JP4322610B2 - Cold-rolled steel sheet with excellent impact characteristics and method for producing the same - Google Patents
Cold-rolled steel sheet with excellent impact characteristics and method for producing the same Download PDFInfo
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Description
本発明は、主として自動車のオートマチックトランスミッションの構成部材であるセパレートプレート、フリクションプレート、バッキングプレート等として好適に使用される衝撃特性（靭性）に優れた冷延鋼板に関する。 The present invention relates to a cold-rolled steel sheet having excellent impact characteristics (toughness) that is suitably used as a separate plate, friction plate, backing plate, and the like, which are constituent members of automatic transmissions of automobiles.
自動車のオートマチックトランスミッション（ＡＴ）を構成するセパレートプレート（ドリブンプレート又はメーティングプレート等とも称される）、フリクションプレート（ドライブプレート，コアープレート又はディスク等とも称される）、バッキングプレート（リテーニングプレート，リアクションプレート又はエンドプレート等とも称される）等の部材（以下「ＡＴプレート」）は、鋼板をほぼ円環形状にプレス打ち抜きした成形品である。セパレートプレートとフリクションプレートは摩擦材を介して交互に配置され、これにバッキングプレート等を組付けられてトルク伝達機構が構成される。これらの部材料の機能上、硬度及び表面性状の要求特性（硬さHv≧230，表面粗さRa≦0.4μｍ）と併せて、良好な衝撃特性が要求される。とりわけ局所的な応力集中に起因する材料破壊を防止する保安上の観点から衝撃特性は重要である。 Separate plate (also referred to as driven plate or mating plate), friction plate (also referred to as drive plate, core plate or disk), backing plate (retaining plate, etc.) constituting the automatic transmission (AT) of an automobile A member such as a reaction plate or an end plate (hereinafter referred to as an “AT plate”) is a molded product obtained by press punching a steel plate into a substantially annular shape. The separate plate and the friction plate are alternately arranged via a friction material, and a torque transmission mechanism is configured by assembling a backing plate or the like. In view of the functions of these materials, good impact characteristics are required in combination with the required characteristics of hardness and surface properties (hardness Hv ≧ 230, surface roughness Ra ≦ 0.4 μm). In particular, impact characteristics are important from the viewpoint of security to prevent material destruction caused by local stress concentration.
従来、ＡＴプレート素材としてJIS G3311に規定の機械構造用鋼、主としてＳ３５Ｃの冷延鋼板が使用され、これは、「製鋼→連続鋳造→熱間圧延→酸洗→焼鈍→冷間圧延→脱脂→精整」の工程で製造されている。この製造工程において、ＡＴプレート用冷延鋼板の要求特性（硬さＨｖ≧230，表面粗度Ｒａ≦0.4μｍ）を満たすために、冷間圧延の圧下率を５０％以上とすることが必要とされている。その冷間圧延に先立って「焼鈍」を行なうのは、熱延鋼板のままでは硬質で、冷間圧延（圧下率≧50％）の安定操業に支障をきたすことがあり、また熱延鋼板のままでは熱延鋼板の粗大なパーライト組織が冷延鋼板に持ち越されるために、ＡＴプレートのプレス打ち抜き性に支障をきたすだけでなく、衝撃特性の低下が大きな問題となるからである。 Conventionally, machine structural steel specified in JIS G3311 as an AT plate material, mainly S35C cold-rolled steel sheet, is used. This is called “steel making → continuous casting → hot rolling → pickling → annealing → cold rolling → degreasing → Manufactured in the process of refining. In this manufacturing process, in order to satisfy the required characteristics (hardness Hv ≧ 230, surface roughness Ra ≦ 0.4 μm) of the cold-rolled steel sheet for AT plates, it is necessary to set the reduction ratio of cold rolling to 50% or more. Has been. The “annealing” performed prior to the cold rolling is hard if it is a hot-rolled steel sheet, which may interfere with the stable operation of the cold-rolling (rolling ratio ≧ 50%). This is because the coarse pearlite structure of the hot-rolled steel sheet is carried over to the cold-rolled steel sheet, which not only hinders the press punching property of the AT plate, but also deteriorates the impact characteristics.
上記のように冷間圧延前に行なっている「焼鈍」は、熱延鋼板の軟質化と炭化物の球状化を目的とするものであり、その焼鈍の実施により圧下率５０％以上の冷間圧延の安定操業が維持されると共に、製品冷延鋼板のプレス打ち抜き性や衝撃特性を確保することが可能となる。従ってＳ３５Ｃを素材とする従来のＡＴプレート用冷延鋼板の製造においては、冷間圧延前に熱延鋼板を焼鈍することが必須の工程とされ、その焼鈍処理は通常タイトコイル焼鈍（ＴＣＡ）として実施されている。 The “annealing” performed before the cold rolling as described above is intended to soften the hot-rolled steel sheet and spheroidize the carbide, and cold rolling with a reduction rate of 50% or more by performing the annealing. As a result, it becomes possible to maintain the press punchability and impact characteristics of the product cold-rolled steel sheet. Therefore, in the manufacture of the conventional cold rolled steel sheet for AT plate using S35C as a raw material, it is an essential process to anneal the hot rolled steel sheet before cold rolling, and the annealing treatment is usually as tight coil annealing (TCA). It has been implemented.
近時、小型大衆車ＮＢＣ（New Basic Car）の開発動向に見られるように、低価格化の要求が時代の趨勢となっている。その一環としてオートマチックトランスミッションについても低価格化への対応が急務とされ、所要の硬度及び衝撃特性等を備えた低価格材の開発要求が一段と強くなっている。しかるにＳ３５Ｃ鋼を素材とする従来のＡＴプレート用冷延鋼板は、前記のように冷間圧延前の焼鈍の実施を必須とし、しかもＴＣＡ焼鈍による長時間の処理（通常は均熱：約10Hr以上）を要するため、コストアップの大きな要因となっている。 Recently, as seen in the development trend of small mass transit vehicles NBC (New Basic Car), the demand for lower prices has become the trend of the times. As part of this effort, there is an urgent need to reduce the price of automatic transmissions, and there is an increasing demand for the development of low-priced materials with the required hardness and impact characteristics. However, the conventional cold-rolled steel sheet for AT plates made of S35C steel is required to be annealed before cold rolling as described above, and is treated for a long time by TCA annealing (usually soaking: about 10 hours or more) ) Is a major factor in increasing costs.
本発明は上記に鑑み、従来ＡＴプレートの製造工程で必須とされている冷間圧延前の焼鈍処理を省略してコストアップの要因を排除しながら、ＡＴプレート用素材等としての硬度，表面性状等の要求特性を確保すると共に、良好な衝撃特性を具備せしめた冷延鋼板及びその製造方法を提供するものである。 In view of the above, the present invention eliminates the factor of cost increase by omitting the annealing process before cold rolling, which has been essential in the conventional AT plate manufacturing process, while maintaining the hardness and surface properties of the AT plate material and the like. The cold-rolled steel sheet having the required characteristics such as the above and having good impact characteristics and a method for manufacturing the cold-rolled steel sheet are provided.
本発明に係る冷延鋼板（請求項１）は、
質量％で、Ｃ：０．１５〜０．２５％，Ｓｉ：０．２５％以下，Ｍｎ：０．３〜０．９％，Ｐ：０．０２０％以下，Ｓ：０．００５％以下，Ａｌ：０．０８％以下，Ｎ：０．００８％以下，残部はＦｅと不可避的不純物からなり、パーライト＋セメンタイト分率：２０％以上、フェライト粒径：５〜２０μｍの熱延鋼板を、焼鈍処理することなく圧下率５０％以上で冷間圧延することにより製造される冷延鋼板である。
Engaging Ru cold-rolled steel sheet in the present invention (claim 1),
In mass%, C: 0.15 to 0.25%, Si: 0.25% or less, Mn: 0.3 to 0.9%, P: 0.020% or less, S: 0.005% or less, Al: 0.08% or less, N: 0.008% or less, balance is Fe and inevitable impurities , pearlite + cementite fraction: 20% or more, ferrite grain size: 5-20μm hot rolled steel sheet It is a cold-rolled steel sheet manufactured by cold rolling at a rolling reduction of 50% or more without treatment.
本発明の冷延鋼板の製造方法（請求項２）は、
質量％で、Ｃ：０．１５〜０．２５％，Ｓｉ：０．２５％以下，Ｍｎ：０．３〜０．９％，Ｐ：０．０２０％以下，Ｓ：０．００５％以下，Ａｌ：０．０８％以下，Ｎ：０．００８％以下，残部はＦｅと不可避的不純物からなるスラブを、熱延仕上げ温度Ａｒ ３ 変態点直上、巻取り温度５００〜６００℃で熱間圧延することにより、パーライト＋セメンタイト分率：２０％以上、フェライト粒径：５〜２０μｍの熱延鋼板を得、酸洗処理の後、焼鈍処理することなく圧下率５０％以上で冷間圧延することからなる。
The method for producing a cold-rolled steel sheet of the present invention (Claim 2)
In mass%, C: 0.15 to 0.25%, Si: 0.25% or less, Mn: 0.3 to 0.9%, P: 0.020% or less, S: 0.005% or less, Al: 0.08% or less, N: 0.008% or less, and the remainder is hot-rolled at a coiling temperature of 500 to 600 ° C. just above the hot rolling finishing temperature Ar 3 transformation point , with the slab consisting of Fe and inevitable impurities. From this, a hot rolled steel sheet having a pearlite + cementite fraction of 20% or more and a ferrite particle size of 5 to 20 μm is obtained, and after the pickling treatment, it is cold-rolled at a reduction rate of 50% or more without annealing. Become .
本発明の鋼組成のＣ量，Ｐ量及びＳ量の規定は重要である。Ｃ量は、従来材（S35C）より低い範囲に規定され、そのＣ量制限により熱延鋼板のパーライト量を少なくして熱延鋼板を軟質化し、冷間圧延前における熱延鋼板の軟質化および炭化物（Ｆｅ３Ｃ）の球状化を目的とする焼鈍処理の省略を可能にしている。Ｐは、結晶粒界に偏析して粒界強度を低下させ、冷延鋼板の衝撃特性を悪くする不純分元素である。そこで本発明は、Ｐ量の上限規定（Ｐ量≦0.020%）により、高レベルの衝撃特性を得るようにしている。またＳはＭｎＳのＡ系介在物（一般的に加工工程で粘性変形により細長く延びた形態を呈し局部的な応力集中が生じた場合に割れの起点になり易い）を形成し、衝撃特性を損なう要因となるため、Ｓ量を制限（S量≦0.005%）し、衝撃特性に対するＳの実質的な悪影響を回避している。 C content of the steel composition of the present invention, provisions of P content and S content are important. The amount of C is defined in a range lower than that of the conventional material (S35C), and by limiting the amount of C, the amount of pearlite of the hot-rolled steel sheet is reduced to soften the hot-rolled steel sheet, and softening of the hot-rolled steel sheet before cold rolling and This makes it possible to omit the annealing treatment for the purpose of spheroidizing the carbide (Fe 3 C). P is segregated in the grain boundaries to lower the grain boundary strength, Ru impurities elements der to bad impact properties of cold-rolled steel sheet. Its invention in This, by the upper limit provisions of P amount (P amount ≦ 0.020%), and to obtain a high level of impact properties. In addition, S forms an A-based inclusion of MnS (generally, it forms an elongated shape due to viscous deformation in the processing step, and easily becomes a starting point of cracking when local stress concentration occurs), and impairs impact characteristics. Therefore, the amount of S is limited (S amount ≦ 0.005%) to avoid a substantial adverse effect of S on impact characteristics.
更に、本発明は冷延鋼板の金属組織を、パーライト＋セメンタイト分率：２０％以上の均一微細な炭化物組織、及びフェライト粒径：５〜２０μｍの細粒化されたフェライト組織としている。この微細均質組織は、ＡＴプレート用素材等に要求される硬度及び衝撃特性等を得るのに必要である。 Further, in the present invention, the metal structure of the cold-rolled steel sheet is a uniform and fine carbide structure having a pearlite + cementite fraction of 20% or more and a fine ferrite structure having a ferrite particle diameter of 5 to 20 μm. The fine homogeneous tissue, Ru required der to obtain the hardness and impact properties, etc. required for the AT plate material for such.
本発明は、上記化学組成に基づく効果として、従来不可欠とされていた冷間圧延前の焼鈍（熱延鋼板の軟質化及び炭化物球状化処理）を省略しながら、冷間圧延（圧下率≧５０％）の安定操業を可能にすると共に、主としてＡＴプレート用冷延鋼板等の要求特性（硬さHv≧230、表面粗さRa≦0.4μｍ）、及び良好な衝撃特性（靭性）を確保し、その冷延鋼板は、打ち抜き加工後、調質のための熱処理を必要とせず、そのまま（硬引き材のまま）ＡＴプレート等として使用することを可能にしている。 In the present invention, as an effect based on the above chemical composition, cold rolling (rolling rate ≧ 50) is performed while omitting annealing (softening and carbide spheroidizing treatment of hot-rolled steel sheet) before cold rolling, which has been considered essential in the past. %) And stable characteristics such as cold rolled steel sheets for AT plates (hardness Hv ≧ 230, surface roughness Ra ≦ 0.4μm) and good impact characteristics (toughness) The cold-rolled steel sheet does not require heat treatment for tempering after punching, and can be used as it is (as a hard-drawn material) as an AT plate or the like.
本発明の冷延鋼板は、前記化学組成に調整された鋼のスラブを、熱間圧延（熱延温度≧Ａｒ３変態点）し、５００〜６００℃で巻き取った熱延鋼板を、酸洗処理の後、焼鈍処理することなく、圧下率５０％以上で冷間圧延する工程により製造される。冷間圧延は、後述のように、酸洗処理前の冷間圧延（プレ圧延）と酸洗処理後の冷間圧延（仕上げ圧延）とに分け、前後の圧延（プレ圧延と仕上げ圧延）の合計圧下率が５０％以上となるように２段階の冷間圧延として実施することもできる。 The cold-rolled steel sheet of the present invention is a steel slab adjusted to the above chemical composition, hot-rolled (hot-rolling temperature ≧ Ar 3 transformation point) and wound at 500 to 600 ° C. After the treatment, it is manufactured by a cold rolling process at a reduction rate of 50% or more without annealing. Cold rolling is divided into cold rolling (pre-rolling) before pickling treatment and cold rolling (finish rolling) after pickling treatment, as described later, and before and after rolling (pre-rolling and finishing rolling). It can also be implemented as a two-stage cold rolling so that the total rolling reduction is 50% or more.
本発明の鋼組成は次のように規定される。元素含有量は全て質量％である。
Ｃ：０．１５〜０．２５％
冷延鋼板の硬度（230Hv以上）を確保する観点からはＣ量が高いほど有利であるが、０．２５％を超えると、熱延鋼板の炭化物の球状化と軟質化のための焼鈍処理を省略することができなくなる。一方０．１５％に満たないと、ATプレート用冷延鋼板に必要な硬度を確保することが困難となる。このためＣ量は０．１５〜０．２５％であることを要する。
The steel composition of the present invention is defined as follows. All element contents are mass%.
C: 0.15-0.25%
From the viewpoint of ensuring the hardness (230Hv or more) of the cold-rolled steel sheet, the higher the amount of C, the more advantageous. However, when it exceeds 0.25%, the annealing treatment for spheroidizing and softening the carbide of the hot-rolled steel sheet is performed. It can no longer be omitted. On the other hand, if it is less than 0.15%, it will be difficult to ensure the required hardness for the cold rolled steel sheet for AT plates. For this reason, the amount of C needs to be 0.15-0.25%.
Ｓｉ：０．２５％以下
Ｓｉは通常、鋼の溶製工程での脱酸剤として添加される。そのための添加量は０．２５％までで十分である。またそれを超えると熱延鋼板の酸洗処理性の低下、及び酸洗後のスケール残存による表面欠陥の発生原因ともなり、ＡＴプレート用素材としての表面品質の低下をきたすので、これを上限とする。
Si: 0.25% or less Si is usually added as a deoxidizer in the steel melting process. For this purpose, it is sufficient to add up to 0.25%. If it exceeds that, it will cause deterioration of pickling treatment of hot-rolled steel sheet and cause surface defects due to residual scale after pickling, which will cause deterioration of surface quality as a material for AT plates. To do.
Ｍｎ：０．３〜０．９％
Ｍｎは、鋼の熱間脆性の防止、及びマトリックスの強化のために添加される。０．３％に満たないとその効果が少なくマトリックスの強度が不足する。増量により効果を増すが、０．９％を超えると過度に硬質化し加工性が損なわれる。
Mn: 0.3 to 0.9%
Mn is added to prevent hot brittleness of the steel and strengthen the matrix. If it is less than 0.3%, the effect is small and the strength of the matrix is insufficient. The effect is increased by increasing the amount, but if it exceeds 0.9%, it becomes too hard and the workability is impaired.
Ｐ：０．０２０％以下
Ｐは、結晶粒界に偏析して粒界強度を低下させ、冷延鋼板の衝撃特性に大きな影響を及ぼす不純分である。
図１に冷延鋼板のシャルピー衝撃値（J/cm２）とＰ量の関係を示す（供試材は後記実施例欄の表1及び3に記載のNo.1-4及びNo.13,14）。Ｐ量の増加に伴う衝撃値の低下は大きく、Ｐ量が０．０２０％を超えると、ＡＴプレート用素材に望まれる衝撃値を確保し得なくなる。このためＰ量は０．０２０％を超えてはならず、より好ましくは０．０１５％以下に制限される。
P: 0.020% or less under
P is segregated in the grain boundaries to lower the grain boundary strength, Ru Oh big influence impurities to impact properties of cold-rolled steel sheet.
Charpy impact value of the cold-rolled steel sheet in FIG. 1 (J / cm 2) and shows the amount of P relationship (test specimen No.1 -4 and described in Table 1 and 3 of the Examples below column No.13, 14 ). The decrease in impact value accompanying an increase in the amount of P is large, and if the amount of P exceeds 0.020%, the desired impact value for the AT plate material cannot be secured. Therefore P content should not exceed 0.020%, and more preferably Ru is limited to 0.015% or less.
Ｓ：０．００５％以下
ＳはＭｎＳのＡ系介在物を形成する。Ａ系介在物は一般に加工により粘性変形して加工方向に細長い形態を呈する。このため、鋼板に局部的な応力集中が生じた場合に、割れの起点になり易く、衝撃特性を損なう要因となる。Ｓ量が０．００５％を越えると、衝撃特性に及ぼす影響が大きくなるので、これを上限とする。
S: 0.005% or less S forms A-based inclusions of MnS. In general, the A-type inclusions are viscously deformed by processing and have a shape elongated in the processing direction. For this reason, when local stress concentration occurs in the steel sheet, it tends to be a starting point of cracking, which is a factor that impairs impact characteristics. If the amount of S exceeds 0.005%, the impact on the impact characteristics increases, so this is the upper limit.
Ａｌ：０．０８％以下
Ａｌは鋼の溶製過程における脱酸剤として添加される。このための添加量は０．０８％までで十分である。またこれを超えると、鋼の清浄度が損なわれると共に表面疵が生じ易くなり製品鋼板の表面品質が低下するので、これを上限とする。本発明ではＳｉも脱酸剤としてはたらくので、Ａｌの下限量を規定する必要は特にないが、Ａｌは鋼中のＮをＡｌＮとして固定する作用を有し、このことは熱延鋼板のフェライト組織の細粒化に役立つ。このため好ましくは０．０２〜０．０８％とする。
Al: 0.08% or less Al is added as a deoxidizer in the melting process of steel. The addition amount for this is sufficient up to 0.08%. Moreover, since the cleanliness of steel will be impaired and surface flaws will occur easily and the surface quality of the product steel sheet will deteriorate if this value is exceeded, this is the upper limit. In the present invention, since Si also acts as a deoxidizer, it is not particularly necessary to define the lower limit amount of Al, but Al has the action of fixing N in the steel as AlN, which is the ferrite structure of the hot-rolled steel sheet. Useful for grain refinement. For this reason, it is preferably 0.02 to 0.08%.
Ｎ：０．００８％以下
Ｎは不可避的に混入する不純分元素であり、含有量が多くなると、窒化物（ＡｌＮ等）等の生成量が増加し、過度の硬質化を招くので、０．００８％以下に制限することを要する。
N: 0.008% or less N is an impure element mixed inevitably. If the content increases, the amount of nitride (AlN, etc. ) generated increases, leading to excessive hardening. It is necessary to limit it to 0.008% or less.
削除 Delete
削除 Delete
次に本発明の冷延鋼板の製造工程について説明する。
[鋼の溶製・鋳造]
まず製鋼炉で本発明に規定する化学組成を有する鋼を溶製し、造塊・分塊圧延または連続鋳造によりスラブとし、表面手入れを適宜実施した後、熱間圧延する。連続鋳造による場合、熱鋳片（スラブ）をそのまま加熱炉に装入して熱間圧延するようにしてもよい。
Next, the manufacturing process of the cold rolled steel sheet of the present invention will be described.
[Smelting and casting of steel]
First, a steel having a chemical composition defined in the present invention is melted in a steelmaking furnace, made into a slab by ingot-making / bundling rolling or continuous casting, surface-treated appropriately, and then hot-rolled. In the case of continuous casting, the hot slab (slab) may be inserted into a heating furnace as it is and rolled hot.
[熱間圧延]
熱間圧延は、熱延鋼板の品質及び熱延効率等の点から、熱延仕上げ温度はＡｒ３変態点直上に調整される。熱延鋼板の巻取りは５００〜６００℃の温度域で行なうことを要する。５００℃未満の低温巻取りでは、結晶粒径が過度に微細化して熱延鋼板の硬質化をきたし、一方６００℃を超える高温巻取りを行なうと、炭化物が凝集し易く、良好な打ち抜き加工性等を得るのに必要な炭化物の均一分散性（パーライト＋セメンタイト分率）、及び細粒化されたフェライト組織（フェライト粒径）の確保が困難となるからである。好ましくは５００〜５５０℃である。
[Hot rolling]
In hot rolling, the hot rolling finishing temperature is adjusted to be just above the Ar 3 transformation point from the viewpoint of the quality of the hot rolled steel sheet and the hot rolling efficiency. The hot-rolled steel sheet needs to be wound in a temperature range of 500 to 600 ° C. Low-temperature winding below 500 ° C causes the crystal grain size to become excessively fine and hardens the hot-rolled steel sheet. On the other hand, if high-temperature winding above 600 ° C is performed, carbides tend to agglomerate and good punching workability is achieved. This is because it is difficult to ensure the uniform dispersibility (perlite + cementite fraction) of the carbide necessary for obtaining the above and the like and the refined ferrite structure (ferrite particle size). Preferably it is 500-550 degreeC.
上記熱延鋼板は、結晶粒径（JIS G0552「附属書２(規定)交差線分(粒径)による判定方法」）が５〜２０μｍの範囲に細粒化されたフェライト組織であることを要する。前記下限粒径に満たない極微細のフェライト組織では鋼が過度の硬質化をきたし、他方上限粒径を超える粗い組織では、良好な衝撃特性を得ることが困難となるからである。 The hot-rolled steel sheet has a ferrite structure in which the crystal grain size (JIS G0552 “Appendix 2 (normative) Judgment method by crossing line segment (grain size)”) is refined to a range of 5 to 20 μm. Cost. This is because the steel is excessively hardened in an extremely fine ferrite structure that is less than the lower limit particle diameter, whereas it is difficult to obtain good impact characteristics in a coarse structure that exceeds the upper limit particle diameter.
熱延鋼板は、上記フェライト粒径の規定と併せ、炭化物の面積率の評価指標として、点算法により測定される「パーライト＋セメンタイト分率」の規定が付加される。ここに点算法とは、金属便覧（社団法人日本金属学会編,丸善(株)）改定６版所載の光学顕微鏡組織の定量解析法（第264頁）を指し、顕微鏡視野内にグリッドを置き、炭化物が占める格子点の総数をカウントし、グリッド格子点の総数に対する比として算定される。改良された衝撃特性を得るために、パーライト＋セメンタイト分率は２０％以上であることを要する。衝撃特性の観点からは上限の規定は特に必要としないが、６０％を超えると、硬度が不必要に高くなる場合があるので、これを超えないことが望ましい。 In addition to the above-mentioned definition of the ferrite grain size, the hot-rolled steel sheet is additionally provided with a “pearlite + cementite fraction” rule that is measured by the point calculation method as an evaluation index of the carbide area ratio. Here, the point calculation method refers to the quantitative analysis method (page 264) of the optical microscope structure described in the Metal Handbook (edited by the Japan Institute of Metals, Maruzen Co., Ltd.) Revised 6th edition. The total number of grid points occupied by carbides is counted and calculated as a ratio to the total number of grid grid points. To obtain improved impact properties, pearlite + cementite fraction requires that the 20% or more. The upper limit is not particularly required from the viewpoint of impact characteristics, but if it exceeds 60%, the hardness may become unnecessarily high, so it is desirable not to exceed this.
熱延鋼板におけるフェライト粒径及びパーライト＋セメンタイト分率で規定される均一微細組織は、前記Ｃ量の規定の効果として前記熱延条件により確保される。このようにフェライト粒が細粒化され、かつ炭化物が均一微細に分散した組織（熱延鋼板）とすることにより、ＡＴプレート用素材等として望まれる最終製品（冷延鋼板）の衝撃特性を一段と高めることが可能となる。 Uniform microstructure defined by ferrite grain size and pearlite + cementite fraction in hot rolled steel sheet is ensured by the hot-rolled condition as provisions of the effect of the C amount. In this way, the ferrite particles are refined and the carbide is uniformly and finely dispersed (hot-rolled steel plate), thereby further improving the impact characteristics of the final product (cold-rolled steel plate) desired as a material for AT plates. It becomes possible to raise.
[冷間圧延]
熱延鋼板は、酸洗処理で表面のスケールを除去された後、冷間圧延に付される。冷間圧延における圧下率は５０％以上であることを要する。これは、ＡＴプレート用冷延鋼板等として必要な硬度（Hv≧230）及び表面粗さ（Ra≦0.4μm）を得るためである。なお、硬さ（Hv）は、望ましくは240〜280Hvである。240Hvに満たないと、スペック下限に近くＡＴプレートの機能の安定性の面で得策でなく、他方280Hvを超えるとＡＴプレートのプレス打ち抜きの作業負担が大きくなるからである。この硬さの調節は、圧下率の調整により行なわれる。また冷間圧延では、所要の表面粗さが確保されるように、圧延ロールの表面粗度管理が適宜実施される。
[Cold rolling]
The hot-rolled steel sheet is subjected to cold rolling after the surface scale is removed by pickling treatment. The rolling reduction in cold rolling needs to be 50% or more. This is to obtain the hardness (Hv ≧ 230) and surface roughness (Ra ≦ 0.4 μm) required for cold rolled steel sheets for AT plates. The hardness (Hv) is desirably 240 to 280 Hv. If it is less than 240 Hv, it is close to the lower specification limit, and it is not a good idea in terms of the stability of the function of the AT plate. On the other hand, if it exceeds 280 Hv, the work burden of stamping the AT plate increases. The hardness is adjusted by adjusting the rolling reduction. In cold rolling, the surface roughness of the rolling roll is appropriately controlled so as to ensure the required surface roughness.
冷間圧延は、酸洗処理前のプレ圧延と処理後の仕上げ圧延との２段階に分けて実施することもできる。プレ圧延（酸洗処理前）によるスケールの破砕効果として脱スケール性が大きく改善され、酸洗処理時間の大幅な短縮とコスト低減が可能となる。この場合、プレ圧延（酸洗処理前）と仕上げ圧延（酸洗処理後）とは連続しなくても構わないが、酸洗槽の入側にプレ圧延機を、出側に仕上げ圧延機をそれぞれ設置し、プレ圧延-酸洗処理-仕上げ圧延の連続構成とすることが生産効率の面から有利である。 Cold rolling can also be carried out in two stages: pre-rolling before pickling treatment and finish rolling after treatment. As a scale crushing effect by pre-rolling (before pickling treatment), the descaling property is greatly improved, and the pickling treatment time can be greatly shortened and the cost can be reduced. In this case, pre-rolling (before pickling treatment) and finish rolling (after pickling treatment) may not be continuous, but a pre-rolling machine is provided on the entry side of the pickling tank and a finish rolling mill is provided on the exit side. It is advantageous from the standpoint of production efficiency that each is installed and has a pre-rolling-pickling treatment-finish rolling continuous configuration.
上記２段階の冷間圧延におけるプレ圧延（酸洗処理前）は、圧下率を２５％以下に抑えるのが好ましい。これを超える高い圧下率でプレ圧延すると、スケールの鋼板表面への押込みによる疵が発生し表面品質を損なうおそれがあるからである。仕上げ圧延（酸洗処理後）における圧下率は、全圧下率（=プレ圧延の圧下率＋仕上げ圧延の圧下率）が５０％以上となるように設定される。全圧下率をこのように調整するのは、前記の場合（冷間圧延を酸洗後の１段階で実施）と同じように、ＡＴプレート用素材等の要求特性（硬さ：Hv≧230,表面粗さ：Ra≦0.4μｍ）を充足させるためである。 In the pre-rolling (before the pickling treatment) in the two-stage cold rolling, the rolling reduction is preferably suppressed to 25% or less. This is because if pre-rolling is performed at a high rolling reduction exceeding this range, wrinkles due to the pressing of the scale onto the steel sheet surface may occur, and the surface quality may be impaired. The reduction ratio in finish rolling (after pickling treatment) is set so that the total reduction ratio (= pre-rolling reduction ratio + finishing rolling reduction ratio) is 50% or more. The total reduction ratio is adjusted in this manner, as in the case described above (cold rolling is performed in one stage after pickling), and the required characteristics of the AT plate material (hardness: Hv ≧ 230, This is because the surface roughness: Ra ≦ 0.4 μm is satisfied.
[脱脂・精整]
冷間圧延の後、脱脂処理（電解洗浄等）により鋼板表面を浄化し、ついで所定の検査（板厚・板幅等の諸元寸法,表面疵等）及び形状修正等のための精整工程を経て製品冷延鋼板を得る。これらの処理工程は常法に従って行なえばよい。
[Degreasing and refining]
After cold rolling, the steel sheet surface is purified by degreasing (electrolytic cleaning, etc.), and then a specified inspection (special dimensions such as plate thickness and width, surface flaws, etc.) and refining process for shape correction, etc. The product cold-rolled steel sheet is obtained. These treatment steps may be performed according to ordinary methods.
こうして得られる本発明の冷延鋼板を、自動車用ＡＴプレート素材等として適用する場合は、プレス打ち抜き加工を行なって所要の円環形状に成形すればよく、得られた成形品は調質のための熱処理を特に必要とせず、そのまま(硬引き材のまま)、ＡＴプレートとして実機使用に供することができる。 When the cold-rolled steel sheet of the present invention thus obtained is applied as an AT plate material for automobiles, etc., it may be formed into a required annular shape by performing press punching, and the resulting molded product is tempered. This heat treatment is not particularly required and can be used as it is (as a hard-drawn material) as an AT plate.
[１]供試鋼板の製造
転炉及び脱ガス処理装置により溶製・成分調整を行なった溶鋼を連続鋳造に付してスラブ（200ｍｍ厚）とし、下記のＡ工程（焼鈍省略）又はＢ工程（焼鈍実施）によりＡＴプレート用冷延鋼板を得る。
Ａ：熱延→酸洗→冷延(１段又は2段圧延)→脱脂→精整（検査）
Ｂ：熱延→酸洗→焼鈍→冷延(1段圧延)→脱脂→精整（検査）
[1] Manufacture of test steel sheet The molten steel, which has been melted and adjusted by a converter and degassing equipment, is subjected to continuous casting to form a slab (200 mm thick), and the following process A (annealing omitted) or process B A cold-rolled steel sheet for AT plates is obtained by (annealing).
A: Hot rolling → Pickling → Cold rolling (1 or 2 rolling) → Degreasing → Refinement (inspection)
B: Hot rolling → Pickling → Annealing → Cold rolling (1 step rolling) → Degreasing → Refinement (inspection)
(1)供試材
表１〜表４。No.1〜４は発明材、No.13,14（比較例イ）は本発明に類似の鋼組成を有しているが、P含有量が本発明の規定から外れている例、No.26-35（比較例ハ）は従来材（S35C相当材）である。
(1) Test materials Tables 1 to 4. Nos. 1 to 4 are invention materials, Nos. 13 and 14 (Comparative Example A) have a steel composition similar to that of the present invention, but the P content is not within the scope of the present invention , No. 26-35 (Comparative Example C) is a conventional material (S35C equivalent material).
(2)熱間圧延
No.1〜４（発明例）及びNo.13,14（比較例イ）
加熱温度：1230℃,熱延仕上温度：880℃,巻取温度：540℃
熱延板の板厚：4.0〜5.5ｍｍ
No.26〜35（比較例ハ）
加熱温度：1230℃,熱延仕上温度：860℃,巻取温度：600℃
熱延板の板厚：4.0ｍｍ
(2) Hot rolling
No. 1 to 4 (Invention Example) and No. 13,14 (Comparative Example A)
Heating temperature: 1230 ° C, hot rolling finishing temperature: 880 ° C, coiling temperature: 540 ° C
Thickness of hot rolled sheet: 4.0~5.5m m
No. 26-35 (Comparative example C)
Heating temperature: 1230 ° C, hot rolling finishing temperature: 860 ° C, winding temperature: 600 ° C
Thickness of hot-rolled sheet: 4.0mm
(3)焼鈍処理
No.26〜35（比較例ハ=S35C材）において実施（No.1-4,13,14は焼鈍なし）。
焼鈍方式：タイトコイル焼鈍（TCA）
処理温度・時間：700℃・10Ｈｒ
(3) Annealing treatment
Conducted in Nos. 26 to 35 (Comparative Example C = S35C material) (Nos. 1-4, 13, and 14 were not annealed).
Annealing method: Tight coil annealing (TCA)
Processing temperature / time: 700 ℃ ・ 10Hr
(4)冷間圧延
圧下率（２段圧延の場合は合計圧下率）
No.1-4,13-14 ：６７％
No.26-35 ：５５％
製品鋼板厚さ：1.8ｍｍ
(5)脱脂
電解洗浄（処理液：オルソ珪酸ソーダ）
(4) Cold rolling reduction ratio (total reduction ratio in the case of two-stage rolling)
No.1-4,13-14: 67 %
No .26-35: 55%
Product steel plate thickness: 1.8mm
(5) Degreasing Electrolytic cleaning (treatment liquid: sodium orthosilicate)
［２］衝撃試験
JIS Z2242「金属材料衝撃試験方法」に準拠し下記条件で行なった。
(1)試験装置
試験機：50Jシャルピー衝撃試験機／（株）米倉製作所製
秤 量：５０Ｊ
日本海事協会認定機：2002年11月12日
(2)試験片の調製
試験片サイズ：厚さ1.8×幅10×長さ55 (mm)
サンプル採取：圧延方向（L方向）
ノッチ形状 ：２mmＵノッチ
ノッチ方向 ：圧延直角方向（C方向）
(3)試験温度 室温（22℃）
[2] Impact test
The test was conducted under the following conditions in accordance with JIS Z2242 “Metal material impact test method”.
(1) Test equipment Test machine: 50J Charpy impact tester / manufactured by Yonekura Seisakusho Weighing: 50J
Japan Maritime Association Certified Machine: November 12, 2002
(2) Preparation of test piece Test piece size: thickness 1.8 x width 10 x length 55 (mm)
Sample collection: rolling direction (L direction)
Notch shape: 2 mm U notch Notch direction: Direction perpendicular to rolling (C direction)
(3) Test temperature Room temperature (22 ℃)
図１は発明材No.1-４及び比較材No.13,14について、Ｐ量とシャルピー衝撃値（Ｊ/cm２）の関係を示している（比較材No.13,14はＰ量が本発明の上限規定から外れているほかは本発明の規定を満たしている供試材である）。グラフａは、Ｐ量の上限規定により良好な衝撃特性が得られることを示している。 FIG. 1 shows the relationship between the amount of P and the Charpy impact value (J / cm 2 ) for invention materials No. 1 to 4 and comparative materials No. 13 and 14 (comparative materials No. 13 and 14 have a P amount). It is a test material that satisfies the provisions of the present invention except that it deviates from the upper limit of the present invention). Graph a shows that good impact characteristics can be obtained by defining the upper limit of the P amount.
図３は発明材No.１の衝撃試験片の破面を示している（SEM像,倍率×1000）。図における[I]は衝撃試験片の破断方向中央部（ノッチ側と最終破断側との中間位置）、[II]は最終破断側である（図２参照）。図３の破面は、所謂ディンプル・パターンを呈し、その衝撃破壊は、延性破壊であって、脆性破壊ではないことを示している。 Figure 3 shows the fracture surface of the impact test piece of invention material No.1 (SEM image, magnification × 1000). In the figure , [I] is the central part in the direction of fracture of the impact test piece (intermediate position between the notch side and the final fracture side), and [II] is the final fracture side (see FIG. 2). The fracture surface in FIG. 3 exhibits a so-called dimple pattern, indicating that the impact fracture is a ductile fracture and not a brittle fracture.
図４は発明材No.１、図５は比較材No.26（S35C材）について、それぞれの冷延鋼板の金属組織（倍率×400）を示している。発明材No.1（図４）は焼鈍工程が省略されているにも拘わらず、炭化物（Fe３C）が均一微細に分散し、従来材No.26（焼鈍実施のS35C材）（図５）と同等ないしほぼそれに準ずる細粒化された微細均質な組織を有している。 FIG. 4 shows the metal structure (magnification × 400) of each cold-rolled steel sheet for Invention Material No. 1 and FIG. 5 for Comparative Material No. 26 (S35C material). Inventive material No. 1 (FIG. 4), although the annealing process is omitted, carbide (Fe 3 C) is uniformly and finely dispersed, and conventional material No. 26 (S35C material subjected to annealing) (FIG. 5 ) ) through equivalent to that we have a fine homogeneous structure which is comminuted substantially analogous thereto.
表３及び表４に、熱延鋼板のフェライト粒径(μｍ),パーライト＋セメンタイト分率（％）、冷延鋼板の硬さＨＶ（測定荷重：98Ｎ）,表面粗度Ｒａ及び衝撃試験結果等を製造条件と共に示す。発明例（No.1-４）は、ＡＴプレート用冷延鋼板として要求される硬さ及び表面粗度スペック（硬さ：Ｈｖ≧230,表面粗さＲａ≦0.4μｍ）を十分に満たすと共に、従来材のS35C（No.26-35）（表４）と同等ないしそれを超える衝撃特性を具備している。これらの諸特性は、前記した鋼の化学組成と細粒化された均質微細な組織に基づくものである。 Table 3 and Table 4 show the ferrite grain size (μm), pearlite + cementite fraction (%), cold rolled steel sheet hardness H V (measuring load: 98 N), surface roughness Ra, and impact test results. Etc. are shown together with manufacturing conditions. The invention example (No. 1-4 ) sufficiently satisfies the hardness and surface roughness specifications (hardness: Hv ≧ 230, surface roughness Ra ≦ 0.4 μm) required as a cold rolled steel sheet for AT plates, It has impact characteristics equivalent to or better than the conventional material S35C (No.26-35) (Table 4). These properties are based on the chemical composition of the steel described above and the fine, fine and fine structure.
なお、比較例No.13,14をみると、衝撃値はS35C(比較例ハ)より劣っている。
No.13,14（Ｐ量過剰）の衝撃値が低いのは、フェライト粒界にＰの偏析が生じ、粒界強度が低下したことによる。
このように比較例イ、ハはいずれも発明例の改良された衝撃特性及びその他の材料特性に及ばない。
Incidentally, when viewing the comparative example No. 13, 14, opposition撃値is inferior S35C (Comparative Example C).
The reason why the impact values of Nos . 13 and 14 (excess P amount) are low is that the segregation of P occurs at the ferrite grain boundary and the grain boundary strength is lowered .
Comparative Reii as this, Ha both fall short in improved impact properties and other material properties of the inventive example.
本発明によれば、自動車のＡＴプレート用冷延鋼板の製造工程において従来不可欠とされてきた焼鈍処理が不要となり、製造コストを大幅に削減しながら、ＡＴプレート用素材等として要求される硬さ、表面性状等と共に、良好な衝撃特性を備えた冷延鋼板を得ることができる。また、熱延鋼板の冷間圧延を酸洗処理の前後に実施する二段階圧延により酸洗処理の負荷が大幅に軽減され一段と低コスト化効果が得られる。しかも、これを打ち抜き加工して得られるＡＴプレートは、調質のための熱処理を必要とせず、そのまま（硬引き材のまま）実機使用に供することができる。従って本発明は、近時の小型大衆車ＮＢＣの開発動向等に関連するオートマチックトランスミッションの低価格化の要請に対処し得るものである。
なお、本発明の冷延鋼板は、上記ＡＴプレート用途のみらなず、これと同じように打ち抜き加工性や硬度、表面粗度及び衝撃特性等を要求される各種分野の素材として広く適用され、品質の安定、コスト削減等の効果をもたらすものである。
According to the present invention, the annealing process, which has conventionally been indispensable in the manufacturing process of a cold rolled steel sheet for an AT plate of an automobile, is unnecessary, and the hardness required as a material for an AT plate or the like while greatly reducing the manufacturing cost. A cold-rolled steel sheet having good impact characteristics as well as surface properties can be obtained. Moreover, the load of the pickling treatment is greatly reduced by the two-stage rolling in which the cold rolling of the hot-rolled steel sheet is performed before and after the pickling treatment, and the cost can be further reduced. In addition, the AT plate obtained by punching it does not require heat treatment for tempering and can be used as it is (as a hard-drawn material) for actual use. Therefore, the present invention can cope with a request for a reduction in the price of an automatic transmission related to the recent development trend of a small-sized popular car NBC.
In addition, the cold-rolled steel sheet of the present invention is widely applied not only to the above AT plate application, but also widely used as a material in various fields that require punching workability, hardness, surface roughness, impact characteristics, etc. It brings about effects such as quality stability and cost reduction.
Claims (2)
In mass%, C: 0.15 to 0.25%, Si: 0.25% or less, Mn: 0.3 to 0.9%, P: 0.020% or less, S: 0.005% or less, Al: 0.08% or less, N: 0.008% or less, and the remainder is hot-rolled at a coiling temperature of 500 to 600 ° C. just above the hot rolling finishing temperature Ar 3 transformation point , with the slab consisting of Fe and inevitable impurities. From this, a hot rolled steel sheet having a pearlite + cementite fraction of 20% or more and a ferrite particle size of 5 to 20 μm is obtained, and after the pickling treatment, it is cold-rolled at a reduction rate of 50% or more without annealing. A method for producing a cold-rolled steel sheet having excellent impact characteristics .
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN101956126A (en) * | 2010-09-30 | 2011-01-26 | 河北钢铁股份有限公司邯郸分公司 | Cold-base high-strength galvanized sheet and production method thereof |
| CN104018062A (en) * | 2014-06-18 | 2014-09-03 | 内蒙古包钢钢联股份有限公司 | Low-alloy and high-strength Q390C medium plate and production method thereof |
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| DE102006001628A1 (en) * | 2006-01-11 | 2007-07-26 | Thyssenkrupp Steel Ag | Galvanized hard-rolled cold-rolled flat product and process for its preparation |
| JP5070824B2 (en) * | 2006-11-30 | 2012-11-14 | Ｊｆｅスチール株式会社 | Cold-rolled steel sheet excellent in flatness and end face properties after punching and method for producing the same |
| JP4858286B2 (en) * | 2007-04-20 | 2012-01-18 | 住友金属工業株式会社 | Full hard cold rolled steel sheet |
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| JP5618431B2 (en) | 2013-01-31 | 2014-11-05 | 日新製鋼株式会社 | Cold rolled steel sheet and method for producing the same |
| CN103993228B (en) * | 2014-05-19 | 2016-05-18 | 攀钢集团攀枝花钢铁研究院有限公司 | Cold-rolled steel sheet and preparation method thereof and hot-dip galvanizing sheet steel and preparation method thereof |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101956126A (en) * | 2010-09-30 | 2011-01-26 | 河北钢铁股份有限公司邯郸分公司 | Cold-base high-strength galvanized sheet and production method thereof |
| CN104018062A (en) * | 2014-06-18 | 2014-09-03 | 内蒙古包钢钢联股份有限公司 | Low-alloy and high-strength Q390C medium plate and production method thereof |
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