JP2013094799A - Diameter-reducing rolling method of seamless steel pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for effectively preventing falling-down mark in a pipe material of high alloy steel.SOLUTION: In the diameter-reducing rolling method of a seamless steel pipe using a stretch reducer having a plurality of 3-roll rolling stands which are serially disposed, a roll having an edge release amount x satisfying the following expression (1) relative to a stand having a diameter reduction rate per unit stand of Y. 0.80Y-4.44≤x≤1.22Y-6.81...(1) where Y denotes the diameter reduction rate per unit stand (%), and x denotes edge release amount (mm).

Description

  The present invention relates to a diameter reduction rolling method for seamless steel pipes, and in particular, diameter reduction rolling of seamless steel pipes for effectively preventing the occurrence of collapsed flaws when reducing difficult-to-work materials such as high alloy steels. Regarding the method.

Recently, in order to effectively apply the superior performance of seamless steel pipes, in addition to cylinders and hydraulic pipes for construction machinery and steel pipes for automobiles, the demand for weight reduction of automobile bodies has been increasing. This is expanding to applications of steel pipes that require fatigue resistance, such as steel pipes for drive shafts.
The seamless steel pipe manufacturing methods for such applications are usually divided into mandrel mill pipe manufacturing methods and plug mill pipe manufacturing methods as hot pipes after drilling, but they have excellent dimensional accuracy and production efficiency. Mannesmann pipe manufacturing method is adopted. Depending on the required performance, the raw pipes manufactured by hot pipe making are appropriately cold-coated to improve the dimensional accuracy of the outer diameter, inner diameter and wall thickness, improve the surface properties, and ensure the mechanical strength. Cold processing such as drawing is often performed.

  The Mannesmann-Mandrel mill pipe manufacturing method for hot pipe production of seamless steel pipes includes piercing and rolling for drilling a hole in the center of a solid billet, and drawing and rolling for the main purpose of wall thickness processing of the drilled hollow shell. , Constant diameter rolling to reduce the outer diameter of the raw tube and finish to the target dimension. Usually, a piercing and rolling machine such as a Mannesmann Piercer and a cross-type piercing and rolling machine is used for piercing rolling, a rolling machine such as a mandrel mill is used for stretching rolling, and a piercing rolling machine such as a stretch reducer is used for constant diameter rolling.

  In Patent Document 1, as a means for efficiently suppressing wrinkles generated on the inner surface of a steel pipe rolled by the Mannesmann-mandrel mill pipe manufacturing method, the reheating conditions after Mannesmann piercing rolling and mandrel stretch rolling are set to 800. 1050 ° C., according to the finish dimension t / D of constant diameter rolling by a stretch reducer, the average ellipticity of the perforated roll is described to be finish-rolled under a condition that satisfies a specific relational expression with t / D. Yes.

JP 2008-221250 A

A stretch reducer is composed of a plurality of three-roll rolling stands arranged in series. Usually, any two stands that follow each other have a circumferential roll phase angle difference of 60 °, and tension is added. However, the diameter is reduced (or further reduced). All three rolls in the same stand have the same material, shape and dimensions.
However, in the case of a difficult-to-work material such as high alloy steel, for example, as shown in FIG. 3, local portions of the tube material 4 that is the work material are connected to both edges of the caliber portion 2 of the roll 1 in the diameter reduction process. Biting out from the gap between the flange part 3 and the flange part 3 of the adjacent roll 1 (the roll gap δ which is the size of this gap is normally set to 1 mm or less), the biting part 5 is the roll 1 of the next stand. The frequency of occurrence of so-called collapsed wrinkles 6 that are crushed and collapsed at the center of the caliber portion 2 is high. In order to prevent this, conventionally, the rolling schedule has been changed, the amount of additional tension has been changed, and the like. However, the effect was poor for high alloy steels.

  As described above, conventionally, there has been a problem that it is impossible to effectively prevent the occurrence of collapse of the high-alloy steel pipe material.

The inventor conducted the following studies in order to solve the above-described problems.
In other words, from the viewpoint of preventing the deterioration of the product cross-section unevenness, the roll caliber design has not been changed in the past, but there must be a range of roll caliber designs that can achieve both the prevention of uneven thickness and the prevention of falling wrinkles. , Repeated earnest experiments. As a result, it has been found that by regulating the relationship between the diameter reduction rate of each stand and the edge escape amount of the roll within a certain range, it is possible to effectively reduce the occurrence of collapse and wrinkles without deteriorating the uneven thickness.

Here, the edge escape amount will be described with reference to FIG.
Usually, in the roll 1, the caliber portion 2 has an arc-shaped curved shape in which the roll profile has a center of curvature outside the roll. The flange portion 3 has a straight line shape in which the roll profile is inclined so as to approach the roll center axis toward the end side in the roll center axis direction. A connection area called an edge relief 7 is provided at the boundary between the caliber part 2 and the flange part 3, and the roll profile of the connection area is a straight line parallel to the roll center axis. A point P in FIG. 2 indicates an arc formed by further extending an arc forming the roll profile on the extreme end side of the caliber portion 2 toward the edge relief portion 7 (the center of curvature of the arc is the portion of the arc before the extension). The same as that) and the straight line formed by extending the inclined line segment forming the roll profile of the flange part 3 toward the edge relief part 7 (the direction of the straight line is the same as that of the inclined line part before extension). . The edge escape amount x is defined by the shortest distance x from the intersection point P to the edge relief portion 7.

The present invention has been made based on the above findings, and the gist thereof is as follows.
[1] A method of reducing the diameter of a seamless steel pipe using a stretch reducer in which a plurality of three-roll rolling stands are arranged in series, and the amount of edge relief x is less than that of a stand whose diameter reduction rate per single stand is Y. A roll reduction method for seamless steel pipes characterized by using a roll satisfying the following formula (1).

0.80Y−4.44 ≦ x ≦ 1.22Y−6.81 (1)
Y: Diameter reduction per single stand (%), x: Edge relief (mm).

  According to the present invention, even when the seamless steel pipe is a difficult-to-work material such as high alloy steel, it is possible to perform diameter reduction rolling without causing deterioration of uneven thickness and effectively suppressing the occurrence of collapsed flaws.

It is a graph which shows the relationship between the diameter reduction rate which concerns on this invention, and edge escape amount. It is definition explanatory drawing of edge escape amount. It is a schematic diagram which shows the mode of generation | occurrence | production of the fallen wrinkle.

FIG. 1 is a graph showing the relationship between the diameter reduction rate and the edge escape amount according to the present invention. The straight lines L1, L2 and plot points in FIG. 1 were obtained as follows.
(Line L1)
Of the steel composition of the Cr content of 8 to 16 mass% among the SCr steel, all the 3 stand test and research stretches are made of seamless steel pipes having the steel composition shown in Table 1 and an outer diameter of 110 mmφ. Rolled with a reducer, the diameter reduction rate was 2% and the edge relief amount was 0.1 mm except for the second stand, and the second stand was obtained by changing the diameter reduction rate Y and the edge relief amount x variously. As a result of visual determination of the presence or absence of the collapsed flaws on the steel pipe, it was found that the boundary between the region with and without the collapsed flaws was represented by a straight line L1 of x = 0.80Y−4.44. Here, when x on the straight line L1 is set to x1, there is a falling wrinkle when x <x1, and there is no falling wrinkle (good) when x ≧ x1.

(Line L2)
The raw tube was rolled with a stretch reducer for test research of all 11 stands. At that time, the diameter reduction rate was 2% and the edge relief amount was 0.1 mm except for the 5th stand, and the 5th stand was the diameter reduction rate. Y and edge escape amount x (where x ≧ x1) are changed in various ways, and the obtained steel pipe has an uneven thickness ratio (= [(maximum thickness−minimum thickness) / average thickness] in the circumferential direction) × 100 (%))) As a result of evaluating the size of the uneven thickness, the boundary between the uneven thickness region and the uneven thickness region is represented by a straight line L2 where x = 1.22Y−6.81. I understood that it was done. Here, when x on the straight line L2 is set to x2, the thickness deviation is large when x> x2, and is small (good) when x ≦ x2.

Thus, the range that can prevent the occurrence of collapse of wrinkles without deteriorating the uneven thickness can be defined by the relationship between the diameter reduction rate Y and the edge relief amount x, and the range is sandwiched between the straight line L1 and the straight line L2 in FIG. Since it was found that this was a region, that is, a region represented by the formula (1), this was made a requirement of the present invention.
Since x> 0 mm, the application range of the formula (1) is naturally limited to the range of Y ≧ 5.6%. However, in the case of Y <5.6%, there is almost no occurrence of falling-down wrinkles in the actual machine, and therefore equation (1) may be applied only to the stand where Y ≧ 5.6%. If Y> 7%, the product shape may be damaged, so Y ≦ 7% is preferable. Therefore, the present invention is preferably applied to a stand with Y = 5.6 to 7%.

(Plot point)
In order to verify the effectiveness of Equation (1), the raw tube is rolled by three methods (○ ▲ ■) using a stretch reducer for testing and research in a total of 15 stands, each with a plurality of individual conditions. did. In any rolling, the first to third stands and the thirteenth to fifteen stands were set to have a diameter reduction ratio ≦ 3% and an edge relief amount ≦ 0.2 mm. The remaining 4th to 12th stands were as follows.

In the case of ◯: For each stand, the diameter reduction ratio and the edge escape amount were satisfied as the Y coordinate value and the x coordinate value of the same ◯ point in FIG.
In the case of ▲: the diameter reduction rate and the edge escape amount are the same in FIG. 1 for at least one stand, respectively, so that the edge escape amount x falls outside the range of the expression (1) as the Y coordinate value and the x coordinate value of the point. I made it.

In the case of (2): The diameter reduction ratio and the edge escape amount are the same in FIG. 1 for at least one stand, respectively. The edge escape amount x is out of the range of the formula (1) as the Y coordinate value and the x coordinate value of the point. I made it.
As a result, in the case of ◯, there was no collapse of wrinkles and the uneven thickness was small and good. On the other hand, in the case of ▲, the uneven thickness was small but collapsed wrinkles occurred, and in the case of ■, there was no collapsed wrinkles but the uneven thickness increased. Thus, it was verified that the formula (1) is effective.

  This invention was implemented with respect to the diameter reduction rolling process which finishes the said raw tube (outer diameter 110mm) to outer diameter 25-56mm in the actual machine stretch reducer of all 28 stands. Before the implementation, the uneven thickness was small, but the incidence of collapsed wrinkles was 4.5%, but after the implementation, there was no deterioration of uneven thickness and the incidence of collapsed defects was 0.49%. The effect of the present invention has been manifested.

1 Roll 2 Caliber part 3 Flange part 4 Tubing material 5 Biting part 6 Falling collar 7 Edge relief part

Claims (1)

This is a method of reducing the diameter of a seamless steel pipe using a stretch reducer in which a plurality of three-roll rolling stands are arranged in series, and the edge escape amount x is expressed by the following equation for a stand where the reduction ratio per single stand is Y: A method for reducing the diameter of a seamless steel pipe, characterized by using a roll satisfying 1).
0.80Y−4.44 ≦ x ≦ 1.22Y−6.81 (1)
Y: Diameter reduction per single stand (%), x: Edge relief (mm).

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