JP2011006717A - LOW-CARBON MARTENSITIC Cr-CONTAINING STEEL SUPERIOR IN HEAT RESISTANCE - Google Patents
LOW-CARBON MARTENSITIC Cr-CONTAINING STEEL SUPERIOR IN HEAT RESISTANCE Download PDFInfo
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Abstract
Description
本発明は、オートバイ、自転車など二輪車のディスクブレーキにおけるディスク（ブレーキパッドによる摺動部）用素材として好適であり、適正な焼入れ硬さを有し、ブレーキ制動発熱に対する焼戻し軟化抵抗に優れる低炭素マルテンサイト系Cr含有鋼に関するものである。 The present invention is suitable as a material for a disc (sliding portion by a brake pad) in a disc brake of a motorcycle such as a motorcycle or a bicycle, and has low quenching hardness and excellent temper softening resistance against brake braking heat generation. This relates to site-based Cr-containing steel.
オートバイや自転車等などの二輪車のディスクブレーキのディスク（ブレーキパッドとの摺動部材）は、制動には、ブレーキパッドとの摩擦熱により５００℃程度まで繰り返し昇温される場合がある。そのため、ブレーキのディスクに用いられる素材には、制動時の発熱に対して軟質化しない耐熱性（耐焼戻し軟化性）が必要とされる。 A disc brake disc (sliding member with a brake pad) of a motorcycle such as a motorcycle or a bicycle may be repeatedly heated to about 500 ° C. due to frictional heat with the brake pad. Therefore, the material used for the brake disc is required to have heat resistance (temper softening resistance) that does not soften against heat generated during braking.
一方、ディスクが硬過ぎると、制動時にブレーキ鳴きを起こしたり、ブレーキパッドの磨耗が大きくなったりする。従って、ブレーキディスクには、適正な硬さ範囲が存在し、通常、ＨＲＣ（ロックウェル硬さのCスケール）で３０〜３８程度が適正とされている。ただし、その上限は、ブレーキパッドの種類やブレーキパッドとディスクとの組み合わせによっても変化するため、ＨＲＣで４０を超えるレベルまで許容される場合もある。 On the other hand, if the disc is too hard, brake squeal will occur during braking, and wear of the brake pads will increase. Therefore, the brake disk has an appropriate hardness range, and usually 30 to 38 is appropriate for HRC (C scale of Rockwell hardness). However, since the upper limit varies depending on the type of brake pad and the combination of the brake pad and the disc, the upper limit may be allowed to exceed 40 in HRC.
また、ブレーキディスクは、美観上の問題や、ブレーキ性能劣化への悪影響が懸念されることから、耐食性（耐錆性）に優れることも要求される。このため、ブレーキディスク用の素材としては、従来、ブレーキディスクとして必要とされる耐食性を有するだけでなく、焼入れままの状態で適正な硬さを有し、かつ、５００℃で１時間程度の焼戻し処理を受けても、ほぼ適正な硬さを保持することができる、１２〜１３質量％のＣｒを含有する低炭素マルテンサイト系ステンレス鋼が多く使用されている。 In addition, the brake disc is required to have excellent corrosion resistance (rust resistance) because there are concerns about aesthetic problems and adverse effects on brake performance deterioration. Therefore, as a material for brake discs, not only has the corrosion resistance conventionally required for brake discs, but also has an appropriate hardness in the as-quenched state and is tempered at 500 ° C. for about 1 hour. Many low-carbon martensitic stainless steels containing 12 to 13% by mass of Cr, which can maintain almost proper hardness even when subjected to the treatment, are used.
しかしながら、ブレーキの高性能化や軽量化、あるいはデザイン性の多様化を図る観点からは、ブレーキディスクおよびその素材に対して、さらに優れた耐熱性が求められるようになってきている。この要求に応えるため、各種の高耐熱鋼が提案されている。 However, from the viewpoint of improving the performance and weight of the brake, or diversifying the design, further excellent heat resistance is required for the brake disc and its material. In order to meet this demand, various high heat resistant steels have been proposed.
例えば、特許文献１および特許文献２には、Ｃ、Ｃｕ、Ｎｂ、Ｖ、Ｍｏなどの焼戻し軟化抵抗を高める元素を添加または増量して、焼入れ後だけでなく、５５０〜６５０℃で1時間程度の焼戻し後においても、ＨＲＣで３０以上の硬さを保持することができる耐焼戻し軟化性に優れる鋼が提案されている。 For example, in Patent Document 1 and Patent Document 2, an element that increases temper softening resistance such as C, Cu, Nb, V, and Mo is added or increased, and not only after quenching but also at 550 to 650 ° C. for about 1 hour. Even after tempering, a steel excellent in tempering softening resistance that can maintain a hardness of 30 or more by HRC has been proposed.
通常、オートバイや自転車などの制動時に、ブレーキディスクが６５０〜７００℃の温度域まで加熱されることはほとんどない。しかし、ブレーキディスク用の素材がそのような温度域でも耐熱性を有することによって、ブレーキの高性能化や薄肉化による軽量化、あるいはデザインの自由度の拡大などのメリットが生じる。特に、大・中型オートバイ、中でもスポーツタイプのオートバイでは、そのメリットが大きく、素材の高耐熱化に対する期待は大きい。 Usually, when braking a motorcycle or a bicycle, the brake disc is hardly heated to a temperature range of 650 to 700 ° C. However, since the material for the brake disc has heat resistance even in such a temperature range, there are merits such as higher performance of the brake, weight reduction by thinning, and expansion of design freedom. In particular, large / medium-sized motorcycles, especially sports-type motorcycles, have great advantages and high expectations for higher heat resistance of materials.
そこで、本発明では、従来から使用されあるいは提案されている素材よりも高い耐熱性（耐焼戻し軟化性）を有するブレーキディスク用素材を提供することにある。具体的な本発明の目標は、７００℃で1時間の焼戻し処理を行った後でもＨＲＣ３０以上の適正な硬さを保持することができる耐焼戻し軟化性を有するブレーキディスク用素材を提供することにある。 Accordingly, an object of the present invention is to provide a brake disc material having higher heat resistance (tempering softening resistance) than conventionally used or proposed materials. A specific goal of the present invention is to provide a brake disc material having temper softening resistance that can maintain an appropriate hardness of HRC30 or higher even after tempering at 700 ° C. for 1 hour. is there.
本発明者らは、上記課題を解決するため、Ｃｒ含有鋼の耐熱性に及ぼす各種成分の影響について詳細に調査した。その結果、焼入れ加熱時に生成し、焼き入れ後も残存するδフェライト相を低減するよう各元素の含有量を調整した上で、Ｃ、Ｎ、ＮｂやＶを適正量同時含有することにより、これらの元素の固溶効果と析出物の効果によって、７００℃以下の温度での焼戻しに対しても十分な耐熱性を有することを見出した。 In order to solve the above-mentioned problems, the present inventors investigated in detail the influence of various components on the heat resistance of Cr-containing steel. As a result, by adjusting the content of each element so as to reduce the δ ferrite phase that is generated during quenching heating and remains even after quenching, these are included by simultaneously containing appropriate amounts of C, N, Nb, and V. It has been found that due to the solid solution effect of the element and the effect of precipitates, it has sufficient heat resistance even for tempering at a temperature of 700 ° C. or lower.
特に窒素量については、含有量だけでなく、形態別定量の考察から鋼中の含有窒素量[Ｎ]から安定な析出状態の窒素量[Ｎ']を差し引いたものの量（[Ｎ]-[Ｎ']）を確保することが材質特性に良好な影響を与えることを見出した。さらに、Ｍｏ、Ｗを適正量含有することにより、より安定して耐熱性を確保できること、および、Ｂを適正量含有することによって、耐食性や製造性（熱間加工性）の改善を図ることができることを見出した。本発明は、上記知見にさらに検討を加えて発明したものであり、本発明の要旨は以下の通りである。 In particular, regarding the nitrogen content, not only the content but also the amount obtained by subtracting the nitrogen amount [N '] in the stable precipitation state from the nitrogen content [N] in the steel from the consideration of the quantification by form ([N]-[ It has been found that ensuring N ′]) has a good influence on the material properties. Furthermore, by including appropriate amounts of Mo and W, heat resistance can be secured more stably, and by including an appropriate amount of B, corrosion resistance and manufacturability (hot workability) can be improved. I found out that I can do it. The present invention was invented by further studying the above knowledge, and the gist of the present invention is as follows.
第一の発明は、質量％で、Ｃ：０．０２〜０．１０％、Ｎ：０．０２〜０．１０％、Ｃ＋Ｎ：０．０８〜０．１６％、Ｓｉ：０．５％以下、Ａｌ：０．１％以下（０％を含む）、Ｍｎ：０．３〜３．０％、Ｃｒ：１０．５〜１３．５％、Ｎｂ：０．０５〜０．６０％、Ｖ：０．１５〜０．８０％、Ｎｂ＋Ｖ：０．２５〜０．９５％、Ｎｉ：０．０２〜２．０％を含有し、残部はFeおよび不可避的不純物からなり、式（１）で表されるＦｐ値が８０．０〜９６．０であり、鋼中の含有窒素量を[Ｎ]、臭素-メタノール混合溶液を用いて定量される析出状態の窒素量を[Ｎ']とした場合に、７００℃で１時間の焼戻し後の[Ｎ]-[Ｎ']の値が０．０５７質量％以上であることを特徴とする耐熱性に優れた低炭素マルテンサイト系Ｃｒ含有鋼である。 1st invention is the mass%, C: 0.02-0.10%, N: 0.02-0.10%, C + N: 0.08-0.16%, Si: 0.5% or less Al: 0.1% or less (including 0%), Mn: 0.3 to 3.0%, Cr: 10.5 to 13.5%, Nb: 0.05 to 0.60%, V: 0.15 to 0.80%, Nb + V: 0.25 to 0.95%, Ni: 0.02 to 2.0%, with the balance being Fe and inevitable impurities, represented by the formula (1) When the Fp value is 80.0 to 96.0, the amount of nitrogen contained in the steel is [N], and the amount of nitrogen in the precipitated state quantified using a bromine-methanol mixed solution is [N '] And a low-carbon martensitic Cr-containing steel excellent in heat resistance, characterized in that the value of [N]-[N ′] after tempering at 700 ° C. for 1 hour is 0.057% by mass or more. .
第二の発明は、さらに、質量％で、ＭｏおよびＷの中から選ばれる１種または２種を合計で０．１〜２．０％含有することを特徴とする第一の発明に記載の耐熱性に優れた低炭素マルテンサイト系Ｃｒ含有鋼である。 The second invention further includes 0.1 to 2.0% in total of one or two selected from Mo and W by mass%. It is a low carbon martensitic Cr-containing steel with excellent heat resistance.
第三の発明は、さらに、質量％で、Ｂ：０．０００２〜０．００６０％を含有することを特徴とする第一または第二の発明に記載の耐熱性に優れた低炭素マルテンサイト系Ｃｒ含有鋼である。 The third invention further comprises, in mass%, B: 0.0002 to 0.0060%, and the low carbon martensite system having excellent heat resistance according to the first or second invention Cr-containing steel.
第四の発明は、第一乃至第三の発明のいずれか一つの発明に記載の低炭素マルテンサイト系Ｃｒ含有鋼を用いて製造されたことを特徴とする耐熱性に優れたブレーキディスクである。 A fourth invention is a brake disk excellent in heat resistance, characterized in that it is manufactured using the low carbon martensitic Cr-containing steel according to any one of the first to third inventions. .
本発明によれば、７００℃の温度で焼戻しを受けても、ＨＲＣ３０以上の硬さを維持できる低炭素マルテンサイト系Cr含有鋼を提供することができる。したがって、本発明の鋼をオートバイや自転車等のブレーキディスクに用いた場合には、ブレーキの高性能化や軽量化が図れるだけでなく、デザインの自由度を拡大することも可能となる。 ADVANTAGE OF THE INVENTION According to this invention, even if it receives tempering at the temperature of 700 degreeC, the low carbon martensitic Cr containing steel which can maintain the hardness more than HRC30 can be provided. Therefore, when the steel of the present invention is used for a brake disc of a motorcycle or a bicycle, not only can the performance and weight of the brake be improved, but also the degree of freedom in design can be expanded.
本発明の低炭素マルテンサイト系Cr含有鋼は、ブレーキディスク用として焼入れままの状態における硬さがＨＲＣ３０以上であり、かつ、７００℃で1時間の焼戻し後においてもＨＲＣ３０以上の硬さを維持できる耐熱性（耐焼戻し軟化性）を有することに特徴を有する。なお、上記焼入れままの状態には、焼入れ後、目的に応じて軽度の歪取り焼鈍や焼戻し処理を行なった状態も含むものとする。
以下、本発明を詳細に説明する。
The low carbon martensitic Cr-containing steel of the present invention has a hardness in an as-quenched state for brake discs of HRC30 or higher, and can maintain a hardness of HRC30 or higher even after tempering at 700 ° C. for 1 hour. It is characterized by having heat resistance (tempering softening resistance). The as-quenched state includes a state after mild quenching and tempering according to the purpose.
Hereinafter, the present invention will be described in detail.
１．成分組成について
以下に、本発明に係る耐熱性に優れた低炭素マルテンサイト系Ｃｒ含有鋼の成分組成の限定理由を説明する。 なお、成分組成を示す単位は、全て質量％とする。
1. About component composition Below, the reason for limitation of the component composition of the low carbon martensitic Cr containing steel excellent in the heat resistance which concerns on this invention is demonstrated. In addition, the unit which shows a component composition shall be mass% altogether.
Ｃ：０．０２〜０．１０％、Ｎ：０．０２〜０．１０％、Ｃ＋Ｎ：０．０８〜０．１６％
Ｃ、Ｎは、固溶し、または、ＮｂやＶなどと炭窒化物を形成して析出し、焼入れ後や焼戻し後の硬さを高める効果を有する本発明において重要な元素である。焼入れ後および焼戻し後においても所定の硬さを確保するためには、Ｃ量、Ｎ量は、それぞれ、０．０２％以上含有することが必要であり、さらにＣとＮの合計で０．０８％以上含有することが必要である。
C: 0.02-0.10%, N: 0.02-0.10%, C + N: 0.08-0.16%
C and N are important elements in the present invention that have the effect of increasing the hardness after quenching or tempering by forming a solid solution or forming a carbonitride with Nb or V to form a carbonitride. In order to ensure a predetermined hardness after quenching and tempering, the C content and N content must each be 0.02% or more, and the total of C and N is 0.08%. % Or more must be contained.
しかし、Ｃは０．１％を越えて含有すると、粗大な析出物が増加し、却って、焼戻し軟化を抑制する効果を低下させ、また、耐食性や靭性も低下させる。また、Ｎも０．１％を越えて含有すると、鋳造性や熱間加工性が著しく低下し、鋼の製造が困難になる。 However, when C exceeds 0.1%, coarse precipitates increase, and on the contrary, the effect of suppressing temper softening is reduced, and corrosion resistance and toughness are also reduced. Further, when N is contained in an amount exceeding 0.1%, castability and hot workability are remarkably lowered, and it becomes difficult to manufacture steel.
よって、Ｃ量およびＮ量の上限は、それぞれ、０．１０％とする。さらにＣとＮの合計量が０．１６％を越えると、製造性、打抜き加工性、耐熱性の何れの特性も低下する。よって、Ｃ量、Ｎ量はそれぞれ０．０２〜０．１０％の範囲とし、ＣとＮの合計量は、０．０８〜０．１６％の範囲とする。 Therefore, the upper limit of the C amount and the N amount is 0.10%, respectively. Further, when the total amount of C and N exceeds 0.16%, all the characteristics of productivity, punching workability, and heat resistance are deteriorated. Therefore, the C amount and the N amount are each in the range of 0.02 to 0.10%, and the total amount of C and N is in the range of 0.08 to 0.16%.
なお、耐熱性を安定して確保する観点からは、Ｃ量は０．０３％以上、Ｎ量は０．０４％以上であることが好ましく、ＣとＮの合計量は０．１０％以上であることが好ましい。 From the viewpoint of stably ensuring heat resistance, the C content is preferably 0.03% or more, the N content is preferably 0.04% or more, and the total amount of C and N is 0.10% or more. Preferably there is.
Ｓｉ： ０．５％以下
Ｓｉは、脱酸剤として含有される元素であり、その効果を得るためには、０．０５％以上含有することが望ましい。しかし、０．５％を越えて含有すると、焼入れ時にフェライト相が生成し易くなり、硬さが低下する原因となる。よって、Ｓｉ量の上限は０．５％以下とする。
Si: 0.5% or less Si is an element contained as a deoxidizer, and in order to obtain the effect, it is desirable to contain 0.05% or more. However, if the content exceeds 0.5%, a ferrite phase is easily generated during quenching, which causes a decrease in hardness. Therefore, the upper limit of Si content is 0.5% or less.
Ａｌ： ０．１％以下（０％を含む）
Ａｌを脱酸剤として含有される元素であるが、０．０４％を越えて含有しても脱酸効果が飽和する。また、Ａｌの過剰な含有は、Ａｌ系介在物による表面欠陥の増加や打抜き加工性の低下を引き起こす。特にＡｌの含有量が０．１％を越えると、その悪影響が顕著となるので、Ａｌ量の上限は０．１％とする。好ましくは、０．０４％以下（０％を含む）である。
Al: 0.1% or less (including 0%)
Although it is an element containing Al as a deoxidizer, the deoxidation effect is saturated even if it contains more than 0.04%. Further, excessive inclusion of Al causes an increase in surface defects due to Al inclusions and a decrease in punching workability. In particular, when the Al content exceeds 0.1%, the adverse effect becomes significant, so the upper limit of the Al content is set to 0.1%. Preferably, it is 0.04% or less (including 0%).
さらにＡｌはＳｉと同様、焼入れ時にフェライト相を生成し易くするため、硬さ低下の原因にもなる。したがって、Ｓｉを０．１％以上含有する場合には、Ａｌ量の上限は０．０２％以下（０％を含む）とするのが好ましい。 Furthermore, Al, like Si, easily forms a ferrite phase during quenching, which causes a decrease in hardness. Therefore, when the Si content is 0.1% or more, the upper limit of the Al content is preferably 0.02% or less (including 0%).
Ｍｎ： ０．３〜３．０％
Ｍｎは、脱酸効果がある他、焼入れ時のフェライト相の生成を抑制し、焼入れ後に安定して適正な硬さを確保するために有用な元素であり、この効果を得るためには、０．３％以上含有する必要がある。しかし、過剰に含有すると、打抜き加工性や耐食性が著しく低下するため、Ｍｎ量の上限を３．０％以下とする。なお、焼入れ性を安定して確保する観点からは、２．５％以下であることが好ましい。
Mn: 0.3 to 3.0%
Mn has a deoxidizing effect, is an element useful for suppressing the formation of a ferrite phase during quenching, and ensuring stable and appropriate hardness after quenching. To obtain this effect, Mn is 0 It is necessary to contain 3% or more. However, if contained excessively, punching workability and corrosion resistance are remarkably lowered, so the upper limit of the Mn amount is 3.0% or less. In addition, from a viewpoint of ensuring hardenability stably, it is preferable that it is 2.5% or less.
Ｃｒ： １０．５〜１３．５％
Ｃｒは、本発明の鋼では、耐食性を向上するための必須元素であり、ブレーキディスク用素材に求められる耐食性を得るためには１０．５％以上の含有が必要である。一方、１３．５％を超えて含有すると、打抜き加工性や靭性が低下すると共に、焼入れ後に十分なマルテンサイト相が生成せず、適正な焼入れ硬さの確保が困難になる。よって、Ｃｒ量は１０．５〜１３．５％の範囲とする。なお、耐錆性を重視する場合には１１．０％以上、打抜き加工性や耐熱性を重視する場合には１３．０％以下であることが好ましい。
Cr: 10.5 to 13.5%
Cr is an essential element for improving the corrosion resistance in the steel of the present invention, and it is necessary to contain 10.5% or more in order to obtain the corrosion resistance required for the material for brake disks. On the other hand, if the content exceeds 13.5%, punching workability and toughness are lowered, and a sufficient martensite phase is not formed after quenching, making it difficult to ensure proper quenching hardness. Therefore, the Cr content is in the range of 10.5 to 13.5%. In addition, when importance is attached to rust resistance, it is preferably 11.0% or more, and when importance is given to punching workability and heat resistance, it is preferably 13.0% or less.
Ｎｂ：０．０５〜０．６０％、Ｖ：０．１５〜０．８０％、Ｎｂ＋Ｖ：０．２５〜０．９５%
ＮｂおよびＶは、鋼中に固溶したり、Ｃ、Ｎと炭窒化物を形成したりすることにより、焼戻しによる軟質化を抑制する効果が高く、本発明が目的とする耐熱性、即ち、７００℃で1時間の焼戻し後においてもＨＲＣ：３０以上の硬さを確保するために必要な元素である。また、その効果を得るためには、ＮｂとＶを同時に含有することが重要であり、Ｎｂ量を０．０５％以上、Ｖ量を０．１５％以上、ＮｂとＶの合計量を０．２５％以上とする必要がある。しかし、Ｎｂ、Ｖを過剰に含有すると、焼入れ時にフェライト相が生成し、却って、焼入れ後あるいは焼戻し後の硬さが低下する原因となるので、Ｎｂ量、Ｖ量は、それぞれ、０．６０％以下、０．８０％以下、ＮｂとＶの合計量を０．９５％以下とする。
Nb: 0.05 to 0.60%, V: 0.15 to 0.80%, Nb + V: 0.25 to 0.95%
Nb and V have a high effect of suppressing softening due to tempering by forming a solid solution in steel or forming a carbonitride with C, N, and the heat resistance aimed by the present invention, that is, Even after tempering at 700 ° C. for 1 hour, it is an element necessary for ensuring hardness of HRC: 30 or more. In order to obtain the effect, it is important to contain Nb and V at the same time. The Nb amount is 0.05% or more, the V amount is 0.15% or more, and the total amount of Nb and V is 0.00. It is necessary to make it 25% or more. However, if Nb and V are contained excessively, a ferrite phase is generated during quenching, and on the contrary, the hardness after quenching or tempering decreases, so the Nb content and V content are each 0.60%. Hereinafter, 0.80% or less, and the total amount of Nb and V is 0.95% or less.
よって、Ｎｂ量は、０．０５〜０．６０％の範囲、Ｖ量は、０．１５〜０．８０％の範囲、ＮｂとＶの合計量を０．２５〜０．９５％の範囲とする。なお、耐熱を安定して確保する観点からは、Ｎｂ量を０．１０％以上とし、ＮｂとＶの合計量は０．３５％以上とすることが好ましい。 Therefore, the Nb amount is in the range of 0.05 to 0.60%, the V amount is in the range of 0.15 to 0.80%, and the total amount of Nb and V is in the range of 0.25 to 0.95%. To do. From the viewpoint of stably ensuring heat resistance, the Nb content is preferably 0.10% or more, and the total amount of Nb and V is preferably 0.35% or more.
Ｎｉ：０．０２〜２．０％
Ｎｉは、焼入れ時のフェライト相の生成を抑制し、焼入れ性を高めたり、耐食性を向上したりする元素である。それらの効果を得るためには０．０２％以上含有する必要がある。一方、過剰に含有すると、焼入れ前の硬さが増加して打抜き加工性が低下し、また焼入れ後の硬さが、所定の範囲を越える場合もあるため、Ｎｉ量の上限は２．０％とする。特に打抜き加工性を確保するために、焼入れ前の硬さをＨＲＢで９５以下とするには、Ｎｉ量は１．５％以下であることが好ましい。より好ましくは、０．１〜１．４％の範囲である。
Ni: 0.02 to 2.0%
Ni is an element that suppresses the formation of a ferrite phase during quenching, enhances hardenability, and improves corrosion resistance. In order to acquire those effects, it is necessary to contain 0.02% or more. On the other hand, if contained excessively, the hardness before quenching increases and the punching workability decreases, and the hardness after quenching may exceed a predetermined range, so the upper limit of Ni content is 2.0%. And In particular, in order to ensure the punching workability, the Ni content is preferably 1.5% or less for the hardness before quenching to be 95 or less in HRB. More preferably, it is 0.1 to 1.4% of range.
７００℃で１時間の焼戻し後の[Ｎ]-[Ｎ'] ： ０．０５７質量％以上
ここで、鋼中の含有窒素量[Ｎ]とは、鋼中に含有される全ての形態（固溶状態および析出状態の両方を含む）の窒素量であり、燃焼-赤外線吸収法等により求められる。
一方、析出物として析出した窒素の量は、鋼を適当な溶液で溶解し、その溶解液をろ過して得られる残渣として、鋼中に存在する介在物や析出物を分離した後、この残渣を混酸により加圧分解し、蒸留および吸光光度法で残渣中の窒素量を定量することにより、鋼に対する量（単位は質量％）として算出することができる。
[N]-[N ′] after tempering at 700 ° C. for 1 hour: 0.057% by mass or more Here, the nitrogen content [N] in steel refers to all the forms contained in steel (solid The amount of nitrogen (including both dissolved and precipitated states) is obtained by a combustion-infrared absorption method or the like.
On the other hand, the amount of nitrogen deposited as a precipitate is determined by separating the inclusions and precipitates present in the steel as a residue obtained by dissolving the steel in an appropriate solution and filtering the solution. Can be calculated as an amount based on steel (unit: mass%) by subjecting the mixture to pressure decomposition with a mixed acid and quantifying the amount of nitrogen in the residue by distillation and absorptiometry.
上記鋼より析出物や介在物を分離する時に用いる溶解用の溶液の1つに臭素-メタノール液（以下、Ｂｒ-ＭｅＯＨ溶液と記載）があり、この溶液を用いて定量される析出状態の窒素量を[Ｎ']とする。 One of the dissolution solutions used to separate precipitates and inclusions from the steel is bromine-methanol solution (hereinafter referred to as Br-MeOH solution), and nitrogen in a precipitated state quantified using this solution Let the amount be [N '].
同溶液による析出物の分離は、一般的には酸化物としての定量値を求める際の1工程であり、同溶液に対する、析出物や介在物の溶解挙動はやや複雑である。この溶液に対し、通常、ほとんどの酸化物は不溶、炭化物は可溶である。 Separation of precipitates by the same solution is generally one step for obtaining a quantitative value as an oxide, and the dissolution behavior of precipitates and inclusions in the same solution is somewhat complicated. In general, most oxides are insoluble and carbides are soluble in this solution.
そして窒化物の挙動については、窒化物の組成にも依存するが、通常は不溶なものが多い。但し、微細なＶＮの様な不安定な窒化物は溶解する場合がある。従って、[Ｎ]-[Ｎ’]の意味するものは、固溶窒素量およびＢｒ-ＭｅＯＨ溶液に溶解する不安定な窒化物に含まれる窒素量の合計値と考えられる。 The behavior of nitrides is usually insoluble, although it depends on the nitride composition. However, unstable nitrides such as fine VN may dissolve. Therefore, the meaning of [N]-[N '] is considered to be the total value of the amount of solid solution nitrogen and the amount of nitrogen contained in the unstable nitride dissolved in the Br-MeOH solution.
ここで、溶解しやすい析出物の物理化学的な特徴として、大きさが小さいことが考えられる。一方で微細な析出物は転位や粒界移動の抑制因子となるため、硬さを保持する観点からは好ましい影響を与えると考えられることから、微細な窒化物の量を反映していると推定される[Ｎ]-[Ｎ’]量で鋼材を規定することは、非常に重要である。後述の図２に一例を示すが、この図から、当該鋼中の含有窒素量［Ｎ］から７００℃で１時間焼戻した後の析出状態の窒素量[Ｎ']を引いた量[Ｎ]-[Ｎ'] （本願ではこの量を、７００℃で１時間の焼戻し後の[Ｎ]-[Ｎ']と呼ぶ）として０．０５７質量％以上が得られれば、７００℃で１時間の焼戻し後においてもＨＲＣ３０以上の良好な値が得られていると判断される。 Here, it is considered that the size is small as a physicochemical characteristic of the precipitate that is easily dissolved. On the other hand, since fine precipitates are factors that suppress dislocations and grain boundary migration, it is thought to have a favorable effect from the viewpoint of maintaining hardness, and it is assumed that this reflects the amount of fine nitrides It is very important to define the steel material by the amount of [N]-[N ′] to be given. An example is shown in FIG. 2 to be described later. From this figure, an amount [N] obtained by subtracting the amount of nitrogen [N ′] in the precipitated state after tempering at 700 ° C. for 1 hour from the amount of nitrogen contained in the steel [N]. -[N '] (This amount is referred to as [N]-[N'] after tempering at 700 ° C for 1 hour) If more than 0.057% by mass is obtained, 1 hour at 700 ° C Even after tempering, it is judged that a good value of HRC30 or higher is obtained.
Ｆｐ値：８０．０〜９６．０
本発明が目的とする耐熱性（耐焼戻し軟化性）を得るためには、上記した成分組成が、所定の範囲内にあることの他に、さらに、下記式（１）で定義されるＦｐ値が、８０．０〜９６．０の範囲を満たすよう含有することが必要である。
Fp value: 80.0-96.0
In order to obtain the target heat resistance (tempering softening resistance) of the present invention, in addition to the above-described component composition being within a predetermined range, the Fp value defined by the following formula (1) However, it is necessary to contain so that the range of 80.0-96.0 may be satisfy | filled.
このＦｐ値は、焼入れ時におけるδフェライト相の生成のし易さを示すものであり、値が大きいほどδフェライト形成能が高いことを示す。焼入れ時に生成するδフェライト相の量が多いほど、焼戻しによる軟質化が進みやすくなる。特に７００℃という高温の焼戻しに対して適正な硬さを維持するためには、少なくともδフェライト相が体積％で５％以下であることが必要であり、好ましくは３％以下、さらに好ましくは１％以下である。そのためには、Ｆｐ値は９６．０以下である必要がある。好ましくは、９５．０以下である。 This Fp value indicates the ease with which the δ ferrite phase is generated during quenching, and the larger the value, the higher the δ ferrite forming ability. The greater the amount of δ ferrite phase generated during quenching, the easier the softening by tempering. In particular, in order to maintain an appropriate hardness against tempering at a high temperature of 700 ° C., at least the δ ferrite phase needs to be 5% or less by volume, preferably 3% or less, more preferably 1 % Or less. For this purpose, the Fp value needs to be 96.0 or less. Preferably, it is 95.0 or less.
一方、Ｆｐ値が８０．０より低くなると、焼入れ前の硬さ増加による打抜き加工性の低下や焼入れ後の硬さ超過、あるいは残留オーステナイト相形成により、７００℃焼戻し後に適正な硬さが得られなくなるので、８０．０以上とする。よって、Ｆｐ値は、８０．０〜９６．０の範囲とする。好ましくは、８５．０〜９５．０の範囲である。 On the other hand, when the Fp value is lower than 80.0, appropriate hardness is obtained after tempering at 700 ° C. due to a decrease in punching workability due to an increase in hardness before quenching, excess hardness after quenching, or residual austenite phase formation. It will be 80.0 or more. Therefore, the Fp value is in the range of 80.0 to 96.0. Preferably, it is the range of 85.0-95.0.
本発明の低炭素マルテンサイト系Ｃｒ含有鋼は、上記成分に加えてさらに、耐熱性を向上するために、ＭｏおよびＷの中から選ばれる１種または２種を、合計量で０．１〜２．０％の範囲で含有することができる。 In addition to the above components, the low carbon martensitic Cr-containing steel of the present invention further contains one or two selected from Mo and W in a total amount of 0.1 to 0.1% in order to improve heat resistance. It can contain in 2.0% of range.
ＭｏおよびＷは、鋼中に固溶しあるいは析出物を形成することにより、焼戻しによる軟質化を抑制する効果がある。特に、焼戻し温度が６５０℃を超える温度領域における軟質化の抑制に効果があるので、７００℃での焼戻し後の硬さの低下も小さくなる。この効果を得るためには、ＭｏおよびＷの中から選ばれる１種また２種を合計で０．１％以上含有することが好ましい。 Mo and W have the effect of suppressing softening due to tempering by forming a solid solution or forming precipitates in the steel. In particular, since it is effective in suppressing softening in a temperature range where the tempering temperature exceeds 650 ° C., the decrease in hardness after tempering at 700 ° C. is also reduced. In order to obtain this effect, it is preferable to contain one or two selected from Mo and W in a total of 0.1% or more.
しかし、過剰に含有すると、熱間変形抵抗の増加による製造性の低下や、焼入れ前の硬さ上昇による打抜き加工性の低下、あるいは組織中に偏在して焼入れ時のフェライト相生成による７００℃焼戻し後の硬さ低下などの原因となるため、合計で２．０％以下とすることが好ましい。 However, if it is contained excessively, the productivity decreases due to an increase in hot deformation resistance, the punching workability decreases due to an increase in hardness before quenching, or it is unevenly distributed in the structure and 700 ° C. tempered due to the formation of a ferrite phase during quenching. In order to cause later hardness reduction, the total content is preferably 2.0% or less.
よって、ＭｏおよびＷは、耐熱性の要求レベルに応じて、１種または２種を合計で０．１〜２．０％の範囲で含有することが好ましい。なお、耐熱性向上の観点からは、０．２％以上であることがより好ましく、また、製造性や加工性あるいはコスト低減の観点からは、１．５％以下であることが好ましい。 Therefore, it is preferable that Mo and W contain 1 type or 2 types in the range of 0.1 to 2.0% in total according to the required level of heat resistance. From the viewpoint of improving heat resistance, it is more preferably 0.2% or more, and from the viewpoint of manufacturability, workability, or cost reduction, it is preferably 1.5% or less.
また、本発明の低炭素マルテンサイト系Ｃｒ含有鋼は、上記成分に加えてさらに、製造性や耐食性を向上するために、Ｂ：０．０００２〜０．００６０％を含有することができる。 In addition to the above components, the low-carbon martensitic Cr-containing steel of the present invention can further contain B: 0.0002 to 0.0060% in order to improve manufacturability and corrosion resistance.
Ｂは、熱間加工性に有害なＳやＰの悪影響を抑制し、熱間圧延などの製造性の向上に効果がある。その効果を得るためには、０．０００２％以上含有することが好ましい。しかし、過剰に含有すると、Ｂは、鋳造性や熱間加工性を低下させるため、０．００６０％以下とするのが好ましい。 B suppresses the adverse effects of S and P, which are harmful to hot workability, and is effective in improving manufacturability such as hot rolling. In order to acquire the effect, it is preferable to contain 0.0002% or more. However, if contained in excess, B lowers the castability and hot workability, so 0.0060% or less is preferable.
よって、Ｂ量は、必要に応じて０．０００２〜０．００６０％の範囲で含有することが好ましい。より好ましくは０．０００５〜０．００６０％の範囲である。 Therefore, it is preferable to contain B amount in 0.0002 to 0.0060% of range as needed. More preferably, it is 0.0005 to 0.0060% of range.
本発明の低炭素マルテンサイト系Ｃｒ含有鋼は、上記成分以外の残部は、Ｆｅおよび不可避的不純物からなる。ただし、不可避的不純物のうち、ＰやＳは、熱間加工性や靭性、耐食性を低下させる有害元素であるため、できるだけ低減するのが好ましく、Ｐ：０．０５ ％以下、Ｓ：０．００８％以下とすることが好ましい。さらに好ましくは、Ｐ：０．０３％以下、Ｓ：０．００５％以下である。 In the low carbon martensitic Cr-containing steel of the present invention, the balance other than the above components consists of Fe and inevitable impurities. However, among unavoidable impurities, P and S are harmful elements that reduce hot workability, toughness, and corrosion resistance. Therefore, it is preferable to reduce them as much as possible. P: 0.05% or less, S: 0.008 % Or less is preferable. More preferably, P: 0.03% or less, S: 0.005% or less.
また、本発明の低炭素マルテンサイト系Ｃｒ含有鋼は、本発明の作用効果を害さない範囲内であれば、上記以外の成分の含有を拒むものでなく、例えば、耐熱性、耐食性、および製造性を向上する観点から、Ｔａを０．１〜２．０％、Ｃａを０．０００２〜０．００３０％、Ｍｇを０．０００２〜０．００３０％、Ｃｕを１．５％以下、より好ましくは０．５％以下、Ｔｉを０．１％以下、Ｃｏを０．４％以下、あるいはＲＥＭ、Ｈｆ、Ｙ、Ｚｒ、Ｓｂを合計で０．０５％以下含有しても良い。 Further, the low carbon martensitic Cr-containing steel of the present invention does not reject the inclusion of components other than those described above, as long as the effects of the present invention are not impaired, for example, heat resistance, corrosion resistance, and production From the viewpoint of improving the properties, 0.1 to 2.0% of Ta, 0.0002 to 0.0030% of Ca, 0.0002 to 0.0030% of Mg, and 1.5% or less of Cu are more preferable. May contain 0.5% or less, Ti 0.1% or less, Co 0.4% or less, or REM, Hf, Y, Zr, Sb in total 0.05% or less.
２．低炭素マルテンサイト系Ｃｒ含有鋼の製造方法について
本発明の低炭素マルテンサイト系Cr含有鋼の製造方法について説明する。
上述した成分組成を有する鋼を、転炉、電気炉などで溶製し、さらに溶鋼をＶＯＤやＡＯＤなどで二次精錬した後、連続鋳造法あるいは造塊-分塊圧延法で、厚さ１００〜２５０ｍｍのスラブとする。なお、生産性や鋼板材質の均質性観点からは、連続鋳造法が好ましい。
2. About the manufacturing method of the low carbon martensitic Cr containing steel The manufacturing method of the low carbon martensitic Cr containing steel of this invention is demonstrated.
The steel having the above-mentioned composition is melted in a converter, electric furnace, etc., and the molten steel is secondarily refined by VOD, AOD, etc., and then the thickness is 100 by continuous casting or ingot-bundling rolling. The slab is ˜250 mm. Note that the continuous casting method is preferable from the viewpoint of productivity and homogeneity of the steel plate material.
次いで、前記スラブを、１０００〜１３００℃に加熱後、熱間圧延して、板厚が３〜１０ｍｍの熱延鋼板とし、必要に応じて熱延板焼鈍し、ショットブラストや酸洗、研削などを施してスケール除去し、さらに必要に応じてスキンパス圧延などの形状矯正を行い、ブレーキディスク用素材とする。この際、ブレーキディスクへの打抜き加工性を容易にするため、熱延板所焼鈍は６５０〜９００℃の温度で行い、硬さをＨＲＢ（ロックウェル硬さＢスケール）で１００以下にするのが好ましい。ＨＲＢ９５以下であればさらに好ましい。 Next, the slab is heated to 1000 to 1300 ° C. and then hot-rolled to obtain a hot-rolled steel sheet having a thickness of 3 to 10 mm, and hot-rolled sheet annealing is performed as necessary, shot blasting, pickling, grinding, etc. The scale is removed by applying, and shape correction such as skin pass rolling is performed as necessary to obtain a brake disc material. At this time, in order to facilitate the punching workability to the brake disk, the hot rolling plate annealing is performed at a temperature of 650 to 900 ° C., and the hardness is set to 100 or less by HRB (Rockwell hardness B scale). preferable. If it is HRB95 or less, it is more preferable.
なお、厚さが３ｍｍ以下のブレーキディスクの場合には、その素材は、３ｍｍ以下に熱間圧延した熱延鋼板を用いるか、あるいは、３ｍｍ以上の熱延鋼板に、さらに冷間圧延を施し、さらに必要に応じて焼鈍、スケール除去、形状矯正などを行なった冷延鋼板を用いるのが好ましい。 In the case of a brake disk having a thickness of 3 mm or less, the material is a hot-rolled steel sheet hot-rolled to 3 mm or less, or cold-rolled to a hot-rolled steel sheet of 3 mm or more, Furthermore, it is preferable to use a cold-rolled steel sheet that has been subjected to annealing, scale removal, shape correction, and the like as necessary.
３．ブレーキディスクの製造方法
次に、ブレーキディスクの製造方法について説明する。
上述した熱延鋼板あるいは冷延鋼板のコイルあるいは切り板から、打抜き加工などにより円盤状に打抜き、さらに冷却や磨耗粉などの排出機能を有する溝や小孔などを打抜き加工し、所望の形状とする。次いで、高周波誘導加熱装置や、バッチ式あるいは連続式の熱処理炉や高周波加熱装置を用いて、９５０〜１２５０℃の温度に加熱後、空冷以上の冷却速度で冷却する焼入れ処理を行い、その後、酸洗処理や表面研磨によるスケール除去、不動態化処理などの酸処理や塗装による防錆処理などを施してブレーキディスクとするのが好ましい。また必要に応じて、歪取り焼鈍を行なってもよい。さらに本発明の鋼は、焼入れ処理のみでブレーキディスクに使用できること（焼戻し処理不要）が大きな特徴の１つであるが、焼戻し処理を行ってから使用してもよい。
3. Brake Disk Manufacturing Method Next, a brake disk manufacturing method will be described.
From the coil or cut plate of the hot-rolled steel plate or cold-rolled steel plate described above, it is punched into a disk shape by punching, etc., and further, a groove or a small hole having a discharge function such as cooling or wear powder is punched to obtain a desired shape To do. Next, using a high-frequency induction heating device, a batch-type or continuous heat-treatment furnace, or a high-frequency heating device, after heating to a temperature of 950 to 1250 ° C., a quenching treatment is performed to cool at a cooling rate equal to or higher than air cooling. The brake disk is preferably subjected to acid treatment such as washing, surface removal by surface polishing, or passivation treatment, or rust prevention treatment by painting. Moreover, you may perform strain relief annealing as needed. Furthermore, the steel of the present invention is one of the major features that it can be used for a brake disk only by a quenching process (no tempering process is required), but it may be used after a tempering process.
４．ブレーキディスクの硬さとマルテンサイト組織中の転位密度との関係
次に、発明者等はブレーキディスクの硬さとマルテンサイト組織中の転位密度との関係を調査した。その結果、硬さとマルテンサイト中の転位密度とは密接な関係があり、マルテンサイト中の転位密度を適正範囲に調整することにより、ブレーキディスクの硬さを適正範囲に制御することが可能であること、そして、ブレーキディスクの焼戻しによる軟化を防止するためには、マルテンサイト組織中の転位の回復を抑制することが有効であることを知見した。
4). Next, the inventors investigated the relationship between the hardness of the brake disk and the dislocation density in the martensite structure. As a result, there is a close relationship between the hardness and the dislocation density in martensite. By adjusting the dislocation density in martensite to an appropriate range, it is possible to control the hardness of the brake disc to an appropriate range. In order to prevent softening due to tempering of the brake disk, it has been found that it is effective to suppress recovery of dislocations in the martensite structure.
鋼成分として前記式１を満たす合金（Ｃ：０．０５％、Ｎ：０．０６％、Ｓｉ：０．３％、Ａｌ：０．００３％、Ｍｎ：１．５％、Ｃｒ：１２．２％、Ｎｂ：０．２％、Ｖ：０．２％、Ｎｉ：０．６％、残部がFeおよび不可避的不純物からなる低炭素マルテンサイト系Ｃｒ含有鋼）を作製し、ＨＲＣ硬さと転位密度の相関を調査した結果を表３に示す。 Alloy satisfying Formula 1 as a steel component (C: 0.05%, N: 0.06%, Si: 0.3%, Al: 0.003%, Mn: 1.5%, Cr: 12.2 %, Nb: 0.2%, V: 0.2%, Ni: 0.6%, low carbon martensitic Cr-containing steel consisting of Fe and unavoidable impurities), HRC hardness and dislocation density The results of investigating the correlation are shown in Table 3.
なお、転位密度に関しては、以下の方法で求めた。
供試材から２５ｍｍ角の測定試料を切り出して測定面を鏡面研磨し、Ｃｕ-Ｋα線(λ＝0.1788965ｎｍ)を線源とするＸ線回折(θ-2θ測定)を実施した。次に、測定された回折ピークの拡がりからWilliamson-Hall法を適用して、不均一歪(ε)を導出した。すなわち、母相ｂｃｃ鉄の（１１０）、（２１１）および（２２０）面の回折ピークを用い、測定した回折ピークの半価幅(β)と回折角(θ)およびＸ線の波長との間でβcosθ/λとsinθ/λの関係をプロットし、これらの直線の傾きからεを導出した。表２の転位密度（ρ）はこのεとｂｃｃ鉄のバーガースベクトル(ｂ)を用いて次記式(２)（非特許文献２より）から求めたものである。
The dislocation density was determined by the following method.
A 25 mm square measurement sample was cut out from the test material, the measurement surface was mirror-polished, and X-ray diffraction (θ-2θ measurement) using Cu—Kα rays (λ = 0.1788965 nm) as a radiation source was performed. Next, the nonuniform strain (ε) was derived by applying the Williamson-Hall method from the broadening of the measured diffraction peak. That is, using the diffraction peaks of the (110), (211) and (220) planes of the bcc iron of the parent phase, between the half width (β) of the measured diffraction peak, the diffraction angle (θ), and the X-ray wavelength Plot the relationship between βcosθ / λ and sinθ / λ, and derive ε from the slope of these lines. The dislocation density (ρ) in Table 2 is obtained from the following equation (2) (from Non-Patent Document 2) using this ε and Burgers vector (b) of bcc iron.
転位密度は、焼入れ後に較べて、焼戻し処理によって低下するものの、７００℃以上の焼戻しによっても依然として１０１５ /ｍ２オーダーの転位密度が維持されており、焼戻し後の硬度低下が顕著でないこととよく整合している。すなわち本発明鋼においては、初期の焼入れマルテンサイト組織の高密度転位組織が、焼戻しに代表される熱活性化過程においても回復しないことを示していると推定される。 Although the dislocation density is reduced by tempering as compared with after tempering, the dislocation density on the order of 10 15 / m 2 is still maintained even after tempering at 700 ° C. or higher, and the decrease in hardness after tempering is not significant. Consistent. That is, in the steel of the present invention, it is presumed that the high-density dislocation structure of the initial quenched martensite structure does not recover even in the thermal activation process represented by tempering.
さらに、転位の回復を阻害する手段について検討した結果、焼戻しを受けた際に、炭化物を転位上に微細に析出させる、あるいは固溶状態にある合金元素が存在することに加えて、鋼中の析出形態およびこれらの分散状態が密接に関係していると推定されたので、その理由について説明する。 Furthermore, as a result of examining the means for inhibiting the recovery of dislocations, when tempering, in addition to the presence of alloy elements finely precipitated on the dislocations or in a solid solution state, Since it was estimated that the precipitation form and these dispersion | distribution states are closely related, the reason is demonstrated.
すなわち、高温焼入れ処理によって得られる高い初期転位密度、焼戻しマルテンサイトラス組織の界面に析出する炭化物等に加え、粒内の可動転位障害となる極微細析出物の分散が重要であると知見された。特に、本発明鋼においては、透過型電子顕微鏡（以下ＴＥＭ）観察により、母相と特定方位関係を有するＭＸ型の極薄板状析出が高密度に粒内分散することで、焼戻し軟化抵抗が飛躍的に向上することが分かった。 That is, in addition to the high initial dislocation density obtained by the high-temperature quenching treatment, carbides precipitated at the interface of the tempered martensitic structure, etc., it was found that the dispersion of ultrafine precipitates that would interfere with dislocations in the grains was important. In particular, in the steel of the present invention, MX type ultrathin plate precipitates having a specific orientation relationship with the parent phase are dispersed in the grains at high density by observation with a transmission electron microscope (hereinafter referred to as TEM). It was found that it improved.
この時の析出物の形態としては、厚み(ｄ)が最大２ｎｍ程度、外形(l)が約１０ｎｍ程度の板状あり、１／ｄをアスペクト比と規定した場合、そのほとんどが１０以下であることが判明した。図１に典型的な板状析出形態の分散状況を示すＴＥＭ写真を示す。 The form of the precipitate at this time is a plate having a maximum thickness (d) of about 2 nm and an outer shape (l) of about 10 nm. When 1 / d is defined as the aspect ratio, most of them are 10 or less. It has been found. FIG. 1 shows a TEM photograph showing a dispersion state of a typical plate-like precipitation form.
上記板状析出は、一定の分散密度がないと可動転位の移動障害とならない。使用中の温度上昇が低い場合は、析出自体が起こらず、組織回復も進行しないため実質問題とはならないが、想定外の温度上昇や、不適切な成分設計により、析出物の成長が促進すると、使用中に好適な分散状態が維持できず、可動転位障害としての効果が発揮出来ない。発明者らが、想定される使用温度範囲で焼戻しをした材料中の析出物分散密度を、１０万倍のＴＥＭ観察により評価した結果を表３に合わせて示す。 The plate-like precipitation does not hinder the movement of movable dislocations without a certain dispersion density. When the temperature rise during use is low, precipitation itself does not occur and the structure recovery does not progress, so there is no real problem, but if the unexpected temperature rise or improper component design promotes the growth of precipitates During use, a suitable dispersed state cannot be maintained, and the effect as a movable dislocation failure cannot be exhibited. Table 3 shows the results of the inventors' evaluation of the precipitate dispersion density in the material tempered in the assumed operating temperature range by TEM observation at a magnification of 100,000 times.
７００℃の耐熱性の達成指標となる１時間の焼戻し処理後の硬さがＨＲＣで３０以上を示す材料においては、上記板状析出の平均的な視野中分散密度が２．０x１０１８/ｃｍ２以上確保され、一般的なマルテンサイト組織の転位密度よりも高いレベルで析出物が存在することを確認した。 In a material whose hardness after tempering treatment for 1 hour, which is an index for achieving heat resistance at 700 ° C., is 30 or more in HRC, the average dispersion density in the visual field of the plate-like precipitation is 2.0 × 10 18 / cm 2. As a result, it was confirmed that precipitates exist at a level higher than the dislocation density of a general martensitic structure.
なお、ＴＥＭ観察からの析出物分散密度の評価においては、この板状析出物が母相と特定の方位関係を有し、直交する3つのバリアントのうち観察面内に平行なものは極薄のために見えていないことを考慮し、観察視野内での析出物数を１．５倍して分散密度に換算した。ＴＥＭ観察では、観察方向での析出物重なりに起因した数え落しがあるため、実質的には上記密度よりも更に高い存在が推定される。 In the evaluation of the precipitate dispersion density from TEM observation, this plate-like precipitate has a specific orientation relationship with the parent phase, and among the three orthogonal variants, those parallel to the observation plane are extremely thin. Therefore, considering the fact that it was not visible, the number of precipitates in the observation field was multiplied by 1.5 and converted to a dispersion density. In TEM observation, since there are counts due to the overlap of precipitates in the observation direction, it is estimated that the density is substantially higher than the density.
このことから、本発明の低炭素マルテンサイト系Ｃｒ含有鋼においては、７００℃以下で１時間の焼戻し処理を実施した際、焼戻しマルテンサイト母相中にアスペクト比１０以下の極薄板状析出が分散し、この極薄板状析出の分散密度が２．０x１０１８/ｃｍ２以上であることが特徴として挙げられる。 Therefore, in the low carbon martensitic Cr-containing steel of the present invention, when a tempering treatment is performed at 700 ° C. or less for 1 hour, an ultrathin plate-like precipitate having an aspect ratio of 10 or less is dispersed in the tempered martensite matrix. The dispersion density of this ultrathin plate-like precipitate is 2.0 × 10 18 / cm 2 or more.
各種材料について 焼戻し後の[Ｎ]および[Ｎ’]を分析し、硬さとの相関を調査した。具体的には、以下の手順で試料作製および分析を行ない、発明内容の検証を行なった。 About various materials [N] and [N '] after tempering were analyzed, and the correlation with hardness was investigated. Specifically, sample preparation and analysis were performed according to the following procedure, and the contents of the invention were verified.
各種成分組成の鋼を高周波溶解炉で溶製し、１００ｋｇの鋼塊とした。次いで、１１５０℃に加熱後、熱間圧延によって、板厚４ｍｍの熱延鋼板とした。さらに、８００〜８５０℃で１０時間保持した後、２００℃まで２０℃/時間で徐却し、その後空冷する焼鈍を施した。この熱延焼鈍板を１１５０〜１２００℃で1分加熱、空冷する焼入れ処理を施した後、さらに、５５０〜７００℃で０分（焼入れまま）から２４０時間までの各種の焼戻し処理を行なった。 Steels of various component compositions were melted in a high frequency melting furnace to form a 100 kg steel ingot. Subsequently, after heating to 1150 degreeC, it was set as the hot-rolled steel plate of 4 mm in thickness by hot rolling. Furthermore, after hold | maintaining at 800-850 degreeC for 10 hours, it annealed by 20 degreeC / hour to 200 degreeC, and gave the annealing which air-cools after that. The hot-rolled annealed plate was subjected to a quenching treatment in which it was heated at 1150 to 1200 ° C. for 1 minute and air-cooled, and further subjected to various tempering treatments at 550 to 700 ° C. from 0 minutes (as-quenched) to 240 hours.
各試料の化学組成と７００℃で１時間の焼戻し後の[Ｎ]−[Ｎ’]を表１に、熱処理条件を表２に示す。
鋼種１、２は、１１５０℃で１分焼入れた後、表２に示す各条件で焼戻しを行った。鋼種３〜１２は、それぞれ１１５０℃で１分、１２００℃で２分 の２水準で焼入れた後、７００℃で１時間の焼戻し処理を行なった。
Table 1 shows the chemical composition of each sample and [N]-[N ′] after tempering at 700 ° C. for 1 hour, and Table 2 shows the heat treatment conditions.
Steel types 1 and 2 were tempered at 1150 ° C. for 1 minute and then tempered under the conditions shown in Table 2. Steel types 3 to 12 were quenched at 1150 ° C. for 1 minute and 1200 ° C. for 2 minutes, respectively, and then tempered at 700 ° C. for 1 hour.
焼入れ後の硬さ（ＨＲＣ）と焼戻し後の硬さ（ＨＲＣ）は、焼入れ、または、さらに焼戻し処理を行った試験片について、表面のスケールを研削、研磨して除去後、ＪＩＳ Ｚ２２４５の規定に準拠してロックウエル硬度計で表面硬さＨＲＣを５点測定し、その平均値を求めたものである。得られた試料の焼入れ条件と焼入れ後の硬さ（ＨＲＣ）、さらに焼戻し条件と焼戻し後の硬さ（ＨＲＣ）を、表２に示す。 Hardness after quenching (HRC) and hardness after tempering (HRC) are determined according to JIS Z2245 after removing the surface scale by grinding and polishing the specimen that has been quenched or further tempered. In accordance with this, the surface hardness HRC was measured at five points with a Rockwell hardness meter, and the average value was obtained. Table 2 shows the quenching conditions and the hardness after quenching (HRC) of the obtained sample, and further the tempering conditions and the hardness after tempering (HRC).
鋼中の含有窒素量[Ｎ]については、焼戻し処理を施した試料から切り粉を採取し、表面を酸で洗浄した後、適量を燃焼赤外法-酸素・窒素分析装置に供して定量した。但し、焼戻し処理により変化する可能性があるのは、固溶量-析出量のみであるため、鋼中の含有窒素量[Ｎ]は焼戻し前の試料を用いて定量しても構わない。 The amount of nitrogen contained in the steel [N] was quantified by collecting chips from a sample that had been tempered, washing the surface with acid, and then subjecting the sample to a combustion infrared method-oxygen / nitrogen analyzer. . However, since it is only the amount of solid solution and the amount of precipitation that may be changed by the tempering treatment, the nitrogen content [N] in the steel may be quantified using a sample before tempering.
一方、安定な析出物として析出状態にある窒素量[Ｎ’]については以下の手順で分析した。まず、メタノール１００ｍｌと臭素１０ｍｌを混合した溶液中に５ｍｍ×５ｍｍ×１ｍｍｔ程度の大きさに加工した各材料を浸漬させ、約０．５ｇ程度を溶解させた。なお、実際の溶解量は浸漬前後の重量から求めた。続いて、未溶解試料を取り出した後の溶解液孔径を０．２μｍのフィルタを用いて吸引ろ過し、得られた残渣をフィルタ上に捕捉する。同溶液に対して溶解性の無いものであれば材質は問わないが、セルロースアセテートやポリカーボネート製など、汎用的に入手できるものを使用できる。更に、外部加熱方式の加圧分解法で残渣を分解した後、蒸留-中和滴定法で定量した。 On the other hand, the nitrogen amount [N ′] in a precipitated state as a stable precipitate was analyzed by the following procedure. First, each material processed into a size of about 5 mm × 5 mm × 1 mmt was immersed in a solution in which 100 ml of methanol and 10 ml of bromine were mixed, and about 0.5 g was dissolved. The actual amount of dissolution was determined from the weight before and after immersion. Subsequently, the pore size of the solution after removing the undissolved sample is suction filtered using a 0.2 μm filter, and the resulting residue is captured on the filter. Any material can be used as long as it is not soluble in the solution, but a commonly available material such as cellulose acetate or polycarbonate can be used. Further, after the residue was decomposed by an external heating pressure decomposition method, it was quantified by a distillation-neutralization titration method.
以上の特性評価結果と分析結果から、焼戻し後の硬さ（ＨＲＣ）と[Ｎ]-[Ｎ']との関係をまとめたものを図２に示す。横軸に焼戻し後の硬さ（ＨＲＣ）を、縦軸には焼戻し後の[Ｎ]-[Ｎ']の値を示す。この図から、焼戻し後の硬さ（ＨＲＣ）と[Ｎ]-[Ｎ’]には、相関があることが明らかである。 FIG. 2 shows a summary of the relationship between the hardness after tempering (HRC) and [N]-[N ′] from the above characteristic evaluation results and analysis results. The horizontal axis shows the hardness (HRC) after tempering, and the vertical axis shows the value of [N]-[N ′] after tempering. From this figure, it is clear that there is a correlation between the hardness after tempering (HRC) and [N]-[N ′].
つまり、焼戻し後の[Ｎ]-[Ｎ’]から焼戻し後の硬さ（ＨＲＣ）が推測可能ということを示している。これは同鋼種の機械特性に鋼中窒素の存在形態が深く関与していることを示しており、成分設計を行なう際に、極めて有益な情報ともなり得る。さらにこの結果では、試料３−１〜９（符号：△）と試料４−１〜９（符号：▲）においては２点を除き、焼戻し後の[Ｎ]-[Ｎ’]が０．０５７質量％以上であれば焼戻し後の硬さ（ＨＲＣ）が３０以上を満たしている。外れた２点は鋼種７で、組成に関して本発明の規定を満たしていない。 That is, the hardness (HRC) after tempering can be estimated from [N]-[N ′] after tempering. This indicates that the presence of nitrogen in the steel is deeply related to the mechanical properties of the same steel type, and can be extremely useful information when designing the components. Furthermore, in this result, in samples 3-1 to 9 (symbol: Δ) and samples 4-1 to 9 (symbol: ▲), [N]-[N ′] after tempering is 0.057 except for two points. If it is at least mass%, the hardness after tempering (HRC) satisfies 30 or more. The two points that were deviated were steel type 7, which did not satisfy the provisions of the present invention regarding the composition.
また、鋼種２について焼戻し温度と時間を変化させた場合（試料２−１〜９、符号□）も、４点外れているが、これらは何れも焼戻し温度が高かったり、時間が長かったりした場合（試料２−６〜９）である。 Moreover, when tempering temperature and time were changed about the steel type 2 (samples 2-1-9, code | symbol □), although 4 points | pieces are outside, all of these are cases where tempering temperature is high or time is long. (Samples 2-6 to 9).
以上、この図２と表１、表２より本発明に規定された組成を有し、７００℃で１時間の焼戻し後の[Ｎ]-[Ｎ’]が０．０５７質量％を満たせば、焼入れ後の硬さ（ＨＲＣ）は３０以上、かつ、焼戻し後の硬さ(ＨＲＣ)も、３０以上が確保できることとが明確になった。 2 and Table 1 and Table 2 have the composition defined in the present invention, and [N]-[N ′] after tempering at 700 ° C. for 1 hour satisfies 0.057 mass%, It became clear that the hardness (HRC) after quenching was 30 or more and the hardness (HRC) after tempering was 30 or more.
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| WO2012157680A1 (en) * | 2011-05-16 | 2012-11-22 | 新日鐵住金ステンレス株式会社 | Martensitic stainless steel plate for bicycle disc brake rotor and manufacturing method therefor |
| CN107760992A (en) * | 2017-10-30 | 2018-03-06 | 马钢(集团)控股有限公司 | A kind of tungstenic brake disc of high-speed train steel |
| CN109913761A (en) * | 2019-04-09 | 2019-06-21 | 攀钢集团攀枝花钢铁研究院有限公司 | Railway freight-car composite brake beam steel and its manufacturing method containing V, Ni |
| CN110629110A (en) * | 2018-06-25 | 2019-12-31 | 宝山钢铁股份有限公司 | Steel for ultra-supercritical thermal power generating unit with steam corrosion oxidation resistance and good high-temperature durability and preparation method thereof |
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| JPH0517850A (en) * | 1991-06-03 | 1993-01-26 | Sumitomo Metal Ind Ltd | High chromium ferrite-based heat resistant steel excellent in copper checking resistance |
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Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2012157680A1 (en) * | 2011-05-16 | 2012-11-22 | 新日鐵住金ステンレス株式会社 | Martensitic stainless steel plate for bicycle disc brake rotor and manufacturing method therefor |
| JP5863785B2 (en) * | 2011-05-16 | 2016-02-17 | 新日鐵住金ステンレス株式会社 | Martensitic stainless steel sheet for bicycle disc brake rotor and method for manufacturing the same |
| CN107760992A (en) * | 2017-10-30 | 2018-03-06 | 马钢(集团)控股有限公司 | A kind of tungstenic brake disc of high-speed train steel |
| CN110629110A (en) * | 2018-06-25 | 2019-12-31 | 宝山钢铁股份有限公司 | Steel for ultra-supercritical thermal power generating unit with steam corrosion oxidation resistance and good high-temperature durability and preparation method thereof |
| CN109913761A (en) * | 2019-04-09 | 2019-06-21 | 攀钢集团攀枝花钢铁研究院有限公司 | Railway freight-car composite brake beam steel and its manufacturing method containing V, Ni |
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