JPH11323482A - Grain coarsening resistant case hardening steel material, surface hardened parts excellent in strength and toughness, and their manufacture - Google Patents
Grain coarsening resistant case hardening steel material, surface hardened parts excellent in strength and toughness, and their manufactureInfo
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- JPH11323482A JPH11323482A JP13651298A JP13651298A JPH11323482A JP H11323482 A JPH11323482 A JP H11323482A JP 13651298 A JP13651298 A JP 13651298A JP 13651298 A JP13651298 A JP 13651298A JP H11323482 A JPH11323482 A JP H11323482A
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- steel
- carbosulfide
- machinability
- toughness
- cleanliness
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Abstract
Description
【０００１】[0001]
【発明の属する技術分野】本発明は、肌焼鋼材及び表面
硬化部品と、その表面硬化部品の製造方法に関し、より
詳しくは、被削性に優れた耐粗粒化肌焼鋼材並びに強度
と靭性に優れた表面硬化部品及びその製造方法に関す
る。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a case hardened steel material and a case hardened part, and a method of manufacturing the surface hardened part. More specifically, the present invention relates to a coarse grained case hardened steel excellent in machinability and strength and toughness. And a method of manufacturing the same.
【０００２】[0002]
【従来の技術】従来、自動車用や産業機械用などの各種
機械構造部品、特に歯車を代表とする表面硬化部品は、
肌焼鋼を素材として、これを熱間鍛造や冷間鍛造した後
に切削加工して所望の形状に成形加工し、次いで、耐摩
耗性や疲労強度を向上させる目的で部品表面に浸炭処理
や浸炭窒化処理などの表面硬化処理を施してから使用に
供されている。2. Description of the Related Art Conventionally, various mechanical structural parts such as those for automobiles and industrial machines, especially surface hardened parts represented by gears,
Using case hardened steel as a material, it is hot forged or cold forged, then cut and formed into a desired shape, and then carburized or carburized on the component surface for the purpose of improving wear resistance and fatigue strength. After being subjected to a surface hardening treatment such as nitriding treatment, it is used.
【０００３】表面硬化部品の素材鋼となる機械構造用肌
焼鋼としては、従来、JIS G 4106に規格された機械構造
用マンガン鋼（ＳＭｎ鋼）及びマンガンクロム鋼（ＳＭ
ｎＣ鋼）、JIS G 4105に規格されたクロムモリブデン鋼
（ＳＣＭ鋼）、JIS G 4104に規格されたクロム鋼（ＳＣ
ｒ鋼）、JIS G 4103に規格されたニッケルクロムモリブ
デン鋼（ＳＮＣＭ鋼）、JIS G 4102に規格されたニッケ
ルクロム鋼（ＳＮＣ鋼）などが用いられてきた。[0003] As case hardening steels for machine structures that are used as material steels for surface hardened parts, manganese steels (SMn steels) and manganese chrome steels (SM steels) for machine structures conventionally specified in JIS G 4106 have been used.
nC steel), Chromium molybdenum steel (SCM steel) specified in JIS G 4105, Chromium steel (SC) specified in JIS G 4104
r), nickel chrome molybdenum steel (SNCM steel) specified in JIS G 4103, nickel chrome steel (SNC steel) specified in JIS G 4102, and the like have been used.
【０００４】しかし、前記のＪＩＳ規格鋼を母材として
所定の部品形状に加工された鋼材の場合には、浸炭処理
や浸炭窒化処理などの表面硬化処理時に９００〜９５０
℃の温度に加熱されると結晶粒の粗大化や異常粒成長
（以下、結晶粒の粗大化と異常粒成長をまとめて「粗粒
化」という）が生じ易い。このため、焼入れ時の歪発生
や強度や靭性など材料特性の低下が生ずるという問題が
ある。However, in the case of a steel material processed into a predetermined component shape using the above-mentioned JIS standard steel as a base material, 900 to 950 is required during surface hardening treatment such as carburizing treatment or carbonitriding treatment.
When heated to a temperature of ° C., coarsening of crystal grains and abnormal grain growth (hereinafter, coarsening of crystal grains and abnormal grain growth are collectively referred to as “coarse grain”) are likely to occur. For this reason, there is a problem that distortion occurs during quenching and material properties such as strength and toughness are reduced.
【０００５】このため、従来のＪＩＳ規格鋼に代わっ
て、Ｎｂを添加した鋼、例えば、特開昭６０−２１３５
９号公報に記載のＮｂ添加鋼などが浸炭部品の母材とな
る肌焼鋼として重用されてきた。こうした鋼は、Ｎｂの
添加によって析出した微細なＮｂＣのピン止め効果を利
用することで、浸炭処理や浸炭窒化処理などの表面硬化
処理における加熱時のオーステナイト粒の粗粒化を防止
しようとするものである。既に述べたように、従来の浸
炭処理や浸炭窒化処理などの表面硬化処理は９００〜９
５０℃程度の温度で行われていたために、ＮｂＣのピン
止め効果によって粗粒化を防止することが可能であっ
た。しかしながら、単にＮｂを添加しただけの鋼の場合
には鋼塊（ここでいう「鋼塊」にはJIS G 0203に規定さ
れているように連鋳鋼片（鋳片）を含む）の表面性状が
悪いという問題がある。したがって、鋼片や各種の鋼材
に加工した後に疵が生じるので、疵の手入れをしなけれ
ばならず、この疵手入れのために歩留まりが低下すると
ともにコストが嵩んでいた。For this reason, instead of the conventional JIS standard steel, a steel to which Nb is added, for example, Japanese Patent Application Laid-Open No. 60-2135.
Nb-added steel described in Japanese Patent Publication No. 9 has been heavily used as case hardening steel used as a base material of carburized parts. Such steel aims to prevent coarsening of austenite grains during heating in surface hardening treatments such as carburizing and carbonitriding by utilizing the pinning effect of fine NbC precipitated by the addition of Nb. It is. As described above, the conventional surface hardening treatment such as carburizing treatment or carbonitriding treatment is 900-9.
Since the heating was performed at a temperature of about 50 ° C., coarsening could be prevented by the pinning effect of NbC. However, in the case of steel to which only Nb is simply added, the surface properties of the steel ingot (here, the “steel ingot” includes continuously cast steel slabs (cast slabs) as defined in JIS G 0203) There is a problem of bad. Therefore, flaws occur after processing into billets and various steel materials, so that flaws must be repaired, and the maintenance of the flaws has reduced the yield and increased the cost.
【０００６】更に近年、表面硬化処理の能率を大幅に向
上させるために、所謂「プラズマ浸炭処理」など高温で
の表面硬化処理が採用されるようになってきた。この
「プラズマ浸炭処理」は、１０５０℃もの高温で浸炭処
理を行うものであり、こうした高温に加熱される場合に
は、前記の単にＮｂを添加しただけの鋼では粗粒化を防
止することは不可能であった。すなわち、１０５０℃で
のプラズマ浸炭処理時には、従来の９００〜９５０℃程
度の処理の場合には粗粒化防止に有効であったＮｂＣが
凝集・粗大化してしまい、ピン止め効果を充分に発揮す
ることができないからである。In recent years, in order to greatly improve the efficiency of the surface hardening treatment, a surface hardening treatment at a high temperature such as a so-called "plasma carburizing treatment" has been adopted. This "plasma carburizing treatment" is to carry out carburizing treatment at a temperature as high as 1050 ° C. When heated to such a high temperature, it is impossible to prevent coarsening of steel simply added with Nb. It was impossible. That is, at the time of plasma carburizing treatment at 1050 ° C., NbC, which was effective in preventing the coarsening in the case of the conventional treatment at about 900 to 950 ° C., is agglomerated and coarsened, and exhibits a sufficient pinning effect. Because they cannot do it.
【０００７】そこで、例えば特開平４−１７６８１６号
公報に記載されているような、Ｎｂと、Ｔｉ及び／又は
Ｖとを複合添加した浸炭用鋼が提案されている。しか
し、前記公報に記載されているような単に、Ｎｂと、Ｔ
ｉ及び／又はＶとを複合添加しただけの浸炭用鋼の場合
には、浸炭時に粗粒化が生じてしまう場合もあった。[0007] Therefore, a carburizing steel in which Nb and Ti and / or V are added in a combined manner, as described in, for example, JP-A-4-176816, has been proposed. However, simply as described in the above publication, Nb and T
In the case of a carburizing steel in which only i and / or V are added in a complex manner, coarsening may occur during carburizing.
【０００８】又、近年、機械構造部品の高強度化に伴っ
て、熱間鍛造や冷間鍛造した後に所望の形状に成形する
ための切削加工のコストが嵩むという問題が生じてい
る。このため、切削加工を容易にし、低コスト化を図る
ために被削性に優れた快削肌焼鋼に対する要求がますま
す大きくなっている。In recent years, with the increase in strength of mechanical structural parts, there has been a problem that the cost of cutting for forming into a desired shape after hot forging or cold forging has increased. For this reason, there is an increasing demand for free-cutting case hardened steel having excellent machinability in order to facilitate cutting and reduce costs.
【０００９】従来、被削性を高めるために、鋼にＰｂ、
Ｔｅ、Ｂｉ、Ｃａ及びＳなどの快削元素を単独あるいは
複合添加することが行われてきた。しかし、ＪＩＳ規格
鋼である機械構造用鋼や、前記した特開昭６０−２１３
５９号公報に記載のＮｂ添加鋼や、特開平４−１７６８
１６号公報に記載されているような、Ｎｂと、Ｔｉ及び
／又はＶとを複合添加した浸炭用鋼などに、単に上記の
快削元素を添加しただけの場合には、所望の機械的性
質、なかでも靭性を確保できないことが多い。Conventionally, in order to improve machinability, Pb,
Free-cutting elements such as Te, Bi, Ca and S have been used alone or in combination. However, JIS standard steel for machine structural use and the aforementioned Japanese Patent Application Laid-Open No.
No. 59, JP-A-4-1768
In the case where the above-mentioned free-cutting element is simply added to a carburizing steel or the like to which Nb and Ti and / or V are added in combination, as described in JP-A-16, desired mechanical properties In particular, in many cases, toughness cannot be ensured.
【００１０】鉄と鋼（ｖｏｌ．５７（１９７１年）Ｓ４
８４）には、脱酸調整快削鋼にＴｉを添加すれば被削性
が高まる場合のあることが報告されている。しかし、Ｔ
ｉの多量の添加はＴｉＮが多量に生成することもあって
工具摩耗を増大させ、被削性の点からは好ましくないこ
とも述べられている。例えば、Ｃ：０．４５％、Ｓｉ：
０．２９％、Ｍｎ：０．７８％、Ｐ：０．０１７％、
Ｓ：０．０４１％、Ａｌ：０．００６％、Ｎ：０．００
８７％、Ｔｉ：０．２２８％、Ｏ：０．００４％及びＣ
ａ：０．００１％を含有する鋼では却ってドリル寿命が
低下して被削性が劣っている。このように、鋼に単にＴ
ｉを添加するだけでは被削性は向上するものではない。[0010] Iron and steel (vol. 57 (1971) S4)
84) reports that the addition of Ti to deoxidized adjusted free-cutting steel may enhance machinability. But T
It is also described that the addition of a large amount of i increases tool wear due to generation of a large amount of TiN, and is not preferable from the viewpoint of machinability. For example, C: 0.45%, Si:
0.29%, Mn: 0.78%, P: 0.017%,
S: 0.041%, Al: 0.006%, N: 0.00
87%, Ti: 0.228%, O: 0.004% and C
a: In the steel containing 0.001%, the drill life is rather shortened and the machinability is inferior. Thus, simply adding T to the steel
Just adding i does not improve machinability.
【００１１】又、硫黄快削鋼の硫化物形態制御の目的で
Ｚｒが添加されることがあるが、例えば、鉄と鋼（ｖｏ
ｌ．６２（１９７６年）ｐ．８８５）に記されているよ
うに、Ｚｒは被削性に対してはほとんど影響を及ぼさな
い。つまり、鋼に単にＺｒを添加するだけでは被削性は
向上するものではない。In some cases, Zr is added for the purpose of controlling the sulfide form of the sulfur free-cutting steel.
l. 62 (1976) p. 885), Zr has little effect on machinability. That is, the machinability is not improved simply by adding Zr to steel.
【００１２】[0012]
【発明が解決しようとする課題】本発明は上記現状に鑑
みなされたもので、充分な強度−靭性バランスを有し
て、過酷な環境下での使用に充分耐え得る表面硬化部品
及びその素材となる耐粗粒化肌焼鋼材と、その表面硬化
部品の製造方法を提供することを目的とする。なかで
も、本発明は、鋼材表面の温度が１０５０℃にも到るよ
うなプラズマ浸炭処理を初めとする高い温度での表面硬
化処理を受ける場合にも粗粒化を生ずることがなく、熱
処理歪の小さい高強度・高靭性の表面硬化部品と、その
素材となる鋼塊の表面性状が良好で且つ被削性にも優れ
た耐粗粒化肌焼鋼材及びその表面硬化部品の製造方法を
提供することを目的とする。DISCLOSURE OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and provides a surface-hardened component having a sufficient strength-toughness balance and sufficient durability to be used in a severe environment, and a material therefor. It is an object of the present invention to provide a coarse-grained case hardened steel material and a method for producing a surface-hardened component thereof. In particular, the present invention does not cause coarsening even when subjected to high-temperature surface hardening treatment such as plasma carburizing treatment in which the steel material surface temperature reaches 1050 ° C. Provided is a high-strength, high-toughness surface-hardened part with a low hardness, a coarse-grained case-hardened steel material with good surface properties of a steel ingot and excellent machinability, and a method for producing the surface-hardened part The purpose is to do.
【００１３】なお、本発明でいう「耐粗粒化鋼材」と
は、「JIS G 0551の表１に示されるオーステナイト結晶
粒度番号５以上の整細粒鋼材」のことを指す。The term "coarse-grained steel" in the present invention refers to "fine-grained steel having an austenite grain size of 5 or more shown in Table 1 of JIS G 0551".
【００１４】[0014]
【課題を解決するための手段】本発明の要旨は、下記
（１）に示す化学組成を有する被削性に優れた耐粗粒化
肌焼鋼材、（２）に示す強度と靭性に優れた表面硬化部
品及び（３）、（４）に示す強度と靭性に優れた表面硬
化部品の製造方法にある。The gist of the present invention is to provide a coarse-grained case hardened steel material having the following chemical composition (1) and excellent machinability, and excellent strength and toughness (2). The present invention relates to a method for producing a surface-hardened part and a surface-hardened part having excellent strength and toughness described in (3) and (4).
【００１５】（１）重量％で、Ｃ：０．１〜０．３％、
Ｓｉ：０．０１〜０．５％、Ｍｎ：０．６〜２．０％、
Ｐ：０．０３％以下、Ｓ：０．００２〜０．２％、Ｎ
ｂ：０．００５〜０．１０％、Ｔｉ：１．０％以下、Ｚ
ｒ：１．０％以下で、且つ、Ｔｉ（％）＋Ｚｒ（％）：
０．０４〜１．０％、Ｎ：０．００２〜０．００８％、
Ｃｒ：０〜２．０％、Ｍｏ：０〜１．０％、Ｗ：０〜
１．０％及びＡｌ：０〜０．１０％を含み、下記式で
表されるｆｎ１の値が０％を超え、残部はＦｅ及び不可
避不純物の化学組成で、更に、鋼中のＴｉ炭硫化物及び
Ｚｒ炭硫化物の最大直径が１０μｍ以下で、且つ、その
量の和が清浄度で０．０５％以上である被削性に優れた
耐粗粒化肌焼鋼材。(1) By weight%, C: 0.1-0.3%,
Si: 0.01 to 0.5%, Mn: 0.6 to 2.0%,
P: 0.03% or less, S: 0.002 to 0.2%, N
b: 0.005 to 0.10%, Ti: 1.0% or less, Z
r: 1.0% or less, and Ti (%) + Zr (%):
0.04 to 1.0%, N: 0.002 to 0.008%,
Cr: 0 to 2.0%, Mo: 0 to 1.0%, W: 0 to 0%
1.0% and Al: 0 to 0.10%, the value of fn1 represented by the following formula exceeds 0%, and the balance is the chemical composition of Fe and unavoidable impurities. A coarse-grained case hardening steel excellent in machinability, wherein the maximum diameter of the material and Zr carbosulfide is 10 μm or less, and the sum of the amounts is 0.05% or more in cleanliness.
【００１６】 ｆｎ１＝Ｔｉ（％）＋Ｚｒ（％）−１．２Ｓ（％）・・・・ （２）上記（１）に記載の化学組成、大きさ及び量のＴ
ｉ炭硫化物とＺｒ炭硫化物を備え、更に、芯部硬度がＨ
ｖ３００以上、衝撃値が２０Ｊ／ｃｍ2 以上である表面
硬化部品。Fn1 = Ti (%) + Zr (%)-1.2S (%) (2) T of the chemical composition, size and amount described in the above (1)
i Carbosulfide and Zr carbosulfide, and the core hardness is H
Surface-hardened parts with v300 or more and an impact value of 20 J / cm 2 or more.
【００１７】（３）上記（１）に記載の鋼材を、表面硬
化処理に先立って１１５０℃以上に加熱してから熱間鍛
造することによる表面硬化部品の製造方法。(3) A method of manufacturing a surface-hardened part by heating the steel material according to the above (1) to 1150 ° C. or more before hot-hardening and then hot forging.
【００１８】（４）上記（１）に記載の鋼材を、分塊、
圧延及び熱処理の少なくとも１つの工程を１１５０℃以
上に加熱して行い、その後鍛造し、更に表面硬化処理す
ることによる表面硬化部品の製造方法。(4) The steel material according to the above (1),
A method for producing a surface-hardened component by performing at least one step of rolling and heat treatment at a temperature of 1150 ° C. or higher, forging, and further performing a surface hardening treatment.
【００１９】以下、上記（１）〜（４）に記載のものを
（１）〜（４）の発明ということがある。Hereinafter, the inventions described in the above (1) to (4) may be referred to as the inventions (1) to (4).
【００２０】なお、本発明でいう「Ｔｉ炭硫化物」には
単なるＴｉ硫化物を、又、「Ｚｒ炭硫化物」には単なる
Ｚｒ硫化物をそれぞれ含むものとする。又、「（Ｔｉ及
びＺｒの炭硫化物の）最大直径」とは「個々のＴｉ及び
Ｚｒの炭硫化物における最も長い径」のことを指す。Ｔ
ｉ炭硫化物の清浄度やＺｒ炭硫化物の清浄度は、光学顕
微鏡の倍率を４００倍として、JIS G 0555に規定された
「鋼の非金属介在物の顕微鏡試験方法」によって６０視
野測定した値をいう。In the present invention, "Ti carbosulfide" includes simple Ti sulfide, and "Zr carbosulfide" includes simple Zr sulfide. Also, the "maximum diameter (of Ti and Zr carbosulfides)" refers to "the longest diameter of individual Ti and Zr carbosulfides." T
i The cleanliness of carbosulfides and Zr carbosulfides were measured in 60 fields of view using the “microscope test method for nonmetallic inclusions in steel” specified in JIS G 0555, with the magnification of an optical microscope set to 400 times. Value.
【００２１】表面硬化部品の芯部とは表面硬化処理を受
けても硬化していない部分のことをいう。又、衝撃値は
ＪＩＳ３号シャルピー衝撃試験片を用いて常温（室温）
で衝撃試験した場合のものをいう。The core of the surface-hardened part means a part that has not been hardened even after undergoing a surface hardening treatment. The impact value was measured at room temperature (room temperature) using a JIS No. 3 Charpy impact test piece.
It refers to the one when the impact test was performed.
【００２２】（４）の発明における鍛造は、熱間、温
間、冷間のいずれかで行われるもの、又は、これらを組
み合わせたものを指す。The forging in the invention (4) refers to a forging performed during any of hot, warm and cold, or a combination thereof.
【００２３】本発明者らは、プラズマ浸炭処理を初めと
する高い温度での表面硬化処理時にも粗粒化を防止する
ことができるように、１０５０℃でも成長・凝集せず微
細に分散している析出物について調査・研究を行った。The inventors of the present invention have made it possible to prevent coarsening even during surface hardening treatment at a high temperature such as plasma carburizing treatment, so that they are not dispersed and grown at 1050 ° C. Investigations and research were conducted on the precipitates.
【００２４】その結果、ＮｂとＴｉやＺｒとを複合添加
した鋼において、ＮｂとＴｉの複合炭窒化物〔ＮｂＴｉ
（ＣＮ）〕やＮｂとＺｒの複合炭窒化物〔ＮｂＺｒ（Ｃ
Ｎ）〕が１０５０℃でも成長・凝集せず、微細に分散し
ている場合があることがわかった。As a result, in a steel in which Nb and Ti or Zr are added in a complex manner, a composite carbonitride of Nb and Ti [NbTi
(CN)] or a composite carbonitride of Nb and Zr [NbZr (C
N)] did not grow and agglomerate even at 1050 ° C., but was finely dispersed in some cases.
【００２５】そこで本発明者らは更に詳細な研究を続
け、その結果、次の知見を得るに到った。Therefore, the present inventors continued further detailed research, and as a result, came to the following knowledge.
【００２６】（ａ）ＮｂとＴｉやＺｒとを複合添加した
鋼において凝固時に析出する炭窒化物はＮｂＣ、ＴｉＣ
やＺｒＣ、ＮｂＮ、ＴｉＮやＺｒＮ、Ｎｂ（ＣＮ）及び
Ｔｉ（ＣＮ）やＺｒ（ＣＮ）といった単独元素の炭化
物、窒化物や炭窒化物ではなく、ＮｂとＴｉやＺｒの複
合炭窒化物である〔ＮｂＴｉ（ＣＮ）〕や〔ＮｂＺｒ
（ＣＮ）〕である。しかし、凝固時に析出した〔ＮｂＴ
ｉ（ＣＮ）〕や〔ＮｂＺｒ（ＣＮ）〕は粗大であるの
で、粗粒化防止のためのピン止め作用を有しない。(A) In a steel in which Nb and Ti or Zr are added in combination, carbonitrides precipitated during solidification are NbC, TiC
Nb, Ti, ZrN, Nb (CN), Ti (CN), Zr (CN), and other single elements such as carbides, nitrides, and carbonitrides. [NbTi (CN)] or [NbZr
(CN)]. However, it precipitated during solidification [NbT
Since i (CN)] and [NbZr (CN)] are coarse, they do not have a pinning action for preventing coarsening.
【００２７】（ｂ）複合炭窒化物〔ＮｂＴｉ（ＣＮ）〕
や〔ＮｂＺｒ（ＣＮ）〕の固溶と加熱温度（Ｔ）の関係
については以下のとおりである。(B) Composite carbonitride [NbTi (CN)]
The relationship between the solid solution of [NbZr (CN)] and the heating temperature (T) is as follows.
【００２８】（イ）Ｔ＜１１５０℃の場合：上記の複合
炭窒化物は鋼中で安定に存在する。(A) When T <1150 ° C .: The above-mentioned composite carbonitride exists stably in steel.
【００２９】（ロ）１１５０℃≦Ｔ≦１３５０℃の場
合：上記の複合炭窒化物のＮｂだけが固溶し、炭窒化物
中にＴｉやＺｒが濃化する。(B) In the case of 1150 ° C. ≦ T ≦ 1350 ° C .: Only Nb of the above composite carbonitride forms a solid solution, and Ti and Zr are concentrated in the carbonitride.
【００３０】（ハ）１３５０℃＜Ｔの場合：上記の複合
炭窒化物は完全に固溶する（Ｔｉ、Ｚｒも固溶する）。(C) When 1350 ° C. <T: The above composite carbonitride is completely dissolved (Ti and Zr are also dissolved).
【００３１】（ｃ）表面硬化処理の前に素材鋼及び／又
は表面硬化部品が１１５０℃以上の温度域に加熱される
と、凝固時に析出した粗大な〔ＮｂＴｉ（ＣＮ）〕や
〔ＮｂＺｒ（ＣＮ）〕が固溶するとともに、その後の冷
却過程、あるいは冷却後に行われる処理の加熱過程で
〔ＮｂＴｉ（ＣＮ）〕や〔ＮｂＺｒ（ＣＮ）〕が微細に
再析出し、そのピン止め効果で表面硬化処理時の異常粒
成長を防止することができる。なお、複合炭窒化物〔Ｎ
ｂＴｉ（ＣＮ）〕や〔ＮｂＺｒ（ＣＮ）〕が完全に固溶
しなくても、複合炭窒化物中のＮｂが優先的に固溶しさ
えすれば、その後の冷却過程、あるいは冷却後に行われ
る処理の加熱過程で〔ＮｂＴｉ（ＣＮ）〕や〔ＮｂＺｒ
（ＣＮ）〕が微細に再析出する。(C) When the material steel and / or the surface-hardened component are heated to a temperature range of 1150 ° C. or higher before the surface hardening treatment, coarse [NbTi (CN)] or [NbZr (CN) )] Forms a solid solution, and [NbTi (CN)] and [NbZr (CN)] are finely reprecipitated in the subsequent cooling process or in the heating process of the process performed after the cooling, and the surface is hardened by its pinning effect. Abnormal grain growth during processing can be prevented. In addition, composite carbonitride [N
Even if bTi (CN)] and [NbZr (CN)] do not completely dissolve, as long as Nb in the composite carbonitride preferentially forms a solid solution, the subsequent cooling process or after the cooling is performed. [NbTi (CN)] or [NbZr
(CN)] is finely reprecipitated.
【００３２】（ｄ）表面硬化処理後、Ｈｖ３００以上の
芯部硬度と２０Ｊ／ｃｍ2 以上の衝撃値を有すれば、そ
の表面硬化部品は自動車や産業機械が使用される過酷な
環境においても充分な耐久性を示す。(D) After the surface hardening treatment, if the core has a core hardness of Hv 300 or more and an impact value of 20 J / cm 2 or more, the surface hardened part is sufficient even in a harsh environment where automobiles and industrial machines are used. High durability.
【００３３】（ｅ）鋼に適正量のＴｉやＺｒを添加し、
鋼中の介在物制御として硫化物をＴｉ炭硫化物やＺｒ炭
硫化物に変え、こうした炭硫化物を微細に分散させれ
ば、鋼材の被削性が飛躍的に向上する。そこで、更に研
究を続けた結果、下記の事項を見いだした。(E) adding an appropriate amount of Ti or Zr to steel,
If the sulfides are changed to Ti carbosulfides or Zr carbosulfides to control inclusions in the steel, and these carbosulfides are finely dispersed, the machinability of the steel material is dramatically improved. Therefore, as a result of further research, the following matters were found.
【００３４】（ｆ）Ｓとのバランスを考慮して鋼にＴｉ
とＺｒのいずれかを積極的に添加して行くと、鋼中にＴ
ｉ炭硫化物あるいはＺｒ炭硫化物が形成され、Ｔｉ及び
Ｚｒを添加すると、鋼中にはＴｉ炭硫化物とＺｒ炭硫化
物とが形成される。(F) Considering the balance with S, Ti
When either of Zr and Zr is actively added, T
i carbosulfide or Zr carbosulfide is formed, and when Ti and Zr are added, Ti carbosulfide and Zr carbosulfide are formed in the steel.
【００３５】（ｇ）鋼中に上記したＴｉ炭硫化物やＺｒ
炭硫化物が生成すると、ＭｎＳの生成量が減少する。(G) The above-mentioned Ti carbosulfide or Zr in steel
When the carbosulfide is formed, the amount of MnS generated decreases.
【００３６】（ｈ）鋼中のＳ含有量が同じ場合には、Ｔ
ｉ炭硫化物やＺｒ炭硫化物はＭｎＳよりも大きな被削性
改善効果を有する。これは、Ｔｉ炭硫化物やＺｒ炭硫化
物の融点がＭｎＳのそれよりも低いため、切削加工時に
工具のすくい面での潤滑作用が大きくなることに基づ
く。(H) When the S content in steel is the same, T
i carbosulfide and Zr carbosulfide have a greater machinability improvement effect than MnS. This is based on the fact that the melting point of Ti carbosulfide or Zr carbosulfide is lower than that of MnS, so that the lubricating action on the rake face of the tool during cutting is increased.
【００３７】（ｉ）Ｔｉ炭硫化物やＺｒ炭硫化物の効果
を充分発揮させるためには、Ｎ含有量を低くすることが
重要である。これは、Ｎ含有量が多いとＴｉＮやＺｒＮ
としてＴｉやＺｒが固定されてしまい、Ｔｉ炭硫化物や
Ｚｒ炭硫化物の生成が抑制されてしまうためである。(I) In order to sufficiently exert the effects of Ti carbosulfide and Zr carbosulfide, it is important to lower the N content. This is because when the N content is large, TiN or ZrN
This is because Ti and Zr are fixed, and the production of Ti carbosulfide and Zr carbosulfide is suppressed.
【００３８】（Ｊ）製鋼時に生成したＴｉ炭硫化物やＺ
ｒ炭硫化物は、通常の熱間加工のための加熱温度及びプ
ラズマ浸炭処理を初めとする高温の表面硬化処理におけ
る１０５０℃程度の温度では基地に固溶しないし、凝集
もしない。したがって、オーステナイト領域において所
謂「ピン止め作用」が発揮されるので、オーステナイト
粒の粗大化防止に有効である。(J) Ti carbosulfide and Z produced during steelmaking
rCarbosulfide does not form a solid solution in the matrix or agglomerate at a heating temperature for normal hot working and a temperature of about 1050 ° C. in a high-temperature surface hardening treatment such as a plasma carburizing treatment. Therefore, a so-called "pinning action" is exhibited in the austenite region, which is effective in preventing austenite grains from becoming coarse.
【００３９】（Ｋ）Ｔｉ炭硫化物やＺｒ炭硫化物によっ
て被削性を高めるとともに大きな強度、特に、大きな疲
労強度を確保するためには、Ｔｉ炭硫化物やＺｒ炭硫化
物のサイズと、その清浄度で表される量（以下、単に
「清浄度」という）を適正化しておくことが重要であ
る。(K) In order to improve machinability by Ti carbosulfide and Zr carbosulfide and to secure large strength, particularly, large fatigue strength, the size of Ti carbosulfide and Zr carbosulfide and It is important to optimize the amount represented by the cleanliness (hereinafter simply referred to as “cleanliness”).
【００４０】本発明は、上記の知見に基づいて完成され
たものである。The present invention has been completed based on the above findings.
【００４１】[0041]
【発明の実施の形態】以下、本発明の各要件について詳
しく説明する。なお、化学成分の含有量の「％」は「重
量％」を意味する。DESCRIPTION OF THE PREFERRED EMBODIMENTS Each requirement of the present invention will be described in detail below. In addition, “%” of the content of the chemical component means “% by weight”.
【００４２】（Ａ）素材鋼の化学組成 Ｃ：Ｃは、ＳとともにＴｉやＺｒと結合してＴｉ炭硫化
物やＺｒ炭硫化物を形成し、被削性を高める作用を有す
る。更に、Ｃは鋼の強度を確保するとともに複合炭窒化
物の〔ＮｂＴｉ（ＣＮ）〕や〔ＮｂＺｒ（ＣＮ）〕を形
成させるのにも有効な元素である。しかし、その含有量
が０．１％未満では添加効果に乏しく、一方、０．３％
を超えて含有させると鋼の靭性が低下することになるの
で、その含有量を０．１〜０．３％とした。(A) Chemical composition of raw steel C: C combines with S and Ti or Zr to form Ti carbosulfide or Zr carbosulfide, and has an effect of improving machinability. Further, C is an element effective in securing the strength of steel and forming [NbTi (CN)] and [NbZr (CN)] as composite carbonitrides. However, if the content is less than 0.1%, the effect of the addition is poor, while the content is 0.3%.
If the content exceeds 0.1%, the toughness of the steel will be reduced. Therefore, the content is set to 0.1 to 0.3%.
【００４３】Ｓｉ：Ｓｉは、鋼の脱酸及び焼入れ性を高
める作用を有する。更に、強度の向上及び高温での表面
酸化の防止にも有効な元素である。しかし、その含有量
が０．０１％未満では所望の静的強度が確保できないこ
とに加えて高温での表面の耐酸化性が劣化し、０．５％
を超えると靭性の劣化を招くこととなる。したがって、
Ｓｉの含有量を０．０１〜０．５％とした。Si: Si has the effect of improving the deoxidizing and hardenability of steel. Further, they are effective elements for improving strength and preventing surface oxidation at high temperatures. However, if the content is less than 0.01%, the desired static strength cannot be secured, and in addition, the oxidation resistance of the surface at high temperatures is deteriorated, and 0.5%
If it exceeds, the toughness will be degraded. Therefore,
The content of Si was set to 0.01 to 0.5%.
【００４４】Ｍｎ：Ｍｎは、鋼の焼入れ性を高めるとと
もに熱間延性を向上させる効果を有する。しかし、その
含有量が０．６％未満では充分な焼入れ性が得られず、
２．０％を超えて含有させると偏析を生じ、却って熱間
延性が低下するようになる。したがって、Ｍｎの含有量
を０．６〜２．０％とした。Mn: Mn has the effect of improving the hardenability of steel and improving the hot ductility. However, if the content is less than 0.6%, sufficient hardenability cannot be obtained,
When the content exceeds 2.0%, segregation occurs, and the hot ductility is rather lowered. Therefore, the content of Mn is set to 0.6 to 2.0%.
【００４５】Ｐ：Ｐは、鋼の靭性を劣化させるととも
に、冷間及び熱間での鍛造性を低下させてしまう。特
に、その含有量が０．０３％を超えると靭性及び冷間・
熱間鍛造性の劣化が著しくなる。したがって、Ｐの含有
量を０．０３％以下とした。P: P degrades the toughness of the steel and lowers the cold and hot forgeability. In particular, if the content exceeds 0.03%, the toughness and the cold /
Deterioration of hot forgeability is remarkable. Therefore, the content of P is set to 0.03% or less.
【００４６】Ｓ：Ｓは、ＣとともにＴｉやＺｒと結合し
てＴｉ炭硫化物やＺｒ炭硫化物を形成し、被削性を高め
る作用を有する。しかし、その含有量が０．００２％未
満では所望の効果が得られない。S: S combines with C with Ti and Zr to form Ti carbosulfide and Zr carbosulfide, and has an effect of improving machinability. However, if the content is less than 0.002%, the desired effect cannot be obtained.
【００４７】従来、快削鋼にＳを添加する目的は、Ｍｎ
Ｓを形成させて被削性を改善させることにあった。しか
し、本発明者らの検討によると、上記のＭｎＳの被削性
向上作用は、切削時の切り屑と工具表面との潤滑性を高
める機能に基づくことが判明した。しかもＭｎＳは巨大
化し、鋼材本体の地疵を大きくし、欠陥となる場合があ
る。本発明におけるＳの被削性改善作用は、適正量のＣ
とＴｉやＺｒとの複合添加によってＴｉ炭硫化物やＺｒ
炭硫化物を形成させることで初めて得られる。このため
には、上記したように０．００２％以上のＳの含有量が
必要である。一方、Ｓを０．２％を超えて含有させても
被削性に与える効果に変化はないが、鋼中に粗大なＭｎ
Ｓが再び生じるようになり、地疵等の問題が生じる。更
に、熱間での加工性が著しく劣化し熱間加工が困難にな
るし、靭性が低下することもある。したがって、Ｓの含
有量を０．００２〜０．２％とした。なお、Ｓの好まし
い含有量は０．００５〜０．１％である。Conventionally, the purpose of adding S to free-cutting steel is to add Mn
The purpose is to improve the machinability by forming S. However, according to the study of the present inventors, it has been found that the above-described action of improving the machinability of MnS is based on a function of enhancing lubricity between chips and the tool surface during cutting. In addition, MnS increases in size, increases the ground flaw of the steel material main body, and sometimes becomes a defect. In the present invention, the machinability improving action of S is based on an appropriate amount of C
Addition of Ti and Zr to Ti carbosulfide and Zr
Obtained only by forming carbosulfide. For this purpose, the content of S is required to be 0.002% or more as described above. On the other hand, although the effect on machinability is not changed even when S is contained in excess of 0.2%, coarse Mn is contained in steel.
S is generated again, and problems such as ground flaws occur. Further, the hot workability is remarkably deteriorated, so that hot working becomes difficult, and the toughness may be reduced. Therefore, the content of S is set to 0.002 to 0.2%. In addition, the preferable content of S is 0.005 to 0.1%.
【００４８】Ｎｂ：Ｎｂは、ＴｉやＺｒとともに複合炭
窒化物〔ＮｂＴｉ（ＣＮ）〕や〔ＮｂＺｒ（ＣＮ）〕を
形成し、鋼の結晶粒を微細にして靭性を高めるととも
に、表面硬化処理のための加熱時の粗粒化を防止するの
に有効な元素である。しかし、その含有量が０．００５
％未満では添加効果に乏しく、一方、０．１０％を超え
て含有させても結晶粒微細化の効果が飽和して経済性を
損なうばかりであるし、変形抵抗が上昇して冷間鍛造性
や熱間鍛造性が劣化するようにもなる。したがって、Ｎ
ｂの含有量を０．００５〜０．１０％とした。Nb: Nb forms complex carbonitrides [NbTi (CN)] and [NbZr (CN)] together with Ti and Zr, refines the crystal grains of steel to increase toughness, and performs surface hardening treatment. Is an element effective for preventing coarsening during heating. However, its content is 0.005
%, The effect of addition is poor. On the other hand, if the content exceeds 0.10%, the effect of crystal grain refinement is saturated and the economic efficiency is only impaired. Also, hot forgeability deteriorates. Therefore, N
The content of b was set to 0.005 to 0.10%.
【００４９】Ｔｉ、Ｚｒ：Ｔｉ、Ｚｒは本発明において
介在物を制御するための重要な合金元素であって、それ
ぞれＣ及びＳと結合してＴｉ炭硫化物やＺｒ炭硫化物を
形成し、被削性を高める作用を有する。Ti, Zr: Ti and Zr are important alloying elements for controlling inclusions in the present invention, and combine with C and S to form Ti carbosulfide and Zr carbosulfide, respectively. Has the effect of enhancing machinability.
【００５０】上記の効果は、ＴｉとＺｒの含有量に関
し、Ｔｉ（％）＋Ｚｒ（％）の値が０．０４％以上の場
合に確実に得られる。しかし、Ｔｉ（％）＋Ｚｒ（％）
の値で１．０％を超えるＴｉとＺｒを含有させても被削
性向上効果は飽和するのでコストが嵩んでしまう。な
お、Ｔｉ（％）＋Ｚｒ（％）の値が０．０４〜１．０％
でありさえすれば良いので、必ずしもＴｉとＺｒを複合
して含有させる必要はない。Ｚｒを添加しない、つまり
Ｔｉを単独で添加する場合に、Ｔｉを１．０％超えて含
有させるとＴｉ炭硫化物による被削性向上効果が飽和し
てコストが嵩むばかりか、Ｔｉ炭硫化物が粗大化して却
って靭性の低下を招いてしまう。逆に、Ｔｉを添加しな
い、つまりＺｒを単独で添加する場合に、Ｚｒを１．０
％を超えて含有させるとＺｒ炭硫化物による被削性向上
効果が飽和してコストが嵩むばかりか、Ｚｒ炭硫化物が
粗大化して却って靭性の低下を招いてしまう。したがっ
て、ＴｉとＺｒの含有量をいずれも１．０％以下で、且
つ、Ｔｉ（％）＋Ｚｒ（％）の値を０．０４〜１．０％
とした。なお、良好な被削性と靭性を安定して得るため
には、ＴｉとＺｒの含有量の上限はそれぞれ０．８％と
することが好ましい。The above effect can be surely obtained when the value of Ti (%) + Zr (%) is 0.04% or more with respect to the contents of Ti and Zr. However, Ti (%) + Zr (%)
If the content of Ti and Zr exceeds 1.0%, the effect of improving machinability is saturated, so that the cost increases. The value of Ti (%) + Zr (%) is 0.04 to 1.0%
Therefore, it is not always necessary to include Ti and Zr in combination. When Zr is not added, that is, when Ti is added alone, if the content of Ti exceeds 1.0%, the effect of improving the machinability due to Ti carbosulfide is saturated and the cost is increased. Is coarsened, and the toughness is rather lowered. Conversely, when Ti is not added, that is, when Zr is added alone, Zr is 1.0%.
%, The effect of improving the machinability by the Zr carbosulfide is saturated and not only the cost is increased, but also the Zr carbosulfide is coarsened and the toughness is rather lowered. Therefore, the content of both Ti and Zr is 1.0% or less, and the value of Ti (%) + Zr (%) is set to 0.04 to 1.0%.
And In order to stably obtain good machinability and toughness, the upper limits of the contents of Ti and Zr are each preferably 0.8%.
【００５１】Ｎ：Ｎは、Ｎｂ、Ｔｉ、Ｚｒ及びＣと結合
して複合炭窒化物〔ＮｂＴｉ（ＣＮ）〕や〔ＮｂＺｒ
（ＣＮ）〕を形成し、鋼の結晶粒を微細化して靭性を向
上させるとともに、表面硬化処理のための加熱時の粗粒
化を防止するのに有効な元素である。しかし、その含有
量が０．００２％未満では添加効果に乏しい。一方、Ｎ
はＴｉやＺｒとの親和力が大きいために容易にＴｉやＺ
ｒと結合してＴｉＮやＺｒＮを形成し、ＴｉやＺｒを固
定してしまうので、Ｎを多量に含有する場合には前記し
たＴｉ炭硫化物やＺｒ炭硫化物の被削性向上効果が充分
に発揮できないこととなる。特に、ＴｉやＺｒの含有量
が低めの場合には、Ｎ含有量の影響が顕著となる。更
に、粗大なＴｉＮやＺｒＮは靭性及び被削性を低下させ
てしまう。特に、Ｎ含有量が０．００８％を超えると靭
性及び被削性の低下が著しくなる。したがって、Ｎの含
有量を０．００２〜０．００８％とした。なお、Ｔｉ炭
硫化物やＺｒ炭硫化物の効果を高めるために、Ｎ含有量
の上限は０．００６％とすることが好ましい。N: N combines with Nb, Ti, Zr and C to form a composite carbonitride [NbTi (CN)] or [NbZr
(CN)], and is an element effective in refining the crystal grains of steel to improve toughness and preventing coarsening during heating for surface hardening treatment. However, if the content is less than 0.002%, the effect of addition is poor. On the other hand, N
Has a high affinity for Ti and Zr, so that Ti and Z
Since it combines with r to form TiN or ZrN and fixes Ti or Zr, the effect of improving the machinability of the aforementioned Ti carbosulfide or Zr carbosulfide is sufficient when a large amount of N is contained. Can not be demonstrated. In particular, when the content of Ti or Zr is relatively low, the influence of the N content becomes significant. Furthermore, coarse TiN and ZrN reduce toughness and machinability. In particular, when the N content exceeds 0.008%, the toughness and machinability are significantly reduced. Therefore, the content of N is set to 0.002 to 0.008%. In order to enhance the effects of Ti carbosulfide and Zr carbosulfide, the upper limit of the N content is preferably set to 0.006%.
【００５２】Ｃｒ：Ｃｒは添加しなくても良い。添加す
れば鋼の焼入れ性を向上させるとともに、浸炭処理など
の表面硬化処理時にＣと結合して複合炭化物を形成する
ので耐摩耗性を向上させる効果がある。この効果を確実
に得るには、Ｃｒは０．０５％以上の含有量とすること
が好ましい。しかし、その含有量が２．０％を超えると
靭性が劣化する。したがって、Ｃｒ含有量を０〜２．０
％とした。Cr: Cr need not be added. When added, it has the effect of improving the hardenability of the steel, and improving the wear resistance since it combines with C to form a composite carbide during surface hardening treatment such as carburizing treatment. To ensure this effect, the content of Cr is preferably set to 0.05% or more. However, if the content exceeds 2.0%, toughness deteriorates. Therefore, the Cr content is set to 0 to 2.0.
%.
【００５３】Ｍｏ：Ｍｏは添加しなくても良い。添加す
れば鋼の焼入れ性を向上させるとともに、表面硬化処理
後の芯部硬度を上げる作用がある。この効果を確実に得
るには、Ｍｏは０．０５％以上の含有量とすることが望
ましい。しかし、その含有量が１．０％を超えると、Ｔ
ｉ炭硫化物やＺｒ炭硫化物を微細に分散させた場合にお
いても被削性が大幅に劣化するようになる。したがっ
て、Ｍｏ含有量を０〜１．０％とした。Mo: Mo may not be added. When added, it has the effect of improving the hardenability of the steel and increasing the core hardness after the surface hardening treatment. To ensure this effect, it is desirable that the content of Mo be 0.05% or more. However, if the content exceeds 1.0%, T
Even when i-carbon sulfide or Zr-carbon sulfide is finely dispersed, the machinability is greatly deteriorated. Therefore, the Mo content was set to 0 to 1.0%.
【００５４】Ｗ：Ｗは添加しなくても良い。添加すれば
鋼の焼入れ性を向上させるとともに、表面硬化処理後の
芯部硬度を上げる作用がある。この効果を確実に得るに
は、Ｗは０．１０％以上の含有量とすることが望まし
い。しかし、その含有量が１．０％を超えると、Ｔｉ炭
硫化物やＺｒ炭硫化物を微細に分散させた場合において
も被削性が大幅に劣化するようになる。したがって、Ｗ
の含有量を０〜１．０％とした。W: W need not be added. When added, it has the effect of improving the hardenability of the steel and increasing the core hardness after the surface hardening treatment. To ensure this effect, it is desirable that the content of W be 0.10% or more. However, when the content exceeds 1.0%, the machinability is greatly deteriorated even when Ti carbosulfide or Zr carbosulfide is finely dispersed. Therefore, W
Was set to 0 to 1.0%.
【００５５】Ａｌ：Ａｌは添加しなくてもよい。添加す
れば鋼の脱酸の安定化及び均質化を図る作用がある。こ
の効果を確実に得るには、Ａｌは０．００５％以上の含
有量とすることが望ましい。しかし、その含有量が０．
１０％を超えると前記効果が飽和することに加えて靭性
が劣化するようになる。したがって、Ａｌの含有量を０
〜０．１０％とした。なお、Ｔｉ炭硫化物やＺｒ炭硫化
物のサイズと清浄度を所定の値とするためにはＴｉやＺ
ｒの酸化物が過剰に生成することを防ぐことが重要であ
るので、Ｓｉ含有量が０．０５％未満の場合には、少な
くとも０．００５％のＡｌを含有させることとするのが
良い。Al: Al may not be added. If added, it has the effect of stabilizing and homogenizing steel deoxidation. To ensure this effect, the content of Al is desirably 0.005% or more. However, when its content is 0.1.
If it exceeds 10%, the effect is saturated and the toughness is deteriorated. Therefore, the content of Al is reduced to 0.
０．１0.10%. In order to set the size and cleanliness of Ti and Zr carbosulfides to predetermined values, Ti and Zr are used.
Since it is important to prevent the oxide of r from being generated excessively, when the Si content is less than 0.05%, it is preferable to contain at least 0.005% of Al.
【００５６】ｆｎ１：Ｎ含有量の上限を０．００８％と
し、前述の式で表されるｆｎ１が０％を超える値（ｆ
ｎ１＝Ｔｉ（％）＋Ｚｒ（％）−１．２×Ｓ（％）＞０
％）の場合に前記したＴｉ炭硫化物やＺｒ炭硫化物の被
削性向上効果が確保できる。ｆｎ１が０％以下の値（ｆ
ｎ１≦０％）の場合には、Ｓ量が過剰となるため、その
分ＭｎＳが過剰生成してＴｉ炭硫化物やＺｒ炭硫化物に
よる被削性向上効果が低下してしまう。したがって、
式で表されるｆｎ１に関して０％を超える値（ｆｎ１＞
０％）と規定した。このｆｎ１の値の上限は特に規定さ
れるものではなく、Ｔｉ（％）＋Ｚｒ（％）の値が１．
０％でＳが０．００２％の場合の値であっても良い。Fn1: The upper limit of the N content is set to 0.008%, and the value of fn1 represented by the above equation exceeding 0% (f
n1 = Ti (%) + Zr (%) − 1.2 × S (%)> 0
%), The effect of improving the machinability of the above-mentioned Ti carbosulfide and Zr carbosulfide can be secured. fn1 is 0% or less (f
In the case of (n1 ≦ 0%), the amount of S is excessive, so that MnS is excessively generated and the effect of improving the machinability by Ti carbosulfide or Zr carbosulfide is reduced. Therefore,
A value exceeding 0% for fn1 represented by the formula (fn1>
0%). The upper limit of the value of fn1 is not particularly defined, and the value of Ti (%) + Zr (%) is 1.
It may be a value when S is 0.002% at 0%.
【００５７】上記の化学組成を有する素材鋼は、例えば
熱間で分塊されて鋼片となり、次いで熱間で圧延された
後、熱間あるいは冷間で鍛造され、必要に応じて焼準を
施され、更に切削加工が施されて所定の表面硬化部品の
形状に加工される。そして最終的に表面硬化処理を施さ
れることとなる。The raw steel having the above-mentioned chemical composition is, for example, hot-lumped into a billet, then hot-rolled, and then hot- or cold-forged. Then, a cutting process is performed to form a predetermined surface-hardened component. Then, a surface hardening treatment is finally performed.
【００５８】（Ｂ）Ｔｉ炭硫化物及びＺｒ炭硫化物のサ
イズと清浄度 上記の化学組成を有する鋼材の被削性をＴｉ炭硫化物や
Ｚｒ炭硫化物によって高めるとともに大きな強度と良好
な靭性をも確保するためには、Ｔｉ炭硫化物やＺｒ炭硫
化物のサイズと清浄度（ＴｉとＺｒを複合添加する場合
にはＴｉ炭硫化物とＺｒ炭硫化物の清浄度の和）で表さ
れる量を適正化しておくことが重要である。(B) Size and cleanliness of Ti carbosulfide and Zr carbosulfide The machinability of steel having the above-mentioned chemical composition is enhanced by Ti carbosulfide and Zr carbosulfide, and large strength and good toughness are obtained. In order to secure the minimum value, the size and cleanliness of Ti and Zr carbosulfides (or the sum of cleanliness of Ti and Zr carbosulfides when Ti and Zr are added in combination) are expressed in It is important to optimize the amount that is given.
【００５９】鋼中のＴｉ炭硫化物及びＺｒ炭硫化物の最
大直径が１０μｍを超えると疲労強度や靭性が低下して
しまう。なお、Ｔｉ炭硫化物及びＺｒ炭硫化物の最大直
径はいずれも７μｍ以下とすることが好ましい。Ｔｉ炭
硫化物とＺｒ炭硫化物は、それらの最大直径が小さすぎ
ると被削性向上効果が小さくなってしまう。したがっ
て、Ｔｉ炭硫化物とＺｒ炭硫化物の最大直径の下限値は
０．５μｍ程度とすることが好ましい。If the maximum diameter of Ti carbosulfide and Zr carbosulfide in the steel exceeds 10 μm, the fatigue strength and toughness decrease. Note that the maximum diameter of each of the Ti carbosulfide and the Zr carbosulfide is preferably 7 μm or less. If the maximum diameter of Ti carbosulfide and Zr carbosulfide is too small, the effect of improving machinability is reduced. Therefore, it is preferable that the lower limit value of the maximum diameter of Ti carbosulfide and Zr carbosulfide is about 0.5 μm.
【００６０】最大直径が１０μｍ以下のＴｉ炭硫化物及
びＺｒ炭硫化物の量の和が清浄度で０．０５％未満の場
合には、Ｔｉ炭硫化物及びＺｒ炭硫化物による被削性向
上効果が発揮できない。したがって、Ｔｉ炭硫化物及び
Ｚｒ炭硫化物の最大直径が１０μｍ以下で、且つその量
の和を清浄度で０．０５％以上とした。なお、前記の清
浄度の和は０．０８％以上とすることが好ましい。上記
のＴｉ炭硫化物とＺｒ炭硫化物の清浄度の和の値が大き
すぎると疲労強度が低下する場合があるので、上記の清
浄度の和の上限値は２．０％程度とすることが好まし
い。When the sum of the amounts of Ti carbosulfide and Zr carbosulfide having a maximum diameter of 10 μm or less is less than 0.05% in cleanliness, the machinability is improved by Ti carbosulfide and Zr carbosulfide. No effect. Therefore, the maximum diameter of Ti carbosulfide and Zr carbosulfide was 10 μm or less, and the sum of the amounts was 0.05% or more in terms of cleanliness. It is preferable that the sum of the cleanliness is 0.08% or more. If the sum of the cleanliness of the Ti and Zr carbosulfides is too large, the fatigue strength may decrease. Therefore, the upper limit of the sum of the cleanliness should be about 2.0%. Is preferred.
【００６１】上記したようなＴｉ炭硫化物とＺｒ炭硫化
物の形態は基本的にはＴｉ、Ｚｒ、Ｓ及びＮの含有量で
決定される。しかし、Ｔｉ炭硫化物やＺｒ炭硫化物のサ
イズと清浄度（清浄度の和）を上述の値とするために
は、ＴｉやＺｒの酸化物が過剰に生成することを防ぐこ
とが重要である。このためには、鋼が前記（Ａ）項で述
べた化学組成を有しているだけでは充分でない場合があ
るので、例えば、Ｓｉ及びＡｌで充分脱酸し、最後にＴ
ｉやＺｒを添加する製鋼法を採れば良い。The form of Ti carbosulfide and Zr carbosulfide as described above is basically determined by the contents of Ti, Zr, S and N. However, in order to set the size and cleanliness (sum of cleanliness) of Ti carbosulfides and Zr carbosulfides to the above-mentioned values, it is important to prevent the oxides of Ti and Zr from being excessively generated. is there. In some cases, it is not sufficient for the steel to have the chemical composition described in the above item (A). For example, the steel is sufficiently deoxidized with Si and Al, and finally T
A steelmaking method in which i or Zr is added may be employed.
【００６２】なお、Ｔｉ炭硫化物とＺｒ炭硫化物は、鋼
材から採取した試験片を鏡面研磨し、その研磨面を被検
面として倍率４００倍以上で光学顕微鏡観察すれば、色
と形状から容易に他の介在物と識別できる。すなわち、
前記の条件で光学顕微鏡観察すれば、Ｔｉ炭硫化物及び
Ｚｒ炭硫化物の「色」は極めて薄い灰色で、「形状」は
ＪＩＳのＢ系介在物やＣ系介在物に相当する粒状（球
状）として認められる。Ｔｉ炭硫化物及びＺｒ炭硫化物
の詳細判定は、前記の被検面をＥＤＸ（エネルギー分散
型Ｘ線分析装置）などの分析機能を備えた電子顕微鏡で
観察することによって行うこともできる。It should be noted that Ti carbosulfide and Zr carbosulfide can be obtained from the color and the shape by polishing a specimen taken from a steel material by mirror polishing and observing the polished surface as a test surface with an optical microscope at a magnification of 400 or more. It can be easily distinguished from other inclusions. That is,
Observation under an optical microscope under the above conditions shows that the “color” of Ti carbosulfide and Zr carbosulfide is extremely light gray, and the “shape” is a granular (spherical) equivalent to JIS B-based inclusion or C-based inclusion. ). The detailed determination of Ti carbosulfide and Zr carbosulfide can also be performed by observing the test surface with an electron microscope equipped with an analysis function such as EDX (energy dispersive X-ray analyzer).
【００６３】前記のＴｉ炭硫化物やＺｒ炭硫化物の清浄
度は、既に述べたように、光学顕微鏡の倍率を４００倍
として、JIS G 0555に規定された「鋼の非金属介在物の
顕微鏡試験方法」によって６０視野測定した値をいう。
なお、Ｔｉ炭硫化物やＺｒ炭硫化物の最大直径も、倍率
が４００倍の光学顕微鏡で６０視野観察して調査すれば
良い。As described above, the cleanliness of the Ti carbosulfide and the Zr carbosulfide is determined by setting the magnification of the optical microscope to 400 times, as described in JIS G 0555. It refers to the value measured in 60 visual fields by the "test method".
In addition, the maximum diameter of Ti carbosulfide or Zr carbosulfide may be investigated by observing 60 visual fields with an optical microscope having a magnification of 400 times.
【００６４】（Ｃ）熱間鍛造、分塊、圧延及び熱処理 本発明は、１０５０℃にも到る高温での表面硬化処理の
加熱時に、複合炭窒化物〔ＮｂＴｉ（ＣＮ）〕や〔Ｎｂ
Ｚｒ（ＣＮ）〕を微細に析出させておき、そのピン止め
効果により表面硬化処理時の粗粒化の発生を抑制しよう
とするものである。そして、表面硬化処理の加熱時に、
複合炭窒化物〔ＮｂＴｉ（ＣＮ）〕や〔ＮｂＺｒ（Ｃ
Ｎ）〕を微細に析出させておくためには、溶製後の凝固
時に粗大に析出した複合炭窒化物〔ＮｂＴｉ（ＣＮ）〕
や〔ＮｂＺｒ（ＣＮ）〕を、表面硬化処理の前段階で一
旦鋼中に固溶させ、微細な〔ＮｂＴｉ（ＣＮ）〕や〔Ｎ
ｂＺｒ（ＣＮ）〕析出の素地を作っておく必要がある。
このためには、表面硬化処理の前工程で、一旦高温に加
熱しておけばよい。(C) Hot forging, lumping, rolling and heat treatment The present invention provides a method for producing a composite carbonitride [NbTi (CN)] or [Nb
Zr (CN)] is finely precipitated, and its pinning effect is intended to suppress the occurrence of coarsening during surface hardening. And at the time of heating of the surface hardening treatment,
Composite carbonitrides [NbTi (CN)] and [NbZr (C
In order to precipitate N)] finely, the composite carbonitride [NbTi (CN)] coarsely precipitated during solidification after melting.
And [NbZr (CN)] are once dissolved in steel before the surface hardening treatment, and fine [NbTi (CN)] and [N
bZr (CN)] It is necessary to prepare a base for precipitation.
For this purpose, it is only necessary to temporarily heat to a high temperature in a process before the surface hardening treatment.
【００６５】既に述べたように、ＮｂとＴｉやＺｒと
を複合添加した鋼において凝固時に析出する炭窒化物
は、ＮｂとＴｉやＺｒの粗大な複合炭窒化物〔ＮｂＴｉ
（ＣＮ）〕や〔ＮｂＺｒ（ＣＮ）〕である。複合炭窒
化物〔ＮｂＴｉ（ＣＮ）〕や〔ＮｂＺｒ（ＣＮ）〕の固
溶と加熱温度（Ｔ）の関係については以下のとおりであ
る。As described above, carbonitride precipitated during solidification in steel to which Nb and Ti or Zr are added in combination is a coarse composite carbonitride of Nb, Ti or Zr [NbTi
(CN)] and [NbZr (CN)]. The relationship between the solid solution of the composite carbonitride [NbTi (CN)] or [NbZr (CN)] and the heating temperature (T) is as follows.
【００６６】（イ）Ｔ＜１１５０℃の場合：上記の複合
炭窒化物は鋼中で安定に存在する。(A) When T <1150 ° C .: The above-mentioned composite carbonitride exists stably in steel.
【００６７】（ロ）１１５０℃≦Ｔ≦１３５０℃の場
合：上記の複合炭窒化物のＮｂだけが固溶し、炭窒化物
中にＴｉやＺｒが濃化する。(B) When 1150 ° C. ≦ T ≦ 1350 ° C .: Only Nb of the above-mentioned composite carbonitride is dissolved, and Ti and Zr are concentrated in the carbonitride.
【００６８】（ハ）１３５０℃＜Ｔの場合：上記の複合
炭窒化物は完全に固溶する（Ｔｉ、Ｚｒも固溶する）。(C) When 1350 ° C. <T: The above composite carbonitride completely dissolves (Ti and Zr also dissolve).
【００６９】したがって、本発明においては、微細に再
析出した〔ＮｂＴｉ（ＣＮ）〕や〔ＮｂＺｒ（ＣＮ）〕
のピン止め作用を利用して粗粒化の発生を防止するため
に、表面硬化処理の前の工程で一旦１１５０℃以上に加
熱する。Therefore, in the present invention, [NbTi (CN)] or [NbZr (CN)]
In order to prevent the occurrence of coarse particles by utilizing the pinning action of the above, the material is once heated to 1150 ° C. or more in a step before the surface hardening treatment.
【００７０】そこで、表面硬化部品への加工工程に熱間
鍛造が含まれる場合には、少なくともこの熱間鍛造にお
ける加熱温度を１１５０℃以上としてＮｂを固溶させれ
ば良いことになる（（３）の発明）。In the case where hot forging is included in the process of forming a surface-hardened part, it is sufficient that at least the heating temperature in this hot forging is set to 1150 ° C. or more to form a solid solution of Nb ((3) ) Invention).
【００７１】あるいは、既に述べた表面硬化処理の前工
程のうち、熱間鍛造以外で「加熱」処理を伴うものは分
塊、圧延及び所謂「熱処理」であるため、これら分塊、
圧延及び熱処理の少なくとも１つの工程において加熱温
度を１１５０℃以上とすれば良いことになる（（４）の
発明）。Alternatively, among the pre-processes of the above-mentioned surface hardening treatment, those involving “heating” processing other than hot forging are lumping, rolling and so-called “heat treatment”.
In at least one of the rolling and heat treatment steps, the heating temperature may be set to 1150 ° C. or higher (the invention of (4)).
【００７２】なお、本発明においては、微細に再析出し
た〔ＮｂＴｉ（ＣＮ）〕や〔ＮｂＺｒ（ＣＮ）〕のピン
止め作用を利用することに加えて、Ｔｉ炭硫化物やＺｒ
炭硫化物のピン止め作用も利用して表面硬化処理時の異
常粒成長の防止を図る。このＴｉ炭硫化物やＺｒ炭硫化
物は１３５０℃以下の温度では基地に固溶し難い。この
ため、上記した（３）の発明及び（４）の発明における
加熱温度の上限は、Ｔｉ炭硫化物やＺｒ炭硫化物のピン
止め作用を確保するために１３５０℃とするのが良い。
加熱温度の上限を１３５０℃とすれば、加熱時の表面酸
化を低減することもできる。In the present invention, in addition to utilizing the pinning action of finely reprecipitated [NbTi (CN)] and [NbZr (CN)], Ti carbosulfide and Zr
The pinning action of carbosulfide is also used to prevent abnormal grain growth during surface hardening. The Ti carbosulfide and the Zr carbosulfide hardly form a solid solution at a temperature of 1350 ° C. or lower. Therefore, the upper limit of the heating temperature in the above-mentioned inventions (3) and (4) is preferably set to 1350 ° C. in order to secure the pinning action of Ti carbosulfide and Zr carbosulfide.
If the upper limit of the heating temperature is 1350 ° C., surface oxidation during heating can be reduced.
【００７３】なお、プラズマ浸炭処理を初めとする高い
温度での表面硬化処理のための加熱時に、ＮｂとＴｉや
Ｚｒとの複合炭窒化物〔ＮｂＴｉ（ＣＮ）〕や〔ＮｂＺ
ｒ（ＣＮ）〕を微細に析出させておくためには、上記の
加熱後の冷却速度は０．２℃／ｓ以上とすることが望ま
しい。At the time of heating for surface hardening treatment at a high temperature such as plasma carburizing treatment, composite carbonitrides of Nb and Ti or Zr [NbTi (CN)] or [NbZ
[r (CN)], the cooling rate after the above-mentioned heating is desirably 0.2 ° C./s or more in order to precipitate finely.
【００７４】（Ｄ）表面硬化処理 本発明が対象とする表面硬化処理は、処理の能率を大幅
に高めることができる「プラズマ浸炭処理」を初めとす
る高温での表面硬化処理である。この表面硬化処理は、
所定の表面硬化部品の表面を硬化させ、製品として必要
な耐摩耗性や疲労強度を確保するのに必要不可欠の処理
である。この処理方法は特に規定されるものではなく、
通常の方法で行えば良い。なお、当然のことながら、本
発明は、表面硬化処理が９００〜９５０℃の温度に加熱
される従来の浸炭処理や浸炭窒化処理などの場合にも適
用できる。(D) Surface Hardening Treatment The surface hardening treatment targeted by the present invention is a high-temperature surface hardening treatment such as “plasma carburizing treatment” which can greatly improve the efficiency of the treatment. This surface hardening treatment
This is an indispensable process for hardening the surface of a predetermined surface-hardened component to secure the required wear resistance and fatigue strength as a product. This processing method is not particularly specified,
It can be done in the usual way. Naturally, the present invention can also be applied to the case of conventional carburizing treatment or carbonitriding treatment in which the surface hardening treatment is heated to a temperature of 900 to 950 ° C.
【００７５】（Ｅ）表面硬化処理後の表面硬化部品の芯
部硬度と靭性 表面硬化部品が、自動車や産業機械が使用される過酷な
環境においても充分な耐久性を発揮するためには、表面
硬化処理後、Ｈｖ３００以上の芯部硬度と２０Ｊ／ｃｍ
2 以上の衝撃値を有することが必要である。これらの一
方及び／又は両方から外れる場合は表面硬化部品の実環
境での耐久性は極めて劣化したものとなってしまう。し
たがって、表面硬化部品の芯部硬度はＨｖ３００以上、
且つ、衝撃値は２０Ｊ／ｃｍ2 以上とした。(E) Core Hardness and Toughness of Surface-Hardened Parts After Surface Hardening Treatment In order for the surface-hardened parts to exhibit sufficient durability even in harsh environments where automobiles and industrial machines are used, the surface must be hardened. After hardening treatment, core hardness of Hv300 or more and 20 J / cm
It is necessary to have an impact value of 2 or more. If it is out of one and / or both, the durability of the surface-hardened component in a real environment is extremely deteriorated. Therefore, the core hardness of the surface-hardened part is Hv300 or more,
In addition, the impact value was set to 20 J / cm 2 or more.
【００７６】なお、既に述べたように、表面硬化部品の
芯部とは表面硬化処理を受けても硬化していない部分
を、又、衝撃値はＪＩＳ３号シャルピー衝撃試験片を用
いて常温（室温）で衝撃試験した場合のものを指す。As described above, the core of the surface-hardened part is the part that has not been hardened even after undergoing the surface hardening treatment, and the impact value is measured at room temperature (room temperature) using a JIS No. 3 Charpy impact test piece. ) Indicates the impact test.
【００７７】（Ｆ）焼戻し 低温で焼戻しを行うと表面硬度の大きな低下を伴うこと
なく靭性を改善できるので、本発明の表面硬化部品は、
表面硬化処理の後に必要に応じて焼戻しを実施したもの
であっても良い。焼戻しをする場合は、表面硬度を確保
するためにその温度を１５０〜２００℃とするのが望ま
しい。(F) Tempering Tempering at a low temperature can improve toughness without a significant decrease in surface hardness.
After the surface hardening treatment, tempering may be performed as necessary. When performing tempering, it is desirable to set the temperature to 150 to 200 ° C. in order to secure surface hardness.
【００７８】[0078]
【実施例】（実施例１）表１、表２に示す化学組成の鋼
を通常の方法によって試験炉を用いて溶製した。なお、
鋼Ｇと鋼Ｈを除いて、Ｔｉ酸化物及びＺｒ酸化物の生成
を防ぐために、Ｓｉ及びＡｌで充分脱酸し種々の元素を
添加した最後にＴｉとＺｒを添加して、Ｔｉ炭硫化物と
Ｚｒ炭硫化物のサイズと清浄度（清浄度の和）を調整す
るようにした。鋼Ｇと鋼ＨについてはＳｉ及びＡｌで脱
酸する際に同時にＴｉとＺｒを添加した。EXAMPLES (Example 1) Steels having the chemical compositions shown in Tables 1 and 2 were melted by a conventional method using a test furnace. In addition,
Except for steel G and steel H, in order to prevent the formation of Ti oxides and Zr oxides, sufficiently deoxidize with Si and Al and add various elements. Finally, add Ti and Zr to form Ti carbosulfide. The size and cleanliness (sum of cleanliness) of Zr and Zr carbosulfide were adjusted. For steel G and steel H, Ti and Zr were simultaneously added when deoxidizing with Si and Al.
【００７９】表１における鋼Ａ〜Ｈは化学組成が本発明
で規定する範囲内にある本発明例、表２における鋼Ｉ〜
Ｓは成分のいずれかが本発明で規定する含有量の範囲か
ら外れた比較例である。比較例に係る鋼のうち鋼Ｑ、鋼
Ｒ及び鋼ＳはそれぞれＪＩＳのＳＭｎ４２０鋼、ＳＣｒ
４２０鋼及びＳＣＭ４２０鋼に相当する鋼である。Steels A to H in Table 1 are examples of the present invention whose chemical composition is within the range specified in the present invention, and steels I to H in Table 2
S is a comparative example in which any of the components was out of the range of the content specified in the present invention. Among the steels according to the comparative examples, steel Q, steel R and steel S are JIS SMn420 steel and SCr, respectively.
It is a steel corresponding to 420 steel and SCM420 steel.
【００８０】[0080]
【表１】 [Table 1]
【００８１】[0081]
【表２】 [Table 2]
【００８２】次いで、これらの鋼を１１４０℃に加熱し
た後に通常の方法によって鋼片とし、更に１１００℃に
加熱して、１１００〜１０００℃の温度で直径３０ｍｍ
の丸棒に熱間鍛造した。なお、鋼片に加工した後、一部
のものについては表面の手入れを行った。この表面の手
入れの有無を表１、表２に併せて示す。Next, these steels were heated to 1140 ° C., turned into steel slabs by a conventional method, further heated to 1100 ° C., and heated at a temperature of 1100 to 1000 ° C. and a diameter of 30 mm
Hot forged into round bars. After processing into a billet, the surface of some of them was cleaned. Tables 1 and 2 also show whether or not the surface was cared for.
【００８３】こうして得られた熱間鍛造後の丸棒からJI
S G 0555の図１に則って試験片を採取し、鏡面研磨した
幅が１５ｍｍで高さが２０ｍｍの被検面を、倍率が４０
０倍の光学顕微鏡で６０視野観察して、Ｔｉ炭硫化物及
びＺｒ炭硫化物を他の介在物と区分しながらその清浄度
（清浄度の和）を測定した。Ｔｉ炭硫化物及びＺｒ炭硫
化物の最大直径も、倍率が４００倍の光学顕微鏡で６０
視野観察して調査した。From the thus obtained hot forged round bar, JI
A test piece was sampled according to FIG. 1 of SG 0555, and a mirror-polished test surface having a width of 15 mm and a height of 20 mm was placed at a magnification of 40.
By observing 60 visual fields with a 0-magnification optical microscope, the cleanliness (sum of cleanliness) was measured while separating Ti and Zr carbosulfides from other inclusions. The maximum diameters of Ti and Zr carbosulfides were also 60
The field of view was examined.
【００８４】又、上記の熱間鍛造後の丸棒から８ｍｍ直
径×１２ｍｍ長さの粗粒化測定試験片を切り出し、この
試験片を用いて下記の４条件の加工熱処理試験を行い、
粗粒化の発生率を倍率１００倍の光学顕微鏡で１０視野
観察して調査した。Further, a test piece for coarse-graining measurement of 8 mm diameter × 12 mm length was cut out from the round bar after the hot forging, and a working heat treatment test under the following four conditions was performed using this test piece.
The incidence of coarse graining was investigated by observing 10 visual fields with an optical microscope having a magnification of 100 times.
【００８５】（条件１）真空中で、試験片を１１００
℃、１１７５℃及び１２５０℃の温度でそれぞれ１５分
間加熱した後、圧縮加工により３０％の変形量を与えて
常温（室温）まで１．０℃／ｓの冷却速度で冷却した。
この後、１０５０℃×４ｈｒ（炭素ポテンシャル：０．
８％）の浸炭処理を行った後油焼入した。(Condition 1) A test piece was placed in a vacuum at 1100
After heating at a temperature of 1 ° C., 1175 ° C., and 1250 ° C. for 15 minutes, a deformation amount of 30% was given by compression, and then cooled to room temperature (room temperature) at a cooling rate of 1.0 ° C./s.
Thereafter, 1050 ° C. × 4 hr (carbon potential: 0.
8%) and then oil quenched.
【００８６】（条件２）真空中で、試験片を１１００℃
で１５分間加熱し、続いて圧縮加工により３０％の変形
量を与え、一旦常温まで２．０℃／ｓの冷却速度で冷却
した。この後、更に、１１００℃、１１７５℃及び１２
５０℃の温度で１５分間加熱した後、常温まで１．０℃
／ｓの冷却速度で冷却した。次いで、１０５０℃×４ｈ
ｒ（炭素ポテンシャル：０．８％）の浸炭処理を行った
後油焼入した。(Condition 2) A test piece was heated at 1100 ° C. in a vacuum.
For 15 minutes, followed by compression to give a deformation of 30%, and once cooled to room temperature at a cooling rate of 2.0 ° C./s. After this, 1100 ° C, 1175 ° C and 12
After heating at a temperature of 50 ° C for 15 minutes, it is 1.0 ° C to room temperature.
/ S cooling rate. Then, 1050 ° C x 4h
After performing carburization treatment of r (carbon potential: 0.8%), oil quenching was performed.
【００８７】（条件３）大気中で、試験片に常温で圧縮
加工により３０％の変形量を与えた。次いで、真空中
で、１１００℃、１１７５℃及び１２５０℃の温度でそ
れぞれ１５分間加熱した後、常温まで１．０℃／ｓの冷
却速度で冷却した。この後、１０５０℃×４ｈｒ（炭素
ポテンシャル：０．８％）の浸炭処理を行った後油焼入
した。(Condition 3) In the atmosphere, a test piece was subjected to compression at room temperature to give a deformation amount of 30%. Then, after heating in vacuum at 1100 ° C., 1175 ° C., and 1250 ° C. for 15 minutes each, it was cooled to room temperature at a cooling rate of 1.0 ° C./s. Thereafter, after carburizing at 1050 ° C. × 4 hr (carbon potential: 0.8%), oil quenching was performed.
【００８８】（条件４）真空中で、試験片を１１００
℃、１１７５℃及び１２５０℃の温度でそれぞれ１５分
間加熱した後、一旦常温まで１．０℃／ｓの冷却速度で
冷却した。次いで、真空中で１１００℃で１５分間加熱
し、更に、圧縮加工により３０％の変形量を与え、常温
まで２．０℃／ｓの冷却速度で冷却した。この後、１０
５０℃×４ｈｒ（炭素ポテンシャル：０．８％）の浸炭
処理を行った後油焼入した。(Condition 4) The test piece was placed in a vacuum at 1100
After heating for 15 minutes at a temperature of ° C, 1175 ° C, and 1250 ° C, it was once cooled to room temperature at a cooling rate of 1.0 ° C / s. Next, the mixture was heated at 1100 ° C. for 15 minutes in a vacuum, further subjected to compression processing to give a deformation amount of 30%, and cooled to room temperature at a cooling rate of 2.0 ° C./s. After this, 10
After carburizing at 50 ° C. × 4 hr (carbon potential: 0.8%), oil quenching was performed.
【００８９】表３に、熱間鍛造後の丸棒におけるＴｉ炭
硫化物及びＺｒ炭硫化物の清浄度及び最大直径の調査結
果、並びに条件１〜４の加工熱処理試験を行った場合の
粗粒化発生率の調査結果を示す。なお、表の「Ｔｉ、Ｚ
ｒ炭硫化物」とした欄において、ＴｉとＺｒとを複合添
加した場合には「最大直径」はいずれか大きい方の炭硫
化物の値であり、清浄度は清浄度の和を意味する。又、
粗粒化の発生率は１００倍の倍率で１０視野検鏡した場
合の面積割合で表示したものである。Table 3 shows the results of examination of the cleanliness and the maximum diameter of Ti carbosulfide and Zr carbosulfide in the round bar after hot forging, and the coarse grains obtained by performing the thermomechanical test under the conditions 1 to 4. The results of the survey on the rate of formation In the table, “Ti, Z”
In the column of "r carbosulfide", when Ti and Zr are added in combination, the "maximum diameter" is the value of the larger one of the carbosulfides, and the cleanliness means the sum of cleanliness. or,
The rate of occurrence of coarsening is represented by the area ratio when a 10-field microscope is used at a magnification of 100 times.
【００９０】[0090]
【表３】 [Table 3]
【００９１】表３から、化学組成及び最大直径が１０μ
ｍ以下の「Ｔｉ、Ｚｒ炭硫化物」の清浄度が本発明で規
定する範囲内にある本発明例に係る場合と、比較例に係
る鋼のうち鋼Ｌ、鋼Ｎ及び鋼 Ｏを素材とする場合だけ
が本発明で規定した条件で加熱処理した場合に異常粒成
長しないことが明らかである。Table 3 shows that the chemical composition and the maximum diameter were 10 μm.
m and the steel L, steel N, and steel O of the steels according to the present invention example in which the cleanliness of “Ti, Zr carbosulfide” is within the range specified in the present invention. It is clear that abnormal grain growth does not occur when heat treatment is performed under the conditions specified in the present invention.
【００９２】（実施例２）前記の実施例１で作製した鋼
Ａ〜Ｓの鋼片を１１９０℃に加熱してから、１１９０〜
１０００℃の温度で３０ｍｍ直径の丸棒に熱間鍛造し
た。(Example 2) The steel slabs of the steels A to S produced in Example 1 were heated to 1190 ° C, and then heated to 1190 ° C.
It was hot forged into a 30 mm diameter round bar at a temperature of 1000 ° C.
【００９３】こうして得られた熱間鍛造後の丸棒から実
施例１の場合と同様に、JIS G 0555の図１に則って試験
片を採取し、鏡面研磨した幅が１５ｍｍで高さが２０ｍ
ｍの被検面を、倍率が４００倍の光学顕微鏡で６０視野
観察して、Ｔｉ炭硫化物及びＺｒ炭硫化物を他の介在物
と区分しながらその清浄度（清浄度の和）を測定した。
Ｔｉ炭硫化物及びＺｒ炭硫化物の最大直径も、倍率が４
００倍の光学顕微鏡で６０視野観察して調査した。A test piece was taken from the thus obtained hot-forged round bar in the same manner as in Example 1 according to FIG. 1 of JIS G 0555, and the mirror-polished width was 15 mm and the height was 20 m.
The surface to be inspected for m is observed with an optical microscope having a magnification of 400 times in 60 visual fields, and its cleanliness (sum of cleanliness) is measured while distinguishing Ti and Zr carbosulfides from other inclusions. did.
The maximum diameter of Ti and Zr carbosulfides is also 4
Investigation was performed by observing 60 visual fields with an optical microscope of 00 times.
【００９４】又、上記の熱間鍛造後の丸棒の中心部から
ＪＩＳ３号シャルピ−衝撃試験片を切り出し、表面硬化
処理として１０５０℃×４ｈｒ（炭素ポテンシャル：
０．８％）の浸炭処理を行った後油焼入れし、更に、１
６０℃で焼戻しを行った。次いで、常温で衝撃試験を行
うとともに試験片中心部すなわち芯部の硬度測定を行っ
た。Further, a JIS No. 3 Charpy impact test piece was cut out from the center of the round bar after the hot forging, and subjected to a surface hardening treatment at 1050 ° C. × 4 hr (carbon potential: 4 hours).
0.8%), followed by oil quenching,
Tempering was performed at 60 ° C. Next, an impact test was performed at room temperature, and the hardness of the center of the test piece, that is, the core was measured.
【００９５】被削性評価のため、ドリル穿孔試験も実施
した。すなわち、前記した熱間鍛造後の３０ｍｍ直径の
丸棒を２５ｍｍの長さに輪切りにしたものを用いて、Ｒ
／２部（Ｒは丸棒の半径）についてその長さ方向に貫通
孔をあけ、刃先摩損により穿孔不能となったときの貫通
孔の個数を数え、被削性の評価を行った。穿孔条件は、
ＪＩＳ高速度工具鋼ＳＫＨ５１のφ５ｍｍストレ−トシ
ャンクドリルを使用し、水溶性の潤滑剤を用いて、送り
０．１５ｍｍ／ｒｅｖ、回転数９８０ｒｐｍで行った。For the evaluation of machinability, a drilling test was also performed. That is, a round bar having a diameter of 30 mm after the above-described hot forging was cut into 25 mm lengths, and R was used.
For / 2 parts (R is the radius of the round bar), through holes were made in the length direction, and the number of through holes when drilling was impossible due to wear of the cutting edge was counted to evaluate the machinability. The drilling conditions are
This was carried out at a feed rate of 0.15 mm / rev and a rotation speed of 980 rpm using a φ5 mm straight shank drill made of JIS high-speed tool steel SKH51 and a water-soluble lubricant.
【００９６】表４に各種試験の結果を示す。なお、この
表についても、「Ｔｉ、Ｚｒ炭硫化物」とした欄におい
て、ＴｉとＺｒとを複合添加した場合には「最大直径」
はいずれか大きい方の炭硫化物の値であり、清浄度は清
浄度の和を意味する。Table 4 shows the results of various tests. Also in this table, in the column of “Ti, Zr carbosulfide”, when Ti and Zr are added in combination, the “maximum diameter”
Is the larger value of the carbosulfide, and the cleanliness means the sum of the cleanliness.
【００９７】[0097]
【表４】 [Table 4]
【００９８】表４から、化学組成及び最大直径が１０μ
ｍ以下の「Ｔｉ、Ｚｒ炭硫化物」の清浄度が本発明で規
定する範囲内にある本発明例に係る場合にＨｖ３００以
上の芯部硬度と２０Ｊ／ｃｍ2 以上の衝撃値が得られる
ことが明らかである。更に、被削性も良好なことがわか
る。したがって、本発明に係る鋼材を素材とする表面硬
化部品は自動車や産業機械が使用される過酷な環境にお
いても充分な耐久性を発揮できることになる。From Table 4, it can be seen that the chemical composition and the maximum diameter are 10 μm.
m, a core hardness of Hv 300 or more and an impact value of 20 J / cm 2 or more can be obtained when the cleanliness of “Ti, Zr carbosulfide” of m or less is within the range specified in the present invention. Is evident. Furthermore, it turns out that machinability is also favorable. Therefore, the surface-hardened component made of steel according to the present invention can exhibit sufficient durability even in a harsh environment where automobiles and industrial machines are used.
【００９９】一方、前記実施例１において本発明で規定
した条件で加熱処理した場合に異常粒成長しなかった比
較例に係る鋼の鋼Ｌ、鋼Ｎ及び鋼Ｏを素材とする場合に
は、芯部硬度と衝撃値のいずれかが低く、表面硬化部品
の実環境での耐久性は極めて劣化したものとなってしま
う。On the other hand, when the steel L, steel N and steel O of the comparative example which did not undergo abnormal grain growth when subjected to the heat treatment under the conditions specified in the present invention in Example 1 were used as the raw materials, Either the core hardness or the impact value is low, and the durability of the surface-hardened component in a real environment is extremely deteriorated.
【０１００】又、比較例のうち、最大直径が１０μｍ以
下の「Ｔｉ、Ｚｒ炭硫化物」の清浄度が０．０５％を下
回る鋼Ｏ〜Ｓ、並びにＴｉ＋Ｚｒの含有量が本発明で規
定する値を下回る鋼Ｋ及び鋼Ｏ〜Ｓを素材とする場合に
はドリル貫通孔の個数が１００個に達せず被削性が劣っ
ている。In the comparative examples, the steels O to S having a cleanliness of less than 0.05% of “Ti, Zr carbosulfide” having a maximum diameter of 10 μm or less and the content of Ti + Zr are defined in the present invention. When using steel K and steels O to S below the values, the number of drill through holes does not reach 100 and the machinability is inferior.
【０１０１】（実施例３）前記の実施例１で作製した鋼
Ａ〜Ｈ、鋼Ｌ及び鋼Ｎの鋼片を１１８０℃で真空中の熱
処理を行い、一旦常温まで０．２５℃／ｓの冷却速度で
冷却した。その後、１１００℃に加熱してから、１１０
０〜１０００℃の温度で３０ｍｍ直径の丸棒に熱間鍛造
した。(Example 3) The steel slabs of the steels A to H, the steel L, and the steel N produced in the above-mentioned Example 1 were subjected to a heat treatment in vacuum at 1180 ° C, and once to room temperature at a rate of 0.25 ° C / s. Cool at the cooling rate. Then, after heating to 1100 ° C.,
It was hot forged into a round bar having a diameter of 30 mm at a temperature of 0 to 1000 ° C.
【０１０２】こうして得られた熱間鍛造後の丸棒から実
施例１の場合と同様に、JIS G 0555の図１に則って試験
片を採取し、鏡面研磨した幅が１５ｍｍで高さが２０ｍ
ｍの被検面を、倍率が４００倍の光学顕微鏡で６０視野
観察して、Ｔｉ炭硫化物及びＺｒ炭硫化物を他の介在物
と区分しながらその清浄度（清浄度の和）を測定した。
Ｔｉ炭硫化物及びＺｒ炭硫化物の最大直径も、倍率が４
００倍の光学顕微鏡で６０視野観察して調査した。In the same manner as in Example 1, a test piece was taken from the thus obtained hot forged round bar in accordance with FIG. 1 of JIS G 0555, and the mirror-polished width was 15 mm and the height was 20 m.
The surface to be inspected for m is observed with an optical microscope having a magnification of 400 times in 60 visual fields, and its cleanliness (sum of cleanliness) is measured while distinguishing Ti and Zr carbosulfides from other inclusions. did.
The maximum diameter of Ti and Zr carbosulfides is also 4
Investigation was performed by observing 60 visual fields with an optical microscope of 00 times.
【０１０３】又、上記の熱間鍛造後の丸棒の中心部から
ＪＩＳ３号シャルピ−衝撃試験片を切り出し、表面硬化
処理として１０５０℃×４ｈｒ（炭素ポテンシャル：
０．８％）の浸炭処理を行った後油焼入れし、更に、１
７０℃で焼戻しを行った。次いで、常温での衝撃試験と
ともに試験片中心部硬度すなわち芯部硬度の測定を行っ
た。Further, a JIS No. 3 Charpy impact test piece was cut out from the center of the round bar after the hot forging and subjected to surface hardening treatment at 1050 ° C. × 4 hr (carbon potential: 4 hours).
0.8%), followed by oil quenching,
Tempering was performed at 70 ° C. Next, the hardness at the center of the test piece, that is, the core hardness was measured together with the impact test at room temperature.
【０１０４】被削性評価のためのドリル穿孔試験も実施
した。その試験片、試験方法及び評価方法は実施例２で
述べたとおりである。A drilling test for evaluating machinability was also performed. The test piece, test method, and evaluation method are as described in Example 2.
【０１０５】表５に各種試験の結果を示す。なお、この
表についても、「Ｔｉ、Ｚｒ炭硫化物」とした欄におい
て、ＴｉとＺｒとを複合添加した場合には「最大直径」
はいずれか大きい方の炭硫化物の値であり、清浄度は清
浄度の和を意味する。Table 5 shows the results of various tests. Also in this table, in the column of “Ti, Zr carbosulfide”, when Ti and Zr are added in combination, the “maximum diameter”
Is the larger value of the carbosulfide, and the cleanliness means the sum of the cleanliness.
【０１０６】[0106]
【表５】 [Table 5]
【０１０７】表５から、化学組成及び最大直径が１０μ
ｍ以下の「Ｔｉ、Ｚｒ炭硫化物」の清浄度が本発明で規
定する範囲内にある本発明例に係る場合にＨｖ３００以
上の芯部硬度と２０Ｊ／ｃｍ2 以上の衝撃値が得られる
ことが明らかである。更に、被削性も良好なことがわか
る。したがって、本発明に係る鋼材を素材とする表面硬
化部品は自動車や産業機械が使用される過酷な環境にお
いても充分な耐久性を発揮できることになる。From Table 5, it is found that the chemical composition and the maximum diameter are 10 μm.
m, a core hardness of Hv 300 or more and an impact value of 20 J / cm 2 or more can be obtained when the cleanliness of “Ti, Zr carbosulfide” of m or less is within the range specified in the present invention. Is evident. Furthermore, it turns out that machinability is also favorable. Therefore, the surface-hardened component made of steel according to the present invention can exhibit sufficient durability even in a harsh environment where automobiles and industrial machines are used.
【０１０８】一方、前記実施例１において本発明で規定
した条件で加熱処理した場合に粗粒化が生じなかった比
較例に係る鋼のうち鋼Ｌ及び鋼Ｎを素材とする場合は、
芯部硬さと衝撃値のいずれかが低く、表面硬化部品の実
環境での耐久性は極めて劣化したものとなってしまう。On the other hand, when the steel L and the steel N of the steels according to the comparative example in which the coarsening did not occur when the heat treatment was performed under the conditions specified in the present invention in Example 1 were used,
Either the core hardness or the impact value is low, and the durability of the surface-hardened component in a real environment is extremely deteriorated.
【０１０９】[0109]
【発明の効果】本発明による表面硬化部品は強度と靭性
に優れ、粗粒化も生じないので、自動車や産業機械など
の各種機械構造部品、特に歯車を代表とする表面硬化部
品として利用することができる。本発明の耐粗粒化肌焼
鋼材は被削性に優れるので、上記の表面硬化部品は、本
発明の耐粗粒化肌焼鋼材を素材とし、これに本発明方法
を適用することによって、比較的容易に製造することが
できる。The surface-hardened parts according to the present invention are excellent in strength and toughness, and do not cause coarsening. Therefore, they can be used as various mechanical structural parts such as automobiles and industrial machines, especially as surface-hardened parts such as gears. Can be. Since the coarse-grained case hardened steel material of the present invention is excellent in machinability, the above-mentioned surface-hardened parts are made of the coarse-grained case hardened steel material of the present invention, and by applying the method of the present invention thereto, It can be manufactured relatively easily.
フロントページの続き (51)Int.Cl.6 識別記号 ＦＩ // Ｃ２３Ｃ 8/22 Ｃ２３Ｃ 8/22 Continued on the front page (51) Int.Cl. 6 Identification symbol FI // C23C 8/22 C23C 8/22
Claims (4)
０．０１〜０．５％、Ｍｎ：０．６〜２．０％、Ｐ：
０．０３％以下、Ｓ：０．００２〜０．２％、Ｎｂ：
０．００５〜０．１０％、Ｔｉ：１．０％以下、Ｚｒ：
１．０％以下で、且つ、Ｔｉ（％）＋Ｚｒ（％）：０．
０４〜１．０％、Ｎ：０．００２〜０．００８％、Ｃ
ｒ：０〜２．０％、Ｍｏ：０〜１．０％、Ｗ：０〜１．
０％及びＡｌ：０〜０．１０％を含み、下記式で表さ
れるｆｎ１の値が０％を超え、残部はＦｅ及び不可避不
純物の化学組成で、更に、鋼中のＴｉ炭硫化物及びＺｒ
炭硫化物の最大直径が１０μｍ以下で、且つ、その量の
和が清浄度で０．０５％以上である被削性に優れた耐粗
粒化肌焼鋼材。 ｆｎ１＝Ｔｉ（％）＋Ｚｒ（％）−１．２Ｓ（％）・・・・C. 0.1 to 0.3% by weight, Si:
0.01-0.5%, Mn: 0.6-2.0%, P:
0.03% or less, S: 0.002 to 0.2%, Nb:
0.005 to 0.10%, Ti: 1.0% or less, Zr:
1.0% or less, and Ti (%) + Zr (%): 0.
04-1.0%, N: 0.002-0.008%, C
r: 0 to 2.0%, Mo: 0 to 1.0%, W: 0 to 1.
0% and Al: 0 to 0.10%, the value of fn1 represented by the following formula exceeds 0%, and the balance is the chemical composition of Fe and unavoidable impurities. Zr
A coarse-grained case hardening steel excellent in machinability, in which the maximum diameter of carbon sulfide is 10 μm or less and the sum of the amounts is 0.05% or more in cleanliness. fn1 = Ti (%) + Zr (%)-1.2S (%)
のＴｉ炭硫化物とＺｒ炭硫化物を備え、更に、芯部硬度
がＨｖ３００以上、衝撃値が２０Ｊ／ｃｍ2 以上である
表面硬化部品。2. It has the chemical composition, size and amount of Ti carbosulfide and Zr carbosulfide according to claim 1, and has a core hardness of Hv 300 or more and an impact value of 20 J / cm 2 or more. Surface hardened parts.
先立って１１５０℃以上に加熱してから熱間鍛造するこ
とを特徴とする強度と靭性に優れた表面硬化部品の製造
方法。3. A method for producing a surface-hardened part having excellent strength and toughness, wherein the steel material according to claim 1 is heated to 1150 ° C. or more prior to the surface hardening treatment and then hot forged.
熱処理の少なくとも１つの工程を１１５０℃以上に加熱
して行い、その後鍛造し、更に表面硬化処理することを
特徴とする強度と靭性に優れた表面硬化部品の製造方
法。4. A strength characterized in that the steel material according to claim 1 is subjected to at least one of the steps of lumping, rolling and heat treatment at a temperature of 1150 ° C. or higher, then forged, and further subjected to a surface hardening treatment. Method for manufacturing surface-hardened parts with excellent toughness.
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP13651298A JP3879251B2 (en) | 1998-05-19 | 1998-05-19 | Manufacturing method of surface hardened parts with excellent strength and toughness |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP13651298A JP3879251B2 (en) | 1998-05-19 | 1998-05-19 | Manufacturing method of surface hardened parts with excellent strength and toughness |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH11323482A true JPH11323482A (en) | 1999-11-26 |
| JP3879251B2 JP3879251B2 (en) | 2007-02-07 |
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ID=15176913
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|---|---|---|---|
| JP13651298A Expired - Fee Related JP3879251B2 (en) | 1998-05-19 | 1998-05-19 | Manufacturing method of surface hardened parts with excellent strength and toughness |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6362132B1 (en) * | 2000-09-06 | 2002-03-26 | Eastman Kodak Company | Dye-donor element containing transferable protection overcoat |
| WO2011114775A1 (en) * | 2010-03-16 | 2011-09-22 | 新日本製鐵株式会社 | Steel for nitrocarburization, nitrocarburized components, and production method for same |
-
1998
- 1998-05-19 JP JP13651298A patent/JP3879251B2/en not_active Expired - Fee Related
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6362132B1 (en) * | 2000-09-06 | 2002-03-26 | Eastman Kodak Company | Dye-donor element containing transferable protection overcoat |
| WO2011114775A1 (en) * | 2010-03-16 | 2011-09-22 | 新日本製鐵株式会社 | Steel for nitrocarburization, nitrocarburized components, and production method for same |
| JP4819201B2 (en) * | 2010-03-16 | 2011-11-24 | 新日本製鐵株式会社 | Soft nitriding steel, soft nitriding steel component and manufacturing method thereof |
| US9284632B2 (en) | 2010-03-16 | 2016-03-15 | Nippon Steel & Sumitomo Metal Corporation | Steel for nitrocarburizing, nitrocarburized steel part, and producing method of nitrocarburized steel part |
| US10196720B2 (en) | 2010-03-16 | 2019-02-05 | Nippon Steel & Sumitomo Metal Corporation | Steel for nitrocarburizing, nitrocarburized steel part, and producing method of nitrocarburized steel part |
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| Publication number | Publication date |
|---|---|
| JP3879251B2 (en) | 2007-02-07 |
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