JPH05185114A - Production of rolled clad seamless pipe - Google Patents

Abstract

PURPOSE:To suppress the generation of the galling flaws on the inside surface of a clad pipe stock by an elongater, the degradation in yield by boundary peeling and the degradation in pipe making efficiency and working rate by rolling the pipe at an elnogation rate of a specific range. CONSTITUTION:The clad pipe consisting of an inside pipe of an austenitic stainless steel contg. <=0.2% C, >=16.0% Cr and >=12.0% Ni, further, contg. >=1 kinds among >=1.0% Mo, >=0.1% Ti and >=0.1% Nb at need, and consisting of the balance Fe and unavoidable impurities and an outside pipe consisting of an ordinary steel is rolled. The clad pipe stock is elongated at >=5 deg. inclination angle of rolls and >=1.2 and <=1.7 elongation rate by the elongater. The production ratio is thus suppressed and the boundary peeling is prevented while the galling flaws of the inside surface are prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a rolled clad seamless tube by rolling a clad tube by a plug mill rolling method.

[0002]

2. Description of the Related Art A seamless pipe made of a hard-to-work steel material such as stainless steel is not only expensive but also has a high resistance to deformation and a low deformability when its alloy component is high. Inclined roll piercing / rolling with a Mannesmann piercing / rolling machine or the like becomes difficult, and it has to be produced by a hot extrusion pipe making method or the like, resulting in high production cost. On the other hand, for applications such as boiler tubes where difficult-to-work steel materials such as stainless steel need to be on the outer surface of the seamless pipe, for difficult-to-work steel materials on the outside and steel materials with good workability on the inside. By using a clad tube in which is arranged, expensive materials such as stainless steel can be saved. Also, in the case of a line pipe, if it is a good application if the hard-to-work steel material such as stainless steel is on the inner surface of the seamless steel pipe,
By using a clad tube with a hard-to-work steel material on the inside and a steel material with good workability on the outside, expensive materials such as stainless steel can be saved.

However, the rolled clad seamless pipe is
For example, when stainless steel is on the outside and ordinary steel is on the inside, the piercing and rolling technique may be the rolling technique of ordinary steel. When the ordinary steel is the outer side, the piercing and rolling technique must be the rolling technique of stainless steel, which causes a problem of inner surface flaw. Therefore, as disclosed in Japanese Patent Publication No. 61-2445, there has been proposed a method for producing a rolled clad seamless pipe in which stainless steel is the outside and ordinary steel is the inside, but stainless steel is the inside and ordinary steel. A method for producing a rolled clad seamless tube with the outside as the outer side has not been proposed yet.

In the production of a seamless pipe by the Mannesmann plug mill rolling method, stainless steel is difficult to work, has a large deformation resistance, and as shown in Table 1, the heat generated during drawing and rolling with an elongator is large. It is easy for rashes to occur. In particular, SUS31 containing Mo
For 6 series and high Ni alloys with Ni ≧ 30%, the tendency is particularly remarkable, and the deformation resistance is larger and the melting point is lower than that of SUS304 series. There was a tendency for internal rashes to occur frequently due to.

[0005]

[Table 1]

In the production of rolled clad seamless pipe, pressure rolling with an elongator is a necessary condition. Therefore, as a rolling condition with the inclined roll type elongator, the roll inclination angle is increased to make a half rotation of the clad element pipe. It is considered desirable to increase the wall thickness reduction between the contact roll and the plug and increase the draw ratio to increase the wall thickness working ratio. However, in order to achieve a high inclination angle and a high draw ratio of a rolling roll in an elongator, an inner surface fray defect that occurs when a high Ni stainless steel that is difficult to work and has a large deformation resistance is used as the inner pipe is a problem. Become.

[0007]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
The technique disclosed in Japanese Patent No. 8405 aims at descaling for carbon steel or the like against internal pit defects, and as a concomitant effect, extends the life of the plug by the cooling effect. And a hard material such as stainless steel or Cr-
It is described that Mo steel has very few pit defects in the expansion rolling in the elongator. On the other hand, mechanical flaws caused by tools are considered to be more likely to occur because the deformation resistance increases as the temperature decreases, and in general, when rolling high alloy steel, water-cooling the inner surface of the hollow shell is considered from the conventional way of thinking. It can be said that it is out of common sense.

An object of the present invention is to manufacture a rolled clad seamless pipe having a difficult-to-work steel material disposed inside thereof. A rolled clad seamless pipe capable of preventing the occurrence of internal blurring defects in stretch rolling of a clad element pipe by an elongator. It is to provide a manufacturing method of.

[0009]

[Means for Solving the Problems] The inventors of the present invention have made extensive studies to achieve the above object. As a result, the occurrence of internal surface blemishes in the stretch rolling of the hollow shell, which is difficult to process in the elongator, is likely to occur in thin products with a large degree of processing in the elongator, and the thinner the products before and after stretching and rolling in the elongator. Data was obtained that the inner surface temperature was low. Based on this result, the temperature history before and after stretching and rolling with a single elongator with an inner surface of the hollow shell shows that the temperature of the thin product is lower than that of the medium product at the time of measurement, as shown in Fig. 1. Presumed. That is, the cause of the inner surface fogging defect in the stretching and rolling in the elongator is that the large working degree (stretching ratio) causes an excessive shearing force and the surface temperature rise (1300 ° C. or more) due to the working heat, so that the concentration of impurities is particularly high. It is considered that this is due to the breakage / melting of easy crystal grain boundaries. Therefore, if we can suppress the temperature rise of the inner surface of the hollow shell by specifying the stretch ratio in the elongator during stretch rolling, we believe that it is possible to prevent internal bleeding flaws as well. I confirmed that I could do it. In consideration of the need for crimp rolling on the inner pipe made of difficult-to-work steel and the outer pipe made of steel with good workability, which requires crimp rolling with an elongator, the roll inclination angle should be considered. It was clarified that it is possible to prevent the occurrence of rash defects and prevent interfacial peeling by combining the above and the specification of the stretching ratio, and arrived at the present invention.

That is, according to the present invention, C: 0.2% or less,
An austenitic stainless steel containing Cr: 16.0% or more and Ni: 12.0% or more, with the balance being Fe and unavoidable impurities as the inner pipe and the ordinary steel as the outer pipe is rolled into a clad shell. In the method for producing a rolled clad seamless tube, the clad element tube is stretch-rolled by an inclined roll type elongator at a roll inclination angle of 5 ° or more and a stretching ratio of 1.2 or more and 1.7 or less.

C: 0.2% or less, Cr: 16.0
%, Ni: 12.0% or more, and Mo:
1.0% or more, Ti: 0.1% or more, Nb: 0.1% or more, one or two or more kinds, and the balance is austenitic stainless steel composed of Fe and unavoidable impurities as an inner tube. In a method for producing a rolled clad seamless tube by rolling a clad tube having an ordinary steel as an outer tube, the clad tube is an inclined roll type elongator, and a roll inclination angle is 5 ° or more and a draw ratio is 1.2 or more. Stretch rolling is performed at 1.7 or less.

[0012]

According to the present invention, the clad shell consisting of the austenitic stainless steel inner pipe and the ordinary steel outer pipe is
With the tilt roll type elongator, the roll tilt angle is 5 ° or more,
Since the stretch rolling is performed at a stretch ratio of 1.2 or more and 1.7 or less, the workability (stretch ratio) in the stretch rolling with the elongator can be suppressed, and the increase in the inner surface temperature of the clad element pipe can be suppressed to 1300 ° C. or less. It is possible to prevent the crystal grain boundaries from melting due to the temperature rise of the inner surface, and to prevent the occurrence of fog defects. In particular, SUS316 series, SUS317 series, SU in which one or more kinds of Mo, Ti and Nb are added
In the clad shell made of S321 series and SUS347 series austenitic stainless steel as the inner tube, the high temperature strength is increased by the addition of these elements, the deformation resistance in the stretch rolling becomes large, and the processing heat is easily generated. ,
Especially effective.

The method for producing the clad shell before elongating and rolling with an elongator is not particularly limited, but an inner tube made of difficult-to-work stainless steel or the like is inserted into an outer tube of ordinary steel, and then the inner tube is inserted. One that is pressed and plastically deformed from the inside to be joined to the inner surface of the outer tube, or an inner tube made of difficult-to-process stainless steel, etc., is inserted into an ordinary steel outer tube and then joined by combined drawing, Or after inserting an inner pipe made of difficult-to-work stainless steel into an outer pipe of ordinary steel,
Any of those heated and diffusion-bonded may be used. In addition,
The roll inclination angle in the elongator is set to 5 ° or more because interfacial peeling occurs when the roll inclination angle is less than 5 °. The reason why the stretching ratio is 1.2 or more and 1.7 or less is that interfacial peeling occurs when the stretching ratio is less than 1.2, and inner surface blemishes occur when it exceeds 1.7.

[0014]

[Example] After inserting the inner tube into the outer tube, pressurize the inner tube from the inside.
An outer diameter of 210 mm that is plastically deformed and joined to the inner surface of the outer tube,
Clad element tube with wall thickness 45 mm and length 3900 mm (inner tube: SUS316L and SUS304L austenitic stainless steel outer diameter 137 mm, wall thickness 8.5 m
m, outer tube: 210 mm outer diameter of high strength steel for line pipe,
The thickness of 36.5 mm was stretch-rolled at a temperature of 1150 ° C. in an inclined roll type elongator while changing the inclination angle in the range of 4 to 9 ° and the stretching ratio of 1.1 to 1.8 as shown in Table 2. , Outer diameter 229mm, then plug mill,
A rolled clad seamless pipe having a diameter of 219.1 mm was finished with a sizer and a reeler. Then, the appearance of the crystal grain boundary peeling on the inner surface of the clad tube and the occurrence of inner surface blemishes at the exit of the elongator were visually observed. The results are shown in Table 2. The stretching ratio in the elongator was obtained by dividing the length after rolling by the length before rolling.

[0015]

[Table 2]

As shown in Table 2, Test No. 1 in which the roll inclination angle of the elongator is 5 ° or more and the stretch ratio is 1.2 or more and 1.7 or less. 3-5, 8, 11-13,
In the case of the method of the present invention of 18, the interfacial peeling and the inner surface fogging defect are not generated at all. On the other hand, the test No. in which the roll inclination angle of the elongator is less than 5 °. In the case of 1, 2, 15, and 16, interfacial peeling has occurred. The stretch ratio is 1.2
Test No. In the cases of Nos. 11 and 17, interfacial peeling occurred and the stretch ratio exceeded 1.8. 6,
In the cases of Nos. 7, 9 and 14, the inner surface blemishes have occurred.

[0017]

As described above, according to the method of the present invention, in the stretch rolling of the clad shell in the elongator, the roll inclination angle is 5 ° or more and the stretch ratio is 1.2 or more.
By setting it to 7 or less, it is possible to prevent the interfacial peeling of the clad tube in the elongator and the occurrence of inner surface fray defect, and to reduce the yield due to the inner surface defect of the rolled clad seamless tube, and to improve the pipe manufacturing efficiency and operation rate. The decrease can be suppressed. In particular, the inner tube stainless steel clad seamless tube has a large material cost and the cost of manufacturing the billet, and it is an important point to prevent the occurrence of product defects, and the method of the present invention has a great effect.

[Brief description of drawings]

FIG. 1 is a graph of estimation of internal surface temperature transition during stretch rolling of a hollow shell in an elongator.

Claims (2)

[Claims] 1. An austenitic stainless steel containing C: 0.2% or less, Cr: 16.0% or more, Ni: 12.0% or more, with the balance being Fe and inevitable impurities as an inner tube, In a method for producing a rolled clad seamless tube by rolling a clad tube with an ordinary steel as an outer tube, the clad tube is an inclined roll type elongator with a roll inclination angle of 5 ° or more and a draw ratio of 1.2 or more 1. A method for producing a rolled clad seamless pipe, which comprises drawing and rolling at 7 or less. 2. C: 0.2% or less, Cr: 16.0% or more, Ni: 12.0% or more, and Mo: 1.
0% or more, Ti: 0.1% or more, Nb: 0.1% or more, one or more, and the balance is Fe and unavoidable impurities. In a method for producing a rolled clad seamless tube by rolling a clad tube having steel as an outer tube, the clad tube is an inclined roll type elongator and the roll angle is 5 ° or more and the draw ratio is 1.2 or more. A method for producing a rolled clad seamless pipe, which comprises drawing and rolling at 7 or less.