JPH0696758B2 - Titanium seamless pipe manufacturing method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a titanium seamless pipe, which comprises producing a seamless pipe made of pure titanium or α-type titanium alloy in a rolling process including drawing rolling. In the present specification, unless otherwise specified, titanium means pure titanium or α-type titanium alloy.

[Conventional technology]

This type of titanium is used industrially, ASTM Gr
-1,2,3,4 and ASTM Gr-7 (Ti-0.15Pd), Gr-12
(Ti-0.3Mo-0.8Ni), Gr-6 (Ti-5Al-2.5Sn), and the like, which are used as pipes for the chemical industry.

Pipes made of titanium for the chemical industry are usually seamless pipes, and titanium seamless pipes are generally manufactured by the Eugene method, which is a typical hot extrusion method. However, the Euge method is low in production efficiency, and from an efficiency standpoint, it is desirable to produce it on a continuous pipe continuous production line typified by Mannesmann piercer. As shown in "320", an attempt of processing by an inclined roll punching machine has been started.

Further, regarding the production of titanium seamless pipes by a seamless pipe continuous production line, the present applicant has continued to develop the same, and some new facts have already been found, and Japanese Patent Application No. 62-153978,
Japanese Patent Application No. 63-23317 proposes a new method for producing a titanium seamless tube based on this fact.

When manufacturing a titanium seamless pipe in a seamless pipe continuous production line, first, a heated billet made of titanium is pierced and rolled by an inclined roll piercing and rolling machine to form a hollow hollow piece.
The obtained hollow piece is subsequently stretch-rolled by a mandrel mill or a plug mill to obtain a hollow shell.
After the stretching and rolling, if necessary, it is reheated, then drawn and rolled by a stretch reducer, or is sized by a sizer.

[Problems to be Solved by the Invention]

In the production of titanium seamless pipes with such a seamless pipe continuous production line, when the final rolling process adopts draw rolling with a stretch reducer, the titanium seamless pipes after the final rolling are more prominent than those of ordinary steel etc. A defective shape called a flat inner surface is generated. As shown in FIG. 2, this is a phenomenon in which the inner surface of the pipe becomes hexagonal and the wall thickness becomes uneven in the circumferential direction. With this phenomenon, for the titanium seamless pipe after the final rolling, , A considerable amount of internal cutting is required. As a result, the efficiency and the yield decrease due to cutting.

It is an object of the present invention to provide a method for producing a titanium seamless pipe, which can suppress the internal surface squareness, which is a problem when final rolling is performed by drawing rolling, to a degree without problems.

[Means for solving problems]

The inventors of the present invention have continued research on the production of titanium seamless pipes by a continuous production line for seamless pipes, and in the process of this, the following findings were obtained regarding the inner surface angular tension which is a problem in drawing rolling.

When a hollow shell made of titanium is drawn and rolled by a stretch reducer, the internal squareness becomes more remarkable than in the case of plain steel rolled under the same conditions, but it is because the texture formed after stretch rolling is further increased during drawing and rolling. The cause is the development.

That is, since the inner surface side of the hollow shell is not constrained in the reduction rolling by the stretch reducer,
The inner surface will be squared regardless of the material,
In the case of a titanium hollow shell, deformation is not isotropic due to the texture that develops during drawing and rolling, and the inner surface squareness is promoted.

When the hollow shell is made of steel, technology has been developed to suppress inner surface tension to the extent that it does not hinder the roll design of the stretch reducer, etc. As a result, a considerable amount of internal cutting is forced.

If the cause of remarkable inner surface swelling in titanium is the development of texture that occurs after stretch rolling, if the texture is not formed after stretch rolling, the inner surface swelling in titanium will be similar to that of steel. For textures formed after stretch rolling that are suppressed and are suppressed to the extent that existing measures are not hindered, the time at which the hollow shell is cooled to βtransus or less during stretch rolling and between stretch rolling and before drawing rolling. It turned out to be due to the transformation. It was also clarified that the texture due to this transformation can be prevented from being formed by intentionally increasing the cooling rate after the stretching and rolling, which can solve the problem of inner surface swelling in titanium.

The present invention has been made based on such knowledge, when producing a titanium seamless pipe in a rolling process including a reduction rolling by a stretch reducer, the rolling mill outlet temperature in the rolling process before the reduction rolling is βtransus-150 ° C. Above, 1100 ℃ or less, from this temperature range the material temperature 60
The gist is a method for producing a titanium seamless tube, which comprises lowering the temperature to 0 ° C. or lower, reheating to 650 ° C. or higher and β transus or lower, and then performing reduction rolling.

[Action]

The reasons for limiting the conditions in the method for producing a titanium seamless pipe of the present invention will be described below.

The rolling process before draw rolling is a stretch rolling process in a seamless pipe continuous production line such as Mannelman piercer, and when draw rolling is performed by a stretch reducer after stretch rolling, this draw rolling is performed by a mandrel mill. To be done.

In a seamless pipe production line including drawing rolling, as shown in Fig. 1 (a), a billet heated to a predetermined temperature is usually perforated by a piercer to form a hollow shell, and subsequently stretch-rolled by a mandrel mill. During this time, the material temperature continues to drop. The hollow shell obtained by stretching and rolling was immediately sent to a reheating furnace, and after reheating to a predetermined temperature,
It undergoes reduction rolling by a stretch reducer.

In contrast to such a conventional method, in the manufacturing method of the present invention, as shown in FIG. 1 (b), after controlling the outlet temperature Ts of the stretching and rolling mill, the hollow piece after the stretching and rolling is cooled once at a cooling rate of not less than air cooling. Rapidly cools to a specified cooling end temperature Tf, and then
It is reheated to a predetermined reheating temperature Tr and subjected to drawing rolling by a stretch reducer.

When the temperature Ts at the outlet of the rolling mill before quenching is less than βtransus-150 ° C, the internal surface angulation cannot be eliminated because the structure is transformed into the α phase and the texture is formed at the end of rolling. On the contrary, when the rolling mill outlet temperature Ts exceeds 1100 ° C, before the rolling process is started (before piercing and rolling in the seamless pipe continuous production line).
The heating temperature exceeds 1200 ° C, and heating at such a high temperature causes large scale loss and rough outer surface. Therefore, the rolling mill outlet temperature Ts in the rolling process before the reduction rolling
Is βtransus-150 ° C or higher and 1100 ° C or lower.

Further, if the material cooling rate at the exit of the rolling mill is slower than that of air cooling, a transformation texture is formed during cooling and the inner surface squareness after drawing rolling becomes remarkable. Therefore, the cooling at the outlet of the rolling mill should be a rapid cooling equal to or higher than the air cooling. In this case, when the cooling end temperature Tf exceeds 600 ° C., there is no effect of the rapid cooling, and as a result, it becomes impossible to suppress the inner surface angling after the squeeze rolling. Therefore, the cooling end temperature Tf is set to 600 ° C. or higher. Here, the term “more than air cooling” means, for example, natural cooling, forced air cooling, and water cooling, which has a higher cooling rate than forced air cooling.
Refers to cooling at 1 ° C / sec or higher.

After the cooling, squeeze rolling is performed through reheating, but if the reheating temperature Tr is higher than β transus, a gas absorption hardening layer is formed on the inner surface of the pipe, and roughening of the inner surface occurs after squeeze rolling. If the temperature is less than 650 ° C, cracking will occur during the reduction rolling.
Therefore, the reheating temperature Tr before squeeze rolling is 650 ° C. or higher and βtransus or lower.

The rolling mill outlet temperature Ts and the cooling end temperature Tf refer to the material surface temperature.

〔Example〕

Next, the manufacturing method of the present invention will be described in detail with reference to its examples.

A billet with a diameter of 150 mm made of pure titanium ASTM Gr-3 (βtransus915 ° C) is heated and then pierced with a piercer,
110m in diameter by subsequent drawing and rolling with a mandrel mill
It was a hollow piece with m and a wall thickness of 9 mm. At the outlet of the mandrel mill, the hollow piece temperature was variously controlled, and the hollow piece was cooled to various temperatures by three types of cooling methods from the controlled temperature: slow cooling, air cooling (natural cooling), and water cooling. After that, the hollow piece was conveyed to a reheating furnace, reheated to various temperatures, and drawn by a stretch reducer with three rolls and 23 stands to finish a seamless pipe having a diameter of 60 mm and a wall thickness of 9.5 mm.

The temperature at the exit of the mandrel mill and the temperature at the end of cooling were controlled by the outer surface temperature, and the outer surface temperature was measured with a radiation thermometer above 500 ° C and with a surface thermometer below 500 ° C, respectively. In addition, gradual cooling of the hollow piece means that the outer surface of the hollow piece that exits the mandrel mill is wrapped with a heat insulating material to suppress its cooling. Was done.

From the seamless pipe obtained by the squeeze rolling, a pipe sample having a thickness of 10 mm was collected from the central portion in the longitudinal direction. And
The wall thickness was measured in 0.001 mm units with a micrometer at a total of 24 points, 15 degrees each in the circumferential direction of each tube sample, and the difference between the maximum and minimum values of the measured data was divided by the average value of the wall thickness. The thing was made into the variation of wall thickness. The data are shown in Table 1 together with the production conditions.

When carbon steel (S20C) seamless pipes are manufactured on the same pipe manufacturing line, the average wall thickness variation of 20 pipes is 6.0%,
Therefore, for the titanium seamless pipe, if the variation in wall thickness is more than 6.0% larger than the carbon steel,
The following items were evaluated by ○.

As is clear from Table 1, in the case of the conventional method in which the hollow piece was directly sent to the reheating furnace for stretch rolling (NO.14), the variation in wall thickness exceeded 10%. Even when the hollow piece after stretch rolling was intentionally cooled, when the mandrel mill outlet temperature was high (NO.1), the outer surface was severely roughened, and rolling after reheating was impossible. Conversely, if the outlet temperature is too low (NO.6), the cooling rate is insufficient (NO.8,1)
0), if the cooling end temperature is too high (NO.13,16,17), if the reheating temperature is high (NO.18) and low (NO.23)
Has rough skin and cracks, and the variation in wall thickness exceeds 6.0%. However, when these conditions are suitable for the production method of the present invention (NO.2 to 5,7,9,11,12,15,19 to 22)
, The variation in wall thickness is suppressed to 6.0% or less, and in many cases it is superior to that of carbon steel (6.0%). In addition, the skin is not roughened or cracked.

Next, an example of α-type titanium alloy will be described. Ti-5Al-2 which is a typical ASTM Gr-6 as an α-type titanium alloy.
Using 55Sn (βtransus1030 ° C) as a material, a billet with a diameter of 180 mm was finished into a seamless pipe with a diameter of 110 mm and a wall thickness of 8.5 mm by the same procedure as the above example.

Table 2 shows the manufacturing conditions and wall thickness variations of the manufactured seamless pipes. As is clear from the table, in the case of α-type titanium alloy, the inner surface squareness is suppressed to be equal to or less than that of carbon steel by the manufacturing method of the present invention.

[Effects of the Invention] The method for producing a titanium seamless pipe of the present invention is a seamless pipe made of pure titanium or an α-type titanium alloy, which is a problem when produced on a continuous seamless pipe production line including drawing rolling. Squareness can be suppressed to the same level as or lower than that of carbon steel. Therefore, the number of man-hours and yield reduction accompanying the inner surface cutting are suppressed to a minimum, and it is possible to omit the cutting depending on the application, and the titanium seamless pipe which is a difficult-to-machine material is efficiently manufactured like the carbon steel pipe, Its manufacturing costs are significantly reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing a heat pattern in the method of the present invention in comparison with the conventional method, and FIG.

Claims (1)

[Claims] 1. When manufacturing a titanium seamless pipe in a rolling process including drawing rolling, the rolling mill outlet temperature in the rolling process before drawing rolling is set to βtransus-150 ° C. or more and 1100 ° C. or less, and the material is drawn from this temperature range. A method for producing a titanium seamless tube, which comprises lowering the temperature to 600 ° C or lower at a rate of air cooling or higher, then reheating to 650 ° C or higher and βtransus or lower, and then drawing rolling.