JP3759355B2 - Steel wire rod and manufacturing method thereof - Google Patents
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Description
【０００１】
【発明の属する技術分野】
本発明は、伸線加工に供する鋼線用線材に関する。
【０００２】
【従来の技術】
従来の鋼線用線材として製造される鋼は、転炉等で精錬を完了した後、精錬完了時に溶鋼中に含まれる酸素を除去するために、鋳造に先立って脱酸剤が投入され、酸化物として酸素が除去される。生成した酸化物は鋳造時に、タンディッシュ内あるいはモールド内において衝突による合体や成長により大型化し、浮上除去される。鋼線用線材として製造される鋼中には、非金属介在物は少ない方がよいとされ、その代表的なものである酸化物を極力少なくするために、精錬完了後鋳造開始までに除去する様々な工夫がなされてきた。そのため、鋳片を圧延加工して得られる線材には有害となる介在物は存在せず、伸線加工しても介在物による断線はほとんど見られなかった。このような材料を伸線加工した後、パテンティングにより組織を調整する場合、熱処理時の結晶粒を一定の大きさにコントロールし、均一な熱処理組織とすることが重要となる。これまでは、パテンティングにより均一な組織を得るためには、オーステナイト化の温度と時間を調整することにより行ってきた。
【０００３】
【発明が解決しようとする課題】
上に記述したように、伸線後の線材は熱処理（パテンティング処理）により一定の強度を得ることができる。この熱処理では、組織をオーステナイト一相にした後、適当な鉛浴または流動層中でパーライトに変態させて強度を調整する。パーライト変態は、オーステナイト過冷されて一定温度において起こることが望ましい。一般に粒径が大きい方が過冷されやすく、その後の変態も一定温度で実現する。しかし、粒径が大きすぎると変態開始から終了までの時間がかかるため、適正な粒径にコントロールすることが必要であった。そのため、従来は温度と時間を調整してオーステナイト粒径を制御してきた。しかし、熱処理条件がわずかに変動してもオーステナイト粒径がばらついてしまい、材質にばらつきが生ずることが問題となった。
【０００４】
【課題を解決するための手段】
本発明は、上記課題を解決するためになされたものであり、その趣旨とするところは以下の通りである。
【０００５】
その第一は、質量％で、Ｃ：０．３５〜１．０％、Ｓｉ：０．１０〜０．３５％、Ｍｎ：０．４０〜１．０％、Ｔｉ：０．００５〜０．０３％、Ｃａ：０．０００５〜０．００３０％、Ｏ：０．００４〜０．０１０％を含み、Ａｌ：０．００５％以下であり、残部Ｆｅ及び不可避不純物からなる熱処理安定性に優れた鋼線用線材である。
その第二は上記第一に加え質量％で、Ｃｒ：０．００５〜２．０％、Ｍｏ：０．０５〜０．３５％、Ｃｕ：０．０５〜１．０％、Ｎｉ：０．０５〜１．０％、Ｖ：０．００５〜０．０６％、Ｂ：０．０００５〜０．００５％のいずれか１つまたは２つ以上を含有する鋼線用線材である。
その第三は、線材の圧延方向に垂直な断面を走査型電子顕微鏡（ＳＥＭ）により観察される直径０．１μｍ以上０．３μｍ以下の介在物が、１５００個／ｍｍ2以上３０００個／ｍｍ2以下である上記第一又は第二の鋼線用線材である。
その第四は、線材の圧延方向に平行な断面において光学顕微鏡により観察される介在物の圧延方向に垂直な厚みが１００μｍ以下であり、同断面内に観察される厚みが２０μｍ超１００μｍ以下の介在物個数に対する、同介在物の圧延方向に平行な長さが前記厚みの５倍以上である介在物個数の比率が９０％以上である上記第一乃至第三のいずれかに記載の鋼線用線材である。
【０００６】
その第五はビレット連続鋳造により得られた鋳片を減面率９０％以上の熱間圧延により上記第一乃至第４のいずれかの鋼線用線材を製造する鋼線用線材製造方法である。
【０００７】
その第六は、質量％で、Ｃ：０．３５〜１．０％、Ｓｉ：０．１０〜０．３５％、Ｍｎ：０．４０〜１．０％、Ｔｉ：０．００５〜０．０３％、Ｃａ：０．０００５〜０．００３０％、Ｏ：０．００４〜０．０１０％を含み、Ａｌ：０．００５％以下であり、残部Ｆｅ及び不可避不純物からなる線材用連続鋳造ビレットである。
その第七は、更に質量％で、Ｃｒ：０．０５〜２．０％、Ｍｏ：０．０５〜０．３５％、Ｃｕ：０．０５〜１．０％、Ｎｉ：０．０５〜１．０％、Ｖ：０．００５〜０．０６％、Ｂ：０．０００５〜０．００５％のいずれか１種または２種以上を含有する上記第六の線材用連続鋳造ビレットである。
その第八は、上記第六又は第七の線材用連続鋳造ビレットであって、当該ビレットを減面率９０％以上の熱間圧延して得られた線材の圧延方向に垂直な断面を走査型電子顕微鏡（ＳＥＭ）により観察される直径０．１μｍ以上０．３μｍ以下の介在物が、１５００個／ｍｍ2以上３０００個／ｍｍ2以下であることを特徴とする線材用連続鋳造ビレットである。
その第九は、上記第六乃至第八のいずれかの線材用連続鋳造ビレットであって、当該ビレットを減面率９０％以上の熱間圧延して得られた線材の圧延方向に平行な断面において光学顕微鏡により観察される介在物の圧延方向に垂直な厚みが１００μｍ以下であり、同断面内に観察される厚みが２０μｍ超１００μｍ以下の介在物個数に対する、同介在物の圧延方向に平行な長さが前記厚みの５倍以上である介在物個数の比率が９０％以上であることを特徴とする線材用連続鋳造ビレットである。
【０００８】
【発明の実施の形態】
鋼線用線材として製造される鋼中には、非金属介在物は少ない方がよいとされている。その代表的なものである酸化物を極力少なくするために、鋼中に脱酸剤を投入し酸素を酸化物として固定し、生成した酸化物を精錬完了から鋳造時までに除去する様々な工夫がなされてきた。本発明は意図的に鋼中の酸素を高くすることにより介在物を分散させ、オーステナイト化温度における結晶粒成長を抑制するものである。しかし、単に鋼中酸素を高くしてしまうと大型の酸化物が生成し、伸線中の断線原因となる。
【０００９】
本発明は溶鋼中の酸素濃度を高く保ち、凝固中に酸化物を微細に生成させ結晶粒径制御に有効活用し、大型の酸化物が存在しても線材圧延時に伸延して長さと厚みの比が５以上であれば介在物が伸線加工時に破壊されることを利用して上記課題を解決することを特徴とする。
【００１０】
以下、本発明の説明を行う。
Ｃの下限を０．３５％としたのは、パーライト変態を利用して材質を制御する鋼線を得るためである。Ｃの上限を１．０％としたのは、それ以上の含有量では組織中に初析セメンタイトが生成し、材質のコントロールが困難となるからである。
【００１１】
Ｓｉの下限を０．１０％としたのは、鋳造中のＯと結びついて生成する酸化物を低融点である複合系とするためである。Ｓｉの上限を０．３５％としたのは、酸化物中のＳｉＯ2の濃度を必要以上に高くしないためである。
【００１２】
Ｍｎの下限を０．４０％としたのは、鋼材の熱処理性を確保するためである。Ｍｎの上限を１．０％としたのは、１．０％を超えると鋼の冷間加工性が低下して必要な品質が得られないからである。
【００１３】
Ａｌを０．００５％以下としたのはＡｌが０．００５％を超えると生成する非金属介在物の組成がＡｌ2Ｏ3主体となり、介在物融点が高くなって伸線断線の原因となり易いからである。なお、Ａｌ含有量には酸化物として存在するＡｌをも含んでいる。
【００１４】
Ｔｉ下限を０．００５％としたのは、０．００５％未満では脱酸力が不足し、鋳造中の鋳片表面に気泡性の欠陥が発生するためである。Ｔｉ上限を０．０３％としたのは、Ｔｉの添加量を増加し鋼中の全酸素と結合してしまうと結晶粒成長を抑制する微細な介在物が減少するためである。
【００１５】
Ｏの下限を０．００４％としたのは、再結晶の制御粒子としての酸化物を必要量確保するために必要となる酸素量であるからである。Ｏの上限については、Ｏの一部は脱酸されずに一旦は鋼中に固溶し、鋼材の冷却中に鋼材中の空孔（ポロシティー）にガスが生成し、鋼中の酸素濃度に依存し高い圧力が発生する。全酸素が０．０１％を超えると、ガス圧が高くなり圧延や冷間加工では密着しなくなり欠陥の原因となるため、製品中の全酸素の上限を０．０１％とした。
【００１６】
Ｃａの下限を０．０００５％としたのは、酸化物中にＣａＯを成分として含有させ加工時の変形抵抗を小さくするためである。Ｃａの上限を０．００３０％としたのはそれを超える含有量でＣａＯ単体が晶出してしまい、変形抵抗が高くなるからである。
【００１７】
Ｃｒ、Ｍｏ、Ｃｕ、Ｎｉ、Ｖは強度を調整する元素として用いられる。その範囲（％）はＣｒ：０．０５〜２．０、Ｍｏ：０．０５〜０．３５、Ｃｕ：０．０５〜１．０、Ｎｉ：０．０５〜１．０、Ｖ：０．００５〜０．０６とした。
【００１８】
Ｂは鋼中のＮを固定する元素であり、０．０００５％以上を添加することにより、Ｎを固定する。０．００５％を越える添加は、鋼を脆化させるため上限を０．００５％とした。
【００１９】
本発明では、鋼中に酸化物を分散させて加熱時のオーステナイトの成長を制御することを目的としている。分散させる介在物の適正量は、鋼片または鋳片を、熱間圧延により得られた線材の圧延方向に垂直な断面を走査型電子顕微鏡（ＳＥＭ）により観察される直径０．１μｍ以上０．３μｍ以下の介在物が、１５００個／ｍｍ2以上３０００個／ｍｍ2以下である。介在物の観察方法を透過電子顕微鏡としたのは、他の方法では０．３μｍ以下の介在物を測定することが困難だからである。結晶粒成長抑制に有効な大きさは、直径０．３μｍ以下であることが明らかになった。０．１μｍ以上としたのは、ＳＥＭにより安定して観察可能だからである。また、その量が１５００個／ｍｍ2 未満であると、酸化物が少ないために、介在物の間隔が大きくなり、局所的に加熱時のオーステナイト粒が粗大になってしまう。一方、介在物量が３０００個／ｍｍ2 超であると、介在物が多すぎるためにオーステナイト粒径が微細になりすぎてしまう。
【００２０】
鋼中のＯが高くなると鋼中の酸化物が多くなり、大型のものが認められることがある。本発明において、減面率９０％以上の熱間圧延して得られた線材の圧延方向に平行な断面において光学顕微鏡により観察される介在物の圧延方向に垂直な厚みが２０μｍ以下の介在物であれば、通常の伸線加工では破断に至ることがないことが明らかとなった。減面率９０％以上としたのは、凝固組織を完全に均一な加工組織にし、粒径を均一にするためである。また、厚みが２０μｍを越えるものでも、厚みが１００μｍ以下の軟質な介在物であれば、伸線加工中に破砕され、伸線方向に変形するため、鋼の変形を損なうことがないことが明らかとなった。この変形が起きるかどうかの基準が圧延方向に平行な長さが厚みの５倍以上である。本発明の線材は、Ａｌレスとし、Ｔｉ、Ｓｉ、Ｃａによる共同脱酸を採用しているため、生成する介在物はＴｉＯ2−ＳｉＯ2−ＣａＯ系の軟質介在物となり、上記条件を満足することができる。即ち、上記第四の発明に記載の鋼成分及び介在物分布とすることにより、良好な伸線加工性を確保することができる。
【００２１】
以上述べてきた線材を得るには、微細な介在物を鋳片段階から得ることが重要である。大断面の鋳造では、微細な酸化物が合体して大型化したり、溶鋼との比重差により浮上分離して必要量が確保できない。本発明に規定される線材は、鋳型寸法が１５０ｍｍ×１５０ｍｍ以下の矩形あるいは直径１７０ｍｍ以下の円形であるビレット鋳造に代表される小断面高速連鋳機により、溶鋼が鋳型において冷却され始めてから凝固完了までの時間が短いビレット連続鋳造法が最適である。これにより、上記第三の発明にあるように微細でかつ多数の介在物を生成することができる。
【００２２】
本発明において、転炉による脱炭後、精錬工程での脱酸材の投入量を最小限にとどめ、取鍋での脱ガス等の二次精錬処理を行わない溶鋼を大気に解放された（酸化防止策を施さない）タンディッシュを経て鋳造することにより、線材中のＯ濃度を０．００４〜０．０１０％に調整することができる。
【００２３】
【実施例】
転炉精錬法にて溶鋼量２４０トンの溶鋼を溶製し、連続鋳造法において、鋳型サイズは１２５ｍｍ×１２５ｍｍ、鋳造速度は２．６〜３．２ｍ／ｍｉｎの条件で鋳造を行った。連続鋳造で製造したビレットの鋼片検査実施後、加熱炉で約１１００℃に加熱し、線材圧延機で直径５．５ｍｍに圧延し、空冷による冷却工程を経てコイルに捲きとった。得られた線材を伸線加工により直径２ｍｍのワイヤに加工した。伸線後のワイヤを９５０℃にて１０分、３０分の加熱を行い水中に焼き入れオーステナイト粒径測定用のサンプルを作成した。
【００２４】
表１、表２に示す成分の鋼を溶製した。上記方法で得られた線材について圧延方向に垂直な断面を走査型電子顕微鏡（ＳＥＭ）により観察し直径０．１μｍ以上０．３μｍ以下の介在物調査を行い、得られた線材の圧延方向に平行な断面において光学顕微鏡により大型の介在物観察を行った。熱処理のワイヤの組織観察によりオーステナイトの大きさをＪＩＳに基づき測定した。
【００２５】
【表１】
【表２】
表１のＮｏ．１〜１７は、本発明例の製造結果である。分析結果はすべて本発明範囲内にある。表２は比較例の製造結果である。
【００２８】
Ｎｏ．１８〜２０はＴｉが本発明の下限以下の場合の例である。酸化物量は多くなるものの、鋳造時に鋳片表層に気泡性の欠陥が発生してしまい、製品としては使用できない。
【００２９】
Ｎｏ．２１〜２３は、Ｔｉ含有量が本発明上限以上である。微細な酸化物が減少し、大型のものに変化してしまい、断線が発生した。
【００３０】
Ｎｏ．２５はＡｌ添加量が本発明の上限以上である。微細な介在物が存在せず、混粒が発生してしまう。
【００３１】
Ｎｏ．２６，２７は、微細な介在物量が本発明範囲の上限以上の場合である。オーステナイトが小さくなりすぎ必要な強度が得られなかった。
【００３２】
Ｎｏ．２８，２９は成分は請求範囲内であるが鋳造時の冷却速度が遅く、介在物が凝固過程で大型化し、微細な介在物が本発明範囲の下限以下の場合である。オーステナイトの異常成長が観察された。
【００３３】
【発明の効果】
本発明により、伸線後の線材を熱処理した時のオーステナイト結晶粒径が均一になり、製品の材質のばらつきが低下した。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a wire rod for steel wire used for wire drawing.
[0002]
[Prior art]
Steel that is manufactured as a conventional wire rod for steel wire, after completing refining in a converter or the like, is deoxidized prior to casting in order to remove oxygen contained in the molten steel when refining is completed, and oxidized As a result, oxygen is removed. The produced oxide is increased in size by casting and coalescence and growth in the tundish or mold during casting, and is lifted and removed. In steel manufactured as steel wire rods, it is better to have less non-metallic inclusions, and in order to minimize oxides, which are typical of them, they are removed by the start of casting after completion of refining. Various ideas have been made. For this reason, there are no harmful inclusions in the wire obtained by rolling the slab, and even if the wire drawing is performed, almost no disconnection due to the inclusions was observed. When the structure is adjusted by patenting after drawing such a material, it is important to control the crystal grains during the heat treatment to have a uniform size to obtain a uniform heat-treated structure. Until now, in order to obtain a uniform structure by patenting, the austenitizing temperature and time have been adjusted.
[0003]
[Problems to be solved by the invention]
As described above, the wire after drawing can have a certain strength by heat treatment (patenting treatment). In this heat treatment, the structure is changed to austenite and then transformed into pearlite in an appropriate lead bath or fluidized bed to adjust the strength. It is desirable that the pearlite transformation occurs at a constant temperature after being overcooled with austenite. In general, the larger the particle size, the easier it is to cool, and the subsequent transformation is also realized at a constant temperature. However, if the particle size is too large, it takes time from the start to the end of transformation, so it was necessary to control the particle size to an appropriate value. Therefore, conventionally, the austenite grain size has been controlled by adjusting the temperature and time. However, even if the heat treatment conditions fluctuate slightly, the austenite grain size varies, which causes a problem of variation in materials.
[0004]
[Means for Solving the Problems]
The present invention has been made to solve the above problems, and the gist of the present invention is as follows.
[0005]
The first is mass%, C: 0.35-1.0%, Si: 0.10-0.35%, Mn: 0.40-1.0%, Ti: 0.005-0. 03%, Ca: 0.0005 to 0.0030%, O: 0.004 to 0.010%, Al: 0.005% or less, and excellent heat treatment stability consisting of the balance Fe and inevitable impurities It is a wire rod for steel wire.
The second is mass% in addition to the first, Cr: 0.005 to 2.0%, Mo: 0.05 to 0.35%, Cu: 0.05 to 1.0%, Ni: 0.00. It is a wire rod for steel wire containing any one or more of 05-1.0%, V: 0.005-0.06%, B: 0.0005-0.005%.
Its Third, inclusions below 0.3μm diameter 0.1μm or more, which is observed by a scanning electron microscope cross-section perpendicular to the rolling direction of the wire (SEM) is 1500 / mm 2 or more 3,000 / mm 2 It is the said 1st or 2nd wire rod for steel wires which is the following.
Its Fourth, vertical thickness to the rolling direction of the inclusions observed by an optical microscope in a cross section parallel to the rolling direction of the wire is not less 100μm or less, intervening thickness observed in the cross section below 20μm ultra 100μm The steel wire according to any one of the first to third aspects, wherein the ratio of the number of inclusions whose length parallel to the rolling direction of the inclusions is 5 times or more of the thickness to the number of objects is 90% or more. It is a wire.
[0006]
The fifth is a wire manufacturing method for steel wire, in which the slab obtained by continuous billet casting is manufactured by hot rolling with a surface area reduction ratio of 90% or more to manufacture any one of the first to fourth steel wire rods. .
[0007]
The sixth is mass%, C: 0.35-1.0%, Si: 0.10-0.35%, Mn: 0.40-1.0%, Ti: 0.005-0. It is a continuous casting billet for wire comprising 03%, Ca: 0.0005 to 0.0030%, O: 0.004 to 0.010%, Al: 0.005% or less, and the balance Fe and inevitable impurities. is there.
The 7th is further mass%, Cr: 0.05-2.0%, Mo: 0.05-0.35%, Cu: 0.05-1.0%, Ni: 0.05-1 0.0%, V: 0.005 to 0.06%, and B: 0.0005 to 0.005%. The sixth continuous casting billet for wire rods according to any one or more of the above.
The eighth is the above-described sixth or seventh continuous casting billet for wire rods, which is a scanning type of a cross section perpendicular to the rolling direction of the wire rod obtained by hot rolling the billet with a reduction in area of 90% or more. It is a continuous casting billet for a wire, wherein inclusions having a diameter of 0.1 μm or more and 0.3 μm or less observed by an electron microscope (SEM) are 1500 pieces / mm 2 or more and 3000 pieces / mm 2 or less.
The ninth is the continuous cast billet for wire rods according to any one of the sixth to eighth portions, and a cross section parallel to the rolling direction of the wire rod obtained by hot-rolling the billet with a reduction in area of 90% or more. The thickness perpendicular to the rolling direction of the inclusions observed with an optical microscope is 100 μm or less, and the thickness observed in the same section is parallel to the rolling direction of the inclusions with respect to the number of inclusions exceeding 20 μm and 100 μm or less. A continuous casting billet for a wire rod, wherein the ratio of the number of inclusions having a length of 5 times or more of the thickness is 90% or more.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
In steel manufactured as a wire rod for steel wires, it is said that it is better to have less non-metallic inclusions. In order to minimize oxides, which are typical of these, various devising agents are used to fix the oxygen as an oxide by introducing a deoxidizer into the steel, and to remove the generated oxide from the completion of refining to the time of casting. Has been made. In the present invention, inclusions are dispersed by intentionally increasing the oxygen in the steel, and crystal grain growth at the austenitizing temperature is suppressed. However, if the oxygen in the steel is simply increased, a large oxide is generated, causing disconnection during wire drawing.
[0009]
The present invention keeps the oxygen concentration in the molten steel high, finely produces oxide during solidification, and effectively uses it for controlling the crystal grain size. If the ratio is 5 or more, the above-mentioned problem is solved by utilizing the fact that inclusions are broken during wire drawing.
[0010]
The present invention will be described below.
The lower limit of C is set to 0.35% in order to obtain a steel wire whose material is controlled using pearlite transformation. The reason why the upper limit of C is set to 1.0% is that when the content is higher than that, pro-eutectoid cementite is generated in the structure, making it difficult to control the material.
[0011]
The reason why the lower limit of Si is set to 0.10% is to make the oxide generated in combination with O during casting into a composite system having a low melting point. The upper limit of Si is set to 0.35% because the SiO 2 concentration in the oxide is not increased more than necessary.
[0012]
The lower limit of Mn is set to 0.40% in order to ensure the heat treatment property of the steel material. The reason why the upper limit of Mn is set to 1.0% is that if it exceeds 1.0%, the cold workability of the steel is lowered and the required quality cannot be obtained.
[0013]
The reason why Al is made 0.005% or less is that when Al exceeds 0.005%, the composition of non-metallic inclusions produced is mainly Al 2 O 3 , and the inclusion melting point becomes high, which tends to cause wire breakage. Because. The Al content includes Al present as an oxide.
[0014]
The reason why the lower limit of Ti is set to 0.005% is that if it is less than 0.005%, the deoxidizing power is insufficient, and bubble defects occur on the surface of the slab during casting. The reason why the upper limit of Ti is set to 0.03% is that when the amount of Ti added is increased and combined with all the oxygen in the steel, the fine inclusions that suppress the grain growth decrease.
[0015]
The lower limit of O is set to 0.004% because it is the amount of oxygen necessary to secure the required amount of oxide as control particles for recrystallization. As for the upper limit of O, a part of O is not deoxidized but is once dissolved in the steel, and gas is generated in the porosity in the steel during cooling of the steel, and the oxygen concentration in the steel High pressure is generated depending on If the total oxygen exceeds 0.01%, the gas pressure becomes high, and it does not adhere in rolling or cold working, causing defects, so the upper limit of the total oxygen in the product is set to 0.01%.
[0016]
The reason why the lower limit of Ca is set to 0.0005% is that CaO is contained as a component in the oxide to reduce deformation resistance during processing. The reason why the upper limit of Ca is set to 0.0030% is that CaO is crystallized at a content exceeding the upper limit and deformation resistance becomes high.
[0017]
Cr, Mo, Cu, Ni, and V are used as elements for adjusting the strength. The ranges (%) are Cr: 0.05 to 2.0, Mo: 0.05 to 0.35, Cu: 0.05 to 1.0, Ni: 0.05 to 1.0, V: 0.00. 005 to 0.06.
[0018]
B is an element for fixing N in steel, and N is fixed by adding 0.0005% or more. Addition over 0.005% causes the steel to become brittle, so the upper limit was made 0.005%.
[0019]
The object of the present invention is to control the growth of austenite during heating by dispersing an oxide in steel. The appropriate amount of inclusions to be dispersed is a steel slab or cast slab whose diameter perpendicular to the rolling direction of the wire obtained by hot rolling is 0.1 μm or more and observed by a scanning electron microscope (SEM). Inclusions of 3 μm or less are 1500 / mm 2 or more and 3000 / mm 2 or less. The reason for using the transmission electron microscope as the observation method of the inclusions is that it is difficult to measure inclusions of 0.3 μm or less by other methods. It has been found that the effective size for suppressing crystal grain growth is a diameter of 0.3 μm or less. The reason why the thickness is 0.1 μm or more is that it can be observed stably by SEM. On the other hand, when the amount is less than 1500 / mm 2 , since the amount of oxide is small, the interval between inclusions becomes large, and the austenite grains during heating locally become coarse. On the other hand, if the amount of inclusions is more than 3000 / mm 2 , the austenite grain size becomes too fine because there are too many inclusions.
[0020]
When O in steel becomes high, the oxide in steel increases and a large thing may be recognized. In the present invention, inclusions whose thickness is perpendicular to the rolling direction of the inclusions observed by an optical microscope in a section parallel to the rolling direction of the wire rod obtained by hot rolling with a reduction in area of 90% or more are 20 μm or less. If it exists, it became clear that it does not reach a fracture | rupture in normal wire drawing. The reason why the area reduction ratio is 90% or more is to make the solidified structure completely uniform and have a uniform particle size. In addition, even if the thickness exceeds 20 μm, if it is a soft inclusion with a thickness of 100 μm or less, it will be crushed during the wire drawing process and deformed in the direction of wire drawing, so that it does not impair the deformation of the steel. It became. The standard for determining whether or not this deformation occurs is that the length parallel to the rolling direction is at least 5 times the thickness. Since the wire rod of the present invention is Al-less and employs joint deoxidation with Ti, Si, and Ca, the generated inclusion becomes a TiO 2 —SiO 2 —CaO-based soft inclusion and satisfies the above conditions. be able to. That is, by using the steel component and inclusion distribution described in the fourth invention, good wire drawing workability can be ensured.
[0021]
In order to obtain the wire described above, it is important to obtain fine inclusions from the slab stage. In casting with a large cross section, the fine oxides coalesce and become large, or float and separate due to the difference in specific gravity from the molten steel, and the required amount cannot be secured. The wire rod defined in the present invention is solidified after the molten steel begins to be cooled in the mold by a small-section high-speed continuous casting machine represented by billet casting with a mold size of a rectangle of 150 mm x 150 mm or less or a circle of 170 mm or less in diameter. The billet continuous casting method with the shortest time to completion is optimal. Thereby, as in the third aspect of the invention, fine and numerous inclusions can be generated.
[0022]
In the present invention, after decarburization by the converter, the amount of deoxidizing material input in the refining process is minimized, and the molten steel that is not subjected to secondary refining treatment such as degassing in the ladle is released to the atmosphere ( The O concentration in the wire can be adjusted to 0.004 to 0.010% by casting through a tundish (which does not take an antioxidant measure).
[0023]
【Example】
Molten steel having a molten steel amount of 240 tons was melted by the converter refining method, and in the continuous casting method, casting was performed under the conditions of a mold size of 125 mm × 125 mm and a casting speed of 2.6 to 3.2 m / min. After the billet manufactured by continuous casting was inspected for the billet, it was heated to about 1100 ° C. in a heating furnace, rolled to a diameter of 5.5 mm by a wire rod rolling mill, and wound into a coil through a cooling process by air cooling. The obtained wire was processed into a wire having a diameter of 2 mm by wire drawing. The wire after drawing was heated at 950 ° C. for 10 minutes and 30 minutes, and quenched in water to prepare a sample for austenite particle size measurement.
[0024]
Steels having the components shown in Tables 1 and 2 were melted. The cross section perpendicular to the rolling direction of the wire obtained by the above method is observed with a scanning electron microscope (SEM), the inclusions having a diameter of 0.1 μm or more and 0.3 μm or less are examined, and the obtained wire is parallel to the rolling direction. Large inclusions were observed with an optical microscope in a simple cross section. The size of austenite was measured based on JIS by observing the structure of the heat treated wire.
[0025]
[Table 1]
[Table 2]
No. in Table 1 1 to 17 are the production results of the examples of the present invention. All analysis results are within the scope of the present invention. Table 2 shows the production results of the comparative examples.
[0028]
No. 18 to 20 are examples when Ti is not more than the lower limit of the present invention. Although the amount of oxide increases, a bubble defect occurs on the surface of the slab during casting, and it cannot be used as a product.
[0029]
No. As for 21-23, Ti content is more than this invention upper limit. The fine oxide decreased, and it changed into a large thing, and the disconnection generate | occur | produced.
[0030]
No. No. 25 has an Al addition amount equal to or higher than the upper limit of the present invention. Fine inclusions do not exist and mixed grains are generated.
[0031]
No. 26 and 27 are cases in which the amount of fine inclusions is not less than the upper limit of the range of the present invention. Austenite was too small to obtain the required strength.
[0032]
No. 28 and 29 are cases where the components are within the scope of the claims, but the cooling rate during casting is slow, the inclusions increase in size during the solidification process, and the fine inclusions are below the lower limit of the scope of the present invention. Abnormal growth of austenite was observed.
[0033]
【The invention's effect】
According to the present invention, the austenite crystal grain size is uniform when heat-treating the wire after drawing, and the variation in the material of the product is reduced.
Claims (9)
Priority Applications (1)
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| JP32844699A JP3759355B2 (en) | 1999-11-18 | 1999-11-18 | Steel wire rod and manufacturing method thereof |
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| JP32844699A JP3759355B2 (en) | 1999-11-18 | 1999-11-18 | Steel wire rod and manufacturing method thereof |
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| JP3759355B2 true JP3759355B2 (en) | 2006-03-22 |
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| KR101665886B1 (en) | 2015-09-04 | 2016-10-13 | 주식회사 포스코 | Non-quenched and tempered steel having excellent cold workability and impact toughness and method for manufacturing same |
| KR102120699B1 (en) * | 2018-08-21 | 2020-06-09 | 주식회사 포스코 | Wire rod and steel wire for spring with improved toughness and corrosion fatigue resistance and method for manufacturing the same |
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