equation 1, and the vertical axis represents YR (%). Further, even in a temperature range where aging does not occur, a temperature of 100 ° C. or higher is preferable because the rolling load can be reduced.
更に,この時効が生じない温度範囲の上限Tmaxを下記数式1で求めることが好ましい。ここで,数式1において,(N%),(Ti%)及び(Al%)は,それぞれ,N,Ti及びAlの含有量を質量%で表した数値を意味している。 Furthermore, it is preferable to obtain the upper limit T max of the temperature range in which this aging does not occur using the following Equation 1. Here, in Formula 1, (N%), (Ti%), and (Al%) mean numerical values representing the contents of N, Ti, and Al in mass%, respectively.
Tmax=250−26000*[(N%)−(Ti%)/3.4−(Al%)/29](℃)
(但し,[(N%)−(Ti%)/3.4−(Al%)/29]<0の場合は,Tmaz=0とする)
・・・(数式1)
T max = 250-26000 * [(N%)-(Ti%) / 3.4- (Al%) / 29] (° C.)
(However, if [(N%)-(Ti%) / 3.4- (Al%) / 29] <0, T maz = 0)
... (Formula 1)
次に,本発明の製造方法を使用して製造される鋼材の成分は通常の鋼材と同様であるが,その添加量の限定理由について説明する。 Next, the components of the steel material manufactured using the manufacturing method of the present invention are the same as those of a normal steel material, but the reason for limiting the amount added will be described.
Cは,鋼の強度を向上させる有効な成分として下限を0.01%とし,また過剰の添加は,鋼材の溶接性やHAZ(Heat Affected Zone)靭性などを著しく低下させるので,上限を0.20%とした。 C is an effective component for improving the strength of steel, and the lower limit is set to 0.01%. Excessive addition significantly lowers the weldability and HAZ (Heat Affected Zone) toughness of the steel, so the upper limit is set to 0. 20%.
Siは,溶製時の脱酸に必要な元素であり,適量添加するとマトリクスを固溶強化するため,0.02%以上添加する。一方,1.0%超添加すると,HAZの硬化により靭性が低下するため,上限を1.0%とした。 Si is an element necessary for deoxidation at the time of melting. If an appropriate amount is added, the matrix is solid-solution strengthened, so 0.02% or more is added. On the other hand, if added over 1.0%, the toughness decreases due to the hardening of the HAZ, so the upper limit was made 1.0%.
Mnは,母材の強度,靭性の確保に有効な成分として0.20%以上の添加が必要であるが,溶接部の靭性,割れ性などの許容できる範囲で上限を2.5%とした。 Mn needs to be added in an amount of 0.20% or more as an effective component for securing the strength and toughness of the base metal, but the upper limit is set to 2.5% within an acceptable range of toughness and cracking of the welded part. .
P,Sは,含有量が少ないほど望ましいが,これを工業的に低減させるためには多大なコストがかかることから,それぞれ0.025%,0.020%を上限とした。 P and S are desirable as the content is small. However, in order to reduce this industrially, it takes a great deal of cost, so 0.025% and 0.020% were set as upper limits, respectively.
Alは,重要な脱酸元素であるため,下限値を0.002%とした。また,Alが多量に存在すると鋳片の表面品位が劣化するため,上限を0.10%とした。 Since Al is an important deoxidizing element, the lower limit was set to 0.002%. In addition, since the surface quality of the slab deteriorates when a large amount of Al is present, the upper limit was made 0.10%.
Nは,AlNとして析出することでオーステナイトを微細化させる効果があるが,過剰添加により固溶Nが増大するとHAZ靭性の低下を招くことから,0.0010〜0.0080%の範囲に制限した。 N has the effect of refining austenite by precipitating as AlN. However, if the solid solution N increases due to excessive addition, the HAZ toughness is reduced, so it is limited to a range of 0.0010 to 0.0080%. .
また,選択添加元素の添加量は,以下の理由により限定される。 Moreover, the addition amount of the selective additive element is limited for the following reasons.
Cu,Cr,Mo,W,Taは,鋼材の焼入れ性向上により高強度化させるために有効であることから,0.05%以上添加するが,多量に添加すると溶接性,HAZ靭性を低下させるため,Cuについては1.5%,Crについては1.0%,Mo,W,Taについては0.5%を上限とした。 Cu, Cr, Mo, W, and Ta are effective for increasing the hardenability of steel materials, so 0.05% or more is added, but if added in a large amount, weldability and HAZ toughness are reduced. Therefore, the upper limit is 1.5% for Cu, 1.0% for Cr, and 0.5% for Mo, W, and Ta.
Niは,鋼材の強度および靭性を向上させることから,0.05%以上添加することが好ましいが,Ni量の増加はコストを上昇させるので,3.5%を上限とした。 Ni improves the strength and toughness of the steel material, so 0.05% or more is preferably added. However, since increasing the amount of Ni increases the cost, the upper limit is set to 3.5%.
Nb,Tiは,微量の添加により結晶粒の微細化と析出強化の面で有効に機能するため,0.003%以上添加するが,過剰に添加すると溶接部靭性を著しく低下させるため,Nbについては0.050%,Tiについては0.10%を上限とした。 Nb and Ti function effectively in terms of grain refinement and precipitation strengthening by adding a small amount, so 0.003% or more is added, but if added excessively, the toughness of the welded portion is significantly reduced. The upper limit was 0.050%, and Ti was 0.10%.
Vは,焼入れ性を向上させるとともに炭窒化物を形成して高強度化に寄与するため,0.005%以上添加するが,多量に添加するとHAZ靭性を劣化させるため,0.10%を上限とした。 V improves hardenability and contributes to strengthening by forming carbonitride, so 0.005% or more is added, but if added in a large amount, HAZ toughness deteriorates, so 0.10% is the upper limit. It was.
Bは,HAZ靭性に有害な粒界フェライト,フェライトサイドプレートの成長抑制と高強度化に有効であることから,0.0003%以上添加するが,過剰に添加すると靭性を劣化させることから,0.0030%を上限とした。 B is effective in suppressing the growth of grain boundary ferrite and ferrite side plates, which are harmful to HAZ toughness, and increasing the strength. Therefore, B is added in an amount of 0.0003% or more. The upper limit was .0030%.
Ca,Mg,REMは,酸化物や硫化物を形成し,HAZ結晶粒粗大化の防止,及び母材の異方性の軽減を目的に添加するが,添加量が少ないと効果がなく,過度の添加は靭性を損なうため,Ca:0.0003〜0.0050%,Mg:0.0005〜0.0060%,REM:0.0005〜0.0060%の範囲で添加する。なお,REMとは,La,Ceなどの希土類元素のことである。 Ca, Mg, and REM form oxides and sulfides and are added for the purpose of preventing coarsening of HAZ crystal grains and reducing the anisotropy of the base material. Addition of Ca impairs toughness, so Ca is added in the range of 0.0003 to 0.0050%, Mg: 0.0005 to 0.0060%, and REM: 0.0005 to 0.0060%. Note that REM refers to rare earth elements such as La and Ce.
下記表1に,鋼材の化学成分,表2に製造条件,母材組織及び機械的性質を示す。 Table 1 below shows the chemical composition of the steel material, and Table 2 shows the manufacturing conditions, base material structure and mechanical properties.
鋼材のYP,TS,ELについては,JIS4号引張試験片を用いて評価し,YRをYP/TS×100[%]により算出した。破面遷移温度(vTrs)は,JIS4号衝撃試験片を用いて評価した。なお,試験片は,板厚中心部から圧延方向と直角な方向に採取した。 About YP, TS, EL of steel materials, it evaluated using the JIS No. 4 tensile test piece, and YR was computed by YP / TSx100 [%]. The fracture surface transition temperature (vTrs) was evaluated using a JIS No. 4 impact test piece. The test specimens were collected from the center of the plate thickness in a direction perpendicular to the rolling direction.
本発明の実施例のNo.1〜8は,本発明の範囲内の条件で製造したため,いずれも降伏比が75%以下と低く,低降伏比鋼材として良好な特性を有していた。 No. of the embodiment of the present invention. Since Nos. 1 to 8 were manufactured under the conditions within the scope of the present invention, all had low yield ratios of 75% or less, and had good characteristics as low yield ratio steel materials.
一方,比較例のNo.1〜8は,製造条件,または組織のいずれかが本発明の範囲を逸脱していたために,降伏比が80%以上と高くなってしまった。No.1〜3は,軽圧下圧延の温度が高かったために,YPが下がらずYRが低下しなかった。No.4,5は,軽圧下圧延を実施しなかった,または圧下率が小さかったために,YRが低下しなかった。No.6は,圧下率が大きかったためにYPが上昇に転じ,YRが高くなった。No.7は,軽圧下圧延の温度が高く,圧下率も大きかったため,YRが上昇してしまった。No.8は,熱間圧延後の冷却速度が過大,かつ停止温度が低かったために,フェライト分率が低くなり,軽圧下圧延を実施してもYRを下げることができなかった。 On the other hand, no. For 1 to 8, the yield ratio was as high as 80% or more because either the manufacturing conditions or the structure deviated from the scope of the present invention. No. In 1-3, since the temperature of the light rolling was high, YP did not decrease and YR did not decrease. No. In Nos. 4 and 5, YR did not decrease because light rolling was not performed or the rolling reduction was small. No. No. 6 had a large rolling reduction, so that YP started to rise and YR became high. No. In No. 7, the YR increased because the temperature of the light rolling was high and the rolling reduction was large. No. In No. 8, since the cooling rate after hot rolling was excessive and the stop temperature was low, the ferrite fraction was low, and YR could not be lowered even when light rolling was performed.
また,従来例のNo.1,2は,軽圧下圧延ではなく二相域焼入れや熱処理を実施したために,YRは低くなったが,生産性が著しく低下してしまった。従来例のNo.1は,熱間圧延後,温度が二相域まで低下してから水冷を開始したため,YRは実施例のNo.2と同等であったが,靭性が低下し,生産性も低下してしまった。従来例のNo.2は,熱間圧延・加速冷却と焼戻し工程の間に二相域熱処理を実施したため,実施例のNo.3と同程度まで低YR化したものの,生産性が顕著に低下してしまった。 In addition, No. of the conventional example. For Nos. 1 and 2, the YR was lowered because of the two-phase quenching and heat treatment rather than the light rolling, but the productivity was significantly reduced. No. of the conventional example. In No. 1, since water cooling was started after the temperature dropped to the two-phase region after hot rolling, However, the toughness decreased and the productivity also decreased. No. of the conventional example. No. 2 of Example No. 2 because the two-phase region heat treatment was performed during the hot rolling / accelerated cooling and tempering steps. Although the YR was reduced to the same level as 3, the productivity was significantly reduced.
以上示したように,本発明の方法を適用することにより,従来法よりも効率的に低降伏比鋼材を製造できることが確認された。 As described above, it was confirmed that by applying the method of the present invention, a low yield ratio steel material can be manufactured more efficiently than the conventional method.
以上,添付図面を参照しながら本発明の好適な実施形態について説明したが,本発明はかかる例に限定されないことは言うまでもない。当業者であれば,特許請求の範囲に記載された範疇内において,各種の変更例または修正例に想到し得ることは明らかであり,それらについても当然に本発明の技術的範囲に属するものと了解される。 As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to this example. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.
Claims (3)
0.02〜1.0質量%のSiと,
0.20〜2.5質量%のMnと,
0.025質量%以下のPと,
0.020質量%以下のSと,
0.002〜0.10質量%のAlと,
0.0010〜0.0080質量%のNと,
残部として,Feおよび不可避不純物と,
からなり,かつ,フェライト分率が20%以上である鋼材を,
100℃以上,かつ,時効が生じない温度で,圧下率0.1〜0.5%で軽圧下圧延を行うことを特徴とする,低降伏比鋼材の製造方法。 0.01 to 0.20% by mass of C;
0.02 to 1.0 mass% Si,
0.20 to 2.5% by mass of Mn,
0.025 mass% or less of P,
0.020 mass% or less of S,
0.002 to 0.10% by mass of Al,
0.0010 to 0.0080 mass% N;
As the balance, Fe and inevitable impurities,
And a steel material having a ferrite fraction of 20% or more,
A method for producing a low yield ratio steel material, characterized by performing light reduction rolling at a reduction rate of 0.1 to 0.5% at a temperature of 100 ° C. or higher and at which aging does not occur.
T≦250−26000*[(N%)−(Ti%)/3.4−(Al%)/29](℃)
(但し,[(N%)−(Ti%)/3.4−(Al%)/29]<0の場合は,T=0とする)
・・・(数式1)
3. The method for producing a low yield ratio steel according to claim 1, wherein the temperature T at which the aging does not occur is a temperature that satisfies the following formula 1.
T ≦ 250-26000 * [(N%) − (Ti%) / 3.4− (Al%) / 29] (° C.)
(However, if [(N%)-(Ti%) / 3.4- (Al%) / 29] <0, T = 0)
... (Formula 1)
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