JP2002038243A - Stainless steel having plural phase structure and its production method - Google Patents
Stainless steel having plural phase structure and its production methodInfo
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- JP2002038243A JP2002038243A JP2000226993A JP2000226993A JP2002038243A JP 2002038243 A JP2002038243 A JP 2002038243A JP 2000226993 A JP2000226993 A JP 2000226993A JP 2000226993 A JP2000226993 A JP 2000226993A JP 2002038243 A JP2002038243 A JP 2002038243A
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- stainless steel
- phase
- martensite
- phase structure
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Abstract
Description
【0001】[0001]
【発明の属する技術分野】本発明は、高強度でありなが
ら加工性に優れ、かつ高疲労特性を有する安価な複相組
織ステンレス鋼板およびその製造方法に関するものであ
る。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inexpensive dual phase stainless steel sheet having high strength, excellent workability and high fatigue properties, and a method for producing the same.
【0002】本発明にかかるステンレス鋼板は、多種形
状への加工後に使用されるバネないしバネ部品、バネ性
を必要とする電子機器、機械部品全般への使用に適す
る。より具体的には、自動車やオートバイのエンジン用
ガスケットに最適である。The stainless steel sheet according to the present invention is suitable for use in springs or spring parts used after processing into various shapes, electronic equipment requiring spring properties, and mechanical parts in general. More specifically, it is most suitable for gaskets for engines of automobiles and motorcycles.
【0003】[0003]
【従来の技術】エンジン用ガスケットは燃焼ガス、冷却
水、潤滑油を密閉することを目的としてシリンダーヘッ
ドとブロックとの間の隙間に挿入されるシール部品であ
り、一般的にはエンジンの燃焼室(形状、数)に対応す
る穴 (ポア) の開いた複数(1〜3)枚のステンレス鋼薄板
を重ねた外観からなる。2. Description of the Related Art An engine gasket is a seal component inserted into a gap between a cylinder head and a block for the purpose of sealing off combustion gas, cooling water and lubricating oil. It has the appearance of multiple (1-3) stainless steel sheets with holes (pores) corresponding to (shape, number).
【0004】その基本構造はポアの周囲にプレス加工等
により円環状の凸部(ビード)が形成され、燃焼に伴い
発生する上述の隙間をその反発力で密閉するものであ
る。従来、ガスケット用材料には高強度でありながら加
工性に優れることが要求され、Cr、Niを主成分とするSU
S301、SUS304等を中心とする準安定オーステナイト系ス
テンレス鋼の調質圧延材が使用されてきた。The basic structure is such that an annular convex portion (bead) is formed around the pore by press working or the like, and the above-mentioned gap generated due to combustion is sealed by the repulsive force. Conventionally, gasket materials have been required to have high strength but excellent workability.
A temper-rolled material of metastable austenitic stainless steel centering on S301, SUS304 and the like has been used.
【0005】この材料は加工誘起変態による高硬度中間
相であるマルテンサイト相の生成により加工硬化率が大
きく、圧延により比較的容易に高強度が得られる。ま
た、同変態に伴う変形部の硬化によりネッキング (くび
れ) が抑制されて高い均一伸びを示し、加工性にも優れ
る。[0005] This material has a high work hardening rate due to the formation of a martensite phase which is a high hardness intermediate phase due to work induced transformation, and high strength can be obtained relatively easily by rolling. In addition, necking (constriction) is suppressed due to the hardening of the deformed portion due to the transformation, showing high uniform elongation, and excellent workability.
【0006】なお、材料の強度と加工性は一般的に相反
する特性であり、高強度化に伴い必要な加工性を維持す
ることが難しくなる。これらのことは、準安定オーステ
ナイト鋼が極めて優れた材料であることを示す。しか
し、高価なNiを多量に含有するため、同材も高価なもの
となっていた。また、強度が圧延率、圧延温度等の条件
に強く依存するため安定した強度を得ることが難しく、
品質的にバラッキが大きいという問題もあった。[0006] The strength and workability of a material are generally contradictory characteristics, and it becomes difficult to maintain the required workability as the strength increases. These facts indicate that metastable austenitic steel is a very excellent material. However, the material was expensive because it contained a large amount of expensive Ni. Further, it is difficult to obtain a stable strength because the strength is strongly dependent on conditions such as a rolling ratio and a rolling temperature,
There was also a problem that the quality was large.
【0007】これらの問題に際して、高価なNiを殆ど含
有せず、10〜20% 程度のCrを主成分とするステンレス鋼
の焼入材の適用も特開平7-278758号公報等において検討
され始めている。このステンレス鋼は室温において本来
はフェライト相構造となるはずであるが、Ac1変態点以
上に加熱、高温でのオーステナイト相領域から急冷(焼
入れ) することにより室温において侵入型固溶元素(C
、N)が過飽和に固溶した高硬度中間相であるマルテン
サイト相に変態し、高硬度が得られる。なお、Ac1変態
点は加熱時のオーステナイト相への変態開始温度であ
る。In view of these problems, application of a stainless steel quenching material containing almost no expensive Ni and containing about 10 to 20% of Cr as a main component has been studied in Japanese Patent Application Laid-Open No. 7-278758. I have. Although this stainless steel should originally have a ferrite phase structure at room temperature, it is heated to a temperature higher than the Ac 1 transformation point and quenched (quenched) from the austenite phase region at a high temperature to form an interstitial solid solution element (C
, N) are transformed into a martensite phase, which is a high hardness intermediate phase in which the solid solution is supersaturated, and high hardness is obtained. The Ac 1 transformation point is the temperature at which transformation to the austenite phase starts during heating.
【0008】しかし、一般にマルテンサイト単相組織と
した場合、焼入まま材は硬くなり過ぎてその後の製品形
状への加工が難しい場合が多い。このため、加工性改善
を目的とした(500 ℃前後での)焼戻しが必要となる。
ただし、この焼戻しが炭化物等の析出による脆化やCr欠
乏相発生によりステンレス鋼として必要な耐食性を損な
う原因になるとともに、製造コストを上昇させる原因と
なっていた。However, in general, when the steel has a martensite single phase structure, the material after quenching becomes too hard, and it is often difficult to process the product into a subsequent product shape. For this reason, tempering (at around 500 ° C.) is required to improve workability.
However, this tempering causes embrittlement due to precipitation of carbides and the like and generation of a Cr-deficient phase, thereby impairing the corrosion resistance required for stainless steel, and increasing the production cost.
【0009】これらの状況から、本発明者らは特開2000
−109957号公報 (特願平10-282758号) において、侵入
型固溶元素の量を調整した10〜17% のCrを含有するステ
ンレス鋼をAc1変態点以上のオーステナイトとフェライ
トの二相温度域から焼入することで、硬度調整されたマ
ルテンサイトと残存するフェライトの二相組織とし、そ
の相比率の最適化により焼戻しを施すことなく高硬度と
優れた加工性を両立させたガスケット用材料を提案して
いる。[0009] Under these circumstances, the present inventors have disclosed in
In -109957 Patent Publication (Japanese Patent Application No. Hei 10-282758), interstitial solid solution elements in an amount of a stainless steel containing 10-17% of Cr adjusted above Ac 1 transformation point of the austenite and ferrite two-phase temperature Material for gasket that achieves both high hardness and excellent workability without tempering by quenching from the zone to form a two-phase structure of martensite and residual ferrite with hardness adjusted by optimizing the phase ratio Has been proposed.
【0010】[0010]
【発明が解決しようとする課題】しかし、最近のエンジ
ンはユーザニーズ等から高出力傾向にあると同時に、厳
しい排ガス規制に伴う燃費向上 (環境問題) に対応する
ため様々な方法での軽量化も同時に進められている。こ
のような軽量化は、エンジン剛性が低下し、燃焼に伴い
シリンダーヘッドとブロックとの間に発生する隙間が増
大する傾向にあることを示す。However, recent engines have tended to have a high output due to user needs and the like, and at the same time, have been reduced in weight by various methods in order to cope with the improvement of fuel efficiency (environmental problem) due to strict exhaust gas regulations. It is proceeding at the same time. Such weight reduction indicates that the engine rigidity is reduced and the gap generated between the cylinder head and the block tends to increase with combustion.
【0011】すなわち、ガスケットの使用環境は更に過
酷となっている。これに伴いガスケット用材料にも上述
のように安価かつ高強度で加工性に優れるとともに、繰
返して付与される変動応力(隙間の増減)に耐える高疲
労特性を有することも要求されている。That is, the usage environment of the gasket is becoming severer. Along with this, the gasket material is also required to be inexpensive, have high strength and excellent workability as described above, and also have high fatigue properties that can withstand repeated stresses (increase / decrease in gaps).
【0012】本発明の課題は、安価で高強度かつ加工性
に優れるとともに、高疲労特性を有する例えばバネ用と
して有用なステンレス鋼板とその安定供給を可能とする
製造方法を提供することである。An object of the present invention is to provide a stainless steel sheet which is inexpensive, has high strength and is excellent in workability and has high fatigue characteristics, and is useful for, for example, a spring, and a manufacturing method capable of stably supplying the stainless steel sheet.
【0013】[0013]
【課題を解決するための手段】ところで、少なくとも前
述のようなCrを主成分とする二相組織ステンレス鋼板
に、増大する隙間に対応して更にビードを高くする等の
厳しい加工を施す場合、ガスケットへの加工自体が可能
であるばかりでなく最も厳しい加工が行われるビード部
の表層においてもシワないし微少割れ等の欠陥の発生が
みられない材料が求められる。そのような欠陥のみられ
る材料を疲労試験に供した場合、表層部の欠陥が応力集
中により急激に成長し、ガスケットには早い段階で板を
貫通する割れを生じるおそれがある。In the case where at least the above-described duplex stainless steel sheet containing Cr as a main component is subjected to severe processing such as further increasing a bead in response to an increased gap, a gasket is required. In addition to being capable of processing itself, a material that does not generate defects such as wrinkles or minute cracks in the surface layer of the bead where the most severe processing is performed is required. When a material having only such defects is subjected to a fatigue test, defects in the surface layer grow rapidly due to stress concentration, and a gasket may crack at an early stage through the plate.
【0014】なお、表層部の欠陥は硬質なマルテンサイ
ト相と軟質なフェライト相の結晶粒界で主に生じると考
えられる。すなわち、ある限度以上の加工を施した場
合、ガスケットへの加工は可能であっても、表層にはそ
のような欠陥が不可避的に発生すると考えられる。しか
し、このことは逆に加工を伴い、加工部に変動応力が繰
返し付与されるようなガスケット、更には同様の状況で
使用される多種バネないしバネ部品の長寿命化には加工
部の表層部に発生する欠陥、言い換えると疲労破壊起点
の発生を抑制することが極めて効果的であることを示す
ものである。It is considered that the surface layer defects mainly occur at the grain boundaries of the hard martensite phase and the soft ferrite phase. In other words, when processing beyond a certain limit is performed, it is considered that such a defect is unavoidably generated in the surface layer even if processing into a gasket is possible. However, this conversely involves processing, and gaskets in which fluctuating stress is repeatedly applied to the processed part, and furthermore, various types of springs or spring parts used in similar situations have a long service life. In other words, it is extremely effective to suppress the occurrence of defects that occur at the same time, in other words, the occurrence of fatigue fracture starting points.
【0015】すなわち、本発明は、Crを主成分とするス
テンレス鋼に対し、焼入に先立つAc1変態点以上の温度
への加熱、保持を、最も強力なオーステナイト安定化元
素の一つである窒素を含むガス雰囲気中で行うことによ
り、表層部を窒化してオーステナイト相を形成すること
で材料の加工性が大幅に改善されるとともに、加工部表
層での欠陥の発生が抑制され疲労特性が飛躍的に向上す
ることを発見したことにもとづくものである。[0015] That is, the present invention is one of the most powerful austenite stabilizing elements for heating and holding a stainless steel containing Cr as a main component to a temperature higher than the Ac 1 transformation point prior to quenching. By performing the process in a gas atmosphere containing nitrogen, the workability of the material is greatly improved by nitriding the surface layer to form an austenite phase, and the occurrence of defects in the processed surface layer is suppressed and the fatigue characteristics are reduced. It is based on the discovery of a dramatic improvement.
【0016】この場合、焼入後の (内部) 組織は従来と
同様のマルテンサイトとフェライトの二相とともに、マ
ルテンサイト単相としても充分な性能が得られる。N は
C とともに最も強力なオーステナイト安定化元素であ
り、溶解時に両元素ないしその何れか一方を多量に固溶
させること等により、高価なNiを殆ど含有することなく
材料をオーステナイト単相化することは実験室的には可
能である。In this case, the (internal) structure after quenching can obtain sufficient performance as a single phase of martensite together with a conventional two phase of martensite and ferrite. N is
It is the most powerful austenite stabilizing element together with C. It is an experiment to convert a material to an austenite single phase with almost no expensive Ni by dissolving both elements or one of them in a large amount during melting. It is possible in a room.
【0017】ただし、通常の工業的溶解装置でそのよう
な量のN およびC を固溶させることは困難であり、特殊
な装置を用いた場合には極めて高価な材料になると考え
られる。仮に固溶させたとしても、その後の板製造が極
めて困難となる。However, it is difficult to dissolve such amounts of N and C in a normal industrial dissolution apparatus, and it is considered that an extremely expensive material is used when a special apparatus is used. Even if a solid solution is formed, the subsequent manufacture of the plate becomes extremely difficult.
【0018】本発明は、通常使用される工業的装置での
製造が可能であるとともに、他の製造工程に負担をかけ
ることなく、最終の焼入工程において安価なCrを主成分
とするステンレス鋼の表層部のみをオーステナイト化す
ることで (準安定) オーステナイト系ステンレス鋼と同
等以上の高性能を得るものである。The present invention provides a stainless steel containing Cr as a main component, which can be manufactured by a commonly used industrial apparatus and is inexpensive in the final quenching step without burdening other manufacturing steps. By austeniticizing only the surface layer of (a), (metastable) high performance equivalent to or higher than that of austenitic stainless steel is obtained.
【0019】ここに、本発明はつぎの通りである。 (1) 質量% で C+N : 0.06%以上、0.50% 以下 Si : 0.1% 以上、2.0%以下 Mn : 0.1% 以上、3.0%以下 Cr : 10.0%以上、17.0% 以下 Ni : 1.0% 以下 Cu : 2.0% 以下 残部はFeおよび不純物元素から成る化学組成を備え、マ
ルテンサイト単相またはマルテンサイトとフェライトの
二相組織からなる材料の表層部をオーステナイト単相ま
たは同相を含む複相組織としたステンレス鋼板。Here, the present invention is as follows. (1) In mass% C + N: 0.06% or more, 0.50% or less Si: 0.1% or more, 2.0% or less Mn: 0.1% or more, 3.0% or less Cr: 10.0% or more, 17.0% or less Ni: 1.0% or less Cu : 2.0% or less The balance has a chemical composition consisting of Fe and impurity elements, and the surface layer of a material consisting of a single phase of martensite or a dual phase structure of martensite and ferrite has a single phase of austenite or a double phase structure containing the same phase. steel sheet.
【0020】(2) 上記(1) 記載の化学組成を備えた、
マルテンサイト単相またはマルテンサイトとフェライト
の二相組織からなるステンレス鋼板を、所定の板厚に減
厚後、窒素ガスまたは窒素ガスと還元性ガス (例:水
素) を混合した雰囲気中においてAc1変態点以上に加
熱、保持後、焼入することを特徴とする複相組織ステン
レス鋼板の製造方法。(2) having the chemical composition described in (1) above,
After reducing the thickness of a stainless steel sheet composed of a single phase of martensite or a two-phase structure of martensite and ferrite to a predetermined thickness, Ac 1 is obtained in an atmosphere containing nitrogen gas or a mixture of nitrogen gas and a reducing gas (eg, hydrogen). A method for producing a stainless steel sheet having a dual phase structure, wherein the steel sheet is heated and maintained at a temperature equal to or higher than the transformation point and then quenched.
【0021】(3) 上記(1) の複相組織ステンレス鋼を
用いたエンジン用ガスケット。(3) An engine gasket using the duplex stainless steel according to (1).
【0022】[0022]
【発明の実施の形態】本発明において、化学組成および
製造工程を上述のように規定した理由について説明す
る。本明細書において、化学組成を規定する「%」は、
とくにことわりのない限り「質量%」である。BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the reason for defining the chemical composition and the manufacturing process as described above will be described. In the present specification, “%” defining the chemical composition is:
Unless otherwise specified, it is “% by mass”.
【0023】C +N: 0.06%以上、0.50% 以下 C およびN は強力なオーステナイト安定化元素であると
ともに侵入型固溶元素でもあり、主にマルテンサイト相
を硬化する。それらの効果は両元素でほぼ同等と考えら
れる。両元素合計の含有量が0.06% 未満では焼入後にHv
300 以上の必要な硬度を得ることが難しい。逆に過度に
含有した場合、硬くなり過ぎるため、その後の板製造、
製品への加工が難しくなる。また、0.50% を超えた含有
量の増加により窒化が抑制され、表層部のオーステナイ
ト化が難しくなる。C + N: 0.06% or more and 0.50% or less C and N are not only strong austenite stabilizing elements but also interstitial solid solution elements, and mainly harden the martensite phase. These effects are considered to be almost the same for both elements. If the total content of both elements is less than 0.06%, Hv after quenching
It is difficult to obtain the required hardness of 300 or more. Conversely, if it is contained excessively, it will be too hard, so subsequent board production,
Processing into products becomes difficult. In addition, an increase in the content exceeding 0.50% suppresses nitriding, and makes it difficult to austenitize the surface layer.
【0024】したがって、両元素合計含有量を0.06% 以
上、0.50% 以下とした。更に好ましくは、0.10% 以上、
0.40% 以下である。なお、両元素合計の含有量は窒化後
の「表層部に窒素の濃化した」材料での平均値とした。Therefore, the total content of both elements is set to 0.06% or more and 0.50% or less. More preferably, 0.10% or more,
0.40% or less. Note that the total content of both elements was the average value of the material after nitriding, "the surface layer of which nitrogen was concentrated".
【0025】Si:0.1%以上、2.0%以下 Siは固溶強化元素であり、C +N 含有量により調整が必
要となるが含有量0.1%未満では焼入後にHv300 以上の硬
度を得ることが難しい。ただし、過度の添加は材料を硬
化し過ぎるとともに、介在物等を形成して板製造、製品
への加工が難しくなる。また、Siはフェライト安定化元
素であるとともに、窒素固溶量を減少して窒化を抑制す
ると考えられ、表層部のオーステナイト化を阻害する。
したがって、含有量を0.1%以上、2.0%以下とした。更に
好ましくは、0.15% 以上、1.8%以下である。Si: 0.1% or more and 2.0% or less Si is a solid solution strengthening element, and it is necessary to adjust the content according to the C + N content, but if the content is less than 0.1%, it is difficult to obtain a hardness of Hv300 or more after quenching. . However, excessive addition hardens the material too much and forms inclusions and the like, making it difficult to manufacture a plate and process it into a product. Further, Si is a ferrite stabilizing element, and is considered to suppress nitriding by decreasing the amount of solid solution of nitrogen, and inhibits austenitization of a surface layer portion.
Therefore, the content is set to 0.1% or more and 2.0% or less. More preferably, it is 0.15% or more and 1.8% or less.
【0026】Mn: 0.1%以上、3.0%以下 Mnはオーステナイト安定化元素である。また、窒素固溶
量を増加して窒化を促進すると考えられ、表層部のオー
ステナイト化のために有効な元素であり、含有量0.1%以
上が必要である。ただし、過度に添加した場合、介在物
等を形成してその後の板製造、製品への加工が難しくな
るとともに、材料がオーステナイト化して逆に焼入後に
必要な硬度を得ることが困難になる。したがって、Mn含
有量を0.1%以上、3.0%以下とした。更に好ましくは、0.
3%以上、2.6%以下である。Mn: 0.1% or more and 3.0% or less Mn is an austenite stabilizing element. Further, it is considered that nitriding is promoted by increasing the amount of solid solution of nitrogen, and is an element effective for austenitizing the surface layer portion, and the content is required to be 0.1% or more. However, if added excessively, it becomes difficult to form inclusions and the like and subsequently manufacture the plate and work into a product, and the material becomes austenite and conversely, it becomes difficult to obtain the required hardness after quenching. Therefore, the Mn content is set to 0.1% or more and 3.0% or less. More preferably, 0.
3% or more and 2.6% or less.
【0027】Cr: 10.0% 以上,17.0% 以下 Crはステンレス鋼の基本元素であり、有効な耐食性を得
るためには10.0% 以上添加する。また、窒化を促進する
と考えられるものの、フェライト安定化元素であり、過
度の添加は表層部のオーステナイト化を阻害する。した
がって、その上限を17.0% 以下とした。好ましくは、1
6.0% 以下であり、更に好ましくは15.6%以下である。Cr: 10.0% or more, 17.0% or less Cr is a basic element of stainless steel, and is added at 10.0% or more to obtain effective corrosion resistance. Although it is thought to promote nitriding, it is a ferrite stabilizing element, and excessive addition impairs austenitization of the surface layer. Therefore, the upper limit was set to 17.0% or less. Preferably, 1
It is at most 6.0%, more preferably at most 15.6%.
【0028】Ni: 1.0%以下 Niは最も強力なオーステナイト安定化元素であり、Mn、
Cu含有量により調整が必要となる。ただし、上述のよう
に高価な元素であるとともに、窒化を抑制すると考えら
れる。したがって、その含有量を1.0%以下とした。更に
好ましくは、 0.9% 以下である。Ni: 1.0% or less Ni is the most powerful austenite stabilizing element.
Adjustment is required depending on the Cu content. However, it is considered that it is an expensive element as described above and also suppresses nitriding. Therefore, its content is set to 1.0% or less. More preferably, it is 0.9% or less.
【0029】Cu: 2.0%以下 Cuはオーステナイト安定化元素であり、Mn、Ni含有量に
より調整が必要となる。窒化への影響は小さいと考えら
れる。ただし、過度に添加した場合、粒界等に析出して
板製造、製品への加工が難しくなる。したがって、その
含有量を2.0%以下とした。更に好ましくは、1.3%以下で
ある。Cu: 2.0% or less Cu is an austenite stabilizing element and needs to be adjusted depending on the contents of Mn and Ni. The effect on nitriding is considered to be small. However, if it is added excessively, it will precipitate at the grain boundaries and the like, making it difficult to manufacture a plate and process it into a product. Therefore, the content is set to 2.0% or less. More preferably, it is at most 1.3%.
【0030】残部はFeおよび不純物元素からなる。な
お、これらの成分以外に工業的側面より添加される元
素、例えば溶製時に脱酸剤として使用されるCa、Al、Ti
あるいはREM(希土類金属)、熱間加工性の改善が見込ま
れる B、耐食性を大幅に向上することが期待されるMo等
を必要に応じて総計で1.0%以下含有しても差し支えな
い。The balance consists of Fe and impurity elements. In addition, elements added from an industrial aspect other than these components, for example, Ca, Al, Ti used as a deoxidizing agent during melting.
Alternatively, a total of 1.0% or less of REM (rare earth metal), Mo, for which hot workability is expected to be improved, and Mo, which is expected to greatly improve corrosion resistance, may be included as necessary.
【0031】次に、出発材料の組織の限定理由について
説明する。出発材料の組織をマルテンサイト単相または
マルテンサイトとフェライトの二相組織とするのは、高
硬度のマルテンサイト相により焼入後の材料を強化する
ためである。Next, the reasons for limiting the structure of the starting material will be described. The reason why the structure of the starting material is a martensite single phase or a two-phase structure of martensite and ferrite is to strengthen the material after quenching by a martensite phase having high hardness.
【0032】なお、材料の硬度はガスケットを完全に圧
縮した後にも充分なビード高さを維持可能と考えられる
Hv300 以上が望ましい。また、同硬度を満たした上で材
料が優れた加工性を示す相比率は、マルテンサイト量40
体積% 以上90体積% 以下、残部フェライト相の二相状態
であるが、表層部窒化後にはマルテンサイト量30体積%
以上、残部フェライト相の範囲に拡大した。It is considered that the hardness of the material can maintain a sufficient bead height even after the gasket is completely compressed.
Hv300 or more is desirable. The phase ratio at which the material exhibits excellent workability while satisfying the same hardness is a martensite content of 40%.
Volume% or more and 90 volume% or less, the two-phase state of the remaining ferrite phase, but after nitriding the surface layer, the martensite content is 30 volume%.
As described above, the range was expanded to the range of the remaining ferrite phase.
【0033】材料の表層部をオーステナイト単相または
同相を含む複相組織とするのは、加工性が改善されると
ともに、加工にともなう表層でのシワ、微小割れ等の欠
陥発生が抑制されて製品加工後に高疲労特性を得られる
ためである。The material having a surface layer having an austenite single phase or a multi-phase structure containing the same phase improves the workability and suppresses the occurrence of defects such as wrinkles and microcracks on the surface during the processing. This is because high fatigue characteristics can be obtained after processing.
【0034】オーステナイト相を不安定化して同相を含
む複相組織とするのは、加工誘起マルテンサイト変態で
の変形部の硬化により表層部での欠陥発生の更なる抑制
が期待されるためである。The reason why the austenite phase is destabilized to have a dual phase structure containing the same phase is that the generation of defects in the surface layer is expected to be further suppressed by the hardening of the deformed portion due to the work-induced martensitic transformation. .
【0035】ここに「表層部」は窒化処理によってオー
ステナイト相が形成される領域であり、通常表層より20
μm、好ましくは15μm程度の深さの領域である。実験
結果より、表層部のオーステナイト相比率は10体積% 以
上で充分な効果が認められた。また、その厚さは3 μm
以上とすることが望ましい。Here, the “surface layer” is a region where an austenite phase is formed by the nitriding treatment, and is usually 20 minutes from the surface layer.
μm, preferably a region having a depth of about 15 μm. From the experimental results, a sufficient effect was recognized when the austenite phase ratio in the surface layer was 10% by volume or more. The thickness is 3 μm
It is desirable to make the above.
【0036】次に本発明にかかる製造方法における各工
程の限定理由について説明する。まず、本発明にあって
は、マルテンサイト単相またはマルテンサイトとフェラ
イトの二相組織からなるステンレス鋼板を出発材料とす
るが、これは所定の強度を確保するためと、経済性を考
慮した結果である。Next, the reasons for limiting each step in the manufacturing method according to the present invention will be described. First, in the present invention, a stainless steel sheet composed of a single phase of martensite or a two-phase structure of martensite and ferrite is used as a starting material, and this is a result of securing predetermined strength and considering economic efficiency. It is.
【0037】このようにして用意した出発材料を、例え
ば熱間圧延、冷間圧延等適宜手段で所定厚さに減厚し、
Ac1変態点以上の温度域に加熱後、焼入するのはマルテ
ンサイト相を得るためである。実験結果より、加熱温度
は 850℃以上、焼入時の冷却速度はマルテンサイト変態
を完了すると考えられる200 ℃程度までを10℃/秒以上
とすることが望ましい。加熱、保持中の雰囲気を窒素ガ
スまたは窒素ガスと還元性ガスの混合状態とするのは、
窒素が最も強力なオーステナイト安定化元素の一つであ
り、窒化により表層部をオーステナイト単相または同相
を含む複相組織とすることが可能なためである。窒素ガ
ス単独の場合、一部をArガス等の不活性ガスで置換して
もよい。The starting material thus prepared is reduced to a predetermined thickness by a suitable means such as hot rolling or cold rolling.
The reason for quenching after heating to a temperature range equal to or higher than the Ac 1 transformation point is to obtain a martensite phase. From the experimental results, it is desirable that the heating temperature be 850 ° C or higher, and the cooling rate during quenching be 10 ° C / sec or higher up to about 200 ° C, which is considered to complete martensitic transformation. The atmosphere during heating and holding is set to nitrogen gas or a mixed state of nitrogen gas and reducing gas.
Nitrogen is one of the strongest austenite stabilizing elements, and the surface layer can have a single phase of austenite or a multiphase structure containing the same phase by nitriding. In the case of using nitrogen gas alone, a part thereof may be replaced with an inert gas such as Ar gas.
【0038】鋼材成分、表面被膜状態等による違いがあ
るものの、窒化は加熱温度が高いほど、保持時間が長い
ほど進行する。したがって、加熱温度は先述のAc1変態
温度も併せて考えるに900 ℃以上、工業的側面より1200
℃以下、保持時間は少なくとも10秒以上、工業的側面よ
り300秒以下が望ましい。水素等の還元性ガスを混合さ
せるのは窒化を阻害する酸化被膜等を減少させるためで
ある。Although there are differences depending on the steel material composition, the state of the surface coating, and the like, nitriding proceeds as the heating temperature is higher and the holding time is longer. Therefore, the heating temperature is 900 ° C. or more in consideration of the above-mentioned Ac 1 transformation temperature, and 1200 ° C. from the industrial aspect.
C. or lower, the holding time is preferably at least 10 seconds or more, and 300 seconds or less from an industrial viewpoint. The reason why the reducing gas such as hydrogen is mixed is to reduce an oxide film or the like that inhibits nitriding.
【0039】したがって、上記熱処理の直前ないし前工
程では、必要に応じて酸洗による被膜除去と低温での乾
燥ないし還元性ガス雰囲気下での予備焼鈍を施してもよ
い。このようにして得られる本発明にかかる複相組織ス
テンレス鋼板は、代表的にはガスケットとして用いられ
るが、その他自動車等のホーン (振動板) 等にも用いる
ことでその優れた特性を発揮することができる。Therefore, immediately before or before the heat treatment, if necessary, the film may be removed by pickling and dried at a low temperature or pre-annealed in a reducing gas atmosphere. The thus obtained dual-phase stainless steel sheet according to the present invention is typically used as a gasket, but exhibits excellent properties when used in other horns (diaphragms) of automobiles and the like. Can be.
【0040】[0040]
【実施例】表1に示す7種の化学組成からなるCrを主成
分とするステンレス鋼を10Kgの鋳塊にて溶製し、熱間圧
延、焼鈍、脱スケール後、冷間圧延および軟化焼鈍を繰
返して厚さ0.25mmの冷間圧延板を作成し、次の焼入熱処
理を施した。EXAMPLE A stainless steel containing Cr as a main component having the seven chemical compositions shown in Table 1 was smelted in a 10 kg ingot and subjected to hot rolling, annealing, descaling, cold rolling and softening annealing. Was repeated to prepare a cold-rolled sheet having a thickness of 0.25 mm, and subjected to the following quenching heat treatment.
【0041】熱処理雰囲気は 50 体積% 窒素と 50 体積
% 水素の混合ガスを主として、一部で100%窒素および真
空についても実施した。加熱温度は 900〜1200℃とし、
各温度までの加熱速度を20℃/秒にて固定した。加熱後
の保持時間は30秒を主として、一部180 秒でも実施し
た。その後の焼入れに際しての冷却速度は20℃/秒を主
として、一部10℃/秒でも実施した。The heat treatment atmosphere is 50% by volume nitrogen and 50% by volume.
The test was also carried out mainly on a mixed gas of% hydrogen, and partially on 100% nitrogen and vacuum. The heating temperature is 900-1200 ℃,
The heating rate to each temperature was fixed at 20 ° C./sec. The holding time after the heating was mainly 30 seconds, and was partially 180 seconds. The cooling rate during the subsequent quenching was mainly 20 ° C./sec, and was partially performed at 10 ° C./sec.
【0042】本実施例に関しては焼入熱処理前に酸化皮
膜等の除去を目的とした特別な処理を施していない。焼
入熱処理後の薄鋼板について、窒素含有量、炭素含有
量、相比率、硬さ、曲げ加工性および疲労強度を調査し
た。In this embodiment, no special treatment for removing an oxide film or the like was performed before the quenching heat treatment. The nitrogen content, carbon content, phase ratio, hardness, bending workability, and fatigue strength of the steel sheet after the quenching heat treatment were investigated.
【0043】窒素含有量は材料全体の平均値を化学分析
にて測定した。相比率はそのままの板表面 (表層部) お
よび片面からのエッチングにより板厚を半分まで除去し
た後の表面 (内層部) について、X線回折および光学顕
微鏡でのミクロ組織観察により測定した。The nitrogen content was determined by chemical analysis of the average value of the entire material. The phase ratio was measured by X-ray diffraction and microstructure observation with an optical microscope for the plate surface as it is (surface layer portion) and the surface after removing the plate thickness to half by one side (inner layer portion).
【0044】腐食後の試験片断面をSEM 観察し、窒化さ
れた表層部の厚さも測定した。硬さは上述の表層部およ
び内層部での板表面について、9.8Nの加重でのビッカー
ス硬度を測定した。The cross section of the test piece after corrosion was observed by SEM, and the thickness of the nitrided surface layer was also measured. The hardness was measured by measuring the Vickers hardness under a load of 9.8 N with respect to the surface of the plate at the surface layer portion and the inner layer portion.
【0045】曲げ加工性は圧延方向と平行に採取した幅
(w)20mm ×長さ(L)60mm の短冊状試験片を用いてJIS-Z2
248 に規定されているV曲げ試験を行い、曲げ加工可能
な最小半径(R)に対する薄鋼板の厚さ(t:0.25mm)の比
(R/t)を測定した。The bending workability is the width taken parallel to the rolling direction.
(w) 20 mm × length (L) 60 mm using JIS-Z2
Perform the V-bending test specified in 248, and ratio of the thickness (t: 0.25mm) of the thin steel sheet to the minimum radius (R) that can be bent.
(R / t) was measured.
【0046】疲労強度は圧延方向と平行に採取したw10m
m ×L40mm の短冊状試験片に、図1に寸法を付して示す
ようなビード加工を施した試験片を用いて、片振り平面
曲げ試験で106 回後に破断に至らない最大の曲げ応力を
測定した。The fatigue strength was w10m taken in parallel with the rolling direction.
a strip specimen of m × L40mm, using a specimen subjected to beading shown denoted by the dimensions in Figure 1, the maximum does not lead to fracture after 10 six times with pulsating plane bending test bending stress Was measured.
【0047】表2に各特性の調査結果を示す。表2に示
すように本発明鋼の組成を満たす例No.1〜6、8〜13は
表層に5 μm以上の厚さからなるオーステナイト相また
は同相を含む複相組織からなる部分が形成され、Hv300
を越える高硬度と1 〜1.4 の優れた曲げ加工性が両立す
るとともに、800 〜1000N/mm2 の高疲労強度を示す。特
に内層部がマルテンサイト単相となった例No.12 につい
ても、窒素雰囲気下での焼入を施していない従来の二相
組織材に対応する例No.7を越える高性能を示した。Table 2 shows the results of an examination of each characteristic. As shown in Table 2, in Examples Nos. 1 to 6 and 8 to 13 satisfying the composition of the steel of the present invention, a portion composed of an austenite phase having a thickness of 5 μm or more or a multiphase structure containing the same phase was formed on the surface layer, Hv300
With excellent bending workability of a high hardness and from 1 to 1.4 are compatible exceeding displays high fatigue strength of 800 ~1000N / mm 2. In particular, Example No. 12, in which the inner layer became a martensite single phase, also exhibited higher performance than Example No. 7, which corresponds to a conventional two-phase structure material that was not quenched in a nitrogen atmosphere.
【0048】窒化による表層部オーステナイト化は加熱
温度の上昇とともに、保持時間の延長、窒素ガス単独に
比べて窒素ガスと水素ガスの混合状態とすることでも進
行することが確認され、優れた曲げ加工性を示すと同時
に疲労強度が上昇する傾向も認められた。It has been confirmed that the austenitization of the surface layer by nitriding proceeds with an increase in the heating temperature, an increase in the holding time, and a mixed state of nitrogen gas and hydrogen gas as compared with nitrogen gas alone. At the same time, the fatigue strength tended to increase.
【0049】これらに対して、窒素雰囲気下での焼入を
施していない例No.7は表層にオーステナイト相含む組織
からなる部分が形成されず、二相組織化によりHv300 を
超える高硬度と1.6 の優れた曲げ加工性を示すものの、
ビード加工部の表層には多くの微少割れが発生して疲労
特性が半減した。On the other hand, in Example No. 7 in which quenching was not performed in a nitrogen atmosphere, a portion composed of a structure containing an austenite phase was not formed on the surface layer, and a high hardness exceeding Hv 300 and 1.6 Although it shows excellent bending workability,
Many microcracks occurred on the surface layer of the bead, and the fatigue characteristics were reduced by half.
【0050】同様に例No.14 はマルテンサイト単相組織
からなり、Hv460 前後の高強度を示したものの、曲げ加
工性が極端に劣るとともに、疲労強度も更に低下した。
本発明鋼の組成から外れた材料に関して、例No.15 〜16
は硬度がHv300 に未達であるとともに、疲労強度も300
〜400N/mm2の低い値に留まった。更に、例No.17 はHv30
0 を越える高強度を示すものの、曲げ加工性が劣るとと
もに疲労強度が同等の値に留まった。Similarly, Example No. 14 was composed of a martensitic single-phase structure and exhibited high strength around Hv460, but the bending workability was extremely poor and the fatigue strength was further reduced.
Regarding materials deviating from the composition of the steel of the present invention, Examples Nos. 15 to 16
Has not reached hardness Hv300 and has fatigue strength of 300
It remained low value of ~400N / mm 2. Example No.17 is Hv30
Although high strength exceeding 0 was exhibited, bending workability was poor and fatigue strength remained at the same value.
【0051】[0051]
【表1】 [Table 1]
【0052】[0052]
【表2】 [Table 2]
【0053】[0053]
【発明の効果】本発明により、多種形状への加工後に使
用されるバネないしバネ部品、バネ性を必要とする電子
機器、機械部品全般に適し、特にエンジン用ガスケット
に最適な高強度でありながら加工性に優れ、かつ高疲労
特性を有する安価な複相組織ステンレス鋼板を製造コス
ト上昇を招くことのない一般的製造工程で安定供給する
ことが可能となる。According to the present invention, it is suitable for a spring or a spring part used after machining into various shapes, electronic equipment and mechanical parts in general requiring a spring property, and has a high strength which is most suitable for an engine gasket. An inexpensive duplex stainless steel sheet having excellent workability and high fatigue properties can be stably supplied in a general manufacturing process without causing an increase in manufacturing cost.
【図1】ビード加工後の疲労試験片形状を示す模式図で
ある。FIG. 1 is a schematic view showing the shape of a fatigue test piece after bead processing.
───────────────────────────────────────────────────── フロントページの続き (72)発明者 柘植 信二 大阪府大阪市中央区北浜4丁目5番33号 住友金属工業株式会社内 (72)発明者 御所窪 賢一 新潟県上越市港町2丁目12番1号 株式会 社住友金属直江津内 (72)発明者 青木 正紘 新潟県上越市港町2丁目12番1号 株式会 社住友金属直江津内 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Shinji Tsuge 4-5-33 Kitahama, Chuo-ku, Osaka-shi, Osaka Sumitomo Metal Industries, Ltd. (72) Inventor Kenichi Goshokubo 2--12 Minatomachi, Joetsu-shi, Niigata 1 Sumitomo Metal Naoetsu, Ltd. (72) Inventor Masahiro Aoki 2-12-1, Minatomachi, Joetsu-shi, Niigata Prefecture Sumitomo Metal Naoetsu, Ltd.
Claims (3)
ルテンサイト単相またはマルテンサイトとフェライトの
二相組織からなる材料の表層部をオーステナイト単相ま
たは同相を含む複相組織としたステンレス鋼板。[Claim 1] In mass%, C + N: 0.06% or more, 0.50% or less Si: 0.1% or more, 2.0% or less Mn: 0.1% or more, 3.0% or less Cr: 10.0% or more, 17.0% or less Ni: 1.0% Cu: 2.0% or less The balance has a chemical composition consisting of Fe and impurity elements, and the surface layer of a material consisting of a single phase of martensite or a two-phase structure of martensite and ferrite has a single-phase structure of austenite or a double-phase structure containing the same phase Stainless steel plate.
テンサイト単相またはマルテンサイトとフェライトの二
相組織からなるステンレス鋼板を、所定の板厚に減厚
後、窒素ガスまたは窒素ガスと還元性ガスを混合した雰
囲気中においてAc1変態点以上に加熱、保持後、焼入す
ることを特徴とする複相組織ステンレス鋼板の製造方
法。2. A stainless steel sheet having a chemical composition according to claim 1 and having a single phase of martensite or a dual phase structure of martensite and ferrite is reduced to a predetermined plate thickness, and then is subjected to nitrogen gas or nitrogen gas. A method for producing a stainless steel sheet having a dual-phase structure, comprising heating and holding at a temperature higher than the Ac 1 transformation point in an atmosphere containing a reducing gas, followed by quenching.
いたエンジン用ガスケット。3. A gasket for an engine using the stainless steel sheet having a dual phase structure according to claim 1.
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Cited By (10)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP2002194504A (en) * | 2000-12-21 | 2002-07-10 | Sumitomo Metal Ind Ltd | Chromium stainless steel foil and production method of the same |
JP2007322589A (en) * | 2006-05-31 | 2007-12-13 | Nisshin Steel Co Ltd | Precoated steel sheet for diaphragm of electric horn |
US7731807B2 (en) | 2004-09-28 | 2010-06-08 | Sumitomo Metal Industries, Ltd. | Stainless steel sheet for a gasket |
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JP2002194504A (en) * | 2000-12-21 | 2002-07-10 | Sumitomo Metal Ind Ltd | Chromium stainless steel foil and production method of the same |
US7731807B2 (en) | 2004-09-28 | 2010-06-08 | Sumitomo Metal Industries, Ltd. | Stainless steel sheet for a gasket |
JP2007322589A (en) * | 2006-05-31 | 2007-12-13 | Nisshin Steel Co Ltd | Precoated steel sheet for diaphragm of electric horn |
CN104080936A (en) * | 2011-11-28 | 2014-10-01 | 新日铁住金株式会社 | Stainless steel and method of manufacturing same |
JP2014077172A (en) * | 2012-10-10 | 2014-05-01 | Tokyo Gakugei Univ | Manufacturing method of stainless steel |
JP2016079482A (en) * | 2014-10-20 | 2016-05-16 | 新日鐵住金株式会社 | Dual phase stainless steel and manufacturing method therefor |
KR20170130546A (en) | 2015-04-21 | 2017-11-28 | 제이에프이 스틸 가부시키가이샤 | Martensitic stainless steel |
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