JP4133103B2 - Seamless steel pipe manufacturing method - Google Patents

Description

【００１１】
【実施例】
以下、本発明について実施例によって具体的に説明する。
対象鋼種である、例えば軸受鋼、ＳＴＫＭ１３ＡおよびＳＣｒ４２０なる鋼を加熱炉にて、それぞれ１１３０℃、１２００℃、および１２００℃の温度に加熱したビレットを圧延穿孔した後、次いで各々例えばＤ／Ｔ＝１０．０なるものをアッセルミルを用いて延伸圧延するにあたり、コンバージェンス量（傾斜角）θを１．７°、２．２°および３．０°に調整して圧延した結果、表１に示すように、１．７°に調整して圧延したものは、マンドレルバーを引き抜く時にバースト性が悪く、マンドレルバーを引き抜くことが出来なかった。また、３．０°に調整して圧延したものは中空素管の偏肉の悪化、螺旋形状が生じて製品として得ることが出来なかった。これに対し、式（１）による最適傾斜角θ（２．１〜２．４°）である２．２°に調整して圧延したものは、中空素管の偏肉の悪化、螺旋形状が生じることなく、かつ圧延後のバースト性も良好であった。
【００１２】
【発明の効果】
以上述べたように、本発明によるアッセルミルでの圧伸時でのコンバージェンスを調整することにより螺旋形状の改善およびマンドレルバーの抜取りを容易にすることにより形状不良およびバースト不良を軽減させ生産性の向上を図ることが出来る極めて優れた効果を奏するものである。
【図面の簡単な説明】
【図１】一般的な継目無鋼管を製造する工程を示す図である。
【図２】アッセルミルの延伸圧延状態を示す概略図である。
【図３】アッセルミルの延伸圧延状態の詳細図である。
【図４】アッセルミル圧延後の中空素管の外径／肉厚比とふくれ代との関係を示す図である。
【符号の説明】
１ ビレット
２ 回転炉床式加熱炉
３ ピアサ穿孔機
４ アッセルミル
５ アッセルミル断面
６ 再加熱炉
７ シンキングミル
８ ロータリーサイザー
９ 冷却床
１０ マンドレルバー
１１ 中空素管
１２ ロール
１３ ロールシャフト
１４ ふくれ代[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a seamless steel pipe at the time of Assel mill stretch rolling.
[0002]
[Prior art]
Conventionally, when producing a seamless steel pipe, there is a method in which a billet is heated and then drilled to produce a hollow shell, and this hollow shell is stretch-rolled with an assel mill, and then finish-rolled with a sizer or stretch reducer. Widely used. Drawing 1 is a figure showing the process of manufacturing a general seamless steel pipe. As shown in this figure, a billet 1, which is a seamless steel pipe base tube, is heated in a rotary hearth type heating furnace 2, and the billet 1 heated to a high temperature is pierced by a piercer piercing machine 3 and stretched by an assel mill 4. The Assel mill 4 at that time is shown by an Assel mill section 5. Then, it is reheated in the reheating furnace 6, finished to a predetermined size by the sinking mill 7, adjusted in outer diameter by the rotary sizer 8, fed to the cooling bed 9 and cooled.
[0003]
[Problems to be solved by the invention]
When the billet 1 heated at high temperature is drawn and rolled in the Assel mill as described above, the hollow shell becomes a spiral shape due to the steel type and the size of the tube during drawing, and troubles due to defective extraction of the mandrel bar occur. There is a problem of inhibiting sex. In particular, the problem appears remarkably in Cr alloys and bearing steels.
[0004]
[Means for Solving the Problems]
In order to solve the problems as described above, the inventors have made extensive studies, and as a result, the twist amount of the product is prevented by finely adjusting the convergence amount according to the size and the like, and the product is expanded to extract the mandrel bar. The present invention provides a method for manufacturing a seamless pipe in assel mill rolling, which can reduce shape defects and mandrel bar extraction defects (hereinafter referred to as burst defects).
The gist of the invention is that, in the method for producing a seamless steel pipe, the amount of convergence (θ) at the time of drawing and rolling in an Assel mill is set within a range that satisfies the following expression (1), and the shape defect and burst The present invention relates to a method for manufacturing a seamless steel pipe characterized by reducing defects.
3.2482-0.1155 × D / T <θ <3.2755-0.0791 × D / T (1)
However, D: outer diameter after Assel mill rolling , T: wall thickness after Assel mill rolling
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the drawings.
2A and 2B are schematic views showing the stretch rolling state of the Assel mill, FIG. 2A is a perspective view, and FIG. 2B is a cross-sectional view. As shown in FIG. 2, the hollow shell 11 into which the mandrel bar 10 is inserted is rotated and fed by three stepped rolls 12 called humps, and the hollow shell in a state in which the mandrel bar 10 is inserted. 11 is continuously spiraled by these rolls 12 to reduce the outer diameter and thickness of the hollow shell 11, and the thickness of the hollow shell 11 is reduced between the roll 12 and the mandrel bar 10.
[0006]
FIG. 3 is a detailed view of the stretch rolling state of the Assel mill. As shown in this figure, the roll shafts 13 of the three rolls incorporated in the Assel mill body are inclined at an angle of 2.0 to 3.0 ° toward the entrance side, and this angle is set to convergence (θ ). Moreover, the outer diameter of the hollow shell 11 after rolling becomes larger than the roll gorge diameter (the circumscribed circle). This is called blistering of the hollow shell 11. The blister 14 varies depending on the feed angle a, the inclination angle θ, and the outer diameter / thickness ratio (D / T) of the hollow shell. If the blister 14 of the hollow shell 11 is made as small as possible, deterioration of uneven thickness, spiral shape and flare of the rear end can be prevented. Conversely, if it is too small, the mandrel bar will not come out when the mandrel bar is pulled out. Cause trouble.
[0007]
FIG. 4 is a diagram showing the relationship between the outer diameter / thickness ratio of the hollow shell after Assel mill rolling and the blister. As shown in this figure, it can be seen that when the outer diameter / thickness ratio (D / T) of the hollow shell after Assel mill rolling is increased, the blistering is also increased in proportion to that. Therefore, it is necessary to reduce the blister allowance of the hollow shell as much as possible in consideration of the ease of pulling out the mandrel bar according to the outer diameter / thickness ratio (D / T) of the hollow shell, that is, considering the burst property. . As a result, deterioration of the uneven thickness of the hollow shell, spiral shape, and flare at the rear end can be prevented.
[0008]
Table 1 shows the relationship between the outer diameter / thickness ratio (D / T), the helical shape, and the burst property with respect to the amount of convergence (inclination angle) when producing a seamless steel pipe by Assel mill rolling of bearing steel. As can be seen from Table 1, the occurrence of the spiral shape and the burst property are in a contradictory relationship, and the convergence amount (tilt angle) for satisfying both is the outer diameter / thickness ratio (D / T). It can be seen that the amount of convergence (tilt angle) needs to be adjusted to be smaller as the value increases. Formula (1) summarizes the results of Table 1.
[0009]
As shown in Table 1, in order to satisfy both the spiral shape and the burst property, an optimum inclination angle range may be determined and adjusted within a range satisfying the expression (1). The relationship between the outer diameter / thickness ratio (D / T) with respect to each convergence amount (tilt angle) θ, the spiral shape, and the burst property may be obtained, and the optimum tilt angle range for each D / T section may be determined. .
[0010]
[Table 1]

[0011]
【Example】
Hereinafter, the present invention will be specifically described with reference to examples.
After subjecting the billet which is a target steel type, for example, bearing steel, STKM13A and SCr420, to a temperature of 1130 ° C., 1200 ° C., and 1200 ° C. in a heating furnace, respectively, then, for example, D / T = 10 As shown in Table 1, as a result of rolling by adjusting the amount of convergence (tilt angle) θ to 1.7 °, 2.2 °, and 3.0 ° Rolls adjusted to 1.7 ° had poor burstability when the mandrel bar was pulled out, and the mandrel bar could not be pulled out. Moreover, what was rolled after adjusting to 3.0 degree produced the deterioration of the uneven thickness of a hollow shell, and the spiral shape produced, and could not be obtained as a product. On the other hand, when the roll is adjusted to 2.2 ° which is the optimum inclination angle θ (2.1 to 2.4 °) according to the formula (1), the uneven thickness of the hollow shell is deteriorated and the helical shape is reduced. It did not occur and the burstability after rolling was also good.
[0012]
【The invention's effect】
As described above, by adjusting the convergence at the time of drawing with the Assel mill according to the present invention, the spiral shape is improved and the mandrel bar is easily removed, thereby reducing the shape defect and the burst defect and improving the productivity. It is possible to achieve extremely excellent effects.
[Brief description of the drawings]
FIG. 1 is a diagram showing a process for producing a general seamless steel pipe.
FIG. 2 is a schematic view showing a stretch-rolled state of an Assel mill.
FIG. 3 is a detailed view of the stretch rolling state of the Assel mill.
FIG. 4 is a view showing a relationship between an outer diameter / thickness ratio of a hollow shell after Assel mill rolling and a blister.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Billet 2 Rotary hearth type heating furnace 3 Piercer drilling machine 4 Assel mill 5 Assel mill cross section 6 Reheating furnace 7 Sinking mill 8 Rotary sizer 9 Cooling floor 10 Mandrel bar 11 Hollow shell 12 Roll 13 Roll shaft 14 Blowing allowance

Claims (1)

In the method for producing a seamless steel pipe, the convergence amount (θ) is set within a range that satisfies the following formula (1) at the time of drawing and rolling in an Assel mill to reduce shape defects and burst defects. A method for producing seamless steel pipes.
3.2482-0.1155 × D / T <θ <3.2755-0.0791 × D / T (1)
Where D: outer diameter after Assel mill rolling , T: wall thickness after Assel mill rolling

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