JP2005054227A - Low carbon free cutting steel - Google Patents
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- 229910000915 Free machining steel Inorganic materials 0.000 title claims abstract description 80
- 229910052799 carbon Inorganic materials 0.000 title claims abstract description 39
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 title claims abstract description 12
- 238000005096 rolling process Methods 0.000 claims abstract description 35
- 229910052760 oxygen Inorganic materials 0.000 claims abstract description 26
- 229910052717 sulfur Inorganic materials 0.000 claims abstract description 26
- 229910052757 nitrogen Inorganic materials 0.000 claims abstract description 22
- 229910052748 manganese Inorganic materials 0.000 claims abstract description 18
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims abstract description 17
- 239000001301 oxygen Substances 0.000 claims abstract description 17
- 229910052719 titanium Inorganic materials 0.000 claims abstract description 17
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- 229910052698 phosphorus Inorganic materials 0.000 claims abstract description 9
- 229910000831 Steel Inorganic materials 0.000 claims description 128
- 239000010959 steel Substances 0.000 claims description 128
- 229910052718 tin Inorganic materials 0.000 claims description 14
- 229910052804 chromium Inorganic materials 0.000 claims description 10
- 239000012535 impurity Substances 0.000 claims description 9
- 229910052761 rare earth metal Inorganic materials 0.000 claims description 9
- 229910052714 tellurium Inorganic materials 0.000 claims description 8
- 229910052797 bismuth Inorganic materials 0.000 claims description 5
- 229910052711 selenium Inorganic materials 0.000 claims description 5
- 229910052750 molybdenum Inorganic materials 0.000 claims description 4
- 229910052759 nickel Inorganic materials 0.000 claims description 3
- 229910052758 niobium Inorganic materials 0.000 claims description 3
- 229910052720 vanadium Inorganic materials 0.000 claims description 3
- 229910052802 copper Inorganic materials 0.000 claims 2
- 229910052742 iron Inorganic materials 0.000 claims 1
- 239000000203 mixture Substances 0.000 abstract description 18
- 150000001247 metal acetylides Chemical class 0.000 abstract description 15
- 239000002131 composite material Substances 0.000 abstract description 14
- 238000003754 machining Methods 0.000 abstract description 7
- YQCIWBXEVYWRCW-UHFFFAOYSA-N methane;sulfane Chemical compound C.S YQCIWBXEVYWRCW-UHFFFAOYSA-N 0.000 abstract description 4
- 238000010348 incorporation Methods 0.000 abstract 1
- 238000005520 cutting process Methods 0.000 description 71
- 230000000694 effects Effects 0.000 description 58
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 42
- 239000000463 material Substances 0.000 description 42
- 230000003746 surface roughness Effects 0.000 description 35
- DXHPZXWIPWDXHJ-UHFFFAOYSA-N carbon monosulfide Chemical compound [S+]#[C-] DXHPZXWIPWDXHJ-UHFFFAOYSA-N 0.000 description 29
- 150000004767 nitrides Chemical class 0.000 description 23
- 238000005255 carburizing Methods 0.000 description 17
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- 239000011159 matrix material Substances 0.000 description 5
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- 238000007514 turning Methods 0.000 description 5
- 229910052726 zirconium Inorganic materials 0.000 description 5
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 4
- 239000002244 precipitate Substances 0.000 description 4
- 239000011593 sulfur Substances 0.000 description 4
- 230000015572 biosynthetic process Effects 0.000 description 3
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- 229910000859 α-Fe Inorganic materials 0.000 description 2
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 1
- 229910001122 Mischmetal Inorganic materials 0.000 description 1
- 229910004298 SiO 2 Inorganic materials 0.000 description 1
- 241001422033 Thestylus Species 0.000 description 1
- 229910010037 TiAlN Inorganic materials 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
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- 229910001566 austenite Inorganic materials 0.000 description 1
- JCXGWMGPZLAOME-UHFFFAOYSA-N bismuth atom Chemical compound [Bi] JCXGWMGPZLAOME-UHFFFAOYSA-N 0.000 description 1
- 238000011109 contamination Methods 0.000 description 1
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- 229910052738 indium Inorganic materials 0.000 description 1
- 230000006698 induction Effects 0.000 description 1
- 229910052747 lanthanoid Inorganic materials 0.000 description 1
- 150000002602 lanthanoids Chemical class 0.000 description 1
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- 230000019086 sulfide ion homeostasis Effects 0.000 description 1
- PORWMNRCUJJQNO-UHFFFAOYSA-N tellurium atom Chemical compound [Te] PORWMNRCUJJQNO-UHFFFAOYSA-N 0.000 description 1
- 238000005496 tempering Methods 0.000 description 1
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/008—Ferrous alloys, e.g. steel alloys containing tin
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
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- Mechanical Engineering (AREA)
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- Heat Treatment Of Steel (AREA)
- Treatment Of Steel In Its Molten State (AREA)
- Heat Treatment Of Sheet Steel (AREA)
Abstract
Description
本発明は、鉛(Pb)を含有しない低炭素快削鋼に関する。特に、鉛を含まないにもかかわらず、従来の鉛快削鋼および鉛と他の快削性改善元素を併用した複合快削鋼に較べて、超硬工具を用いる切削の場合にも優れた被削性を有し、熱間加工性および切削後の仕上げ面の性状にも優れ、且つ安価に製造できる低炭素快削鋼に関する。本発明はまた、上記の諸特性と共に、浸炭特性にも優れた低炭素快削鋼に関する。 The present invention relates to a low carbon free cutting steel containing no lead (Pb). In particular, although it does not contain lead, it is also superior in the case of cutting with carbide tools compared to conventional free-cutting steel and composite free-cutting steel that uses lead and other free-machining improvement elements in combination. The present invention relates to a low-carbon free-cutting steel that has machinability, is excellent in hot workability and finished surface properties after cutting, and can be manufactured at low cost. The present invention also relates to a low-carbon free-cutting steel excellent in carburizing characteristics as well as the above-mentioned various characteristics.
従来、強度をあまり必要としない軟質の小物部品には、生産性向上のため、被削性に優れた鋼材、いわゆる快削鋼が用いられている。最もよく知られている快削鋼は、Sを多量に添加してMnSにより被削性を改善した硫黄快削鋼、Pbを添加した鉛快削鋼、およびSとPbの両者を含む複合快削鋼である。特にPbを含む快削鋼は、工具寿命の延長をもたらし、切屑分断性に優れ、加工後の鋼材表面の仕上げ面粗さに優れるといった特性を有している。さらに被削性改善の目的でTe(テルル)やBi(ビスマス)等を含有する快削鋼もある。これらは、自動車用のブレーキパーツ等の小物部品やパソコン周辺機器部品をはじめ、電気機器部品や金型等の各種機械部品に大量に使用されている。 Conventionally, steel parts having excellent machinability, so-called free-cutting steel, have been used for soft small parts that do not require much strength in order to improve productivity. The most well-known free-cutting steels are sulfur free-cutting steel with a large amount of S added to improve machinability with MnS, lead free-cutting steel with Pb added, and composite free-cutting steel containing both S and Pb. Cutting steel. In particular, free-cutting steel containing Pb has characteristics such as extending the tool life, excellent chip separation, and excellent finished surface roughness of the steel material after processing. There are also free-cutting steels containing Te (tellurium), Bi (bismuth), etc. for the purpose of improving machinability. These are used in large quantities in various machine parts such as electric equipment parts and dies, as well as small parts such as brake parts for automobiles and PC peripheral equipment parts.
一方、近年の切削機械の性能向上により高速度での切削が可能となり、それに伴って上記のような部品の素材となる鋼材にも、高速切削加工時における被削性の向上が強く望まれている。 On the other hand, the recent improvement in performance of cutting machines has enabled high-speed cutting, and accordingly, steel materials that are the materials of the above parts are also strongly desired to improve machinability during high-speed cutting. Yes.
さらに、上記部品は切削加工によって所定の形状に仕上げた後、表面の強度を確保するために浸炭処理が施される場合がある。従って、これらの部品に用いられる鋼材には高い被削性を有すると共に、浸炭特性に優れることが望まれることがある。 Further, the above parts may be carburized in order to ensure the strength of the surface after being finished into a predetermined shape by cutting. Therefore, it may be desired that the steel materials used for these parts have high machinability and excellent carburization characteristics.
上記のような部品の素材として用いられる鋼材には優れた被削性が求められるのであるが、その被削性としては、工具寿命を延長するばかりではなく、切屑が細かく分断する性質、つまり「切屑処理性」に優れることが重要視される。この切屑処理性は、加工ラインの自動化に欠かせないものであって、生産性の向上のためには必須である。また、工具寿命や切屑処理性以外にも加工精度の観点から切削後の鋼材表面における仕上げ面の性状に優れること、即ち、仕上げ面粗さが小さいことが望まれている。前記の快削鋼の中でも鉛快削鋼やPbと共に他の快削性改善元素を含有する複合快削鋼は、これらの諸特性に優れ、現存の鋼材の中では最も被削性に優れるとされている。 The steel material used as the material for the above parts is required to have excellent machinability, but the machinability not only extends the tool life, but also has the property that chips are finely divided, that is, `` It is important to have excellent chip disposal. This chip disposal is indispensable for the automation of the processing line, and is essential for improving the productivity. In addition to tool life and chip disposal, it is desired that the finished surface on the steel surface after cutting is excellent in properties, that is, the finished surface roughness is small, from the viewpoint of machining accuracy. Among the above-mentioned free-cutting steels, lead free-cutting steel and composite free-cutting steel containing Pb and other free-machining improving elements are excellent in these properties, and most excellent in machinability among existing steel materials. Has been.
近年、環境問題への関心が高まる中でPbを含有しない快削鋼が強く望まれている。これは、人体や地球環境に対して有害であるPbを含む鋼材は、その製造過程において大がかりな排気設備を必要とするばかりでなく、環境保全の観点からPbの使用を抑制する動きが高まっているからである。 In recent years, free-cutting steel containing no Pb has been strongly demanded with increasing interest in environmental problems. This is because steel materials containing Pb, which is harmful to the human body and the global environment, not only require extensive exhaust equipment in the manufacturing process, but also have been increasingly used to suppress the use of Pb from the viewpoint of environmental conservation. Because.
上記の要望に応えるべく、鉛快削鋼に替わるものとしてPbを含有しない低炭素硫黄快削鋼に関する種々の提案がなされている。しかし、工具寿命の延長に寄与し、切屑処理性に優れ、仕上げ面粗さが小さいといったPbを含有する快削鋼の特徴の全てを満足する快削鋼は未だ開発されていない。 In order to meet the above requirements, various proposals have been made regarding low-carbon sulfur free-cutting steel that does not contain Pb as an alternative to lead-free-cutting steel. However, free-cutting steels that satisfy all the characteristics of free-cutting steels containing Pb that contribute to the extension of tool life, excellent chip controllability, and low finished surface roughness have not yet been developed.
特許文献1(特開2003-49240号公報)には、Tiまたは/およびZrの炭硫化物系介在物を存在させ、被削性を改善させた快削鋼が開示されている。この快削鋼ではMnSと共にTi炭硫化物或いはZr炭硫化物を鋼中に分散させているために、MnSの擬似的な潤滑効果が得がたく、工具と被削材の間における摩擦力が上昇する。その結果、切削抵抗が上昇して工具刃先に構成刃先が生成しやすくなる。構成刃先が生成してしまうと、仕上げ切削後の仕上げ面粗さが大きくなり、部品における加工精度が損なわれる。 Patent Document 1 (Japanese Patent Application Laid-Open No. 2003-49240) discloses a free-cutting steel in which a carburide-based inclusion of Ti or / and Zr is present to improve machinability. In this free-cutting steel, Ti carbon sulfide or Zr carbon sulfide is dispersed in the steel together with MnS, so it is difficult to obtain a pseudo lubricating effect of MnS, and the frictional force between the tool and the work material is low. Rise. As a result, the cutting resistance increases, and the component cutting edge is easily generated at the tool cutting edge. If the component cutting edge is generated, the finished surface roughness after finish cutting increases, and the machining accuracy of the part is impaired.
特許文献1の中にはTi含有量が0.1%以下である実施例は見当たらない。このことは、特許文献1の発明が多量のTiを含有させることによってTi炭硫化物を生成させることを目的としていることを示しており、実際にMnSと共にTi炭硫化物系介在物が粒形状でマトリクス内に分散されていると記載されている。この場合には、工具寿命、切屑処理性、仕上げ面粗さといった前記部品に用いられる鋼材に求められる性能を満足し得ない。 In Patent Document 1, there is no example in which the Ti content is 0.1% or less. This indicates that the invention of Patent Document 1 aims to produce Ti carbosulfide by containing a large amount of Ti. Actually, Ti carbosulfide inclusions together with MnS have a grain shape. In the matrix. In this case, the performance required for the steel materials used for the parts, such as tool life, chip disposal, and finished surface roughness, cannot be satisfied.
特許文献2(特開2003-49241号公報)には、(Ti+0.52Zr)/S<2の範囲でTiまたは/およびZrを含有させ、Ti或いはZrの炭硫化物を介在物として含有する快削鋼であって、旋削加工およびドリル加工における工具寿命を高めた快削鋼が開示されている。この特許文献2の発明ではTi炭硫化物を鋼中に生成させることで、旋削加工時の工具寿命改善を図っている。この技術では、確かにある程度の工具寿命の改善はなし得るが、Ti或いはZrの炭硫化物の存在によってMnSの潤滑効果が得がたく、工具と被削材との間での摩擦力が上昇する。その結果、切削抵抗が上昇し、工具刃先に構成刃先が生成しやすくなる。構成刃先が生成してしまうと切削後の仕上げ面粗さが大きくなり、結果として加工精度が劣化する。 Patent Document 2 (Japanese Patent Laid-Open No. 2003-49241) contains Ti or / and Zr in the range of (Ti + 0.52Zr) / S <2, and contains Ti or Zr carbon sulfide as an inclusion. Free-cutting steel is disclosed that has improved tool life in turning and drilling. In the invention of Patent Document 2, Ti carbon sulfide is generated in steel to improve the tool life during turning. This technology can certainly improve the tool life to some extent, but the presence of Ti or Zr carbosulfides makes it difficult to obtain the lubrication effect of MnS, and the frictional force between the tool and the work material increases. . As a result, the cutting resistance increases, and the component cutting edge is easily generated on the tool cutting edge. If the constituent cutting edges are generated, the finished surface roughness after cutting increases, and as a result, the machining accuracy deteriorates.
なお、特許文献2には、後述する本発明で規定するようなSを0.21%以上の範囲で含有し、Ti量が0.1%以下である快削鋼の実施例は見受けられない。このことから、特許文献2の発明が仕上げ面粗さや切屑処理性の向上を狙った発明ではないことが明らかである。つまり、特許文献2の発明ではMnSと共にTi或いはZrの炭硫化物がマトリクス内に分散されているので、所望の仕上げ面粗さおよび切屑処理性を得ることはできない。 In Patent Document 2, there is no example of free cutting steel containing S in the range of 0.21% or more and Ti content of 0.1% or less as specified in the present invention described later. From this, it is clear that the invention of Patent Document 2 is not an invention aimed at improving the finished surface roughness and chip disposal. That is, in the invention of Patent Document 2, Ti or Zr carbon sulfide is dispersed in the matrix together with MnS, so that it is not possible to obtain desired finished surface roughness and chip disposal.
特許文献3(特開2000-319753号公報)には0.4%を超えるSを含有させてMnSを増量したPbを添加しない低炭素硫黄快削鋼が開示されている。しかし、この鋼では超硬工具寿命の改善の効果が小さい。また、この鋼は、工具寿命と共に重要視される切屑処理性が改善されたものではなく、従来の硫黄快削鋼の性能を大きく改良したものではない。 Patent Document 3 (Japanese Patent Application Laid-Open No. 2000-319753) discloses a low-carbon sulfur free-cutting steel not containing Pb, which contains more than 0.4% S and increases MnS. However, this steel has a small effect of improving the carbide tool life. Further, this steel does not improve the chip disposability considered important with the tool life, and does not greatly improve the performance of conventional sulfur free-cutting steel.
特許文献4(特開平09-53147号公報)には、C:0.01〜0.2%、Si:0.10〜0.60%、Mn:0.5〜1.75%、P:0.005〜0.15%、S:0.15〜0.40%、O(酸素):0.001〜0.010%、Ti:0.0005〜0.020%、N0.003〜0.03%を含有し、超硬工具に対する被削性、特に工具寿命に優れる快削鋼の発明が開示されている。この発明では、Tiと共にSiを0.1〜0.6%含有させることを必須として超硬工具の寿命改善を図っている。また、この発明では、本発明のようにSiを含有させなくても「Ti炭化物または/およびTi炭窒化物が内在する実質的なMnS」を鋼材中に存在させることによって、工具寿命のみならず、切屑処理性、仕上げ面粗さの向上までをも意図したものではない。 In Patent Document 4 (Japanese Patent Laid-Open No. 09-53147), C: 0.01 to 0.2%, Si: 0.10 to 0.60%, Mn: 0.5 to 1.75%, P: 0.005 to 0.15%, S: 0.15 to 0.40%, An invention of free-cutting steel containing O (oxygen): 0.001 to 0.010%, Ti: 0.0005 to 0.020%, N 0.003 to 0.03% and excellent in machinability for carbide tools, particularly excellent tool life is disclosed. . In the present invention, it is essential to contain 0.1 to 0.6% of Si together with Ti to improve the life of the carbide tool. Further, according to the present invention, not only the tool life but also the tool life can be obtained by allowing “substantially MnS in which Ti carbide or / and Ti carbonitride is present” to exist in the steel material without containing Si as in the present invention. It is not intended to improve chip disposability and finish surface roughness.
特許文献5(特許第3390988号公報)にはC:0.02〜0.15%、Mn:0.3〜1.8%、S:0.225〜0.5%、Ti:0.1〜0.6%、Zr:0.1〜0.6%を含有し、且つTi+Zr:0.3〜0.6%、(Ti+Zr)/S比:1.1〜1.5を満足させて、機械的異方性を改善した低炭素硫黄快削鋼の発明が開示されている。この発明は、上記の組成にすることによって熱間での変形抵抗の高いTiやZrの硫化物を生成させ、鋼材の機械的異方性や被削性を改善したものである。しかし、変形抵抗の高いこれらの硫化物では切削時に硫化物による潤滑効果が得難いために、切削抵抗が高くなり、工具寿命の劣化や仕上げ面粗度の劣化を引き起こす。 Patent Document 5 (Patent No. 3390988) contains C: 0.02 to 0.15%, Mn: 0.3 to 1.8%, S: 0.225 to 0.5%, Ti: 0.1 to 0.6%, Zr: 0.1 to 0.6%, In addition, an invention of a low carbon sulfur free-cutting steel with improved mechanical anisotropy satisfying Ti + Zr: 0.3 to 0.6% and (Ti + Zr) / S ratio: 1.1 to 1.5 is disclosed. According to the present invention, Ti and Zr sulfides having high deformation resistance in the hot state are produced by using the above composition, and the mechanical anisotropy and machinability of the steel material are improved. However, since these sulfides having high deformation resistance are difficult to obtain a lubrication effect due to sulfide during cutting, the cutting resistance is increased, and the tool life and the roughness of the finished surface are deteriorated.
本発明の課題は、環境に有害なPbを含有することなく、従来のPb快削鋼やPbとともにその他の快削性付与元素を併用した複合快削鋼に比較して、特に超硬工具を用いた切削の場合に優れた被削性を示し、熱間加工性に優れ、さらに切削後の表面性状にも優れ、安価に製造できる低炭素快削鋼を提供することにある。また、上記の諸特性に加えて優れた浸炭性をも有する低炭素快削鋼を提供することも本発明の課題である。 The problem of the present invention is that, in particular, cemented carbide tools are used as compared with conventional Pb free-cutting steel and composite free-cutting steel using Pb in combination with other free-cutting property imparting elements without containing Pb harmful to the environment. An object of the present invention is to provide a low-carbon free-cutting steel that exhibits excellent machinability in the case of the cutting used, is excellent in hot workability, has excellent surface properties after cutting, and can be manufactured at low cost. It is also an object of the present invention to provide a low carbon free-cutting steel having excellent carburizability in addition to the above various characteristics.
硫化物などの介在物の状態が鋼の被削性に大きく影響することはよく知られている。 そして、C、Ti、S、N、Oが含有されている鋼において観察される介在物には様々なものがある。例えば、Ti硫化物、Ti炭硫化物、Ti炭化物、Ti炭窒化物、Ti窒化物、Ti酸化物である。さらにMnが含有されていれば、「MnS」の化学式で表されるMn硫化物も存在する。これらの外に、AlやSiが含まれていればこれらの酸化物も存在する。これらの存在形態は多種多様であり、これらの介在物の組成や存在形態が鋼の被削性や他の機械特性等に大きく影響するのである。 It is well known that the state of inclusions such as sulfides greatly affects the machinability of steel. There are various inclusions observed in steel containing C, Ti, S, N, and O. For example, Ti sulfide, Ti carbon sulfide, Ti carbide, Ti carbonitride, Ti nitride, and Ti oxide. Further, if Mn is contained, Mn sulfide represented by the chemical formula “MnS” is also present. In addition to these, if Al or Si is contained, these oxides also exist. These forms exist in various ways, and the composition and form of these inclusions greatly affect the machinability and other mechanical properties of steel.
本発明者らは、先に特願2002-26368号によってPbを含まない低炭素硫黄快削鋼に関する発明を特許出願した。その快削鋼は、C、Mn、S、Ti、Si、P、Al、OおよびNを規定量含有し、TiとSの含有量が下記の (A) 式を満たし、MnとSの原子比が下記の(B)式を満たし、且つTi硫化物または/及びTi炭硫化物が内在するMnSを含有することを特徴とする低炭素硫黄快削鋼である。 The present inventors previously filed a patent application for an invention related to low-carbon sulfur free-cutting steel containing no Pb by Japanese Patent Application No. 2002-26368. The free-cutting steel contains C, Mn, S, Ti, Si, P, Al, O, and N, and the contents of Ti and S satisfy the following formula (A). A low carbon sulfur free-cutting steel characterized in that the ratio satisfies the following formula (B) and contains MnS containing Ti sulfide or / and Ti carbon sulfide.
Ti(質量%)/S(質量%)<1・・・(A)
Mn/S≧1・・・(B)
この先願発明の鋼は、工具寿命がPb快削鋼に比べても遙かに優れ、且つ優れた切屑処理性を有するものである。しかし、この鋼では、切削後の表面性状に若干の難点がある。即ち、仕上げ切削を実施した場合、仕上げ面粗さが大きくなる場合があるという問題が明らかになった。
Ti (mass%) / S (mass%) <1 ... (A)
Mn / S ≧ 1 ... (B)
The steel of the prior invention has much longer tool life than Pb free-cutting steel and has excellent chip disposal. However, this steel has some difficulties in surface properties after cutting. That is, when finishing cutting was performed, the problem that the finished surface roughness sometimes increased became clear.
マトリックス中に実質的なTi硫化物または/およびTi炭硫化物が存在すると、MnSの擬似的な潤滑効果が得がたくなるために、切削抵抗が上昇し、工具刃先に構成刃先が生成するために、切削後の鋼材の表面に光沢度を与えず、仕上げ面粗さを劣化させると考えられる。なお、上記の「実質的なTi硫化物または/およびTi炭硫化物」というのは、一個の介在物の中でTi硫化物およびTi炭硫化物が占める面積率の合計が50%以上である介在物を意味し、後述する図1の(a)にその幾つかが示されている。 If substantial Ti sulfide and / or Ti carbosulfide is present in the matrix, it becomes difficult to obtain the pseudo lubrication effect of MnS, resulting in increased cutting resistance and the formation of a component edge at the tool edge. Further, it is considered that the finished surface roughness is deteriorated without giving gloss to the surface of the steel material after cutting. The above "substantial Ti sulfide or / and Ti carbosulfide" means that the total area ratio occupied by Ti sulfide and Ti carbosulfide in one inclusion is 50% or more. This means inclusions, some of which are shown in FIG.
そこで上記の問題を解決するために検討を行った結果、次に述べるような新しい知見が得られた。 As a result of studies to solve the above problems, the following new findings were obtained.
(1)「実質的なTi硫化物または/およびTi炭硫化物」がマトリクス中に存在する鋼を切削した場合、構成刃先が工具刃先に生成して仕上げ表面の粗さが劣化する。 (1) When cutting steel in which “substantially Ti sulfide or / and Ti carbosulfide” is present in the matrix, the component cutting edge is generated in the tool cutting edge and the roughness of the finished surface is deteriorated.
(2)「実質的なTi硫化物または/およびTi炭硫化物」の生成をできる限り抑制し、且つMnSを鋼中に多く存在させることによって、構成刃先の生成は抑制され、良好な仕上げ面粗さを得ることができる。 (2) Suppressing the generation of “substantial Ti sulfide and / or Ti carbosulfide” as much as possible, and by making MnS present in the steel as much as possible, the generation of the component cutting edge is suppressed, and a good finished surface Roughness can be obtained.
(3)しかし、Tiを含有せずMnSだけが存在する鋼では、超硬工具寿命が劣化する。超硬工具寿命を向上させるためには、Tiを添加し、かつ「Ti炭化物または/およびTi炭窒化物が内在する実質的なMnS」を存在させる必要がある。 (3) However, the tool life of cemented carbide deteriorates in steel that does not contain Ti and contains only MnS. In order to improve the carbide tool life, it is necessary to add Ti and to have “substantially MnS in which Ti carbide or / and Ti carbonitride is inherent”.
(4)「Ti炭化物または/およびTi炭窒化物が内在する実質的なMnS」は、工具寿命を向上させる一方で、MnSの擬似的潤滑効果を損なうことがない。 (4) “Substantially MnS containing Ti carbide and / or Ti carbonitride” improves the tool life while not impairing the pseudo lubricating effect of MnS.
上記の知見を基にして、さらに化学組成と介在物形態との関係を詳細に検討した。その結果、以下に示す低炭素快削鋼を発明するに到った。この低炭素快削鋼は、Pb快削鋼や複合快削鋼と同等以上の被削性を有する。なお、成分含有量に関する%は質量%である。 Based on the above findings, the relationship between chemical composition and inclusion morphology was further examined in detail. As a result, the inventors have invented the following low-carbon free-cutting steel. This low carbon free-cutting steel has machinability equivalent to or better than Pb free-cutting steel and composite free-cutting steel. In addition,% regarding component content is the mass%.
C:0.05%から0.20%未満、Mn:0.4〜2.0%、S:0.21〜1.0%、Ti:0.002〜0.10%、P:0.001〜0.30%、Al:0.2%以下、O(酸素):0.001〜0.03%、N:0.0005〜0.02%を含有し、残部がFeおよび不純物からなる鋼であって、鋼中に含有される介在物が下記イ式およびロ式を満たすことを特徴とする低炭素硫黄快削鋼。 C: 0.05% to less than 0.20%, Mn: 0.4 to 2.0%, S: 0.21 to 1.0%, Ti: 0.002 to 0.10%, P: 0.001 to 0.30%, Al: 0.2% or less, O (oxygen): 0.001 to Low carbon sulfur containing 0.03%, N: 0.0005-0.02%, the balance being Fe and impurities, and inclusions contained in the steel satisfy the following formulas (A) and (B) Free-cutting steel.
(A+B)/C≧ 0.8・・・・イ
NA≧5・・・・ロ
ここで、A、B、CおよびNAの意味は下記の通りである。
(A + B) /C≧0.8
N A ≧ 5... B Here, the meanings of A, B, C and N A are as follows.
A;圧延方向に平行な断面の1mm2中における円相当直径1μm以上の介在物のうち、Ti炭化物または/およびTi炭窒化物が内在する実質的なMnSが占める総面積。 A: Total area occupied by substantial MnS in which Ti carbide and / or Ti carbonitride is contained in inclusions having an equivalent circle diameter of 1 μm or more in 1 mm 2 of a cross section parallel to the rolling direction.
B;圧延方向に平行な断面の1mm2中における円相当直径1μm以上の介在物のうち、Ti炭化物およびTi炭窒化物が内在しない実質的なMnSが占める総面積。 B: Total area occupied by substantial MnS in which Ti carbide and Ti carbonitride are not present among inclusions having an equivalent circle diameter of 1 μm or more in 1 mm 2 of a cross section parallel to the rolling direction.
C;圧延方向に平行な断面の1mm2中における円相当直径1μm以上の全介在物が占める総面積。 C: Total area occupied by all inclusions having a circle-equivalent diameter of 1 μm or more in 1 mm 2 of a cross section parallel to the rolling direction.
NA;圧延方向に平行な断面の1mm2中における円相当直径1μm以上の介在物のうち、Ti炭化物または/およびTi炭窒化物が内在する実質的なMnSの個数。 N A : The substantial number of MnS in which Ti carbide and / or Ti carbonitride is contained among inclusions having an equivalent circle diameter of 1 μm or more in 1 mm 2 of a cross section parallel to the rolling direction.
上記の低炭素快削鋼は、下記の第1群から第3群までのうちの少なくとも1群から選んだ1種以上の成分を含むことができる。 Said low carbon free-cutting steel can contain 1 or more types of components chosen from at least 1 group from the following 1st group to 3rd group.
第1群
Se:0.0005〜0.10%、Te:0.0005〜0.10%、Bi:0.01〜0.3%、Sn:0.01〜0.3%、Ca:0.0001〜0.01%、Mg:0.0001〜0.005%、B:0.0002〜0.02%および希土類元素:0.0005〜0.02%。
First group
Se: 0.0005-0.10%, Te: 0.0005-0.10%, Bi: 0.01-0.3%, Sn: 0.01-0.3%, Ca: 0.0001-0.01%, Mg: 0.0001-0.005%, B: 0.0002-0.02% and rare earth Element: 0.0005-0.02%.
第2群
Cu:0.01〜1.0%、Ni:0.01〜2.0%、Mo:0.01〜0.5%、V:0.005〜0.5%およびNb:0.005〜0.5%。
Second group
Cu: 0.01-1.0%, Ni: 0.01-2.0%, Mo: 0.01-0.5%, V: 0.005-0.5% and Nb: 0.005-0.5%.
第3群
Si:0.1〜2.0% およびCr:0.03〜1.0%。
3rd group
Si: 0.1-2.0% and Cr: 0.03-1.0%.
ここで、「Ti炭化物または/およびTi炭窒化物が内在する実質的なMnS」とは、後に詳述するとおり、一個の介在物の中でMnSが占める面積率が50%以上であって、Ti炭化物または/およびTi炭窒化物が内在(共存)する介在物をいう。一方、「Ti炭化物およびTi炭窒化物が内在しない実質的なMnS」とは、一個の介在物の中でMnSが占める面積率が50%以上であって、Ti炭化物およびTi炭窒化物が内在(共存)していない介在物をいう。また、これらの「Ti炭化物または/およびTi炭窒化物が内在する実質的なMnS」および「Ti炭化物およびTi炭窒化物が内在しない実質的なMnS」は、いずれもその中にTi炭化物およびTi炭窒化物以外の硫化物、炭硫化物、炭化物、窒化物等が内在しているものでもよい。 Here, “substantially MnS in which Ti carbide or / and Ti carbonitride is inherent” means, as will be described in detail later, the area ratio occupied by MnS in one inclusion is 50% or more, An inclusion in which Ti carbide and / or Ti carbonitride is present (coexist). On the other hand, “substantially MnS free of Ti carbide and Ti carbonitride” means that the area ratio occupied by MnS in one inclusion is 50% or more, and Ti carbide and Ti carbonitride are inherent. An inclusion that does not coexist. These “substantially MnS containing Ti carbide and / or Ti carbonitride” and “substantially MnS not containing Ti carbide and Ti carbonitride” are both included in Ti carbide and Ti carbide. It may contain sulfides other than carbonitrides, carbonitrides, carbides, nitrides and the like.
上記本発明の低炭素快削鋼の主な特徴は、下記のとおりである。 The main features of the low carbon free-cutting steel of the present invention are as follows.
(1) Cを0.05%から0.20%未満とし、Sを0.21〜0.7%の範囲で含有させ、且つTiの含有量を0.002〜0.1%とする。 (1) C is 0.05% to less than 0.20%, S is contained in the range of 0.21 to 0.7%, and the Ti content is 0.002 to 0.1%.
(2) TiはC、S、NおよびOと結合して硫化物、炭硫化物、炭化物、炭窒化物および酸化物を形成する。TiはMnよりも硫化物形成傾向が強いためにTi硫化物やTi炭硫化物を形成しやすい。しかし、MnやTi、SおよびNの含有量バランスを慎重に考慮すれば、「実質的なTi炭硫化物または/およびTi硫化物」を多くは生成させずに、「Ti炭化物または/およびTi炭窒化物が内在する実質的なMnS」および「Ti炭化物およびTi炭窒化物が内在しない実質的なMnS」を多く存在させることができる。 (2) Ti combines with C, S, N, and O to form sulfide, carbon sulfide, carbide, carbonitride, and oxide. Ti has a tendency to form sulfides more easily than Mn, so Ti sulfide and Ti carbon sulfide are easily formed. However, if careful consideration is given to the content balance of Mn, Ti, S and N, a large amount of “substantial Ti carbosulfide or / and Ti sulfide” is not produced, and “Ti carbide or / and Ti There can be many "substantially MnS in which carbonitride is inherent" and "substantially MnS in which Ti carbide and Ti carbonitride are not present".
(3)上記(1)に示した化学組成にして、且つ上記(2)に示すような介在物形態が得られる場合、マトリックス中に存在する介在物は、切削中に軟質化して潤滑効果を発揮する「実質的なMnS」が全介在物の大半を占め、この「実質的なMnS」以外の硫化物、即ち、「実質的なTi硫化物または/およびTi炭硫化物」はほとんどない状態になる。このとき、良好な仕上げ面粗さを得るためには、全介在物の生成量のうちで「実質的なMnS」の生成量がそのほとんどを占めなければならない。具体的には、圧延方向断面の観察面1mm2における円相当直径が1μm以上の「実質的なMnS」の総面積が、円相当直径が1μm以上の全介在物の総面積の8割以上を占める必要がある。この場合に限り、「実質的なTi硫化物または/およびTi炭硫化物」の存在によって引き起こされる工具刃先への構成刃先の生成が抑制され、良好な仕上げ面粗さを得ることができる。 (3) When the inclusion composition as shown in (2) above is obtained with the chemical composition shown in (1) above, the inclusions present in the matrix soften during cutting and have a lubricating effect. “Substantial MnS” exerts the majority of all inclusions, and there is almost no sulfide other than “substantial MnS”, that is, “substantial Ti sulfide or / and Ti carbon sulfide”. become. At this time, in order to obtain a good finished surface roughness, the production amount of “substantially MnS” must occupy most of the production amount of all inclusions. Specifically, the total area of “substantially MnS” with an equivalent circle diameter of 1 μm or more on the observation surface 1 mm 2 in the cross section in the rolling direction is 80% or more of the total area of all inclusions with an equivalent circle diameter of 1 μm or more. Need to occupy . Only in this case, the generation of the component cutting edge on the tool cutting edge caused by the presence of “substantial Ti sulfide or / and Ti carbon sulfide” is suppressed, and good finished surface roughness can be obtained.
上記の「実質的なMnS」とは、一個の介在物に占めるMnSの面積率が50%以上の介在物であり、「Ti炭化物または/およびTi炭窒化物が内在する実質的なMnS」と「Ti炭化物およびTi炭窒化物が内在しない実質的なMnS」からなる。 The above “substantially MnS” is an inclusion whose area ratio of MnS in one inclusion is 50% or more, and “substantially MnS in which Ti carbide or / and Ti carbonitride is contained” It consists of “substantially MnS free of Ti carbide and Ti carbonitride”.
前記のイ式で示すとおり、「8割以上を占める」のは、イ式の「A+B」である。そして、AとBの定義は、圧延方向に平行な断面の1mm2中における円相当直径が1μm以上の硫化物のうち、「Ti炭化物または/およびTi炭窒化物が内在する実質的なMnS」が占める面積および「Ti炭化物およびTi炭窒化物が内在しない実質的なMnS」が占める面積、である。 As shown in the above equation (a), “occupies 80% or more” is the equation (A + B). The definition of A and B is “substantially MnS in which Ti carbide and / or Ti carbonitride is inherent” among sulfides having an equivalent circle diameter of 1 μm or more in 1 mm 2 of a cross section parallel to the rolling direction. And the area occupied by “substantially MnS free of Ti carbide and Ti carbonitride”.
そして、「Ti炭化物または/およびTi炭窒化物が内在する実質的なMnS」、「Ti炭化物およびTi炭窒化物が内在しない実質的なMnS」、「実質的なTi硫化物または/およびTi炭硫化物」およびそれ以外の硫化物、炭硫化物、炭化物、窒化物、酸化物、Al2O3、SiO2等の総面積を合計したものがイ式のCである。 And “substantially MnS containing Ti carbide and / or Ti carbonitride”, “substantially MnS not containing Ti carbide and Ti carbonitride”, “substantial Ti sulfide and / or Ti charcoal” The sum of the total areas of “sulfides” and other sulfides, carbon sulfides, carbides, nitrides, oxides, Al 2 O 3 , SiO 2, etc. is C in formula (a).
(4) 上記(3)で示す様な介在物を含有する鋼材、つまり「実質的なTi硫化物または/およびTi炭硫化物」がほとんど存在せず、鋼中に含有される介在物の大半が「実質的なMnS」であっても、「Ti炭化物または/およびTi炭窒化物を内在する実質的MnS」が存在すれば、切削温度が高くなる高速度域で切削した場合、工具表面に硬質のTiN膜が形成され、工具を保護することによって優れた工具寿命を得ることができる。 (4) Steel materials containing inclusions as shown in (3) above, that is, “substantial Ti sulfide or / and Ti carbon sulfide” hardly exist, and most of the inclusions contained in the steel Is “substantially MnS”, but if “substantially MnS containing Ti carbide and / or Ti carbonitride” exists, when cutting at a high speed range where the cutting temperature is high, A hard TiN film is formed and an excellent tool life can be obtained by protecting the tool.
(5) 「Ti炭化物または/および炭窒化物が内在する実質的MnS」が存在する鋼では、その「実質的なMnS」は、従来のJIS SUM22L〜24Lの複合快削鋼に含まれるMnSに比べて、微細であり、個数が増大する。この場合、これらの微細な「実質的なMnS」が切削中における応力集中の起点となって亀裂伝播を助長し易いために、複合快削鋼と同等以上の切屑処理性を得ることができる。 (5) In steels with “substantially MnS containing Ti carbide and / or carbonitride”, the “substantial MnS” is included in MnS included in conventional free-cutting steels of JIS SUM22L to 24L. Compared with it, it is fine and the number increases. In this case, since these fine “substantially MnS” is a starting point of stress concentration during cutting and facilitates crack propagation, chip treatability equal to or higher than that of the composite free-cutting steel can be obtained.
(6) 「Ti炭化物または/およびTi炭窒化物が内在する実質的なMnS」を存在させた鋼は、熱間加工性に全く問題がないので、被削性改善に有効なS含有量を多くすることが可能であり、その場合においても連続鋳造設備等によって製造するのにも何ら支障をきたさない。また、添加されるTi量も少量で充分な効果を発揮するから、製造にかかるコストも少なくて済み、安価な鋼材として適用可能である。 (6) Steel with “substantially MnS containing Ti carbide and / or Ti carbonitride” has no problem in hot workability. It is possible to increase the number, and even in that case, there is no problem in manufacturing with a continuous casting facility or the like. In addition, since a sufficient amount of Ti is added even if the amount of Ti added is small, the manufacturing cost can be reduced and the steel can be applied as an inexpensive steel material.
前述したように、合金成分の範囲を限定し、介在物の形態を調整すれば、優れた被削性が得られる。しかし、自動車部品に用いられる鋼材は被削性以外に浸炭特性に優れることが望まれる場合がある。そこで、SiおよびCrの鋼の特性への影響を調査した結果、Si量やCr量の調整によって前記の介在物の形態を損なうことなく、従って、鋼材の被削性を劣化させずに、浸炭特性を改善できることが明らかとなった。 As described above, excellent machinability can be obtained by limiting the range of alloy components and adjusting the form of inclusions. However, in some cases, it is desired that steel materials used for automobile parts have excellent carburization characteristics in addition to machinability. Therefore, as a result of investigating the influence of Si and Cr on the steel properties, the carburization was performed without deteriorating the form of the inclusions by adjusting the Si content and Cr content, and therefore without degrading the machinability of the steel material. It became clear that the characteristics could be improved.
SiおよびCrはオーステナイト中に固溶し、鋼の焼入れ性を高めることで、浸炭処理における浸炭深さおよび浸炭層の硬さを増大させる。SiやCr以外に焼入れ性を高める元素としてはMn、Mo、P等もある。しかし、Mnは被削性あるいは熱間加工性の観点からS量に対して充分な量含有させる必要があり、大量の添加を必要とする。この場合、焼入れ性向上のために、さらなるMnの添加はコストが嵩むばかりである。また、Moも鋼の焼入れ性を高めるのに有効ではあるが、MoがSiやCr以上に高価であるために、同等の効果が得られる相当量のMoを添加すると製造コストが嵩む。Pも同じ効果を有するが、添加すると鋼材そのものの硬さを急激に増大させるために被削性を劣化させてしまう。但し、これら元素は、材料コストにとらわれない場合には、被削性や機械的性質を損なわない範囲で添加しても構わない。しかし、被削性を損なわず、且つ安価に製造したい場合には浸炭特性を改善する成分としてはSiおよびCrが望ましい。 Si and Cr are dissolved in austenite to increase the hardenability of the steel, thereby increasing the carburization depth and the hardness of the carburized layer in the carburizing process. In addition to Si and Cr, elements that enhance hardenability include Mn, Mo, and P. However, Mn must be contained in a sufficient amount relative to the amount of S from the viewpoint of machinability or hot workability, and requires a large amount of addition. In this case, in order to improve the hardenability, the addition of Mn further increases the cost. Mo is also effective in enhancing the hardenability of steel, but Mo is more expensive than Si and Cr, so if a considerable amount of Mo that can obtain the same effect is added, the manufacturing cost increases. P has the same effect, but if added, the hardness of the steel material itself is rapidly increased, so that the machinability is deteriorated. However, these elements may be added within a range that does not impair the machinability and mechanical properties when not limited by the material cost. However, Si and Cr are desirable as components for improving carburization characteristics when it is desired to manufacture at low cost without impairing the machinability.
1.「Ti炭化物または/およびTi炭窒化物が内在する実質的なMnS」について
TiはS、C、N、Oと結合してTiSおよびTi4C2S2の化学式で表されるTi硫化物やTi炭硫化物、TiCやTi(CN)、TiN、TiOの化学式で表されるTi炭化物、Ti炭窒化物、Ti窒化物、Ti酸化物といったTi系介在物を形成する。また、TiはMnS中に固溶して(Mn,Ti)Sとして存在する場合もあるが、そのMnS中に固溶するTi量は微量であるから、この硫化物は実質的にMnSである。
1. About "substantially MnS containing Ti carbide and / or Ti carbonitride"
Ti combines with S, C, N, O and is represented by the chemical formula of Ti sulfide and Ti carbon sulfide, TiC, Ti (CN), TiN, and TiO represented by the chemical formula of TiS and Ti 4 C 2 S 2 Ti-based inclusions such as Ti carbide, Ti carbonitride, Ti nitride, and Ti oxide are formed. Ti may be dissolved in MnS and exist as (Mn, Ti) S, but the amount of Ti dissolved in MnS is very small, so this sulfide is substantially MnS. .
一方、Tiは、MnS中に固溶するのではなく、一個の介在物中にMnSとは明白に相分離して存在する場合もある。そのTiは、TiCまたは/およびTi(C,N) という形で、即ち、MnSとは明らかにその組成が異なる形で存在し、その存在形態は一個の硫化物周辺付近に存在する場合やMnS中に取り囲まれる形で存在するなど多種多様である。 On the other hand, Ti may not exist as a solid solution in MnS, but may exist in a single inclusion in an apparent phase separation from MnS. The Ti exists in the form of TiC and / or Ti (C, N), that is, the composition clearly differs from that of MnS, and the existence form exists in the vicinity of one sulfide or MnS. There are various types such as being surrounded by the inside.
図1は、Tiを含む快削鋼中に存在する介在物を模式的に示した図で、(a) が比較例の快削鋼、(b)が本発明の快削鋼である。図1の(a)に示す鋼では、単独に存在するTiの硫化物や炭硫化物、或いは一個の介在物中でMnSと共存している場合にもTiの硫化物や炭硫化物に占める面積率が50%以上であって実質的にTiの硫化物や炭硫化物であるとみなすことができる介在物、即ち、前述の「実質的なTi硫化物または/およびTi炭硫化物」が多く存在している。一方、図1の(b)に示す本発明鋼では、Ti炭化物または/およびTi炭窒化物がMnSの外周部または内部に取り込まれて存在する介在物、即ち、「Ti炭化物または/およびTi炭窒化物が内在する実質的なMnS」および「Ti炭化物およびTi炭窒化物が内在しない実質的なMnS」が多く存在する。 FIG. 1 is a diagram schematically showing inclusions present in free-cutting steel containing Ti. (A) is a free-cutting steel of a comparative example, and (b) is a free-cutting steel of the present invention. The steel shown in FIG. 1 (a) occupies Ti sulfide and carbon sulfide even when coexisting with MnS in a single Ti sulfide or carbon sulfide, or in one inclusion. Inclusions that have an area ratio of 50% or more and can be regarded as substantially Ti sulfide or carbon sulfide, that is, the above-mentioned "substantial Ti sulfide or / and Ti carbon sulfide" There are many. On the other hand, in the steel of the present invention shown in FIG. 1 (b), Ti carbides and / or Ti carbonitrides are included in the outer peripheral portion or inside of MnS, that is, “Ti carbide or / and Ti charcoal”. There are many "substantially MnS in which nitride is inherent" and "substantially MnS in which Ti carbide and Ti carbonitride are not present".
上記の図1の(b)に示す鋼であって、Ti硫化物やTi炭硫化物或いはTi炭化物やTi炭窒化物、Ti窒化物、Ti酸化物およびこれら以外の介在物がMnSと明白に相分離して内在する場合にも、MnSが占める面積率が50%以上であるものは、実質的に一個のMnS、即ち、「実質的なMnS」と判断する。逆に、一個の介在物のうち、これらのTi系介在物或いはその他の成分からなる酸化物、窒化物、炭化物等が占める面積率が50%以上である介在物は、「実質的なMnS」ではなく、実質的に一個のTi系介在物やその他の成分からなる酸化物、窒化物、炭化物等と判断する。 In the steel shown in FIG. 1 (b), Ti sulfide, Ti carbon sulfide, Ti carbide, Ti carbonitride, Ti nitride, Ti oxide and other inclusions are clearly MnS. Even in the case where the phase ratio is inherent in the phase separation, if the area ratio occupied by MnS is 50% or more, it is determined as substantially one MnS, that is, “substantially MnS”. On the contrary, inclusions whose area ratio occupied by oxides, nitrides, carbides, etc. composed of these Ti-based inclusions or other components in one inclusion is 50% or more is “substantially MnS”. Rather, it is determined as an oxide, nitride, carbide, or the like substantially consisting of one Ti-based inclusion or other component.
上記MnSのうち、特にTi炭化物または/およびTi炭窒化物がMnSとは明白に相分離して内在し、MnSが占める面積率が50%以上である介在物を「Ti炭化物または/およびTi炭窒化物が内在する実質的なMnS」と定義する。一方、「Ti炭化物およびTi炭窒化物が内在しない実質的なMnS」とは、Ti炭化物およびTi炭窒化物を除いた上記Ti系介在物、或いはその他の成分からなる酸化物、窒化物、炭化物等の介在物とMnSが一個の介在物中で明白に相分離して存在し、且つMnSが占める面積率50%以上で、実質的にMnSとしての役割を担うMnS、および上記Ti系介在物やその他の成分からなる酸化物、窒化物、炭化物等の介在物が全く存在しないMnSである。つまり、「Ti炭化物または/およびTi炭窒化物が内在する実質的なMnS」と「Ti炭化物およびTi炭窒化物が内在しない実質的なMnS」の合計が、実質的にMnSとみなされる介在物(前記の「実質的なMnS」)の合計を表しており、これ以外の介在物は、Ti硫化物、Ti炭硫化物、Ti炭化物、Ti炭窒化物、Ti窒化物、Ti酸化物といったTi系介在物とその他の元素で構成される酸化物、炭化物および窒化物等である。 Among the above MnS, in particular, Ti carbides and / or Ti carbonitrides are clearly phase-separated from MnS and include inclusions whose area ratio occupied by MnS is 50% or more, “Ti carbides and / or Ti charcoal. It is defined as “substantially MnS in which nitride is inherent”. On the other hand, “substantially MnS without Ti carbide and Ti carbonitride” means that the above Ti-based inclusions excluding Ti carbide and Ti carbonitride, or oxides, nitrides and carbides composed of other components MnS and MnS, which are clearly separated from each other in one inclusion, have an area ratio of 50% or more occupied by MnS, and substantially play a role as MnS, and the above Ti-based inclusions MnS is free from inclusions such as oxides, nitrides and carbides composed of other components. That is, the sum of “substantially MnS containing Ti carbide and / or Ti carbonitride” and “substantially MnS not containing Ti carbide and Ti carbonitride” is considered to be substantially regarded as MnS. (Increased “substantially MnS”), and other inclusions include Ti sulfide, Ti carbon sulfide, Ti carbide, Ti carbonitride, Ti nitride, and Ti oxide. Oxides, carbides, nitrides, and the like composed of system inclusions and other elements.
前述した一個の介在物中に占めるMnSやTi系介在物の面積率は、切削試験に供した丸棒から切り出したミクロ試験片に対してEPMA(電子線マイクロアナライザー)やEDX(エネルギー分散型X線分析装置)等によって面分析及び定量分析を行うことによって把握できる。また、鋼中の「Ti炭化物または/およびTi炭窒化物が内在する実質的なMnS」や「Ti炭化物およびTi炭窒化物が内在しない実質的なMnS」、およびその他の介在物も同様の方法で確認することができ、その総面積や個数も画像解析等による手法によって測定することができる。その際、観察視野面積の合計が1mm2を超えるように複数の視野で測定した場合に、それぞれの介在物の総面積及び個数を1mm2当たりの平均総面積、平均個数に換算すればよい。 The area ratio of MnS and Ti inclusions in one inclusion mentioned above is the EPMA (electron beam microanalyzer) or EDX (energy dispersive X) compared to the micro specimen cut out from the round bar subjected to the cutting test. This can be grasped by performing surface analysis and quantitative analysis using a line analyzer. In addition, “substantially MnS containing Ti carbide and / or Ti carbonitride” or “substantially MnS not containing Ti carbide and Ti carbonitride” in steel, and other inclusions are similarly processed. The total area and number can be measured by a technique such as image analysis. At that time, when measurement is performed with a plurality of visual fields so that the total area of the observation visual field exceeds 1 mm 2 , the total area and the number of each inclusion may be converted into the average total area and the average number per 1 mm 2 .
2.(A+B)/C≧ 0.8とする理由
前記イ式のAは、圧延方向に平行な断面の1mm2中における円相当直径1μm以上の介在物のうち、「Ti炭化物または/およびTi炭窒化物が内在する実質的なMnS」が占める総面積であり、Bは、圧延方向に平行な断面の1mm2中における円相当直径1μm以上の介在物のうち、「Ti炭化物およびTi炭窒化物が内在しない実質的なMnS」が占める総面積である。ここで「円相当直径」とは、一個の介在物の面積を前記の画像解析等の手法によって求め、同じ面積を有する円に換算した時の直径を指す。「円相当直径が1μm以上」と限定するのは、1μm未満の介在物は、被削性に及ぼす影響をほとんど持たないからである。
2. (A + B) /C≧0.8 Reason A in the formula (A) is “inclusion of Ti carbide and / or Ti carbonitride among inclusions having an equivalent circle diameter of 1 μm or more in 1 mm 2 of a cross section parallel to the rolling direction. B is the total area occupied by "substantial MnS", and B is "inclusion of Ti carbide and Ti carbonitride among inclusions having an equivalent circle diameter of 1 µm or more in 1 mm 2 of a cross section parallel to the rolling direction" The total area occupied by “substantially MnS”. Here, “circle equivalent diameter” refers to a diameter when the area of one inclusion is obtained by the above-described technique such as image analysis and converted into a circle having the same area. The reason why the circle-equivalent diameter is limited to 1 μm or more is that inclusions less than 1 μm have almost no effect on machinability.
前記のイ式は、このAとBの合計が、円相当直径1μm以上の全介在物が占める総面積の80%以上必要であることを示している。この範囲であれば良好な被削性を得ることはできるが、更に好ましいのは90%以上である。また、前述したとおりAおよびBで表される以外の介在物とは単独で存在する窒化物、炭化物、酸化物、「実質的なTi硫化物または/およびTi炭硫化物」等を指している。つまり、イ式は、「実質的なMnS」以外のこれら介在物の総面積が、全介在物の占める総面積(イ式のC)の20%未満であることを示している。この総面積が10%未満であれば更に好ましい。 The above-mentioned formula (A) shows that the sum of A and B needs to be 80% or more of the total area occupied by all the inclusions having an equivalent circle diameter of 1 μm or more. Within this range, good machinability can be obtained, but more preferably 90% or more. In addition, as described above, inclusions other than those represented by A and B indicate nitrides, carbides, oxides, “substantial Ti sulfides and / or Ti carbon sulfides” and the like that exist alone. . In other words, the formula (A) indicates that the total area of these inclusions other than “substantial MnS” is less than 20% of the total area occupied by all the inclusions (C in the formula (C)). More preferably, the total area is less than 10%.
被削性向上のために多量のSを含有する鋼にTiを添加すると、TiはMnよりも硫化物形成傾向が強いためにTi硫化物やTi炭硫化物を形成しやすい。しかし、本発明で規定するイ式は、Tiの添加を前提としながらも、Ti硫化物やTi炭硫化物の生成を抑制することを意図している。これは、Ti硫化物やTi炭硫化物は切削中にMnSの擬似的な潤滑効果を阻害するからである。MnSの擬似的な潤滑効果が損なわれると、工具と被削材との間における摩擦力が上昇し、構成刃先が工具刃先に生成するために仕上げ面粗さが劣化すると考えられる。従って、Ti硫化物やTi炭硫化物の生成は抑制しなければならない。つまり、イ式で規定されるように、単独で存在する「実質的なTi硫化物または/およびTi炭硫化物」が鋼中にほとんど存在せず、鋼中に含有される介在物の80%以上を「実質的なMnS」にすると、切削中における擬似的な潤滑効果を得ることができる。 When Ti is added to steel containing a large amount of S to improve machinability, Ti has a tendency to form sulfides more than Mn, so Ti sulfide and Ti carbon sulfide are easily formed. However, the formula (a) defined in the present invention is intended to suppress the formation of Ti sulfide and Ti carbon sulfide while assuming the addition of Ti. This is because Ti sulfide or Ti carbon sulfide inhibits the pseudo lubricating effect of MnS during cutting. When the pseudo lubrication effect of MnS is impaired, it is considered that the frictional force between the tool and the work material is increased, and the finished surface roughness is deteriorated because the constituent cutting edge is generated at the tool cutting edge. Therefore, generation of Ti sulfide and Ti carbosulfide must be suppressed. That is, as defined by the formula (1), “substantial Ti sulfide or / and Ti carbon sulfide” present alone is hardly present in the steel, and 80% of the inclusions contained in the steel. By setting the above to “substantially MnS”, a pseudo lubricating effect during cutting can be obtained.
このように、本発明で規定される鋼の組成範囲に限定され、且つイ式を満たす場合には、仕上げ切削において従来のPb快削鋼や複合快削鋼と同等以上の良好な仕上げ面粗さを得ることができる。一方、本願発明で規定される化学組成の範囲内にあっても、イ式を満たしていなければ、良好な被削性を得ることはできない。 As described above, when the composition range of the steel specified in the present invention is limited and the formula (1) is satisfied, the finish surface roughness is excellent in surface finish, which is equal to or better than that of the conventional Pb free-cutting steel or composite free-cutting steel. You can get it. On the other hand, even within the range of the chemical composition defined in the present invention, good machinability cannot be obtained unless the formula (1) is satisfied.
3.NA≧5とする理由
前記ロ式のNAは「圧延方向に平行な断面の1mm2中における円相当直径1μm以上の介在物のいち、Ti炭化物または/およびTi炭窒化物が内在する実質的なMnSの個数」である。この「Ti炭化物または/およびTi炭窒化物が内在する実質的なMnS」は、前記のとおり、一個の介在物中に占めるMnSの面積率が50%以上のものを指す。そして、この「Ti炭化物または/およびTi炭窒化物が内在する実質的なMnS」は、擬似的な潤滑効果を実質的に損なわないので、構成刃先が形成されがたく、被切削材の仕上げ面粗度が劣化しない。
3. N A ≧ 5 and reason the B-type N A is "circle equivalent diameter 1μm or more inclusions in 1mm 2 in a cross section parallel to the rolling direction, located, Ti carbide and / or Ti carbonitride parenchyma nitride inherent The number of MnS. This “substantially MnS in which Ti carbide or / and Ti carbonitride is inherent” indicates that the area ratio of MnS in one inclusion is 50% or more as described above. This “substantially MnS containing Ti carbide and / or Ti carbonitride” does not substantially impair the pseudo-lubricating effect. Roughness does not deteriorate.
また、「Ti炭化物または/およびTi炭窒化物が内在する実質的なMnS」が存在する鋼を、超硬工具を使用して100m/minを超える高速域で切削した後、その工具表面を詳細に観察すると、工具表面にTiNが形成されていることが判明した。切削中に被削材と接触する工具表面において、Ti系介在物が摩擦による温度上昇に伴って反応、変質して厚さが数μmから数十μmの層状を呈する硬質のTiNが形成されると考えられる。その存在は切削終了後に工具表面の炭素系汚染(油分等)をArスパッタリング等で除去した工具表面に対し、AES(オージェ電子分光)やEPMA(電子線マイクロアナライザー)による面分析および点分析によって確認することができた。それによると、工具に付着したTiNの表面積は被削材と工具との接触面積の10〜80%であって、残りは切削加工時に付着したMnSやFeもしくは付着物のない工具素地であった。この硬質なTiNが工具表面に形成されることによって、工具の熱的拡散摩耗や硬質介在物による機械的な摩耗が抑制され、従来のS快削鋼やPbとの複合快削鋼に比較しても格段に優れた工具寿命が得られるものと考えられる。 In addition, after cutting steel with “substantially MnS containing Ti carbide and / or Ti carbonitride” at a high speed range exceeding 100 m / min using a carbide tool, the tool surface is detailed. When observed, TiN was found to be formed on the tool surface. On the tool surface that comes into contact with the work material during cutting, Ti-based inclusions react and change as the temperature rises due to friction, resulting in the formation of a hard TiN with a thickness of several μm to several tens of μm. it is conceivable that. Its existence is confirmed by surface analysis and point analysis using AES (Auger Electron Spectroscopy) or EPMA (Electron Beam Microanalyzer) on the tool surface after carbon-based contamination (oil content, etc.) has been removed by Ar sputtering after the end of cutting. We were able to. According to it, the surface area of TiN adhering to the tool was 10 to 80% of the contact area between the work material and the tool, and the rest was a tool base without MnS or Fe adhering to the tool or adhering during machining. . By forming this hard TiN on the tool surface, thermal diffusion wear of the tool and mechanical wear due to hard inclusions are suppressed, compared to conventional S free cutting steel and composite free cutting steel with Pb. However, it is considered that a much superior tool life can be obtained.
上記のような効果を得るためには、「Ti炭化物または/およびTi炭窒化物が内在する実質的なMnS」が、圧延方向断面における観察面1mm2中に5個以上、好ましくは10個以上、存在すればよい。 In order to obtain the effect as described above, “substantially MnS containing Ti carbide and / or Ti carbonitride” is 5 or more, preferably 10 or more in 1 mm 2 of the observation surface in the cross section in the rolling direction. It only has to exist.
一方、本願発明で規定される化学組成の範囲内にあっても、ロ式を満たしていなければ良好な被削性を得ることはできない。 On the other hand, even within the range of the chemical composition defined in the present invention, good machinability cannot be obtained unless the formula is satisfied.
Tiを添加してイ式およびロ式を満足する介在物形態とした鋼では、MnSが非常に微細に存在する。即ち、MnSの個数が著しく多い。この微細なMnSは切削時に生成する切屑の応力集中点として作用し、切屑内での亀裂伝播を助長するために切屑処理性が向上する。 MnS is very finely present in steels with inclusions satisfying A and B by adding Ti. That is, the number of MnS is remarkably large. This fine MnS acts as a stress concentration point of chips generated during cutting, and promotes crack propagation in the chips, thereby improving chip disposal.
以上、要するに、「Ti炭化物または/およびTi炭窒化物が内在する実質的なMnS」を鋼中に安定して存在させ、圧延方向断面の観察面1mm2中に5個以上し、圧延方向断面の観察面1mm2中における「Ti炭化物または/およびTi炭窒化物が内在する実質的なMnS」と「Ti炭化物およびTi炭窒化物が内在しない実質的なMnS」の総面積の合計が全介在物総面積の8割以上であれば、上記で示したように、Pb快削鋼や複合快削鋼と同等以上の工具寿命、仕上げ面粗さ及び切屑処理性を得ることができる。より安定してこのような介在物形態を実現し、優れた被削性を有する鋼材を連続鋳造法等によって安価に製造するためには、Mn、Ti、SおよびNの含有量のバランスを考慮する必要がある。具体的には以下のとおりにすればよい。 In short, “substantially MnS containing Ti carbide and / or Ti carbonitride” is stably present in the steel, and 5 or more in 1 mm 2 of the observation surface of the rolling direction section, The total area of “substantially MnS containing Ti carbide and / or Ti carbonitride” and “substantially MnS not containing Ti carbide and Ti carbonitride” in the 1 mm 2 observation surface If it is 80% or more of the total object area, as shown above, tool life, finished surface roughness and chip treatability equivalent to or better than Pb free-cutting steel and composite free-cutting steel can be obtained. Considering the balance of the contents of Mn, Ti, S and N in order to realize such inclusion form more stably and to produce steel materials with excellent machinability at low cost by continuous casting method etc. There is a need to. Specifically, the following may be performed.
(a)Ti(%)/S(%)≦ 0.25
S量に対してTiを多く添加した場合、つまり、質量%比でTi/Sが0.25を超える場合、Ti硫化物やTi炭硫化物が多く存在することになる。その結果、イ式を満たさなくなり、MnSによる擬似的な潤滑効果が損なわれる。この時には切削抵抗が上昇して工具刃先に構成刃先が形成されやすい傾向にあり、その結果、仕上げ切削時の表面粗さが劣化し、加工精度が悪くなる。
(A) Ti (%) / S (%) ≦ 0.25
When a large amount of Ti is added to the amount of S, that is, when Ti / S exceeds 0.25 by mass ratio, a large amount of Ti sulfide or Ti carbon sulfide is present. As a result, the equation (1) is not satisfied, and the pseudo lubricating effect by MnS is impaired. At this time, the cutting resistance is increased, and the component cutting edge tends to be easily formed on the tool cutting edge. As a result, the surface roughness at the time of finish cutting is deteriorated, and the processing accuracy is deteriorated.
逆に、S量に対してTiを微量に添加する場合、つまりそれぞれの質量比でTi/Sが0.25以下である場合、TiはTi炭化物あるいはTi炭窒化物を形成し、「実質的なTi硫化物または/およびTi炭硫化物」は、単独ではほとんど存在しなくなる。 Conversely, when adding a small amount of Ti to the amount of S, that is, when Ti / S is 0.25 or less at each mass ratio, Ti forms Ti carbide or Ti carbonitride, “Sulphides or / and Ti carbosulfides” are hardly present alone.
Ti炭化物やTi炭窒化物は様々な形態で析出するが、一個のMnSに内在される形態で存在する場合がある。そして、「Ti炭化物または/およびTi炭窒化物が内在する実質的なMnS」を含む鋼を、超硬工具を使用して高速域で切削した場合には優れた工具寿命を得ることができる。つまり、単独で存在する「実質的なTi硫化物または/およびTi炭硫化物」の生成を抑えるには、Ti(%)/S(%)を0.25以下に調整すればよい。 Ti carbide and Ti carbonitride precipitate in various forms, but may exist in a form inherent in one MnS. When a steel containing “substantially MnS containing Ti carbide and / or Ti carbonitride” is cut in a high speed region using a carbide tool, an excellent tool life can be obtained. That is, in order to suppress the generation of “substantial Ti sulfide or / and Ti carbon sulfide” existing alone, Ti (%) / S (%) may be adjusted to 0.25 or less.
(b)MnとSの量が原子比で[Mn]/[S]≧1
Sは熱間加工時に割れを誘発する元素である。しかし、原子比、即ち、原子数(モル数)の比にて[Mn]/[S]≧1とした適切な組成を維持すればMnはMnSとして晶出するので、たとえTi(%)/S(%)≦0.25であっても熱間加工性には問題が無い。また、この範囲であれば、例えば連続鋳造による製造を前提としても、熱間加工性に何ら問題が無いためにSを多く添加して、被削性改善に有効なMnSを増加させることが可能であり、且つ高いS含有量であってもイ式およびロ式で表される介在物形態を損なうことはない。
(B) The amount of Mn and S is atomic ratio [Mn] / [S] ≧ 1
S is an element that induces cracking during hot working. However, since Mn crystallizes as MnS if the appropriate composition of [Mn] / [S] ≧ 1 is maintained in the atomic ratio, that is, the ratio of the number of atoms (number of moles), even if Ti (%) / Even if S (%) ≦ 0.25, there is no problem in hot workability. Also, within this range, for example, even with the premise of production by continuous casting, since there is no problem in hot workability, it is possible to increase MnS effective for improving machinability by adding a large amount of S. In addition, even if the S content is high, the inclusion forms represented by the formulas (a) and (b) are not impaired.
[Mn]/[S]<1である場合には、Ti量がS量を超えるように添加しなければFeSがMnSおよびTiSに多く固溶した硫化物が主体となり、熱間加工性を改善することはできない。なお、[Mn]/[S]<1である場合であっても、S量を超える範囲でTiを添加すれば、熱間加工性は改善できる。しかし、その場合にはTiの硫化物生成傾向がMnよりも大きいために主な生成硫化物はMnSでなく、MnSよりも硬質なTi硫化物あるいはTi炭硫化物が主体となる。その場合、前述したように切削時に工具と被削材との間において軟質な硫化物による擬似的な潤滑効果が得られず、切削抵抗が上昇し、仕上げ面粗さが劣化する。つまり、MnとSの量を原子比で[Mn]/[S]≧1とすることは、MnSによる被削性向上の効果を伴わせると同時に良好な熱間延性を得るために望まれる条件である。 When [Mn] / [S] <1, if not added so that Ti content exceeds S content, FeS is mainly composed of sulfides in MnS and TiS, improving hot workability. I can't do it. Even when [Mn] / [S] <1, the hot workability can be improved by adding Ti in a range exceeding the amount of S. However, in this case, since the Ti sulfide generation tendency is larger than that of Mn, the main generated sulfide is not MnS but mainly Ti sulfide or Ti carbon sulfide which is harder than MnS. In this case, as described above, a pseudo lubrication effect due to the soft sulfide is not obtained between the tool and the work material during cutting, and the cutting resistance increases and the finished surface roughness deteriorates. In other words, the amount of Mn and S in terms of atomic ratio [Mn] / [S] ≧ 1 is accompanied by the effect of improving machinability by MnS and at the same time desired conditions for obtaining good hot ductility It is.
(c)Ti(%)/N(%)≧ 1.35
本発明の快削鋼の大きな特徴は、「Ti炭化物または/およびTi炭窒化物が内在する実質的なMnS」を含有していることにある。仮にTi(%)/N(%)<1.35である場合には、この「Ti炭化物または/およびTi炭窒化物が内在する実質的なMnS」を充分に得ることができないことがある。この場合には、添加されたほとんどのTiは凝固の早い段階でTiNとして晶出するため、「Ti炭化物または/およびTi炭窒化物が内在する実質的なMnS」を形成させるのに充分なTiを確保できないものと考えられる。従って、Ti(%)/N(%)が1.35以上であることが望ましく、より安定して「Ti炭化物または/およびTi炭窒化物が内在する実質的なMnS」を得るには、Ti(%)/N(%)を1.5以上とすればよい。
(C) Ti (%) / N (%) ≧ 1.35
A major feature of the free-cutting steel of the present invention is that it contains “substantially MnS containing Ti carbide and / or Ti carbonitride”. If Ti (%) / N (%) <1.35, this “substantially MnS containing Ti carbide and / or Ti carbonitride” may not be sufficiently obtained. In this case, most of the added Ti crystallizes as TiN at an early stage of solidification, so that sufficient Ti is formed to form “substantially MnS in which Ti carbide and / or Ti carbonitride is inherent”. This is considered to be impossible to secure. Therefore, it is desirable that Ti (%) / N (%) is 1.35 or more. To obtain “substantially MnS containing Ti carbide or / and Ti carbonitride” more stably, Ti (% ) / N (%) may be 1.5 or more.
2.化学組成の限定理由
以下、本発明において化学組成を限定した理由を、それぞれの成分の作用効果とともに説明する。
2. Reasons for limiting chemical composition Hereinafter, the reasons for limiting the chemical composition in the present invention will be described together with the effects of the respective components.
C:0.05%から0.20%未満
Cは被削性に大きな影響を及ぼす重要な元素である。C含有量が0.20%以上になると鋼材の強度を高めて被削性を劣化させるので、被削性が重要視される用途の鋼材としては不適当である。但し、0.05%未満では鋼材が軟質になり過ぎ、切削中にむしれを生じてかえって工具摩耗を促進させるうえ、仕上げ面粗度も大きくなる。よってCの適正含有量は、0.05%から0.20%未満である。なお、さらに良い被削性を得るためのC量のより適正な範囲は0.07〜0.18%である。
C: 0.05% to less than 0.20% C is an important element that greatly affects the machinability. When the C content is 0.20% or more, the strength of the steel material is increased and the machinability is deteriorated, so that it is unsuitable as a steel material for use in which machinability is regarded as important. However, if it is less than 0.05%, the steel material becomes too soft, causing flaking during cutting, which in turn promotes tool wear and increases the finished surface roughness. Therefore, the proper content of C is 0.05% to less than 0.20%. In addition, the more suitable range of C amount for obtaining further better machinability is 0.07 to 0.18%.
Mn:0.4〜2.0%
MnはSとともに硫化物系介在物を形成して被削性に大きな影響を及ぼす重要な元素である。0.4%未満では硫化物としての絶対量が不足して満足な被削性を得ることはできない。また、Mnは鋼の焼入れ性を高める元素であるので、優れた浸炭特性を得たい場合には含有量を多くすればよい。但し、MnはSと共にMnSを形成するために、多量のSを含む本発明鋼では多量のMnを含有することが必要となる。浸炭特性を高めるためにMnを添加するとMn含有量が加算されることになるので、製造コストの面からも好ましくない。そこでMn量の上限を2.0%とした。2.0%を超えると、鋼材の強度が上昇して切削抵抗が高くなるのに加え、工具寿命を低下させる。さらに切削抵抗の低減、工具寿命の向上、切り屑処理性の向上、仕上げ面粗度の向上、熱間加工性の改善を図るためにはS量との関係が重要である。なお、これらの性能を確実に得るためにはMn含有量は0.6〜1.8%とすることが好ましい。
Mn: 0.4-2.0%
Mn is an important element that forms sulfide inclusions with S and has a great influence on machinability. If it is less than 0.4%, the absolute amount as a sulfide is insufficient and satisfactory machinability cannot be obtained. Further, since Mn is an element that enhances the hardenability of steel, the content may be increased in order to obtain excellent carburizing characteristics. However, since Mn forms MnS together with S, the steel of the present invention containing a large amount of S needs to contain a large amount of Mn. If Mn is added to enhance the carburizing characteristics, the Mn content is added, which is not preferable from the viewpoint of manufacturing cost. Therefore, the upper limit of Mn content was set to 2.0%. If it exceeds 2.0%, the strength of the steel material increases and the cutting resistance increases, and the tool life is reduced. Furthermore, the relationship with the amount of S is important in order to reduce cutting resistance, improve tool life, improve chip disposal, improve finished surface roughness, and improve hot workability. In order to ensure these performances, the Mn content is preferably 0.6 to 1.8%.
S:0.21〜1.0%
SはMnと共に硫化物を形成して被削性を改善するのに有効な元素である。MnSによる被削性向上効果は、その生成量に応じて向上するのでSの含有量の選定は重要である。0.21%未満では十分な量の硫化物系介在物が得られず、満足な被削性は期待できない。一方、S量は通常ならば0.35%を超えると熱間加工性を劣化させ、鋼塊中央部のS偏析を助長し、鍛造時に割れを誘発するが、適切な組成を維持すればその上限を1.0%まで高めることができる。MnSによる被削性向上のためには更なるSの添加が好ましく、0.35%以上であればより好ましい。より一層の改善には0.40%を超える含有量が更に好ましい。但し、過剰な添加は歩留まりの悪化によるコスト上昇に繋がるため、S含有量の好ましい上限は0.70%である。
S: 0.21 to 1.0%
S is an element effective for improving machinability by forming a sulfide together with Mn. Since the machinability improving effect by MnS is improved according to the amount of production, selection of the S content is important. If it is less than 0.21%, a sufficient amount of sulfide inclusions cannot be obtained, and satisfactory machinability cannot be expected. On the other hand, if the amount of S exceeds 0.35%, hot workability is deteriorated and S segregation in the central part of the steel ingot is promoted, and cracking is induced during forging. Can be increased to 1.0%. In order to improve machinability by MnS, addition of further S is preferable, and 0.35% or more is more preferable. For further improvement, a content exceeding 0.40% is even more preferable. However, excessive addition leads to cost increase due to deterioration of yield, so the preferable upper limit of S content is 0.70%.
Ti:0.002〜0.10%
TiはNやCとともにTi炭化物または/およびTi炭窒化物を形成し、これらが内在するMnSを鋼中に存在させるために重要な必須元素である。前記のとおり、「Ti炭化物または/およびTi炭窒化物が内在する実質的なMnS」が鋼材中に存在すると、超硬工具を用いた高速切削での工具寿命が飛躍的に向上する。このようなMnSを存在させるためには、0.002%以上の含有が必要であるが、これを安定して鋼中に分散させ、仕上げ面粗さを劣化させずに、良好な工具寿命を得るためにはTiの含有量はSやNの含有量とのバランスを考慮する必要がある。また、Ti含有量が0.10%を超えると、「実質的なTi硫化物または/およびTi炭硫化物」が鋼中に存在するために、仕上げ切削における仕上げ面粗度を劣化させる。よって、Tiの上限は0.10%とした。より安定して優れた仕上げ面粗度を得るためには、Ti含有量は0.08%以下であることが好ましい。さらに0.03%未満であれば一層好ましい。
Ti: 0.002-0.10%
Ti forms Ti carbide and / or Ti carbonitride together with N and C, and these are essential elements that are important for the presence of MnS in the steel. As described above, when “substantially MnS containing Ti carbide and / or Ti carbonitride” is present in the steel material, the tool life in high-speed cutting using a cemented carbide tool is dramatically improved. In order to make such MnS exist, the content of 0.002% or more is necessary. In order to stably disperse this in steel and obtain a good tool life without deteriorating the finished surface roughness. Therefore, it is necessary to consider the balance between the Ti content and the S or N content. On the other hand, if the Ti content exceeds 0.10%, “substantial Ti sulfide or / and Ti carbon sulfide” is present in the steel, so that the finished surface roughness in finish cutting is deteriorated. Therefore, the upper limit of Ti is set to 0.10%. In order to obtain a more stable and excellent finished surface roughness, the Ti content is preferably 0.08% or less. Furthermore, it is more preferable if it is less than 0.03%.
一方、Tiの含有量が0.002%未満の場合は、工具寿命を向上させるのに充分な量の「Ti炭化物または/およびTi炭窒化物が内在する実質的なMnS」を生成させることはできない。このMnSをより確実に生成させ、超硬工具寿命を改善させるためには0.01%を超えるTiの含有が望ましい。 On the other hand, when the Ti content is less than 0.002%, it is not possible to produce “substantially MnS containing Ti carbide and / or Ti carbonitride” sufficient to improve the tool life. In order to more reliably generate this MnS and improve the life of the carbide tool, it is desirable that the Ti content exceeds 0.01%.
P:0.001〜0.30%
Pは鋼の焼入れ性を高めると共に、強度も高める。その効果を得るためには、0.001%以上含有させればよい。また、0.30%以下であれば、被削性を劣化させずに、焼入れ性及び強度を確保できるが、含有量が0.30%を超えると強度が高くなりすぎて被削性を劣化させるばかりでなく、鋼塊の偏析を助長して熱間加工性を劣化させる。従って、Pの含有量は0.001〜0.30%とした。なお、良好な被削性と強度を安定して維持するのにより好まししい含有量は0.005〜0.13%である。
P: 0.001 ~ 0.30%
P increases the hardenability of the steel and increases the strength. In order to obtain the effect, 0.001% or more may be contained. In addition, if it is 0.30% or less, hardenability and strength can be secured without degrading machinability, but if the content exceeds 0.30%, the strength becomes too high and machinability is deteriorated. It promotes segregation of steel ingots and degrades hot workability. Therefore, the content of P is set to 0.001 to 0.30%. A more preferable content is 0.005 to 0.13% for stably maintaining good machinability and strength.
Al:0.2%以下(無添加でもよい)
Alは強力な脱酸元素として用いられ、0.2%以下であれば含有されていても良い。しかし脱酸によって生成する酸化物は硬質であって含有量が0.2%を超えると硬質酸化物が大量に生成し、被削性を劣化させる。従って、より好ましいのは0.1%以下とすることである。また、CやMnの添加によって充分な脱酸が可能である場合にはAlは添加しなくてもよく、その含有量は0.002%以下の不純物レベルであってもよい。
Al: 0.2% or less (may not be added)
Al is used as a powerful deoxidizing element, and may be contained as long as it is 0.2% or less. However, the oxide produced by deoxidation is hard, and if the content exceeds 0.2%, a large amount of hard oxide is produced, and the machinability is deteriorated. Therefore, it is more preferable to make it 0.1% or less. Moreover, when sufficient deoxidation is possible by addition of C or Mn, Al may not be added, and the content thereof may be an impurity level of 0.002% or less.
O(酸素):0.001〜0.03%
本発明鋼における酸素の効果は脱酸状態によって損なわれるものではないが、適切な量の酸素を含有させることで、MnS中に固溶して圧延によるMnSの延伸を防ぎ、機械的性質の異方性を改善する。さらに被削性、熱間加工性、S偏析の改善にも有効である。しかし0.03%を超えると溶製時における耐火物の劣損を招く等の支障をきたす。よって酸素含有量の範囲を0.001〜0.03%とした。上記の効果を適切に得るためのより好ましい範囲は0.0015〜0.01%である。
O (oxygen): 0.001 to 0.03%
The effect of oxygen in the steel of the present invention is not impaired by the deoxidized state, but by containing an appropriate amount of oxygen, the solution of MnS by solid solution in MnS is prevented, and mechanical properties differ. Improve directionality. Furthermore, it is effective for improving machinability, hot workability, and S segregation. However, if it exceeds 0.03%, problems such as inferior deterioration of the refractory during melting will occur. Therefore, the range of oxygen content was made 0.001 to 0.03%. A more preferable range for appropriately obtaining the above effect is 0.0015 to 0.01%.
N:0.0005〜0.02%
NはAlやTiと共に硬質な窒化物を形成しやすい。これらの窒化物は結晶粒を微細化する効果を有する。しかし、これらの窒化物が大量に存在することによって工具摩耗が促進されやすく、被削性を劣化させる。本発明鋼にはTiを必須成分として添加するので、Nの含有量は少ないほど好ましいのであるが、前記の効果を得るために0.0005%以上含有させることとした。一方、N含有量が過剰になると粗大なTiNが生成し、被削性を損なう恐れがあるので、Nの上限を0.02%とした。より良い被削性を確保するためには、N量の上限は0.015%であることが好ましい。また、本発明においては「Ti炭化物または/およびTi炭窒化物が内在する実質的なMnS」の存在によって被削性の向上を図っているため、このMnSを安定して鋼中に存在させるためには、TiとNがTi(%)/N(%)≧1.35を満たしていることが好ましい。これは、前記のように、Ti(%)/N(%)<1.35である場合には、添加されたTiのほとんどが凝固の早い段階でTiNとして生成してしまい、「Ti炭化物または/およびTi炭窒化物が内在する実質的なMnS」を安定して得ることができないからである。
N: 0.0005-0.02%
N tends to form a hard nitride together with Al and Ti. These nitrides have the effect of refining crystal grains. However, the presence of a large amount of these nitrides facilitates tool wear and degrades machinability. Since Ti is added as an essential component to the steel of the present invention, the smaller the N content, the better. However, in order to obtain the above effect, 0.0005% or more is included. On the other hand, if the N content is excessive, coarse TiN is generated, which may impair the machinability, so the upper limit of N was set to 0.02%. In order to ensure better machinability, the upper limit of the N content is preferably 0.015%. In the present invention, since the machinability is improved by the presence of “substantially MnS containing Ti carbide and / or Ti carbonitride”, this MnS is stably present in the steel. It is preferable that Ti and N satisfy Ti (%) / N (%) ≧ 1.35. As described above, when Ti (%) / N (%) <1.35, most of the added Ti is generated as TiN at an early stage of solidification, and “Ti carbide or / and This is because the substantial MnS in which Ti carbonitride is inherent cannot be obtained stably.
以上のように含有量をそれぞれ調整された元素で構成される化学組成、およびイ式とロ式で規定される介在物形態によって優れた被削性、熱間加工性および仕上げ面性状を有する低炭素快削鋼を得ることができる。 As described above, the chemical composition composed of the elements whose contents are adjusted respectively, and the inclusion form defined by the formulas (a) and (b) have excellent machinability, hot workability, and finished surface properties. Carbon free-cutting steel can be obtained.
本発明の低炭素快削鋼は、さらに前記第1群から第3群の少なくとも1群の中から選んだ1種以上の成分を含むことができる。 The low-carbon free-cutting steel of the present invention can further contain one or more components selected from at least one of the first group to the third group.
(1)第1群の元素
第1群の元素は、上述の主要組成の他に本発明によって得られる効果を害することなく、鋼の被削性をさらに向上させる元素である。従って、より優れた被削性を得るために、1種以上を含有させても良い。
(1) Element 1 of Group 1 The element of Group 1 is an element that further improves the machinability of steel without harming the effects obtained by the present invention in addition to the main composition described above. Therefore, in order to obtain more excellent machinability, one or more kinds may be contained.
Se:0.0005〜0.10%、Te:0.0005%〜0.10%
SeおよびTeは、Mnと共にMn(S,Se)およびMn(S,Te)を生成する。これらはMnSと同様に切削中に擬似的な潤滑効果の役割を果たすので被削性改善に有効な元素であり、さらなる被削性向上のためには上記の範囲内で含有させても良い。しかし、それぞれの含有量が0.0005%未満では効果に乏しい。一方、Se、Teともにその含有量が0.10%を超えると効果が飽和するばかりでなく、経済的でなくなる上に熱間加工性を劣化させる。より安定して優れた熱間加工性及び被削性を両立させるためには、それぞれ0.0010〜0.05%であることが好ましい。
Se: 0.0005-0.10%, Te: 0.0005% -0.10%
Se and Te generate Mn (S, Se) and Mn (S, Te) together with Mn. These elements are effective elements for improving the machinability since they play a pseudo lubricating effect during cutting, like MnS, and may be contained within the above range for further improving machinability. However, if each content is less than 0.0005%, the effect is poor. On the other hand, when the content of both Se and Te exceeds 0.10%, not only is the effect saturated, but also the workability is deteriorated and the hot workability is deteriorated. In order to achieve both stable and excellent hot workability and machinability, the content is preferably 0.0010 to 0.05%.
Bi:0.01〜0.3%、Sn:0.01〜0.3%
BiとSnは鋼の被削性を改善する効果を有する。これはPbと同じく低融点金属介在物として切削時に潤滑効果を発揮するためと考えられる。その効果を確実に得るためには、それぞれの含有量を0.01%以上とするのがよい。但し、その含有量がそれぞれ0.3%を超えるとその効果が飽和するばかりでなく、熱間加工性を劣化させる。より安定して優れた熱間加工性及び被削性を両立させるためには、それぞれ0.03〜0.1%であることが好ましい。
Bi: 0.01 to 0.3%, Sn: 0.01 to 0.3%
Bi and Sn have the effect of improving the machinability of steel. This is presumably because, like Pb, it exhibits a lubricating effect during cutting as a low melting point metal inclusion. In order to surely obtain the effect, each content is preferably 0.01% or more. However, when the content exceeds 0.3%, not only the effect is saturated but also hot workability is deteriorated. In order to achieve both more stable and excellent hot workability and machinability, the content is preferably 0.03% to 0.1%.
Ca:0.0001〜0.01%
CaはSやO(酸素)に対して大きな親和力を有すので、鋼中で硫化物および酸化物を形成する。また、CaはMnS中に固溶して(Mn,Ca)Sを形成するが、その中に固溶するCaは微量であるため、MnSとしての効果を損なわない。また、Caによって形成される酸化物は低融点酸化物であって、本発明鋼においても被削性をさらに向上させるために有効な添加元素である。Caの添加による被削性改善の効果を確実に得ようとすれば、Ca量の下限は0.0001%であることが好ましい。但し、Caは添加歩留まりが悪いために、Caの含有量を多くするには多量のCaの添加を必要とし、製造コストの面からも好ましくない。従って、Ca含有量の上限は0.01%とした。さらに好ましい上限は0.005%である。
Ca: 0.0001-0.01%
Since Ca has a large affinity for S and O (oxygen), it forms sulfides and oxides in steel. In addition, Ca forms a solid solution in MnS to form (Mn, Ca) S. However, since the amount of Ca that forms a solid solution is very small, the effect as MnS is not impaired. Further, the oxide formed by Ca is a low melting point oxide, and is an effective additive element for further improving the machinability in the steel of the present invention. In order to reliably obtain the effect of improving machinability by the addition of Ca, the lower limit of the Ca content is preferably 0.0001%. However, since Ca has a poor addition yield, a large amount of Ca is required to increase the Ca content, which is not preferable from the viewpoint of manufacturing cost. Therefore, the upper limit of the Ca content is set to 0.01%. A more preferred upper limit is 0.005%.
Mg:0.0001〜0.005%
Mgも鋼中でSやO(酸素)に対して大きな親和力を有するので、硫化物もしくは酸化物を形成する。Mgを含有する硫化物や酸化物はMnSの晶出核として機能し、MnSの延伸を抑制する効果を有する。このような効果を得たい場合にには添加しても良い。その効果を充分に得るためには、Mg量の下限は0.0001%以上であることが好ましい。しかし、Mgによって形成される酸化物は硬質なので、Mgの含有量があまり多ければ被削性を劣化させる要因となる。従ってMgの上限を0.005%とした。更に、MnSの延伸を抑制する効果と優れた被削性を両立させるために好ましい上限は0.002%である。
Mg: 0.0001-0.005%
Since Mg also has a large affinity for S and O (oxygen) in steel, it forms sulfides or oxides. A sulfide or oxide containing Mg functions as a crystallization nucleus of MnS and has an effect of suppressing the stretching of MnS. If such an effect is desired, it may be added. In order to sufficiently obtain the effect, the lower limit of the Mg amount is preferably 0.0001% or more. However, since the oxide formed by Mg is hard, if there is too much Mg content, it will become a factor which degrades machinability. Therefore, the upper limit of Mg is set to 0.005%. Furthermore, the preferable upper limit is 0.002% in order to achieve both the effect of suppressing the stretching of MnS and the excellent machinability.
B:0.0002〜0.02%
Bは、O(酸素)あるいはNと結合し、酸化物、窒化物を形成し、被削性を向上させる効果を有するので必要に応じて添加しても良い。その効果を得るためには、0.0002%以上含有させればよい。より確実にその効果を得るためには0.0010%以上が望ましい。しかし、Bの含有量が0.02%を超えると、その効果が飽和するばかりでなく、熱間加工性を劣化させる。
B: 0.0002-0.02%
B binds to O (oxygen) or N to form oxides and nitrides, and has the effect of improving machinability, so may be added as necessary. In order to obtain the effect, 0.0002% or more may be contained. In order to obtain the effect more reliably, 0.0010% or more is desirable. However, if the B content exceeds 0.02%, not only the effect is saturated, but also hot workability is deteriorated.
希土類元素:0.0005〜0.02%
希土類元素はランタノイドとして分類される元素群である。これを添加する場合には通常これらを主成分とするミッシュメタル等を用いる。本発明における希土類元素の含有量は、希土類元素の中の1種または2種以上の元素の合計量で表す。希土類元素は、酸素と共に酸化物を形成し、Sとも結合して硫化物を形成して、被削性を向上させる。その効果を確実に得るためには、0.0005%以上含有させればよい。しかし、含有量が0.02%を超えると効果は飽和する。また、希土類元素は添加歩留まりが低いので多量に含有させることは経済的ではない。
Rare earth elements: 0.0005-0.02%
Rare earth elements are a group of elements classified as lanthanoids. When this is added, misch metal or the like mainly containing these is usually used. The rare earth element content in the present invention is represented by the total amount of one or more elements in the rare earth elements. The rare earth element forms an oxide together with oxygen and combines with S to form a sulfide, thereby improving machinability. In order to ensure the effect, 0.0005% or more may be contained. However, when the content exceeds 0.02%, the effect is saturated. Moreover, since rare earth elements have a low addition yield, it is not economical to contain a large amount.
(2)第2群の元素
第2群の元素は、いずれも鋼の強度を上げる作用を持つものである。必要に応じて、これらの中の1種以上を含有させることができる。
(2) Element 2 Group 2 All elements of Group 2 have the effect of increasing the strength of steel. If necessary, one or more of them can be contained.
Cu:0.01〜1.0%
Cuは析出強化によって鋼の強度を向上させる効果がある。この効果を得るためにはその含有量を0.01%以上にする必要がある。より確実にその効果を得るためには0.1%以上添加することが望ましい。しかし、含有量が1.0%を超えると熱間加工性の劣化を招いたり、Cuの析出物の粗大化によって前記の効果が飽和するばかりでなく、被削性の低下を招く。
Cu: 0.01-1.0%
Cu has the effect of improving the strength of steel by precipitation strengthening. In order to obtain this effect, the content must be 0.01% or more. In order to obtain the effect more reliably, it is desirable to add 0.1% or more. However, if the content exceeds 1.0%, not only the hot workability is deteriorated but also the above effect is saturated by the coarsening of the Cu precipitates, and the machinability is also lowered.
Ni:0.01〜2.0%
Niには固溶強化によって鋼の強度を向上させる効果がある。この効果を確実に得るためにはその含有量を0.01%以上とすることが好ましい。しかし、2.0%を超えると被削性の劣化を招くと共に熱間加工性も劣化する。
Ni: 0.01-2.0%
Ni has the effect of improving the strength of the steel by solid solution strengthening. In order to reliably obtain this effect, the content is preferably set to 0.01% or more. However, if it exceeds 2.0%, machinability is deteriorated and hot workability is also deteriorated.
Mo:0.01〜0.5%
Moは焼入れ性を高めることができる元素であるが、浸炭特性を向上させるために、SiやCrの添加と同等の効果が得られる相当量のMoを添加するとSiやCr以上に高価であるために、製造コストが嵩む難点がある。しかし、Moは組織を微細化し、靭性を改善する効果も有する。これらの効果を得たい場合には添加しても良い。その効果を確実に得るためには含有量を0.01%以上とすることが望ましい。但し、0.5%を超えると効果が飽和するばかりでなく、鋼の製造コストが上昇する。
Mo: 0.01-0.5%
Mo is an element that can enhance the hardenability, but it is more expensive than Si or Cr if a significant amount of Mo is added to obtain the same effect as the addition of Si or Cr in order to improve carburizing characteristics. However, there is a drawback that the manufacturing cost increases. However, Mo has the effect of refining the structure and improving toughness. If these effects are desired, they may be added. In order to reliably obtain the effect, the content is desirably 0.01% or more. However, if it exceeds 0.5%, not only will the effect be saturated, but the manufacturing cost of steel will increase.
V:0.005〜0.5%
Vは微細な窒化物や炭窒化物として析出し、鋼の強度を向上させる。その効果は0.005%以上の含有により得ることが可能であるが、より確実に効果を得たい場合には、0.01%以上の含有が好ましい。しかし、0.5%を超えると、前記の効果が飽和するばかりでなく、窒化物や炭化物が過剰に生成するために、被削性の低下を招く。
V: 0.005-0.5%
V precipitates as fine nitrides and carbonitrides and improves the strength of the steel. The effect can be obtained with a content of 0.005% or more. However, when the effect is desired to be obtained more reliably, the content is preferably 0.01% or more. However, if it exceeds 0.5%, not only the above effects are saturated, but also nitrides and carbides are generated excessively, leading to a decrease in machinability.
Nb:0.005〜0.5%
Nbは微細な窒化物や炭窒化物として析出し、鋼の強度を向上させる。その効果は0.005%以上の含有により得ることが可能であるが、より確実に効果を得たい場合には、0.01%以上の含有が好ましい。しかし、0.5%を超えると、前記の効果が飽和するばかりでなく、窒化物や炭化物が過剰に生成するために、被削性の低下を招くばかりでなく、経済的でない。
Nb: 0.005-0.5%
Nb precipitates as fine nitrides and carbonitrides and improves the strength of the steel. The effect can be obtained with a content of 0.005% or more. However, when the effect is desired to be obtained more reliably, the content is preferably 0.01% or more. However, if it exceeds 0.5%, not only the above effects are saturated, but also nitrides and carbides are excessively generated, which leads to a decrease in machinability and is not economical.
(3)第3群の元素
第3群の元素は、鋼の浸炭特性を高めたい場合に、その一方または両方を下記の範囲内で含有させてよい元素である。
(3) Group 3 element The group 3 element is an element that may contain one or both of the elements within the following range when it is desired to enhance the carburizing characteristics of the steel.
Si:0.1〜2.0%
請求項1から4までに係る発明の快削鋼では、Siを積極的に添加しない。従って、Siは不純物の一つであり、その含有量は0.1%未満である。なお、請求項1から4までに係る発明の快削鋼でも鋼中の酸素を適度な量にするためSiを脱酸元素として添加する場合があるが、その場合も積極的に残留させる必要はなく、鋼中に残存するSiは不純物であって、0.1%未満である。
Si: 0.1-2.0%
In the free cutting steel of the invention according to claims 1 to 4, Si is not positively added. Therefore, Si is one of impurities, and its content is less than 0.1%. In addition, in the free-cutting steel of the invention according to claims 1 to 4, Si may be added as a deoxidizing element in order to make the oxygen in the steel an appropriate amount. In addition, Si remaining in the steel is an impurity and is less than 0.1%.
また、Siはフェライトに固溶して鋼の強度を向上させると共に、鋼の焼入れ性を高める効果を有する。鋼の焼入れ性を高めることによって、自動車部品として望まれる浸炭特性の向上を図ることができる。その場合に限ってはSiを0.1%以上含有させればよい。より確実に浸炭特性を向上させたい場合には、0.6%を超える含有量が望ましい。但し2.0%を超えると熱間加工性が劣化したり、フェライト相を固溶強化するために切削抵抗が高くなる等、被削性に悪影響を及ぼす。なお、0.1%未満の不純物のレベルであっても、C、Mn、Alの適切な添加で鋼中酸素量が適切な範囲とすることができる。 Moreover, Si has the effect of improving the hardenability of the steel while improving the strength of the steel by dissolving in the ferrite. By improving the hardenability of steel, it is possible to improve the carburizing characteristics desired for automobile parts. Only in that case, Si may be contained by 0.1% or more. When it is desired to improve the carburizing characteristics more reliably, a content exceeding 0.6% is desirable. However, if it exceeds 2.0%, the hot workability deteriorates and the machinability is adversely affected, for example, the cutting resistance increases because the ferrite phase is solid-solution strengthened. Even if the impurity level is less than 0.1%, the amount of oxygen in the steel can be in an appropriate range by appropriate addition of C, Mn, and Al.
Cr:0.03〜1.0%
Crは鋼の焼入れ性を高めるために、少量の添加によって浸炭特性を向上させることのできる元素である。Crを含有した鋼では浸炭特性が改善され、浸炭処理後の浸炭層硬さが高く、有効硬化深さも高めることができる。その効果を得るためには、Crを0.03%以上含有すればよい。また、より確実に浸炭特性を向上させたい場合には、0.05%を超える含有量が望ましい。但し、Cr含有量が1.0%を超えると被削性を劣化させるばかりでなく、製造コストが嵩む。
Cr: 0.03-1.0%
Cr is an element that can improve carburizing characteristics by adding a small amount in order to enhance the hardenability of steel. Steel containing Cr has improved carburizing characteristics, has a high carburized layer hardness after carburizing treatment, and can increase the effective hardening depth. In order to obtain the effect, 0.03% or more of Cr may be contained. Moreover, when it is desired to improve the carburizing characteristics more reliably, a content exceeding 0.05% is desirable. However, if the Cr content exceeds 1.0%, not only the machinability is deteriorated, but also the production cost increases.
上記のSiまたは/およびCrを含有させると、優れた被削性および熱間加工性に加えて優れた浸炭特性を持つ鋼を得ることができる。 When the Si or / and Cr are contained, a steel having excellent carburizing characteristics in addition to excellent machinability and hot workability can be obtained.
1.試料の作製
高周波加熱誘導炉を用いて表1および表2に示す種々の組成を有する150kg鋼塊(直径:約220mm)を作製した。表1に示すのが本発明鋼、表2に示すのが従来鋼または比較鋼である。これらの鋳片を「Ti炭化物または/およびTi炭窒化物が内在する実質的なMnS」を安定して生成させるために、1250℃の高温まで加熱した後、2時間以上保持して1000℃以上で仕上げる鍛造を行い、空冷によって直径65mmの丸棒を得た。その後、この鍛伸材を950℃まで加熱し、1時間保持後、空冷する焼準処理を行った。なお、比較例の鋼No.51〜53は熱間加工性が劣悪であり、鍛造の際に割れが発生して鍛伸材とすることができなかったので、以下の調査を実施していない。
1. Preparation of Samples 150 kg steel ingots (diameter: about 220 mm) having various compositions shown in Tables 1 and 2 were prepared using a high-frequency heating induction furnace. Table 1 shows the steel of the present invention, and Table 2 shows the conventional steel or the comparative steel. In order to stably produce “substantially MnS containing Ti carbide and / or Ti carbonitride”, these slabs are heated to a high temperature of 1250 ° C. and then held for 2 hours or more and 1000 ° C. or more. The forging was finished with, and a round bar with a diameter of 65mm was obtained by air cooling. Thereafter, this forged material was heated to 950 ° C., held for 1 hour, and then subjected to a normalizing process in which it was air-cooled. In addition, the steel No. 51 to 53 of the comparative example is inferior in hot workability, cracks occurred during forging and could not be a forged material, so the following investigation was not conducted .
2.介在物形態の調査
圧延方向に平行な断面で観察される介在物は、加工方向に伸ばされたものや不特定形状のものが多い。介在物の個数や面積の調査に際しては、鍛伸材のDf/4(Df;鍛伸材の直径)部の縦断面方向からミクロ観察用試験片を切り出し、樹脂に埋め込んだ後、鏡面研磨を行って400倍の光学顕微鏡観察にて写真撮影を行い、画像解析等の手法によってその介在物の個数と面積を求めた。その際、同じ面積を有する円に換算した時の直径、円相当直径が1μm以上のものを対象とした。円相当直径が1μm以上に限定したのは、前述のとおり、1μm未満の介在物は被削性に及ぼす効果がほとんどないからである。
2. Investigation of Inclusion Forms Inclusions observed in a cross section parallel to the rolling direction are often elongated in the processing direction or unspecified shapes. When investigating the number and area of inclusions, a specimen for micro observation was cut out from the longitudinal section of the Df / 4 (Df: diameter of forged material) part of forged material, embedded in resin, and then mirror polished. The photograph was taken with an optical microscope of 400 times, and the number and area of the inclusions were obtained by a technique such as image analysis. In that case, the diameter when converted into a circle having the same area and the equivalent circle diameter of 1 μm or more were used. The reason why the equivalent circle diameter is limited to 1 μm or more is that, as described above, inclusions less than 1 μm have little effect on machinability.
また、これらの介在物の組成は、次のようにして確認した。即ち、上記のように鍛伸材のDf/4(Df;鍛伸材の直径)部の縦断面方向から切り出したミクロ試験片を、樹脂に埋め込んだ後、鏡面研磨を行ってEPMA(電子線マイクロアナライザー)やEDX(エネルギー分散型X線分析装置)等によって面分析および定量分析を行った。このときの観察倍率は10000倍を超えない範囲で選べばよく、この観察倍率で一個の介在物中にMnSとTi炭化物または/およびTi炭窒化物が明白に相分離して観察され、かつMnSの面積率が50%以上であることが確認された介在物が「Ti炭化物または/およびTi炭窒化物が内在する実質的なMnS」である。このようにして観察した結果から、円相当直径1μm以上の個々の「Ti炭化物または/およびTi炭窒化物が内在する実質的なMnS」と「Ti炭化物およびTi炭窒化物が内在しない実質的なMnS」の面積を求めた上で、圧延方向断面1mm2におけるこれらの介在物の面積の合計を算出し、さらに、圧延方向断面1mm2における全介在物が占める面積の合計を算出した上で(A+B)/Cを求めた。 The composition of these inclusions was confirmed as follows. That is, as described above, the micro test piece cut out from the longitudinal cross-sectional direction of the Df / 4 (Df: diameter of forged material) part of the forged material is embedded in resin, and then mirror polished to EPMA (electron beam). Surface analysis and quantitative analysis were performed using a microanalyzer) or EDX (energy dispersive X-ray analyzer). The observation magnification at this time may be selected within a range not exceeding 10000 times, and at this observation magnification, MnS and Ti carbide or / and Ti carbonitride are clearly phase-separated and observed in one inclusion, and MnS The inclusion that was confirmed to have an area ratio of 50% or more is “substantially MnS containing Ti carbide and / or Ti carbonitride”. From the results observed in this way, individual “substantially MnS containing Ti carbide and / or Ti carbonitride” having an equivalent circle diameter of 1 μm or more and “substantially free of Ti carbide and Ti carbonitride” after having determined the area of MnS ", it calculates the sum of the areas of these inclusions in the rolling direction cross-section 1 mm 2, further, in order to calculate the total area occupied by all the inclusions in the rolling direction cross-section 1 mm 2 ( A + B) / C was determined.
上記の結果から「Ti炭化物または/およびTi炭窒化物が内在する実質的なMnS」の個数を測定し、圧延方向断面1mm2当たりの平均個数が5個以上存在した鋼については「○」とした。逆に、「Ti炭化物または/およびTi炭窒化物が内在する実質的なMnS」が5個に満たなかった鋼については「×」とした。なお、表2に示す比較例の鋼No.35〜37はTiを含有しないPb快削鋼やS快削鋼であり、実質的に「Ti炭化物または/およびTi炭窒化物が内在する実質的なMnS」が存在しなかったので、これらの算出を行っていない。 Based on the above results, the number of “substantially MnS containing Ti carbide and / or Ti carbonitride” was measured, and “○” was indicated for steels with an average number of 5 or more per 1 mm 2 in the rolling direction. did. On the other hand, “x” was assigned to the steel in which “substantially MnS containing Ti carbide and / or Ti carbonitride” was less than five. In addition, steel Nos. 35 to 37 of comparative examples shown in Table 2 are Pb free cutting steel and S free cutting steel not containing Ti, and substantially “substantially containing Ti carbide and / or Ti carbonitride. Since there was no “MnS”, these calculations were not performed.
3.被削性試験
被削性試験では、前記鍛伸材を直径60mmまで外削した丸棒を用いて、工具寿命と仕上げ表面粗さを調査するための試験を行った。工具寿命試験はコーティング処理が施されていないJISに規定されるP20種の超硬工具を用いて、切削速度;150m/min、送り;0.10mm/rev、切り込み;2.0mmで、乾式の条件で旋削を行い、切削開始から30分後の平均逃げ面摩耗量を測定した。なお、30分以内に平均逃げ面摩耗量が200μm以上に到達した供試材については、その到達時間とその時の平均逃げ面摩耗量(VB)を測定した。
3. Machinability test In the machinability test, a test for investigating the tool life and the finished surface roughness was performed using a round bar obtained by cutting the forged material to a diameter of 60 mm. Tool life test uses P20 class carbide tools specified by JIS without coating treatment, cutting speed: 150m / min, feed: 0.10mm / rev, cutting depth: 2.0mm, under dry conditions Turning was performed, and the average flank wear was measured 30 minutes after the start of cutting. For the specimens whose average flank wear amount reached 200 μm or more within 30 minutes, the arrival time and the average flank wear amount (VB) at that time were measured.
評価は、平均逃げ面摩耗量(VB)が100μmに達する時間を工具寿命の目安として行った。なお、試験途中で耐摩耗性に優れ、摩耗進行速度が極めて小さいために供試材が不足したものについては、旋削時間-工具摩耗曲線から平均逃げ面摩耗量が100μmに達する時間を回帰により算出した。また、切屑処理性はこの時排出された切屑のうち代表的なものを200個採取し、その重量を測定した上で単位重量当たりの個数を算出して評価した。 The evaluation was performed using the time for the average flank wear (VB) to reach 100 μm as a guide for the tool life. For samples with insufficient wear due to excellent wear resistance during the test and extremely low wear progression rate, the time to reach the average flank wear amount of 100 μm from the turning time-tool wear curve is calculated by regression. did. Further, the chip disposability was evaluated by collecting 200 representative chips out of the chips discharged at this time, measuring the weight, and calculating the number per unit weight.
仕上げ面粗さは仕上げ切削後の表面粗さによって評価されるので、以下の条件で切削した後の被削材の表面を触針粗さ計を用いて評価した。切削条件は、TiAlN多層コーティングが施されたJIS K種超硬工具を用いて、切削速度;100m/min、送り;0.05mm/rev、切り込み;0.5mmとし、水溶性エマルジョン型の潤滑油を用いた湿式の条件での旋削とした。供試鋼をこの条件にて1分間切削した後の試験片に対し、触針粗さ計にて軸方向に触針を移動させて平均仕上げ面粗さ(Ra)を測定し、仕上げ面粗さを評価した。 Since the finished surface roughness is evaluated by the surface roughness after finish cutting, the surface of the work material after cutting under the following conditions was evaluated using a stylus roughness meter. Cutting conditions were JIS K class carbide tools with TiAlN multilayer coating, cutting speed: 100m / min, feed: 0.05mm / rev, cutting depth: 0.5mm, and water-soluble emulsion type lubricant was used. Turning was performed under wet conditions. Move the stylus in the axial direction with a stylus roughness meter and measure the average finished surface roughness (Ra) on the test piece after cutting the test steel for 1 minute under these conditions, and the finished surface roughness Was evaluated.
4.熱間加工性試験
熱間加工性は連続鋳造設備による製造条件を模擬するために、前記と同様の手法で作製した150kg鋼塊の表面部に近いDi/8(Di;鋼塊の直径)の位置を中心として、鋼塊高さ方向から直径10mm、長さ130mmの高温引張試験片とし、固定間隔を110mmとした上で直接通電によって1250℃まで加熱し、5分保持した後、10℃/secの冷却速度で1100℃まで冷却して10秒保持した後、歪み速度;10-3/sにて引張試験を行った。その際、破断部の絞りを測定して熱間加工性を評価した。
4). Hot workability test In order to simulate the manufacturing conditions with continuous casting equipment, hot workability is Di / 8 (Di; diameter of steel ingot) close to the surface of 150kg steel ingot produced by the same method as above. A high temperature tensile test piece with a diameter of 10 mm and a length of 130 mm from the height of the steel ingot centered on the position, heated to 1250 ° C by direct energization with a fixed interval of 110 mm, held for 5 minutes, then 10 ° C / After cooling to 1100 ° C. at a cooling rate of sec and holding for 10 seconds, a tensile test was performed at a strain rate of 10 −3 / s. At that time, the hot workability was evaluated by measuring the squeezing of the fractured portion.
5.浸炭試験
浸炭試験は以下のとおりに実施した。即ち、試験片には直径24mm、長さ50mmの円柱状の鋼材を用いた。これは前述の直径65mmの焼準材のR/2の位置から採取した。この試験片を900℃に加熱して浸炭処理し、その後850℃にて拡散処理した。このときの浸炭時の炭素ポテンシャル(C.P.)値は0.8%、処理時間は75分であり、拡散時のC.P.値は0.7%、処理時間は20分である。浸炭処理を終えた試験片を80℃の油中で冷却することにより焼入れ処理を施した。最後に試験片を190℃に加熱し、この温度で60分間保持して焼戻し処理を施した。浸炭性の評価方法は以下のとおりである。
5). Carburization test Carburization test was conducted as follows. That is, a cylindrical steel material having a diameter of 24 mm and a length of 50 mm was used for the test piece. This was taken from the R / 2 position of the normalizing material with a diameter of 65 mm. The test piece was heated to 900 ° C. and carburized, and then diffused at 850 ° C. At this time, the carbon potential (C.P.) value during carburization is 0.8%, the treatment time is 75 minutes, and the C.P. P. The value is 0.7% and the processing time is 20 minutes. The test piece after the carburizing treatment was quenched in oil at 80 ° C. Finally, the test piece was heated to 190 ° C. and kept at this temperature for 60 minutes for tempering treatment. The evaluation method of carburizing property is as follows.
浸炭焼入れ・焼戻し処理した試験片の端から25mmの位置(すなわち長さ方向の中央)の横断面で、表面から内部へのビッカース硬さ分布を測定し、Hv400となる有効硬化深さを求め、その値が従来の鉛複合快削鋼よりも大きいか小さいかを判定した。従来の鉛複合快削鋼は、表2の鋼No.35であり、この有効硬化深さは0.25mmであった。浸炭性の評価としては、有効硬化深さが鋼No.35に対して±0.05mmの場合、すなわち0.20〜0.30mmの場合、同等であるとし、0.20mm未満の場合は劣るとし、0.30mmを超えるとき優れると判定した。その結果を表3および表4に○、×および◎で示す。同等の場合が「○」、劣る場合が「×」、優れる場合が「◎」である。 Measure the Vickers hardness distribution from the surface to the inside at a position 25mm from the end of the carburized and tempered specimen (namely, the center in the length direction), and obtain the effective hardening depth of Hv400. It was judged whether the value was larger or smaller than the conventional lead composite free-cutting steel. The conventional lead composite free-cutting steel is steel No. 35 in Table 2, and this effective hardening depth was 0.25 mm. Carburizability is evaluated in the case where the effective hardening depth is ± 0.05 mm with respect to steel No. 35, that is, 0.20 to 0.30 mm, and is equivalent, and less than 0.20 mm is inferior. When exceeded, it was determined to be excellent. The results are shown in Tables 3 and 4 as ◯, × and ◎. An equivalent case is “◯”, an inferior case is “×”, and an excellent case is “◎”.
以上の試験結果をまとめて示したのが表3および表4である。また、図2にイ式の(A+B)/Cと仕上げ表面粗さの関係、図3に仕上げ面粗さと工具寿命の関係、図4に切屑処理性と工具寿命の関係をそれぞれ示す。 Table 3 and Table 4 collectively show the above test results. FIG. 2 shows the relationship between the formula (A + B) / C and the finished surface roughness, FIG. 3 shows the relationship between the finished surface roughness and the tool life, and FIG. 4 shows the relationship between the chip disposal and the tool life.
表2の鋼No.35および36は複合快削鋼、鋼No.37は硫黄快削鋼で、これまで被削性に最も優れるとされていた鋼である。表3、表4、図2および図3から明らかなように、本発明鋼は工具寿命と仕上げ面粗さが共に優れている。さらに本発明鋼No.1〜34は、優れた熱間加工性を有し、連続鋳造設備等による実用的な製造を模擬した高温引張試験による絞りも表3に示すように複合快削鋼や硫黄快削鋼と同等以上であって何ら問題がない。 Steels No. 35 and 36 in Table 2 are composite free-cutting steels, and steel No. 37 is sulfur free-cutting steels, which have been considered to have the best machinability so far. As is apparent from Tables 3, 4 and 2 and 3, the steel of the present invention is excellent in both tool life and finished surface roughness. Furthermore, the inventive steel Nos. 1 to 34 have excellent hot workability, and as shown in Table 3, the drawing by the high temperature tensile test simulating the practical production by continuous casting equipment etc. It is equal to or better than sulfur free-cutting steel and has no problem.
表1の鋼No.12〜17は浸炭性向上のために、SiおよびCrの少なくとも1種を規定範囲内で含有させたものである。これらの鋼は本発明鋼の中でも特に優れた浸炭特性を示していることがわかる。一方、鋼No.35〜55のように、本発明で規定する介在物の状態や化学組成などの一つでも外れているものは、工具寿命、仕上げ面粗さ、切屑処理性、熱間加工性のうち、少なくとも一つが本発明鋼に比べて劣っている。 Steel Nos. 12 to 17 in Table 1 contain at least one of Si and Cr within a specified range in order to improve carburization. It can be seen that these steels exhibit particularly excellent carburizing characteristics among the steels of the present invention. On the other hand, things such as steel Nos. 35 to 55 that are out of the inclusion state or chemical composition defined in the present invention are tool life, finished surface roughness, chip disposal, hot working At least one of the properties is inferior to the steel of the present invention.
本発明の快削鋼は、Pbを含有しないにもかかわらず、従来のPb快削鋼および複合快削鋼と同等以上の被削性を有し、しかも切削後の仕上げ面性状も優れている。また、Siまたは/およびCrを含むものは優れた浸炭特性をも有する。さらにこの鋼は、熱間加工性にも優れ、連続鋳造法によっても安価に製造できる。Pbを含まないので環境汚染のおそれもない。従って、本発明の快削鋼は、各種機械部品の素材としてきわめて好適な鋼材である。 The free-cutting steel of the present invention has machinability equivalent to or better than conventional Pb free-cutting steel and composite free-cutting steel even though it does not contain Pb, and also has excellent finished surface properties after cutting. . Further, those containing Si or / and Cr also have excellent carburizing characteristics. Furthermore, this steel is excellent in hot workability and can be manufactured at low cost by a continuous casting method. Since Pb is not included, there is no risk of environmental pollution. Therefore, the free-cutting steel of the present invention is a steel material that is extremely suitable as a material for various machine parts.
Claims (5)
(A+B)/C≧0.8・・・・イ
NA≧5・・・・ロ
ここで、A、B、CおよびNAの意味は下記の通りである。
A;圧延方向に平行な断面の1mm2中における円相当直径1μm以上の介在物のうち、Ti炭化物または/およびTi炭窒化物が内在する実質的なMnSが占める総面積。
B;圧延方向に平行な断面の1mm2中における円相当直径1μm以上の介在物のうち、Ti炭化物およびTi炭窒化物が内在しない実質的なMnSが占める総面積。
C;圧延方向に平行な断面の1mm2中における円相当直径1μm以上の全介在物が占める総面積。
NA;圧延方向に平行な断面の1mm2中における円相当直径1μm以上の介在物のうち、Ti炭化物または/およびTi炭窒化物が内在する実質的なMnSの個数。 In mass%, C: 0.05% to less than 0.20%, Mn: 0.4-2.0%, S: 0.21-1.0%, Ti: 0.002-0.10%, P: 0.001-0.30%, Al: 0.2% or less, O (oxygen ): 0.001 to 0.03% and N: 0.0005 to 0.02%, with the balance being steel composed of Fe and impurities, the inclusions contained in the steel satisfy the following formulas (A) and (B): Low carbon free cutting steel.
(A + B) /C≧0.8
N A ≧ 5... B Here, the meanings of A, B, C and N A are as follows.
A: Total area occupied by substantial MnS in which Ti carbide and / or Ti carbonitride is contained in inclusions having an equivalent circle diameter of 1 μm or more in 1 mm 2 of a cross section parallel to the rolling direction.
B: Total area occupied by substantial MnS in which Ti carbide and Ti carbonitride are not present among inclusions having an equivalent circle diameter of 1 μm or more in 1 mm 2 of a cross section parallel to the rolling direction.
C: Total area occupied by all inclusions having a circle-equivalent diameter of 1 μm or more in 1 mm 2 of a cross section parallel to the rolling direction.
N A : The substantial number of MnS in which Ti carbide and / or Ti carbonitride is contained among inclusions having an equivalent circle diameter of 1 μm or more in 1 mm 2 of a cross section parallel to the rolling direction.
(A+B)/C≧0.8・・・・イ
NA≧5・・・・ロ
ここで、A、B、CおよびNAの意味は下記の通りである。
A;圧延方向に平行な断面の1mm2中における円相当直径1μm以上の介在物のうち、Ti炭化物または/およびTi炭窒化物が内在する実質的なMnSが占める総面積。
B;圧延方向に平行な断面の1mm2中における円相当直径1μm以上の介在物のうち、Ti炭化物およびTi炭窒化物が内在しない実質的なMnSが占める総面積。
C;圧延方向に平行な断面の1mm2中における円相当直径1μm以上の全介在物が占める総面積。
NA;圧延方向に平行な断面の1mm2中における円相当直径1μm以上の介在物のうち、Ti炭化物または/およびTi炭窒化物が内在する実質的なMnSの個数。 In mass%, C: 0.05% to less than 0.20%, Mn: 0.4-2.0%, S: 0.21-1.0%, Ti: 0.002-0.10%, P: 0.001-0.30%, Al: 0.2% or less, O (oxygen ): 0.001-0.03% and N: 0.0005-0.02%, and Se: 0.0005-0.10%, Te: 0.0005-0.10%, Bi: 0.01-0.3%, Sn: 0.01-0.3%, Ca: 0.0001- 0.01%, Mg: 0.0001-0.005%, B: 0.0002-0.02%, and rare earth elements: 0.0005-0.02%, one or more selected from the group consisting of steel and the balance consisting of Fe and impurities, A low-carbon free-cutting steel characterized in that inclusions contained therein satisfy the following formulas (a) and (b).
(A + B) /C≧0.8
N A ≧ 5... B Here, the meanings of A, B, C and N A are as follows.
A: Total area occupied by substantial MnS in which Ti carbide and / or Ti carbonitride is contained in inclusions having an equivalent circle diameter of 1 μm or more in 1 mm 2 of a cross section parallel to the rolling direction.
B: Total area occupied by substantial MnS in which Ti carbide and Ti carbonitride are not present among inclusions having an equivalent circle diameter of 1 μm or more in 1 mm 2 of a cross section parallel to the rolling direction.
C: Total area occupied by all inclusions having a circle-equivalent diameter of 1 μm or more in 1 mm 2 of a cross section parallel to the rolling direction.
N A : The substantial number of MnS in which Ti carbide and / or Ti carbonitride is contained among inclusions having an equivalent circle diameter of 1 μm or more in 1 mm 2 of a cross section parallel to the rolling direction.
(A+B)/C≧0.8・・・・イ
NA≧5・・・・ロ
ここで、A、B、CおよびNAの意味は下記の通りである。
A;圧延方向に平行な断面の1mm2中における円相当直径1μm以上の介在物のうち、Ti炭化物または/およびTi炭窒化物が内在する実質的なMnSが占める総面積。
B;圧延方向に平行な断面の1mm2中における円相当直径1μm以上の介在物のうち、Ti炭化物およびTi炭窒化物が内在しない実質的なMnSが占める総面積。
C;圧延方向に平行な断面の1mm2中における円相当直径1μm以上の全介在物が占める総面積。
NA;圧延方向に平行な断面の1mm2中における円相当直径1μm以上の介在物のうち、Ti炭化物または/およびTi炭窒化物が内在する実質的なMnSの個数。 In mass%, C: 0.05% to less than 0.20%, Mn: 0.4-2.0%, S: 0.21-1.0%, Ti: 0.002-0.10%, P: 0.001-0.30%, Al: 0.2% or less, O (oxygen ): 0.001 to 0.03% and N: 0.0005 to 0.02%, and Cu: 0.01 to 1.0%, Ni: 0.01 to 2.0%, Mo: 0.01 to 0.5%, V: 0.005 to 0.5% and Nb: 0.005 to Low steel characterized in that it contains at least one selected from the group consisting of 0.5%, the balance being Fe and impurities, and the inclusions contained in the steel satisfy the following formulas (a) and (b): Carbon free-cutting steel.
(A + B) /C≧0.8
N A ≧ 5... B Here, the meanings of A, B, C and N A are as follows.
A: Total area occupied by substantial MnS in which Ti carbide and / or Ti carbonitride is contained in inclusions having an equivalent circle diameter of 1 μm or more in 1 mm 2 of a cross section parallel to the rolling direction.
B: Total area occupied by substantial MnS in which Ti carbide and Ti carbonitride are not present among inclusions having an equivalent circle diameter of 1 μm or more in 1 mm 2 of a cross section parallel to the rolling direction.
C: Total area occupied by all inclusions having a circle-equivalent diameter of 1 μm or more in 1 mm 2 of a cross section parallel to the rolling direction.
N A : The substantial number of MnS in which Ti carbide and / or Ti carbonitride is contained among inclusions having an equivalent circle diameter of 1 μm or more in 1 mm 2 of a cross section parallel to the rolling direction.
(A+B)/C≧0.8・・・・イ
NA≧5・・・・ロ
ここで、A、B、CおよびNAの意味は下記の通りである。
A;圧延方向に平行な断面の1mm2中における円相当直径1μm以上の介在物のうち、Ti炭化物または/およびTi炭窒化物が内在する実質的なMnSが占める総面積。
B;圧延方向に平行な断面の1mm2中における円相当直径1μm以上の介在物のうち、Ti炭化物およびTi炭窒化物が内在しない実質的なMnSが占める総面積。
C;圧延方向に平行な断面の1mm2中における円相当直径1μm以上の全介在物が占める総面積。
NA;圧延方向に平行な断面の1mm2中における円相当直径1μm以上の介在物のうち、Ti炭化物または/およびTi炭窒化物が内在する実質的なMnSの個数。 In mass%, C: 0.05% to less than 0.20%, Mn: 0.4-2.0%, S: 0.21-1.0%, Ti: 0.002-0.10%, P: 0.001-0.30%, Al: 0.2% or less, O (oxygen ): 0.001-0.03% and N: 0.0005-0.02%, and Se: 0.0005-0.10%, Te: 0.0005-0.10%, Bi: 0.01-0.3%, Sn: 0.01-0.3%, Ca: 0.0001- One or more selected from the group consisting of 0.01%, Mg: 0.0001-0.005%, B: 0.0002-0.02% and rare earth elements: 0.0005-0.02%, Cu: 0.01-1.0%, Ni: 0.01-2.0%, Mo : Steel containing at least one selected from the group consisting of 0.01 to 0.5%, V: 0.005 to 0.5% and Nb: 0.005 to 0.5%, the balance being Fe and impurities, and contained in the steel A low-carbon free-cutting steel characterized in that inclusions satisfy the following formulas A and B:
(A + B) /C≧0.8
N A ≧ 5... B Here, the meanings of A, B, C and N A are as follows.
A: Total area occupied by substantial MnS in which Ti carbide and / or Ti carbonitride is contained in inclusions having an equivalent circle diameter of 1 μm or more in 1 mm 2 of a cross section parallel to the rolling direction.
B: Total area occupied by substantial MnS in which Ti carbide and Ti carbonitride are not present among inclusions having an equivalent circle diameter of 1 μm or more in 1 mm 2 of a cross section parallel to the rolling direction.
C: Total area occupied by all inclusions having a circle-equivalent diameter of 1 μm or more in 1 mm 2 of a cross section parallel to the rolling direction.
N A : The substantial number of MnS in which Ti carbide and / or Ti carbonitride is contained among inclusions having an equivalent circle diameter of 1 μm or more in 1 mm 2 of a cross section parallel to the rolling direction.
The low-carbon free-cutting steel according to any one of claims 1 to 4, which contains one or two of Si: 0.1 to 2.0 mass% and Cr: 0.03 to 1.0 mass%.
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JP2003285463A JP3918787B2 (en) | 2003-08-01 | 2003-08-01 | Low carbon free cutting steel |
TW093119223A TWI247815B (en) | 2003-08-01 | 2004-06-29 | Low-carbon free cutting steel |
KR1020040057909A KR100615465B1 (en) | 2003-08-01 | 2004-07-24 | Low-carbon free cutting steel |
US10/898,963 US20050025658A1 (en) | 2003-08-01 | 2004-07-27 | Low-carbon free cutting steel |
DE602004007730T DE602004007730T2 (en) | 2003-08-01 | 2004-07-30 | Low-carbon free-cutting steel. |
EP04254607A EP1507016B1 (en) | 2003-08-01 | 2004-07-30 | Low-carbon free cutting steel |
CNB2004100588611A CN1306056C (en) | 2003-08-01 | 2004-08-02 | Low-carbon free cutting steel |
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US (1) | US20050025658A1 (en) |
EP (1) | EP1507016B1 (en) |
JP (1) | JP3918787B2 (en) |
KR (1) | KR100615465B1 (en) |
CN (1) | CN1306056C (en) |
DE (1) | DE602004007730T2 (en) |
TW (1) | TWI247815B (en) |
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-
2004
- 2004-06-29 TW TW093119223A patent/TWI247815B/en not_active IP Right Cessation
- 2004-07-24 KR KR1020040057909A patent/KR100615465B1/en not_active IP Right Cessation
- 2004-07-27 US US10/898,963 patent/US20050025658A1/en not_active Abandoned
- 2004-07-30 DE DE602004007730T patent/DE602004007730T2/en not_active Expired - Fee Related
- 2004-07-30 EP EP04254607A patent/EP1507016B1/en not_active Expired - Lifetime
- 2004-08-02 CN CNB2004100588611A patent/CN1306056C/en not_active Expired - Fee Related
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Also Published As
Publication number | Publication date |
---|---|
CN1580312A (en) | 2005-02-16 |
EP1507016A1 (en) | 2005-02-16 |
TW200506071A (en) | 2005-02-16 |
KR20050016017A (en) | 2005-02-21 |
KR100615465B1 (en) | 2006-08-25 |
TWI247815B (en) | 2006-01-21 |
CN1306056C (en) | 2007-03-21 |
DE602004007730T2 (en) | 2008-04-30 |
US20050025658A1 (en) | 2005-02-03 |
JP3918787B2 (en) | 2007-05-23 |
EP1507016B1 (en) | 2007-07-25 |
DE602004007730D1 (en) | 2007-09-06 |
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