JP4974285B2 - Medium and high carbon steel sheet with excellent workability and manufacturing method thereof - Google Patents

Medium and high carbon steel sheet with excellent workability and manufacturing method thereof Download PDF

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JP4974285B2
JP4974285B2 JP2007150121A JP2007150121A JP4974285B2 JP 4974285 B2 JP4974285 B2 JP 4974285B2 JP 2007150121 A JP2007150121 A JP 2007150121A JP 2007150121 A JP2007150121 A JP 2007150121A JP 4974285 B2 JP4974285 B2 JP 4974285B2
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聡 田頭
幸男 片桐
恆年 洲崎
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日新製鋼株式会社
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本発明は、優れた加工性を有し、部品形状に成形された後に熱処理が施され、所望の機械的特性を発現させて使用される中・高炭素鋼板及びその製造方法に関する。   The present invention relates to a medium and high carbon steel sheet that has excellent workability, is heat-treated after being formed into a part shape, and is used by expressing desired mechanical properties, and a method for producing the same.
ギア等、複雑形状をもち高い寸法精度、耐摩耗性が要求される機械構造部品は、中・高炭素鋼板を素材とし、切削加工により部品形状に適宜成形した後、焼入れ・焼戻し等の必要な熱処理を施すことにより製造されている。しかしながら、切削加工では製造コストが高くつくため、切削加工を打抜き加工等の塑性加工に変えることが検討されている。
ところで、塑性加工性は、多くの場合硬さが低いほど良好である。このため、加工性を重視する場合には素材鋼板をできるだけ軟質化させるような製造条件の設定が行われている。
Gears and other mechanical structural parts that have complex shapes and require high dimensional accuracy and wear resistance are made of medium- and high-carbon steel sheets, and are appropriately formed into parts by cutting, followed by quenching and tempering. Manufactured by heat treatment. However, since the manufacturing cost is high in the cutting process, it is considered to change the cutting process to a plastic process such as a punching process.
By the way, in many cases, the lower the hardness is, the better the plastic workability is. For this reason, when emphasizing workability, the production conditions are set so as to make the material steel plate as soft as possible.
炭素鋼板を軟質化させるには、結晶組織を大きくし、また生成される炭化物を大きくかつ丸く成長させることが有効である。このため、Ac1変態点直下で長時間加熱する技術や、Ac1変態点以上の温度に加熱して一部をオーステナイト化した後、適切な方法で冷却することで、炭化物の粒径を大きく成長させて軟質化を図ることが提案されている。
本発明者等も、炭素鋼板を軟質化して加工性を良くするために、成分組成と炭化物の存在形態について検討した技術を特許文献1,2で紹介した。
特開2000−265239号公報 特開2000−265240号公報
In order to soften the carbon steel sheet, it is effective to increase the crystal structure and grow the generated carbides large and round. For this reason, a technique of heating for a long time just below the Ac1 transformation point, or heating to a temperature equal to or higher than the Ac1 transformation point to partially austenite, and then cooling by an appropriate method increases the grain size of the carbide. It has been proposed to make it softer.
The present inventors also introduced, in Patent Documents 1 and 2, technologies for examining the component composition and the existence form of carbides in order to soften the carbon steel sheet and improve workability.
JP 2000-265239 A JP 2000-265240 A
上記特許文献で紹介された技術は、炭化物の粒径を大きくしているために、炭素鋼板の軟質化には非常に有効な方法である。しかしながら、軟質化された割に加工性が向上していない点に若干の不満も残っている。具体的には、十分に軟質化された場合でも、穴拡げ性や金型寿命がほとんど向上しないか、逆に低下する場合がある。
本発明者等の調査の結果では、前記穴拡げ性や金型寿命が向上しない理由は、前述の方法が炭化物の粒径を粗大化させることを目的とするものであって、炭化物の形状制御を行っていないために、硬さは低下させることができても加工性に不利な形状の炭化物を多量に生成させてしまったことにある、と考えられる。
The technique introduced in the above patent document is a very effective method for softening the carbon steel sheet because the particle size of the carbide is increased. However, some dissatisfaction still remains in that the workability is not improved in spite of being softened. Specifically, even when softened sufficiently, the hole expandability and the mold life may be hardly improved or may be decreased.
As a result of the investigation by the present inventors, the reason why the hole expansibility and the mold life are not improved is that the above-described method aims to increase the particle size of the carbide, and the shape control of the carbide. Therefore, it is considered that a large amount of carbide having a shape unfavorable for workability was generated even though the hardness could be reduced.
一般的には、炭化物の成長・粗大化だけを狙った場合、炭化物の形状が棒状や板状になったりする現象が頻発する。また、炭化物形状が鋭角な角を持つ多角形になっている場合もある。
このような板状や棒状の炭化物が存在すると、局部的な塑性変形能が低下するために、穴拡げ性のような局部的塑性変形能に依存する加工性が低下する。また、炭化物の形状が棒状、板状或いは多角形になっていると、特にファインブランキング加工を行う際、金型を摩耗させる要因にもなる。
Generally, when only the growth and coarsening of carbide is aimed at, a phenomenon that the shape of the carbide becomes a rod shape or a plate shape frequently occurs. Moreover, the carbide | carbonized_material shape may be a polygon with an acute angle | corner.
When such a plate-like or rod-like carbide is present, the local plastic deformability is lowered, so that the workability depending on the local plastic deformability such as hole expansibility is lowered. Moreover, when the shape of the carbide is rod-shaped, plate-shaped or polygonal, it becomes a factor that wears the mold particularly when performing fine blanking.
打抜き加工、特にファインブランキング加工を行う鋼板としては、金型寿命の観点からも、硬さを可能な限り低減した方が良いと言われている。しかしながら、この考え方は一般論であって、具体的にどの程度の硬さが有効であり、どのような組織形態に調整すれば金型の長寿命化が可能な鋼板が得られるかについての明確な指針はない。
金型が損傷・摩耗した場合、当初の打抜き品形状が得られず、ダレが大きくなったり、破断面や二次せん断面が形成されやすくなったりする。例えば歯車等、打抜き端面の性状が製品の性能に関わっている場合には、金型の損傷・摩耗が製品の特性を大きく低下させることになる。このため、金型寿命の改善は、成形加工品の性能向上に繋がる重要な要因であるとも言える。
It is said that it is better to reduce the hardness as much as possible from the viewpoint of die life as a steel plate for punching, particularly fine blanking. However, this idea is a general theory, and specifically how hard it is to be effective and what kind of structure should be adjusted to obtain a steel sheet that can extend the life of the mold. There are no good guidelines.
When the mold is damaged or worn, the initial punched product shape cannot be obtained, and the sag becomes large, or a fracture surface or a secondary shear surface is likely to be formed. For example, when the properties of the punched end face, such as gears, are related to the performance of the product, the damage and wear of the mold greatly deteriorates the product characteristics. For this reason, it can be said that the improvement of the mold life is an important factor that leads to the improvement of the performance of the molded product.
本発明は、このような問題を解消すべく案出されたものであり、中・高炭素鋼板において塑性加工性と熱処理後の高硬度及び高靭性を兼備させるために必要な諸条件を明らかにし、塑性加工時に加工金型を損耗させることのない加工性に優れた中・高炭素鋼板を提供することを目的とする。   The present invention has been devised to solve such problems, and clarifies various conditions necessary for combining plastic workability with high hardness and toughness after heat treatment in medium and high carbon steel sheets. An object of the present invention is to provide a medium / high carbon steel sheet excellent in workability without damaging a working die during plastic working.
本発明の加工性に優れた中・高炭素鋼板は、その目的を達成するため、C:0.30〜1.30質量%,Si:1.0質量%以下,Mn:0.2〜1.5質量%,P:0.02質量%以下,S:0.02質量%以下を含み、残部がFe及び不可避的不純物である成分組成を有し、フェライト結晶粒界上の炭化物数CGBとフェライト結晶粒内の炭化物数CIGの間に、CGB/CIG≦0.8の関係が成り立つように炭化物が分散した組織を有し、さらに断面硬さが160HV以下であることを特徴とする。
本発明鋼板は、さらに、Ni:1.8質量%以下,Cr:2.0質量%以下,V:0.5質量%以下,Mo:0.5質量%以下,Nb:0.3質量%以下,Ti:0.3質量%以下,B:0.01質量%以下,Ca:0.01質量%以下の1種又は2種以上を含む成分組成とすることもできる。
In order to achieve the object, the medium / high carbon steel sheet excellent in workability of the present invention has C: 0.30 to 1.30 mass%, Si: 1.0 mass% or less, Mn: 0.2 to 1 0.5% by mass, P: 0.02% by mass or less, S: 0.02% by mass or less, with the balance being Fe and inevitable impurities, the number of carbides on the ferrite grain boundary C GB And the number of carbides C IG in the ferrite crystal grains have a structure in which carbides are dispersed so that a relationship of C GB / C IG ≦ 0.8 is satisfied, and the cross-sectional hardness is 160 HV or less. And
The steel sheet according to the present invention further includes Ni: 1.8% by mass or less, Cr: 2.0% by mass or less, V: 0.5% by mass or less, Mo: 0.5% by mass or less, Nb: 0.3% by mass Hereinafter, it can also be set as the component composition containing 1 type, or 2 or more types of Ti: 0.3 mass% or less, B: 0.01 mass% or less, Ca: 0.01 mass% or less.
なお、本明細書で規定する「炭化物」は次の通り定義する。
鋼板断面の金属組織を観察するとき、炭化物総数が1000個以上になる領域を観察視野にとり、その炭化物をフェライト結晶粒界上に存在するものとフェライト結晶粒内に存在するものとに区分し、フェライト結晶粒界上に存在する炭化物の数をCGB,フェライト結晶粒内に存在する炭化物の数をCIGとしている。
The “carbide” defined in this specification is defined as follows.
When observing the metal structure of the steel sheet cross section, the region where the total number of carbides is 1000 or more is taken as an observation field, and the carbides are classified into those existing on ferrite crystal grain boundaries and those existing in ferrite crystal grains, The number of carbides present on the ferrite crystal grain boundary is C GB , and the number of carbides present in the ferrite crystal grain is C IG .
このような中・高炭素鋼板は、C:0.30〜1.30質量%,Si:1.0質量%以下,Mn:0.2〜1.5質量%,P:0.02質量%以下,S:0.02質量%以下を、さらに必要に応じて、Ni:1.8質量%以下,Cr:2.0質量%以下,V:0.5質量%以下,Mo:0.5質量%以下,Nb:0.3質量%以下,Ti:0.3質量%以下,B:0.01質量%以下,Ca:0.01質量%以下の1種又は2種以上を含み、残部がFe及び不可避的不純物である成分組成を有する熱延酸洗板に、熱延板焼鈍或いは冷延及び冷延板焼鈍を施した後、仕上げ冷延及び仕上げ焼鈍を施して冷延焼鈍板を製造する際、前記仕上げ冷延の前の最終工程が焼鈍工程であり、それまでのいずれかの焼鈍時に、Ac1〜(Ac1+50℃)に5〜20h保持→600℃までを−10℃/h以下の速度の冷却→600℃〜室温を任意の速度で冷却する焼鈍を一回以上含み、8〜24%の冷延率で最終の仕上げ冷延し、その後、640℃〜Ac1点の温度域に2h以上保持する仕上げ焼鈍を施すことにより製造される。   Such medium and high carbon steel sheets are: C: 0.30 to 1.30 mass%, Si: 1.0 mass% or less, Mn: 0.2 to 1.5 mass%, P: 0.02 mass% Hereinafter, S: 0.02% by mass or less, if necessary, Ni: 1.8% by mass or less, Cr: 2.0% by mass or less, V: 0.5% by mass or less, Mo: 0.5 1% or more of Nb: 0.3% by mass or less, Ti: 0.3% by mass or less, B: 0.01% by mass or less, Ca: 0.01% by mass or less, and the balance Is subjected to hot-rolled sheet annealing or cold-rolled and cold-rolled sheet annealing, and then subjected to finish cold-rolling and finish-annealing to obtain a cold-rolled annealed sheet. When manufacturing, the final step before the finish cold rolling is an annealing step, and during any annealing up to that time, Ac1 to (Ac1 + 50 ° C.) Hold for 20 hours → Cool to 600 ° C. at a rate of −10 ° C./h or less → 600 ° C. to annealing at room temperature at an arbitrary rate once or more, final finish cooling at a cold rolling rate of 8 to 24% Then, it is manufactured by applying a finish annealing for 2 hours or more in the temperature range of 640 ° C. to Ac1 point.
本発明により、中・高炭素鋼板の成分組成と組織、特に炭化物粒子のフェライト結晶粒界上と結晶粒内の分散状態を、結晶粒内炭化物数の方が多くなるように調整することにより、結果的に分散された炭化物粒子を小さく、かつ丸くして金型等を損耗させる硬質の剥落粒子を無害化することができる。
このため、本発明による中・高炭素鋼板を素材として所望形状への打抜き加工等の塑性加工を施しても、金型等の損耗が抑えられるので、複雑形状の自動車部品等、高硬度及び高靭性を必要とする各種機械部品を、低コストで生産性良く製造することができる。
According to the present invention, by adjusting the component composition and structure of the medium and high carbon steel sheet, in particular, the ferrite grain boundary of the carbide particles and the dispersion state in the crystal grains so that the number of carbides in the crystal grains is larger, As a result, the dispersed carbide particles can be made small and round, and hard exfoliated particles that wear the mold and the like can be made harmless.
For this reason, even if plastic working such as punching into a desired shape is performed using the medium and high carbon steel plate according to the present invention, wear of molds and the like can be suppressed. Various machine parts that require toughness can be manufactured with low cost and high productivity.
本発明者等は、炭素鋼板に打抜き加工等の塑性加工を施す際に金型等が損耗する原因について鋭意検討した。
通常、打抜き加工等では、被加工鋼板の硬さが低いほど加工荷重は小さいので、金型にかかる負荷は小さく、金型の損耗頻度は軽減される。そして被加工鋼板の硬さが硬くなるほど、金型の損耗頻度は高くなる。また、金型の摩耗は、加工品の断面や金型破損部から剥落して形成される硬質な摩耗粒子によるアブレッシブ摩耗である。被加工鋼板の硬さが低いと、金型の破損が低減し、また鋼材からの硬質粒子の剥落も減少するので、金型を摩耗させる硬質粒子が減少することになる。すなわち、被加工鋼板の硬さが低いほど金型は長寿命化する。
The inventors of the present invention have intensively studied the cause of the wear of molds and the like when plastic working such as punching is performed on a carbon steel sheet.
Usually, in punching or the like, the lower the hardness of the steel plate to be processed, the smaller the processing load, so the load applied to the mold is small and the wear frequency of the mold is reduced. And the wear frequency of a metal mold | die becomes high, so that the hardness of a to-be-processed steel plate becomes hard. The mold wear is abrasive wear caused by hard wear particles formed by peeling off from a cross section of a processed product or a damaged portion of the mold. If the hardness of the steel plate to be processed is low, breakage of the mold is reduced, and peeling of the hard particles from the steel material is also reduced, so that the hard particles that wear the mold are reduced. In other words, the die has a longer life as the hardness of the steel plate to be processed is lower.
しかしながら、上記知見自体は一般論である。
本発明者等は、金型損耗の原因について鋭意検討する段階で、金型寿命向上の効果が実用上有効に発揮されるのは、断面硬さが160HVまで軟化した場合であり、かつ炭化物の存在形態が大きく影響することを見出した。
以下に、その詳細を説明する。
However, the above findings are general theory.
The inventors of the present invention, at the stage of earnestly examining the cause of the wear of the mold, the effect of improving the mold life is effectively exhibited practically when the cross-sectional hardness is softened to 160 HV, and the carbide We found that the existence form has a great influence.
The details will be described below.
本発明が対象とするような中・高炭素鋼にあっては、炭化物はフェライト結晶の粒界上や粒内に分散析出する。そして、フェライト結晶の粒界上あるいは粒内に析出した炭化物粒子は、図1にその形態を模式的に示すように、析出した部位に応じて形状が異なる。
図1の(a),(b),(c)に示すように、フェライト結晶粒界上に析出した炭化物粒子は、結晶粒内に析出した炭化物粒子と比べて、粗大なものが多く、しかも棒状,板状等、アスペクト比が大きく、かつ角張ったものが多い。一方、図1の(d)に示すように、フェライト結晶粒内に析出した炭化物粒子は、結晶粒界上に析出した炭化物粒子と比べて、細かく、しかも突起物のない丸い炭化物粒子が多い。
In medium and high carbon steels as the subject of the present invention, carbides are dispersed and precipitated on the grain boundaries and in the grains of ferrite crystals. And the carbide | carbonized_material particle | grains which precipitated on the grain boundary of a ferrite crystal or in the grain | grain differ in a shape according to the site | part which precipitated, as the form is typically shown in FIG.
As shown in FIGS. 1A, 1B, and 1C, the carbide particles precipitated on the ferrite crystal grain boundaries are much coarser than the carbide particles precipitated in the crystal grains, and Many of them are rod-shaped, plate-shaped, etc. with a large aspect ratio and angularity. On the other hand, as shown in FIG. 1D, the carbide particles precipitated in the ferrite crystal grains are finer and more round carbide particles having no protrusions than the carbide particles precipitated on the crystal grain boundaries.
結晶粒界上に析出する炭化物が粗大化しやすい理由は、結晶粒内よりも拡散しやすい粒界を通じたC(炭素)の長距離拡散により、炭化物は成長しやすくなると考えられる。また、結晶粒界と炭化物の交点で炭化物が鋭い突起状の形状を取りやすい理由は、界面自由エネルギーの釣り合いで粒界の形状が決まるためであると考えられる。フェライト結晶粒界から離れた炭化物はこのような現象が起こらないために、炭化物の表面自由エネルギーの低くするべく丸い形状を取りやすく、粗大粒に成長し難くなる。   The reason why the carbides precipitated on the crystal grain boundaries are likely to be coarse is considered to be that the carbides are likely to grow due to long-distance diffusion of C (carbon) through the grain boundaries that are more diffusible than in the crystal grains. Also, the reason why the carbide tends to take a sharp projecting shape at the intersection of the crystal grain boundary and the carbide is considered to be because the shape of the grain boundary is determined by the balance of the interface free energy. Since this phenomenon does not occur in the carbide separated from the ferrite grain boundary, it is easy to take a round shape to reduce the surface free energy of the carbide, and it is difficult to grow into a coarse grain.
ところで、前記したように、塑性加工用の金型を摩耗させる硬質粒子は、主として鋼材から剥落された粒子、特に炭化物粒子である。塑性加工を施す鋼板の硬さが160HV程度であっても、炭化物粒子自体の硬さは1000HV以上であるため、炭化物粒子は金型よりも硬くなっている。そして、炭化物粒子の形態は、粒径が大きいほど,鋭角な突出部を持つほど、金型に大きな摩耗損傷を与えるものと推測される。
したがって、金型の摩耗を軽減させるためには、塑性加工を施す鋼板の金属組織を、炭化物粒子を極力小さく、かつ丸く調整することが有効と考えられる。ただし、炭化物粒径を微細化すると鋼材の硬さが上昇して加工し難くなるので、過度に微細化することはできない。
By the way, as described above, the hard particles that wear the mold for plastic working are mainly particles peeled off from the steel material, particularly carbide particles. Even if the hardness of the steel plate subjected to plastic working is about 160 HV, the carbide particles are harder than the mold because the hardness of the carbide particles themselves is 1000 HV or more. And it is estimated that the carbide | carbonized_particle form will carry out a big abrasion damage to a metal mold | die, so that it has a sharp protrusion part, so that a particle size is large.
Therefore, in order to reduce the wear of the mold, it is considered effective to adjust the metal structure of the steel sheet to be subjected to plastic working as small and round as possible. However, if the carbide particle size is made finer, the hardness of the steel material increases and it becomes difficult to process, so it cannot be made too fine.
前記課題の項に記載したように、炭化物の形状,大きさだけではなく、炭化物の分散状態も金型の摩耗に大きな影響を及ぼしている。そして、上述したように、フェライト結晶粒界上に析出した炭化物粒子は、結晶粒内に析出した炭化物粒子と比べて粗大なものが多く、しかも角張ったものが多い。
したがって、炭化物はフェライト結晶の粒界上に析出させるよりも、結晶粒内に析出させた方が、金型摩耗の軽減という観点では有効となる。フェライト結晶粒界上に多く存在する粗大で角張った炭化物を少なくすることにより、金型損耗の原因となる剥落粒子を極力無害化することが金型寿命の向上に有効になると思われる。
As described in the section of the problem, not only the shape and size of the carbide but also the dispersion state of the carbide has a great influence on the wear of the mold. As described above, the carbide particles precipitated on the ferrite crystal grain boundaries are often coarser and more angular than the carbide particles precipitated in the crystal grains.
Therefore, it is more effective in terms of reducing mold wear to precipitate carbide in the crystal grains than to precipitate it on the grain boundaries of the ferrite crystal. By reducing the amount of coarse and angular carbides present on the ferrite grain boundaries, it would be effective to improve the mold life by making the exfoliated particles that cause mold wear as harmless as possible.
ところで、炭素鋼板を軟質化するためには、「炭化物を粗大化させて粒子間隔を大きくすること」と「フェライト結晶粒径を粗大化させること」の二つの手段が有効である。
特許文献1,2等、従来実施されている焼鈍方法は、主として炭化物の粗大化を狙った方法であり、フェライト結晶粒径の粗大化は意図していない。炭化物を粗大化させる方法としては、Ac1変態点以上の温度域に加熱して一部をオーステナイト化し、これを適切な冷却方法で冷却することで炭化物を成長させようとするものである。
By the way, in order to soften the carbon steel sheet, two means of “roughening the carbide to increase the particle spacing” and “to increase the ferrite crystal grain size” are effective.
Conventional annealing methods such as Patent Documents 1 and 2 are mainly aimed at coarsening carbides, and are not intended to increase the ferrite crystal grain size. As a method of coarsening the carbide, the carbide is grown by heating to a temperature range of the Ac1 transformation point or higher to partially austenite and cooling it with an appropriate cooling method.
炭化物の成長は、拡散速度の速い結晶粒界(オーステナイト粒界、フェライト粒界、オーステナイト/フェライト界面)を通じた炭素原子の拡散によって進行するので、大きく粗大化した炭化物は結晶粒界に多く存在することになる。
結晶粒界上に存在する炭化物の形状が、金型寿命に対して悪影響を及ぼすことは前記した通りである。したがって、生成する炭化物を結晶粒界から引き離すことが必要となる。
そして、生成する炭化物を結晶粒界から引き離すためには、フェライト結晶粒径を積極的に粗大化させておくことが有効であると考えられる。
Carbide growth proceeds by the diffusion of carbon atoms through grain boundaries (austenite grain boundaries, ferrite grain boundaries, austenite / ferrite interfaces) with a high diffusion rate, so that large and coarse carbides exist in the grain boundaries. It will be.
As described above, the shape of the carbide existing on the grain boundary has an adverse effect on the mold life. Therefore, it is necessary to separate the generated carbides from the grain boundaries.
In order to separate the generated carbide from the crystal grain boundary, it is considered effective to positively increase the ferrite crystal grain size.
フェライト結晶粒径が粗大になれば、結晶粒界から引き離される炭化物の個数が多くなり、相対的に結晶粒内にある炭化物の比率が増加する。結晶粒内にある炭化物は前述の通り角のとれたスムーズな形状を有しており、金型寿命に悪影響を与えにくい。また、結晶粒界上の炭化物は板状や棒状の形状を呈しやすいが、粒内の炭化物は球状になりやすく、局部延性を劣化させることがない。さらに、フェライト粒径を粗大化させることで鋼板は軟質化するので、塑性加工性の点では非常に有利になる。
このように、本発明では、フェライト結晶粒径を粗大化させることで、炭化物の形状制御を行い、塑性加工性を高めることができるようになったものもである。
If the ferrite crystal grain size becomes coarse, the number of carbides separated from the grain boundaries increases, and the ratio of carbides in the crystal grains relatively increases. The carbides in the crystal grains have a smooth shape with a corner as described above, and do not adversely affect the mold life. In addition, carbides on the grain boundaries are likely to have a plate-like or rod-like shape, but the carbides in the grains are likely to be spherical, and local ductility is not deteriorated. Furthermore, since the steel sheet is softened by increasing the ferrite grain size, this is very advantageous in terms of plastic workability.
Thus, in the present invention, the shape of the carbide can be controlled by increasing the grain size of the ferrite crystal so as to improve the plastic workability.
フェライト結晶粒径の粗大化には、基本的に、冷間加工+再結晶焼鈍のプロセスを利用する。炭化物粒子が存在する炭素鋼板では、炭化物粒子が結晶粒界をピン止めするので、再結晶で粒径を粗大化させるにはある程度の冷間加工率が必要になる。一方、冷間加工率が大きすぎると再結晶核が多くなりすぎて結晶粒径が逆に微細化される場合もある。
また、冷間加工+再結晶焼鈍のプロセスを実施する前の素材組織についても制約が必要である。すなわち、冷間加工+再結晶焼鈍のプロセスは、フェライト結晶粒の粗大化を意図したものであり、炭化物粒径を有効に粗大化することができないので、予め炭化物粒径を粗大化(粒子間隔を大きく)させた素材を用いなければ、塑性加工性の良好な鋼板を製造することはできない。
For the coarsening of the ferrite crystal grain size, a process of cold working + recrystallization annealing is basically used. In a carbon steel sheet in which carbide particles are present, the carbide particles pin the crystal grain boundaries, and thus a certain degree of cold work is required to increase the particle size by recrystallization. On the other hand, if the cold working rate is too large, the number of recrystallized nuclei increases and the crystal grain size may be refined.
In addition, there is a restriction on the material structure before the cold working + recrystallization annealing process is performed. That is, the process of cold working + recrystallization annealing is intended to coarsen ferrite crystal grains, and the carbide grain size cannot be coarsened effectively. A steel plate with good plastic workability cannot be manufactured without using a material having a large ().
そこで、本発明は、仕上げ冷延及びその後の再結晶仕上げ焼鈍を、フェライト結晶粒径を粗大化させるべく、条件を細かく設定したものとするとともに、その仕上げ冷延及び仕上げ焼鈍を施す前の中間素材として、特定の条件で焼鈍して予め炭化物粒径を粗大化(粒子間隔を大きく)させたものとすることにより、前記仕上げ冷延及び仕上げ焼鈍と相俟って、結晶粒界上よりも結晶粒内に存在する炭化物を多く、しかもその炭化物を大きくすることが可能になり、金型等を損傷させることいなく、容易に塑性加工できる鋼板を提供できたものである。
以下に、本発明の特徴点を詳しく説明する。
なお、本発明の特徴点である軟質化のための前記「冷間加工+再結晶焼鈍」のプロセスを、「LPRA処理(Light-Pass rolling and Recrystallization Annealing)」と称する。
Therefore, in the present invention, the finish cold rolling and the subsequent recrystallization finish annealing are finely set in order to increase the ferrite crystal grain size, and the intermediate before the finish cold rolling and finish annealing are performed. As a raw material, the carbide grain size is preliminarily coarsened (larger particle spacing) by annealing under specific conditions, and in combination with the finish cold rolling and finish annealing, than on the grain boundaries. This makes it possible to provide a steel plate that has a large amount of carbides present in crystal grains and that can be enlarged, and that can be easily plastically processed without damaging a mold or the like.
The characteristic points of the present invention are described in detail below.
The process of “cold working + recrystallization annealing” for softening, which is a feature of the present invention, is referred to as “LPRA treatment (Light-Pass rolling and Recrystallization Annealing)”.
まず、本発明鋼板の鋼組成、炭化物の析出状態を含めた組織形態等について説明する。
C:0.30〜1.30質量%
本発明は、機械構造部品や刃物・工具等に使用される炭素鋼板を素材として、C量は0.30質量%以上1.30質量%までの中・高炭素鋼を対象としている。C量が0.30質量に満たない低炭素鋼では塑性加工性が問題になることはないので、本発明の対象外とする。また、C量が1.30質量%を超えると、組織制御によって塑性加工性を高めることは非常に難しくなるので、1.30質量%以下のCを含有する中・高炭素鋼を対象とした。
First, the steel composition of this invention steel plate, the structure | tissue form including the precipitation state of carbide, etc. are demonstrated.
C: 0.30 to 1.30% by mass
The present invention is intended for medium- and high-carbon steels having a carbon content of 0.30% by mass to 1.30% by mass using carbon steel plates used for machine structural parts, blades, tools, and the like. Since low carbon steel having a C content of less than 0.30 mass has no problem with plastic workability, it is excluded from the scope of the present invention. Further, if the C content exceeds 1.30% by mass, it is very difficult to improve plastic workability by microstructure control. Therefore, it is intended for medium and high carbon steels containing 1.30% by mass or less of C. .
Si:1.0質量%以下
Siは脱酸作用を有する。ただし、本発明の場合、Siを積極的に添加しなくても脱酸不良を起こすようなことはない。反面、添加量が多くなりすぎると加工性を低下させることになる。その上限は1.0質量%である。
Mn:0.2〜1.5質量%
Mnは焼入れ性を確保するために必要な元素である。添加量が0.2質量%に満たないとその効果は小さい。逆に1.5質量%を超えて添加すると、Ms点が低くなって残留オーステナイトが増加して所望の硬さが得られず、却って靭性が低下するという弊害が生じる。
Si: 1.0% by mass or less Si has a deoxidizing action. However, in the case of the present invention, no deoxidation failure occurs even if Si is not actively added. On the other hand, if the added amount is too large, the workability is lowered. The upper limit is 1.0 mass%.
Mn: 0.2 to 1.5% by mass
Mn is an element necessary for ensuring hardenability. If the added amount is less than 0.2% by mass, the effect is small. On the other hand, if added over 1.5% by mass, the Ms point is lowered, the retained austenite is increased, the desired hardness cannot be obtained, and the adverse effect that the toughness is lowered is caused.
P:0.02質量%以下
Pはオーステナイト粒界に偏析し、靭性を低下させる元素である。したがって、少ない方が好ましい。0.02質量%を超えて含有させると延性−脆性遷移温度の上昇を招くので、P含有量の上限は0.02質量%とする。
S:0.02質量%以下
SはMnS系介在物を形成し靭性を低下させる。したがって、少ない方が好ましい。材質上弊害のない水準は0.02質量%以下である。
P: 0.02% by mass or less P is an element that segregates at austenite grain boundaries and lowers toughness. Therefore, the smaller one is preferable. If the content exceeds 0.02% by mass, the ductile-brittle transition temperature rises, so the upper limit of the P content is 0.02% by mass.
S: 0.02 mass% or less S forms MnS inclusions and lowers toughness. Therefore, the smaller one is preferable. The level that is not harmful to the material is 0.02% by mass or less.
本発明鋼板は、必要に応じてさらにNi,Cr,V,Mo,Nb,Ti,B,Caを含むこともできる。
Ni:1.8質量%以下
Niは靭性を向上させる作用と、Mnと同様に焼入れ性を向上させる作用を有する。しかし、1.8質量%を超えて過剰に添加しても、コストに見合った靭性向上効果は得られない。したがって、添加する場合は1.8質量%を上限とする。
The steel sheet of the present invention can further contain Ni, Cr, V, Mo, Nb, Ti, B, and Ca as necessary.
Ni: 1.8% by mass or less Ni has an effect of improving toughness and an effect of improving hardenability like Mn. However, even if the amount exceeds 1.8% by mass, an effect of improving toughness commensurate with the cost cannot be obtained. Therefore, when added, the upper limit is 1.8% by mass.
Cr:2.0質量%以下
Crは焼入れ性を有する元素である。強度を向上させるばかりでなく、耐摩耗性をも向上させる。しかし、2.0質量%を超えて過剰に添加すると靭性が低下する。
V:0.5質量%以下
Vは焼入れ時にオーステナイト結晶粒径を微細化する作用がある。本発明の合金成分系では、旧オーステナイト結晶粒径微細化作用を発揮させるには、0.5質量%までの添加で十分である。添加量が過剰に多くなると製造性に困難を来たすので、添加する場合は0.5質量%を上限とする。
Cr: 2.0% by mass or less Cr is an element having hardenability. Not only improves strength, but also improves wear resistance. However, when it exceeds 2.0 mass% and it adds excessively, toughness will fall.
V: 0.5% by mass or less V has an effect of refining the austenite grain size during quenching. In the alloy component system of the present invention, addition of up to 0.5% by mass is sufficient to exert the effect of refining the prior austenite crystal grain size. When the addition amount is excessively large, the productivity becomes difficult. Therefore, when added, the upper limit is 0.5 mass%.
Mo:0.5質量%以下
Moは焼入れ性を向上させる効果を有する。またNiとの複合添加で鋼の強靭性を高める作用も発揮する。さらに、特殊炭化物を形成することによって耐摩耗性を向上させる作用も有している。本発明の合金成分系では、上記作用を発揮させるのは0.5質量%のまでの添加で十分である。これ以上添加しても、それに見合った効果が得られないばかりでなく、製造性を悪化させるようになる。したがって添加する場合は0.5質量%を上限とする。
Mo: 0.5% by mass or less Mo has an effect of improving hardenability. Moreover, the effect | action which raises the toughness of steel by composite addition with Ni is also exhibited. Furthermore, it has the effect | action which improves abrasion resistance by forming a special carbide. In the alloy component system of the present invention, it is sufficient to add up to 0.5% by mass to exert the above effect. Even if it adds more than this, not only the effect commensurate with it will be acquired, but productivity will also be deteriorated. Therefore, when added, the upper limit is 0.5 mass%.
Nb:0.3質量%以下
Nbは、焼入れ時のオーステナイト粒径を微細化させる効果を有する。本発明の合金成分系では、旧オーステナイト結晶粒径微細化作用を発揮させるには、0.3質量%までの添加で十分である。0.3質量%を超えて添加しても、効果は飽和するので、添加する場合も0.3質量%を上限とする。
Nb: 0.3% by mass or less Nb has the effect of refining the austenite grain size during quenching. In the alloy component system of the present invention, addition of up to 0.3% by mass is sufficient to exert the effect of refining the prior austenite crystal grain size. Even if added over 0.3% by mass, the effect is saturated, so even when added, the upper limit is 0.3% by mass.
Ti:0.3質量%以下
Tiも、焼入れ時のオーステナイト粒径を微細化させる効果を有する。本発明の合金成分系では、旧オーステナイト結晶粒径微細化作用を発揮させるには、0.3質量%までの添加で十分である。0.3質量%を超えて添加しても、効果は飽和するので、添加する場合も0.3質量%を上限とする。
Ti: 0.3% by mass or less Ti also has an effect of reducing the austenite grain size during quenching. In the alloy component system of the present invention, addition of up to 0.3% by mass is sufficient to exert the effect of refining the prior austenite crystal grain size. Even if added over 0.3% by mass, the effect is saturated, so even when added, the upper limit is 0.3% by mass.
B:0.01質量%以下
Bは、旧オーステナイト結晶粒界の強度を高め、靭性を向上させる作用を発揮する。本発明の合金成分系では、0.01質量%までの添加でこの効果が得られる。しかし、0.01%を超えて添加してもその効果は飽和するので、添加する場合は0.01%を上限とする。
B: 0.01% by mass or less B exhibits the effect of increasing the strength of the prior austenite grain boundaries and improving the toughness. In the alloy component system of the present invention, this effect can be obtained by adding up to 0.01% by mass. However, even if added over 0.01%, the effect is saturated, so when added, the upper limit is made 0.01%.
Ca:0.01質量%以下
CaはMnS系介在物の形態制御、すなわち、MnS系介在物の形態を細長い板状から球状に変える性質を有することから、塑性加工性を向上できる。細長い形状の介在物があると、塑性加工、特に打抜き加工時にミクロボイド生成の起点となって打抜き面に破断面を形成しやすいのに対し、介在物を球状化させるとミクロボイドの生成が抑えられ打抜き加工性を向上できる。添加量が0.01%を超えても特性向上に繋がらないので、添加する場合の上限は0.01%とする。
Ca: 0.01% by mass or less Ca has the property of controlling the form of MnS-based inclusions, that is, changing the form of MnS-based inclusions from an elongated plate shape to a spherical shape, thereby improving plastic workability. When there are inclusions with an elongated shape, it becomes the starting point for microvoid generation during plastic processing, especially punching, and it is easy to form a fracture surface on the punched surface. Workability can be improved. Even if the added amount exceeds 0.01%, the characteristics are not improved. Therefore, the upper limit when added is 0.01%.
断面硬さ:160HV以下
塑性加工用金型の寿命を決める最も重要な要因は、塑性加工される鋼板の硬さである。断面硬さが160HV以下であれば、金型寿命の低下に大きな影響を及ぼすことがない。160HVを超えて硬くなると、金型が損傷しやすくなる。特にチッピングが起こりやすくなる。
Cross-sectional hardness: 160 HV or less The most important factor that determines the life of a metal mold for plastic working is the hardness of the steel sheet to be plastic processed. If the cross-sectional hardness is 160 HV or less, there is no significant effect on the reduction of the mold life. If the hardness exceeds 160 HV, the mold tends to be damaged. In particular, chipping is likely to occur.
炭化物の存在形態
加工治具の長寿命化の観点からは、フェライト結晶粒界上の大きく、尖った炭化物を少なく、フェライト結晶粒内の細かく、丸い炭化物を多くすることが好ましい。
本発明等は、フェライト結晶粒界上の炭化物数をCGB、フェライト結晶粒内の炭化物数をCIGとしたとき、CGBとCIGの間に、CGB/CIG≦0.8の関係が成り立つように炭化物が分散した組織を有していると、金型の長寿命化が図れることを、予備実験を繰り返すことにより確認した。特にCGB/CIG≦0.4を満たすとき、金型の損傷が極めて少なくなり、金型の寿命はより長期化することが確認できている。一方、CGB/CIGが0.8を超えて大きくなると、金型の摩耗損傷が大きくなり、結果的にバリ高さが大きくなる。
From the viewpoint of extending the life of the processing tool for the presence of carbide, it is preferable to increase the number of fine and round carbides in the ferrite crystal grains while reducing the large and sharp carbides on the ferrite crystal grain boundaries.
The present invention and the like, the number of carbides on ferrite grain boundaries C GB, when the number of carbide in ferrite grain was C IG, between C GB and C IG, the C GB / C IG ≦ 0.8 It was confirmed by repeating the preliminary experiment that the mold could have a long life if the carbide was dispersed so that the relationship was established. In particular, when C GB / C IG ≦ 0.4 is satisfied, it has been confirmed that the damage to the mold is extremely reduced and the life of the mold is further extended. On the other hand, when C GB / C IG exceeds 0.8, the wear damage of the mold increases, and as a result, the burr height increases.
次に、本発明鋼板を製造する方法について簡単に説明する。
前記した通り、本発明は、「LPRA処理」を施してフェライト結晶粒径を粗大化し、それに伴って結晶粒内で生成する炭化物を結晶粒界に生成する炭化物に比べて多くすることを特徴とするが、「LPRA処理」を施す前の素材組織を、炭化物粒径を予め粗大化したものでなければ、目的とする塑性加工性の良好な鋼板を製造することはできない。
この意味から、熱延板を酸洗した後に、熱延板焼鈍或いは冷延及び冷延板焼鈍を施した後、前記「LPRA処理」を施す際に、熱延板焼鈍又は冷延板焼鈍として、次の条件の焼鈍を施す必要がある。
Next, a method for producing the steel sheet of the present invention will be briefly described.
As described above, the present invention is characterized in that the ferrite crystal grain size is increased by performing “LPRA treatment”, and accordingly, the carbide generated in the crystal grain is increased compared to the carbide generated in the crystal grain boundary. However, unless the material structure before the “LPRA treatment” is obtained by preliminarily coarsening the grain size of carbides, a target steel sheet with good plastic workability cannot be manufactured.
In this sense, after pickling the hot-rolled sheet, after performing hot-rolled sheet annealing or cold-rolling and cold-rolled sheet annealing, when performing the "LPRA treatment", as hot-rolled sheet annealing or cold-rolled sheet annealing, It is necessary to perform annealing under the following conditions.
Ac1〜Ac1+50℃に5〜20h保持→600℃までを−10℃/h以下の速度の冷却→600℃〜室温を任意の速度で冷却する焼鈍
「LPRA処理」の効果を十分に発揮させるためには、当該処理の前工程において、炭化物粒径を十分に粗大化させるために、上記条件の焼鈍を少なくとも一回施しておくことが必要になる。
この焼鈍を施していないと、炭化物の形状が球状にならず、粒径が粗大にならないために「LPRA処理」で十分にフェライト粒径を粗大化させることができない。その結果、軟質化の効果が発揮されない。また、この焼鈍工程で、保持温度がAc1点温度に満たないと炭化物粒径が十分に粗大化されず、逆にAc1+50℃を超えるほどに高いと炭化物形状が板状や棒状になるために「LPRA処理」の効果が得られない。さらに、600℃までの冷却速度が−10℃/hよりも速いと、炭化物形状が板状や棒状になりやすくなるために「LPRA処理」の効果が得られない。600℃〜室温までの冷却速度は任意で構わない。
Ac1 to Ac1 + 50 ° C held for 5 to 20 hours → cooling to 600 ° C at a rate of -10 ° C / h or lower → 600 ° C to fully exhibit the effect of "LPRA treatment" that cools room temperature at an arbitrary rate In the pre-process of the said process, in order to fully coarsen a carbide | carbonized_material particle size, it is necessary to give annealing of the said conditions at least once.
If this annealing is not performed, the shape of the carbide does not become spherical and the particle diameter does not become coarse, so that the ferrite particle diameter cannot be sufficiently increased by “LPRA treatment”. As a result, the softening effect is not exhibited. Further, in this annealing step, if the holding temperature does not reach the Ac1 point temperature, the carbide particle size is not sufficiently coarsened, and conversely if it is high enough to exceed Ac1 + 50 ° C., the carbide shape becomes a plate shape or a rod shape. The effect of “LPRA processing” cannot be obtained. Furthermore, if the cooling rate to 600 ° C. is faster than −10 ° C./h, the carbide shape tends to be plate-like or rod-like, so the “LPRA treatment” effect cannot be obtained. The cooling rate from 600 ° C. to room temperature may be arbitrary.
「LPRA処理」の効果を十分に発揮させるためには、フェライト結晶粒の再結晶による粗大化を促進するために適切な仕上げ冷延を施す必要がある。そのためには、「LPRA処理」を施す素材鋼板は加工歪みのない状態であることが必要である。したがって、「LPRA処理」を施す前の最終工程は焼鈍でなければならない。   In order to sufficiently exhibit the effect of the “LPRA treatment”, it is necessary to perform appropriate finish cold rolling in order to promote the coarsening due to recrystallization of ferrite crystal grains. For that purpose, it is necessary that the material steel plate subjected to the “LPRA treatment” has no processing distortion. Therefore, the final process before the “LPRA treatment” must be annealed.
「LPRA処理」における仕上げ冷延;冷延率8〜24%
適切な組織形態を有する焼鈍鋼板に冷延を施すことで、鋼板組織中に転位を導入する(加工硬化させる)ことが、引続いて施される仕上げ焼鈍で、フェライト結晶粒を再結晶・粗大化させるために必須となる。このための冷延率は少なくとも8%は必要である。冷延率が8%に満たないほどに小さいと、フェライトの再結晶が不完全(サブグレイン組織)になり、硬さを十分に低下させることができない。逆に冷延率が24%を超えるほどに大きいと、導入される転位が多くなりすぎ、再結晶の核生成サイトの密度が増大して、再結晶粒が逆に微細化されてしまう。最も有効にフェライト粒径を粗大化させる冷延率は、10〜20%の範囲である。
Finish cold rolling in “LPRA treatment”; cold rolling rate 8-24%
By applying cold rolling to an annealed steel sheet having an appropriate structure form, introducing dislocations into the steel sheet structure (work hardening) is a subsequent annealing process that recrystallizes and coarsens the ferrite crystal grains. It is essential to make it. For this purpose, the cold rolling rate should be at least 8%. If the cold rolling rate is so small that it is less than 8%, the recrystallization of ferrite becomes incomplete (subgrain structure), and the hardness cannot be lowered sufficiently. On the contrary, if the cold rolling rate is larger than 24%, too many dislocations are introduced, the density of recrystallization nucleation sites increases, and the recrystallized grains are conversely refined. The cold rolling rate that most effectively coarsens the ferrite grain size is in the range of 10 to 20%.
「LPRA処理」における仕上げ焼鈍;640℃〜Ac1点の温度域に2h以上保持
冷間加工されたフェライト結晶粒を再結晶させ、粒径を粗大化するための処理である。保持温度が640℃に満たないと再結晶されにくいので、最低でも640℃以上の温度で保持する必要がある。保持温度がAc1点を超えると、組織の一部がオーステナイト化されるようになる。オーステナイト結晶が形成され、フェライト+オーステナイト+炭化物の混合組織になると、フェライト結晶がオーステナイト相にピン止めされて粗大化できなくなる。したがって、仕上げ焼鈍はAc1点を超えてはならない。また、再結晶を十分に行わせるためには、2h以上の保持が必要である。
Finish annealing in “LPRA treatment”: a treatment for recrystallization of ferrite crystal grains that have been cold-worked for 2 hours or more in the temperature range of 640 ° C. to Ac1 to increase the grain size. If the holding temperature is less than 640 ° C., it is difficult to recrystallize. Therefore, it is necessary to hold at a temperature of at least 640 ° C. When the holding temperature exceeds the Ac1 point, a part of the structure is austenitized. When an austenite crystal is formed and a mixed structure of ferrite + austenite + carbide is formed, the ferrite crystal is pinned to the austenite phase and cannot be coarsened. Therefore, the finish annealing must not exceed the Ac1 point. Further, in order to sufficiently perform recrystallization, it is necessary to hold for 2 hours or more.
実施例1:
表1に示す化学成分を有する鋼を溶製し、連続鋳造でスラブを得た後、スラブ加熱温度1250℃,仕上げ温度850℃及び巻取り温度600℃の熱延を施し、塩酸浴による酸洗を施して、板厚4.0mmの熱延酸洗板を得た。
各熱延酸洗板を、(イ)730℃×20h→炉冷の焼鈍を施した後、冷延率50%の冷延とその後の730℃×20h→炉冷の焼鈍を施したもの、(ロ)710℃×20h→炉冷の焼鈍を施した後、30%の冷延と710℃×20h→炉冷の焼鈍を二度繰り返したもの、(ハ)710℃×10h→炉冷の焼鈍を施した後、50%の冷延を施し、その後に750℃×10hの加熱→−10℃/hの冷却速度で680℃まで冷却→680℃×10hの保持→炉冷の焼鈍を施したもの、の三種類の通常の条件で軟質化した。なお、焼鈍はいずれも水素雰囲気のバッチ炉で行った。
Example 1:
After melting the steel having the chemical components shown in Table 1 and obtaining a slab by continuous casting, hot rolling was performed at a slab heating temperature of 1250 ° C, a finishing temperature of 850 ° C and a winding temperature of 600 ° C, and pickling in a hydrochloric acid bath. As a result, a hot rolled pickled plate having a thickness of 4.0 mm was obtained.
Each hot-rolled pickled plate was subjected to (i) 730 ° C. × 20 h → furnace cooling annealing, followed by 50% cold rolling and subsequent 730 ° C. × 20 h → furnace cooling annealing, (B) After annealing 710 ° C. × 20 h → furnace cooling, 30% cold rolling and 710 ° C. × 20 h → furnace cooling annealing were repeated twice, (c) 710 ° C. × 10 h → furnace cooling After annealing, 50% cold rolling is applied, followed by heating at 750 ° C. × 10 h → cooling to 680 ° C. at a cooling rate of −10 ° C./h→holding at 680 ° C. × 10 h → furnace cooling annealing And softened under three normal conditions. All annealing was performed in a batch furnace in a hydrogen atmosphere.
上記三種類の方法で軟質化した冷延焼鈍板について、圧延方向と板厚方向を含む断面を研磨紙で湿式研磨した後、ビッカース硬度計で硬さを測定した。その結果を表2に示す。
さらに、前記(ハ)の工程で軟質化した冷延焼鈍板に、表2に示す条件の「LPRA処理」を施した。これらの鋼板についても同様にビッカース硬度計で硬さを測定した。そして、単に軟質化した冷延焼鈍板と比べて、硬度がどのように変化したかを調べた。その結果を表2に併せて示す。また、図3に、本発明の採用による硬さの低減状況を図示した。
表2及び図3からもわかるように、本発明範囲の鋼では「LPRA処理」によって、硬さを10%以上低下させることができている。
一方、本発明範囲外の鋼では、硬さ低下率が低いか、又は硬さが高く塑性加工に適した160HV以下の軟質の鋼板を製造することができなかった。
About the cold-rolled annealed sheet softened by the above three methods, the cross section including the rolling direction and the thickness direction was wet-polished with abrasive paper, and then the hardness was measured with a Vickers hardness meter. The results are shown in Table 2.
Furthermore, the “LPRA treatment” under the conditions shown in Table 2 was applied to the cold-rolled annealed sheet softened in the step (c). The hardness of these steel plates was similarly measured with a Vickers hardness tester. And it was investigated how the hardness changed compared with the softened cold-rolled annealing board. The results are also shown in Table 2. Further, FIG. 3 shows a hardness reduction state by adopting the present invention.
As can be seen from Table 2 and FIG. 3, the steel within the scope of the present invention can reduce the hardness by 10% or more by “LPRA treatment”.
On the other hand, with steels outside the scope of the present invention, it was not possible to produce a soft steel plate with a hardness reduction rate of 160 HV or less that is low in hardness or suitable for plastic working.
実施例2:
表1中、C鋼及びJ鋼について、「LPRA処理」時の圧延・焼鈍条件の影響について、検討した。
実施例1と同じ方法で板厚4.0〜5.0mmの熱延酸洗板を製造した。この熱延酸洗板に、(A)冷延率50%の冷延の後570℃×18hの焼鈍を施したもの、(B)710℃×20hの焼鈍→冷延率50%の冷延→750℃×20hの焼鈍を施したもの、(C)710℃×20hの焼鈍→冷延率50%の冷延→750℃×10hの加熱の後−10℃/hの冷却速度で680℃まで冷却し、680℃×10hの保持後に室温まで冷却する焼鈍を施したもの、の三種類の冷延焼鈍板を作製した。
Example 2:
In Table 1, the influence of rolling / annealing conditions during “LPRA treatment” was examined for steel C and steel J.
A hot rolled pickled plate having a thickness of 4.0 to 5.0 mm was produced in the same manner as in Example 1. This hot-rolled pickled sheet is (A) cold rolled at a cold rolling rate of 50% and then annealed at 570 ° C. × 18 h, (B) 710 ° C. × 20 h of annealing → cold rolling at a cold rolling rate of 50% -> Annealed at 750 ° C x 20h, (C) Annealed at 710 ° C x 20h-> Cold rolled at a cold rolling rate of 50%-After heating at 750 ° C x 10h, 680 ° C at a cooling rate of -10 ° C / h Three types of cold-rolled annealed plates were prepared, one that was cooled to room temperature after being cooled to room temperature after being held at 680 ° C. for 10 hours.
なお、上記(A)は球状化が不十分な炭化物を微細に分散させるべく、低い温度で焼鈍したものであり、(B)は(γ+α)二相域に加熱して再生パーライトを生成させて球状化率を低くするべく、高い温度で焼鈍したものである。そして、(C)が、適当な球状化率で球状化し、大きな粒子間隔で十分に粗大化した炭化物を得るべく、「LPRA処理」の効果を有効にするべき、最適な前処理を施したものである。
上記三種類の冷延焼鈍板に、表3に示すように、圧延率及び焼鈍温度を種々に変えた「LPRA処理」を施した。
The above (A) is annealed at a low temperature to finely disperse carbides that are insufficiently spheroidized, and (B) is heated to (γ + α) two-phase region to produce regenerated pearlite. In order to lower the spheroidization rate, it is annealed at a high temperature. And (C), which has been subjected to an optimal pretreatment that should make the effect of “LPRA treatment” effective to obtain a carbide that has been spheroidized at an appropriate spheroidization rate and sufficiently coarsened with a large particle spacing It is.
As shown in Table 3, the three types of cold-rolled annealed plates were subjected to “LPRA treatment” in which the rolling rate and the annealing temperature were variously changed.
「LPRA処理」された各冷延焼鈍板について、実施例1と同じように硬さの測定を行うとともに、組織形態を観察した。
組織形態については、冷延焼鈍板断面を5%ナイタールで腐食した後、走査電子顕微鏡によりフェライト結晶粒界上とフェライト粒内にある炭化物総数が1000個になるまで、フェライト結晶粒界上の炭化物数CGBとフェライト粒内の炭化物数CIGを計測した。
About each cold-rolled annealing board which was "LPRA process", while measuring hardness similarly to Example 1, the structure | tissue form was observed.
Regarding the microstructure, after corroding the cold-rolled annealed plate section with 5% nital, until the total number of carbides on the ferrite grain boundaries and in the ferrite grains reaches 1000 by scanning electron microscope, the carbides on the ferrite grain boundaries The number C GB and the number of carbides C IG in the ferrite grains were measured.
また、「LPRA処理」された板厚2.0mmの各冷延焼鈍板について、ファインブランキング加工試験を行った。
ファインブランキング加工は、ポンチ・ダイス材質:DC53(61HRC),ポンチ外径:40mmφ,モジュール:0.8,クリアランス:0.01mm(板厚の0.5%)の金型と、320tFBプレス機を使用し、カウンター圧:25t,Vリング圧:50t,加工スピード:10mm/s,潤滑油:FB805Dなる条件で行った。
連続して5000ショットの打抜きを行った後、ポンチの欠損状況と、バリ高さを測定して、金型寿命を評価した。
Further, a fine blanking processing test was performed on each cold rolled annealed sheet having a thickness of 2.0 mm that was “LPRA treated”.
Fine blanking is performed using a punch and die material: DC53 (61HRC), punch outer diameter: 40mmφ, module: 0.8, clearance: 0.01mm (0.5% of plate thickness) and 320tFB press machine. Pressure: 25 t, V ring pressure: 50 t, processing speed: 10 mm / s, lubricating oil: FB805D.
After punching 5000 shots continuously, the punch life and burr height were measured to evaluate the die life.
なお、ポンチの欠損状況は、ポンチ欠損が転写された打抜き品を目視判定し、欠損の大きさで1〜5の五段階の評価点を付した。図2に示すように、損傷がないものを評価点1,僅かな点状又は線状の欠陥があるものを評価点2,歯先角部が折損したものを評価点3,歯先全体が折損したものを評価点4,激しい折損をしたものを評価点5とし、10箇所の歯先の評価点平均値を取り、評価点平均値が1〜3をOK、4〜5をNGと判定した。ここで、評価点2の場合は、面Aには評価点1の場合と同様に損傷は認められないが、面Bに肌荒れやごく軽微な剥離又は損耗が認められるものを指す。
また、上記ポンチ欠損評価点が3以下の歯先について、100ショット後及び5000ショット後のバリ高さを測定顕微鏡で計測した。各歯先の5000ショット後のバリ高さから100ショット後のバリ高さから初期値を差し引いて、バリ高さの増加量を求めた。
供試鋼の最終仕上げ焼鈍前の処理条件及び最終仕上げ冷延とその後の焼鈍条件の違いによる、炭化物の分散状況,硬さ、及びそれに伴うファインブランキング加工性の関係の調査結果を、表4に併せて示す。
In addition, the defect | deletion condition of a punch evaluated the punching goods to which the punch defect | transfer was transcribed | transferred visually, and attached | subjected the five-step evaluation score of 1-5 with the magnitude | size of a defect | deletion. As shown in FIG. 2, the evaluation point 1 indicates that there is no damage, the evaluation point 2 indicates that there is a slight point or linear defect, the evaluation point 3 indicates that the tooth tip corner is broken, and the entire tooth tip The broken one was evaluated as 4, the severely broken one was evaluated as 5, and the average value of the 10 tooth tips was taken. The average value of the evaluation points was 1 to 3, OK, and 4 to 5 were judged as NG. did. Here, in the case of the evaluation point 2, no damage is observed on the surface A as in the case of the evaluation point 1, but the surface B indicates that the surface B is roughened or very slightly peeled off or worn.
Further, the burr height after 100 shots and after 5000 shots was measured with a measuring microscope for the tooth tips having the punch defect evaluation score of 3 or less. The initial value was subtracted from the burr height after 100 shots from the burr height after 5000 shots of each tooth tip to determine the amount of increase in burr height.
Table 4 shows the results of the investigation of the relationship between carbide dispersion, hardness, and accompanying fine blanking workability, depending on the processing conditions before final finish annealing of the test steel and the difference between the final finish cold rolling and the subsequent annealing conditions. It shows together with.
表4に示す結果からも明らかなように、「LPRA処理」を施す前の素材の組織形態が適切で、その後に施す「LPRA処理」の条件が適切である試験No.4,10,11では、炭化物の分散状況が適切で、軟化しており、極めて良好な打抜き加工性を呈し、金型の損耗もなかった。
これに対して、素材組織の炭化物が微細であった試験No.1,7では、適切な「LPRA処理」を施してもフェライト結晶粒形が粗大化せずに硬かったため、ファインブランキング加工でポンチが破損した。また、素材組織の炭化物が棒状であった試験No.2,8では、適切な「LPRA処理」を施しても、処理後に良好な炭化物分散状態が得られなかったために、ファインブランキング加工時に金型摩耗が激しかった。さらに、素材組織の炭化物形態が適切であっても「LPRA処理」を施さないと、所望の特性は得られていない(試験No.3,9)。
As is clear from the results shown in Table 4, the test structure No. 1 in which the texture form of the material before the “LPRA treatment” is appropriate and the conditions of the “LPRA treatment” to be applied thereafter are appropriate. In Nos. 4, 10, and 11, the state of carbide dispersion was appropriate and softened, exhibiting extremely good punching workability and no wear of the mold.
On the other hand, Test No. in which the carbide in the material structure was fine was used. In Nos. 1 and 7, since the ferrite crystal grain shape was not coarsened and hardened even when appropriate “LPRA treatment” was performed, the punch was damaged by fine blanking. Further, Test No. in which the carbide of the material structure was rod-shaped. In Nos. 2 and 8, even if an appropriate “LPRA treatment” was performed, a good carbide dispersion state was not obtained after the treatment, and therefore, die wear was severe during fine blanking. Furthermore, even if the carbide form of the material structure is appropriate, the desired characteristics are not obtained unless “LPRA treatment” is performed (Test Nos. 3 and 9).
素材組織の炭化物形態が適切であっても、「LPRA処理」を施す際の冷延率や焼鈍温度が適切でないと所望の特性は得られていない。冷延を行わなかった試験No.16,17や圧延率が低かった試験No.5,14では、軟質化が不十分であった。圧延率が高すぎた試験No.6,15も、軟質化が不十分であった。また、「LPRA処理」の焼鈍条件が適切でなかった試験No.12,13では、再生パーライトが生成したり、炭化物の分散状態が悪かったりして、打抜き金型の摩耗が激しかった。   Even if the carbide form of the material structure is appropriate, the desired characteristics cannot be obtained unless the cold rolling rate and annealing temperature when performing the “LPRA treatment” are appropriate. Test No. which was not cold-rolled Nos. 16 and 17 and test No. with a low rolling rate 5 and 14, the softening was insufficient. Test No. whose rolling rate was too high. 6 and 15 also had insufficient softening. In addition, test No. in which the annealing conditions of “LPRA treatment” were not appropriate. In Nos. 12 and 13, regenerated pearlite was generated, and the carbide dispersion state was bad, and the die was severely worn.
さらに、C鋼及びJ鋼について、表3,4に示していない条件の「LPRA処理」も実施し、従来の焼鈍材と比較して、硬さや炭化物の分散状況の違いとファインブランキング加工性の関係をも調査した。なお、ファインブランキング加工試験は、いずれも板厚2.0mmの鋼板を素材として、前記と同じ方法で実施した。
その結果を、図4〜7に示す。
In addition, “LPRA treatment” of conditions not shown in Tables 3 and 4 was also carried out for steel C and steel J. Differences in hardness and carbide dispersion and fine blanking workability compared to conventional annealed materials The relationship was also investigated. The fine blanking test was carried out in the same manner as described above, using a steel plate having a thickness of 2.0 mm as a raw material.
The results are shown in FIGS.
C鋼、J鋼ともに、通常の焼鈍材と比べて「LPRA処理」の方が、バリ高さ増大量が小さくなっている。特に同程度の硬さであっても、「LPRA処理」の方が好ましい結果が得られている。また、フェライト結晶粒界上の炭化物数CGBとフェライト結晶粒内の炭化物数CIGとの関係にあっては、CGB/CIG≦0.8で、明らかにバリ高さ増大量が小さくなっている。
硬さや炭化物の分散状況の違いと金型の欠損状況をみると、CGB/CIGよりも、むしろ硬さの方に依存している。これはポンチ欠損が打抜き時の最大荷重に依存しているためと思われる。いずれにしても、硬さをHV160以下にしておけば、ポンチ欠損評価点が4を越えることはない。
In both C steel and J steel, the amount of increase in burr height is smaller in “LPRA treatment” than in normal annealing materials. In particular, even with the same degree of hardness, “LPRA treatment” is more preferable. In addition, regarding the relationship between the number of carbides C GB on the ferrite grain boundaries and the number of carbides C IG in the ferrite grains, C GB / C IG ≦ 0.8, and the burr height increase is clearly small. It has become.
Looking at the difference in hardness, the dispersion of carbides, and the state of chip defects, it depends on the hardness rather than C GB / C IG . This seems to be because punch defects depend on the maximum load at the time of punching. In any case, if the hardness is set to HV160 or less, the punch defect evaluation score does not exceed 4.
実施例3:
表1中、C鋼、J鋼及びR鋼について、「LPRA処理」時の冷延率の影響について、検討した。
実施例1と同じ方法で板厚4.0〜5.0mmの熱延酸洗板を製造した。この熱延酸洗板に、実施例1で(ハ)とした、「710℃×10h→炉冷の焼鈍を施した後、50%の冷延を施し、その後に750℃×10hの加熱→−10℃/hの冷却速度で680℃まで冷却→680℃×10hの保持→炉冷」の焼鈍を施した冷延焼鈍板に、冷延率を0〜50%の範囲で種々変更した「LPRA処理」を施した。なお、仕上げ冷延後の仕上げ焼鈍は、710℃×10h保持後に炉冷した。
Example 3:
In Table 1, the influence of the cold rolling rate at the time of “LPRA treatment” was examined for C steel, J steel and R steel.
A hot rolled pickled plate having a thickness of 4.0 to 5.0 mm was produced in the same manner as in Example 1. This hot-rolled pickled plate was subjected to (710) × 10h → furnace cooling annealing in Example 1, and then subjected to 50% cold rolling, followed by heating at 750 ° C. × 10h → The cold rolling rate was variously changed in the range of 0 to 50% on the cold rolled annealing plate subjected to annealing of “cooling to 680 ° C. at a cooling rate of −10 ° C./h→holding 680 ° C. × 10 h → furnace cooling”. LPRA treatment "was performed. The finish annealing after finish cold rolling was furnace-cooled after holding at 710 ° C. for 10 hours.
「LPRA処理」された各冷延焼鈍板について、実施例1と同じように、硬さの測定を行うとともに、組織形態を観察した。なお、フェライト結晶粒径はJIS G0552に準じ、切断法で計測した。
その結果を、圧延率との関係で図8,9,10に示す。
この結果からもわかるように、本発明鋼にあっては、「LPRA処理」の冷延率を8〜24%の範囲内にすると、フェライト結晶粒径が急激に粗大化し、CGB/CIGを0.8以下にすることができ、また、その結果から、冷延率0%の場合よりも軟質化できている。「LPRA処理」の冷延率は、より好ましくは10〜20%の範囲であることもわかる。
For each cold-rolled annealed plate that was “LPRA-treated”, the hardness was measured in the same manner as in Example 1, and the microstructure was observed. The ferrite crystal grain size was measured by a cutting method according to JIS G0552.
The results are shown in FIGS. 8, 9, and 10 in relation to the rolling rate.
As can be seen from these results, in the steel of the present invention, when the cold rolling rate of the “LPRA treatment” is within the range of 8 to 24%, the ferrite crystal grain size is rapidly coarsened, and C GB / C IG Can be made 0.8 or less, and as a result, it is softer than the case where the cold rolling rate is 0%. It can also be seen that the cold rolling rate of the “LPRA treatment” is more preferably in the range of 10 to 20%.
さらに、冷延率を適正範囲に設定することにより、CGB/CIGを小さく制御することが可能になるので、炭化物の存在形態が良好となり、打抜き型等、塑性加工金型の摩耗量減少効果等、加工に有利な機械的特性が得られている。
これに対して、比較鋼であるR鋼では、含有炭素量が多いために、「LPRA処理」を施してもフェライト結晶粒径の粗大化は認められなかった。含有炭素量が多すぎるため、炭化物の体積率が大きく、フェライト結晶粒の粗大化が妨げられている。フェライト結晶粒径の粗大化が認められないため、併せてCGB/CIGも小さくならず、「LPRA処理」を施しても軟質化は達成できていない。
Furthermore, by setting the cold rolling rate within an appropriate range, C GB / C IG can be controlled to be small, so that the presence of carbides is good, and the amount of wear on plastic working dies such as punching dies is reduced. Mechanical properties advantageous for processing such as effects are obtained.
On the other hand, the R steel, which is a comparative steel, has a large amount of carbon, and therefore no coarsening of the ferrite crystal grain size was observed even when the “LPRA treatment” was performed. Since there is too much carbon content, the volume fraction of carbide is large and the coarsening of a ferrite crystal grain is prevented. Since coarsening of the ferrite crystal grain size is not recognized, C GB / C IG is not reduced at the same time, and softening cannot be achieved even if “LPRA treatment” is performed.
炭化物の形態を示す模式図Schematic diagram showing the form of carbide ポンチの欠損状況を示す模式図Schematic diagram showing the punch defect situation 従来法と本発明法とで得られた鋼板の硬さの違いを示したグラフGraph showing the difference in hardness of steel sheets obtained by the conventional method and the present invention method ファインブランキング加工時の、被打抜き鋼板の硬さとバリ高さ増加量の関係を示す図Diagram showing the relationship between the hardness of the punched steel sheet and the burr height increase during fine blanking ファインブランキング加工時の、被打抜き鋼板中炭化物分散状態とバリ高さ増加量の関係を示す図Diagram showing the relationship between carbide dispersion in punched steel sheet and burr height increase during fine blanking ファインブランキング加工時の、被打抜き鋼板の硬さとポンチ欠損評価点の関係を示す図Figure showing the relationship between the hardness of the punched steel sheet and the punch defect evaluation point during fine blanking ファインブランキング加工時の、被打抜き鋼板中炭化物分散状態とポンチ欠損評価点の関係を示す図Diagram showing the relationship between carbide dispersion in punched steel sheet and punch defect evaluation point during fine blanking LPRA処理時の冷延率と処理後のフェライト粒径の関係を示したグラフGraph showing the relationship between the cold rolling rate during LPRA treatment and the ferrite grain size after treatment LPRA処理時の冷延率と処理後の鋼板硬さの関係を示したグラフGraph showing the relationship between the cold rolling rate during LPRA treatment and the steel plate hardness after treatment LPRA処理時の冷延率と処理後の鋼板中炭化物分散状態の関係を示したグラフA graph showing the relationship between the cold rolling rate during LPRA treatment and the carbide dispersion in the steel plate after treatment

Claims (4)

  1. C:0.30〜1.30質量%,Si:1.0質量%以下,Mn:0.2〜1.5質量%,P:0.02質量%以下,S:0.02質量%以下を含み、残部がFe及び不可避的不純物である成分組成を有し、フェライト結晶粒界上の炭化物数CGBとフェライト結晶粒内の炭化物数CIGの間に、CGB/CIG≦0.8の関係が成り立つように炭化物が分散した組織を有し、さらに断面硬さが160HV以下であることを特徴とする加工性に優れた中・高炭素鋼板。 C: 0.30 to 1.30 mass%, Si: 1.0 mass% or less, Mn: 0.2 to 1.5 mass%, P: 0.02 mass% or less, S: 0.02 mass% or less Between the number of carbides C GB on the ferrite grain boundary and the number of carbides C IG in the ferrite crystal grain, C GB / C IG ≦ 0. A medium and high carbon steel sheet excellent in workability, characterized in that it has a structure in which carbides are dispersed so that the relationship of 8 is satisfied, and the cross-sectional hardness is 160 HV or less.
  2. さらにNi:1.8質量%以下,Cr:2.0質量%以下,V:0.5質量%以下,Mo:0.5質量%以下の1種又は2種以上を含む成分組成を有する請求項1に記載の加工性に優れた中・高炭素鋼板。   Furthermore, it has a component composition containing one or more of Ni: 1.8% by mass or less, Cr: 2.0% by mass or less, V: 0.5% by mass or less, Mo: 0.5% by mass or less. Item 10. A medium / high carbon steel sheet excellent in workability according to item 1.
  3. さらにNb:0.3質量%以下,Ti:0.3質量%以下,B:0.01質量%以下,Ca:0.01質量%以下の1種又は2種以上を含む成分組成を有する請求項1又は2に記載の加工性に優れた中・高炭素鋼板。   Furthermore, it has a component composition containing one or more of Nb: 0.3% by mass or less, Ti: 0.3% by mass or less, B: 0.01% by mass or less, and Ca: 0.01% by mass or less. Item 3. A medium / high carbon steel sheet excellent in workability according to item 1 or 2.
  4. 請求項1〜3の何れかに記載された成分組成を有する鋼の熱延酸洗板に、熱延板焼鈍或いは冷延及び冷延板焼鈍を施した後、仕上げ冷延及び仕上げ焼鈍を施して冷延焼鈍板を製造する際、前記仕上げ冷延の前の最終工程が焼鈍工程であり、それまでのいずれかの焼鈍時に、Ac1〜(Ac1+50℃)に5〜20h保持→600℃までを−10℃/h以下の速度の冷却→600℃〜室温を任意の速度で冷却する焼鈍を一回以上含み、8〜24%の冷延率で最終の仕上げ冷延し、その後、640℃〜Ac1点の温度域に2h以上保持する仕上げ焼鈍を施すことを特徴とする加工性に優れた中・高炭素鋼板の製造方法。   The hot-rolled pickled steel sheet having the composition described in any one of claims 1 to 3 is subjected to hot-rolled sheet annealing or cold-rolled and cold-rolled sheet annealing, and then subjected to finish cold-rolling and finish annealing. When producing a cold-rolled annealed sheet, the final step before the finish cold-rolling is an annealing step, and during any annealing up to that time, hold Ac1 to (Ac1 + 50 ° C) for 5 to 20 hours → 600 ° C. Cooling at a rate of −10 ° C./h or less → 600 ° C. to annealing at room temperature at an arbitrary rate one or more times, final finish cold rolling at a cold rolling rate of 8 to 24%, and then 640 ° C. to A method for producing a medium- and high-carbon steel sheet excellent in workability, characterized in that finish annealing is performed in a temperature range of Ac1 point for 2 hours or more.
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