JP5974962B2 - Method for producing aluminum-killed steel with Ca added with excellent HIC resistance and Ca addition treatment method for molten steel - Google Patents
Method for producing aluminum-killed steel with Ca added with excellent HIC resistance and Ca addition treatment method for molten steel Download PDFInfo
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本発明は、鋼中の介在物の組成、個数が制御された耐HIC特性に優れた鋼材、およびその鋼材を製造する方法に関するものである。 The present invention relates to a steel material excellent in HIC resistance in which the composition and number of inclusions in steel are controlled, and a method for producing the steel material.
例えば、ラインパイプや電気抵抗溶接（ERW）管のような、耐水素誘起割れ性（耐HIC性）が必要な鋼材では、割れの起因となるMnSを無害化するためにCaを添加し、鋼中Sと反応させてCaSを生成させることが有効である。
また、Caを添加することで、Caが脱酸生成物であるAl2O3と反応してCaO-Al2O3介在物が生成する。CaO-Al2O3介在物は、CaOの割合が高い場合には耐HIC性能悪化の原因になることが知られている。
For example, in steel materials that require hydrogen-induced cracking resistance (HIC resistance), such as line pipes and electrical resistance welding (ERW) pipes, Ca is added to detoxify MnS that causes cracking. It is effective to react with medium S to produce CaS.
Further, by adding Ca, Ca reacts with Al 2 O 3 which is a deoxidation product, thereby generating CaO—Al 2 O 3 inclusions. CaO—Al 2 O 3 inclusions are known to cause deterioration of HIC resistance when the proportion of CaO is high.
ここで、Caが不足すると鋼中のSと反応しきれずMnSを生成してしまい、逆にCaが過剰であると、CaOの割合の高いCaO-Al2O3介在物が生成し、それぞれが耐HIC性能悪化の要因となる。
そのため、介在物の組成を適正に制御するようにCaを添加することが耐HIC性能向上には必要である。
Here, if Ca is insufficient, it will not react with S in the steel and MnS will be generated. Conversely, if Ca is excessive, CaO-Al 2 O 3 inclusions with a high CaO ratio will be generated. It becomes a factor of deterioration of HIC resistance performance.
Therefore, it is necessary to improve the HIC resistance performance by adding Ca so as to appropriately control the composition of inclusions.
Caの最適な添加量やCaO-Al2O3介在物の最適な組成を制御して、耐HIC性能を向上させる技術として、例えば、特許文献１に開示された耐サワー性の優れた高靱性電縫鋼管用鋼板がある。
特許文献１の高靱性電縫鋼管用鋼板においては、「鋼中のS,O,Caの含有量が、1.0≦(%Ca)(1-72(%O))/1.25(%S)≦2.5を満足したうえで、脱酸生成物を(CaO)m(Al2O3)nの複合介在物とし、その分子構成比をm/n＜１とする」（特許請求の範囲の第１項参照）ことが開示されている。
また、特許文献２では、二次精錬終了後に所定の式の範囲の量のCaを溶鋼中に添加し、介在物中のCaO含有率を30質量%以上55質量%以下に制御する方法（請求項３参照）が開示されている。
さらに、特許文献３では、鋼中の直径が５μｍ以上のＣ系介在物個数が10個/mm2未満である高強度鋼が開示されている。
As a technique for improving the HIC resistance performance by controlling the optimum amount of Ca and the optimum composition of CaO—Al 2 O 3 inclusions, for example, high toughness with excellent sour resistance disclosed in Patent Document 1 There are steel sheets for ERW steel pipes.
In the steel sheet for high toughness ERW steel pipe of Patent Document 1, “the content of S, O, Ca in steel is 1.0 ≦ (% Ca) (1-72 (% O)) / 1.25 (% S) ≦ After satisfying 2.5, the deoxidation product is a complex inclusion of (CaO) m (Al 2 O 3 ) n, and its molecular composition ratio is m / n <1 ”(first claim) Section).
Further, in Patent Document 2, after completion of secondary refining, an amount of Ca in the range of a predetermined formula is added to molten steel, and the CaO content in inclusions is controlled to 30% by mass to 55% by mass (claim) Item 3) is disclosed.
Furthermore, Patent Document 3 discloses a high-strength steel in which the number of C-based inclusions having a diameter of 5 μm or more in the steel is less than 10 pieces / mm 2 .
しかしながら、特許文献１に記載の方法では、Caを添加してもCaO-Al2O3介在物が溶鋼温度での平衡組成になるまでCaO比率が高くなっていない組成（Slag atlas：Verlag Stahleisen m.b.H 編（1981）p.28参照）のため、添加したCaの多くが酸化物と反応し、Sと反応する分が不足することとなる。そのため、鋼中Sと反応させてCaSを生成させることができず、割れの起因となるMnSの無害化が不十分になる。 However, in the method described in Patent Document 1, a composition in which the CaO ratio does not increase until CaO-Al 2 O 3 inclusions reach an equilibrium composition at the molten steel temperature even when Ca is added (Slag atlas: Verlag Stahleisen mbH (See ed. (1981) p. 28), most of the added Ca reacts with the oxide, and the amount reacting with S is insufficient. Therefore, CaS cannot be produced by reacting with S in steel, and the detoxification of MnS that causes cracking becomes insufficient.
また、特許文献２に記載の方法では、介在物組成を狭い範囲に制御しているが、実操業においては、添加するCa合金の状態、組成や、添加速度、添加時の雰囲気、温度等の条件によってCaの反応性が影響を受け、介在物組成を精度良く制御することが困難である。 In addition, in the method described in Patent Document 2, the inclusion composition is controlled within a narrow range. However, in actual operation, the state, composition, addition rate, atmosphere at the time of addition, temperature, etc. of the Ca alloy to be added The reactivity of Ca is affected by conditions, and it is difficult to control the inclusion composition with high accuracy.
また、特許文献３に記載の方法では、特許文献２に記載のように、組成によっては耐HIC性能に悪影響を及ぼさない介在物もあるため、介在物個数を組成によらず低減させることは、製造プロセスに過剰の負荷がかかることになり望ましくない。 In addition, in the method described in Patent Document 3, as described in Patent Document 2, there are inclusions that do not adversely affect the HIC resistance performance depending on the composition. The manufacturing process is overloaded, which is undesirable.
本発明は、かかる課題を解決するためになされたものであり、割れの起因となるMnSが効果的に除去されて耐HIC特性に優れた鋼材、および製造プロセスに過剰の負荷をかけることなく前記耐HIC特性に優れた鋼材を製造する方法を提供することを目的とするものである。 The present invention has been made in order to solve such a problem, steel material excellent in HIC resistance by effectively removing MnS causing cracks, and the above without overloading the manufacturing process An object of the present invention is to provide a method for producing a steel material having excellent HIC resistance.
Caを添加して製造した鋼板についての耐HIC性能試験結果には優劣があることから、劣位の原因を探るべく、耐HIC性能試験結果が劣位な鋼板におけるHICで生じた割れ面（以下、「HIC破面」という）を調査した。その結果、HIC破面には、伸展したMnSとは別の介在物が観察されたことから鋼中の介在物組成を調査した。
調査の結果、多くの介在物がCaO-Al2O3の複合介在物であり、また、耐HIC性能が劣位なものでは、複合介在物中のCaOとAl2O3の質量比率CaO/Al2O3が低いもの（0.3以下）、あるいは、高いもの（4.0以上）の比率が高い傾向があった。そして、これらの複合介在物は状態図上で組成を見ると、高融点のものであった。
Since the HIC performance test results for steel sheets manufactured with Ca added are superior and inferior, the crack surface (hereinafter referred to as “ "HIC fracture surface"). As a result, inclusions other than the extended MnS were observed on the HIC fracture surface, and the inclusion composition in the steel was investigated.
As a result of investigation, many inclusions are CaO-Al 2 O 3 composite inclusions, and those with poor HIC resistance performance, the mass ratio of CaO to Al 2 O 3 in the composite inclusions CaO / Al There was a tendency for the ratio of 2 O 3 to be low (0.3 or less) or high (4.0 or more) to be high. These composite inclusions had a high melting point when viewed from the phase diagram.
これは、低融点の複合介在物は溶鋼中では液体状であるため、複合介在物同士が凝集合体してもあまり大きくはならないが、高融点の複合介在物の場合、凝集合体すると複合介在物が鎖状になり、見かけの径が大きくなるため、耐HIC性能には不利になったものと考えられる。 This is because composite inclusions with a low melting point are in liquid form in molten steel, so even if the composite inclusions agglomerate and coalesce, they do not become too large. Since the chain becomes chain-like and the apparent diameter increases, it is considered that the HIC resistance is disadvantageous.
またCaO/Al2O3の値が低いか、あるいは高いものの比率が高くても耐HIC性能が優位なものがあったため、その要因を調査したところ、それは複合介在物の個数が少ないものであった。
そこで、複合介在物の個数が耐HIC性能に与える影響について調査した。その結果、複合介在物の総個数の如何によらず、高融点の複合介在物（以下、単に「高融点介在物」という）すなわちCaO/Al2O3が低いもの（0.3以下）、あるいは、高いもの（4.0以上）の個数が多い場合に耐HIC性能が劣位であることが判明した。
In addition, even though the CaO / Al 2 O 3 value was low or high, there was an excellent HIC resistance performance even when the ratio was high, and as a result of investigating the cause, it was found that the number of composite inclusions was small. It was.
Therefore, the effect of the number of composite inclusions on HIC resistance was investigated. As a result, regardless of the total number of composite inclusions, high melting point composite inclusions (hereinafter simply referred to as “high melting point inclusions”), that is, those with low CaO / Al 2 O 3 (0.3 or less), or It was found that the resistance to HIC is inferior when the number of high ones (4.0 or higher) is large.
粒径が1.5mm以上の高融点介在物の個数（個/mm2）とHIC試験不合格率（%）との関係を調査し、整理した結果を図１に示す。なお、粒径が1.5mm以上としたのは、粒径が1.5mm未満ではHIC試験に与える影響がほとんどないからである。
図１は、縦軸がHIC試験不合格率（%）で横軸が高融点介在物の個数（個/mm2）である。
図１から分かるように、高融点介在物すなわち、CaO/Al2O3が0.3以下、4.0以上で、粒径が1.5mm以上のものの個数を10個/mm2以下とすることで、HIC試験不合格率を10%以下とすることができ、耐HIC性能の良好な鋼材を得ることができる。
なお、介在物組成・個数を評価する手法としては、粒子解析ＳＥＭ（走査電子顕微鏡）法を利用することができる。近年普及の進む粒子解析ＳＥＭ法では、介在物の組成・サイズ・個数の情報を同時に取得することが可能であり、本発明における耐HIC特性指標として極めて好適に利用できる。粒子解析ＳＥＭ法の代表性を検証するため、測定結果の精度・再現性を調査したが、10mm2、より好ましくは30mm2の領域を対象とすることにより、図１に示すような、耐HIC特性との相関の高い指標を構築することが可能であった。
The relationship between the number of high melting point inclusions (particles / mm 2 ) with a particle size of 1.5 mm or more and the HIC test rejection rate (%) was investigated and summarized. The reason why the particle size is 1.5 mm or more is that when the particle size is less than 1.5 mm, there is almost no influence on the HIC test.
In FIG. 1, the vertical axis represents the HIC test rejection rate (%), and the horizontal axis represents the number of high melting point inclusions (pieces / mm 2 ).
As can be seen from FIG. 1, the high melting point inclusion, that is, CaO / Al 2 O 3 is 0.3 or less, 4.0 or more, and the number of particles having a particle size of 1.5 mm or more is set to 10 pieces / mm 2 or less. The rejection rate can be made 10% or less, and a steel material with good HIC resistance can be obtained.
As a method for evaluating the composition and number of inclusions, a particle analysis SEM (scanning electron microscope) method can be used. In recent years, particle analysis SEM, which has been widely used, can simultaneously acquire information on the composition, size, and number of inclusions, and can be used extremely favorably as an HIC resistance index in the present invention. In order to verify the representativeness of the particle analysis SEM method, the accuracy and reproducibility of the measurement results were investigated. By targeting a region of 10 mm 2 , more preferably 30 mm 2 , the resistance to HIC as shown in FIG. It was possible to build an index highly correlated with characteristics.
上記の複合介在物組成、やその個数を制御するためには、溶鋼成分を制御することが重要である。溶鋼中全Ca濃度（T.[Ca]）が、複合介在物を低融点介在物に制御し、かつSをCaSに制御するために必要なCa濃度より過剰であれば、CaO比率の高い高融点介在物が存在することとなり、耐HIC性能が劣位となる。逆に、溶鋼中全Ca濃度（T.[Ca]）が、前記必要なCa濃度よりも不足であれば、Al2O3介在物を低融点介在物に制御しきらずに高融点のまま存在し、また、SをCaSに制御しきらず、MnSが生成することとなり、耐HIC性能が劣位となる。 In order to control the composite inclusion composition and the number thereof, it is important to control the molten steel components. If the total Ca concentration (T. [Ca]) in molten steel is higher than the Ca concentration necessary to control composite inclusions to low melting point inclusions and to control S to CaS, the CaO ratio is high. Melting point inclusions exist, and the HIC resistance performance is inferior. On the other hand, if the total Ca concentration (T. [Ca]) in the molten steel is lower than the required Ca concentration, Al 2 O 3 inclusions remain at a high melting point without being fully controlled by low melting point inclusions. However, S cannot be controlled by CaS, and MnS is generated, resulting in inferior HIC resistance.
CaO-Al2O3介在物をCaの添加処理により低融点化する場合、目標となる組成は最も融点の低い組成とすべきであり、その組成は質量比でCaO:Al2O3=1:1である（Slag atlas：Verlag Stahleisen m.b.H 編（1981）p.28参照）。その際、介在物中のCaとOの量は以下の関係となる。
WCa-O(kg)＝（17/18）WO(kg)・・・（２）
ここで、WCa-O(kg)：酸化物になるCa質量
WO(kg)：酸化物中O質量
また、SをCaSに制御するには、SとCaがモル比でS:Ca=1:1が必要で、質量比では、以下の関係となる。
WCa-S(kg)＝1.25×WS(kg)・・・（３）
ここで、WCa-S(kg)：硫化物になるCa質量
WS(kg)：S質量
When lowering the melting point of CaO-Al 2 O 3 inclusions by adding Ca, the target composition should be the lowest melting point, and the composition should be CaO: Al 2 O 3 = 1 by mass ratio. : 1 (see Slag atlas: Verlag Stahleisen mbH (1981) p.28). At that time, the amount of Ca and O in the inclusion has the following relationship.
W Ca-O (kg) = (17/18) W O (kg) (2)
Where W Ca-O (kg): the mass of Ca that becomes oxide
W 2 O (kg): O mass in oxide In addition, in order to control S to CaS, S: Ca is required to have a molar ratio of S: Ca = 1: 1, and the mass ratio has the following relationship.
W Ca-S (kg) = 1.25 x W S (kg) (3)
Where W Ca-S (kg): Mass of Ca that becomes sulfide
W S (kg): S mass
上記（２）、（３）式の和が、介在物形態制御に必要なCa量であり、このCa量と、Ca添加後の鋼中のT.Ca濃度との差が、Ca量の過不足量となる。
このCaの過不足量と酸化物介在物量の比が、高融点の介在物の比率と考えた。即ち、この比が大きければ、CaO比率の高い高融点介在物が多く、比が小さければ、Al2O3比率の高い高融点介在物が多くなると考えた。
酸化物介在物量はT.[O]で表すことができるため、以上をまとめるとCaの過不足量と酸化物介在物量の比Ｒは以下の式（４）となる。
Ｒ＝（T.[Ca]−（17/18）×T.[O]−1.25×Ｓ）/T[O]・・・（４）
ここで、R：Ca過不足量と酸化物介在物量の比
T.[Ca]：鋼中全Ca濃度（ppm）
T.[O]：鋼中全酸素濃度（ppm）
S：鋼中S濃度（ppm）
そして、鋼中酸素濃度を25ppm以下、上記（４）式のＲを0.1以上、0.5以下とすることで、介在物組成を低融点に制御でき、介在物組成中CaO/Al2O3が0.3以下、4.0以上で、粒径が1.5mm以上のものの個数を10個/mm2以下とすることが出来ることを見出した。
本発明は以上の知見に基づくものであり、具体的には以下の構成からなるものである。
The sum of the above formulas (2) and (3) is the Ca amount necessary for inclusion morphology control, and the difference between this Ca amount and the T.Ca concentration in the steel after the addition of Ca is the excess of the Ca amount. Insufficient amount.
The ratio between the excess and deficiency of Ca and the amount of oxide inclusions was considered as the ratio of inclusions with a high melting point. That is, it is considered that if this ratio is large, there are many high melting point inclusions with a high CaO ratio, and if the ratio is small, there are many high melting point inclusions with a high Al 2 O 3 ratio.
Since the amount of oxide inclusions can be expressed by T. [O], when the above is summarized, the ratio R between the excess and deficiency of Ca and the amount of oxide inclusions is expressed by the following formula (4).
R = (T. [Ca] − (17/18) × T. [O] −1.25 × S) / T [O] (4)
Where R: Ratio of Ca excess / deficiency and oxide inclusions
T. [Ca]: Total Ca concentration in steel (ppm)
T. [O]: Total oxygen concentration in steel (ppm)
S: S concentration in steel (ppm)
The inclusion composition can be controlled to a low melting point by setting the oxygen concentration in the steel to 25 ppm or less and R in the above formula (4) to 0.1 or more and 0.5 or less, and CaO / Al 2 O 3 is 0.3 in the inclusion composition. Hereinafter, it has been found that the number of particles having a particle size of 4.0 or more and a particle size of 1.5 mm or more can be 10 pieces / mm 2 or less.
The present invention is based on the above knowledge, and specifically comprises the following configuration.
（１）本発明に係る耐HIC特性に優れる鋼材は、鋼中に存在する非金属介在物のうち、その介在物中の(%CaO)/(% Al2O3)が0.3以下あるいは4.0以上で粒径1.5μｍ以上のものが10個/mm2以下であることを特徴とするものである。 (1) The steel material having excellent HIC resistance according to the present invention is a nonmetallic inclusion existing in steel, and (% CaO) / (% Al 2 O 3 ) in the inclusion is 0.3 or less or 4.0 or more The number of particles having a particle size of 1.5 μm or more is 10 pieces / mm 2 or less.
（２）また、上記（１）に記載のものにおいて、介在物組成および個数の評価が、粒子分析ＳＥＭ法によって行ったものであることを特徴とするものである。 (2) Moreover, in the thing of said (1), evaluation of inclusion composition and number is performed by the particle analysis SEM method, It is characterized by the above-mentioned.
（３）本発明に係る耐HIC特性に優れるCaを添加したアルミキルド鋼材の製造方法は、アルミニウムあるいはその合金により脱酸処理された溶鋼中にCaを添加するに際し、（１）式を満たす範囲となるようにCa含有合金を添加することを特徴とするものである。
0.1≦（T.[Ca]−（17/18）×T.[O]−1.25×Ｓ）/T[O]≦0.5 ・・・（１）
T.[Ca]：鋼中全Ca濃度（質量ppm）
T.[O]：鋼中全酸素濃度（質量ppm）
S：鋼中S濃度（質量ppm）
(3) The manufacturing method of the aluminum killed steel material added with Ca having excellent HIC resistance according to the present invention includes a range satisfying the formula (1) when adding Ca to molten steel deoxidized with aluminum or an alloy thereof. Thus, a Ca-containing alloy is added.
0.1 ≦ (T. [Ca] − (17/18) × T. [O] −1.25 × S) / T [O] ≦ 0.5 (1)
T. [Ca]: Total Ca concentration in steel (ppm by mass )
T. [O]: Total oxygen concentration in steel (ppm by mass )
S: S concentration in steel (ppm by mass )
（４）また、上記（３）におけるT.[O]濃度の分析方法が、スパーク放電発光分光法を用いる方法であって、以下のステップを有することを特徴とするものである。
ア）多数回の放電パルスによるアルミニウムと鉄の発光強度比を放電パルス毎に求める強度比計算ステップ
イ）下記式にて求められるアルミナ分率を算出するステップ。
アルミナ分率＝前記発光強度比が閾値αより大きいパルス数／全パルス数
ここで、閾値αは、放電パルス毎の前記発光強度比を横軸、頻度を縦軸とした度数分布図から求められた発光強度比の最頻値のｆ1（1.5≦ｆ1≦2.5）倍
ウ）前記強度比計算ステップにより得られた放電パルス毎の前記発光強度比を小さい方から配列し、小さい方から全パルス数の30％以内の一定位置の前記発光強度比を代表アルミ強度比とし、次いで、前記アルミナ分率算出ステップで得られたアルミナ分率と代表アルミ強度比の積からアルミナ強度比（＝アルミナ分率×代表アルミ強度比）を算出するステップ
エ）予め調査したアルミナ強度比とT.[O]濃度との関係に基づいてT.[O]濃度を算出する定量ステップ
（５）また、本発明に係る溶鋼のCa添加処理方法は、耐HIC特性に優れるアルミキルド鋼材を製造するに際して、アルミニウムあるいはその合金により脱酸処理された溶鋼中に、（１）式を満たす範囲となるようにCa含有合金を添加することを特徴とするものである。
0.1≦（T.[Ca]−（17/18）×T.[O]−1.25×Ｓ）/T[O]≦0.5 ・・・（１）
T.[Ca]：鋼中全Ca濃度（質量ppm）
T.[O]：鋼中全酸素濃度（質量ppm）
S：鋼中S濃度（質量ppm）
なお、T.[O]濃度の分析方法は、以下のステップを有するスパーク放電発光分光法を用いるものである。
ア）多数回の放電パルスによるアルミニウムと鉄の発光強度比を放電パルス毎に求める強度比計算ステップ
イ）下記式にて求められるアルミナ分率を算出するステップ。
アルミナ分率＝前記発光強度比が閾値αより大きいパルス数／全パルス数
ここで、閾値αは、放電パルス毎の前記発光強度比を横軸、頻度を縦軸とした度数分布図から求められた発光強度比の最頻値のｆ 1 （1.5≦ｆ 1 ≦2.5）倍
ウ）前記強度比計算ステップにより得られた放電パルス毎の前記発光強度比を小さい方から配列し、小さい方から全パルス数の30％以内の一定位置の前記発光強度比を代表アルミ強度比とし、次いで、前記アルミナ分率算出ステップで得られたアルミナ分率と代表アルミ強度比の積からアルミナ強度比（＝アルミナ分率×代表アルミ強度比）を算出するステップ
エ）予め調査したアルミナ強度比とT.[O]濃度との関係に基づいてT.[O]濃度を算出する定量ステップ
(4) In addition, the T. [O] concentration analysis method in (3) is a method using spark discharge emission spectroscopy, and has the following steps.
A) Intensity ratio calculation step for obtaining the emission intensity ratio of aluminum and iron for each discharge pulse by a number of discharge pulses a) Step for calculating the alumina fraction obtained by the following formula.
Alumina fraction = number of pulses where the emission intensity ratio is greater than the threshold α / total number of pulses
Here, the threshold value α is the mode f 1 (1.5 ≦ f 1 ≦ 2.5) of the light emission intensity ratio obtained from the frequency distribution diagram with the light emission intensity ratio for each discharge pulse as the horizontal axis and the frequency as the vertical axis. X) Arrange the emission intensity ratio for each discharge pulse obtained by the intensity ratio calculation step from the smaller one, and the emission intensity ratio at a fixed position within 30% of the total number of pulses from the smaller one. Next, the step of calculating the alumina strength ratio (= alumina fraction × representative aluminum strength ratio) from the product of the alumina fraction obtained in the alumina fraction calculation step and the representative aluminum strength ratio d) Alumina strength ratio investigated in advance Step to calculate T. [O] concentration based on the relationship between T. [O] concentration and T. [O] concentration
(5) Further, the Ca addition treatment method for molten steel according to the present invention is a range satisfying the formula (1) in the molten steel deoxidized with aluminum or an alloy thereof when producing an aluminum killed steel material having excellent HIC resistance. A Ca-containing alloy is added so that
0.1 ≦ (T. [Ca] − (17/18) × T. [O] −1.25 × S) / T [O] ≦ 0.5 (1)
T. [Ca]: Total Ca concentration in steel (ppm by mass)
T. [O]: Total oxygen concentration in steel (ppm by mass)
S: S concentration in steel (ppm by mass)
The T. [O] concentration analysis method uses spark discharge emission spectroscopy having the following steps.
A) Intensity ratio calculation step to obtain the emission intensity ratio of aluminum and iron for each discharge pulse by multiple discharge pulses
B) A step of calculating the alumina fraction obtained by the following formula.
Alumina fraction = number of pulses where the emission intensity ratio is greater than the threshold α / total number of pulses
Here, the threshold value α is the mode f 1 (1.5 ≦ f 1 ≦ 2.5) of the light emission intensity ratio obtained from the frequency distribution diagram with the light emission intensity ratio for each discharge pulse as the horizontal axis and the frequency as the vertical axis. Double
C) Arrange the emission intensity ratios for each discharge pulse obtained in the intensity ratio calculation step from the smaller one, and the emission intensity ratio at a fixed position within 30% of the total number of pulses from the smaller one as the representative aluminum intensity ratio. Next, calculating the alumina strength ratio (= alumina fraction × representative aluminum strength ratio) from the product of the alumina fraction obtained in the alumina fraction calculation step and the representative aluminum strength ratio
D) Quantitative step to calculate T. [O] concentration based on the relationship between alumina strength ratio and T. [O] concentration investigated in advance
本発明に係る耐HIC特性に優れる鋼材は、鋼中に存在する非金属介在物のうち、その介在物中の(%CaO)/(% Al2O3)が0.3以下あるいは4.0以上で粒径1.5μｍ以上のものが10個/mm2以下であるので、耐HIC特性に優れている。 The steel material having excellent HIC resistance according to the present invention is a non-metallic inclusion existing in steel, and (% CaO) / (% Al 2 O 3 ) in the inclusion is 0.3 or less or 4.0 or more and the particle size Since it is 10 pieces / mm 2 or less for 1.5 μm or more, it has excellent HIC resistance.
本実施の形態に係る耐HIC特性に優れる鋼材は、鋼中に存在する非金属介在物のうち、その介在物中の(%CaO)/(%Al2O3)が0.3以下あるいは4.0以上で粒径1.5μｍ以上のものが10個/mm2以下であることを特徴とするものである。
上記のような鋼材は以下のようなプロセスを経て製造する。
The steel material having excellent HIC resistance according to the present embodiment is a non-metallic inclusion existing in steel, and (% CaO) / (% Al 2 O 3 ) in the inclusion is 0.3 or less or 4.0 or more. The number of particles having a particle size of 1.5 μm or more is 10 pieces / mm 2 or less.
The steel material as described above is manufactured through the following process.
転炉あるいは電気炉等の精錬炉から取鍋へ出鋼された溶鋼を、取鍋精錬炉等で処理する。ここまでの段階で、Alあるいはその合金により、脱酸処理をしておく。
その後、連続鋳造までの間で、溶鋼が収納された容器、例えば、取鍋、タンディッシュなどにワイヤや粉体状のCa合金を添加する。これにより、Caが鋼中Sと反応してCaSが生成し、割れの起因となるMnSを無害化すると共に、溶鋼中に懸濁しているAl2O3介在物とCaが反応してCaO-Al2O3介在物となる。
The molten steel discharged from a refining furnace such as a converter or electric furnace to a ladle is processed in a ladle refining furnace. At this stage, deoxidation treatment is performed with Al or an alloy thereof.
Thereafter, until the continuous casting, a wire or a powdered Ca alloy is added to a container in which molten steel is stored, for example, a ladle, a tundish or the like. As a result, Ca reacts with S in steel to generate CaS, detoxifies MnS that causes cracking, and Al 2 O 3 inclusions suspended in molten steel react with Ca to cause CaO- Al 2 O 3 inclusions.
ここで、Ca添加量が不足であったり、過剰であったりした場合、CaO-Al2O3介在物中のCaO/Al2O3の値が最適な範囲、すなわち0.3超〜4.0未満から外れるため、鋼中のAl2O3量に応じてCa添加量を調整する必要がある。
鋼中のAl2O3量を知る方法としては、鋼中のT.[O]濃度を分析する、あるいは、Alによる溶鋼脱酸後のT.[O]挙動を予め把握しておき、Ca添加時のAl2O3量を推定する方法がある。
なお、鋼中のT.[O]濃度の定量方法としては燃焼分析法や、スパーク放電発光分光法で直接的にT.[O]濃度を求める方法によることができるが、後述する「アルミナ定量法」によるものが最も好ましい。
また、Caを添加する場合には、歩留まりを考慮して、下記の（１）式を満足するように添加量を決めればよい。
0.1≦（T.[Ca]−（17/18）×T.[O]−1.25×Ｓ）/T[O]≦0.5 ・・・（１）
T.[Ca]：鋼中全Ca濃度（ppm）
T.[O]：鋼中全酸素濃度（ppm）
S：鋼中S濃度（ppm）
その際、Ca添加歩留まり、T.[O]濃度の分析精度、あるいは推定のバラツキを考慮して上記（１）式の中央値を狙う等しておき、Ca添加後、タンディッシュ、あるいは連鋳機鋳型内からの溶鋼のサンプルを分析して確認し、上記（１）式の範囲を外れていれば、圧延前に材料変更等の対応が可能となる。
Here, when the amount of Ca added is insufficient or excessive, the value of CaO / Al 2 O 3 in the CaO-Al 2 O 3 inclusions deviates from the optimum range, that is, more than 0.3 to less than 4.0. Therefore, it is necessary to adjust the amount of Ca added according to the amount of Al 2 O 3 in the steel.
As a method of knowing the amount of Al 2 O 3 in the steel, the T. [O] concentration in the steel is analyzed, or the T. [O] behavior after deoxidation of the molten steel by Al is grasped in advance. There is a method for estimating the amount of Al 2 O 3 at the time of addition.
The T. [O] concentration in steel can be quantified by combustion analysis or a method for directly determining T. [O] concentration by spark discharge emission spectroscopy. The “method” is most preferred.
In addition, when adding Ca, the addition amount may be determined so as to satisfy the following formula (1) in consideration of the yield.
0.1 ≦ (T. [Ca] − (17/18) × T. [O] −1.25 × S) / T [O] ≦ 0.5 (1)
T. [Ca]: Total Ca concentration in steel (ppm)
T. [O]: Total oxygen concentration in steel (ppm)
S: S concentration in steel (ppm)
At that time, considering the Ca addition yield, T. [O] concentration analysis accuracy, or estimation variation, aiming at the median of the above equation (1), etc., after adding Ca, tundish or continuous casting If the molten steel sample from the machine mold is analyzed and confirmed, and it is out of the range of the above formula (1), it is possible to cope with material changes before rolling.
＜「アルミナ定量法」によるT.[O]濃度定量方法＞
鋼中の酸素濃度（T.[O]濃度）の好ましい定量法について以下、説明する。
対象とする材料では、タンディッシュ注入前の溶鋼中の酸素濃度（T.[O]濃度）はほぼ全てAl2O3（以下、アルミナと称す）に起因するものであると考えられる。
したがって、アルミナの濃度を分析することでT.[O]を分析することができる。
<T. [O] concentration determination method by "alumina determination method">
A preferred method for determining the oxygen concentration (T. [O] concentration) in steel will be described below.
In the target material, the oxygen concentration (T. [O] concentration) in the molten steel before the tundish injection is considered to be due to Al 2 O 3 (hereinafter referred to as alumina).
Therefore, T. [O] can be analyzed by analyzing the concentration of alumina.
ところで、製鋼精錬工程で溶鋼に添加されたアルミニウム（以下、Alと称す）は、その一部は鋼中の酸素と反応しアルミナとなって徐々に表面に浮上して溶鋼から取り除かれる。
一方、残りの未反応のAlは鋼中に溶解したまま凝固する。
鋼の凝固後、浮上除去されなかったアルミナはそのままの状態で鋼中に残り、一方、未反応のAlは主として固溶Alとして鋼中に存在する。固溶Alは鋼試料を酸で溶解する際に一緒に溶解するが、アルミナは溶解しないので、酸溶解により互いに分離され、前者は酸可溶性Al（以下、sol.Alと称す）と呼ばれ、後者は酸不溶性Al（以下、insol.Alと称す）と呼ばれる。
By the way, a part of aluminum (hereinafter referred to as “Al”) added to the molten steel in the steel refining process reacts with oxygen in the steel to become alumina and gradually floats on the surface and is removed from the molten steel.
On the other hand, the remaining unreacted Al solidifies while being dissolved in the steel.
After the solidification of the steel, the alumina that has not been lifted and removed remains in the steel as it is, while the unreacted Al is mainly present in the steel as solute Al. Solid solution Al dissolves together when the steel sample is dissolved with acid, but alumina does not dissolve, so they are separated from each other by acid dissolution, the former is called acid-soluble Al (hereinafter referred to as sol.Al), The latter is called acid-insoluble Al (hereinafter referred to as insol.Al).
鉄鋼製造工程においては、鋼組成を制御するための迅速分析法としてスパーク放電発光分光分析法が広く利用され、成分分析のみならず、鋼中における酸化物量の定量法としても様々な取り組みがなされてきた。
しかしながら従来の解析手法では、鋼中50ppm以下の微量なアルミナ量を精度良く分析することは難しかった。
In the steel manufacturing process, spark discharge emission spectrometry is widely used as a rapid analysis method for controlling steel composition, and various efforts have been made not only for component analysis but also for quantitative determination of the amount of oxide in steel. It was.
However, with the conventional analysis method, it was difficult to accurately analyze a small amount of alumina in steel at 50 ppm or less.
これに対し、発明者らはスパーク放電発光現象におけるパルスごとの発光強度、および発光強度分布状態の示す物理化学的な意味を見直すことにより、アルミナ量の定量方法を見出した。
sol.Al濃度が等しくinsol.Al濃度の異なる鋼試料（sol.Al=66ppm、insol.Al=10ppm未満の試料、sol.Al=66ppm 、insol.Al=32ppmの試料）をそれぞれスパーク放電により発光させ、放電パルス毎にAlの発光強度と鉄の発光強度の比（Alの発光強度を鉄の発光強度で除した値であり、以下、Al/Fe強度比と称す）を経時的に観察した。
その結果、insol.Alの多い試料では、スパイク状の点が不規則に数多く確認され、スパイク状の点は、鋼中に不均一に存在するinsol.Alを含んだ放電によって生成されたものと推察される。スパーク放電では介在物（insol.Al）に放電が集中しやすいとされ、観察されるAl強度は、地鉄中のsol.Alからの光と、介在物（insol.Al）からの光から構成されるが、それぞれの割合は放電パルスごとに異なっている。
In contrast, the inventors have found a method for quantifying the amount of alumina by reviewing the luminescence intensity for each pulse in the spark discharge luminescence phenomenon and the physicochemical meaning of the luminescence intensity distribution state.
Each steel sample with the same sol.Al concentration but different insol.Al concentration (sol.Al = 66ppm, insol.Al = less than 10ppm, sol.Al = 66ppm, insol.Al = 32ppm) is emitted by spark discharge. The ratio of the emission intensity of Al to the emission intensity of iron for each discharge pulse (a value obtained by dividing the emission intensity of Al by the emission intensity of iron, hereinafter referred to as the Al / Fe intensity ratio) was observed over time. .
As a result, in the sample with a lot of insol.Al, a lot of spike-like points were confirmed irregularly, and the spike-like points were generated by the discharge containing insol.Al that existed unevenly in the steel. Inferred. In spark discharge, the discharge is likely to concentrate on inclusions (insol.Al), and the observed Al intensity consists of light from sol.Al in the ground iron and light from inclusions (insol.Al). However, each ratio is different for each discharge pulse.
放電パルスを、Al/Fe強度比の小さい順（昇順）に配列し、縦軸をAl/Fe強度比とし、横軸をAl/Fe強度比が小さいものから順に並び変えた位置を％表示したグラフを図２に示す。
図２に示されるように、Al/Fe強度比の大きい側はinsol.Alが支配的で、小さい側はsol.Alが支配的となっている。
sol.Alは地鉄中に均一に存在しているので、放電時に蒸発する地鉄の量が変動しても、sol.Al由来のAl強度はFeとの相対値（Al/Fe強度比）とする限り一定値を示すはずである。
つまり、Al/Fe強度比は、一定のsol.Al強度比と不確定なinsol.Al強度比の和であって、その大きさは不確定なinsol.Al強度比の大小で決定されるため、よりAl/Fe強度比の小さいパルスほどsol.Al強度比に近づき、Al/Fe強度比全体の積算値からsol.Alの寄与する強度積算値を差し引くことにより、アルミナ量を定量することができる。
具体的には以下のようにする。
Discharge pulses are arranged in ascending order of Al / Fe intensity ratio (ascending order), the vertical axis is the Al / Fe intensity ratio, and the horizontal axis is the percentage displayed in order from the smallest Al / Fe intensity ratio. A graph is shown in FIG.
As shown in FIG. 2, insol.Al is dominant on the side where the Al / Fe strength ratio is large, and sol.Al is dominant on the side where the Al / Fe strength ratio is small.
Since sol.Al is present uniformly in the steel, even if the amount of steel that evaporates during discharge fluctuates, the Al strength derived from sol.Al is relative to Fe (Al / Fe strength ratio). It should show a constant value as long as
In other words, the Al / Fe strength ratio is the sum of a constant sol.Al strength ratio and an uncertain insol.Al strength ratio, and its magnitude is determined by the magnitude of the uncertain insol.Al strength ratio. The smaller the Al / Fe intensity ratio, the closer to the sol.Al intensity ratio, and the amount of alumina can be quantified by subtracting the integrated intensity value contributed by sol.Al from the integrated value of the entire Al / Fe intensity ratio. it can.
Specifically:
多数回（例えば、２０００回）の放電パルスによるアルミニウムと鉄のAl/Fe強度比を放電パルス毎に求める（強度比計算ステップ）。 An Al / Fe intensity ratio between aluminum and iron by a number of discharge pulses (for example, 2000 times) is determined for each discharge pulse (intensity ratio calculation step).
下記式にて求められるアルミナ分率を算出する（アルミナ分率を算出ステップ）。
アルミナ分率＝Al/Fe強度比が閾値αより大きいパルス数／全パルス数
「閾値α」は、図３に示すように、放電パルス毎のAl/Fe強度比を横軸、頻度を縦軸とした度数分布図を作図した後、該度数分布図から求められたAl/Fe強度比の最頻値のｆ1倍として特定する。ここで、ｆ1の値は、1.5≦ｆ1≦2.5とするのが好ましい。
同様の手法で処理した試料を同様の測定条件で測定する限り、固溶Alに由来する発光強度比の頻度分布は、同様のバラツキ幅を持つと考えられることから、Al/Fe強度比の最頻値の１より大きい定数倍の値を閾値とすることで、固溶Alの影響度を一定の比率に保って、アルミナ由来の信号成分を分離できると考えられる。
従って、放電パルス毎のAl/Fe強度比が最頻値のｆ1倍より大きいパルス数を求め、求めたパルス数を全パルス数で除したものをアルミナ分率とする。ここで、ｆ1の値は、1.5〜2.5の範囲、より好ましくは1.7〜2.0の範囲とする。ｆ1の値が1.5より小さい場合、固溶アルミに由来するデータが多くなるため、アルミナ量との相関が悪くなる。一方、ｆ1の値が2.5より大きい場合、抽出されるアルミナ由来の信号を含むパルス数が少なくなりすぎるため、分析ばらつきが大きくなる。
The alumina fraction obtained by the following formula is calculated (calculating alumina fraction).
Alumina fraction = Al / Fe intensity ratio is greater than the threshold α / number of pulses / total number of pulses As shown in FIG. Then, the frequency distribution chart is specified as f 1 times the mode value of the Al / Fe intensity ratio obtained from the frequency distribution chart. Here, the value of f 1 is preferably set to 1.5 ≦ f 1 ≦ 2.5.
As long as a sample treated by the same method is measured under the same measurement conditions, the frequency distribution of the emission intensity ratio derived from solute Al is considered to have the same variation width. It is considered that the signal component derived from alumina can be separated by keeping the influence degree of the solid solution Al at a constant ratio by setting the value of a constant multiple larger than 1 as the threshold value.
Therefore, Al / Fe intensity ratio of each discharge pulse is determined the number of pulses greater than 1 times f the mode, what the number of determined pulses divided by the total number of pulses and alumina fractions. Here, the value of f 1 is in the range of 1.5 to 2.5, more preferably in the range of 1.7 to 2.0. When the value of f 1 is smaller than 1.5, data derived from solute aluminum increases, and thus the correlation with the amount of alumina is deteriorated. On the other hand, when the value of f 1 is larger than 2.5, the number of pulses including the signal derived from alumina to be extracted becomes too small, and the analysis variation becomes large.
ここで、アルミナ分率を算出する際のｆ1値の影響を確認するために、ｆ1値を1.4〜2.6の範囲において0.05ステップで変えてアルミナ強度比（insol.Al強度比）を計算した。各ｆ1値におけるアルミナ強度比と化学分析値との相関係数および繰り返し分析時の変動係数を図４および図５にそれぞれ示す。
図４より、ｆ1が1.5以下となるとアルミナ強度比と化学分析値の相関係数が急激に低下することがわかる。これは、固溶アルミ由来の発光の影響によるものと考えられる。また、図５より、ｆ1の値が大きくなるほど、繰り返し分析時のバラツキが大きくなっていることがわかる。これは、抽出されるパルス数が少なくなりすぎるためである。
しかし、ｆ1値が1.5および2.5の場合でも、分析正確さ(σｄ)は、それぞれ、2.4ppm、1.9ppmであり、従来法よりも高精度に分析が可能である。
ｆ1値が2.0の場合の、本発明に係るアルミナ定量法により求めたアルミナ濃度と化学分析値との相関を図６に示す。このときの分析正確さは1.8ppmであった。
Here, in order to confirm the influence of the f 1 value in calculating the alumina fraction, the alumina strength ratio (insol.Al strength ratio) was calculated by changing the f 1 value in the range of 1.4 to 2.6 in 0.05 steps. . The correlation coefficient between the alumina strength ratio and the chemical analysis value at each f 1 value and the coefficient of variation during repeated analysis are shown in FIGS. 4 and 5, respectively.
FIG. 4 shows that when f 1 is 1.5 or less, the correlation coefficient between the alumina strength ratio and the chemical analysis value rapidly decreases. This is considered to be due to the influence of light emission derived from solid solution aluminum. In addition, FIG. 5 shows that the variation during repeated analysis increases as the value of f 1 increases. This is because the number of extracted pulses is too small.
However, even when the f 1 value is 1.5 and 2.5, the analysis accuracy (σd) is 2.4 ppm and 1.9 ppm, respectively, which can be analyzed with higher accuracy than the conventional method.
FIG. 6 shows the correlation between the alumina concentration determined by the alumina quantification method according to the present invention and the chemical analysis value when the f 1 value is 2.0. The analysis accuracy at this time was 1.8 ppm.
強度比計算ステップにより得られた放電パルス毎のAl/Fe強度比を小さい方から配列し、一定位置のAl/Fe強度比を代表アルミ強度比とする。
ここで、「代表アルミ強度比」は、放電パルス毎のAl/Fe強度比を小さい方から配列した際に（図２参照）、Al/Fe強度比の小さい方から全パルス数の30％以内のいずれかの位置となるような強度比とするのが好ましい。この理由は以下の通りである。
30%よりも大きい位置を代表アルミ強度比とした場合には、試料中に存在するアルミナ量の影響が大きくなりすぎ、酸可溶性Al（sol.Al）とアルミナを精度よく分配するための代表値とならずに分析精度が劣化するからである。
次に、アルミナ分率算出ステップで得られたアルミナ分率と代表アルミ強度比の積からアルミナ強度比を算出する。
The Al / Fe intensity ratio for each discharge pulse obtained by the intensity ratio calculation step is arranged from the smaller one, and the Al / Fe intensity ratio at a fixed position is set as the representative aluminum intensity ratio.
Here, the “representative aluminum intensity ratio” is within 30% of the total number of pulses from the smaller Al / Fe intensity ratio when the Al / Fe intensity ratio for each discharge pulse is arranged from the smaller one (see FIG. 2). It is preferable to set the intensity ratio so as to be any one of the positions. The reason is as follows.
When the position greater than 30% is used as the representative aluminum strength ratio, the influence of the amount of alumina present in the sample becomes too great, and the typical value for accurately distributing acid-soluble Al (sol.Al) and alumina. This is because the analysis accuracy deteriorates.
Next, the alumina strength ratio is calculated from the product of the alumina fraction obtained in the alumina fraction calculation step and the representative aluminum strength ratio.
スパーク放電発光分光法における特性値とT.[O]濃度の関係を調査して予め作成した検量線を用いて、目的とするT.[O]濃度を求める。
検量線試料には同じCa添加鋼を用い、各試料について予めスパーク放電発光分光分析法で得られるAl/Fe強度比から必要な各係数を設定した後、算出された特性値と燃焼分析法から求められるT.[O]濃度の相関線を検量線とする。検量線の一例を図７に示す。
なお、溶鋼中の酸素量は継時変化しやすいことから、スパーク放電発光分光分析装置は極力、製造現場に近いことが望ましく、可能であれば機側でのオンサイト分析が最も好適である。
The relationship between the characteristic value and the T. [O] concentration in spark discharge emission spectroscopy is investigated, and the target T. [O] concentration is obtained using a calibration curve prepared in advance.
The same Ca-added steel is used for the calibration curve sample, and after setting each necessary coefficient from the Al / Fe intensity ratio obtained by spark discharge optical emission spectrometry for each sample, the calculated characteristic value and combustion analysis method are used. The correlation line of the obtained T. [O] concentration is used as a calibration curve. An example of a calibration curve is shown in FIG.
Since the amount of oxygen in the molten steel is likely to change over time, it is desirable that the spark discharge optical emission spectrometer is as close as possible to the production site, and if possible, on-site analysis on the machine side is most suitable.
鋼中S量については、ＡＰ処理以降の工程でほとんど変化しないことが調査の結果分かった。すなわち、ＡＰ処理終了後からCa添加までの間に分析を行えば問題なく、高精度な鋼中Sの分析法である、燃焼法などの適用が十分に可能である。
本発明の効果を確認する実験を行ったので、これについて以下の実施例で説明する。
As a result of the investigation, it was found that the amount of S in steel hardly changed in the processes after the AP treatment. That is, there is no problem if the analysis is performed between the end of the AP treatment and the addition of Ca, and the application of the combustion method, which is a highly accurate method for analyzing S in steel, is sufficiently possible.
An experiment for confirming the effect of the present invention was conducted, and this will be described in the following examples.
転炉で約250トンの溶鋼を酸素吹錬した後、取鍋に出鋼し、ＲＨ真空脱ガス装置に搬送した。ＲＨ真空脱ガス装置では、成分調整等の必要に応じた精錬とともに、Al合金を所定量添加し、脱酸処理をした。Al合金添加後、溶鋼サンプルを採取し、機側に設置したスパーク放電発光分光分析装置により分析した結果を基に添加Ca量を決定した。ここで、Caについては通常の分析手段にて定量し、T.[O]については、上述したアルミナ定量法により定量値を算出した。なお、検量線試料には同じCa添加鋼を用いた。各試料について予めスパーク放電発光分光分析法で得られるAl/Fe強度比から必要な各係数を設定した後、算出された特性値と燃焼分析法から求められるT.[O]の相関線を検量線とした。
一方、Sについてはスパーク放電発光分光分析装置による分析精度が充分ではないと判断されたことから、AP終了後の燃焼法による分析結果をそのまま用いた。念の為、T.[Ca],T.[O]分析用のサンプルを保管し、後日、採取した切り粉を用いて燃焼法による定量を行なったが、ほとんど1ppm以内の範囲で一致しており、AP処理終了後の分析値を用いて問題の無いことを確認した。
About 250 tons of molten steel was blown with oxygen in a converter, then the steel was taken out into a ladle and transferred to an RH vacuum degasser. In the RH vacuum degassing apparatus, a predetermined amount of Al alloy was added and deoxidation treatment was performed along with refining as needed for component adjustment and the like. After the addition of the Al alloy, a molten steel sample was taken, and the amount of added Ca was determined based on the result of analysis by a spark discharge optical emission spectrometer installed on the machine side. Here, Ca was quantified by a normal analysis means, and T. [O] was calculated by the above-described alumina quantification method. The same Ca-added steel was used for the calibration curve sample. After setting each necessary coefficient from the Al / Fe intensity ratio obtained by spark discharge optical emission spectrometry for each sample in advance, the calculated characteristic value and T. [O] correlation line obtained from combustion analysis are calibrated. A line.
On the other hand, for S, it was determined that the analysis accuracy by the spark discharge optical emission spectrometer was not sufficient, so the analysis result by the combustion method after the end of AP was used as it was. As a precaution, samples for T. [Ca], T. [O] analysis were stored and quantified by the combustion method using the collected chips at a later date. Therefore, it was confirmed that there was no problem using the analysis value after the AP processing was completed.
これら溶鋼を連続鋳造法によりスラブを鋳造した。鋳造したスラブよりブロックサンプルを採取し、そこからスラブ厚み断面の全体に渡ってサンプルを採取し、適切な加工・研磨を行った後、粒子解析ＳＥＭ法により介在物組成、個数を分析した。その介在物中の(%CaO)/(%Al2O3)が0.3以下あるいは4.0以上で粒径1.5μｍ以上のものが10個/mm2より多いものを比較例とし、それ以外を本発明例とした。 Slabs were cast from these molten steels by a continuous casting method. A block sample was collected from the cast slab, and a sample was collected from the entire slab thickness section. After appropriate processing and polishing, the composition and number of inclusions were analyzed by a particle analysis SEM method. In the inclusions, (% CaO) / (% Al 2 O 3 ) is 0.3 or less or 4.0 or more and a particle size of 1.5 μm or more is more than 10 pieces / mm 2 , and the others are the present invention. As an example.
前記スラブを用いて板厚25.4mm及び33mmの厚鋼板を製造した。
加熱したスラブを熱間圧延により圧延し、その後、加速冷却を施して所定の強度とした。この時のスラブ加熱温度は1050℃、圧延終了温度は800〜840℃、加速冷却開始温度は760〜800℃、加速冷却停止温度は450〜550℃とした。得られた鋼板の強度はいずれもAPIX65を満足するものであり、引張強度は570〜630ＭＰａであった。鋼板の引張特性については、圧延垂直方向の全厚試験片を引張試験片として引張試験を行い、引張強度を測定した。
Thick steel plates with thicknesses of 25.4 mm and 33 mm were manufactured using the slab.
The heated slab was rolled by hot rolling and then subjected to accelerated cooling to a predetermined strength. The slab heating temperature at this time was 1050 ° C., the rolling end temperature was 800-840 ° C., the accelerated cooling start temperature was 760-800 ° C., and the accelerated cooling stop temperature was 450-550 ° C. The strength of the obtained steel sheet satisfied APIX65, and the tensile strength was 570 to 630 MPa. Regarding the tensile properties of the steel sheet, a tensile test was performed using a full thickness test piece in the rolling vertical direction as a tensile test piece, and the tensile strength was measured.
これらの鋼板について、複数の位置から各10〜15個のHIC試験片を採取し、耐HIC特性を調査した。耐HIC特性は、pHが約３の硫化水素を飽和させた5%NaCl+0.5%CH3COOH水溶液（通常のNACE溶液）中に試験片を96時間浸漬した後、超音波探傷により試験片全面の割れの有無を調査し、割れ面積率（CAR）で評価した。ここで、それぞれの試験片の割れ面積率３％以下を合格とした。
表１に各HIC試験片の成分濃度、１（式）計算結果及び判定、介在物個数、及びHIC試験不合格率を示す。なお、介在物個数は、1.5μｍ以上のもの個数（個/mm2）で、粒径介在物中の(%CaO)/(%Al2O3)が0.3以下あるいは4.0以上のものと、0.3より大きく、4.0未満のもの（表１において「左記以外」と表記）を示した。
About these steel plates, 10-15 HIC test pieces were sampled from a plurality of positions, and the HIC resistance characteristics were investigated. The HIC resistance is that the specimen is immersed in a 5% NaCl + 0.5% CH3COOH aqueous solution (normal NACE solution) saturated with hydrogen sulfide with a pH of about 3 for 96 hours, and then the entire specimen is cracked by ultrasonic flaw detection. The crack area ratio (CAR) was evaluated. Here, a crack area ratio of 3% or less for each test piece was regarded as acceptable.
Table 1 shows the component concentration of each HIC test piece, 1 (formula) calculation result and judgment, the number of inclusions, and the HIC test rejection rate. The number of inclusions is 1.5 μm or more (pieces / mm 2 ), and (% CaO) / (% Al 2 O 3 ) in the particle size inclusions is 0.3 or less or 4.0 or more, Those larger than 4.0 (shown as “other than left” in Table 1) are shown.
表１に示すように、介在物個数が本発明例を満たすもの（表中の本発明例１〜６）は、耐HIC試験不合格率が6.7%以下であり、耐HIC性能が極めて良好であった。また、成分が（１）式の範囲にあると、介在物個数が本発明範囲を確実に満たしており、換言すれば成分が（１）式の範囲にあるようにすることで、介在物個数を本発明範囲にすることができることが実証された。
また、表１に示すように、(%CaO)/(%Al2O3)が0.3より大きく、4.0未満の介在物個数についても調査がしたが、この範囲にある介在物の個数はHIC性能には影響しなかった。また、粒径5μｍ以上の介在物個数はどの場合においても、総介在物個数の5％以下であり、HIC性能には影響しなかった。
As shown in Table 1, when the number of inclusions satisfies the present invention examples (Invention Examples 1 to 6 in the table), the HIC test rejection rate is 6.7% or less, and the HIC resistance performance is extremely good. there were. In addition, when the component is in the range of the formula (1), the number of inclusions surely satisfies the scope of the present invention. In other words, by making the component be in the range of the formula (1), Has been demonstrated to be within the scope of the present invention.
As shown in Table 1, the number of inclusions with (% CaO) / (% Al 2 O 3 ) greater than 0.3 and less than 4.0 was also investigated, but the number of inclusions in this range is the HIC performance. Did not affect. In addition, the number of inclusions having a particle size of 5 μm or more was 5% or less of the total number of inclusions in any case, and HIC performance was not affected.
Claims (2)
0.1≦（T.[Ca]−（17/18）×T.[O]−1.25×Ｓ）/T[O]≦0.5 ・・・（１）
T.[Ca]：鋼中全Ca濃度（質量ppm）
T.[O]：鋼中全酸素濃度（質量ppm）
S：鋼中S濃度（質量ppm）
なお、T.[O]濃度の分析方法は、以下のステップを有するスパーク放電発光分光法を用いるものである。
ア）多数回の放電パルスによるアルミニウムと鉄の発光強度比を放電パルス毎に求める強度比計算ステップ
イ）下記式にて求められるアルミナ分率を算出するステップ。
アルミナ分率＝前記発光強度比が閾値αより大きいパルス数／全パルス数
ここで、閾値αは、放電パルス毎の前記発光強度比を横軸、頻度を縦軸とした度数分布図から求められた発光強度比の最頻値のｆ1（1.5≦ｆ1≦2.5）倍
ウ）前記強度比計算ステップにより得られた放電パルス毎の前記発光強度比を小さい方から配列し、小さい方から全パルス数の30％以内の一定位置の前記発光強度比を代表アルミ強度比とし、次いで、前記アルミナ分率算出ステップで得られたアルミナ分率と代表アルミ強度比の積からアルミナ強度比（＝アルミナ分率×代表アルミ強度比）を算出するステップ
エ）予め調査したアルミナ強度比とT.[O]濃度との関係に基づいてT.[O]濃度を算出する定量ステップ Upon addition of Ca of aluminum or its alloys in the molten steel that has been treated deoxidation, excellent HIC resistance, characterized in that the addition of Ca-containing alloy to be in the range satisfying the formula (1), the addition of Ca Method of finished aluminum killed steel.
0.1 ≦ (T. [Ca] − (17/18) × T. [O] −1.25 × S) / T [O] ≦ 0.5 (1)
T. [Ca]: Total Ca concentration in steel (ppm by mass )
T. [O]: Total oxygen concentration in steel (ppm by mass )
S: S concentration in steel (ppm by mass )
The T. [O] concentration analysis method uses spark discharge emission spectroscopy having the following steps.
A) Intensity ratio calculation step for obtaining the emission intensity ratio of aluminum and iron for each discharge pulse by a number of discharge pulses a) Step for calculating the alumina fraction obtained by the following formula.
Alumina fraction = number of pulses where the emission intensity ratio is greater than the threshold α / total number of pulses
Here, the threshold value α is the mode f 1 (1.5 ≦ f 1 ≦ 2.5) of the light emission intensity ratio obtained from the frequency distribution diagram with the light emission intensity ratio for each discharge pulse as the horizontal axis and the frequency as the vertical axis. X) Arrange the emission intensity ratio for each discharge pulse obtained by the intensity ratio calculation step from the smaller one, and the emission intensity ratio at a fixed position within 30% of the total number of pulses from the smaller one. Next, the step of calculating the alumina strength ratio (= alumina fraction × representative aluminum strength ratio) from the product of the alumina fraction obtained in the alumina fraction calculation step and the representative aluminum strength ratio d) Alumina strength ratio investigated in advance Step to calculate T. [O] concentration based on the relationship between T. [O] concentration and T. [O] concentration
0.1≦（T.[Ca]−（17/18）×T.[O]−1.25×Ｓ）/T[O]≦0.5 ・・・（１）
T.[Ca]：鋼中全Ca濃度（質量ppm）
T.[O]：鋼中全酸素濃度（質量ppm）
S：鋼中S濃度（質量ppm）
なお、T.[O]濃度の分析方法は、以下のステップを有するスパーク放電発光分光法を用いるものである。
ア）多数回の放電パルスによるアルミニウムと鉄の発光強度比を放電パルス毎に求める強度比計算ステップ
イ）下記式にて求められるアルミナ分率を算出するステップ。
アルミナ分率＝前記発光強度比が閾値αより大きいパルス数／全パルス数
ここで、閾値αは、放電パルス毎の前記発光強度比を横軸、頻度を縦軸とした度数分布図から求められた発光強度比の最頻値のｆ1（1.5≦ｆ1≦2.5）倍
ウ）前記強度比計算ステップにより得られた放電パルス毎の前記発光強度比を小さい方から配列し、小さい方から全パルス数の30％以内の一定位置の前記発光強度比を代表アルミ強度比とし、次いで、前記アルミナ分率算出ステップで得られたアルミナ分率と代表アルミ強度比の積からアルミナ強度比（＝アルミナ分率×代表アルミ強度比）を算出するステップ
エ）予め調査したアルミナ強度比とT.[O]濃度との関係に基づいてT.[O]濃度を算出する定量ステップ
When producing an aluminum killed steel material with excellent HIC resistance , a Ca-containing alloy is added to the molten steel deoxidized with aluminum or its alloy so that it satisfies the formula (1) . Ca addition treatment method.
0.1 ≦ (T. [Ca] − (17/18) × T. [O] −1.25 × S) / T [O] ≦ 0.5 (1)
T. [Ca]: Total Ca concentration in steel (ppm by mass )
T. [O]: Total oxygen concentration in steel (ppm by mass )
S: S concentration in steel (ppm by mass )
The T. [O] concentration analysis method uses spark discharge emission spectroscopy having the following steps.
A) Intensity ratio calculation step for obtaining the emission intensity ratio of aluminum and iron for each discharge pulse by a number of discharge pulses a) Step for calculating the alumina fraction obtained by the following formula.
Alumina fraction = number of pulses where the emission intensity ratio is greater than the threshold α / total number of pulses
Here, the threshold value α is the mode f 1 (1.5 ≦ f 1 ≦ 2.5) of the light emission intensity ratio obtained from the frequency distribution diagram with the light emission intensity ratio for each discharge pulse as the horizontal axis and the frequency as the vertical axis. X) Arrange the emission intensity ratio for each discharge pulse obtained by the intensity ratio calculation step from the smaller one, and the emission intensity ratio at a fixed position within 30% of the total number of pulses from the smaller one. Next, the step of calculating the alumina strength ratio (= alumina fraction × representative aluminum strength ratio) from the product of the alumina fraction obtained in the alumina fraction calculation step and the representative aluminum strength ratio d) Alumina strength ratio investigated in advance Step to calculate T. [O] concentration based on the relationship between T. [O] concentration and T. [O] concentration
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