JP2000061529A - Bent pipe of austenite stainless steel and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a bent pipe of austenite stainless steel excellent in heat resistance and corrosion resistance at a low cost. SOLUTION: A straight pipe 28 of an austnite stainless steel is manufactured by a horizontal centrifugal casting machine. The straight pipe 28 is bent by a high frequency bending machine to manufacture a bent pipe 44. I.e., by concentrating a bending stress on a heating part while heating the bending part of the straight pipe 28 by a high frequency heating coil, the straight pipe 28 is bent at a required angle. Thus, a bent pipe 44 of austenite stainless steel is manufactured.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a bent pipe of austenitic stainless steel obtained by bending a straight pipe manufactured by a centrifugal casting method, and a manufacturing method thereof.

[0002]

Bending pipes such as elbow pipes and U-shaped pipes as pipe joints used for constructing exhaust gas pipe systems in thermal power plants and various plant plants, etc. As a prerequisite, high heat resistance and corrosion resistance are required. Austenitic stainless steel is known as a steel material having such high heat resistance and corrosion resistance, and conventionally, an ingot or rod-shaped material of this austenitic stainless steel is hot extruded, or jointed by a process such as cold drawing. It is practiced to manufacture a seamless tube and then bend the seamless tube to manufacture a bent tube.

[0003]

However, the manufacturing of the seamless pipe requires many steps and has the drawback of increasing the cost. Therefore, a technique for producing a bent pipe of austenitic stainless steel by casting is proposed. However, it is difficult to manufacture a thin-walled bent tube by casting, and it is pointed out that sufficient heat resistance and corrosion resistance cannot be obtained due to the occurrence of casting defects such as shrinkage cavities and blow holes.

[0004]

Therefore, the applicant of the present application, as a result of intensive studies to solve the above problems, pays attention to a centrifugal casting method capable of casting a dense cast product having few casting defects such as shrinkage cavities and blow holes, By bending the straight pipe manufactured by the centrifugal casting method, it was found that a bent pipe excellent in heat resistance and corrosion resistance could be manufactured from austenitic stainless steel.

That is, the present invention has been proposed in order to solve the above-mentioned drawbacks inherent in the above-mentioned conventional technique, and is excellent in heat resistance and corrosion resistance that can be manufactured at low cost. Another object of the present invention is to provide a bent tube of austenitic stainless steel and a method for manufacturing the same.

[0006]

[Means for Solving the Problems] In order to overcome the above-mentioned problems and preferably achieve the intended purpose, a bent pipe of austenitic stainless steel according to the present invention is formed of an austenitic stainless steel manufactured by a centrifugal casting method. Characterized by bending a straight pipe.

In order to overcome the above problems and preferably achieve the intended purpose, a method for manufacturing a bent pipe of austenitic stainless steel according to another invention of the present application is a straight pipe of austenitic stainless steel by a centrifugal casting method. Is manufactured, and the bent portion of the obtained straight pipe is bent while being subjected to high-frequency induction heating to obtain a bent pipe.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Next, a bent tube of austenitic stainless steel and a method for manufacturing the same according to the present invention will be described.
A preferred embodiment will be described below.

FIG. 1 shows a schematic structure of a horizontal centrifugal casting apparatus used in a method for manufacturing a bent pipe of austenitic stainless steel according to an embodiment of the present invention. The apparatus 10 is a motor (not shown). Roller 1 driven by
The metal mold 14 is placed on the molds 2 and 12 in such a manner that its central axis is horizontal, and the molds 14 are rotated at high speed by rotationally driving the rollers 12 and 12. The mold 14 is made of a hollow cylinder whose both end openings are closed by a front lid 16 and a rear lid 18, respectively. The front lid 16 and the rear lid 18 have openings 16a, 18 at their centers.
a is provided. And the mold 1 rotating at high speed
4, the nozzle 20a of the molten metal injection cup 20 is inserted into the cup 20 from the opening 16a of the front lid 16, and the molten metal 26 of austenitic stainless steel 26 is inserted into the cup 20 from the ladle 24.
The molten metal 26 is poured into the mold 14 through the nozzle 20a. The molten metal 26 adheres to the inner surface of the mold in layers by centrifugal force.

In the horizontal centrifugal casting apparatus 10, a dense austenitic stainless steel straight pipe 28 with few casting defects such as shrinkage cavities and blow holes is manufactured (see FIG. 3 (a)). Further, in the centrifugal casting method, a thin wall straight pipe which is a material for an elbow pipe or a U-shaped pipe as a pipe joint used for constructing an exhaust gas piping system in a thermal power plant or various plant plants as described above. The tube 28 can be easily manufactured. It should be noted that, as a mold coating agent to be applied to the inner surface of the mold 14 before pouring the molten metal 26, a mold cooling agent having a high cooling ability, for example, containing zircon is used to reduce the crystal grain size of the obtained straight pipe 28 and The casting surface can be improved.

The straight pipe 28 of austenitic stainless steel manufactured by the horizontal centrifugal casting apparatus 10 is bent by the high frequency bending apparatus 30 shown in FIG. The high-frequency bending device 30 includes two roller sets 34, each of which includes a pair of guide rollers 32 and 32 for holding the straight pipe 28 from both sides in the radial direction. The roller sets 34 and 34 are directly fed by pushing means (not shown). It is arranged to linearly guide the tube. A high-frequency heating coil 36 is arranged further downstream of the roller set 34 on the downstream side in the extrusion direction, and the straight pipe 28 passing through the coil 36 is partly subjected to high-frequency induction heating. Further, a clamp device 42 is arranged at the tip of an arm 40 which can be swung around a fulcrum 38 whose position is adjustable, and the clamp device 42 is configured to clamp the tip of the straight pipe 28. And
With the tip of the straight pipe 28 clamped by the clamp device 42, the straight pipe 28 is advanced by the pushing means while the bent portion of the straight pipe 28 is induction-heated by the high-frequency heating coil 36, so that the arm 40 is swung to heat. Bending stress concentrates on the part and is bent at a required angle. As a result, the bent tube 44 of austenitic stainless steel is manufactured.
(See FIG. 3 (b)).

That is, the bent pipe 44 of austenitic stainless steel obtained by bending the straight pipe 28 manufactured by the centrifugal casting method has a dense structure with no casting defects such as shrinkage cavities and blow holes, and is high. Has heat resistance and corrosion resistance. Therefore, it can be suitably used as a pipe joint for a high temperature and high pressure exhaust gas pipe system. Moreover, since the manufacturing method is simple and the number of steps is small, it is possible to manufacture at low cost by improving productivity. In the high-frequency bending device 30, the heating temperature can be easily changed according to the steel type, and the bending angle of the bending tube 44 can be set arbitrarily.
It is possible to manufacture ° elbow pipes and 180 ° U-shaped pipes.

[0013]

[Experimental Example] A mold coating agent containing zircon was applied to the inner surface of the mold 14 to a thickness of 0.9 to 1.1 mm.
0.07C-2Si-1 under the condition of rotating at 0 rpm.
The molten metal 26 of austenitic stainless steel composed of components such as 0Ni-22Cr-0.16N-0.06Ce is poured into the mold 14 at a casting temperature of 1640 ° C to 1660 ° C, and the outer diameter is 240 mm, the inner diameter is 206 mm, and the length is 4,500 m.
m straight tube 28 was produced.

Then, the straight pipe 28 thus obtained is bent at a bending radius of 1
The heating temperature is 1100 for each 200 ° bending angle of 35 °.
Bending processing at 1 ℃, 1150 ℃, 1200 ℃
For each example, the cross-section quality of the resulting bent tube 44 was examined.

As a result, the following items were confirmed in the first example. (1) In each heating temperature region, boundary crack defects were generated in the outer and inner surface layers of the outer diameter portion on the tensile side, and particularly, the amount of defects was large in the heating temperature region of 1100 ° C. (2) In each heating temperature region, there was no abnormality in the cross-sectional quality other than boundary cracks in the surface layer. (3) In each heating temperature region, there was no great difference in the depth and microstructure of the boundary crack in the surface layer. The depth of the boundary crack between the outer surface and the inner surface is 0.5 mm or less,
It was confirmed that this can be dealt with by polishing and removing.

From the above results, in the bending tube 44 of the first example bent by the high-frequency bending device 30, a defect occurs on the tensile side, but the defect can be dealt with by polishing and removing, It became clear that there was no practical problem. Regarding the defects on the inner surface side, since the depth of the boundary crack is within the wear margin that is expected in advance, there is no problem even if they are not removed by polishing. Also, heating temperature 1
It was confirmed that the heating temperature of 1200 ° C. was appropriate for the steel type concerned because the amount of defects generated in the region of 100 ° C. was large.

Next, using a straight pipe 28 of the same size manufactured under the same casting conditions as in the above-mentioned first example, the heating temperature was set to 1200.
The following table shows the inspection results of the bending pipes 44 of the second to fifth examples manufactured by changing the bending radius and the bending angle under the condition of being set to ° C. In addition, in the fifth example, the result is obtained by inspecting a plurality of bending pipes 44 in which only the bending angle is changed while keeping the bending radius constant. That is, the bending radius is 1200 mm to 1700
20 ° to 180 ° for mm range and bending angle
It can be seen that in any of the above ranges, it can be put to practical use by polishing and removing the defective portion generated on the outer circumference on the tension side.

In the embodiment, the centrifugal casting method for producing a straight pipe is described by taking the horizontal centrifugal casting method in which the center of rotation of the mold is horizontal as an example, but the present invention is not limited to this. It may be a vertical centrifugal casting method in which the center of rotation of the mold is vertical. Further, when bending the straight pipe manufactured by the centrifugal casting method, as a means for heating the bent portion of the straight pipe, it is not necessary to use high-frequency induction heating as in the embodiment, for example, a heating furnace in which a burner is arranged is used. You may use.

[0019]

As described above, according to the bent pipe of austenitic stainless steel and the method for manufacturing the same according to the present invention, the bent pipe obtained by bending the straight pipe manufactured by the centrifugal casting method has the structure. Since it is dense, has no casting defects, and has excellent heat resistance and corrosion resistance, it can be suitably used as a pipe for high temperature and high pressure gas. Moreover, since a straight pipe is manufactured by the centrifugal casting method, the number of steps is small,
There is an advantage that the productivity is improved and the bent tube can be manufactured at low cost.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a horizontal centrifugal casting apparatus used in a method for manufacturing a bent tube according to the present invention.

FIG. 2 is a schematic configuration diagram showing a high-frequency bending apparatus used in the method for manufacturing a bent tube of the present invention.

FIG. 3 is an explanatory view showing a straight pipe and a bent pipe obtained by the method for manufacturing a bent pipe of the present invention.

[Explanation of symbols]

28 straight pipe 44 Bent tube

Continued front page    F term (reference) 3K059 AA08 AB00 AB07 AB16 AB19                       AB23 AB28 AC54 AD03 AD35                       AD38 AD40                 4E063 AA04 BC11 KA04

Claims (2)

[Claims] 1. A bent pipe of austenitic stainless steel obtained by bending a straight pipe (28) of austenitic stainless steel manufactured by a centrifugal casting method. 2. A straight pipe (28) of austenitic stainless steel is manufactured by a centrifugal casting method, and the bent portion of the obtained straight pipe (28) is bent while being subjected to high-frequency induction heating to be bent (44).
A method for producing a bent pipe of austenitic stainless steel, which comprises: