JP2020056078A - Martensitic stainless steel material, manufacturing method therefor, and slide member - Google Patents
Martensitic stainless steel material, manufacturing method therefor, and slide member Download PDFInfo
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本発明は、アブレッシブな摩耗に対する耐久性を改善したマルテンサイト系ステンレス鋼材およびその製造方法に関する。また、前記マルテンサイト系ステンレス鋼材を用いた摺動部材に関する。 The present invention relates to a martensitic stainless steel material having improved durability against abrasive wear and a method for producing the same. Further, the present invention relates to a sliding member using the martensitic stainless steel material.
マルテンサイト系ステンレス鋼は金属素地が硬いため、一般的に良好な耐摩耗性を有する。しかし、接触相手材の摺動表面や硬質な異物粒子によって材料表面が削り取られる形態の、いわゆる「アブレッシブ摩耗」に対しては、満足できる耐久性を備えていない場合が多い。アブレッシブ摩耗が問題となりやすい用途としては、例えば刃物部材、工具部材、糸と接触する織機部材、他の部材と摺接する通電部材などがある。 Martensitic stainless steel generally has good wear resistance due to its hard metal base. However, in many cases, the material does not have satisfactory durability against so-called "abrasive wear" in which the material surface is scraped off by a sliding surface of a contact partner material or hard foreign particles. Examples of applications where abrasive wear is likely to be a problem include a blade member, a tool member, a loom member that comes into contact with a yarn, and a current-carrying member that comes into sliding contact with another member.
耐アブレッシブ摩耗性を付与する手法として、鋼材のマトリックス(金属素地)中にTi、Nb、Zr、V、Wなどの元素の炭化物を分散させる手法が知られている(特許文献1)。これらの炭化物は融点が高く、極めて硬質である。その生成量は鋳造時にほぼ決まる。 As a method for imparting abrasive wear resistance, a method of dispersing carbides of elements such as Ti, Nb, Zr, V, and W in a matrix (metal base) of a steel material is known (Patent Document 1). These carbides have a high melting point and are extremely hard. The amount generated is substantially determined at the time of casting.
最近では特許文献1に開示される鋼材よりも更に耐アブレッシブ摩耗性を改善したステンレス鋼材の出現が望まれている。ただし、Ti、Nb、Zr、V、Wなどの元素の硬質炭化物による耐アブレッシブ摩耗性の向上には限界がある。また、合金成分の大幅な見直しや、製造工程の大幅な変更には多大なコストがかかる。 Recently, there has been a demand for a stainless steel material having more improved abrasion resistance than the steel material disclosed in Patent Document 1. However, there is a limit to the improvement of abrasive wear resistance by hard carbide of elements such as Ti, Nb, Zr, V, and W. In addition, a significant review of the alloy components and a significant change in the manufacturing process require a great deal of cost.
本発明は、前記の硬質炭化物による耐アブレッシブ摩耗性の向上作用を利用したうえで、既存のマルテンサイト系鋼種において耐アブレッシブ摩耗性の更なる向上を図ったステンレス鋼材を提供しようというものである。 An object of the present invention is to provide a stainless steel material that further improves the abrasive wear resistance of existing martensitic steels by utilizing the effect of improving the abrasive wear resistance of the hard carbide.
マルテンサイト系ステンレス鋼板の製造プロセスでは、通常、熱間圧延後にベル型焼鈍炉などを用いて長時間の「熱延板焼鈍」が施される。この熱延板焼鈍によって、熱延鋼板中に存在するマルテンサイト相をCr系炭化物と軟質なフェライト相に分解させる。冷間圧延前に硬質なマルテンサイト相が存在すると、所定の板厚まで精度良く冷間圧延することが難しくなるからである。また、マルテンサイト組織を得るために行われる「焼入れ処理」では、生産性を重視する場合には通常、所定の加熱温度まで急速に昇温させ、その温度に到達した時点で炉から出して直ちに冷却するヒートパターン(いわゆる「均熱0秒」)が採用される。この場合、マルテンサイト相中に比較的大きいサイズのCr炭化物が多数残存する組織状態の鋼材が得られる。一方、耐摩耗性を重視する用途ではできるだけ硬質なマルテンサイト組織を得ることが有利となる。そのためには、焼入れ処理において高温のオーステナイト温度域で炭化物を十分にオーステナイト相中に固溶させておく必要がある。この場合、Ti、Nb、Zr、V、Wなどの元素の硬質炭化物は残存するが、Cr炭化物はほとんど存在しないマルテンサイト組織が得られる。 In the manufacturing process of a martensitic stainless steel sheet, usually, "hot rolled sheet annealing" is performed for a long time after hot rolling using a bell-type annealing furnace or the like. By this hot-rolled sheet annealing, the martensite phase present in the hot-rolled steel sheet is decomposed into a Cr-based carbide and a soft ferrite phase. This is because if a hard martensite phase exists before cold rolling, it becomes difficult to accurately perform cold rolling to a predetermined thickness. In addition, in the `` quenching treatment '' performed to obtain a martensite structure, when importance is placed on productivity, the temperature is usually rapidly raised to a predetermined heating temperature, and when the temperature is reached, the product is taken out of the furnace and immediately. A cooling heat pattern (so-called "soaking 0 seconds") is employed. In this case, a steel material having a structure in which a large number of relatively large Cr carbides remain in the martensite phase is obtained. On the other hand, in applications where importance is placed on wear resistance, it is advantageous to obtain a martensite structure as hard as possible. For that purpose, it is necessary to sufficiently dissolve the carbide in the austenite phase in the high austenite temperature range in the quenching treatment. In this case, a martensite structure in which hard carbides of elements such as Ti, Nb, Zr, V, and W remain but Cr carbides hardly exist is obtained.
発明者らの研究によれば、Cr炭化物自体も、その存在量およびサイズを特定範囲にコントロールすることによって、アブレッシブ摩耗に対する抵抗力の付与に寄与することがわかった。すなわち本発明では、Ti、Nb、Zr、V、Wなどの元素の硬質炭化物に加え、Cr炭化物をも、耐アブレッシブ摩耗の向上に直接利用する。このような思想はこれまでに見られなかった。具体的には、以下の発明を開示する。 According to the study of the inventors, it has been found that the Cr carbide itself contributes to imparting a resistance to abrasive wear by controlling its abundance and size within a specific range. That is, in the present invention, in addition to hard carbides of elements such as Ti, Nb, Zr, V, and W, Cr carbides are directly used for improving abrasive wear resistance. Such an idea has never been seen before. Specifically, the following invention is disclosed.
[1]質量%で、C:0.10〜0.50%、Si:0.02〜1.0%、Mn:0.02〜1.0%、Ni:0.1〜5.0%、Cr:12.0〜18.0%、Ti:0〜0.5%、Nb:0〜0.5%、Zr:0〜0.5%、V:0〜0.5%、W:0〜0.5%、残部がFeおよび不可避的不純物であり、Ti、Nb、Zr、V、Wの群から選ばれる1種以上を合計0.25〜2.0%含有する化学組成を有し、表面を研磨して電解エッチングにより仕上げた観察面において、炭化物の面積率が1.0%以上、かつ円相当周囲長10.0μm以上の炭化物の個数密度が2200μm2あたり60個以下である、マルテンサイト系ステンレス鋼材。
[2]表面を研磨して電解エッチングにより仕上げた観察面において、円相当周囲長10.0μm以上の炭化物の個数密度が2200μm2あたり90個以上である組織に調整されている鋼素材に対して、最高到達温度TMが1000〜1100℃であり、1000℃以上TM(℃)以下の温度域の滞在時間が3〜10秒である条件で加熱したのち冷却してマルテンサイト組織とする焼入れ処理を施す、上記[1]に記載のマルテンサイト系ステンレス鋼材の製造方法。
[3]前記鋼素材が、板厚0.1〜3.5mmの鋼板を用いたものである上記[2]に記載のマルテンサイト系ステンレス鋼材の製造方法。
[4]前記焼入れ処理の後に、150〜700℃で1〜120分保持する焼戻し処理を施す、上記[2]または[3]に記載のマルテンサイト系ステンレス鋼材の製造方法。
[5]上記[1]に記載のマルテンサイト系ステンレス鋼材を用いた摺動部材。
[1] In mass%, C: 0.10 to 0.50%, Si: 0.02 to 1.0%, Mn: 0.02 to 1.0%, Ni: 0.1 to 5.0% , Cr: 12.0 to 18.0%, Ti: 0 to 0.5%, Nb: 0 to 0.5%, Zr: 0 to 0.5%, V: 0 to 0.5%, W: 0 to 0.5%, with the balance being Fe and inevitable impurities, having a chemical composition containing 0.25 to 2.0% in total of at least one selected from the group consisting of Ti, Nb, Zr, V and W. Then, on an observation surface whose surface is polished and finished by electrolytic etching, the area density of carbides is 1.0% or more, and the number density of carbides having a circumference equivalent to a circle of 10.0 μm or more is 60 or less per 2200 μm 2. , Martensitic stainless steel.
[2] On a steel material whose surface has been adjusted to a structure in which the number density of carbides having a circumference equivalent to 10.0 μm or more is 90 or more per 2200 μm 2 on the observation surface finished by electrolytic etching after polishing the surface. Quenching to form a martensitic structure after heating under the condition that the maximum attained temperature T M is 1000 to 1100 ° C. and the residence time in the temperature range of 1000 ° C. to T M (° C.) is 3 to 10 seconds. The process for producing a martensitic stainless steel material according to the above [1], wherein the process is performed.
[3] The method for producing a martensitic stainless steel material according to the above [2], wherein the steel material is a steel plate having a thickness of 0.1 to 3.5 mm.
[4] The method for producing a martensitic stainless steel material according to the above [2] or [3], wherein after the quenching, a tempering treatment is performed at 150 to 700 ° C for 1 to 120 minutes.
[5] A sliding member using the martensitic stainless steel material according to [1].
ある炭化物粒子の「円相当周囲長」は、その粒子の面積と同面積の円の周長を意味する。 The “circumferential perimeter” of a given carbide particle means the circumference of a circle having the same area as the particle.
本発明によれば、従来公知のマルテンサイト系ステンレス鋼種を用いて、耐アブレッシブ摩耗の更なる改善を図ることができた。 ADVANTAGE OF THE INVENTION According to this invention, the further improvement of the abrasive wear resistance was able to be aimed at using the conventionally well-known martensitic stainless steel type.
〔対象鋼種〕
本発明では、高温のオーステナイト単相温度域から冷却したときに常温でマルテンサイト組織となるマルテンサイト系ステンレス鋼種のうち、特にTi、Nb、Zr、V、Wの1種以上を所定の含有量範囲で含有する鋼種を対象とする。具体的な化学組成範囲は以下の通りである。
質量%で、C:0.10〜0.50%、Si:0.02〜1.0%、Mn:0.02〜1.0%、Ni:0.1〜5.0%、Cr:12.0〜18.0%、Ti:0〜0.5%、Nb:0〜0.5%、Zr:0〜0.5%、V:0〜0.5%、W:0〜0.5%、残部がFeおよび不可避的不純物であり、Ti、Nb、Zr、V、Wの群から選ばれる1種以上を合計0.25〜2.0%含有する化学組成。
(Target steel type)
In the present invention, a specific content of at least one of Ti, Nb, Zr, V, and W among martensitic stainless steels which form a martensitic structure at room temperature when cooled from a high-temperature austenite single-phase temperature region is specified. For steel types contained in the range. The specific chemical composition range is as follows.
In mass%, C: 0.10 to 0.50%, Si: 0.02 to 1.0%, Mn: 0.02 to 1.0%, Ni: 0.1 to 5.0%, Cr: 12.0 to 18.0%, Ti: 0 to 0.5%, Nb: 0 to 0.5%, Zr: 0 to 0.5%, V: 0 to 0.5%, W: 0 to 0% Chemical composition containing 0.2% to 2.0% of at least one selected from the group consisting of Ti, Nb, Zr, V, and W, with the balance being Fe and inevitable impurities.
以下、鋼の化学組成に関する「%」は特に断らない限り質量%を意味する。各元素の含有量は上記の範囲で定めることができるが、マルテンサイト相の硬さレベルを十分に確保することや、コストを考慮すると、C含有量は0.20〜0.50%、Si含有量は0.2〜0.8%、Mn含有量は0.2〜8%、Ni含有量は0.1〜0.5%、Cr含有量は12.0〜15.0%の範囲とすることがより好ましい。 Hereinafter, “%” regarding the chemical composition of steel means mass% unless otherwise specified. The content of each element can be determined within the above range. However, considering a sufficient level of hardness of the martensite phase and cost, the C content is 0.20 to 0.50%, Content is 0.2 to 0.8%, Mn content is 0.2 to 8%, Ni content is 0.1 to 0.5%, and Cr content is 12.0 to 15.0%. Is more preferable.
Ti、Nb、Zr、V、Wは極めて硬質な炭化物を構成する元素である。耐アブレッシブ摩耗性を十分に発揮させるために、これらの元素の1種以上を合計0.25%以上の含有量で含有させる必要がある。一方、Ti、Nb、Zr、V、Wの合計含有量が高くなりすぎると製造性が低下する場合がある。例えばTiは溶製鋳造時の湯流れを悪くし、Nbは金属間化合物として析出し靭性を低下させる要因となる。種々検討の結果、Ti、Nb、Zr、V、Wの合計含有量は2.0%以下の範囲に制限され、0.6%以下とすることがより好ましい。なお、Ti、Nb、Zr、V、W各元素の含有量は、それぞれ0.5%以下の範囲とすることが好ましい。それより高い含有量を狙うと製鋼でのコスト増を招く場合がある。 Ti, Nb, Zr, V and W are elements constituting extremely hard carbide. In order to sufficiently exhibit abrasive wear resistance, one or more of these elements must be contained in a total content of 0.25% or more. On the other hand, if the total content of Ti, Nb, Zr, V, and W is too high, the productivity may be reduced. For example, Ti deteriorates the flow of molten metal at the time of smelting casting, and Nb precipitates as an intermetallic compound and becomes a factor of reducing toughness. As a result of various studies, the total content of Ti, Nb, Zr, V, and W is limited to a range of 2.0% or less, and more preferably 0.6% or less. In addition, it is preferable that each content of each element of Ti, Nb, Zr, V, and W is made into the range of 0.5% or less. Aiming for a higher content may lead to an increase in steelmaking costs.
〔炭化物〕
本発明では、耐アブレッシブ摩耗性を向上させるために、Ti、Nb、Zr、V、Wの1種以上の元素の炭化物が分散した組織状態とする。これらの元素の炭化物は高融点であり、溶鋼中において鋳造前に生成する。その後の製造過程で熱履歴を加えてもほとんど変化せずに鋼材中にとどまる。この種の炭化物は非常に硬い。このような硬質炭化物によって耐アブレッシブ摩耗性が付与されることは特許文献1などに開示されており、本発明でもその作用を利用する。鋼の化学組成を上述の範囲にコントロールすれば、Ti、Nb、Zr、V、Wから選ばれる1種以上の元素の硬質炭化物による耐アブレッシブ摩耗性向上作用が享受できる。
〔carbide〕
In the present invention, in order to improve abrasive wear resistance, a structure state in which carbides of one or more elements of Ti, Nb, Zr, V, and W are dispersed. The carbides of these elements have a high melting point and form in molten steel before casting. Even if a heat history is added in the subsequent manufacturing process, it remains in the steel material with almost no change. This type of carbide is very hard. The provision of abrasive wear resistance by such a hard carbide is disclosed in Patent Document 1 and the like, and the effect of the present invention is also utilized in the present invention. When the chemical composition of the steel is controlled within the above range, the effect of improving abrasive wear resistance by hard carbide of at least one element selected from Ti, Nb, Zr, V and W can be enjoyed.
本発明では更なる耐アブレッシブ摩耗性の改善効果を得るために、比較的小さいサイズにコントロールされたCr炭化物を利用する。Cr炭化物は主としてCr23C6タイプの析出相であり、通常、熱延板焼鈍によってマルテンサイト相をCr炭化物とフェライト相に分解させる際に、鋼材中に多量に生成する。そして、マルテンサイト組織を得るために行われる「焼入れ処理」の高温加熱時に、Cr炭化物はオーステナイト相中に固溶していく。 In the present invention, a Cr carbide whose size is controlled to a relatively small size is used in order to obtain a further effect of improving abrasive wear resistance. Cr carbide is mainly a Cr 23 C 6 type precipitation phase, and is usually generated in a large amount in a steel material when a martensite phase is decomposed into a Cr carbide and a ferrite phase by hot-rolled sheet annealing. Then, at the time of high-temperature heating in the "quenching treatment" performed to obtain a martensite structure, the Cr carbide solid-dissolves in the austenite phase.
一般的にマルテンサイト系ステンレス鋼材を製造する際の焼入れ処理では、オーステナイト単相温度域で均熱0秒の短時間加熱を行うことが多い。この場合はCr炭化物が完全に固溶消失する前に冷却が開始されるので、マルテンサイト相からなるマトリックス(金属素地)中にCr炭化物が残存した組織状態の鋼材が得られる。短時間の熱処理とすることができるので、生産性が高い。また、マルテンサイト相の硬さも比較的低くなるので、加工性の面で有利となる。一方、できるだけ硬質のマルテンサイト組織を得たい場合には、焼入れ処理での加熱を入念に行って、Cr炭化物を構成しているCをオーステナイト母相中にできるだけ固溶させることが有利となる。この場合はCr炭化物がほとんど存在しないマルテンサイト組織が得られ、そのマルテンサイト相中に固溶しているCの量が多いため硬質のマルテンサイト相が得られる。マトリックスの硬質化によって耐摩耗性が向上するので、刃物などの用途には有利となる。ただし、耐アブレッシブ摩耗性に関しては改善の余地がある。 Generally, in the quenching treatment when producing a martensitic stainless steel material, a short-time heating with a soaking temperature of 0 seconds is often performed in the austenite single-phase temperature range. In this case, the cooling is started before the complete dissolution and disappearance of the Cr carbide, so that a steel material having a microstructure in which the Cr carbide remains in a matrix (metal base) composed of a martensite phase is obtained. Since the heat treatment can be performed in a short time, the productivity is high. Further, the hardness of the martensite phase is relatively low, which is advantageous in terms of workability. On the other hand, when it is desired to obtain a martensite structure as hard as possible, it is advantageous to carefully carry out heating in the quenching treatment to cause C constituting the Cr carbide to form a solid solution in the austenite matrix as much as possible. In this case, a martensite structure having almost no Cr carbide is obtained, and a hard martensite phase is obtained because the amount of C dissolved in the martensite phase is large. Since the wear resistance is improved by hardening the matrix, it is advantageous for applications such as cutting tools. However, there is room for improvement in abrasive wear resistance.
本発明では、焼入れ処理の条件を後述のように厳しくコントロールすることにより、耐アブレッシブ摩耗性の向上作用を発揮しうるに足る量のCr炭化物が残存した金属組織とする。具体的には、表面を研磨して電解エッチングにより仕上げた観察面において、炭化物の面積率が1.0%以上であることが必要である。面積率の測定対象となる炭化物には、Ti、Nb、Zr、V、Wの炭化物と、Cr炭化物の両方が含まれる。Ti、Nb、Zr、V、Wの炭化物の量は焼入れ処理によってほとんど変化しないので、Cr炭化物が十分に存在しなければ「炭化物の面積率1.0%以上」の規定を満たすことができない。なお、炭化物の面積率は8.0%以下の範囲で調整されていることがより好ましい。 In the present invention, by controlling the conditions of the quenching treatment strictly as described later, a metal structure in which a sufficient amount of Cr carbides capable of exhibiting the effect of improving the abrasive wear resistance is obtained. Specifically, it is necessary that the area ratio of carbide is 1.0% or more on the observation surface whose surface is polished and finished by electrolytic etching. The carbides for which the area ratio is measured include both Ti, Nb, Zr, V, and W carbides and Cr carbides. Since the amounts of carbides of Ti, Nb, Zr, V, and W hardly change by the quenching treatment, unless the Cr carbide is sufficiently present, the regulation of “area ratio of carbides of 1.0% or more” cannot be satisfied. It is more preferable that the area ratio of the carbide is adjusted in the range of 8.0% or less.
一方、粗大な炭化物が多く存在すると、耐アブレッシブ摩耗性の改善効果が得られなくなる。その理由として、Ti、Nb、Zr、V、Wの炭化物ほど硬質ではないCr炭化物の場合は、比較的小さいサイズの粒子として分散することによってはじめて耐アブレッシブ摩耗性の向上作用を発揮するものと考えられる。また、粗大なCr炭化物が多い場合にはマトリックス中の固溶C量も少なくなっているので、マルテンサイト相からなるマトリックスの硬さが低下することによる耐摩耗性の低下によって、耐アブレッシブ摩耗性の向上にも悪影響が及ぶのではないかと推察される。粗大なCr炭化物が多いと耐食性も低下する。種々検討の結果、円相当周囲長10.0μm以上の炭化物の個数密度が2200μm2あたり60個以下である金属組織にコントロールすることが重要である。上記個数密度の測定対象には、Ti、Nb、Zr、V、Wの炭化物と、Cr炭化物の両方が含まれる。上述のようにTi、Nb、Zr、V、Wの炭化物の量は焼入れ処理によってほとんど変化しない。また、上述の化学組成範囲において、Ti、Nb、Zr、V、Wの炭化物だけでは、円相当周囲長10.0μm以上の炭化物の個数密度が2200μm2あたり60個を超えて多くなることはない。したがって、焼入れ処理時の加熱で粗大なCr炭化物の量を十分に減少させることができた場合に、「円相当周囲長10.0μm以上の炭化物の個数密度が2200μm2あたり60個以下」である金属組織が得られる。 On the other hand, if there are many coarse carbides, the effect of improving abrasive wear resistance cannot be obtained. The reason is that Cr carbide, which is not as hard as Ti, Nb, Zr, V and W carbides, is considered to exhibit the effect of improving abrasive wear resistance only by dispersing as relatively small particles. Can be In addition, when the amount of coarse Cr carbides is large, the amount of solute C in the matrix is also small. Therefore, the wear resistance of the matrix composed of the martensite phase is reduced, and the abrasive wear resistance is reduced. It is presumed that this will have an adverse effect on the improvement of the quality of the water. If there are many coarse Cr carbides, the corrosion resistance also decreases. As a result of various studies, it is important to control the metal structure to have a number density of carbides having a circumference equivalent to a circle of 10.0 μm or more and 60 or less per 2200 μm 2 . The measurement target of the number density includes both carbides of Ti, Nb, Zr, V, and W and Cr carbides. As described above, the amounts of carbides of Ti, Nb, Zr, V, and W hardly change by the quenching treatment. Further, in the above-described chemical composition range, the number density of carbides having a circumference equivalent to a circle of 10.0 μm or more does not increase more than 60 per 2200 μm 2 only by the carbides of Ti, Nb, Zr, V, and W. . Therefore, when the amount of coarse Cr carbides can be sufficiently reduced by heating during the quenching treatment, the number density of carbides having a circumference equivalent to a circle of 10.0 μm or more is 60 or less per 2200 μm 2. A metallographic structure is obtained.
(炭化物の面積率の求め方)
鋼材の表面を研磨してシュウ酸電解エッチングにより仕上げた観察面について光学顕微鏡観察を行い、200万ドット/インチ以上の解像度で観察画像を採取する。観察総面積は無作為に選んだ1つまたは重複しない複数の視野について合計40000μm2以上とする。視野中に存在する炭化物粒子の総面積Sp(μm2)を画像処理装置によって算出し、前記Spを観察総面積(μm2)で除することにより、炭化物の面積率(%)を定める。
(How to determine the area ratio of carbide)
An observation surface obtained by polishing the surface of the steel material and finishing by oxalic acid electrolytic etching is observed with an optical microscope, and an observation image is collected at a resolution of 2,000,000 dots / inch or more. The total observation area is 40,000 μm 2 or more in total for one or a plurality of non-overlapping fields selected at random. The total area Sp (μm 2 ) of the carbide particles present in the visual field is calculated by an image processing device, and the Sp is divided by the total observation area (μm 2 ) to determine the area ratio (%) of the carbide.
(円相当周囲長10.0μm以上の炭化物の個数密度の求め方)
上述の「炭化物の面積率の求め方」に記載した手法で採取した観察総面積40000μm2以上の観察画像について、個々の炭化物粒子の面積を画像処理装置により測定し、円相当周囲長が10.0μm以上である炭化物の数をカウントする。視野境界によって粒子の一部が切断されている粒子については、視野内に存在する部分の面積によって算出される円相当周囲長が10.0μm以上である場合にカウント対象とする。カウントされた炭化物の総数Np(個)と観察視野の総面積(μm2)から、2200μm2あたりの円相当周囲長10.0μm以上の炭化物の個数密度(個/2200μm2)を定める。
(How to find the number density of carbide with a circumference equivalent to 10.0 μm or more)
For an observation image having an observation total area of 40,000 μm 2 or more collected by the method described in the above `` How to Determine the Area Ratio of Carbide '', the area of each carbide particle was measured by an image processing apparatus, and the circumference equivalent to a circle was 10. The number of carbides of 0 μm or more is counted. Particles whose particles are partially cut off by the boundary of the visual field are counted when the circumference equivalent to the circle calculated by the area of the portion existing in the visual field is 10.0 μm or more. From counted the total number of carbide Np (number) and the total area of the observation field ([mu] m 2), defines the number density of the equivalent circle perimeter 10.0μm or more carbides per 2200μm 2 (pieces / 2200μm 2).
〔製造プロセス〕
上記の耐アブレッシブ摩耗性に優れるマルテンサイト系ステンレス鋼材は、例えば以下の鋼板製造プロセスによって製造することができる。
鋳造→熱間圧延→熱延板焼鈍→(冷間圧延→中間焼鈍)→仕上冷間圧延→(仕上焼鈍)→加工→焼入れ処理→(焼戻し処理)
括弧内の工程は必要に応じて行うことができる。また、各焼鈍や、焼入れ処理あるいは焼戻し処理の後には、通常、酸洗が行われる。本発明では上述のように、Cr炭化物を耐アブレッシブ摩耗性の向上に利用する。Cr炭化物の存在形態(量およびサイズ)は熱処理によって制御することができる。上記製造プロセスにおいては特に熱延板焼鈍および焼入れ処理での条件設定が重要となる。
[Manufacturing process]
The martensitic stainless steel having excellent abrasive wear resistance can be manufactured by, for example, the following steel sheet manufacturing process.
Casting → hot rolling → hot strip annealing → (cold rolling → intermediate annealing) → finishing cold rolling → (finishing annealing) → processing → quenching → (tempering)
The steps in parentheses can be performed as needed. After each annealing, quenching or tempering, pickling is usually performed. In the present invention, as described above, Cr carbide is used for improving abrasive wear resistance. The form (amount and size) of the Cr carbide can be controlled by heat treatment. In the above-mentioned manufacturing process, it is particularly important to set conditions for hot-rolled sheet annealing and quenching.
〔熱間圧延〕
鋳片を1150〜1250℃で1時間以上加熱保持したのち抽出して、熱間圧延を施し、熱延鋼板を得る。熱延鋼板の板厚は例えば3.0〜5.0mmの範囲で設定すればよい。
(Hot rolling)
The slab is heated and held at 1150-1250 ° C. for 1 hour or more, extracted, and hot-rolled to obtain a hot-rolled steel sheet. The thickness of the hot-rolled steel sheet may be set, for example, in the range of 3.0 to 5.0 mm.
〔熱延板焼鈍〕
熱間圧延を終えた、いわゆる「as hot」の熱延鋼板に対して750〜850℃で5時間以上保持する熱延板焼鈍を施す。この温度域での加熱保持により、熱延鋼板中に多く存在するマルテンサイト相を、炭化物と軟質なフェライト相とに分解する。保持温度が高すぎるとオーステナイト単相温度域に入り、冷却時に新たなマルテンサイトの生成を招く。保持温度が低すぎる場合および保持時間が短すぎる場合は、マルテンサイト相を十分に分解することができず、焼入れ処理に供するための鋼素材として、粗大炭化物が十分に存在している組織状態(具体的には円相当周囲長10.0μm以上の炭化物の個数密度が2200μm2あたり90個以上である組織状態)のものを用意することが難しくなる。また、マルテンサイト相が残存すると、冷間圧延工程での製造性が悪くなる。
(Hot rolled sheet annealing)
After hot rolling, the so-called “as hot” hot-rolled steel sheet is subjected to hot-rolled sheet annealing at 750 to 850 ° C. for 5 hours or more. By maintaining the heating in this temperature range, the martensite phase, which is often present in the hot-rolled steel sheet, is decomposed into carbide and a soft ferrite phase. If the holding temperature is too high, it enters the austenite single-phase temperature range, which causes the generation of new martensite during cooling. If the holding temperature is too low or the holding time is too short, the martensitic phase cannot be sufficiently decomposed, and the structure state in which the coarse carbides are sufficiently present as a steel material for quenching ( More specifically, it becomes difficult to prepare a carbide having a circle equivalent circumference of 10.0 μm or more in a number density of 90 or more per 2200 μm 2 . Further, when the martensite phase remains, the productivity in the cold rolling step deteriorates.
〔冷間圧延、焼鈍〕
熱延板焼鈍を終えた鋼板は、冷間圧延によって目標板厚の鋼板とされる。目標板厚は0.1〜3.5mmの範囲で設定できる。1.0〜2.0mmの範囲に管理してもよい。必要に応じて中間焼鈍が施される。後述の加工に供する前に行われる最終の冷間圧延を「仕上冷間圧延」と呼ぶ。仕上冷間圧延の後、必要に応じて最終的な焼鈍が施される。その焼鈍を「仕上焼鈍」と呼ぶ。焼鈍条件は、中間焼鈍、仕上焼鈍とも、750〜850℃、均熱0〜60秒とすればよい。仕上焼鈍を省略する場合、仕上冷間圧延での圧延率は5〜50%とすることが好ましい。50%を超える圧延率の冷延鋼板をそのまま後述の加工に供すると、用途によっては加工性が不足する場合がある。
[Cold rolling, annealing]
The steel sheet after the hot-rolled sheet annealing is made a steel sheet having a target thickness by cold rolling. The target plate thickness can be set in a range of 0.1 to 3.5 mm. It may be managed in a range of 1.0 to 2.0 mm. Intermediate annealing is performed if necessary. The final cold rolling performed before being subjected to the processing described below is referred to as “finishing cold rolling”. After finish cold rolling, final annealing is performed as necessary. The annealing is called "finishing annealing". Annealing conditions may be 750 to 850 ° C. and soaking for 0 to 60 seconds for both intermediate annealing and finish annealing. When the finish annealing is omitted, the rolling reduction in the finish cold rolling is preferably 5 to 50%. If a cold-rolled steel sheet having a reduction ratio of more than 50% is subjected to the processing described below as it is, the workability may be insufficient depending on the application.
〔加工〕
本明細書では、焼入れ処理に供する鋼材を「鋼素材」と呼んでいる。この鋼素材は、通常、最終製品と同等の形状あるいはそれに近い形状を有している。上述の仕上冷間圧延を終えた冷延鋼板、あるいは仕上焼鈍を終えた冷延焼鈍鋼板にプレス成形等の加工を施し、焼入れ処理に供するための鋼素材を得る。
〔processing〕
In this specification, a steel material subjected to a quenching process is referred to as a “steel material”. This steel material usually has a shape equal to or close to the shape of the final product. The cold rolled steel sheet after the finish cold rolling or the cold rolled annealed steel sheet after the finish annealing is subjected to a process such as press forming to obtain a steel material to be subjected to a quenching process.
〔焼入れ処理〕
焼入れ処理に供する鋼素材は、フェライト相のマトリックス中に、Ti、Nb、Zr、V、Wの1種以上の元素と炭素が結合した非常に硬質な炭化物と、主として熱延板焼鈍で成長したCr炭化物が分散した金属組織を有している。そのCr炭化物は円相当周囲長が10.0μm以上の大きいサイズのものが多い。以下、円相当周囲長が10.0μm以上の炭化物を「粗大炭化物」と呼ぶ。発明者らの検討によれば、粗大炭化物のなかでもCr炭化物は耐アブレッシブ摩耗性を低下させる要因となる。また、耐食性を低下させる要因にもなる。一方で、小さいサイズのCr炭化物は耐アブレッシブ摩耗性の向上に寄与することがわかった。
[Hardening treatment]
The steel material to be subjected to the quenching treatment was a very hard carbide in which at least one element of Ti, Nb, Zr, V, and W and carbon were bonded in the matrix of the ferrite phase, and grew mainly by hot-rolled sheet annealing. It has a metal structure in which Cr carbide is dispersed. In many cases, the Cr carbide has a large size with a circumference equivalent to a circle of 10.0 μm or more. Hereinafter, carbide having a circle-equivalent circumference of 10.0 μm or more is referred to as “coarse carbide”. According to the study by the inventors, among the coarse carbides, the Cr carbide is a factor that reduces the abrasive wear resistance. It also becomes a factor that lowers corrosion resistance. On the other hand, it was found that the small-sized Cr carbide contributed to the improvement of the abrasive wear resistance.
Cr炭化物による耐アブレッシブ摩耗性の向上作用を享受するために、焼入れ処理の加熱において、マトリックス中に分散している粗大Cr炭化物の固溶化を進行させ、小さいサイズのCr炭化物を残存させる。それによって、Ti、Nb、Zr、V、Wの非常に硬い炭化物と、小さいサイズのCr炭化物の両方の寄与による耐アブレッシブ摩耗性向上効果が得られ、従来よりも耐アブレシブ摩耗性の改善されたマルテンサイト系ステンレス鋼材が実現できる。したがって、Cr炭化物が小さいサイズの状態で十分に残存できる条件にて焼入れ処理を行うことが重要である。 In order to enjoy the effect of improving the abrasion resistance of the Cr carbide, the solid solution of the coarse Cr carbide dispersed in the matrix is advanced during heating in the quenching treatment, and the small-sized Cr carbide remains. Thereby, the effect of improving the abrasive wear resistance by the contribution of both the very hard carbides of Ti, Nb, Zr, V, and W and the small-sized Cr carbide is obtained, and the abrasive wear resistance is improved as compared with the conventional case. Martensitic stainless steel material can be realized. Therefore, it is important to perform the quenching treatment under the condition that the Cr carbide can sufficiently remain in a small size state.
発明者らは詳細な研究の結果、上述の化学組成に調整され、かつ円相当周囲長10.0μm以上の炭化物が2200μm2あたり90個以上の個数密度で存在している鋼素材に対して、最高到達温度TMが1000〜1100℃であり、かつ1000℃以上TM(℃)以下の温度域の滞在時間が3〜10秒となる条件で加熱したのち、冷却する「焼入れ処理」を施すことによって、「炭化物の面積率が1.0%以上、かつ円相当周囲長10.0μm以上の炭化物の個数密度が2200μm2あたり60個以下」である金属組織のマルテンサイト系ステンレス鋼材を得ることができ、耐アブレッシブ摩耗性の改善効果が得られることを見いだした。なお、Ti、Nb、Zr、V、Wの炭化物はこの焼入れ処理でほとんど変化しない。 As a result of detailed research, the inventors have adjusted the above-mentioned chemical composition and, for a steel material in which carbides having a circle equivalent circumference of 10.0 μm or more exist at a number density of 90 or more per 2200 μm 2 , After heating under the condition that the maximum attainment temperature T M is 1000 to 1100 ° C. and the residence time in the temperature range of 1000 ° C. or more and T M (° C.) or less is 3 to 10 seconds, a “quenching treatment” for cooling is performed. In this way, to obtain a martensitic stainless steel material having a metallographic structure in which “the area ratio of carbides is 1.0% or more and the number density of carbides having a circle-equivalent circumference of 10.0 μm or more is 60 or less per 2200 μm 2 ” Was found, and an effect of improving abrasive wear resistance was obtained. The carbides of Ti, Nb, Zr, V and W hardly change by this quenching treatment.
焼入れ処理での加熱中の材料温度は、鋼材の表面温度の値を採用することができる。「1000℃以上TM(℃)以下の温度域の滞在時間」とは、材料温度が1000℃以上最高到達温度TM(℃)以下の範囲にある時間を意味する。1000℃以上TM(℃)以下の温度域の滞在時間が3〜10秒となるような短時間での材料温度のコントロールは、TMよりも高い温度に設定された炉内に材料を装入し、所定のTM(℃)に到達した時点で炉外に出して冷却するか、より低温のゾーンに移すことによって行うことができる。常温からの昇温過程を含めたヒートパターンは、予備実験やコンピュータシミュレーションによって予め求めておくことができる。加熱後は、例えば1000℃から100℃までの平均冷却速度が1〜150℃/s、より好ましくは20〜150℃/sとなるように冷却することが望ましい。この冷却過程でオーステナイト母相はマルテンサイト相に変態する。その結果、マトリックス(金属素地)がマルテンサイト相であり、そのマトリックス中に炭化物が上述した所定の量およびサイズで分散した組織状態が得られる。 As the material temperature during heating in the quenching process, the value of the surface temperature of the steel material can be adopted. “The stay time in the temperature range of 1000 ° C. or more and T M (° C.) or less” means the time during which the material temperature is in the range of 1000 ° C. or more and the maximum temperature T M (° C.) or less. Control of the material temperature in a short time such that the residence time in the temperature range of 1000 ° C. or more and T M (° C.) or less is 3 to 10 seconds is performed by loading the material in a furnace set at a temperature higher than T M. When the temperature reaches a predetermined T M (° C.), it can be removed from the furnace and cooled, or moved to a lower temperature zone. The heat pattern including the process of raising the temperature from room temperature can be obtained in advance by a preliminary experiment or computer simulation. After the heating, for example, it is desirable to cool so that the average cooling rate from 1000 ° C to 100 ° C is 1 to 150 ° C / s, more preferably 20 to 150 ° C / s. In this cooling process, the austenite matrix transforms into a martensite phase. As a result, a matrix (metal base) is a martensite phase, and a structure state in which carbides are dispersed in the matrix in the above-described predetermined amount and size is obtained.
図1に、後述表2AのNo.A2−14の例(比較例)で得られた鋼材についての圧延面に平行な観察面の光学顕微鏡写真を例示する。焼入れ処理の加熱条件は、最高到達温度TMが1050℃、1000℃以上TM(℃)以下の温度域の滞在時間が1秒未満(1050℃均熱0秒)となるようにした。比較的黒く見える粒子がNb炭化物、比較的グレーに見える粒子がCr炭化物である。炭化物の存在量が多い金属組織を呈している。 FIG. 1 illustrates an optical micrograph of an observation surface parallel to a rolled surface of a steel material obtained in Example No. A2-14 (Comparative Example) of Table 2A described below. The heating conditions for the quenching treatment were such that the maximum temperature T M was 1050 ° C., and the residence time in the temperature range of 1000 ° C. or more and T M (° C.) was less than 1 second (soaking at 1050 ° C. and 0 seconds). Particles that appear relatively black are Nb carbides, and particles that appear relatively gray are Cr carbides. It has a metal structure with a large amount of carbides.
図2に、図1の写真を画像処理することによって得られた二値化画像を例示する。この二値化画像を解析した結果、円相当周囲長が10.0μm以上の粗大炭化物は69個/2200μm2と多かった。この鋼板の場合、耐アブレッシブ摩耗性の改善効果は不十分であり、耐食性にも劣った。 FIG. 2 illustrates a binarized image obtained by performing image processing on the photograph of FIG. As a result of analyzing the binarized image, the number of coarse carbides having a circumference equivalent to a circle of 10.0 μm or more was as large as 69/2200 μm 2 . In the case of this steel sheet, the effect of improving the abrasive wear resistance was insufficient, and the corrosion resistance was poor.
図3に、後述表2AのNo.A2−16の例(本発明例)で得られた鋼材についての圧延面に平行な観察面の光学顕微鏡写真を例示する。焼入れ処理の加熱条件は、最高到達温度TMが1050℃、1000℃以上TM(℃)以下の温度域の滞在時間が5秒となるようにした。図1の例との加熱条件の相違は1000℃以上TM(℃)以下の温度域の滞在時間を1秒未満から5秒に増やしたことであるが、炭化物の存在量が大幅に減少していることが判る。この炭化物の減少はCr炭化物の固溶化が進行したことによる。ただし、小さいサイズのCr炭化物は十分に残存している。 FIG. 3 illustrates an optical micrograph of an observation surface parallel to the rolled surface of the steel material obtained in Example No. A2-16 (Example of the present invention) in Table 2A described below. The heating conditions for the quenching treatment were such that the maximum ultimate temperature T M was 1050 ° C., and the residence time in the temperature range of 1000 ° C. or more and T M (° C.) or less was 5 seconds. The difference in the heating conditions from the example of FIG. 1 is that the residence time in the temperature range of 1000 ° C. or more and T M (° C.) or less was increased from less than 1 second to 5 seconds, but the amount of carbides was significantly reduced. You can see that This decrease in carbides is due to the progress of solid solution of Cr carbides. However, the small-sized Cr carbide remains sufficiently.
図4に、図3の写真を画像処理することによって得られた二値化画像を例示する。この二値化画像を解析した結果、円相当周囲長が10.0μm以上の粗大炭化物は5個/2200μm2と少なかった。この場合、図2の例に比べ耐アブレッシブ摩耗性は大幅に向上しており、耐食性も改善された。すなわち、焼入れ処理の加熱でCr炭化物の存在形態をコントロールすることによって、耐アブレッシブ摩耗性の大幅な改善が可能となり、耐食性も十分に確保できる。 FIG. 4 illustrates a binarized image obtained by performing image processing on the photograph of FIG. As a result of analyzing this binarized image, the number of coarse carbides having a circumference equivalent to a circle of 10.0 μm or more was as small as 5/2200 μm 2 . In this case, the abrasive wear resistance was significantly improved as compared with the example of FIG. 2, and the corrosion resistance was also improved. That is, by controlling the existence form of the Cr carbide by heating in the quenching treatment, the abrasive wear resistance can be significantly improved, and the corrosion resistance can be sufficiently secured.
〔焼戻し処理〕
上記の焼入れ処理を終えた鋼材は硬質なマルテンサイト組織を呈している。靭性や加工性を重視する場合は、焼入れ処理後の鋼材に対して、必要に応じて更に焼戻し処理を施すことができる。焼戻し処理は、150〜700℃で1〜120分保持する条件で行うことが好ましい。
[Tempering treatment]
The steel material after the above quenching has a hard martensite structure. When importance is placed on toughness and workability, the steel material after the quenching treatment can be further subjected to a tempering treatment if necessary. The tempering treatment is preferably performed under the condition of holding at 150 to 700 ° C. for 1 to 120 minutes.
以上のようにして得られたマルテンサイト系ステンレス鋼材を素材として、耐アブレッシブ摩耗性に優れる「摺動部材」を製造することができる。刃物も、ここでいう摺動部材に含まれる。 Using the martensitic stainless steel material obtained as described above as a material, a "sliding member" having excellent abrasive wear resistance can be manufactured. The blade is also included in the sliding member.
表1に示す化学組成の鋼を溶製し、得られた鋳片を1150〜1250℃で2時間加熱したのち抽出して、熱間圧延を施し、板厚3.0〜4.0mmの熱延鋼板とした。その熱延鋼板に、750〜850℃の間に設定した温度で6時間保持する条件で熱延板焼鈍を施した。次いで酸洗を行ったのち、冷間圧延、中間焼鈍,酸洗、仕上冷間圧延、仕上焼鈍を行った。中間焼鈍および仕上焼鈍の加熱温度は750〜850℃、仕上冷間圧延の圧延率は30〜50%とした。ここでは、上記の仕上焼鈍を終えた板厚1.0〜2.0mmの鋼板から切り出した試験片を「鋼素材」として、これに表2A、表2Bに示す加熱条件で焼入れ処理を施した。焼入れ処理の冷却は、試験片を2枚の水冷銅板の間に挟み込んで急冷する方法で行った。この場合、1000℃から100℃まで(最高到達温度TMが1000℃未満の例ではTMから100℃まで)の平均冷却速度は25〜150℃/s程の範囲となる。焼入れ処理後の鋼材はいずれもマトリックスがマルテンサイト相である金属組織を呈していた。一部の例(No.A2−22、23、24、25)では、焼入れ処理後に更に300℃で30分保持する焼戻し処理を施した。このようにして得られた焼入れ処理後の板材または焼戻し処理後の板材に酸洗を施した鋼材を供試材として、以下の調査に供した。供試材の板厚は1.0〜2.0mmの範囲にある。 A steel having a chemical composition shown in Table 1 was melted, and the obtained slab was heated at 1150 to 1250 ° C. for 2 hours, extracted, hot-rolled, and heated to a thickness of 3.0 to 4.0 mm. It was a rolled steel sheet. The hot-rolled steel sheet was subjected to hot-rolled sheet annealing under the condition of holding at a temperature set between 750 and 850 ° C. for 6 hours. Next, after pickling, cold rolling, intermediate annealing, pickling, finish cold rolling, and finish annealing were performed. The heating temperature of the intermediate annealing and the finish annealing was 750 to 850 ° C., and the rolling reduction of the finish cold rolling was 30 to 50%. Here, a test piece cut out from a steel sheet having a thickness of 1.0 to 2.0 mm after the above-described finish annealing was used as a “steel material”, which was subjected to a quenching treatment under heating conditions shown in Tables 2A and 2B. . The cooling of the quenching treatment was performed by sandwiching the test piece between two water-cooled copper plates and rapidly cooling. In this case, the range of about average cooling rate is 25 to 150 ° C. / s from 1000 ° C. to 100 ° C. (in the example below the maximum temperature T M is 1000 ° C. to 100 ° C. from T M). Each of the steel materials after the quenching treatment had a metal structure in which the matrix was a martensite phase. In some examples (Nos. A2-22, 23, 24, and 25), after the quenching, a tempering treatment was performed at 300 ° C. for 30 minutes. The steel material obtained by subjecting the plate material after quenching treatment or the plate material after tempering treatment thus obtained to pickling was used as a test material and subjected to the following investigations. The thickness of the test material is in the range of 1.0 to 2.0 mm.
(硬さ測定)
供試材の板面(板厚方向に対して垂直な板表面)について、JIS Z2244:2009に従いビッカース硬さHV30(試験力294.2N)を測定した。
(Hardness measurement)
The Vickers hardness HV30 (test force 294.2N) was measured on the plate surface of the test material (plate surface perpendicular to the plate thickness direction) in accordance with JIS Z2244: 2009.
(炭化物面積率)
上掲の「炭化物の面積率の求め方」に従って供試材の板面(板厚方向に対して垂直な板表面)をシュウ酸電解エッチングにて仕上げた観察面についての光学顕微鏡観察を行い、炭化物の面積率(%)を定めた。観察画像の採取は200万ドット/インチの解像度で行った。無作為に選択した10視野について合計409394.4μm2の面積を観察した。画像処理では、炭化物粒子が黒で表示されるように明度を二値化した。
(Carbide area ratio)
According to the above-mentioned "How to determine the area ratio of carbide", the observation surface obtained by finishing the plate surface of the test material (the plate surface perpendicular to the plate thickness direction) by oxalic acid electrolytic etching is observed by an optical microscope. The area ratio (%) of the carbide was determined. Observation images were collected at a resolution of 2 million dots / inch. An area of a total of 409394.4 μm 2 was observed for 10 randomly selected visual fields. In the image processing, the brightness was binarized so that the carbide particles were displayed in black.
(粗大炭化物の個数密度)
上掲の「円相当周囲長10.0μm以上の炭化物の個数密度の求め方」に従って供試材の板面をシュウ酸電解エッチングにて仕上げた観察面についての光学顕微鏡観察を行い、円相当周囲長10.0μm以上の「粗大炭化物」の個数密度(個/2200μm2)を定めた。ここでは、上記の炭化物面積率の測定と同じ観察画像(合計409394.4μm2の二値化画像)を用いた。
(Number density of coarse carbide)
According to the above-mentioned "How to determine the number density of carbides having a circumference equivalent to a circle of 10.0 μm or more", the observation surface obtained by finishing the plate surface of the test material by oxalic acid electrolytic etching is observed with an optical microscope, and the circumference equivalent to the circle is determined. The number density of “coarse carbide” having a length of 10.0 μm or more (pieces / 2200 μm 2 ) was determined. Here, the same observation image as that of the above-described measurement of the carbide area ratio (a binarized image of a total of 409394.4 μm 2 ) was used.
(比摩耗量)
ピンオンディスク摩耗試験によって耐アブレッシブ摩耗性を評価した。番手800のSiC研磨紙(JIS R6010:2000に規定される粒度P800のSiC砥粒が塗布された研磨紙)を貼り付けたディスクを回転させ、その研磨紙の表面上に、供試材から切り出した直径8mmの円形試験片の表面を付加荷重20Nで押し付けた。回転数140rpm、試験片中心位置の摩擦速度0.66m/s、試験片中心位置の摩擦距離200m、乾式の条件で摩耗試験を行い、下記(1)式により比摩耗量C(mm3/m/N)を算出した。
比摩耗量C=W/(L×F) …(1)
ここで、Wは試験片の摩耗量(mm3)、Lは摩擦距離=200m、Fは付加荷重=20Nである。
この試験において比摩耗量が40×10-5mm3/m/N以下であれば非常に優れた耐アブレッシブ摩耗性を有すると評価できる。したがって、比摩耗量が40×10-5mm3/m/N以下であるものを合格と判定した。
(Specific wear)
The abrasive wear resistance was evaluated by a pin-on-disk wear test. The disk to which the SiC abrasive paper with a count of 800 (abrasive paper coated with SiC abrasive grains having a particle size of P800 specified in JIS R6010: 2000) is rotated, and cut out from the test material on the surface of the abrasive paper The surface of a circular test piece having a diameter of 8 mm was pressed with an additional load of 20N. A wear test was performed under a dry condition under the conditions of a rotational speed of 140 rpm, a friction speed of 0.66 m / s at the center of the test piece, a friction distance of 200 m at the center of the test piece, and a specific wear amount C (mm 3 / m) according to the following equation (1). / N) was calculated.
Specific wear amount C = W / (L × F) (1)
Here, W is the amount of wear (mm 3 ) of the test piece, L is the friction distance = 200 m, and F is the additional load = 20 N.
In this test, if the specific wear amount is 40 × 10 −5 mm 3 / m / N or less, it can be evaluated as having extremely excellent abrasive wear resistance. Therefore, those having a specific wear amount of 40 × 10 −5 mm 3 / m / N or less were determined to be acceptable.
(耐食性)
供試材から切り出した試験片(裏面および端面シール:あり)について、5%塩化ナトリウム水溶液による、35℃、72時間の塩水噴霧試験を行い、赤錆発生の有無を調べた。赤錆の発生が認められなかったものを○(耐食性;良好)、認められたものを×(耐食性;不十分)と評価し、○評価を合格と判定した。
これらの結果を表2A、表2Bに示す。
(Corrosion resistance)
A test piece cut from the test material (back and end face seals: provided) was subjected to a salt spray test with a 5% aqueous solution of sodium chloride at 35 ° C. for 72 hours to check for the occurrence of red rust. When no occurrence of red rust was observed, it was evaluated as ○ (corrosion resistance; good), and when it was observed, it was evaluated as x (corrosion resistance; insufficient).
The results are shown in Tables 2A and 2B.
本発明例の鋼材はCr炭化物の存在形態をコントロールすることにより、Ti、Nb、Zr、V、Wの1種以上の元素の炭化物とCr炭化物の総量(炭化物面積率)が十分に確保され、かつ粗大炭化物の存在量が少ない金属組織が得られた。その結果、耐アブレッシブ摩耗性が向上し、耐食性も良好であった。 In the steel material of the present invention example, by controlling the existence form of Cr carbide, the total amount of carbides of at least one element of Ti, Nb, Zr, V and W and Cr carbide (carbon carbide area ratio) is sufficiently secured, A metal structure with a small amount of coarse carbides was obtained. As a result, the abrasive wear resistance was improved, and the corrosion resistance was also good.
これに対し、比較例A1−1、A1−2、A2−1からA2−6までは、焼入れ処理において最高到達温度TMが低すぎたので、Cr炭化物の固溶化が不十分となり粗大炭化物が多い金属組織となった。その結果、耐アブレッシブ摩耗性に劣り、耐食性も悪かった。 On the other hand, in Comparative Examples A1-1, A1-2, A2-1 to A2-6, the maximum attained temperature T M was too low in the quenching treatment, so that the solution of Cr carbide was insufficient and coarse carbides were formed. Many metal structures. As a result, the abrasion resistance was poor and the corrosion resistance was poor.
比較例A1−3、A1−4、A1−6、A1−7、A2−7、A2−8、A2−11、A2−12、A2−15、A2−15、A2−17、A2−18、A2−21、A2−24は、焼入れ処理において1000℃以上TM以下の滞在時間が短すぎたので、Cr炭化物の固溶化が不十分となり粗大炭化物が多い金属組織となった。その結果、耐アブレッシブ摩耗性に劣り、耐食性も悪かった。 Comparative Examples A1-3, A1-4, A1-6, A1-7, A2-7, A2-8, A2-11, A2-12, A2-15, A2-15, A2-17, A2-18, In A2-21 and A2-24, the residence time at 1000 ° C. or more and T M or less in the quenching treatment was too short, so that the solution of Cr carbide was insufficient and the metal structure was rich in coarse carbides. As a result, the abrasion resistance was poor and the corrosion resistance was poor.
比較例A1−21、A9−2は、焼入れ処理において1000℃以上TM以下の滞在時間が長すぎたので、Cr炭化物の固溶化が過度に進行し、Cr炭化物がほとんど残存しない金属組織となって炭化物面積率が本発明の規定を下回った。この場合、A1−21ではNb炭化物が、A9−2ではTi、Nb、Vの炭化物がそれぞれ存在することにより、耐アブレッシブ摩耗性の向上作用は生じているものの、その向上の程度は本発明例のものより小さかった。 In Comparative Examples A1-21 and A9-2, since the residence time at 1000 ° C. or more and T M or less was too long in the quenching treatment, the solid solution of the Cr carbide excessively progressed, and the metal structure in which the Cr carbide hardly remained remained. As a result, the carbide area ratio was lower than the stipulation of the present invention. In this case, although the presence of Nb carbide in A1-21 and the presence of carbides of Ti, Nb and V in A9-2, respectively, the effect of improving the abrasive wear resistance is produced, but the degree of the improvement is the same as that of the present invention. It was smaller than the one.
比較例B1−1、B2−1は、Ti、Nb、Zr、V、Wの群から選ばれる1種以上の元素を含有しないか、その合計含有量が低すぎるので、それらの元素の硬質炭化物による耐アブレッシブ摩耗性向上作用が発揮されていない。なお、B1−1において耐食性が悪かったのは鋼中の固溶C含有量が多かったことによると考えられる。 Comparative Examples B1-1 and B2-1 do not contain one or more elements selected from the group consisting of Ti, Nb, Zr, V, and W, or the total content thereof is too low. Does not exhibit the effect of improving abrasive wear resistance. The poor corrosion resistance in B1-1 is considered to be due to the high content of solid solution C in the steel.
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WO2017203695A1 (en) * | 2016-05-27 | 2017-11-30 | 新日鐵住金株式会社 | Stainless steel sheet for springs, and production method therefor |
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