JP2004169052A - Steel excellent in machinability, and its production method - Google Patents
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【0001】
【発明の属する技術分野】
本発明は、自動車や一般機械などに用いられる鋼に関するもので、特に切削時の工具寿命と切削表面粗さおよび切り屑処理性に優れた被削性に優れた鋼に関する。
【0002】
【従来の技術】
一般機械や自動車は多種の部品を組み合わせて製造されているが、その部品は要求精度と製造効率の観点から、多くの場合、切削工程を経て製造されている。その際、コスト低減と生産能率の向上が求められ、鋼にも被削性の向上が求められている。特に従来SUM23やSUM24Lは被削性を重要視して開発されてきた。これまで被削性を向上させるためにS、Pbなどの被削性向上元素を添加するのが有効であることが知られている。しかし、需要家によってはPbは環境負荷として使用を避ける場合も有り、その使用量を低減する方向にある。
【0003】
これまでもPbを添加しない鋼の場合には、SのようにMnSのような切削環境下で軟質となる介在物を形成して被削性を向上させる手法が使われている。しかし、いわゆる低炭鉛快削鋼SUM24Lには低炭硫黄快削鋼SUM23と同量のSが添加されている。従って、従来以上のS量を添加する必要がある。しかし、多量S添加ではMnSを単に粗大にするだけで、被削性向上に有効なMnSにならないだけでなく、圧延、鍛造等において破壊起点になって圧延疵等の製造上の問題を多く引き起こす。さらに、SUM23をベースとする硫黄快削鋼では構成刃先が付着しやすく、構成刃先の脱落および切り屑分離現象に伴う、切削表面に凹凸が生じ、表面粗さが劣化する。従って被削性の観点からも表面粗さが劣化による精度低下が問題である。切り屑処理性においても、切り屑が短く分断しやすい方が良好とされているが、単なるS添加だけではマトリックスの延性が大きいため、十分に分断されず、大きく改善できなかった。
【0004】
さらに、S以外の元素、Te、Bi、P等も被削性向上元素として知られているが、ある程度被削性を向上させることができても、圧延や熱間鍛造時に割れを生じ易くなるため、極力少ない方が望ましいとされている。
【0005】
例えば、特許文献1には単独で20μm以上の硫化物、あるいは複数の硫化物が略直列状に連なった長さ20μm以上の硫化物群が圧延方向断面1mm2 の視野内に30個以上存在することによって切屑処理性を高める方法が提案されている。しかし、事実上被削性に最も有効であるサブμmレベルの硫化物の分散については製造方法を含めて言及されておらず、またその成分系からも期待できない。
【0006】
また、特許文献2には、硫化物系介在物の平均サイズが50μm2 以下であり、かつ該硫化物系介在物が1mm2 当たり750個以上存在することによって切屑処理性を高める方法が提案されている。しかし、事実上被削性に最も有効であるサブμmレベルの硫化物の分散については特許文献1同様何ら言及されておらず、またそれを意識して作りこむ技術や調査する方法についても記述されていない。
【0007】
【特許文献1】
特開平11−222646号公報
【特許文献2】
特開平11−293391号公報
【0008】
【発明が解決しようとする課題】
本発明は、圧延や熱間鍛造における不具合を避けつつ、工具寿命と表面粗さの両者を改善し、従来の低炭鉛快削鋼と同等以上の被削性を有する鋼及びその製造方法を提供する。
【0009】
【課題を解決するための手段】
切削は切り屑を分離する破壊現象であり、それを促進させることが一つのポイントとなる。この効果はSを単純に増量するだけでは限界がある。本発明者らは、Sを増量するだけでなく、マトリックスを脆化させることで破壊を容易にして工具寿命を延長するとともに切削表面の凹凸を抑制することで被削性が向上することを知見した。
【0010】
本発明は以上の知見に基づいてなされたもので、その要旨は次のとおりである。
【0011】
(1)質量%で、C:0.005〜0.2%、Mn:0.3〜3.0%、S:0.1〜1.0%を含み、抽出レプリカ法にて採取して透過型電子顕微鏡で観察するMnSに関し、鋼材の圧延方向と平行な断面において円相当径にて0.1〜0.5μmのものの存在密度が10,000個/mm2 以上であることを特徴とする被削性に優れる鋼。
【0012】
(2)上記(1)の鋼が、質量%で、さらに、B:0.0005〜0.05%を含むことを特徴とする(1)記載の被削性に優れる鋼。
【0013】
(3)上記(1)または(2)に記載の鋼を、鋳造に際し、10〜100℃/min の冷却速度で冷却することにより、抽出レプリカ法にて採取して透過型電子顕微鏡で観察するMnSに関し、鋼材の圧延方向と平行な断面において円相当径にて0.1〜0.5μmのものの存在密度が10,000個/mm2 以上にすることを特徴とする被削性に優れる鋼の製造方法。
【0014】
【発明の実施の形態】
本発明は、鉛を添加することなく十分な被削性、特に良好な表面粗さを有する鋼を得るものであり、そのために、MnSを光学顕微鏡では確認し得ない寸法に制御し、その微細分散の程度を従来より大幅に向上させることで良好な表面粗さと工具寿命特性を得ることを見出したものである。
【0015】
先ず、本発明で規定する鋼の成分組成の限定理由について説明する。なお、鋼の成分組成はいずれも質量%である。
【0016】
Cは、鋼材の基本強度と鋼中の酸素量に関係するので被削性に大きな影響を及ぼす。Cを多量に添加して強度を高めると被削性を低下させるのでその上限を0.2%とした。一方、被削性を低下させる硬質酸化物生成を防止しつつ、凝固過程でのピンホール等の高温での固溶酸素の弊害を抑制するため、酸素量を適量に制御する必要がある。単純に吹錬によってC量を低減させすぎるとコストが嵩むだけでなく、鋼中酸素量が多量に残留してピンホール等の不具合の原因となる。従って、ピンホール等の不具合を容易に防止できるC量0.005%を下限とした。
【0017】
Mnは、鋼中硫黄をMnSとして固定・分散させるために必要である。また鋼中酸化物を軟質化させ、酸化物を無害化させるために必要である。その効果は添加するS量にも依存するが、0.3%以下では添加SをMnSとして十分に固定できず、SがFeSとなり脆くなる。Mn量が大きくなると素地の硬さが大きくなり被削性や冷間加工性が低下するので、30%を上限とした。
【0018】
Sは、Mnと結合してMnS介在物として存在する。MnSは被削性を向上させるが、伸延したMnSは鍛造時の異方性を生じる原因の一つである。大きなMnSは避けるべきであるが、被削性向上の観点からは多量の添加が好ましい。従って、MnSを微細分散させることが好ましい。Pbを添加しない場合の被削性向上には0.1%以上の添加が必要である。一方、1%を越えると粗大MnSの生成が避けられないだけでなく、FeS等による鋳造特性、熱間変形特性の劣化から製造中に割れを生じるので、1%を上限とした。
【0019】
次に、MnSの形態と、その分布において、円相当径にて0.1〜0.5μmの存在密度が10.000個/mm2 以上と規定する理由について説明する。
【0020】
MnSは被削性を向上させる介在物であり、微細に高密度で分散させることで被削性を著しく向上する。その効果を発揮するには、円相当径で0.1〜0.5μmのMnSの存在密度が10,000個/mm2 以上とすることが必要である。図3にMnS密度と表面粗さの関係を示した。通常MnS分布は光学顕微鏡にて観察し、その寸法、密度を測定する。当該寸法のMnSは光学顕微鏡での観察では確認することが不可能なものであり、レプリカ法による透過型電子顕微鏡(TEM)ではじめて観察できる。光学顕微鏡観察での寸法、密度に差は無くてもレプリカ法によるTEM観察では明確な差が認められる寸法のMnSであり、本発明ではこれを制御し、存在形態を数値化することにより従来技術との差別化を図るものである。
【0021】
上述した寸法を超えたMnSを10,000個/mm2 以上の密度で存在させるには、本発明の範囲を超えた多量のSの添加を必要とするが、多量添加すると粗大MnSも多数存在する確率が高くなり、鍛造時の異方性の原因となる。本発明に規定する範囲のS添加量でMnSがこの寸法を超えると、MnSの量が不足し、被削性向上に必要な密度を維持できなくなる。また、0.1μm以下のものは実質上被削性には影響を及ぼさない。従って、円相当径にて0.1〜0.5μmのMnSを主成分とする硫化物の存在密度が10,000個/mm2 以上存在することが必要である。このMnSの寸法、密度を得るためには、冷却速度の制御の他、含有するMnとSの比を1.5〜2.5にするとより効果的である。
【0022】
なお、MnSとは、純粋なMnSのみならず、MnSを主体に含み、Fe,Ca,Ti,Zr,Mg,REM等の硫化物がMnSと固溶したり結合して共存している介在物や、MnTeのようにS以外の元素がMnと化合物を形成してMnSと固溶・結合して共存している介在物や、酸化物を核として析出した上記介在物が含まれるものであり、化学式では、(Mn,X)(S,Y)(ここで、X:Mn以外の硫化物形成元素、Y:S以外でMnと結合する元素)として表記できるMn硫化物系介在物を総称して言うものである。
【0023】
Bは、BNとして析出すると被削性向上に効果がある。これらの効果は0,0005%未満では顕著でなく、0.050%を超えて添加するとBNが多く析出し、鋳造特性、熱間変形特性の劣化から製造中に疵が発生しやすくなる。そこで0.0005〜0.050%を範囲とした。
【0024】
本発明の切削性に優れる鋼は低炭快削鋼を想定したものであるが、この鋼材には必要に応じて、C、Mn、S、B以外の添加元素が含まれてもよい。この場合、例えばCr:0.01〜2.0%,V:0.01〜1.0%,Nb:0.005〜0.2%,Mo:0.01〜1.0%,W:0.05〜1.0%,Ni:0.05〜2.0%,Ti:0.005〜0.2%,Ca:0.0002〜0.01%,Zr:0.0005〜0.1%,Mg:0.0003〜0.01%,Al:0.001〜0.1%,Si:0.01〜0.5%,Te:0.0003〜0.2%,total−N:0.001〜0.02%,total−O:0.0005〜0.035%,P:0.001〜0.2%,Zn:0.0005〜0.5%,Sn:0.005〜2.0%,Cu:0.01〜2.0%,Bi:0.005〜0.5%,Pb:0.01〜0.5%の1種または2種以上を含有する鋼が良い。
【0025】
次に、鋳造時の鋳片またはビレットの冷却速度を10〜100℃/min に限定する理由について説明する。
【0026】
MnSの微細分散は被削性向上に有効である。MnSを微細に分散させるにはMnSの晶析出を制御する必要があり、その制御には冷却速度範囲を厳密に制御する必要がある。冷却速度が10℃/min 以下では凝固が遅すぎて晶出したMnSが粗大化してしまい、微細分散できなくなる。冷却速度が100℃/min 以上では生成する微細MnSの密度は飽和し、鋼片の硬度が上昇し割れの発生する危険が増す。この冷却速度を得るには鋳型断面の大きさ、鋳込み速度、鋳込み速度等を適正な値に制御することで容易に得られる。これは連続鋳造法、造塊法共に適用可能である。
【0027】
ここでいう冷却速度とは、鋳片厚み方向Q部における液相線温度から固相線温度までの冷却時の速度のことをいう。冷却速度は凝固後の鋳片厚み方向凝固組織の2次デンドライトアームの間隔から下記式により計算で求める。
【0028】
【数1】
【0029】
ここで Rc:冷却速度(℃/min )、λ2:2次デンドライトアームの間隔(μm)
つまり冷却条件により2次デンドライトアーム間隔が変化するので、これを測定することにより制御した冷却速度を確認した。
【0030】
【実施例】
本発明の効果を実施例によって説明する。
【0031】
表1、表2(表1のつづきの1)、表3(表1のつづきの2)、表4(表1のつづきの3)に示す供試材は一部は270t転炉で溶製後、冷却速度が10〜100℃/min になるように鋳造した。ビレットに分解圧延、さらにφ50mmに圧延した。他は2t真空溶解炉にて溶製し、φ50mmに圧延した。このとき鋳型断面寸法を変えることにより鋳片の冷却速度を調整した。材料の被削性は表5に条件を示すドリル穿孔試験と表6に条件を示すプランジ切削によって評価し、ドリル穿孔試験は累積穴深さ1000mmまで切削可能な最高の切削速度(いわゆるVL1000、単位:m/min )で被削性を評価する方法である。プランジ切削は突切工具によって工具形状を転写して表面粗さを評価する方法である。その実験方法の概要を図4に示す。実験では200溝加工した場合の表面粗さを表面粗さ計で測定した。10点表面粗さRz(単位:μm)を表面粗さを示す指標とした。
【0032】
円相当径にて0.1〜0.5μmの寸法のMnS密度の測定は、φ50mm圧延後の圧延方向と平行な断面のQ部より抽出レプリカ法にて採取して過型電子顕微鏡にて行った。測定は10,000倍で1視野80μm2 を40視野以上行い、それを1平方ミリメートル当たりのMnS数に換算して算出した。
【0033】
図1に本発明例のMnSのTEMレプリカ写真を示す。図2に比較例のMnSのTEMレプリカ写真を示す。このように、光学顕微鏡レベルでは確認できないサイズのMnSが、TEMレプリカの観察により、発明例と比較例では寸法、密度共に明確な差が見られる。
【0034】
被削性では、発明例はいずれも比較例に対してドリル工具寿命に優れるとともに、プランジ切削における表面粗さが良好であった。特に表面粗さについては微細MnSの効果により非常に優れた値を得ることが出きた。
【0035】
【表1】
【0036】
【表2】
【0037】
【表3】
【0038】
【表4】
【0039】
【表5】
【0040】
【表6】
【0041】
【発明の効果】
以上説明したように、本発明は、鋼中のMnSのサイズと分布を厳密に制御することにより、特に切削時の工具寿命と切削表面粗さ、および切削処理性の良好な被削性に優れる鋼を提供することが可能となる。
【図面の簡単な説明】
【図1】本発明による鋼のミクロ組織を示す図で、TEMレプリカ写真である。
【図2】比較鋼のミクロ組織を示す図で、TEMレプリカ写真である。
【図3】MnS密度と表面粗さの関係を示す図である。
【図4】プランジ切削方法を示す図である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to steel used for automobiles, general machines, and the like, and more particularly to steel excellent in machinability, which is excellent in tool life, cutting surface roughness, and chip disposal during cutting.
[0002]
[Prior art]
General machines and automobiles are manufactured by combining various types of parts, and the parts are often manufactured through a cutting process from the viewpoint of required accuracy and manufacturing efficiency. At that time, cost reduction and improvement in production efficiency are required, and steel is also required to have improved machinability. In particular, conventionally, SUM23 and SUM24L have been developed with emphasis on machinability. It has been known that it is effective to add a machinability improving element such as S or Pb in order to improve machinability. However, some customers avoid using Pb as an environmental load, and the amount of Pb used is being reduced.
[0003]
Until now, in the case of steel to which Pb is not added, a method of improving the machinability by forming soft inclusions such as MnS under a cutting environment such as S has been used. However, the same amount of S as that of the low-carbon sulfur free-cutting steel SUM23 is added to the so-called low-carbon lead free-cutting steel SUM24L. Therefore, it is necessary to add a higher S amount than before. However, the addition of a large amount of S merely increases the size of MnS, and does not not only result in MnS effective for improving machinability, but also causes a problem in rolling, forging, etc., which is a starting point of fracture and causes many manufacturing problems such as rolling flaws. . Further, in the case of the sulfur free-cutting steel based on SUM23, the component cutting edge easily adheres, and the cutting surface becomes uneven due to the falling of the component cutting edge and the chip separation phenomenon, and the surface roughness deteriorates. Therefore, from the viewpoint of machinability, there is a problem that accuracy is reduced due to deterioration of surface roughness. In terms of chip controllability as well, it is considered better if the chips are short and easy to separate, but the simple addition of S has a large ductility of the matrix, so that the matrix is not sufficiently separated and cannot be significantly improved.
[0004]
Further, elements other than S, such as Te, Bi, and P, are also known as machinability improving elements. However, even if machinability can be improved to some extent, cracks are likely to occur during rolling or hot forging. Therefore, it is said that it is desirable to have as little as possible.
[0005]
For example, in Patent Literature 1, 30 or more sulfides having a length of 20 μm or more in which a single sulfide having a length of 20 μm or more or a plurality of sulfides are connected in a substantially series are present in a field of view having a cross section of 1 mm 2 in the rolling direction. Thus, there has been proposed a method for improving the chip disposability. However, the dispersion of sulfide at the sub-μm level, which is practically most effective for machinability, is not mentioned including the production method, and cannot be expected from the component system.
[0006]
Further,
[0007]
[Patent Document 1]
JP-A-11-222646 [Patent Document 2]
JP-A-11-293391
[Problems to be solved by the invention]
The present invention improves both tool life and surface roughness while avoiding defects in rolling and hot forging, and provides a steel having a machinability equal to or higher than that of a conventional low-carbon lead free-cutting steel and a method for producing the same. provide.
[0009]
[Means for Solving the Problems]
Cutting is a breaking phenomenon that separates chips, and promoting it is one point. This effect is limited by simply increasing S. The present inventors have found that not only increasing the amount of S, but also enhancing the machinability by suppressing the unevenness of the cutting surface by extending the tool life by making the matrix brittle and facilitating fracture. did.
[0010]
The present invention has been made based on the above findings, and the gist is as follows.
[0011]
(1) In% by mass, C: 0.005 to 0.2%, Mn: 0.3 to 3.0%, S: 0.1 to 1.0%, collected by extraction replica method Regarding MnS observed with a transmission electron microscope, the existence density of 0.1 to 0.5 μm in equivalent circle diameter in a section parallel to the rolling direction of the steel material is 10,000 / mm 2 or more. Steel with excellent machinability.
[0012]
(2) The steel excellent in machinability according to (1), wherein the steel of (1) further contains B: 0.0005 to 0.05% by mass%.
[0013]
(3) The steel described in the above (1) or (2) is cooled at a cooling rate of 10 to 100 ° C./min at the time of casting, and is collected by an extraction replica method and observed with a transmission electron microscope. Regarding MnS, a steel having excellent machinability, characterized in that, in a cross section parallel to the rolling direction of the steel material, an existing density of 0.1 to 0.5 μm in a circle equivalent diameter is 10,000 pieces / mm 2 or more. Manufacturing method.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention is intended to obtain a steel having sufficient machinability, particularly good surface roughness, without adding lead, and therefore, controlling MnS to a size that cannot be confirmed with an optical microscope, It has been found that by greatly improving the degree of dispersion, good surface roughness and tool life characteristics can be obtained.
[0015]
First, the reasons for limiting the composition of the steel specified in the present invention will be described. In addition, all the component compositions of steel are mass%.
[0016]
C has a significant effect on machinability because it relates to the basic strength of the steel material and the amount of oxygen in the steel. If the strength is increased by adding a large amount of C, the machinability decreases, so the upper limit was made 0.2%. On the other hand, it is necessary to control the amount of oxygen to an appropriate amount in order to prevent the formation of hard oxides that reduce machinability and to suppress the adverse effects of dissolved oxygen at high temperatures such as pinholes during the solidification process. If the amount of C is simply reduced too much by blowing, not only the cost increases, but also a large amount of oxygen in the steel remains and causes problems such as pinholes. Therefore, the lower limit of the C content of 0.005% at which inconveniences such as pinholes can be easily prevented is set.
[0017]
Mn is necessary for fixing and dispersing sulfur in steel as MnS. In addition, it is necessary to soften oxides in steel and make the oxides harmless. Although the effect also depends on the amount of S added, if it is 0.3% or less, the added S cannot be sufficiently fixed as MnS, and S becomes FeS and becomes brittle. When the amount of Mn increases, the hardness of the base material increases, and machinability and cold workability deteriorate. Therefore, the upper limit is set to 30%.
[0018]
S bonds with Mn and exists as MnS inclusions. MnS improves machinability, but elongated MnS is one of the causes of anisotropy during forging. Large MnS should be avoided, but a large amount is preferable from the viewpoint of improving machinability. Therefore, it is preferable to finely disperse MnS. To improve machinability when Pb is not added, it is necessary to add 0.1% or more. On the other hand, if it exceeds 1%, not only the generation of coarse MnS is inevitable, but also cracks occur during production due to deterioration of casting properties and hot deformation properties due to FeS or the like, so 1% was made the upper limit.
[0019]
Next, the form of MnS and the reason why the existence density of 0.1 to 0.5 μm in terms of the equivalent circle diameter in the distribution thereof is defined as 10.000 / mm 2 or more will be described.
[0020]
MnS is an inclusion for improving machinability, and remarkably improves machinability by finely dispersing it at high density. In order to exhibit the effect, it is necessary that the existing density of MnS having a circle equivalent diameter of 0.1 to 0.5 μm is 10,000 / mm 2 or more. FIG. 3 shows the relationship between MnS density and surface roughness. Usually, the MnS distribution is observed with an optical microscope, and its size and density are measured. MnS having such dimensions cannot be confirmed by observation with an optical microscope, and can be observed only with a transmission electron microscope (TEM) by a replica method. Although there is no difference in the size and density in the optical microscope observation, MnS has a dimension in which a clear difference is observed in the TEM observation by the replica method. In the present invention, this is controlled and the existing form is quantified by the conventional technology. And to differentiate it from
[0021]
In order for MnS exceeding the above dimensions to be present at a density of 10,000 particles / mm 2 or more, it is necessary to add a large amount of S exceeding the range of the present invention. And the probability of anisotropy during forging increases. If MnS exceeds this size in the amount of S added in the range specified in the present invention, the amount of MnS becomes insufficient, and the density required for improving machinability cannot be maintained. Further, those having a diameter of 0.1 μm or less do not substantially affect the machinability. Therefore, it is necessary that the density of sulfides having a circle equivalent diameter of 0.1 to 0.5 μm containing MnS as a main component is 10,000 or more / mm 2 . In order to obtain the size and density of MnS, it is more effective to control the cooling rate and to set the ratio of Mn to S to 1.5 to 2.5.
[0022]
In addition, MnS means not only pure MnS but also an inclusion mainly containing MnS, and sulfides such as Fe, Ca, Ti, Zr, Mg and REM coexist with MnS by solid solution or bonding. And inclusions such as MnTe in which an element other than S forms a compound with Mn to form a compound with MnS to form a solid solution / bond and coexist with the MnS, or includes the above-mentioned inclusions precipitated with an oxide as a nucleus. In the chemical formula, Mn sulfide-based inclusions that can be expressed as (Mn, X) (S, Y) (here, X: an element other than Mn and a sulfide-forming element other than Y: S that binds to Mn) are collectively referred to. That's what they say.
[0023]
B is effective in improving machinability when precipitated as BN. These effects are not remarkable when the content is less than 0.0005%, and when the content exceeds 0.050%, a large amount of BN precipitates and flaws are easily generated during the production due to deterioration of casting properties and hot deformation properties. Therefore, the range is 0.0005 to 0.050%.
[0024]
The steel having excellent machinability according to the present invention is assumed to be a low-carbon free-cutting steel. However, if necessary, the steel may contain additional elements other than C, Mn, S, and B. In this case, for example, Cr: 0.01 to 2.0%, V: 0.01 to 1.0%, Nb: 0.005 to 0.2%, Mo: 0.01 to 1.0%, W: 0.05-1.0%, Ni: 0.05-2.0%, Ti: 0.005-0.2%, Ca: 0.0002-0.01%, Zr: 0.0005-0. 1%, Mg: 0.0003 to 0.01%, Al: 0.001 to 0.1%, Si: 0.01 to 0.5%, Te: 0.0003 to 0.2%, total-N : 0.001 to 0.02%, total-O: 0.0005 to 0.035%, P: 0.001 to 0.2%, Zn: 0.0005 to 0.5%, Sn: 0.005 -2.0%, Cu: 0.01-2.0%, Bi: 0.005-0.5%, Pb: 0.01-0.5% good.
[0025]
Next, the reason why the cooling rate of the slab or billet at the time of casting is limited to 10 to 100 ° C./min will be described.
[0026]
Fine dispersion of MnS is effective for improving machinability. In order to finely disperse MnS, it is necessary to control the crystallization of MnS, and the control requires strict control of the cooling rate range. If the cooling rate is 10 ° C./min or less, the solidification is too slow, and the crystallized MnS becomes coarse and cannot be finely dispersed. When the cooling rate is 100 ° C./min or more, the density of the generated fine MnS is saturated, the hardness of the slab increases, and the risk of cracking increases. This cooling rate can be easily obtained by controlling the size of the mold section, the casting speed, the casting speed, and the like to appropriate values. This is applicable to both the continuous casting method and the ingot making method.
[0027]
Here, the cooling rate refers to a rate at the time of cooling from the liquidus temperature to the solidus temperature in the portion Q in the slab thickness direction. The cooling rate is calculated by the following formula from the interval between the secondary dendrite arms of the solidified structure in the thickness direction of the slab after solidification.
[0028]
(Equation 1)
[0029]
Where Rc: cooling rate (° C./min), λ2: interval between secondary dendrite arms (μm)
That is, since the interval between the secondary dendrite arms changes depending on the cooling condition, the controlled cooling rate was confirmed by measuring this.
[0030]
【Example】
The effects of the present invention will be described with reference to examples.
[0031]
Some of the test materials shown in Tables 1 and 2 (continuation 1 in Table 1), Table 3 (
[0032]
The measurement of the MnS density of 0.1 to 0.5 μm in a circle equivalent diameter is performed by an extraction replica method by sampling from the Q portion of a cross section parallel to the rolling direction after φ50 mm rolling and using an over-type electron microscope. Was. The measurement was performed at a magnification of 10,000 times for 40 or more visual fields in one visual field of 80 μm 2 , and the calculated value was converted to the number of MnS per square millimeter.
[0033]
FIG. 1 shows a TEM replica photograph of MnS of the present invention. FIG. 2 shows a TEM replica photograph of MnS of the comparative example. As described above, MnS having a size that cannot be confirmed at the optical microscope level is clearly different in both dimensions and density between the invention example and the comparative example by observing the TEM replica.
[0034]
With respect to machinability, all of the inventive examples were superior to the comparative example in terms of the drill tool life, and the surface roughness in plunge cutting was favorable. In particular, a very excellent value has been obtained for the surface roughness due to the effect of fine MnS.
[0035]
[Table 1]
[0036]
[Table 2]
[0037]
[Table 3]
[0038]
[Table 4]
[0039]
[Table 5]
[0040]
[Table 6]
[0041]
【The invention's effect】
As described above, the present invention is excellent in machinability with good tool life and cutting surface roughness, particularly in cutting, and good cutting processability by strictly controlling the size and distribution of MnS in steel. It is possible to provide steel.
[Brief description of the drawings]
FIG. 1 is a TEM replica photograph showing the microstructure of steel according to the present invention.
FIG. 2 is a TEM replica photograph showing the microstructure of a comparative steel.
FIG. 3 is a diagram showing the relationship between MnS density and surface roughness.
FIG. 4 is a view showing a plunge cutting method.
Claims (3)
Priority Applications (10)
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JP2002332668A JP4264247B2 (en) | 2002-11-15 | 2002-11-15 | Steel with excellent machinability and method for producing the same |
TW092132048A TWI249579B (en) | 2002-11-15 | 2003-11-14 | A steel having an excellent cuttability and a method for producing the same |
PCT/JP2003/014547 WO2004050932A1 (en) | 2002-11-15 | 2003-11-14 | Steel excellent in machinability and method for production thereof |
DE60318745T DE60318745T2 (en) | 2002-11-15 | 2003-11-14 | STEEL WITH EXCELLENT CUT-OUTPUT AND MANUFACTURING METHOD THEREFOR |
KR1020057008721A KR100708430B1 (en) | 2002-11-15 | 2003-11-14 | Steel excellent in machinability and method for production thereof |
CN2007101960130A CN101215665B (en) | 2002-11-15 | 2003-11-14 | Steel having excellent machinability and production method therefor |
CNB2003801034255A CN100529136C (en) | 2002-11-15 | 2003-11-14 | Steel excellent in machinability and method for production thereof |
EP03772791A EP1580287B1 (en) | 2002-11-15 | 2003-11-14 | Steel excellent in machinability and method for production thereof |
US10/534,858 US7488396B2 (en) | 2002-11-15 | 2003-11-14 | Superior in machinability and method of production of same |
US12/288,542 US8137484B2 (en) | 2002-11-15 | 2008-10-20 | Method of production of steel superior in machinability |
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Cited By (4)
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WO2006129531A1 (en) * | 2005-05-30 | 2006-12-07 | Sumitomo Metal Industries, Ltd. | Low carbon sulfur free-machining steel |
JP2007146228A (en) * | 2005-11-28 | 2007-06-14 | Nippon Steel Corp | Free cutting steel having excellent high temperature ductility |
WO2007102489A1 (en) * | 2006-03-08 | 2007-09-13 | Sumitomo Metal Industries, Ltd. | Low-carbon resulfurized free-cutting steel material |
EP2096186A1 (en) * | 2006-11-28 | 2009-09-02 | Nippon Steel Engineering Corporation | Free-cutting steel excellent in manufacturability |
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JP4264247B2 (en) | 2009-05-13 |
CN100529136C (en) | 2009-08-19 |
CN1711367A (en) | 2005-12-21 |
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