JP4274344B2

JP4274344B2 - Split rolling method for producing constant strain steel

Info

Publication number: JP4274344B2
Application number: JP2001154082A
Authority: JP
Inventors: 盛彦中崎; 英樹梶原
Original assignee: Sanyo Special Steel Co Ltd
Current assignee: Sanyo Special Steel Co Ltd
Priority date: 2001-05-23
Filing date: 2001-05-23
Publication date: 2009-06-03
Anticipated expiration: 2021-05-23
Also published as: JP2002346601A

Description

【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。
【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。
【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。
【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、外径縦横比１．２以上の矩形鋳型にて鋳造した鋳片を、高さ圧下率１５％以上のパスの強圧下パスで２回以上短辺側から圧下し、かつ、長辺側からの強圧下パス回数を短辺側からの強圧下パス回数と同数未満に設定したパススケジュールで圧延し、製品のマクロパターンの縦横比を１．４以下に抑制することを特徴とする定ひずみ鋼を製造するための分塊圧延方法である。
【０００５】
上記手段の作用を説明すると、外形縦横比１．２以上とするのは、１．２以下の矩形鋳型の鋳片の場合、初期凝固パターンの縦横比が１．４を下回るので本パスによる分塊圧延を使わなくても定ひずみ鋼になり得るためである。
【０００６】
さらに、圧下率１５％以上の強圧下パスとする理由は次の理由による。先ず、図１の（ａ）、（ｂ）の２図にわかり易くするために分けて、圧下率による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、圧下率１５％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、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。
【０００７】
強圧下パスを２回以上とするのは、強圧下パス１回では強圧下効果が低い上、パススケジュールが長くなり、生産性が阻害されることによる。。
【０００８】
長辺側から掛ける強圧下パスを短辺側の強圧下パスと同数未満に設定するのは、長辺側から強圧下を掛けることにより短辺側からの強圧下効果が解消されるため、長辺側からの強圧下パス回数は短辺側の強圧下パス未満でないと効果がでないためである。
【０００９】
製品のマクロパターンの縦横比を１．４以下に抑制するのは、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ｄｙ、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、低ひずみ領域が長辺側に偏りすぎてしまい、不適当と考えられる。
【００１０】
【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溶鋼の縦横比１．２以上の矩形ブルーム、例えば形状４９０ｍｍ×３８０ｍｍ、縦横比１．２９を、高さ圧下率１５％以上の強圧下パスで２回以上短辺側から圧下するとともに、縦横方向を変更して、長辺側からの強圧下パス回数を短辺側からの強圧下パス回数と同数未満に設定したパススケジュールにより分塊圧延した。その後、短辺側を圧下量３ｍｍで最終パスを下後、３ロール・プラネタリー・ミル（以下、「ＰＳＷ］という。）により丸棒、例えばφ１６４ｍｍの丸棒に仕上げ圧延する。かくして熱処理後の製品マクロパターンの縦横比を１．４以下とする。
【００１１】
【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分塊圧延を行う。表１に示すように、パス１〜５までは短辺側から行い、パス４は圧下量６０ｍｍすなわち圧下率１７．６％、パス５は圧下量８０ｍｍすなわち圧下率２８．６％で強圧下し、次いで方向を変えてパス６〜１１を長辺側から行い、ここでは圧下率１５％未満の圧下を行い、再び方向を変えて短辺側からパス１２および１３を行い、パス１２は圧下量６１ｍｍすなわち圧下率２４．８％、パス１３は圧下量３５ｍｍすなわち圧下率１８．９％で強圧下し、再び方向を変えて長辺側からパス１４および１５を行い、パス１４は圧下量４９ｍｍすなわち圧下率２１．４％、パス１５は圧下量３５ｍｍすなわち圧下率１９．４％で強圧下して１４５ｍｍ×１６７ｍｍとし、最後に方向を変えて短辺側からパス１６を行った後、ＰＳＷにより仕上げ圧延してφ１６４ｍｍの丸棒とした。なお、表１で圧下量の太字は圧下率１５％以上の強圧下を示し、この改良パスパターンによる本実施例では、圧下率１５％以上の強圧下を短辺側からはトータルで５回行い、長辺側からはトータルで２回行っている。従って、短辺側からの強圧下の効果は保持されている。
【００１２】
【表１】

【００１３】
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の矩形ブルームを分塊圧延した後、ＰＳＷにより仕上げ圧延して最終的に同一形状の丸棒とした。従って、この従来のパススケジュールでも最終パスを行った鋳片の縦横比は、上記の改良パススケジュールのものと変わることなく、また、パス回数も異ならない。しかしながら、この比較例のパススケジュールでは、短辺側からの圧下率１５％以上の強圧下はトータルで３回であるが、長辺側からの強圧下はトータルで４回であり、長辺側からの方が多く、このため短辺側からの強圧下の効果が解消されている。
【００１４】
【表２】

【００１５】
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抑制されている。すなわち、Ｏリング試験の図４に示す製品のパターン縦横比の関係から、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は、そのマクロパターン縦横比のｘｙ変位差が大きくあり、定ひずみ鋼とはいえないものである。
【００１６】
【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分塊圧延することで、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ので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いので、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。
【図面の簡単な説明】
【図１】分塊圧延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。
【図２】Ｏリング試験のマクロパターンのパターン形状の縦横比とパターン形状を模式的に示す図である。
【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
【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。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a constant strain steel for use in the manufacture of parts such as CVJ for automobile parts which are finished by precision cold forging and are not polished thereafter.
[0002]
[Prior art]
The CVJ of automobile parts is finished by precision cold forging so as to reduce costs by reducing the number of processes, 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, the initial solidification structure is different between the inside and outside of the macro pattern of the cast steel material. For example, there is a big problem that a variation of 0.02% between the inside and outside occurs. This difference in strain between the inside and outside of the pattern poses a serious problem for parts that are 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 medium-diameter round continuous cast piece or a square continuous cast piece. However, this increases the cost by newly installing or remodeling the equipment. Furthermore, there is a problem of deterioration of center segregation due to the shape during casting. That is, there is a knowledge that the round shape is larger in the positive segregation and negative segregation near the final solidification position than in the slab having a rectangular cross section. The medium-diameter round slab or square slab has a problem that the forging ratio is low, and the structure is not sufficiently refined and homogenized.
[0003]
[Problems to be solved by the invention]
The problem to be solved by the present invention is that by adopting a rectangular cross-section slab as it is, the maximum segregation suppressing effect that the positive segregation and the negative segregation in the vicinity of the final solidification position are small is further utilized for forging. A steel material that can take advantage of rectangular slabs that can improve quality by reducing the difference in strain between the inside and outside of the macro pattern by increasing the ratio, and that can suppress product distortion after heat treatment. It is to provide a manufacturing method.
[0004]
[Means for Solving the Problems]
The means of the present invention for solving the above-mentioned problem is that a slab cast with a rectangular mold having an outer diameter aspect ratio of 1.2 or more is subjected to a high-pressure pass of a pass with a height reduction ratio of 15% or more twice or more. Rolling with a pass schedule that reduces from the short side and sets the number of strong reduction passes from the long side to less than the number of strong reduction passes from the short side, and the aspect ratio of the macro pattern of the product is 1. It is a block rolling method for producing a constant strain steel characterized by being controlled to 4 or less.
[0005]
The operation of the above means will be explained. The external aspect ratio is 1.2 or more. In the case of a rectangular mold slab of 1.2 or less, the aspect ratio of the initial solidification pattern is less than 1.4. This is because constant strain steel can be obtained without using lump rolling.
[0006]
Further, the reason for the strong reduction pass with a reduction rate of 15% or more is as follows. First, in order to make it easy to understand in FIGS. 1A and 1B, the difference in deformation behavior depending on the rolling reduction is shown. (A) shows 10% reduction, 15% reduction, and 20% reduction before reduction, and (b) shows repeatedly before reduction and 20% reduction, and further shows 30% reduction and 40% reduction. As can be seen from the difference in deformation behavior due to the rolling reduction in FIG. 1 above, by applying a strong rolling pass with a rolling reduction of 15% or more, the center of the slab is rolled down, and the shape improvement effect due to the swelling of the center appears. By cuddling.
[0007]
The reason why the strong pressure pass is set to two times or more is that the strong pressure reduction effect is low in one strong pressure pass, and the pass schedule becomes longer and the productivity is hindered. .
[0008]
The reason for setting less than the same number of passes under the overwhelming path from the long side to the side under the overwhelming pass on the short side is that the overwhelming effect from the short side is eliminated by applying the overpressure from the long side. This is because the number of passes under strong pressure from the side is not effective unless it is less than the strong pressure pass on the short side.
[0009]
The reason why the aspect ratio of the macro pattern of the product 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) in FIG. 2 is 1.0, (b) is 1.5, and (c) is 2.0 as shown in FIG. The O-ring test is performed with the vertical and horizontal displacements shown in FIG. FIG. 4 is a graph showing the relationship between the xy displacement difference dx−dy and the pattern aspect ratio. From FIG. 4, when the pattern aspect ratio is 1.4 or less, the xy displacement difference dx−dy rapidly decreases to 0.7 or less. From this, it was found that the constant strain effect was obtained when the pattern aspect ratio was 1.4 or less. When the pattern aspect ratio is 1.5 or more, the low strain region is excessively biased toward the long side, which is considered inappropriate.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be shown through the following examples. Continuously cast cold-forged molten steel rectangular bloom with aspect ratio of 1.2 or more, for example, shape 490mm x 380mm, aspect ratio 1.29, reduced from the short side 2 times or more in a strong reduction pass with a height reduction ratio of 15% or more. At the same time, the vertical and horizontal directions were changed, and the block rolling was performed according to a pass schedule in which the number of passes under strong pressing from the long side was set to be less than the number of passes under strong pressing from the short side. Then, after lowering the short path side with a reduction amount of 3 mm and finishing the final pass, it is finish-rolled into a round bar, for example, a φ164 mm round bar, by a 3-roll planetary mill (hereinafter referred to as “PSW”). The aspect ratio of the product macro pattern is set to 1.4 or less.
[0011]
【Example】
Cold rolling forging steel SCR420H by continuous casting is subjected to block rolling with a rectangular bloom having a shape of 490 mm × 380 mm and an aspect ratio of 1.29 according to the improved pass pattern shown in Table 1. As shown in Table 1, passes 1 to 5 are performed from the short side. Pass 4 is strongly reduced with a reduction amount of 60 mm, that is, a reduction rate of 17.6%, and Pass 5 is strongly reduced with a reduction amount of 80 mm, that is, a reduction rate of 28.6%. Next, the direction is changed, and passes 6 to 11 are performed from the long side. Here, the reduction is less than 15%, the direction is changed again, and passes 12 and 13 are performed from the short side. 61 mm, that is, a reduction ratio of 24.8%, and the pass 13 is strongly reduced with a reduction amount of 35 mm, that is, a reduction ratio of 18.9%, and the direction is changed again to perform passes 14 and 15 from the long side. Rolling down 21.4%, pass 15 was rolled down to 35mm, that is, 19.4% rolling down to 145mm x 167mm. Finally, the direction was changed to pass 16 from the short side, then finished with PSW Rolled It was a round bar of φ164mm. In Table 1, the amount of reduction in bold indicates strong reduction with a reduction rate of 15% or more. In this embodiment using this improved pass pattern, strong reduction with a reduction rate of 15% or more is performed five times in total from the short side. From the long side, it is done twice in total. Therefore, the effect of strong pressure from the short side is maintained.
[0012]
[Table 1]

[0013]
As a comparative example, a rectangular bloom of the same 490 mm × 380 mm and aspect ratio of 1.29 as in Table 1 was subjected to block rolling in accordance with a conventional pass schedule in Table 2, and then finish-rolled by PSW to finally obtain a round bar having the same shape. did. Therefore, the aspect ratio of the slab that has undergone the final pass in this conventional pass schedule is the same as that of the above-described improved pass schedule, and the number of passes is not different. However, in the pass schedule of this comparative example, there are 3 times of strong pressures with a reduction rate of 15% or more from the short side, but there are 4 times of strong pressures from the long side. From this, the effect of strong pressure from the short side is eliminated.
[0014]
[Table 2]

[0015]
The product distortion after the heat treatment in the case of the improved pass schedule which is an embodiment of the present invention is suppressed. That is, it can be seen from the relationship of the pattern aspect ratio of the product shown in FIG. 4 of the O-ring test 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 pass schedule, the aspect ratio of the long side of the final pass is not different from this example at first glance, but the effect of strong pressure from the short side is eliminated, The product strain after the heat treatment has a large xy displacement difference in its macro pattern aspect ratio and cannot be said to be a constant strain steel.
[0016]
【The invention's effect】
As described above, by carrying out the batch rolling as the pass schedule in the present invention, the internal pattern of the macro pattern of the product after the heat treatment can be made close to a square, so that a constant strain steel with a uniform overall heat treatment strain can be obtained. Because it can suppress the variation in the shape of the product after heat treatment, it is not necessary to newly install or modify the continuous casting equipment, so it can be carried out without significantly increasing the cost, and the final characteristic of the rectangular bloom The present invention can be used for manufacturing parts that are finished by precision cold forging such as CVJ of automobile parts and are not polished afterwards, such as being able to maintain the excellent point of positive segregation and negative segregation near the solidification position. For example, it is possible to produce a constant strain steel.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a schematic diagram showing the difference in deformation behavior of a slab depending on the rolling reduction in block rolling, where (a) shows a rolling reduction of 20% or less, and (b) shows a rolling reduction of 40% or less.
FIG. 2 is a diagram schematically showing an aspect ratio and pattern shape of a macro pattern of an O-ring test.
FIG. 3 is a schematic diagram showing an xy displacement of a pattern shape in an O-ring test including a pattern portion. FIG. 4 is a graph showing a relationship between a pattern and an xy displacement difference in an O-ring test.

Claims

A slab cast with a rectangular mold having an outer diameter aspect ratio of 1.2 or more is squeezed twice or more from the short side in a pass with a height reduction rate of 15% or more (hereinafter referred to as “strong press pass”). In addition, rolling with a pass schedule in which the number of passes under strong pressure from the long side is set to be less than the number of passes under strong pressure from the short side, the aspect ratio of the macro pattern of the product is suppressed to 1.4 or less. A split rolling method for producing a featured constant strain steel.