JP5324963B2 - Method for producing Cr-containing strip steel - Google Patents
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Description
本発明は、Ｃｒ含有条鋼材の製造方法に関するものであり、特に、スケール除去（以下、「デスケーリング」ということがある）により良好にスケールが剥離されて、表面性状に優れたＣｒ含有条鋼材を熱間圧延で製造する方法に関するものである。 The present invention relates to a method for producing a Cr-containing steel strip, and in particular, the Cr-containing steel strip having excellent surface properties because the scale is peeled off favorably by scale removal (hereinafter sometimes referred to as “descaling”). The present invention relates to a method for producing the material by hot rolling.
自動車等に用いられる冷間圧延用鋼、軸受鋼などの条鋼製品は、強度を確保するためＣｒが添加されることが一般的である。この様なＣｒ含有条鋼材も通常の鋼材と同様に、ビレット等を加熱した後デスケーリングが行われ、次いで熱間圧延して製造される。熱間圧延して製造される製品の表面品質に対する要求は年々厳しくなっている。しかし、鉄鋼を高温で加熱すると、表面に１次スケール（ウスタイト（ＦｅＯ）、マグネタイト（Ｆｅ３Ｏ４）、ヘマタイト（Ｆｅ２Ｏ３）などのＦｅ系酸化物で構成されるスケール）が形成される。またＣｒを含有する鋼種では、Ｃｒを含む鉄酸化物（サブスケール）が１次スケール／地鉄界面に形成される（以下では、１次スケールとサブスケールを併せて「スケール」と総称することがある）。このサブスケールは鋼との密着性が高いため、加熱後に高圧水によるスケール剥離（高圧水デスケーリング）を行っても、上記１次スケールはほぼ除去されるがサブスケールは残留し易い。この残留したサブスケールが熱間圧延時に鋼表面に押し込まれることによって、微細な表面疵や肌荒れなどの表面欠陥がしばしば発生する。 In steel products such as cold rolling steel and bearing steel used in automobiles, Cr is generally added to ensure strength. Such Cr-containing strip steel is produced by heating a billet and the like, followed by descaling, and then hot rolling in the same manner as ordinary steel. The requirements for the surface quality of products manufactured by hot rolling are becoming stricter year by year. However, when steel is heated at a high temperature, a primary scale (scale composed of Fe-based oxides such as wustite (FeO), magnetite (Fe 3 O 4 ), hematite (Fe 2 O 3 )) is formed on the surface. The In addition, in steel types containing Cr, iron oxide (subscale) containing Cr is formed at the primary scale / base metal interface (hereinafter, the primary scale and subscale are collectively referred to as “scale”). There). Since this subscale has high adhesion to steel, even if scale peeling with high pressure water (high pressure water descaling) is performed after heating, the primary scale is almost removed, but the subscale tends to remain. When the remaining subscale is pushed into the steel surface during hot rolling, surface defects such as fine surface defects and rough skin often occur.
この様な事情に鑑みて、デスケーリングによりスケールを良好に剥離して（以下、この様な特性を「スケール剥離性」ということがある）、スケールによる表面欠陥を抑制し、製品の表面品質を高める方法が種々提案されている。 In view of such circumstances, the scale is peeled off satisfactorily by descaling (hereinafter, such a characteristic is sometimes referred to as “scale peelability”), and surface defects due to the scale are suppressed, thereby improving the surface quality of the product. Various methods have been proposed to enhance it.
例えば特許文献１には、加熱炉にて比較的低温で加熱し、更にその後、誘導加熱装置（インダクションヒーター）にて、大気雰囲気で別途誘導加熱してから、鋼材表面部のスケールを除去する技術が開示されている。 For example, Patent Document 1 discloses a technique in which heating is performed at a relatively low temperature in a heating furnace, and after that, induction heating is separately performed in an air atmosphere by an induction heating device (induction heater), and then the scale on the steel material surface portion is removed. Is disclosed.
特許文献２には、スケール内の気孔の成長を促進させて剥離しやすいスケールを形成すべく、熱間圧延前の加熱時に、条鋼材に直接水を供給しながら一定温度で一定時間以上保持することが規定されている。また、特許文献３にも、スケール内の気孔の成長を促進させて剥離しやすいスケールを形成すべく、熱間圧延前の加熱時に２段階加熱を行っており、各加熱段階の加熱温度・時間および水蒸気濃度を規定している。 In Patent Document 2, in order to promote the growth of pores in the scale and form a scale that is easy to peel off, during heating prior to hot rolling, water is directly supplied to the steel bar and kept at a certain temperature for a certain period of time. It is prescribed. Also, in Patent Document 3, two-stage heating is performed at the time of heating before hot rolling in order to promote the growth of pores in the scale and easily peel off, and the heating temperature and time of each heating stage And the water vapor concentration.
しかし、特許文献１に記載の方法をＣｒ含有条鋼材に適用すると、大気中で誘導加熱するため、Ｃｒ濃度の非常に高い、鋼材との密着性の高いサブスケールが、鋼材と１次スケールの間に形成されやすく、スケール剥離性を十分に向上することが難しいと考えられる。 However, when the method described in Patent Document 1 is applied to a Cr-containing strip steel, induction heating is performed in the atmosphere. Therefore, a subscale having a very high Cr concentration and a high adhesion to the steel is formed between the steel and the primary scale. It is considered that it is difficult to sufficiently improve the scale peelability.
また、特許文献２および３では、加熱炉での加熱温度・時間および加熱炉内の水蒸気濃度を制御してスケール剥離性の改善を図っている。しかし該方法では、スケール剥離性を十分改善することが難しい。更に上記特許文献２や特許文献３では、スケール剥離性を高めるべく、サブスケールに発生する気孔を増大させる、即ち、サブスケールの物理的な観点（形状）から改善を図っているが、スケール剥離性をより高めるには、サブスケールの化学的な観点（成分組成）から改善を図ることも重要であると考える。 In Patent Documents 2 and 3, the scale peelability is improved by controlling the heating temperature / time in the heating furnace and the water vapor concentration in the heating furnace. However, with this method, it is difficult to sufficiently improve the scale peelability. Further, in Patent Document 2 and Patent Document 3 described above, the pores generated in the subscale are increased in order to improve the scale peelability, that is, improvement is made from the physical viewpoint (shape) of the subscale. In order to further improve the properties, it is important to improve from the chemical viewpoint (component composition) of the subscale.
本発明は上記の様な事情に着目してなされたものであって、その目的は、スケール剥離性に悪影響を与えるＣｒを含有する条鋼材であっても、デスケーリング工程でスケールを十分に剥離でき、スケールによる表面欠陥が抑制されて、表面性状の良好なＣｒ含有条鋼材を製造する方法を提供することにある。 The present invention has been made paying attention to the circumstances as described above, and its purpose is to sufficiently peel the scale in the descaling process even if it is a strip containing Cr that adversely affects the scale peelability. It is possible to provide a method for producing a Cr-containing strip material having a good surface property in which surface defects due to scale are suppressed.
本発明者らは前記課題を解決するために鋭意検討を重ねた結果、Ｃｒ含有条鋼材であっても、加熱炉での加熱温度を制御すると共に、加熱炉抽出直後に所定の条件で鋼片を急速加熱し、到達温度で所定時間保持すれば（好ましくは、該保持時の雰囲気を規定の雰囲気とすれば）、その後のデスケーリング工程でスケールを十分に剥離でき、表面性状に優れたＣｒ含有条鋼材を熱間圧延で製造できることを見出した。 As a result of intensive investigations to solve the above problems, the present inventors have controlled the heating temperature in the heating furnace even in the case of Cr-containing strip steel material, and the steel slab is subjected to predetermined conditions immediately after extraction in the heating furnace. Is rapidly heated and held at the ultimate temperature for a predetermined time (preferably, if the atmosphere at the time of holding is a specified atmosphere), the scale can be sufficiently peeled off in the subsequent descaling step, and Cr having excellent surface properties It has been found that the steel strip can be produced by hot rolling.
即ち、本発明に係るＣｒ含有条鋼材の製造方法は、Ｃｒを０．１０〜２．０％（質量％の意味。鋼の化学成分において以下同じ。）含む鋼片を加熱炉から取り出し、デスケーリングした後に、熱間圧延するＣｒ含有条鋼材の製造方法であって、
（ａ）前記加熱炉にて、鋼片の表面温度が８００℃以上１１５０℃以下の温度域で１５分以上加熱した後、その表面温度（抽出温度）が前記温度域にある鋼片を加熱炉から取り出し、
（ｂ）直ちにＯ２濃度：１０体積％以上の雰囲気中で、
（ｂ−１）鋼片の表面温度が１２００℃以上１３５０℃以下の範囲内の温度（到達温度）となるまで、５℃／ｓｅｃ以上の昇温速度で前記鋼片を急速加熱し、
（ｂ−２）上記到達温度で０．１秒以上６０秒以下保持した後、
（ｃ）デスケーリングするところに特徴を有する。
That is, in the method for producing a Cr-containing strip according to the present invention, a steel slab containing Cr of 0.10 to 2.0% (meaning mass%; the same applies to the chemical composition of steel) is taken out of the heating furnace, A method for producing a Cr-containing strip steel material to be hot-rolled after scaling,
(A) In the heating furnace, after the surface temperature of the steel slab is heated in the temperature range of 800 ° C. or higher and 1150 ° C. or lower for 15 minutes or longer, the steel slab whose surface temperature (extraction temperature) is in the temperature range is heated in the furnace. Take out from
(B) Immediately in an atmosphere of O 2 concentration: 10% by volume or more,
(B-1) The steel slab is rapidly heated at a rate of temperature increase of 5 ° C./sec or more until the surface temperature of the steel slab reaches a temperature (attainment temperature) in the range of 1200 ° C. or higher and 1350 ° C. or lower,
(B-2) After holding at the ultimate temperature for 0.1 seconds to 60 seconds,
(C) It is characterized by descaling.
前記（ｂ−２）の到達温度で保持する工程の雰囲気は、Ｏ２濃度：１０体積％以上かつＨ２Ｏ濃度：５体積％以上３５体積％以下を満たす雰囲気であることが好ましい。 It is preferable that the atmosphere in the step of holding at the reached temperature (b-2) is an atmosphere satisfying O 2 concentration: 10% by volume or more and H 2 O concentration: 5% by volume or more and 35% by volume or less.
前記鋼片としては、その成分組成が更に、Ｓｉ：０．１０〜０．４０％、Ｃ：０．１０〜１．５０％、およびＭｎ：０．０１〜１．５％を満たし、残部が鉄および不可避不純物からなるものが挙げられる。前記鋼片は、更に、Ｍｏ：０．０１〜０．４０％を含むものであってもよい。 As the steel slab, the component composition further satisfies Si: 0.10 to 0.40%, C: 0.10 to 1.50%, and Mn: 0.01 to 1.5%, and the balance is The thing which consists of iron and an unavoidable impurity is mentioned. The steel slab may further contain Mo: 0.01 to 0.40%.
本発明によれば、サブスケールとして、地鉄との密着性に劣る脆いＦｅＯ主体の酸化層を形成できるため、デスケーリング工程でスケールを十分に剥離でき、表面性状に優れたＣｒ含有条鋼材を熱間圧延で製造することができる。 According to the present invention, as a subscale, a brittle FeO-based oxide layer with poor adhesion to the ground iron can be formed, so that the scale-containing strip steel material having excellent surface properties can be sufficiently peeled off in the descaling process. It can be manufactured by hot rolling.
本発明者らは、スケール剥離性に悪影響を与えるＣｒを含有する条鋼材であっても、スケール剥離性を改善できる方法について既に提案しているが（例えば、特願２００７−２１４０２５号）、デスケーリングにおいてスケールをより容易に除去すべく、更に鋭意研究を行った。その結果、次の様な思想に基づいてサブスケールの組成を制御すればよいとの着想を得た。即ち、サブスケールは、鋼材内部に酸化が進展する（内方酸化が進む）ことにより形成される内方酸化層である。この内方酸化の速度が遅い場合、Ｃｒがゆっくり濃化してＣｒ濃度の高いサブスケールとなる。このＣｒ濃度の高いサブスケールは、上述した通り鋼材との密着性が高いため好ましくない。 The present inventors have already proposed a method capable of improving the scale peelability even in the case of a steel strip containing Cr that adversely affects the scale peelability (for example, Japanese Patent Application No. 2007-214025). Intensive research was conducted to remove scale more easily in scaling. As a result, the idea that the subscale composition should be controlled based on the following idea was obtained. That is, the subscale is an inner oxide layer formed by oxidation progressing (inward oxidation progresses) inside the steel material. When this rate of inward oxidation is slow, Cr is gradually concentrated to form a subscale with a high Cr concentration. This subscale with a high Cr concentration is not preferable because it has high adhesion to the steel as described above.
これに対し、内方酸化の速度が速い場合には、Ｃｒの濃化が進まないうちにサブスケールが形成されるため、ＦｅＯ（ウスタイト）主体のＣｒ濃度が低いサブスケールが形成されると考えられる。このＦｅＯ主体のサブスケールは脆く地鉄と剥離しやすい。よって、内方酸化の速度を速めてＦｅＯ（ウスタイト）主体のサブスケールを形成すれば、スケール剥離性が改善するのではないか、との着想のもとで、内方酸化の速度を増加させるべく詳細な条件について更に検討を進めた。 On the other hand, when the rate of inward oxidation is high, a subscale is formed before Cr concentration progresses, so that a subscale having a low Cr concentration mainly composed of FeO (wustite) is considered to be formed. It is done. This sub-scale mainly composed of FeO is brittle and easily peels off from the base iron. Therefore, increasing the rate of internal oxidation increases the rate of internal oxidation based on the idea that if the FeO (wustite) -based subscale is formed by increasing the rate of internal oxidation, the scale peelability will improve. Further studies were conducted on detailed conditions as much as possible.
その結果、（鋼片を加熱炉で加熱後、抽出）→（デスケーリング）→（熱間圧延）を行う工程において、特に、加熱炉から抽出後に後述する急速加熱を行い、次いで到達温度で所定時間保持（急速加熱・保持）すれば、容易に破壊しやすいサブスケールを形成できると共に、形成されたサブスケールが破壊されやすくなり、スケール剥離性が飛躍的に改善することを見出した。更には到達温度で保持する工程を、Ｏ２濃度やＨ２Ｏ濃度の比較的高い雰囲気下で行うと、内方酸化の速度が更に速くなり、スケール剥離性が更に改善されることを見出した。 As a result, in the process of (extracting the steel slab after heating in the heating furnace) → (descaling) → (hot rolling), in particular, rapid heating described later is performed after extraction from the heating furnace, and then the predetermined temperature is reached. It has been found that if the time is maintained (rapid heating / holding), a subscale that can be easily broken can be formed, the formed subscale is easily broken, and the scale peelability is remarkably improved. Furthermore, it has been found that when the step of holding at the ultimate temperature is performed in an atmosphere having a relatively high O 2 concentration or H 2 O concentration, the rate of inward oxidation is further increased, and the scale peelability is further improved. .
以下、上記急速加熱・保持の条件を規定した理由について、上記加熱炉での加熱条件を規定した理由と共に詳細に述べる。 Hereinafter, the reason why the conditions for the rapid heating / holding are defined will be described in detail together with the reason why the heating conditions in the heating furnace are defined.
〔加熱炉での加熱：鋼片の表面温度（加熱温度）が８００℃以上１１５０℃以下である温度域で１５分以上加熱〕
加熱炉での鋼片の表面温度（以下、温度および昇温速度については、全て鋼片の表面温度、鋼片の表面温度の昇温速度をいう。）が１１５０℃を超えると、１次スケールと鋼材がサブスケールを介して強固に密着するため、後述する急速加熱を施してもその効果が発現しにくい。よって加熱炉での加熱は１１５０℃以下で行う。生産性やエネルギー効率を高める点も併せて考慮すると、１１００℃以下とすることが好ましい。
[Heating in a heating furnace: Heating for 15 minutes or more in a temperature range where the surface temperature (heating temperature) of the steel slab is 800 ° C or higher and 1150 ° C or lower]
When the surface temperature of the steel slab in the heating furnace (hereinafter, the temperature and the heating rate all refer to the surface temperature of the steel slab and the heating rate of the surface temperature of the steel slab) exceeds 1150 ° C., the primary scale And the steel material are in close contact with each other through the subscale, so that the effect is hardly exhibited even if rapid heating described later is performed. Therefore, the heating in the heating furnace is performed at 1150 ° C. or lower. Considering also the point which improves productivity and energy efficiency, it is preferable to set it as 1100 degrees C or less.
一方、鋼片の表面温度が低すぎると、後述する急速加熱を行っても鋼片が十分に加熱されず、熱間圧延が出来なくなるほか、スケールの生成が不十分となり、却ってスケール剥離性を高めることが難しくなる。したがって、加熱炉での加熱温度は８００℃以上とする。好ましくは８５０℃以上である。 On the other hand, if the surface temperature of the steel slab is too low, the steel slab will not be sufficiently heated even if rapid heating described later is performed, and hot rolling will not be possible, scale generation will be insufficient, and scale peelability will be reduced. It becomes difficult to increase. Therefore, the heating temperature in a heating furnace shall be 800 degreeC or more. Preferably it is 850 degreeC or more.
また上記加熱による効果を十分得るには、上記温度域で１５分以上（好ましくは３０分以上）加熱する。一方、上記温度域での保持時間が長すぎると、スケールロスが過剰となるほか、脱炭が著しくなるため、上記保持時間は１８０分以下とすることが好ましい。 In order to sufficiently obtain the effect of the heating, heating is performed in the temperature range for 15 minutes or longer (preferably 30 minutes or longer). On the other hand, if the holding time in the temperature range is too long, the scale loss becomes excessive and decarburization becomes remarkable. Therefore, the holding time is preferably 180 minutes or less.
加熱炉における上記以外の条件については特に問わず、例えばヒートパターンとして、加熱開始から抽出まで上記温度域にある時間が１５分間以上となるよう徐々に昇温させてもよいし、後述する実施例に示す通り、上記温度域まで昇温させた後、該温度域で１５分以上保持する均熱帯を設けてもよい。また、加熱炉内の雰囲気は特に限定されず、例えばＮ２、Ｈ２Ｏ、ＣＯ２、Ｏ２を、７０体積％Ｎ２−１９体積％Ｈ２Ｏ−１０体積％ＣＯ２−１体積％Ｏ２の割合で含む雰囲気とすることが挙げられる。 The conditions other than the above in the heating furnace are not particularly limited. For example, as a heat pattern, the temperature in the temperature range from the start of heating to extraction may be gradually increased to 15 minutes or more. As shown in FIG. 3, after raising the temperature to the above temperature range, a soaking zone may be provided in which the temperature range is maintained for 15 minutes or more. The atmosphere in the heating furnace is not particularly limited, and for example N 2, H 2 O, the CO 2, O 2, 70 vol% N 2 -19 vol% H 2 O-10% by volume of CO 2 -1 vol% For example, an atmosphere containing O 2 may be used.
〔１２００℃以上１３５０℃以下の範囲内の温度（到達温度）までの昇温速度：５℃／ｓｅｃ以上〕
加熱炉にて上記温度で加熱後は、表面温度が上記温度域にある鋼片を加熱炉から取り出し（この加熱炉から取り出す（抽出）時の鋼片の表面温度を「抽出温度」という）、直ちに（約２０秒以内）、該抽出温度から１２００℃以上１３５０℃以下の範囲内の温度（到達温度）まで５℃／ｓｅｃ（秒）以上の昇温速度で加熱する（以下、該昇温速度で到達温度まで加熱することを「急速加熱」ということがある）。この急速加熱を施すことによって、スケールの成長応力を急速に高めて、容易に破壊しやすいサブスケールの形成や、形成されたサブスケールの破壊を促進させることができる。
[Temperature increase rate to a temperature in the range of 1200 ° C. to 1350 ° C. (final temperature): 5 ° C./sec or more]
After heating at the above temperature in the heating furnace, the steel slab whose surface temperature is in the above temperature range is taken out from the heating furnace (the surface temperature of the steel slab at the time of taking out (extraction) from this heating furnace is referred to as “extraction temperature”), Immediately (within about 20 seconds), heating from the extraction temperature to a temperature in the range of 1200 ° C. or higher and 1350 ° C. or lower (attainment temperature) at a heating rate of 5 ° C./sec (seconds) (hereinafter, the heating rate) Heating to the ultimate temperature with the) is sometimes called “rapid heating”). By applying this rapid heating, the growth stress of the scale can be rapidly increased, and the formation of a subscale that is easily broken or the destruction of the formed subscale can be promoted.
昇温速度が５℃／ｓｅｃ未満の場合は、上記効果が不十分となり、また高温域に曝される時間が長くなり、脱炭が進行するため好ましくない。上記昇温速度は１０℃／ｓｅｃ以上とすることが好ましい。尚、昇温速度の上限は特に限定されない。 When the rate of temperature increase is less than 5 ° C./sec, the above effect is insufficient, and the time of exposure to a high temperature range becomes long, and decarburization proceeds. The temperature raising rate is preferably 10 ° C./sec or more. In addition, the upper limit of a temperature increase rate is not specifically limited.
〔急速加熱による到達温度域：１２００℃以上１３５０℃以下〕
急速加熱による到達温度が高いほどスケールの成長が促進され、それに伴い成長応力が増加して、上述した通り、容易に破壊しやすいサブスケールの形成や、形成されたサブスケールの破壊が促進される。この様な効果を発現させるには、急速加熱による到達温度を１２００℃以上とする必要がある。一方、到達温度が高すぎると、スケールが急成長し厚くなりすぎて、スケール剥離性が低下する。またスケールロスも多くなる。よって、到達温度の上限は１３５０℃とする。
[Achieved temperature range by rapid heating: 1200 to 1350 ° C]
The higher the temperature reached by rapid heating, the more the growth of the scale is promoted, and the growth stress increases accordingly. As described above, the formation of the subscale that is easily broken and the destruction of the formed subscale are promoted. . In order to express such an effect, it is necessary to set the temperature reached by rapid heating to 1200 ° C. or higher. On the other hand, if the ultimate temperature is too high, the scale grows rapidly and becomes too thick, and the scale peelability is reduced. Scale loss also increases. Therefore, the upper limit of the ultimate temperature is 1350 ° C.
〔到達温度での保持時間：０．１秒以上６０秒以下〕
上記到達温度まで急速加熱後、該到達温度で０．１秒以上保持することで、急速加熱により破壊されたサブスケールを介して、雰囲気中の酸素がスケールと鋼材の界面に導入され、界面の酸素ポテンシャルを高めて鋼材内部への内方酸化を促進させることができる。好ましくは上記保持時間を１秒以上、更に好ましくは３秒以上とする。一方、上記保持時間が６０秒を超えると、内方酸化が過剰に進行し、スケールロスが増える。また内方酸化が過剰に進行してスケールが急成長し厚くなりすぎて、スケール剥離性が劣化する。よって上記保持時間を６０秒以下（好ましくは３０秒以下）とする。
[Holding time at ultimate temperature: 0.1 to 60 seconds]
After rapid heating to the ultimate temperature, holding at the ultimate temperature for 0.1 second or longer introduces oxygen in the atmosphere to the interface between the scale and the steel material through the subscale destroyed by rapid heating. It is possible to increase the oxygen potential and promote inward oxidation into the steel material. Preferably, the holding time is 1 second or longer, more preferably 3 seconds or longer. On the other hand, when the holding time exceeds 60 seconds, the inward oxidation proceeds excessively and scale loss increases. Moreover, the inward oxidation proceeds excessively, the scale grows rapidly and becomes too thick, and the scale peelability deteriorates. Therefore, the holding time is set to 60 seconds or shorter (preferably 30 seconds or shorter).
〔急速加熱・保持する雰囲気：Ｏ２濃度が１０体積％以上である雰囲気〕
急速加熱・保持する雰囲気中のＯ２濃度を、加熱炉内よりも高くすることにより、内方酸化が促進され、Ｃｒの濃化が進まないうちにサブスケールが形成されるため、結果としてＣｒ濃度の低い、ＦｅＯ（ウスタイト）主体のＣｒ濃度が低いサブスケールが形成されてスケール剥離性が向上する。このような効果を発現させるため、Ｏ２濃度を１０体積％以上とする。好ましくは２０体積％以上である。尚、大気中ではＯ２濃度が２０体積％であり、大気中で所定時間保持すれば、上記効果が発現される。Ｏ２濃度の上限は、酸化ロス防止の観点から３０体積％とすることが好ましい。
[Rapid heating and holding atmosphere: atmosphere in which O 2 concentration is 10% by volume or more]
By increasing the O 2 concentration in the rapid heating / holding atmosphere to be higher than that in the heating furnace, inward oxidation is promoted and a subscale is formed before Cr concentration progresses. A subscale having a low concentration and a low Cr concentration mainly composed of FeO (wustite) is formed, and the scale peelability is improved. In order to express such an effect, the O 2 concentration is set to 10% by volume or more. Preferably it is 20 volume% or more. Note that the O 2 concentration is 20% by volume in the atmosphere, and the above-described effect is exhibited if the O 2 concentration is kept in the atmosphere for a predetermined time. The upper limit of the O 2 concentration is preferably 30% by volume from the viewpoint of preventing oxidation loss.
〔到達温度で保持する雰囲気：Ｏ２濃度が１０体積％以上かつＨ２Ｏ濃度が５体積％以上３５体積％以下である雰囲気〕
到達温度で保持する雰囲気は、上記観点からＯ２濃度：１０体積％以上を満たすと共に、Ｈ２Ｏ濃度：５体積％以上３５体積％以下を満たす雰囲気とすることが好ましい。
[Atmosphere held at ultimate temperature: atmosphere having an O 2 concentration of 10% by volume or more and an H 2 O concentration of 5% by volume to 35% by volume]
The atmosphere held at the ultimate temperature is preferably an atmosphere satisfying O 2 concentration: 10% by volume or more and H 2 O concentration: 5% by volume or more and 35% by volume or less from the above viewpoint.
Ｈ２Ｏ含有雰囲気で鋼材を酸化すると、鋼材側に向かって酸化が進む水蒸気酸化が生じる。この水蒸気酸化は、スケール表面で水分子が解離してプロトンを放出し、プロトンがスケール／鋼材界面でスケール中の酸素を奪い、再び水になり鋼材内方への酸化（内方酸化）が促進されることによって生じると言われている。到達温度で保持する際に、この様な水蒸気酸化の効果を組み合わせることで、脆いＦｅＯを主体とした破壊し易いサブスケールがより形成され易くなり、スケール剥離性が飛躍的に改善する。該効果を十分に発揮させるには、雰囲気中のＨ２Ｏ濃度を５体積％以上とすることが好ましい。より好ましくは１０体積％以上である。一方、Ｈ２Ｏ濃度が高すぎると、相対的に酸素分圧の低下を招く。Ｈ２ＯはＯ２よりも酸化作用が小さいため、Ｈ２Ｏ濃度が増加し過ぎると雰囲気全体として酸化作用が減少し、スケール生成が促進されない。よって、Ｈ２Ｏ濃度は３５体積％以下とすることが好ましい。Ｈ２Ｏ濃度はより好ましくは３０体積％以下である。 When the steel material is oxidized in an H 2 O-containing atmosphere, steam oxidation proceeds toward the steel material side. In this steam oxidation, water molecules dissociate on the scale surface to release protons, and the protons deprive the scale of oxygen at the scale / steel interface, becoming water again and promoting oxidation (inward oxidation) into the steel. It is said that it is caused by being done. By combining such an effect of steam oxidation when held at the ultimate temperature, it becomes easier to form a subscale that is mainly composed of brittle FeO, and the scale peelability is dramatically improved. To sufficiently exhibit the effect, it is preferable to of H 2 O concentration in the atmosphere with 5% by volume or more. More preferably, it is 10 volume% or more. On the other hand, if the H 2 O concentration is too high, the oxygen partial pressure is relatively lowered. Since H 2 O has a smaller oxidizing action than O 2 , if the H 2 O concentration is excessively increased, the oxidizing action is reduced as a whole atmosphere, and scale generation is not promoted. Therefore, the H 2 O concentration is preferably 35% by volume or less. The H 2 O concentration is more preferably 30% by volume or less.
急速加熱・保持の実施形態として、例えば、加熱炉から鋼片を抽出後、直ちに（約２０秒以内）鋼片搬送コンベア上に設置された高周波誘導加熱装置を用いて、例えば大気雰囲気で、規定の到達温度まで急速加熱した後、保温炉（大気雰囲気）にて上記到達温度で所定時間保持することが挙げられる。前記保持時の雰囲気をＨ２Ｏ含有雰囲気とするには、上記保温炉内に、例えば上記Ｏ２濃度およびＨ２Ｏ濃度を満たす加湿空気を供給することによって実現することができる。 As an embodiment of rapid heating / holding, for example, in the atmosphere, using a high-frequency induction heating device installed on a steel piece conveyor, immediately after extraction of steel pieces from a heating furnace (within about 20 seconds) After rapid heating to the ultimate temperature, it is possible to hold for a predetermined time at the ultimate temperature in a heat retaining furnace (atmosphere). The atmosphere at the time of holding may be an H 2 O-containing atmosphere, for example, by supplying humidified air satisfying the O 2 concentration and the H 2 O concentration into the heat retaining furnace.
上記保持後は、直ちに（約２０秒以内）デスケーリングを実施する。デスケーリングとしては、高圧水デスケーリングが一般的であるが、メカニカルデスケーリングを実施してもよい。 Immediately (within about 20 seconds) after the holding, descaling is performed. As descaling, high-pressure water descaling is common, but mechanical descaling may be performed.
その他の製造条件については特に限定されず、例えば、連続鋳造にてビレットを得た場合、該ビレットを加熱炉に導入し、予熱帯、加熱帯、均熱帯を経て、ビレットを規定の抽出温度まで昇温する方法が挙げられる。そして、該抽出温度でビレットを加熱炉から取り出し、上記の通り急速加熱・保持し、次いで高圧水デスケーラーでスケールを除去し、その後、粗圧延、仕上げ圧延、製品水冷、巻取りを順次経て鋼線材を得ることができる。 Other manufacturing conditions are not particularly limited. For example, when a billet is obtained by continuous casting, the billet is introduced into a heating furnace, passed through a pre-tropical zone, a heating zone, a soaking zone, and the billet is brought to a specified extraction temperature. The method of raising temperature is mentioned. Then, the billet is taken out from the heating furnace at the extraction temperature, rapidly heated and held as described above, then the scale is removed with a high-pressure water descaler, and then the steel wire is sequentially subjected to rough rolling, finish rolling, product water cooling, and winding. Can be obtained.
尚、本発明は、強度を付与するために必要な元素であるがスケール剥離性に悪影響を与えるＣｒを含有する条鋼材を対象に、スケール剥離性を改善するものである。よって本発明は、Ｃｒを０．１０％以上（好ましくは０．８０％以上）含むＣｒ含有条鋼材を対象とする。さらに本発明によれば、Ｃｒを多量に含有していても、スケール剥離性を良好にでき、Ｃｒ含有量は、例えば、１．０％以上、好ましくは１．１０％以上、さらに好ましくは１．２０％以上にすることもできる。この様にＣｒを添加すると、強度を向上させることができるが、Ｃｒ量が過剰になると、延性の確保が困難となるため、Ｃｒ量は、２．０％以下、好ましくは１．９０％以下、更に好ましくは１．５０％以下とする。 In addition, this invention improves scale peelability for the steel strip containing Cr which is an element required in order to provide intensity | strength, but has a bad influence on scale peelability. Therefore, the present invention is directed to a Cr-containing strip steel material containing 0.10% or more (preferably 0.80% or more) of Cr. Furthermore, according to the present invention, even if a large amount of Cr is contained, the scale peelability can be improved, and the Cr content is, for example, 1.0% or more, preferably 1.10% or more, more preferably 1 20% or more. When Cr is added in this way, the strength can be improved. However, if the amount of Cr becomes excessive, it becomes difficult to ensure ductility. Therefore, the amount of Cr is 2.0% or less, preferably 1.90% or less. More preferably, it is 1.50% or less.
本発明はＣｒに起因するサブスケールを制御するものであるため、熱間圧延材（条鋼材）として使用できる限り、Ｃｒ以外の鋼成分は特に限定されないが、Ｃｒ以外の元素とその量が、例えば、Ｓｉ：０．１０〜０．４０％、Ｃ：０．１０〜１．５０％、およびＭｎ：０．０１〜１．５％を満たし、残部が鉄および不可避不純物からなるものが挙げられる。更に、Ｍｏ：０．０１〜０．４０％を含むものであってもよい。以下、上記各元素について説明する。 Since the present invention controls the subscale caused by Cr, steel components other than Cr are not particularly limited as long as they can be used as hot-rolled material (strip steel), but the elements other than Cr and their amounts For example, a material satisfying Si: 0.10 to 0.40%, C: 0.10 to 1.50%, and Mn: 0.01 to 1.5%, with the balance being made of iron and inevitable impurities. . Furthermore, Mo: 0.01 to 0.40% may be included. Hereinafter, each of the above elements will be described.
〔Ｓｉ：０．１０〜０．４０％〕
Ｓｉは、強度を確保するための重要な元素であり、冷間圧延用鋼（ＣＨ鋼）に最低限必要なＳｉ量としてその下限を０．１０％とすることが好ましい。一方、延性を確保する観点からは、Ｓｉ量を０．４０％以下とすることが好ましい。
[Si: 0.10 to 0.40%]
Si is an important element for ensuring strength, and the lower limit is preferably set to 0.10% as the minimum amount of Si necessary for cold rolling steel (CH steel). On the other hand, from the viewpoint of ensuring ductility, the Si content is preferably 0.40% or less.
〔Ｃ：０．１０〜１．５０％〕
Ｃも、強度を確保するための重要な元素であり、０．１０％以上含有させることが好ましい。一方、優れた冷間加工性を確保するにはＣ量を１．５０％以下とすることが好ましい。
[C: 0.10 to 1.50%]
C is also an important element for ensuring strength, and is preferably contained in an amount of 0.10% or more. On the other hand, in order to ensure excellent cold workability, the C content is preferably 1.50% or less.
〔Ｍｎ：０．０１〜１．５％〕
Ｍｎは、鋼材の強度および靭性を確保するために有用な元素であり、そのためにはＭｎを０．０１％以上含有させることが好ましい。一方、鋼材の靭性および溶接性を確保する観点からは、Ｍｎ量を１．５％以下とすることが好ましい。
[Mn: 0.01 to 1.5%]
Mn is an element useful for securing the strength and toughness of the steel material. To that end, it is preferable to contain Mn in an amount of 0.01% or more. On the other hand, from the viewpoint of ensuring the toughness and weldability of the steel material, the Mn content is preferably 1.5% or less.
上記Ｃｒ、Ｓｉ、Ｃ、およびＭｎ以外の残部は、鉄および不可避不純物であってもよい。不可避不純物として、例えば、原料、資材、製造設備等の状況によって持ち込まれる不純物が鋼中に含まれることは、当然に許容される。不純物として含まれるＰ、Ｓ、Ｃｕ、Ｎｉについては、下記に詳述する通り鋼材の表面性状や特性に悪影響を及ぼすことから、下記範囲内に抑えることが好ましい。 The balance other than Cr, Si, C, and Mn may be iron and inevitable impurities. As an inevitable impurity, for example, it is naturally allowed that impurities brought into the steel depending on the situation of raw materials, materials, manufacturing equipment, and the like are included in the steel. About P, S, Cu, and Ni contained as impurities, as described in detail below, the surface properties and characteristics of the steel material are adversely affected.
即ち、Ｐの微量添加は鋼材の強度を高めるが、過剰に含まれると脆性が高まるため、Ｐ量は０．０５％以下に抑えることが好ましい。Ｓは、Ｍｎと反応して硫化物系介在物ＭｎＳを形成する。このＭｎＳは熱間加工時に偏析して鋼材を脆化させ、鋼材割れを引き起こす。従ってＳ量を少なくすることが推奨される。Ｓ量は０．０５％以下に抑えることが好ましい。 That is, the addition of a small amount of P increases the strength of the steel material, but if included excessively, brittleness increases, so the P content is preferably suppressed to 0.05% or less. S reacts with Mn to form sulfide inclusion MnS. This MnS segregates during hot working, embrittles the steel material, and causes steel material cracking. Therefore, it is recommended to reduce the amount of S. The amount of S is preferably suppressed to 0.05% or less.
Ｃｕも不可避的に混入する元素である。１３５６Ｋで液相となり、熱間圧延時の変形中にオーステナイト結晶粒界に浸入して、表面割れを発生させる原因となる。よって、Ｃｕ量は０．３０％以下（０％を含む）に抑えることが好ましい。Ｎｉも、不可避的に混入する元素であり、鋼材表面に不均一に濃化し、スケールの表面の凹凸を大きくしてスケール剥離性を悪化させる。この様な悪影響を抑制するため、Ｎｉ量も０．３０％以下（０％を含む）に抑えることが好ましい。 Cu is an element inevitably mixed in. It becomes a liquid phase at 1356K and enters the austenite grain boundary during deformation during hot rolling, causing surface cracks. Therefore, it is preferable to suppress the amount of Cu to 0.30% or less (including 0%). Ni is also an element that is inevitably mixed in, and is unevenly concentrated on the surface of the steel material, increasing the irregularities on the surface of the scale and degrading the scale peelability. In order to suppress such an adverse effect, the Ni content is preferably suppressed to 0.30% or less (including 0%).
本発明のＣｒ含有条鋼材は、必要に応じて下記に示す通りＭｏを更に含んでいてもよい。 The Cr-containing strip steel material of the present invention may further contain Mo as shown below as required.
〔Ｍｏ：０．０１〜０．４０％〕
Ｍｏは、鋼材の強度を高めるのに有効な元素であり、該効果を発揮させるには、０．０１％以上含有させることが好ましい。一方、Ｍｏ量が過剰になると、鋼材の延性が低下するため、Ｍｏ量は０．４０％以下とすることが好ましい。
[Mo: 0.01-0.40%]
Mo is an element effective for increasing the strength of the steel material, and in order to exhibit this effect, it is preferable to contain 0.01% or more. On the other hand, when the amount of Mo becomes excessive, the ductility of the steel material decreases, so the amount of Mo is preferably set to 0.40% or less.
本発明における条鋼材とは、棒状または線状の鋼材の総称であり、例えば自動車用の懸架ばね、弁ばね、軸受などに用いられうる。 The strip steel material in the present invention is a general term for rod-shaped or linear steel materials, and can be used for, for example, suspension springs, valve springs, and bearings for automobiles.
以下、実施例を挙げて本発明をより具体的に説明するが、本発明はもとより下記実施例によって制限を受けるものではなく、前・後記の趣旨に適合し得る範囲で適当に変更を加えて実施することも勿論可能であり、それらはいずれも本発明の技術的範囲に包含される。 EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.
〔実施例１〕
表１に示す合金組成の鋼材を溶製し、φ１０ｍｍ×１２ｍｍｔの円柱状に切り出し加工したサンプルを用意した。このサンプルに対し、雰囲気制御が可能な高温圧縮試験機熱処理炉を用いて、下記の実施例１Ａまたは実施例１Ｂに示す処理を施した後、各到達温度でデスケーリングを模擬してサンプルを圧縮し、スケールの除去を行って表面性状（スケール剥離性）を評価した。
[Example 1]
A steel material having an alloy composition shown in Table 1 was melted and cut into a cylindrical shape of φ10 mm × 12 mmt to prepare a sample. This sample was subjected to the treatment shown in Example 1A or Example 1B below using a high-temperature compression tester heat treatment furnace capable of controlling the atmosphere, and then the sample was compressed by simulating descaling at each ultimate temperature. Then, the scale was removed and the surface properties (scale peelability) were evaluated.
上記圧縮は、大気雰囲気で圧縮歪率５０％、歪速度１０ｍｍ／ｓｅｃの条件で行い、圧縮後はＡｒ雰囲気で試料を常温まで急冷し、剥離後のスケール生成（２次スケール生成）を抑制した。圧縮後は、サンプル側面の外観をスキャナで取り込み、画像を２値化処理し、圧縮後のサンプルにおけるスケール残留部の面積率（残留スケール面積率）を算出した。そして、残留スケール面積率が２０％以下の場合をスケール剥離性に優れていると判断した。 The compression is performed under the conditions of a compression strain rate of 50% and a strain rate of 10 mm / sec in an air atmosphere, and after compression, the sample is rapidly cooled to an ordinary temperature in an Ar atmosphere to suppress scale formation (secondary scale generation) after peeling. . After compression, the appearance of the side surface of the sample was captured with a scanner, the image was binarized, and the area ratio (residual scale area ratio) of the scale remaining portion in the sample after compression was calculated. And when the residual scale area ratio was 20% or less, it was judged that the scale peelability was excellent.
（実施例１Ａ）
実施例１Ａでは、図１に示すヒートパターンで加熱し、圧縮（デスケーリング）を行ってスケール剥離性を評価した。
Example 1A
In Example 1A, it heated with the heat pattern shown in FIG. 1, compression (descaling) was performed, and scale peelability was evaluated.
具体的には、加熱炉雰囲気をＮ２（残部）−１体積％Ｏ２−１０体積％ＣＯ２−２３体積％Ｈ２Ｏとし、表２のＮｏ．１〜１０については、１１００℃で３０分加熱し、１次スケールを生成させた後、大気雰囲気で、表２に示す昇温速度（ｘ℃／ｓｅｃ）で表２に示す到達温度まで昇温させ、次いで、該到達温度で表２に示す時間保持した後、圧縮試験を実施した。圧縮試験の結果（残留スケール面積率）を表２に示す。尚、大気雰囲気において、Ｏ２濃度は約２０体積％、Ｈ２Ｏ濃度は５体積％程度である。 Specifically, the heating furnace atmosphere is N 2 (remainder) -1 vol% O 2 -10 vol% CO 2 -23 vol% H 2 O. About 1-10, after heating at 1100 degreeC for 30 minutes and producing | generating a primary scale, it heats up to the ultimate temperature shown in Table 2 with the temperature increase rate (xdegreeC / sec) shown in Table 2 in air | atmosphere. Then, after holding at the ultimate temperature for the time shown in Table 2, a compression test was performed. Table 2 shows the results of the compression test (residual scale area ratio). In the air atmosphere, the O 2 concentration is about 20% by volume, and the H 2 O concentration is about 5% by volume.
表２のＮｏ．１１は、１１００℃で３０分加熱した後、本発明で規定の急速加熱・保持を行うことなく圧縮試験を実施した例である。また表２のＮｏ．１２は、１２００℃で３０分加熱した後、本発明で規定の急速加熱・保持を行うことなく圧縮試験を実施した例である。 No. in Table 2 11 is an example in which the compression test was carried out without heating and holding as specified in the present invention after heating at 1100 ° C. for 30 minutes. In Table 2, No. No. 12 is an example in which the compression test was carried out without heating and holding as specified in the present invention after heating at 1200 ° C. for 30 minutes.
表２より次の様に考察できる。Ｎｏ．１、２、４、６および７は、いずれも規定のヒートパターンで製造しているため、スケール剥離性に優れている。 From Table 2, it can be considered as follows. No. Since 1, 2, 4, 6 and 7 are all manufactured with a prescribed heat pattern, they are excellent in scale peelability.
これに対しＮｏ．３、５、および８〜１２は、規定する少なくともいずれかの条件を満たしていないため、表面性状に劣るものとなった。詳細には、Ｎｏ．３および５は、到達温度までの昇温速度が遅いため、脆いサブスケールの形成やサブスケールの破壊が不十分となり、残留スケール面積率が高く、表面性状に劣っている。 In contrast, no. Since 3, 5 and 8-12 did not satisfy at least one of the conditions to be defined, the surface properties were inferior. Specifically, no. Nos. 3 and 5 have a slow rate of temperature rise to the ultimate temperature, so that formation of a brittle subscale and destruction of the subscale are insufficient, the residual scale area ratio is high, and the surface properties are inferior.
Ｎｏ．８は、到達温度が１２００℃未満であるため、この場合もサブスケールの破壊が不十分となり、表面性状に劣っている。 No. No. 8 has an ultimate temperature of less than 1200 ° C., and in this case too, the subscale is not sufficiently broken and the surface properties are inferior.
Ｎｏ．９は、到達温度で一定時間保持していないため、破壊したサブスケールを介した酸素の内方拡散が不十分となり、残留スケール面積率が高くなった。 No. Since No. 9 was not maintained at the ultimate temperature for a certain period of time, the inward diffusion of oxygen through the broken subscale became insufficient, and the residual scale area ratio increased.
Ｎｏ．１０は、到達温度での保持時間が長すぎるため、破壊したサブスケールを介した酸素の内方拡散が過剰に進んで、スケールロスが増えると共に、表面性状に劣るものとなった。 No. In No. 10, since the retention time at the ultimate temperature was too long, the inward diffusion of oxygen through the broken subscale progressed excessively, resulting in increased scale loss and poor surface properties.
Ｎｏ．１１および１２は、本発明で規定する急速加熱・保持を行っていないため、残留スケールがかなり多い結果となった。 No. 11 and 12 did not perform the rapid heating and holding specified in the present invention, and therefore the result was that the residual scale was considerably large.
（実施例１Ｂ）
実施例１Ｂでは、図２に示すヒートパターンで加熱し、圧縮（デスケーリング）を行ってスケール剥離性を評価した。
(Example 1B)
In Example 1B, it heated with the heat pattern shown in FIG. 2, compression (descaling) was performed, and scale peelability was evaluated.
具体的には、加熱炉雰囲気をＮ２（残部）−０．５体積％Ｏ２−１０体積％ＣＯ２−３０体積％Ｈ２Ｏとし、１０００℃で６０分加熱して１次スケールを生成させた後、大気雰囲気で急速加熱（昇温速度１５℃／ｓｅｃ、到達温度１２５０℃）を行い、該到達温度にて、表３に示す通り種々のＯ２濃度（Ｘ体積％）及びＨ２Ｏ濃度（Ｙ体積％）の雰囲気下、５秒間保持し、その後に圧縮試験を行った。圧縮試験の結果を表３に示す。 Specifically, the heating furnace atmosphere is N 2 (remainder) -0.5 volume% O 2 -10 volume% CO 2 -30 volume% H 2 O, and heated at 1000 ° C. for 60 minutes to generate a primary scale. after performs rapid heating (heating rate 15 ° C. / sec, reaching temperature 1250 ° C.) in an air atmosphere at該到our temperature, various as shown in Table 3 O 2 concentration (X% by volume) and H 2 This was held for 5 seconds in an atmosphere of O concentration (Y volume%), and then a compression test was conducted. The results of the compression test are shown in Table 3.
表３より以下の様に考察できる。即ち、Ｎｏ．１３〜１６は、Ｏ２濃度を１５体積％で一定とし、Ｈ２Ｏ濃度を変化させた例である。これらの結果から、Ｈ２Ｏ濃度が低すぎても高すぎても残留スケール面積率は増加することが分かる。 From Table 3, it can be considered as follows. That is, no. Nos. 13 to 16 are examples in which the O 2 concentration is constant at 15% by volume and the H 2 O concentration is changed. From these results, it can be seen that the residual scale area ratio increases if the H 2 O concentration is too low or too high.
一方、Ｎｏ．１７〜１９は、Ｈ２Ｏ濃度を２０体積％で一定とし、Ｏ２濃度を変化させた例である。これらの結果から、雰囲気のＯ２濃度の増加に伴い、残留スケール面積率は減少傾向にあることが分かる。 On the other hand, no. 17 to 19 are examples in which the H 2 O concentration was constant at 20% by volume and the O 2 concentration was changed. From these results, it can be seen that the residual scale area ratio tends to decrease as the O 2 concentration in the atmosphere increases.
Ｎｏ．２１は、Ｈ２Ｏ濃度は本発明で推奨する条件を満たすが、Ｏ２濃度がかなり低いため、残留スケール面積率が高くなっている。 No. No. 21, although the H 2 O concentration satisfies the conditions recommended in the present invention, the residual scale area ratio is high because the O 2 concentration is considerably low.
Ｎｏ．２０および２２は、加熱保持雰囲気におけるＯ２濃度及びＨ２Ｏ濃度が共に本発明で推奨する条件を満たしていることから、残留スケールが少なく、スケール剥離性に優れている。 No. In Nos. 20 and 22, both the O 2 concentration and the H 2 O concentration in the heated and held atmosphere satisfy the conditions recommended in the present invention, so that the residual scale is small and the scale peelability is excellent.
［実施例２］
実操業を模擬して加熱およびスケール剥離を実施し、スケール剥離後の鋼材の表面性状を調べた。
[Example 2]
Heating and scale peeling were performed simulating actual operation, and the surface properties of the steel material after scale peeling were examined.
まず、下記の表４に示す鋼材を溶製し、鋳造して１５０ｍｍ角のビレットを得た。そして、加熱炉にて、加熱炉での保持温度（表５）まで昇温させ、該温度で３０分保持する加熱を行った後、該温度の鋼片を加熱炉から抽出し、加熱炉に隣接されたインダクションヒーター（雰囲気：大気）にて、表５に示す到達温度まで表５に示す昇温速度で加熱する急速加熱を行った。インダクションヒーターから抽出後、大気雰囲気（窒素、酸素以外に水蒸気を５体積％程度含む）、または、Ｏ２濃度およびＨ２Ｏ濃度を調整した雰囲気下にて、上記到達温度で表５に示す時間保持した後、１５０ＭＰａの高圧水デスケーリングを施し、次いで熱間圧延して直径８．０ｍｍの鋼線材を製造した。尚、加熱炉の燃焼用ガスにはＬＮＧガスを使用し、加熱炉雰囲気はいずれもＮ２（残部）−１体積％Ｏ２−１０体積％ＣＯ２−２３体積％Ｈ２Ｏに調整した。インダクションヒーターから抽出した後の雰囲気の調整は、ビレットの周囲を覆うブースを設置し、ブース内壁に設置したノズルから酸素ガス、窒素ガス並びに水を導入することで行った。 First, steel materials shown in Table 4 below were melted and cast to obtain 150 mm square billets. And after heating up to the holding temperature (Table 5) in a heating furnace in a heating furnace and performing the heating which hold | maintains at this temperature for 30 minutes, the steel piece of this temperature is extracted from a heating furnace, In the adjacent induction heater (atmosphere: air), rapid heating was performed to heat to the ultimate temperature shown in Table 5 at the rate of temperature rise shown in Table 5. After extraction from the induction heater, the time shown in Table 5 at the above reached temperature in an air atmosphere (containing about 5% by volume of water vapor in addition to nitrogen and oxygen) or in an atmosphere in which the O 2 concentration and H 2 O concentration are adjusted After being held, 150 MPa high-pressure water descaling was performed, and then hot rolling was performed to produce a steel wire having a diameter of 8.0 mm. Incidentally, the combustion gas in the furnace using the LNG gas, the furnace atmosphere were all adjusted to N 2 (balance) -1 vol% O 2 -10 vol% CO 2 -23 vol% H 2 O. The atmosphere after extraction from the induction heater was adjusted by installing a booth covering the periphery of the billet and introducing oxygen gas, nitrogen gas and water from a nozzle installed on the inner wall of the booth.
上記製造された各鋼線材のスケール起因の表面疵を評価するため、鋼線材の断面を１００倍の倍率で光学顕微鏡観察し、表面疵の有無ならびに個数をカウントした。 In order to evaluate the surface defects due to the scale of each steel wire produced as described above, the cross section of the steel wire was observed with an optical microscope at a magnification of 100 times, and the presence and number of surface defects were counted.
尚、本発明で対象とする表面疵とは、「疵深さが１０μｍ以上に達する、スケール起因の表面疵」をいう。疵深さが１０μｍ未満の疵は、表面疵としては認識されず、加工時に割れなどの問題を引き起こすことは実質的にないので、疵深さが１０μｍ以上に達する疵のみを対象とした。また、スケール起因の表面疵であるかどうかの確認は次の方法によった。即ち、全表面疵の断面をＥＰＭＡマッピングにより５００倍の倍率で分析し、Ｃｒ濃度が鋼線材全体の平均Ｃｒ濃度の２倍以上である領域を、サブスケール（ＦｅＣｒ２Ｏ４）が押し込まれたスケール起因の表面疵であると判断した。 In addition, the surface wrinkle targeted in the present invention refers to “a surface wrinkle due to scale in which the wrinkle depth reaches 10 μm or more”. A wrinkle having a wrinkle depth of less than 10 μm is not recognized as a surface wrinkle and does not substantially cause problems such as cracking during processing. Therefore, only wrinkles having a wrinkle depth of 10 μm or more are targeted. In addition, the following method was used to confirm whether the surface wrinkles were caused by scale. That is, the cross section of the entire surface defect was analyzed at 500 times magnification by EPMA mapping, and the subscale (FeCr 2 O 4 ) was pushed in the region where the Cr concentration was more than twice the average Cr concentration of the entire steel wire rod. Judged as surface defects due to scale.
表面性状の評価は、鋼線材の長手方向（鋼の圧延方向）に垂直な１０箇所以上の横断面で観察される上記表面疵の個数を計測し、その平均値（表面疵個数の平均値）を下式（１）により算出し、下記の５段階に分類整理して評価した。そして、ランク１以下の場合を、スケール起因の表面疵に関して製品としては全く問題がないと評価した。これらの結果を表５に示す。
表面疵個数の合計数／測定断面数の合計数＝１測定断面当たりの表面疵個数…（１）
（表面疵のランク）
・ランク０：表面疵個数の平均値が０個（疵なし）のもの
・ランク１：表面疵個数の平均値が０個超１０個以下のもの
・ランク２：表面疵個数の平均値が１０個超２０個未満のもの
・ランク３：表面疵個数の平均値が２０個以上３０個未満のもの
・ランク４：表面疵個数の平均値が３０個以上のもの
The evaluation of the surface properties is performed by measuring the number of surface defects observed at 10 or more cross sections perpendicular to the longitudinal direction (steel rolling direction) of the steel wire, and calculating the average value (average value of the number of surface defects). Was calculated by the following formula (1), and was classified and evaluated in the following five stages. And the case of rank 1 or less was evaluated as having no problem as a product with respect to surface defects caused by scale. These results are shown in Table 5.
Total number of surface defects / total number of measured cross sections = number of surface defects per measured cross section (1)
(Rank of surface flaw)
-Rank 0: The average number of surface defects is 0 (no defects)-Rank 1: The average number of surface defects is more than 0 and less than 10-Rank 2: The average value of surface defects is 10 More than 20 and less than 20 ・ Rank 3: The average number of surface defects is 20 or more and less than 30 ・ Rank 4: The average number of surface defects is 30 or more
表５より次の様に考察できる。即ち、Ｎｏ．２３〜２６は、ＳＣＲ鋼を用い加熱炉からの抽出温度を変化させて検討した例であり、急速加熱・保持の諸条件はすべて規定を満たしている。このうちＮｏ．２３は、加熱温度（加熱炉からの抽出温度）が本発明で規定する温度よりも低いため、急速加熱によるスケール剥離性の改善が不十分であり、表面疵が不合格レベルとなった。Ｎｏ．２６は、加熱温度（加熱炉からの抽出温度）が高すぎるため、加熱炉で生成したサブスケールを介して１次スケールと鋼材が強固に密着してしまい、急速加熱を行ってもスケール剥離性が改善されなかった。 From Table 5, it can be considered as follows. That is, no. Nos. 23 to 26 are examples examined by changing the extraction temperature from the heating furnace using SCR steel, and all the conditions for rapid heating and holding satisfy the regulations. Of these, No. In No. 23, the heating temperature (extraction temperature from the heating furnace) was lower than the temperature defined in the present invention, so that the improvement in scale peelability by rapid heating was insufficient, and the surface flaws were at a reject level. No. In No. 26, since the heating temperature (extraction temperature from the heating furnace) is too high, the primary scale and the steel material are in close contact with each other through the subscale generated in the heating furnace, and even if rapid heating is performed, the scale peelability Was not improved.
Ｎｏ．２４、２５、２７、２９、３２、３４は本発明の条件を満たしており、いずれも疵レベルは合格レベルとなった。 No. 24, 25, 27, 29, 32, and 34 satisfied the conditions of the present invention, and the wrinkle level was an acceptable level.
Ｎｏ．２８および３０は、到達温度までの昇温速度が遅いため、表面疵が不合格レベルとなった。 No. In Nos. 28 and 30, since the rate of temperature rise to the ultimate temperature was slow, the surface defects were at a rejected level.
Ｎｏ．３１は、到達温度が１２００℃未満であるため、表面疵が不合格レベルとなった。一方、Ｎｏ．３５は、到達温度が１３５０℃を超えるため、スケールが急成長し、スケール剥離性が悪化した。 No. In No. 31, since the ultimate temperature was less than 1200 ° C., the surface flaw was at a rejected level. On the other hand, no. In No. 35, the ultimate temperature exceeded 1350 ° C., so the scale grew rapidly and the scale peelability deteriorated.
Ｎｏ．３３は、到達温度に達した後、該到達温度で保持していないため、破壊したサブスケールを介した酸素の内方拡散が不十分となり、表面疵が不合格レベルとなった。 No. Since No. 33 was not held at the ultimate temperature after reaching the ultimate temperature, the inward diffusion of oxygen through the broken subscale was insufficient, and the surface defects were at a reject level.
Ｎｏ．３６は、到達温度での保持時間が長すぎるため、破壊したサブスケールを介した酸素の内方拡散が過剰に進み、スケールが急成長し厚くなりすぎて、スケール剥離性が悪化する結果となった。 No. In No. 36, since the retention time at the ultimate temperature is too long, the inward diffusion of oxygen through the broken subscale proceeds excessively, the scale grows rapidly and becomes too thick, resulting in deterioration of the scale peelability. It was.
Ｎｏ．３７および３８は、規定の急速加熱・保持を行わなかった比較例であり、いずれも疵レベルが高く不合格となっている。 No. Nos. 37 and 38 are comparative examples in which the prescribed rapid heating and holding were not performed, both of which have a high wrinkle level and are rejected.
Claims (4)
前記加熱炉にて、鋼片の表面温度が８００℃以上１１５０℃以下の温度域で１５分以上加熱した後、その表面温度（抽出温度）が前記温度域にある鋼片を加熱炉から取り出し、
直ちにＯ２濃度：１０体積％以上の雰囲気中で、鋼片の表面温度が１２００℃以上１３５０℃以下の範囲内の温度（到達温度）となるまで、５℃／ｓｅｃ以上の昇温速度で前記鋼片を急速加熱し、上記到達温度で０．１秒以上６０秒以下保持した後、
デスケーリングすることを特徴とするＣｒ含有条鋼材の製造方法。 A method for producing a Cr-containing strip steel material, in which a steel slab containing Cr of 0.10 to 2.0% (meaning mass%, the same applies to the chemical components of steel) is taken out of the heating furnace, descaled, and then hot-rolled. Because
In the heating furnace, after the surface temperature of the steel slab is heated at a temperature range of 800 ° C. or higher and 1150 ° C. or lower for 15 minutes or more, the steel slab whose surface temperature (extraction temperature) is in the temperature range is taken out of the heating furnace,
Immediately in an atmosphere of O 2 concentration: 10% by volume or more, at a rate of temperature increase of 5 ° C./sec or more until the surface temperature of the steel slab reaches a temperature (attainment temperature) within a range of 1200 ° C. or higher and 1350 ° C. or lower. After rapidly heating the steel slab and holding at the above temperature for 0.1 seconds to 60 seconds,
A method for producing a Cr-containing strip steel material, characterized by descaling.
Ｓｉ：０．１０〜０．４０％、
Ｃ：０．１０〜１．５０％、および
Ｍｎ：０．０１〜１．５％
を満たし、残部が鉄および不可避不純物からなるものである請求項１または２に記載の製造方法。 The billet further comprises:
Si: 0.10 to 0.40%,
C: 0.10 to 1.50%, and Mn: 0.01 to 1.5%
The manufacturing method according to claim 1, wherein the balance consists of iron and inevitable impurities.
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