JP2005219084A - Method for manufacturing hot-extruded seamless steel tube having excellent inner surface quality - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a hot-extruded seamless steel tube having excellent inner surface quality. <P>SOLUTION: In the method for manufacturing the hot-extruded seamless stainless steel tube having excellent inner surface quality, hot-extrusion is performed by setting the angle θ of inclination of a die to be 10-50° from the perpendicular in the extruding rear end direction. In the method for manufacturing the hot-extruded seamless steel tube having excellent inner surface quality, the angle θ of inclination is set to 20-50°. Unevenness of an inner surface of the steel tube is eliminated, and the quality can be improved. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing a stainless steel hot-extruded seamless steel pipe.

  The inner surface of a seamless stainless steel pipe mainly for piping is particularly required to have a good inner surface property because corrosive fluid passes in many cases. In many cases, such a steel pipe is manufactured by an Eugene Sejurune type extrusion apparatus using a mandrel bar. In that case, in order to obtain a generally good inner surface property, for example, as disclosed in JP-A-2002-338984 (Patent Document 1), it is a lubricant composition used in hot working. A hot powder lubricant composition comprising 40-90% by mass of sodium borate pentahydrate, 6-30% by mass of sodium carbonate, and 5-30% by mass of one or more of Na or Ca salt of fatty acid. Things have been proposed.

  Further, as disclosed in Japanese Patent Application Laid-Open No. 8-164405 (Patent Document 2), the outer diameter of the portion that contacts the seamless steel pipe when rolled is gradually increased from the front end side toward the rear end side. As described in Japanese Patent Application Laid-Open No. 8-71618 (Patent Document 3), a surface using an axial centerline average roughness (Ra) is used. Has been proposed that uses a mandrel bar for hot seamless pipe rolling having a Cr plating film having a thickness of 1.0 to 4.0 μm. Furthermore, as disclosed in Japanese Patent Application Laid-Open No. 9-192724 (Patent Document 4), a method of hot extruding a seamless steel pipe using a hollow billet having a surface roughness Rmax of 30 to 100 μm as an extrusion material. Each has been proposed.

JP 2002-338984 A JP-A-8-164405 JP-A-8-71618 Japanese Patent Laid-Open No. 9-192724

  As in the case of Patent Document 1 described above, the lubricant between the billet and the mandrel is changed, the shape of the mandrel bar is changed as in Patent Document 2, and the surface roughness of the mandrel bar is changed as in Patent Document 3. As proposed in Patent Document 4, the surface roughness of the inner surface of the hollow billet used for extrusion has been proposed to be Rmax of 30 to 100 μm by polishing. However, all studies were made only from the viewpoint of lubrication and roughness of the inner surface. However, the countermeasures from the generation mechanism of the inner surface unevenness were not examined.

  In general, when the extrusion ratio exceeds 15 in the Eugene Sejurune extrusion, irregularities more than the irregularities of the billet are generated on the inner surface of the tube even if the surface roughness of the billet is reduced. When this unevenness is large, not only the appearance is impaired, but also when used as a piping for corrosive fluid, it becomes a starting point for local corrosion, and the tube may reach an early life. Moreover, the change of the lubricant between the billet and the mandrel, the shape of the mandrel bar and the like are effective for seizing the inner surface, but are not effective for the generation of unevenness. As described above, the dice have not been studied for the occurrence of irregularities on the inner surface.

  In order to solve the above-mentioned problems, the inventors have intensively studied, and as a result, the unevenness is affected by the vertical stress between the container and the mandrel applied to the billet. It turns out that it grows. Next, these irregularities start from the minute irregularities on the inner surface of the billet that are generated by deformation due to the stress between the container and the mandrel. As the die approaches, the molten glass flows from the convex part to the concave part. It was found to be caused by a mechanism that is increased by

  In order to reduce the stress between the container mandrels, it is effective to reduce the stress between the pressing disc and the die, and as a means to make the inner surface of the steel pipe good, the standard (surface roughness Ry ≦ 13) or less. It was found that it is effective to extrude the contact surface of the die against which the pad glass hits and incline 10 to 50 degrees toward the rear side. Furthermore, it was found that when the dice angle is 20 degrees or more, very good Ry ≦ 10 μm can be achieved. However, it has been found that when the inclination angle exceeds 50 degrees, the glass film on the outer surface becomes thick, the outer diameter accuracy deteriorates, the basic unit of the pad glass increases, and the cost increases. Based on these findings, the present invention has been completed.

The gist of the invention is that
(1) In the method of manufacturing a stainless steel hot-extruded seamless steel pipe, the inner surface quality is good, characterized in that the die inclination angle θ is inclined 10 to 50 degrees from the vertical line toward the rear end of the extrusion, and hot extrusion is performed. Method for producing a seamless hot-extruded seamless steel pipe.
(2) The method for producing a hot extruded seamless steel pipe having good inner surface quality, characterized in that the inclination angle θ described in (1) is 20 to 50 degrees.

  As described above, the unevenness of the inner surface of the steel pipe is eliminated and the quality is improved by hot extruding by tilting the die inclination angle θ by 10 to 50 degrees in the direction of the rear end of extrusion from the vertical line according to the present invention. It has an extremely excellent effect.

Hereinafter, the present invention will be described in detail with reference to the drawings.
FIG. 1 is an overall conceptual diagram of a seamless steel pipe hot extrusion apparatus according to the present invention. As shown in FIG. 1A, the billet 1 heated to a predetermined temperature is loaded into the container 4 by the stem 3 via the pressing disk 2. At that time, the mandrel 5 is also in the state shown in the figure, and advances simultaneously with the stem 3. At this time, the cylinder (not shown) at the rear of the stem 3 is in a low pressure state. Thereafter, the tip of the billet 1 comes into contact with the die holder 6 and the billet 1 is pressurized at a low pressure. Thereafter, the cylinder is subjected to high pressure, and the billet 1 is pushed to the inner diameter of the die 7 in the die holder 6. Reference numeral 8 is a liner, 9 is a tube, 10 is a packing ring, and 11 is a pad glass.

  FIG. 1B is an enlarged view of the pad glass portion. As shown in FIG. 1B, the glass lubricant in the hot extrusion in the above-described extrusion mechanism of FIG. From the state in which the pad glass 11 is set, the glass on the surface in contact with the billet 1 melts during extrusion, and the glass adheres to the surface of the pipe 9 and lubricates between the dies 7. In this case, as described above, it is effective to reduce the stress between the pressing disk 2 and the die 7 in order to reduce the stress between the container 4 and the mandrel 5. In order to make the surface roughness Ry ≦ 13) or less, it is effective to extrude the contact surface of the die 7 against which the pad glass hits and incline the die inclination angle θ 10 to 50 degrees toward the rear side. Furthermore, when the die inclination angle θ is 20 degrees or more, a very good surface roughness Ry ≦ 10 μm can be achieved.

  FIG. 2 is a view showing the state of occurrence of irregularities on the inner surface of the stainless steel pipe. FIG. 2A shows a state before the stainless steel pipe is extruded, and FIG. 2B shows a state of the billet-tube forming transition area after the extrusion. The unevenness on the inner surface of the steel pipe is affected by the stress in the vertical direction between the container mandrels applied to the billet, and the larger the unevenness, the larger the size of the unevenness. This unevenness is caused by the deformation of the billet inner surface caused by deformation due to stress between the container and the mandrel, and as the die approaches, the molten glass flows from the protrusion to the recess. It can be seen in this figure that this occurs with the mechanism being increased.

  FIG. 3 is a diagram showing the relationship between the die angle θ and Ry. As shown in this figure, it can be seen that the Ry value when the die angle θ is 10 degrees or more is lowered. In particular, in order to satisfy Ry ≦ 10 μm, it is necessary to extrude the contact surface of the die hit by the pad glass and incline 20 degrees backward. That is, the reason why the die inclination angle θ according to the present invention is hot-extruded by inclining by 10 to 50 degrees is that the effect of improving the inner skin is not sufficient if it is less than 10 degrees, and the outer surface is more than 50 degrees. As the glass film becomes thicker, the accuracy of the outer diameter deteriorates, and the amount of glass consumed increases and the cost increases. Therefore, the range was set to 10 to 50 degrees. Preferably, the angle is 20 to 50 degrees.

Hereinafter, the present invention will be specifically described with reference to examples.
Using a steel type of SUS304, an extrusion temperature of 1210 to 1240 ° C. and a billet inner surface Ry of 7.5 μm were performed at the billet diameter, tube diameter, extrusion ratio, and die angle as shown in Table 1. The results are shown in Table 1.

  As shown in Table 1, no. 1-2, 4-6, 9-11 are examples of the present invention. 3, 7-8, 12-13 are comparative examples. Comparative Example No. No. 3 has a high tube inner surface Ry because the die angle is small. Comparative Example No. 7 has a poor outer diameter accuracy due to a large die angle. Comparative Example No. Since No. 8 has a small die angle, the tube inner surface Ry is high. Comparative Example No. No. 12 has a poor outer diameter accuracy due to a large die angle. Comparative Example No. It can be seen that No. 8 has a high tube inner surface Ry because the die angle is zero. On the other hand, No. which is an example of the present invention. 1 to 2, 4 to 6, and 9 to 11 all have a low tube inner surface Ry, it is possible to obtain a steel pipe with excellent outer diameter accuracy by eliminating irregularities on the inner surface of the steel pipe, and improving quality. It was.

1 is an overall conceptual diagram of a seamless steel pipe hot extrusion apparatus according to the present invention. It is a figure which shows the unevenness | corrugation generation | occurrence | production state of a stainless steel pipe inner surface. It is a figure which shows the relationship between die angle (theta) and Ry of a product tube inner surface.

Explanation of symbols

1 Billet 2 Pressing Disc 3 Stem 4 Container 5 Mandrel 6 Die Holder 7 Die 8 Liner 9 Tube 10 Packing Ring 11 Pad Glass θ Dice Tilt Angle


Patent Applicant Sanyo Special Steel Co., Ltd.
Attorney: Attorney Shiina

Claims (2)

In a method for producing a hot-extruded seamless steel pipe made of stainless steel, hot extrusion with good inner surface quality is characterized in that the die inclination angle θ is inclined by 10 to 50 degrees from the vertical line toward the rear end of the extrusion, and hot extrusion is performed. Manufacturing method of extruded seamless steel pipe. A method for producing a hot-extruded seamless steel pipe with good inner surface quality, wherein the inclination angle θ according to claim 1 is 20 to 50 degrees.

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