JP2005344194A - High-carbon steel sheet having excellent workability and hardenability - Google Patents
High-carbon steel sheet having excellent workability and hardenability Download PDFInfo
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Abstract
Description
この発明は、成型時の加工性、熱処理後の耐磨耗性の優れた高炭素鋼板に関する。より具体的には、自動車の駆動系のギヤ部品、クラッチ部品等に用いられる加工性に優れ、焼き入れ性に優れた高炭素鋼板に関する。 The present invention relates to a high carbon steel sheet having excellent workability at the time of molding and wear resistance after heat treatment. More specifically, the present invention relates to a high carbon steel sheet that is excellent in workability and excellent in hardenability used for gear parts, clutch parts and the like of automobile drive systems.
一般に、自動車の駆動系のギヤ部品、クラッチ部品等、リクライナー用ギヤ部品はＪＩＳＧ４５０１に規定されるＳ３５Ｃ、Ｓ４５Ｃ、Ｓ５５Ｃ等の機械構造用鋼を素材鋼板として、これを各目的製品形状に成型加工した後、焼き入れ、焼き戻して、所望の強度に調整される。ここで、前記の各製品の素材鋼板は、成型加工前は軟質で加工がし易く、次の成型加工後に施される熱処理によって初めて所望の強度が得られ、かっ使用時に耐衝撃性、耐磨耗性を発揮する特性が要求される。 In general, gear components for recliners, such as gear parts and clutch parts for automobile drive systems, are made by machining steel for mechanical structures such as S35C, S45C and S55C as defined in JIS G4501 into the desired product shapes. Then, it is tempered and tempered to adjust to a desired strength. Here, the material steel plate of each product is soft and easy to process before molding, and the desired strength is obtained only by the heat treatment applied after the next molding process. Characteristics that exhibit wear are required.
また一般に、高炭素鋼板の加工は、切削や、打ち抜き、曲げ、絞り等で行なわれていた。しかし、プレス加工で複雑な形状に成形が可能であれば、切削や溶接による成形よりはるかに製造コストを下げることが可能なため、高炭素薄鋼板の加工性に対する要求がますます高まる傾向にある。同時に、自動車用製品では、軽量化等の要求から、個々の部品の小型化が進められている。部品の小型化は加工性の要求をますます厳しくしている。例えば、リクライナーシートに組み込まれるアームポールは半抜きで内側にギヤをファインブランキングで成形される部品がある。これらも軽量化、小型化の要請からギヤのモジュールを小さくする傾向にあり、従来に用いられていたＳ４５Ｃでは十分な加工性が得られない。また、焼き入れ、焼戻しの熱処理により、強度を確保するが、焼入れ方法を従来の焼き入れ方法から高周波焼入れ、プラズマ加熱焼入れ等が試みられて、急速加熱、短時間保持の焼き入れ性の要求も増加している。 In general, high-carbon steel sheets have been processed by cutting, punching, bending, drawing, or the like. However, if it is possible to form in a complicated shape by pressing, the manufacturing cost can be reduced much more than by forming by cutting or welding, so there is an increasing demand for workability of high-carbon thin steel sheets. . At the same time, miniaturization of individual parts is being promoted for automobile products due to demands for weight reduction and the like. The miniaturization of parts makes the requirements for processability more and more severe. For example, there is a part in which the arm pole incorporated in the recliner sheet is formed by half blanking and the gear is formed by fine blanking inside. These also tend to reduce the size of the gear module due to demands for weight reduction and miniaturization, and sufficient workability cannot be obtained with S45C used in the past. In addition, the strength is ensured by heat treatment such as quenching and tempering, but the quenching method is changed from the conventional quenching method to induction quenching, plasma heating quenching, etc. It has increased.
加工性、焼き入れ性を改善する方法として、特許文献１、特許文献２、特許文献３、特許文献４、参考文献５が開示されている。特許文献１は球状化焼鈍された炭化物の粒径と量を調整している。しかし、この技術で製造された鋼板は上記の要求される用途に対して、加工性が不十分である。特許文献２は、Ｃ：０．２０％以上の高炭素薄鋼板において、炭化物粒径が１．３μｍ以下、フェライト粒径を１〜４μｍに制御することで加工性と焼き入れ性を改善する技術が開示されている。しかし、この技術では、厳しい加工性が要求されるものには適用できない。特許文献３は、Ｐ量を６×Ｂ＋０．００５以下の添加量に調整した高炭素鋼板を球状化率が９０％以上で、かつ炭化物粒径を０．４〜１．２μｍに炭化物を制御し、加工性と焼き入れ性を改善した技術である。特許文献４は、フェライト粒径を２．０μｍ以上に、炭化物粒径を１．１μｍ以下、かつその形状比を１．５以下に制御する製造法である。特許文献５は、熱延鋼板を球状化焼鈍し、３０％以上の冷間圧延、焼鈍することで、フェライト形状比を１．５以下、炭化物の形状比を１．３以下の鋼板を得る製造法である。
As methods for improving workability and hardenability,
上記の技術で製造した高炭素鋼板は、いずれも、焼き入れ性は十分であるが、加工性が不十分であるか、加工性は満足するが、焼き入れ性が不十分である。また、上記の技術で製造した鋼板は、必ずしも加工性が良好でない場合があり、加工性と焼き入れ性を両立する技術に至っていない。このため、加工性と焼き入れ性を安定して有する高炭素鋼板の提供が待たれている。
本発明は、上述した如く従来技術の課題である、安定した加工牲と安定した焼入れ性の両方に優れた高炭素鋼板を提供することを目的とする。 The object of the present invention is to provide a high-carbon steel sheet which is a problem of the prior art as described above and which is excellent in both stable workability and stable hardenability.
本発明者らは、高炭素鋼板の加工性、焼入れ性について詳細に検討した結果、炭化物のサイズ分布を制御することにより、加工性と焼き入れ性を両立できることを知見した。その要旨は、質量％でＣ：０．２０％以上の高炭素薄鋼板において、炭化物の平均粒径が１．０μｍ以下、かつ、０．３０μｍ以下の炭化物の比率が２０％以下であることを特徴とする加工性の優れた高炭素鋼板にある。 As a result of detailed studies on the workability and hardenability of the high carbon steel sheet, the present inventors have found that the workability and the hardenability can be achieved by controlling the size distribution of the carbide. The gist is that, in a high carbon thin steel sheet of C: 0.20% or more by mass%, the average particle size of carbides is 1.0 μm or less and the ratio of carbides of 0.30 μm or less is 20% or less. It is a high carbon steel sheet with excellent workability.
以下本発明の構成要件について詳述する。
最初に、炭化物サイズ分布を制御することにより、加工性と焼き入れ性を両立できることを知見した事実について説明する。
Ｃ：０．４５％、Ｓｉ：０．１８％、Ｍｎ：０．７８％、Ｐ：０．０１１％、Ｓ：０．００３％の組成の連続鋳造スラブを１２００℃に加熱し、仕上げ温度：８００〜８５０℃、巻取り温度：５５０〜６９０℃の条件で熱間圧延を行い、３．５ｍｍ厚みの鋼帯を製造した。この鋼を酸洗後に６００〜７１０℃で１２〜９６時間の焼鈍を行った。この鋼板を高周波加熱で、加熱速度７０℃／秒で８００℃まで加熱後、直ちに油中に焼き入れし、焼き入れ硬さを測定した。加工性の評価はＪＩＳ５号引張り試験片の平行部中心に両端より２ｍｍ深さのＶノッチを入れ、引張り速度：２００ｍｍ／ｍｉｎの引張り試験を行い、伸びを測定した。加工性の評価にＶノッチ付の引張り試験を行なった理由は、高炭素鋼板のプレス加工が比較的歪が局所に集中するケースが多く、高速引張りでのＶノッチ付引張り試験の伸びと高炭素鋼板の加工性との対応が良い為である。また、この鋼板の炭化物のサイズ分布を走査型電子顕微鏡で調査した。図１は炭化物平均粒径と高周波焼き入れ硬さとの関係を示したもので、図２は０．３μｍ以下の炭化物粒径の割合とＶノッチ引張り試験での伸びの関係を示したものである。
The constituent requirements of the present invention will be described in detail below.
First, the fact that the processability and the hardenability can be achieved by controlling the carbide size distribution will be described.
A continuous cast slab having a composition of C: 0.45%, Si: 0.18%, Mn: 0.78%, P: 0.011%, S: 0.003% is heated to 1200 ° C., and finishing temperature: Hot rolling was performed under conditions of 800 to 850 ° C. and winding temperature: 550 to 690 ° C. to produce a steel strip having a thickness of 3.5 mm. The steel was annealed at 600-710 ° C. for 12-96 hours after pickling. The steel plate was heated to 800 ° C. at a heating rate of 70 ° C./second by high-frequency heating, and immediately quenched in oil, and the quenching hardness was measured. For the evaluation of workability, a V-notch having a depth of 2 mm was inserted from both ends into the center of the parallel part of a JIS No. 5 tensile test piece, a tensile test at a tensile rate of 200 mm / min was performed, and the elongation was measured. The reason why the V-notched tensile test was performed for workability evaluation is that there are many cases where high-carbon steel plate press processing has a relatively high concentration of strain locally. This is because the correspondence with the workability of the steel sheet is good. In addition, the size distribution of carbides in the steel sheet was examined with a scanning electron microscope. FIG. 1 shows the relationship between the average carbide particle size and induction hardening hardness, and FIG. 2 shows the relationship between the proportion of the carbide particle size of 0.3 μm or less and the elongation in the V-notch tensile test. .
図１から分かるように、炭化物の粒径が大きくなるにしたがって、焼き入れ硬さが低下し、１．０μｍを超えると焼き入れ硬さがＨｖ：６００以下になり、焼き入れ性が悪くなる。この事実から炭化物粒径を１．０μｍ以下を特定した。
高炭素鋼板の加工性の指標である、高速引張り時のＶノッチ付引張り伸び値は、０．３μｍ以下の炭化物の割合が多くなるにしたがって低下する。０．３μｍ以下の炭化物の割合が２０％超になると、Ｖノッチ伸び値が４０％以上を安定して得られなくなる。このことから、０．３μｍ以下の炭化物の割合を２０％以下に特定した。安定して高いＶノッチ伸び値が得られる条件として０．３μｍ以下の炭化物の割合を１５％以下にすることが好ましい。
炭化物平均粒径を１．０μｍ以下、０．３μｍ以下の炭化物粒径の比率を２０％以下に制御することによって、加工性と焼き入れ性を両立する特性が得られる。
As can be seen from FIG. 1, as the particle size of the carbide increases, the quenching hardness decreases, and when it exceeds 1.0 μm, the quenching hardness becomes Hv: 600 or less and the quenchability deteriorates. From this fact, the carbide particle size was specified to be 1.0 μm or less.
The tensile elongation value with V notch during high-speed tension, which is an index of workability of a high carbon steel sheet, decreases as the proportion of carbides of 0.3 μm or less increases. If the proportion of carbides of 0.3 μm or less exceeds 20%, the V-notch elongation value cannot be stably obtained at 40% or more. From this, the proportion of carbides of 0.3 μm or less was specified as 20% or less. As a condition for stably obtaining a high V-notch elongation value, the proportion of carbides of 0.3 μm or less is preferably 15% or less.
By controlling the ratio of the carbide particle diameter of 1.0 μm or less and the carbide particle diameter of 0.3 μm or less to 20% or less, characteristics that achieve both workability and hardenability can be obtained.
Ｃは焼き入れ後の硬さを調整するために必要な元素で、Ｃ量が０．２０％未満になると焼き入れ硬さが得られなくなる。一方、Ｃ量が多くなると十分な加工性が得られなくなるので、実質的なＣ量の上限は０．９０％である。
Ｂは焼き入れ性を高める元素としてよく知られている。Ｃ量が少ない場合に、安定した焼き入れ性を必要とする場合に０．０００３〜０．００５０％の範囲で添加する。０．０００３％未満では焼き入れ性を高める効果を安定して発揮できない。一方、０．００５０％超の添加は鋼を製造するときに、鋼飯の欠陥、疵の原因となり、製品歩留りを低下させ製造コストの上昇をまねく。好ましい範囲は、同様の理由から、０．０００５％から０．００３０％である。
ＴｉはＢを添加する場合に、Ｂの添加効果を発揮させるため、０．０１〜０．０５０％の範囲で添加する。
C is an element necessary for adjusting the hardness after quenching. When the C content is less than 0.20%, quenching hardness cannot be obtained. On the other hand, since sufficient workability cannot be obtained when the C amount increases, the upper limit of the substantial C amount is 0.90%.
B is well known as an element that enhances hardenability. If the amount of C is small and stable hardenability is required, it is added in the range of 0.0003 to 0.0050%. If it is less than 0.0003%, the effect of improving the hardenability cannot be stably exhibited. On the other hand, addition of more than 0.0050% causes defects and flaws in the production of steel, resulting in a decrease in product yield and an increase in production cost. A preferable range is 0.0005% to 0.0030% for the same reason.
Ti is added in the range of 0.01 to 0.050% in order to exhibit the effect of adding B when B is added.
炭化物のサイズと分布の制御で加工性と焼き入れ性が両立した鋼板が得られる理由は定かでないが、本発明者等は次のように考えている。高炭素鋼板の球状炭化物は、大きさの異なる炭化物がランダムに分布しておらず、微細な炭化物が多い個所と大きな炭化物が存在する個所が分かれている場合がほとんどである。このような炭化物分布の鋼板を加工すると微細な炭化物が存在する領域の変形が抑制され、大きな炭化物が存在する領域に変形が集中し、大きな炭化物の周りにボイドが生じ、これが合体して鋼板に割れが生じる。一方、微細な炭化物が少ないと炭化物の微細な炭化物が偏在する領域が少なくなり、０．３μｍ以下の炭化物割合が２０％以下になると、微細炭化物が偏在する領域がほとんど無くなり、大きさの異なる炭化物はほぼランダムな分布となる。このような炭化物の分布の鋼板を加工した場合は、加工が全領域で均等に歪を分担し、炭化物の周りでのボイドが生じる加工量を高くする。この機構により、加工性が良好になる。 Although the reason why a steel sheet having both workability and hardenability can be obtained by controlling the size and distribution of carbides is not clear, the present inventors consider as follows. In the spherical carbide of the high carbon steel plate, carbides having different sizes are not distributed at random, and in many cases, the places where there are many fine carbides and the places where there are large carbides are separated. When a steel plate with such carbide distribution is processed, deformation in the region where fine carbides are present is suppressed, deformation is concentrated in the region where large carbides are present, and voids are formed around the large carbides, which combine to form a steel plate. Cracking occurs. On the other hand, if there are few fine carbides, there will be less regions where fine carbides of carbides are unevenly distributed, and if the proportion of carbides of 0.3 μm or less is 20% or less, there will be almost no regions where fine carbides are unevenly distributed, and carbides of different sizes. Has a nearly random distribution. When a steel plate having such a carbide distribution is processed, the processing equally distributes the strain in the entire region, and the processing amount in which voids around the carbide are generated is increased. This mechanism improves the workability.
本発明によれば、炭化物の平均粒径だけでなく、０．３μｍ以下の微細炭化物が加工性に影響することに注目し、炭化物の平均粒径を１．０μｍ以下に制御し、加えて、０．３μｍ以下の炭化物割合を２０％以下に制御すれば、焼入れ性と加工性に優れた高炭素鋼板が提供することができる。このように本発明に係る高炭素鋼板は加工性と焼入れ性に優れることから、ギヤに代表される自動車の変速機部品等を安価でかつ、安定した品質で製造することが可能となり、工業的に極めて有益な発明である。 According to the present invention, not only the average particle size of carbides, but also that fine carbides of 0.3 μm or less affect workability, the average particle size of carbides is controlled to 1.0 μm or less, in addition, If the carbide ratio of 0.3 μm or less is controlled to 20% or less, a high carbon steel sheet excellent in hardenability and workability can be provided. As described above, since the high carbon steel sheet according to the present invention is excellent in workability and hardenability, it becomes possible to manufacture automobile transmission parts and the like represented by gears at low cost and with stable quality. It is a very useful invention.
本発明は、Ｃ：０．２０％以上の高炭素鋼において、炭化物のサイズ分布を制御するのみで加工性と焼き入れ性を両立できるので、Ｓｉ、Ｍｎ、Ｐ、Ｓ、Ｃｒ、Ａｌ等の元素は通常の範囲で添加しても良く、特に規定する必要はない。これらの元素は他の特性との関係で添加量を決めればよく、添加量により本発明の特徴を損なうことはない。ただし、好ましくは、次のようにすればよい。 Since the present invention can achieve both workability and hardenability only by controlling the size distribution of carbides in high carbon steel of C: 0.20% or more, such as Si, Mn, P, S, Cr, Al, etc. The elements may be added in a normal range and need not be specified. The addition amount of these elements may be determined in relation to other characteristics, and the feature of the present invention is not impaired by the addition amount. However, the following is preferable.
Ｓｉは、添加量が多くなると鋼板が硬質になり、加工性を損なうので、０．５０％以下とすることが好ましい。
Ｍｎは焼き入れ性を高める元素として良く知られている。しかし、炭化物に固溶し、炭化物の溶解を遅らし、短時間加熱時の焼き入れ性を低下するので、１．５％以下の範囲で添加することが好ましい。
Ｐは加工性を損なうだけでなく、焼き入れ、焼き戻し後の靭性を劣化させるので０．０３％以下とすることが好ましい。
ＳはＭｎＳ等の介在物を生成し、加工性を劣化させるので、０．０２％以下にすることが好ましい。
ＣｒはＭｎと同様に、焼き入れ性を高める元素であることが良く知られているが、しかし、短時間加熱保持時の焼き入れの場合は、炭化物の溶解を遅らせるため、１．０％以下の範囲で添加することが好ましい。
Ａｌは過剰に添加すると焼き入れ性が悪くなるので、０．０８％以下とすることが好ましい。
その他の不可避的に混入する元素が存在しても本発明の特徴を損なわない。
If Si is added in an increased amount, the steel sheet becomes hard and the workability is impaired, so 0.50% or less is preferable.
Mn is well known as an element that enhances hardenability. However, since it dissolves in the carbide, delays the dissolution of the carbide, and lowers the hardenability during heating for a short time, it is preferably added in a range of 1.5% or less.
P not only impairs workability but also deteriorates toughness after quenching and tempering, so 0.03% or less is preferable.
Since S produces inclusions such as MnS and degrades workability, it is preferably made 0.02% or less.
It is well known that Cr, like Mn, is an element that enhances hardenability. However, in the case of quenching when heated for a short time, the dissolution of carbides is delayed, so that it is 1.0% or less. It is preferable to add in the range.
If Al is added excessively, the hardenability deteriorates, so 0.08% or less is preferable.
The presence of other unavoidably mixed elements does not impair the features of the present invention.
このような組成の鋼は転炉、電気炉等の通常の溶解炉で溶製され、連続鋳造あるいはインゴット―分塊圧延してスラブが造られる。この際、鋼成分の偏析が存在すると、球状化焼鈍、あるいは再結晶焼鈍後の炭化物粒径のバラツキが大きくなり、炭化物サイズ分布の制御が難しくなるので、できるだけ、凝固速度を速める、未凝固域で圧下を加える、電磁攪拌等の手段を用いて偏析を少なくすることが好ましい。 Steel having such a composition is melted in a normal melting furnace such as a converter or an electric furnace, and a slab is formed by continuous casting or ingot-bundling rolling. In this case, if there is segregation of the steel component, the dispersion of the carbide particle size after spheroidizing annealing or recrystallization annealing increases, and it becomes difficult to control the carbide size distribution, so that the solidification rate is increased as much as possible. It is preferable to reduce segregation by using a means such as electromagnetic stirring to reduce the pressure.
次に、熱間圧延されるが、この際の加熱温度は特に本発明の特徴に効果をもたらさないので、何度でも良いが、本発明では１０５０から１２８０℃の範囲で実施している。熱延仕上温度は圧延安定性等からＡｒ3点温度以上とすることが好ましい。熱延後の冷却は球状化焼鈍あるいは再結晶焼鈍後の炭化物の大きさ、分布に影響するので、制御冷却をすることが好ましい。具体的には、フェライト変態温度域は急冷し、パーライト変態温度域は変態発熱に相当する熱量を抜熱する水量を注水し、均一なパーライト組織とすることが好ましい。巻取り温度は５５０〜６５０℃の範囲で行なうことが、球状化焼鈍あるいは再結晶焼鈍後の炭化物のサイズ、分布を制御するために好ましい。 Next, although it is hot-rolled, the heating temperature at this time does not have any effect on the characteristics of the present invention, and may be any number of times, but in the present invention, it is carried out in the range of 1050 to 1280 ° C. The hot rolling finishing temperature is preferably not less than the Ar3 point temperature from the viewpoint of rolling stability. Since cooling after hot rolling affects the size and distribution of carbide after spheroidizing annealing or recrystallization annealing, controlled cooling is preferable. Specifically, it is preferable that the ferrite transformation temperature range is rapidly cooled, and the pearlite transformation temperature range is poured with a quantity of water that removes the amount of heat corresponding to the transformation heat generation to form a uniform pearlite structure. The coiling temperature is preferably in the range of 550 to 650 ° C. in order to control the size and distribution of carbides after spheroidizing annealing or recrystallization annealing.
次に、脱スケールの後、球状化焼鈍あるいは直接に冷間圧延後に焼鈍、あるいは球状化焼鈍後に冷間圧延、再結晶焼鈍される。これらの焼鈍は炭化物の平均粒径および、粒径の分布に影響するので、鋼成分、熱間圧延条件等を考慮して、冷間圧延率、焼鈍条件を選ぶことが好ましい。
このようにして製造された鋼帯は、必要に応じ、調質圧延を行い、製品に供される。
Next, after descaling, spheroidizing annealing or directly annealing after cold rolling, or cold rolling and recrystallization annealing after spheroidizing annealing. Since these annealings affect the average particle size of carbides and the distribution of particle sizes, it is preferable to select the cold rolling rate and annealing conditions in consideration of steel components, hot rolling conditions, and the like.
The steel strip manufactured in this way is subjected to temper rolling as needed and provided to the product.
表１に示す組成の鋼を転炉で溶製し、連続鋳造によりスラブを造り、１２５０℃で加熱し、表２に記載の条件で熱間圧延し、３．２ｍｍの鋼板を造った。この鋼板を酸洗後に表２に記載の条件で焼鈍した。この鋼板の圧延方向に平行な断面を研磨し、ピクリン酸飽和溶液で腐食後、走査型電子顕微鏡を用い炭化物の平均粒径および、０．３μｍ以下の炭化物の割合を測定した。ＪＩＳ５号引張り試験片の平行部の中心に両端部に２ｍｍ深さのＶノッチを付け、引張り速度１００ｍｍ／ｍｉｎで引張り試験を行った。また、鋼板を８００℃×２秒の保定後に油中に焼き入れ、その硬さを測定した。調査結果を表２に記した。鋼ＡはＳ３５Ｃ相当成分、鋼ＢはＳ５５Ｃ相当の成分、鋼ＣはＳＡＥｌ０７０相当の成分の鋼板である。これらの鋼は一部、連続鋳造の冷却速度を変えた条件、電磁攪拌を行い、鋳造した。 Steel having the composition shown in Table 1 was melted in a converter, a slab was made by continuous casting, heated at 1250 ° C., and hot-rolled under the conditions shown in Table 2 to produce a 3.2 mm steel plate. The steel sheet was annealed under the conditions shown in Table 2 after pickling. The cross section parallel to the rolling direction of this steel sheet was polished, and after corrosion with a picric acid saturated solution, the average particle size of carbides and the proportion of carbides of 0.3 μm or less were measured using a scanning electron microscope. A V-notch with a depth of 2 mm was attached to both ends at the center of the parallel part of a JIS No. 5 tensile test piece, and a tensile test was conducted at a tensile speed of 100 mm / min. Moreover, the steel plate was quenched in oil after being held at 800 ° C. for 2 seconds, and the hardness was measured. The survey results are shown in Table 2. Steel A is an S35C equivalent component, Steel B is a component equivalent to S55C, and Steel C is a steel plate equivalent to SAE070. Some of these steels were cast under the conditions of changing the cooling rate of continuous casting under electromagnetic stirring.
Ａ−１は炭化物の平均粒径が０．８５μｍで、０．３μｍ以下の炭化物が７．３％の鋼板である。この鋼板は、スラブを造る際に、電磁攪拌を用い、冷却速度を速めて製造した。熱延の加熱温度は１２００℃、熱延仕上スタンドは、潤滑圧延し、後段３スタンドは等歪の圧下率で圧延し、熱延後の冷却はパーライト変態が６１０〜６２５℃の温度範囲で進行するように注水制御した。この鋼板は焼入れ硬さがＨｖ：６４０、Ｖノッチ付引張り伸び値が５１％で、優れた焼入れ性と、加工性を有している事が分かる。Ａ−２は炭化物の平均粒径が１．４３μｍと本発明範囲から外れた比較例である。この鋼は焼入れ硬さがＨｖ：５２０と焼入れ性が不十分で、加工性が若干低下している。Ａ−３とＡ−４は、熱延条件がほぽ同じであるが、Ａ−３は焼鈍保持中に±１０℃以内で昇温、降温を１４回繰り返えす熱サイクルを採用した鋼で、０．３μｍ以下の炭化物の占める割合が９．８５％で、加工性の指標であるＶノッチ伸びが良好であるに対し、通常の条件で製造したＡ−４は０．３μｍ以下の炭化物の割合が３５．６％と本発明範囲から外れており、Ｖノッチ付引張りの伸びが低く、加工性が悪いことが分かる。 A-1 is a steel plate having an average particle size of carbide of 0.85 μm and 7.3% of carbide of 0.3 μm or less. This steel sheet was manufactured by using electromagnetic stirring at the time of making a slab and increasing the cooling rate. The heating temperature for hot rolling is 1200 ° C., the hot rolling finishing stand is lubricated and rolled, the subsequent three stands are rolled at a uniform strain reduction, and the cooling after hot rolling proceeds in a temperature range of 610 to 625 ° C. in the pearlite transformation. The water injection was controlled. This steel plate has a quenching hardness of Hv: 640 and a tensile elongation value with a V notch of 51%, and it can be seen that it has excellent hardenability and workability. A-2 is a comparative example in which the average particle size of the carbide is 1.43 μm and is out of the scope of the present invention. This steel has a quenching hardness of Hv: 520, which is insufficient in hardenability and has a slight decrease in workability. A-3 and A-4 have the same hot rolling conditions, but A-3 is a steel that adopts a heat cycle that repeats temperature rise and fall within ± 10 ° C and 14 times during annealing. The proportion of carbides of 0.3 μm or less is 9.85%, and the V-notch elongation, which is an index of workability, is good, whereas A-4 produced under normal conditions is 0.3 μm or less of carbides. The ratio is 35.6%, which is out of the scope of the present invention. It can be seen that the elongation of the V-notched tensile is low and the workability is poor.
Ｂ−１は炭化物平均粒径が０．９５μｍ、０．３μｍ以下の炭化物の割合が８．５％と本発明範囲の実施例である。この鋼は、偏析が少なくなる条件の電磁攪拌を付加してスラブを造り、熱延、焼鈍仕上温度、巻取り温度、焼鈍条件は表２記載の条件で製造した。ただし、熱延後の冷却は、パーライト変態温度を２０℃以内に制御する注水を行った。この鋼板の焼入れ性はＨｖ：７４０の焼入れ硬さを有し、優れており、加工性の指標であるＶノッチ引張り伸びも高く、優れた加工性を有することが分かる。鋼Ｂ−２は通常の熱延、焼鈍条件で製造した比較例で、炭化物の平均粒径が１．５１μｍと大きい鋼板である。なを、Ｂ−２の熱延終了後の冷却時のパーライト変態温度は、５８０〜６４０℃であった。この鋼板の焼き入れ硬さはＨｖ：６２０と、Ｂ−１のそれより大幅に硬さが低く、焼入れ性が劣ることが分かる。Ｂ−３，Ｂ−４は、熱延条件はほぽ同じであるが、Ｂ−３の焼鈍は保持の途中で温度を変化させる熱サイクルを採用したものである。炭化物平均粒径はほとんど差がないが、０．３μｍ以下の炭化物の割合がＢ−３の１２．５％に対し、Ｂ−４は３２．３％と両者で大幅に炭化物の粒径分布が異なり、微細な炭化物の多い鋼Ｂ−４の加工性が大きく劣ることが分かる。 B-1 is an example within the scope of the present invention, with a carbide average particle size of 0.95 μm and a ratio of carbides of 0.3 μm or less of 8.5%. This steel was made by adding electromagnetic stirring under conditions that reduce segregation, and was manufactured under the conditions shown in Table 2 for hot rolling, annealing finish temperature, coiling temperature, and annealing conditions. However, cooling after hot rolling was performed by pouring water to control the pearlite transformation temperature within 20 ° C. It can be seen that the hardenability of this steel sheet is excellent with a quenching hardness of Hv: 740, and has a high V-notch tensile elongation, which is an index of workability, and has excellent workability. Steel B-2 is a comparative example produced under normal hot rolling and annealing conditions, and is a steel plate having a large average particle size of carbide of 1.51 μm. The pearlite transformation temperature during cooling after the end of hot rolling of B-2 was 580 to 640 ° C. The quenching hardness of this steel sheet is Hv: 620, which is significantly lower than that of B-1, indicating that the hardenability is inferior. B-3 and B-4 have the same hot rolling conditions, but the annealing of B-3 employs a thermal cycle in which the temperature is changed during the holding. There is almost no difference in the average particle size of carbides, but the proportion of carbides of 0.3 μm or less is 12.5% of B-3, while B-4 is 32.3%. In contrast, it can be seen that the workability of steel B-4 with a lot of fine carbides is greatly inferior.
Ｃ−１、Ｃ−２は、共に偏析が少なくなる条件の電磁攪拌を付加してスラブを製造したものであるが、Ｃ−１は熱延後の冷却中にパーライト変態を６００〜６１０℃の範囲で進行するように注水した。Ｃ−２は通常の方法で冷却した鋼板である。通常の冷却で製造したＣ−２のパーライト変態温度範囲は５７０〜６３０℃であった。Ｃ−１の炭化物平均粒径は０．５６μｍ、０．３μｍ以下の炭化物割合が１２％で本発明範囲内である。Ｃ−２は、０．３μｍ以下の炭化物の割合が、２５％と多い、比較例である。Ｃ−１は焼き入れ性、加工性共に優れた特性を有するが、Ｃ−２はＣ−１に比較して加工性が劣る。Ｃ−３は、炭化物の平均粒径が１．４５μｍと本発明範囲から外れた比較例である。この鋼は、焼入れ硬さが本発明範囲内の実施例より低く、焼入れ性が劣る。 C-1 and C-2 are both manufactured by adding electromagnetic stirring under the condition that segregation is reduced, but C-1 undergoes pearlite transformation at 600 to 610 ° C. during cooling after hot rolling. Water was poured to proceed in the range. C-2 is a steel plate cooled by an ordinary method. The pearlite transformation temperature range of C-2 produced by normal cooling was 570 to 630 ° C. The carbide average particle size of C-1 is 0.56 μm, and the ratio of carbides of 0.3 μm or less is 12%, which is within the scope of the present invention. C-2 is a comparative example in which the proportion of carbides of 0.3 μm or less is as high as 25%. C-1 has excellent hardenability and workability, but C-2 is inferior in processability to C-1. C-3 is a comparative example in which the average particle size of the carbide is 1.45 μm and is out of the scope of the present invention. This steel has lower quenching hardness than the examples within the scope of the present invention and is inferior in hardenability.
表１に示す組成の鋼を転炉で溶製し、連続鋳造によりスラブを造り、１２５０℃で加熱し、表３に記載の条件で熱間圧延し、酸洗、冷間圧延、焼鈍して、２．２ｍｍの鋼板を造った。この鋼板の圧延方向に平行な断面を研磨し、ピクリン酸飽和溶液で腐食後、走査型電子顕微鏡を用い炭化物の平均粒径および、０．３μｍ以下の炭化物の割合を測定した。ＪＩＳ５号引張り試験片の平行部の中心に両端部に２ｍｍ深さのＶノッチを付け、引張り速度１００ｍｍ／ｍｉｎで引張り試験を行った。また、鋼板を８００℃×１０秒の保定後に油中に焼き入れ、その硬さを測定した。調査結果を表２に記した。鋼ＡはＳ３５Ｃ相当成分、鋼ＢはＳ５５Ｃ相当の成分、鋼ＣはＳＡＥｌ０７０相当の成分の鋼板である。これらの鋼は一部、連続鋳造の冷却速度を変えた鋳造、電磁攪拌、未凝固域の圧下を行って鋳造した。 A steel having the composition shown in Table 1 is melted in a converter, a slab is made by continuous casting, heated at 1250 ° C., hot-rolled under the conditions shown in Table 3, pickling, cold-rolling, and annealing. A steel plate of 2.2 mm was made. The cross section parallel to the rolling direction of this steel sheet was polished, and after corrosion with a picric acid saturated solution, the average particle size of carbides and the proportion of carbides of 0.3 μm or less were measured using a scanning electron microscope. A V-notch with a depth of 2 mm was attached to both ends at the center of the parallel part of a JIS No. 5 tensile test piece, and a tensile test was conducted at a tensile speed of 100 mm / min. Moreover, the steel plate was quenched in oil after being held at 800 ° C. for 10 seconds, and its hardness was measured. The survey results are shown in Table 2. Steel A is an S35C equivalent component, Steel B is a component equivalent to S55C, and Steel C is a steel plate equivalent to SAE070. Some of these steels were cast by changing the cooling rate of continuous casting, electromagnetic stirring, and reducing the unsolidified zone.
Ａ−５は連続鋳造時の冷却速度を速めてスラブを造り、表３記載の熱延、冷延、焼鈍した鋼板である。熱延後の冷却中のパーライト変態温度を２０℃以内に制御して冷却した。この鋼板の炭化物の平均粒径が０．７５μｍ、０．３μｍ以下の炭化物割合が８．６％で、本発明範囲内の実施例である。焼入れ後の硬さはＨｖ：６１０で良好な焼入れ性を有し、Ｖノッチ付引張り伸びも高い値を示し、加工性も優れていることが分かる。Ａ−６は特別な手段を講じることなく製造した鋼板で、炭化物平均粒径が１．４２μｍ、０．３μｍ以下の炭化物割合が５．２％の比較例である。この鋼板はＡ−５に比べて、焼き入れ性が大きく劣っており、本発明の目的に合致しない。Ａ−７，Ａ−８は、熱延条件以外はほぼ同一の条件で製造した鋼板である。Ａ−７は、通常の熱延条件で行い、Ａ−８は熱延の仕上圧延中に冷却し、パーライト変態させた後に、急速加熱で８５０℃まで加熱、熱延した。Ａ−７は炭化物の平均粒径が０．４８μｍ、０．３μｍ以下の炭化物割合が２５％の本発明範囲外の比較例である。一方、Ａ−８は炭化物平均粒径が０．６０μｍ、０．３μｍ以下の炭化物割合が９．０％の本発明範囲内の実施例である。Ａ−８はＡ−７に比較して、焼入れ性は良好であると共に、優れた加工性を有することが分かる。Ｂ−５はＳ５５Ｃ相当成分で、熱延までは、Ｂ−１と同じ条件で製造した鋼で、炭化物の平均粒径が０．６６μｍ、０．３μｍ以下の炭化物割合が８．３％の本発明範囲内の実施例で、優れた焼入れ性と加工性を有している事が分かる。Ｂ−６は通常の製造条件で製造した鋼板で、炭化物平均粒径が１．２３μｍ、０．３μｍ以下の炭化物の割合が４．３％の比較例であるが、Ｂ−５に比較して、焼入れ性、加工性共に劣る。Ｂ−７，Ｂ−８は熱延、冷間圧延まではほぼ同じ条件で製造されたが、Ｂ−７が通常の焼鈍で製造したに対し、Ｂ−８は焼鈍の保持中に±１５℃の範囲で１０回の昇温、降温を繰り返す熱サイクルを採用して製造した鋼板である。Ｂ−８の０．３μｍ以下の炭化物が２３％に対し、Ｂ−７のそれは１３％と微細な炭化物が少ない。両者の焼入れ性は同じであるが、加工性の指標であるＶノッチ付引張り伸びは、Ｂ−７が高く、加工性が良好であることが分かる。Ｃ−４，Ｃ−５はＳＡＥｌ０７０相当成分の鋼で、熱延、冷延、焼鈍はほぽ同じ条件で製造し、Ｃ−５は、通常の鋳造条件でスラブを製造し、Ｃ−４は電磁攪拌で従来材に比し、偏析を三分の一程度に低める条件でスラブを製造した。両鋼板の焼入れ性は同じであるが、微細な炭化物の少ないＣ−４の方が加工性の指標であるＶノッチ付引張り伸びが高く、Ｃ−４の加工性が優れていることが分かる。Ｃ−６は通常の製造条件内で製造した鋼板のある。この鋼板の炭化物平均粒径は１．２３μｍで、焼き入れ硬さがＣ−４，５に比較して低く、焼き入れ性が不足していることが分かる。 A-5 is a steel plate that is hot rolled, cold rolled, and annealed as shown in Table 3 by making a slab by increasing the cooling rate during continuous casting. The pearlite transformation temperature during cooling after hot rolling was controlled within 20 ° C. for cooling. This steel plate has an average particle size of carbides of 0.75 μm and a proportion of carbides of 0.3 μm or less of 8.6%, which is an example within the scope of the present invention. It can be seen that the hardness after quenching is Hv: 610, which has good hardenability, has a high V-notched tensile elongation, and is excellent in workability. A-6 is a steel plate manufactured without taking special measures, and is a comparative example in which the average particle size of carbide is 1.42 μm and the proportion of carbides of 0.3 μm or less is 5.2%. This steel sheet is greatly inferior in hardenability compared with A-5, and does not meet the object of the present invention. A-7 and A-8 are steel plates manufactured under substantially the same conditions except for hot rolling conditions. A-7 was performed under normal hot rolling conditions, and A-8 was cooled during hot rolling finish rolling and pearlite transformed, and then heated to 850 ° C. by rapid heating and hot rolled. A-7 is a comparative example outside the scope of the present invention in which the average particle size of carbides is 0.48 μm, and the proportion of carbides of 0.3 μm or less is 25%. On the other hand, A-8 is an example within the scope of the present invention in which the average particle size of carbide is 0.60 μm and the proportion of carbides of 0.3 μm or less is 9.0%. It can be seen that A-8 has excellent hardenability and excellent workability as compared with A-7. B-5 is a component equivalent to S55C, and is a steel manufactured under the same conditions as B-1, up to hot rolling. The average particle size of the carbide is 0.66 μm, and the ratio of the carbide of 0.3 μm or less is 8.3%. It can be seen that the examples within the scope of the invention have excellent hardenability and workability. B-6 is a steel plate manufactured under normal manufacturing conditions, and is a comparative example in which the average particle size of carbide is 1.23 μm and the proportion of carbides of 0.3 μm or less is 4.3%, but compared to B-5. Inferior in both hardenability and workability. B-7 and B-8 were manufactured under the same conditions until hot rolling and cold rolling, but B-7 was manufactured by normal annealing, whereas B-8 was ± 15 ° C. during holding of annealing. It is a steel plate manufactured by adopting a thermal cycle in which the temperature is raised and lowered 10 times in the range. B-8 has a fine carbide of less than 0.3 μm, whereas B-7 has a fine carbide of 13%, compared with 23%. Although both hardenability is the same, the tensile elongation with V notch, which is an index of workability, is high in B-7, and it can be seen that the workability is good. C-4 and C-5 are steels equivalent to SAEl070, and hot rolling, cold rolling and annealing are manufactured under the same conditions, C-5 is a slab manufactured under normal casting conditions, and C-4 is The slab was manufactured under the condition that the segregation was reduced to about one third of that of the conventional material by electromagnetic stirring. The hardenability of both steel plates is the same, but it can be seen that C-4 with less fine carbide has higher V-notched tensile elongation, which is an index of workability, and is superior in workability of C-4. C-6 is a steel plate manufactured under normal manufacturing conditions. This steel plate has a carbide average particle size of 1.23 μm, and its quenching hardness is lower than that of C-4,5, indicating that the hardenability is insufficient.
表１に示す組成の鋼Ｂ，鋼Ｃを転炉で溶製し、連続鋳造によりスラブを造り、１２５０℃で加熱し、熱延圧延し、表４に記載の条件で一次焼鈍、冷間圧延、二次焼鈍を行って、２．２ｍｍの鋼板を造った。この鋼板の圧延方向に平行な断面を研磨し、ピクリン酸飽和溶液で腐食後、走査型電子顕微鏡を用い炭化物の平均粒径および、０．３μｍ以下の炭化物の割合を測定した。ＪＩＳ５号引張り試験片の平行部の中心に両端部に２ｍｍ深さのＶノッチを付け、引張り速度１００ｍｍ／ｍｉｎで引張り試験を行った。また、鋼板を８００℃×１秒の加熱後に油中に焼き入れ、その硬さを測定した。調査結果を表４に記した。これらの鋼は一部、連続鋳造の冷却速度を変えて、または電磁攪拌、未凝固域圧下の一つまたは二つを組み合わせて鋳造した。 Steel B and Steel C having the composition shown in Table 1 are melted in a converter, a slab is formed by continuous casting, heated at 1250 ° C., hot rolled, and subjected to primary annealing and cold rolling under the conditions shown in Table 4. Secondary annealing was performed to produce a 2.2 mm steel plate. The cross section parallel to the rolling direction of this steel sheet was polished, and after corrosion with a picric acid saturated solution, the average particle size of carbides and the proportion of carbides of 0.3 μm or less were measured using a scanning electron microscope. A V-notch with a depth of 2 mm was attached to both ends at the center of the parallel part of a JIS No. 5 tensile test piece, and a tensile test was conducted at a tensile speed of 100 mm / min. Moreover, the steel plate was hardened in oil after heating at 800 ° C. for 1 second, and its hardness was measured. The survey results are shown in Table 4. Some of these steels were cast by changing the cooling rate of continuous casting or by combining one or two of electromagnetic stirring and unsolidified zone pressure.
Ｓ５５ＣのＢ−９とＢ−ｌ０は、鋳造条件以外はほぼ同一条件で製造し、Ｂ−１０が通常の鋳造条件でスラブを造り、Ｂ−９が電磁攪拌で凝固組織の均一となる条件でスラブを造った。両鋼の炭化物平均粒径は大きく変わっていないが、０．３μｍ以下の炭化物に違いが生じ、Ｂ−９のそれは１２％で本発明範囲内に、Ｂ−１０のそれは２２％で本発明範囲から外れている。炭化物の平均粒径、０．３μｍ以下の炭化物割合が本発明範囲内のＢ−９は焼き入れ性、加工性共に優れた特性を有し、０．３μｍ以下の炭化物が本発明範囲より多い、Ｂ−１０の加工性はＢ−９より劣る。Ｂ−１１は炭化物の平均粒径が本発明範囲より大きい比較例であるが、焼入れ後の硬さが本発明範囲内の実施例のＢ−９より軟く、焼き入れ性が劣る。 B-9 and B-10 of S55C are manufactured under almost the same conditions except for the casting conditions, B-10 is a slab made under normal casting conditions, and B-9 is under the condition that the solidified structure becomes uniform by electromagnetic stirring. I made a slab. Although the average particle size of carbides of both steels has not changed significantly, there is a difference in carbides of 0.3 μm or less, that of B-9 is within 12% of the present invention, and that of B-10 is 22% of the present invention. It is off. The average particle size of carbide, B-9 within the scope of the present invention with a carbide ratio of 0.3 μm or less has excellent properties in both hardenability and workability, and 0.3 μm or less of carbide is more than the scope of the present invention. The workability of B-10 is inferior to B-9. B-11 is a comparative example in which the average particle size of the carbide is larger than the range of the present invention, but the hardness after quenching is softer than B-9 of the example within the range of the present invention, and the hardenability is inferior.
ＳＡＥ１０７０のＣ−７，Ｃ−８は、鋳造条件以外はほぽ同一条件で製造し、Ｃ−８は通常の鋳造条件で、Ｃ−７が電磁攪拌と鋳造速度を早めて凝固偏析を少なくする条件で鋳造してスラブとした。両鋼の炭化物平均粒径は大きく変わっていないが、０．３μｍ以下の炭化物に違いが生じ、Ｃ−７のそれは１２％で本発明範囲内に、Ｃ−８のそれは２１．５％で本発明範囲から外れている。炭化物粒径が０．３μｍ以下の炭化物割合が本発明範囲内のＣ−７は焼き入れ性、加工性共に優れた特性を有し、０．３μｍ以下の炭化物が本発明範囲より多い、Ｃ−８の加工性はＣ−７より劣る。Ｃ−９は炭化物の平均粒径が本発明範囲より大きい比較例であるが、焼入れ後の硬さが本発明範囲内の実施例のＣ−７より軟く、焼き入れ性が劣る。 SAE1070 C-7 and C-8 are manufactured under the same conditions except for casting conditions. C-8 is normal casting conditions. C-7 increases electromagnetic stirring and casting speed to reduce solidification segregation. The slab was cast under conditions. The average particle size of the carbides of both steels has not changed greatly, but there is a difference in carbides of 0.3 μm or less, that of C-7 is 12% within the scope of the present invention, that of C-8 is 21.5%. It is out of the scope of the invention. C-7 having a carbide particle size of 0.3 μm or less within the range of the present invention has excellent hardenability and workability, and there are more carbides of 0.3 μm or less than the range of the present invention. The workability of 8 is inferior to C-7. C-9 is a comparative example in which the average particle size of the carbide is larger than the range of the present invention, but the hardness after quenching is softer than C-7 of the examples within the range of the present invention, and the hardenability is inferior.
Ｃ：０．２５％、Ｓｉ：０．１５％、Ｍｎ：０．５５％、Ｃｒ：０．２０％、Ｐ：０．０１６％、Ｓ：０．００５％、Ａｌ：０．０１２％、Ｔｉ：０．０１５％、Ｂ：０．００１５％の鋼を転炉で溶製し、連続鋳造でスラブを造った。このスラブを１２５０℃に加熱後、表５記載の条件で４．０ｍｍ厚みに熱間圧延し、酸洗後に表５記載の条件の焼鈍、０．３％の調質圧延を行い、鋼板を製造した。この鋼板の圧延方向に平行な断面を研磨し、ピクリン酸飽和溶液で腐食後、走査型電子顕微鏡を用い炭化物の平均粒径および、０．３μｍ以下の炭化物の割合を測定した。ＪＩＳ５号引張り試験片の平行部の中心に両端部に２ｍｍ深さのＶノッチを付け、引張り速度１００ｍｍ／ｍｉｎで引張り試験を行った。また、鋼板を８００℃×１秒に加熱後に油中に焼き入れ、その硬さを測定した。 C: 0.25%, Si: 0.15%, Mn: 0.55%, Cr: 0.20%, P: 0.016%, S: 0.005%, Al: 0.012%, Ti : 0.015%, B: 0.0015% steel was melted in a converter, and a slab was made by continuous casting. After heating this slab to 1250 ° C., it is hot-rolled to a thickness of 4.0 mm under the conditions described in Table 5, and after pickling, it is annealed under the conditions described in Table 5 and temper rolled at 0.3% to produce a steel sheet. did. The cross section parallel to the rolling direction of this steel sheet was polished, and after corrosion with a picric acid saturated solution, the average particle size of carbides and the proportion of carbides of 0.3 μm or less were measured using a scanning electron microscope. A V-notch with a depth of 2 mm was attached to both ends at the center of the parallel part of a JIS No. 5 tensile test piece, and a tensile test was conducted at a tensile speed of 100 mm / min. Further, the steel sheet was heated at 800 ° C. for 1 second and then quenched in oil, and the hardness was measured.
鋼Ｎｏ．Ｄ−１は連続鋳造時に電磁攪拌を付与してスラブを造り、熱延後の冷却をパーライト変態が６００〜６１５℃の温度で進行するように注水制御した。Ｄ−２、Ｄ−３は通常の条件でスラブを造り、熱延後の冷却も通常の条件で製造した。Ｄ−２は、熱延後の冷却中のパーライト変態温度が６００〜６６０℃、Ｄ−３は、熱延後の冷却中のパーライト変態温度が５８０〜６４０℃であった。Ｄ−４はＤ−１と同じ条件で熱延まで行い、酸洗後に冷間圧延率：４５％の冷延後に６７０℃×１８時間の焼鈍を行い、鋼板を製造したものである。 Steel No. In D-1, electromagnetic stirring was applied during continuous casting to form a slab, and water injection control was performed so that cooling after hot rolling proceeded at a temperature of 600 to 615 ° C. D-2 and D-3 were slabs produced under normal conditions, and cooling after hot rolling was also produced under normal conditions. D-2 had a pearlite transformation temperature of 600 to 660 ° C. during cooling after hot rolling, and D-3 had a pearlite transformation temperature of 580 to 640 ° C. during cooling after hot rolling. D-4 is performed up to hot rolling under the same conditions as D-1, and after cold pickling with a cold rolling ratio of 45%, annealing is performed at 670 ° C. × 18 hours to produce a steel sheet.
鋼Ｎｏ．Ｄ−１は炭化物平均粒径が０．８５μｍ、０．３μｍ以下の炭化物割合が７．３％の本発明範囲内の実施例である。この鋼板は、焼き入れ硬さがＨｖ：５９０と焼き入れ性が良好で、加工性の指標である伸びも５１％と良好であることがわかる。鋼Ｎｏ．Ｄ−２は炭化物平均粒径が１．４３μｍと本発明範囲から外れた比較例である。この鋼板は、焼き入れ硬さがＨｖ：４９０と焼き入れ性が劣る。鋼Ｎｏ．Ｄ−３は炭化物平均粒径が０．５６μｍ、０．３μｍ以下の炭化物割合が３２％と本発明範囲外の比較例である。この鋼板は加工性の指標である伸びが３８％でＤ−１に比較して大幅に劣る。鋼Ｎｏ．Ｄ−４は炭化物平均粒径が０．７５μｍ、０．３μｍ以下の炭化物の割合が８．３％と本発明範囲内の実施例である。この鋼板も焼き入れ硬さが高く、伸びも良好で、加工性と焼き入れ性が優れていることがわかる。 Steel No. D-1 is an example within the scope of the present invention in which the carbide average particle size is 0.85 μm and the proportion of carbides having a particle size of 0.3 μm or less is 7.3%. This steel sheet has a quenching hardness of Hv: 590, a good hardenability, and an elongation that is an index of workability of 51%. Steel No. D-2 is a comparative example in which the carbide average particle diameter is 1.43 μm and is out of the scope of the present invention. This steel sheet has a quenching hardness of Hv: 490 and a poor hardenability. Steel No. D-3 is a comparative example outside the scope of the present invention, in which the carbide average particle size is 0.56 μm and the proportion of carbides having a particle size of 0.3 μm or less is 32%. This steel sheet has an elongation of 38%, which is an index of workability, and is significantly inferior to D-1. Steel No. D-4 is an example within the scope of the present invention, with a carbide average particle size of 0.75 μm and a ratio of carbides of 0.3 μm or less of 8.3%. This steel sheet also has high quenching hardness, good elongation, and excellent workability and quenchability.
本発明によれば、炭化物の平均粒径だけでなく、０．３μｍ以下の微細炭化物が加工性に影響することに注目し、炭化物の平均粒径を１．０μｍ以下に制御し、加えて、０．３μｍ以下の炭化物割合を２０％以下に制御すれば、焼入れ性と加工性に優れた高炭素鋼板が提供することができる。このように本発明に係る高炭素鋼板は加工性と焼入れ性に優れることから、ギヤに代表される自動車の変速機部品等を安価でかつ、安定した品質で製造することが可能となり、工業的に極めて有益な発明である。 According to the present invention, not only the average particle size of carbides, but also that fine carbides of 0.3 μm or less affect workability, the average particle size of carbides is controlled to 1.0 μm or less, in addition, If the carbide ratio of 0.3 μm or less is controlled to 20% or less, a high carbon steel sheet excellent in hardenability and workability can be provided. As described above, since the high carbon steel sheet according to the present invention is excellent in workability and hardenability, it becomes possible to manufacture automobile transmission parts and the like represented by gears at low cost and with stable quality. It is a very useful invention.
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