JP2002263771A - Constant-strain steel manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a constant-strain steel capable of suppressing the product strain after the heat treatment by increasing the draft to decrease the strain difference between the inside and the outside of a product macro pattern after heat-treating the product after cold forging while fully utilizing the center segregation suppression effect that the positive segregation and negative segregation in the vicinity of the final solidification position are small by a cast slab of rectangular section. SOLUTION: The cast slab cast in a rectangular mold with the outline aspect ratio of at least 1.2 is hot forged in the pass schedule for performing the rolling- down from the short side by the strong rolling-down pass of the draft >=24% shown in Fig. 1, and after the finish rolling, the constant-strain steel capable of suppressing the pattern aspect ratio of the product macro pattern to <=1.4.

Description

【発明の詳細な説明】DETAILED DESCRIPTION OF THE INVENTION

【０００１】[0001]

【発明の属する技術分野】自動車部品のＣＶＪなど、精
密冷間鍛造により仕上げし、その後研磨を行わない部品
の製造に使用するための定ひずみ鋼に関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a constant strain steel, such as CVJ for automobile parts, which is finished by precision cold forging and then used for manufacturing parts which are not subjected to polishing.

【０００２】[0002]

【従来の技術】自動車部品のＣＶＪなどは、省工程化に
よるコストの削減のため、精密冷間鍛造により仕上げる
ことで、その後の研磨を行わなくしている。このために
冷鍛加工に供する鋼の矩形断面を有するインゴット材あ
るいは連鋳片においては、それらの鋳鋼材のマクロパタ
ーンの内部と外部とで初期凝固組織が異なるため、熱処
理後の製品ひずみに、例えば内外で０．０２％異なると
いうバラツキが発生する大きな問題がある。このパター
ン内外のひずみ差が冷鍛後仕上げ研磨または切削を行わ
ない部品には大きな問題がある。これに対して、連鋳片
の断面形状を中径の丸形連鋳片としたり正方形連鋳片と
することも考えられるが、設備を新設あるいは改造する
ことによるコストアップをもたらす。さらに、鋳込み時
の形状による中心偏析悪化の問題がある。すなわち、最
終凝固位置付近の正偏析及び負偏析が矩形断面の鋳片に
比して、丸形の方が大きいという知見がある。中径の丸
形鋳片あるいは正方形鋳片からでは圧鍛比が低くなり組
織の微細化および均一化が不十分となる問題があった。2. Description of the Related Art CVJs of automobile parts are finished by precision cold forging in order to reduce costs by saving steps, so that subsequent polishing is not performed. For this reason, in the ingot material or continuous cast piece having a rectangular cross section of steel subjected to cold forging, since the initial solidification structure differs between the inside and outside of the macro pattern of those cast steel materials, the product strain after heat treatment, For example, there is a large problem that a variation of 0.02% between inside and outside occurs. The difference in strain between the inside and outside of the pattern has a serious problem in a component that is not subjected to finish polishing or cutting after cold forging. On the other hand, it is conceivable that the cross-sectional shape of the continuous cast piece is a round continuous cast piece having a medium diameter or a square continuous cast piece, but the cost is increased by newly installing or modifying the equipment. Furthermore, there is a problem that the center segregation is deteriorated due to the shape at the time of casting. That is, there is a finding that the round shape is larger in the positive segregation and the negative segregation near the final solidification position than the slab having the rectangular cross section. From a medium-diameter round slab or square slab, there is a problem that the forging ratio is low and the microstructure and uniformity of the structure are insufficient.

【０００３】[0003]

【発明が解決しようとする課題】本発明が解決しようと
する課題は、矩形断面形状の鋳片をそのまま採用するこ
とで、最終凝固位置付近の正偏析及び負偏析が小さいと
いう中心偏析抑制効果を最大限に利用しながら、さらに
圧鍛比を大きくすることで製品のマクロパターンの内外
のひずみ差を小さくすることで品質向上を図りうるとい
う、矩形断面の鋳片の利点を活かしつつ、かつ、熱処理
後の製品ひずみを抑制することの可能な鋼材の製造方法
を提供することである。The problem to be solved by the present invention is to use a cast slab having a rectangular cross-sectional shape as it is to reduce the effect of suppressing central segregation in which positive segregation and negative segregation near the final solidification position are small. While taking full advantage of the advantage of the rectangular cross-section slab, it is possible to improve the quality by reducing the difference in strain between the inside and outside of the macro pattern of the product by further increasing the forging ratio while using to the maximum, and An object of the present invention is to provide a method for manufacturing a steel material capable of suppressing product distortion after heat treatment.

【０００４】[0004]

【課題を解決するための手段】上記の課題を解決するた
めの本発明の手段は、請求項１の発明では、外形縦横比
１．２以上の矩形鋳型にて鋳造した鋳片を、インライン
プレスを含む鍛造機で、矩形鋳片の短辺側から１パスあ
たりの圧下率２４％以上の高圧下パスを含むパススケジ
ュールを用いて熱間鍛造することにより製品のマクロパ
ターンのパターン縦横比を１．４以下に抑制することを
特徴とする定ひずみ鋼の製造方法である。According to the first aspect of the present invention, a slab cast in a rectangular mold having an outer aspect ratio of 1.2 or more is formed by an in-line press. Hot forging using a pass schedule that includes a high pressure reduction pass of 24% or more per pass from the short side of the rectangular slab with a forging machine including a rectangular slab, thereby setting the pattern aspect ratio of the macro pattern of the product to 1 A method for producing a constant strain steel, characterized in that the strain is suppressed to 0.4 or less.

【０００５】上記手段の作用を説明すると、矩形鋳型の
外形縦横比１．２以上とするのは、１．２以下の外径縦
横比の場合、初期凝固パターンの縦横比が１．４を下回
るので本手段による熱間鍛造を行わなくても熱処理後の
製品マクロパターンのパターン縦横比のｘｙ変位差の小
さい定ひずみ鋼が製造できるからである。To explain the operation of the above means, the reason why the outer shape aspect ratio of the rectangular mold is set to 1.2 or more is that the aspect ratio of the initial solidification pattern is less than 1.4 when the outer diameter aspect ratio is 1.2 or less. Therefore, a constant strain steel having a small xy displacement difference in the pattern aspect ratio of the product macro pattern after the heat treatment can be manufactured without performing hot forging by this means.

【０００６】さらに、矩形鋳片の短辺側から１パスあた
りの圧下率２４％以上の高圧下パスを含むパススケジュ
ールにより熱間により熱間鍛造する理由は次による。先
ず、図１の（ａ）、（ｂ）にわかり易くするために分け
て、圧下率による鋳片の変形挙動の違いを示す。（ａ）
は圧下前、１０％圧下、１５％圧下、２０％圧下を示
し、（ｂ）は、繰り返して圧下前、２０％圧下を繰り返
し示すとともに、さらに３０％圧下、４０％圧下を示
す。以上の図１の圧下率による変形挙動の違いからわか
るように、短辺側から１パス当たり圧下率２４％以上の
強圧下パスを掛けることにより、鋳片の中心に圧下が掛
かり、より少ないパス回数により中心の膨らみによる形
状改善効果が現われてくることによる。Further, the reason why hot forging is performed by a hot process according to a pass schedule including a high-pressure reduction pass having a reduction ratio of 24% or more per pass from the short side of the rectangular cast piece is as follows. First, FIGS. 1A and 1B separately show the difference in the deformation behavior of the cast slab depending on the rolling reduction, for easy understanding. (A)
Indicates the 10% reduction, 15% reduction, and 20% reduction before reduction, and (b) indicates the reduction before and 20% reduction repeatedly, and further indicates the 30% reduction and 40% reduction. As can be seen from the difference in the deformation behavior depending on the reduction ratio in FIG. 1 described above, by applying a strong reduction pass with a reduction ratio of 24% or more per pass from the short side, a reduction is applied to the center of the slab, and a smaller number of passes is performed. This is because the shape improvement effect due to the center bulge appears depending on the number of times.

【０００７】製品のパターンの縦横比を１．４以下に抑
制する理由は次の理由による。先ず、図２に示すパター
ン部を含むＯリング試験を行う。このときパターン縦横
比、例えば、図２の（ａ）は１．０、（ｂ）は１．５、
（ｃ）は２．０に示すように、それぞれパターン縦横比
を細かく変えて、図３に示す縦、横の変位をそれぞれｄ
ｙ、ｄｘとしてＯリング試験を行う。このときのｘｙ変
位差ｄｘ−ｄｙとパターン縦横比の関係を図４にグラフ
で示す。この図４からパターン縦横比が１．４以下の場
合には、ｘｙ変位差ｄｘ−ｄｙが０．７以下に急激に小
さくなる。このことからパターン縦横比が１．４以下に
なると定ひずみ効果が得られることが判明した。パター
ン縦横比１．５以上の場合では、定ひずみ領域が長辺側
に広がって偏りすぎてしまい、不適当と考えられる。The reason why the aspect ratio of the product pattern is suppressed to 1.4 or less is as follows. First, an O-ring test including the pattern portion shown in FIG. 2 is performed. At this time, the pattern aspect ratio, for example, (a) of FIG. 2 is 1.0, (b) is 1.5,
FIG. 3C shows that the vertical and horizontal displacements shown in FIG.
An O-ring test is performed as y and dx. FIG. 4 is a graph showing the relationship between the xy displacement difference dx-dy and the pattern aspect ratio at this time. From FIG. 4, when the pattern aspect ratio is 1.4 or less, the xy displacement difference dx-dy sharply decreases to 0.7 or less. From this, it was found that the constant distortion effect was obtained when the pattern aspect ratio was 1.4 or less. When the pattern aspect ratio is 1.5 or more, the constant strain region spreads to the long side and is excessively biased, which is considered inappropriate.

【０００８】[0008]

【発明の実施の形態】本発明の実施の形態を以下の実施
例を通じて示す。連続鋳造による冷鍛用鋼の縦横比１．
２以上の矩形ブルーム、例えば形状４９０ｍｍ×３８０
ｍｍ、縦横比１．２９を、短辺側から１パス当たり圧下
率２４％以上の強圧下パスを含むパススケジュールで圧
下して熱間鍛造する。その後特殊なパススケジュールを
用いることなく、得られた鋳片あるいは鍛片は、さら
に、圧延あるいは鍛造、例えば３ロール・プラネタリー
・ミル（以下、「ＰＳＷ」という。）により冷鍛用の丸
棒に仕上げ圧延する。この丸棒から冷間鍛造により自動
車部品のＣＶＪ等の製品にするとき、熱処理後の製品の
マクロパターンのパターン縦横比は１．４以下のものが
得られ、内部のパターン形状を正方形に近づけることで
熱処理ひずみが均一な定ひずみの冷鍛製品が得られる。DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described through the following examples. Aspect ratio of steel for cold forging by continuous casting
Two or more rectangular blooms, for example, shape 490 mm × 380
mm and an aspect ratio of 1.29 are hot-forged by rolling from the short side by a pass schedule including a strong rolling pass with a rolling reduction of 24% or more per pass. Thereafter, without using a special pass schedule, the obtained cast or forged piece is further rolled or forged, for example, by a three-roll planetary mill (hereinafter, referred to as “PSW”) for a round bar for cold forging. Finish rolling. When cold forging this product into a product such as CVJ for an automobile part, the macro-pattern of the product after heat treatment has a pattern aspect ratio of 1.4 or less, and the internal pattern shape should be close to a square. Thus, a cold forged product having a constant strain with a uniform heat treatment strain can be obtained.

【０００９】[0009]

【実施例】連続鋳造による冷鍛用鋼ＳＣＲ４２０Ｈの形
状４９０ｍｍ×３８０ｍｍ、縦横比１．２９の矩形ブル
ームを表１に示す改良パスパターンにより熱間鍛造を行
う。表1に示すように、パス１は短辺側から圧下量１２
０ｍｍ、すなわち圧下率２４．５％の強圧下で圧鍛す
る。次いで、鋳片を反時計回りに９０度回転してパス２
は圧下量１０ｍｍで圧鍛し、さらに反時計回りに９０度
回転してパス３は圧下量１０ｍｍで圧鍛し、さらに反時
計回りに９０度回転してパス４は圧下量５ｍｍで圧鍛し
て、３７０ｍｍ×４３０ｍｍの鍛片とした。この結果、
最終パスを行った鋳片の縦横比１．１６であった。な
お、表１に示すようにこの改良パスパターンによる本実
施例では、パス１のみが圧下率２４．５％以上の強圧下
であり、非常に少ない回数のパススケジュールで冷鍛用
の定ひずみ鋼材が得られた。すなわち、この冷鍛用鋼材
により冷鍛加工し、熱処理した製品は、熱処理後の製品
のマクロパターンのパターン縦横比が１．３であった。EXAMPLE A hot forging is performed on a rectangular bloom having a shape of 490 mm × 380 mm and an aspect ratio of 1.29 of a cold forging steel SCR420H by continuous casting according to the improved pass pattern shown in Table 1. As shown in Table 1, the pass 1 has a rolling reduction of 12 from the short side.
The forging is performed at 0 mm, that is, under a strong pressure of 24.5%. Then, the slab is rotated 90 degrees counterclockwise to pass 2
Is forged with a reduction amount of 10 mm, further rotated 90 degrees counterclockwise, and pass 3 is forged with a reduction amount of 10 mm, and further rotated 90 degrees counterclockwise, and path 4 is forged with a reduction amount of 5 mm. Into a forged piece of 370 mm × 430 mm. As a result,
The aspect ratio of the slab subjected to the final pass was 1.16. In addition, as shown in Table 1, in this embodiment using this improved pass pattern, only pass 1 was subjected to a strong reduction with a rolling reduction of 24.5% or more, and a constant strain steel material for cold forging was produced with a very small number of pass schedules. was gotten. That is, in the product that was cold forged with this steel material for cold forging and heat treated, the pattern aspect ratio of the macro pattern of the product after the heat treatment was 1.3.

【００１０】[0010]

【表１】 [Table 1]

【００１１】比較例として表２に従来のパススケジュー
ルにより、表１と同じ４９０ｍｍ×３８０ｍｍ、縦横比
１．２９の矩形ブルームを熱間鍛造した。この場合、パ
ス１は長辺側から圧鍛し、圧下量８０ｍｍで、圧下率は
２１．０％であった。パス２は反時計周りに９０度回転
して短辺側から圧下量８０ｍｍで圧鍛し、続いてそのま
までパス３で短辺側から圧下量３０ｍｍで圧鍛し、パス
４で再び反時計周りに９０度回転して圧下量４０ｍｍで
圧鍛し、パス５で再び反時計周りに９０度回転して圧下
量２０ｍｍで圧鍛する。この従来のパススケジュールに
よるものは、パス回数が上記の本発明の実施例の改良パ
ススケジュールによるものよりも多い。この比較例で得
られた鍛片から、冷間鍛造して得られた製品は、その熱
処理後の製品マクロパターンのパターン縦横比が１．５
以上と大きく、ひずみに縦横でばらつきが認められた。As a comparative example, a rectangular bloom having the same 490 mm × 380 mm and an aspect ratio of 1.29 as in Table 1 was hot forged by the conventional pass schedule shown in Table 2. In this case, the pass 1 was forged from the long side, the amount of reduction was 80 mm, and the reduction was 21.0%. Pass 2 is rotated counterclockwise by 90 degrees and forged from the short side with a reduction amount of 80 mm, then as it is, pass 3 is forged with a reduction amount of 30 mm from the short side, and pass 4 is again counterclockwise. Then, forging is performed at a reduction amount of 40 mm by rotating 90 °, and is again rotated counterclockwise by 90 degrees at pass 5 and forging is performed at a reduction amount of 20 mm. According to the conventional pass schedule, the number of passes is larger than that according to the improved pass schedule of the embodiment of the present invention. The product obtained by cold forging from the forged piece obtained in this comparative example has a pattern aspect ratio of the product macro pattern after heat treatment of 1.5.
As described above, the strain was varied vertically and horizontally.

【００１２】[0012]

【表２】 [Table 2]

【００１３】本発明の実施例である改良パススケジュー
ルによる場合の熱処理後の製品ひずみは１．３に抑制さ
れている。すなわち、Ｏリング試験の図４に示す関係か
ら、ｘｙ変位差が０．３以下の定ひずみ鋼であることが
わかる。これに対し、従来のパススケジュールによるも
のは、一見したところ最終パスの長辺の縦横比は本実施
例と異なるところはないが、短辺側からの強圧下の効果
が解消されているため、熱処理後の製品ひずみのｘｙ変
位差が大きくあり、定ひずみ鋼とされていない。The product strain after the heat treatment in the case of the improved pass schedule according to the embodiment of the present invention is suppressed to 1.3. That is, from the relationship shown in FIG. 4 in the O-ring test, it is understood that the steel is a constant strain steel having an xy displacement difference of 0.3 or less. On the other hand, according to the conventional path schedule, at first glance, the aspect ratio of the long side of the final path is not different from that of the present embodiment, but the effect of the strong compression from the short side has been eliminated. The xy displacement difference of the product strain after heat treatment is large, and it is not a constant strain steel.

【００１４】[0014]

【発明の効果】以上説明したように、本発明におけるパ
ススケジュールとして熱間鍛造することで、少ないパス
スケジュールで効率良く、熱処理後の製品のマクロパタ
ーンの内部パターンを正方形に近づけることができる、
全体の熱処理ひずみが均一な定ひずみ鋼が得られ、熱処
理後の製品の形状ばらつきを抑えることができ、連続鋳
造設備を新設したり、改変したりする必要がなく、矩形
鋳片の設備を使用することができるので、コストを格別
増大することなく実施でき、かつ、矩形ブルームの特徴
である最終凝固位置付近の正偏析及び負偏析の小さな優
れた点を維持することができるなど、本発明は自動車部
品のＣＶＪなど、精密冷間鍛造により仕上げし、その後
研磨を行わない部品の製造に使用するための定ひずみ鋼
を製造することができるなど従来にない優れた効果を奏
するものである。As described above, by performing hot forging as the pass schedule in the present invention, the internal pattern of the macro pattern of the heat-treated product can be approximated to a square efficiently with a small pass schedule.
A constant strain steel with uniform heat treatment strain can be obtained, the shape variation of the product after heat treatment can be suppressed, and there is no need to install or modify continuous casting equipment. Therefore, the present invention can be carried out without significantly increasing the cost, and it is possible to maintain small and excellent points of positive segregation and negative segregation near the final solidification position which is a characteristic of the rectangular bloom. The present invention has an unprecedented superior effect, such as being able to manufacture a constant strain steel for use in manufacturing parts that are finished by precision cold forging, such as CVJ of automobile parts, and then are not polished.

【図面の簡単な説明】[Brief description of the drawings]

【図１】熱間鍛造における圧下率による鋳片の変形挙動
の違いを示す模式図で、（ａ）は圧下率２０％以下を示
し、（ｂ）は圧下率４０％以下を示す。BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing a difference in deformation behavior of a slab according to a reduction ratio in hot forging, where (a) shows a reduction ratio of 20% or less, and (b) shows a reduction ratio of 40% or less.

【図２】Ｏリング試験のマクロパターンのパターン形状
比とパターン形状を模式的に示す図である。FIG. 2 is a diagram schematically showing a pattern shape ratio and a pattern shape of a macro pattern in an O-ring test.

【図３】パターン部を含むＯリング試験におけるパター
ン形状のｘｙ変位を示す模式図であるFIG. 3 is a schematic diagram showing xy displacement of a pattern shape in an O-ring test including a pattern portion.

【図４】Ｏリング試験におけるパターンとｘｙ変位差の
関係を示すグラフである。FIG. 4 is a graph showing a relationship between a pattern and an xy displacement difference in an O-ring test.

Claims (1)

【特許請求の範囲】[Claims] 【請求項１】 外形縦横比１．２以上の矩形鋳型にて鋳
造した鋳片を、インラインプレスを含む鍛造機で、矩形
鋳片の短辺側から１パスあたりの圧下率２４％以上の高
圧下パスを含むパススケジュールを用いて熱間鍛造する
ことにより製品のマクロパターンのパターン縦横比を
１．４以下に抑制することを特徴とする定ひずみ鋼の製
造方法。1. A slab cast in a rectangular mold having an outer shape aspect ratio of 1.2 or more is subjected to a high-pressure reduction of 24% or more per pass from the short side of the rectangular slab by a forging machine including an in-line press. A method for producing a constant strain steel, wherein a pattern aspect ratio of a macro pattern of a product is suppressed to 1.4 or less by hot forging using a pass schedule including a lower pass.