JP2004074216A - Method for manufacturing seamless steel tube - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a seamless steel tube in Assel mill rolling, wherein shape defects and burst defects are reduced by finely adjusting the convergence amount according to a kind of steel, a size, and the like. <P>SOLUTION: The seamless steel tube is manufactured by setting the convergence amount (θ) within the range satisfying the following formula (1): (3.2482-0.1155×D/T)<θ<(3.2755-0.0791×D/T), wherein D is the outer diameter of the tube and T is the wall thickness of the tube. <P>COPYRIGHT: (C)2004,JPO

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]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing a seamless steel pipe at the time of assell mill elongation rolling.
[0002]
[Prior art]
Conventionally, when manufacturing a seamless steel pipe, a method of producing a hollow shell by drilling after heating a billet, elongating and rolling this hollow shell with an Assel mill, and then finish rolling with a sizer or a stretch reducer is used. Widely used. FIG. 1 is a view showing a process of manufacturing a general seamless steel pipe. As shown in this figure, a billet 1, which is a seamless steel pipe blank, is heated in a rotary hearth heating furnace 2, and the billet 1, which has been heated to a high temperature by a piercer drilling machine 3, is rolled and drilled and stretched by an assell mill 4. The assell mill 4 at that time is shown by an assel mill cross section 5. Then, it is reheated in a reheating furnace 6, finished to a predetermined size by a sinking mill 7, adjusted to an outer diameter by a rotary sizer 8, and sent to a cooling floor 9 for cooling.
[0003]
[Problems to be solved by the invention]
In the above-mentioned assell mill, when elongating and rolling the billet 1 heated at a high temperature, the hollow shell becomes helical due to the type of steel and the size of the shell at the time of drawing, and troubles such as poor pulling out of the mandrel bar occur. There is a problem of inhibiting sex. In particular, the problem appears remarkably in Cr-based alloys and bearing steels.
[0004]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the inventors have conducted intensive studies, and as a result, the product is prevented from twisting by finely adjusting the convergence amount according to the size, etc., and the product is expanded to remove the mandrel bar. And a method for manufacturing a seamless pipe by assell mill rolling, which reduces a shape defect and a mandrel bar pull-out defect (hereinafter, referred to as a burst defect) by facilitating the process.
The gist of the invention is that in a method of manufacturing a seamless steel pipe, the convergence amount (θ) during elongation rolling in an Assel mill is set within a range that satisfies the following expression (1), whereby shape defects and bursts are reduced. 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) where D: outer diameter, T: wall thickness
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the drawings.
FIG. 2 is a schematic view showing a stretch rolling state of the Assel mill, FIG. 2 (a) is a perspective view, and FIG. 2 (b) 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 rolls 12 having a step called a hump, and the hollow shell 11 with the mandrel bar 10 inserted. The outer diameter and thickness of the hollow shell 11 are continuously reduced in a spiral manner by these rolls 12, 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 a stretch rolling state of the Assel mill. As shown in this figure, the roll shafts 13 of the three rolls incorporated in the body of the assell mill are inclined at an angle of 2.0 to 3.0 ° toward the entry side, and this angle is referred to as convergence (θ). ). The outer diameter of the hollow shell 11 after rolling is larger than the diameter of the roll gorge (circumscribed circle). This is called bulging of the hollow shell 11. The blister margin 14 varies depending on the feed angle a, the inclination angle θ, and the outer diameter / thickness ratio (D / T) of the hollow shell. The blister margin 14 of the hollow shell 11 can be reduced as much as possible to prevent the thickness deviation, the spiral shape, and the flare at the rear end. Cause trouble.
[0007]
FIG. 4 is a diagram showing the relationship between the outside diameter / thickness ratio of the hollow shell after assell mill rolling and the blister allowance. As shown in this figure, it can be seen that as the outer diameter / thickness ratio (D / T) of the hollow shell after Assel mill rolling increases, the blister allowance increases substantially proportionally. Therefore, it is necessary to make the mandrel bar easy to pull out according to the outer diameter / thickness ratio (D / T) of the hollow shell, that is, to minimize the blister allowance of the hollow shell in consideration of the burst property. . As a result, it is possible to prevent the uneven thickness of the hollow shell from becoming worse, the spiral shape, and the flare at the rear end.
[0008]
Table 1 shows a relationship between an outer diameter / thickness ratio (D / T), a helical shape, and a burst property with respect to a convergence amount (inclination angle) when a seamless steel pipe is manufactured by assell mill rolling of bearing steel. As can be seen from Table 1, the occurrence of the helical shape and the burst property are in a contradictory relationship, and the convergence amount (inclination angle) for satisfying both of them has an outer diameter / thickness ratio (D / T). It can be seen that the convergence amount (inclination angle) needs to be adjusted smaller as the size 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 tilt angle range may be determined and adjusted within a range satisfying the expression (1). The relationship between the outer diameter / thickness ratio (D / T) for each convergence amount (inclination angle) θ, the helical shape and the burst property may be determined, and the optimal inclination angle range for the D / T division may be determined. .
[0010]
[Table 1]

[0011]
【Example】
Hereinafter, the present invention will be described specifically with reference to Examples.
After subjecting the target steel types, for example, bearing steel, STKM13A and SCr420 steel to a heating furnace to 1130 ° C., 1200 ° C., and 1200 ° C., respectively, and then rolling and perforating billets, then, for example, each D / T = 10 When elongation rolling was performed using an Assel mill, the convergence amount (inclination angle) θ was adjusted to 1.7 °, 2.2 °, and 3.0 °, and as a result, as shown in Table 1, When the mandrel bar was pulled out after being adjusted to 1.7 °, the burst property was poor when the mandrel bar was pulled out, and the mandrel bar could not be pulled out. Moreover, what was rolled by adjusting it to 3.0 ° was not able to be obtained as a product due to the deterioration of wall thickness of the hollow shell and the spiral shape. On the other hand, when the roll is adjusted to 2.2 °, which is the optimum tilt angle θ (2.1 to 2.4 °) according to the formula (1), the unevenness of the hollow shell deteriorates and the spiral shape is reduced. There was no occurrence and the burst property after rolling was good.
[0012]
【The invention's effect】
As described above, the spiral shape is improved by adjusting the convergence at the time of drawing and drawing in the assell mill according to the present invention, and the shape defect and the burst defect are reduced by facilitating the removal of the mandrel bar, thereby improving the productivity. This is an extremely excellent effect that can be achieved.
[Brief description of the drawings]
FIG. 1 is a view showing a process of manufacturing a general seamless steel pipe.
FIG. 2 is a schematic view showing a stretch rolling state of an Assel mill.
FIG. 3 is a detailed view of an elongation rolling state of the Assel mill.
FIG. 4 is a diagram showing a relationship between an outer diameter / thickness ratio of a hollow shell after assell mill rolling and a blister allowance.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 billet 2 rotary hearth heating furnace 3 piercer drill 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 blistering

Claims (1)

In the method for producing a seamless steel pipe, a shape defect and a burst defect are reduced by setting a convergence amount during elongation rolling in an Assel mill within a range satisfying the following expression (1). Manufacturing method.
3.2482-0.1155 × D / T <θ <3.2755-0.0791 × D / T (1) where D: outer diameter, T: wall thickness

Images